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Malignant peripheral nerve sheath tumor (MPNST), a highly malignant tumor that arises in peripheral nerve tissues, is known to be highly resistant to radiation and chemotherapy. Although there are several reports on genetic mutations and epigenetic changes that define the pathogenesis of MPNST, there is insufficient information regarding the microenvironment that contributes to the malignancy of MPNST. In the present study, we demonstrate that adrenaline increases the cancer stem cell population in MPNST. This effect is mediated by adrenaline stimulation of beta-2 adrenergic receptor (ADRB2), which activates the Hippo transducer, YAP/TAZ. Inhibition and RNAi experiments revealed that inhibition of ADRB2 attenuated the adrenaline-triggered activity of YAP/TAZ and subsequently attenuated MPNST cells stemness. Furthermore, ADRB2-YAP/TAZ axis was confirmed in the MPNST patients' specimens. The prognosis of patients with high levels of ADRB2 was found to be significantly worse. These data show that adrenaline exacerbates MPNST prognosis and may aid the development of new treatment strategies for MPNST.

The autonomic nervous system, consisting of sympathetic and parasympathetic/vagal nerves, is known to control the functions of any organ, maintaining whole-body homeostasis under physiological conditions. Recently, there has been increasing evidence linking sympathetic and parasympathetic/vagal nerves to cancers. The present review aimed to summarize recent developments from studies addressing the relationship between sympathetic and parasympathetic/vagal nerves and cancer behavior. Literature review. Human and animal studies have revealed that sympathetic and parasympathetic/vagal nerves innervate the cancer microenvironment and alter cancer behavior. The sympathetic nerves have cancer-promoting effects on prostate cancer, breast cancer, and melanoma. On the other hand, while the parasympathetic/vagal nerves have cancer-promoting effects on prostate, gastric, and colorectal cancers, they have cancer-suppressing effects on breast and pancreatic cancers. These neural effects may be mediated by β-adrenergic or muscarinic receptors and can be explained by changes in cancer cell behavior, angiogenesis, tumor-associated macrophages, and adaptive antitumor immunity. Sympathetic nerves innervating the tumor microenvironment promote cancer progression and are related to stress-induced cancer behavior. The parasympathetic/vagal nerves have variable (promoting or suppressing) effects on different cancer types. Approaches directed toward the sympathetic and parasympathetic/vagal nerves can be developed as a new cancer therapy. In addition to existing pharmacological, surgical, and electrical approaches, a recently developed virus vector-based genetic local neuroengineering technology is a powerful approach that selectively manipulates specific types of nerve fibers innervating the cancer microenvironment and leads to the suppression of cancer progression. This technology will enable the creation of "cancer neural therapy" individually tailored to different cancer types.

Intracranial mesenchymal chondrosarcoma (MCS) is a rare neoplasm. The diagnosis of MCS is confirmed by the presence of a biphasic pattern on histological examination, comprising undifferentiated small round cells admixed with islands of well-differentiated hyaline cartilage; however, a differential diagnosis may be challenging in some cases. A 28-year-old woman with a 2-month history of headache was referred to our hospital. Radiologic studies showed an extra-axial lobulated mass composed of calcified and uncalcified areas occupying the left middle fossa. Surgical resection was planned, but her headache suddenly worsened before her planned hospital admission and she was admitted as an emergency. Radiologic studies showed an acute hemorrhage in the uncalcified part of the mass. The mass was resected via the left zygomatic approach after embolization of the feeder vessels. The most likely histopathological diagnosis was MCS. However, the typical bimorphic pattern was not identified in our surgical samples; each undifferentiated area and well-differentiated area was observed separately in different tissue specimens, and no islands of well-differentiated hyaline cartilage were identified within the undifferentiated areas in the same specimen. Molecular assays confirmed the presence of HEY1-NCOA2 fusion. IRF2BP2-CDX1 fusion and IDH1/2 mutations were negative. The final diagnosis of MCS was made based on the presence of HEY1-NCOA2 gene fusion. MCS should be included in the differential diagnosis when radiologic studies show an extra-axial lobulated mass with calcification. Furthermore, molecular demonstration of HEY1-NCOA2 gene fusion may help make a precise diagnosis of MCS, especially in surgical samples lacking the typical histopathological features.

The effects of autonomic innervation of tumors on tumor growth remain unclear. Here we developed a series of genetic techniques to manipulate autonomic innervation in a tumor- and fiber-type-specific manner in mice with human breast cancer xenografts and in rats with chemically induced breast tumors. Breast cancer growth and progression were accelerated following stimulation of sympathetic nerves in tumors, but were reduced following stimulation of parasympathetic nerves. Tumor-specific sympathetic denervation suppressed tumor growth and downregulated the expression of immune checkpoint molecules (programed death-1 (PD-1), programed death ligand-1 (PD-L1), and FOXP3) to a greater extent than with pharmacological α- or β-adrenergic receptor blockers. Genetically induced simulation of parasympathetic innervation of tumors decreased PD-1 and PD-L1 expression. In humans, a retrospective analysis of breast cancer specimens from 29 patients revealed that increased sympathetic and decreased parasympathetic nerve density in tumors were associated with poor clinical outcomes and correlated with higher expression of immune checkpoint molecules. These findings suggest that autonomic innervation of tumors regulates breast cancer progression.

In obesity and type 2 diabetes, numerous genes are differentially expressed, and microRNAs are involved in transcriptional regulation of target mRNAs, but miRNAs critically involved in the appetite control are not known. Here, we identified upregulation of miR-342-3p and its host gene Evl in brain and adipose tissues in C57BL/6 mice fed with high fat-high sucrose (HFHS) chow by RNA sequencing. Mir342 (-/-) mice fed with HFHS chow were protected from obesity and diabetes. The hypothalamic arcuate nucleus neurons co-express Mir342 and EVL. The percentage of activated NPY+pSTAT3+ neurons were reduced, while POMC+pSTAT3+ neurons increased in Mir342 (-/-) mice, and they demonstrated the reduction of food intake and amelioration of metabolic phenotypes. Snap25 was identified as a major target gene of miR-342-3p and the reduced expression of Snap25 may link to functional impairment hypothalamic neurons and excess of food intake. The inhibition of miR-342-3p may be a potential candidate for miRNA-based therapy.

Glioblastoma (GBM) is the most lethal primary brain tumor characterized by significant cellular heterogeneity, namely tumor cells, including GBM stem-like cells (GSCs) and differentiated GBM cells (DGCs), and non-tumor cells such as endothelial cells, vascular pericytes, macrophages, and other types of immune cells. GSCs are essential to drive tumor progression, whereas the biological roles of DGCs are largely unknown. In this study, we focused on the roles of DGCs in the tumor microenvironment. To this end, we extracted DGC-specific signature genes from transcriptomic profiles of matched pairs of in vitro GSC and DGC models. By evaluating the DGC signature using single cell data, we confirmed the presence of cell subpopulations emulated by in vitro culture models within a primary tumor. The DGC signature was correlated with the mesenchymal subtype and a poor prognosis in large GBM cohorts such as The Cancer Genome Atlas and Ivy Glioblastoma Atlas Project. In silico signaling pathway analysis suggested a role of DGCs in macrophage infiltration. Consistent with in silico findings, in vitro DGC models promoted macrophage migration. In vivo, coimplantation of DGCs and GSCs reduced the survival of tumor xenograft-bearing mice and increased macrophage infiltration into tumor tissue compared with transplantation of GSCs alone. DGCs exhibited a significant increase in YAP/TAZ/TEAD activity compared with GSCs. CCN1, a transcriptional target of YAP/TAZ, was selected from the DGC signature as a candidate secreted protein involved in macrophage recruitment. In fact, CCN1 was secreted abundantly from DGCs, but not GSCs. DGCs promoted macrophage migration in vitro and macrophage infiltration into tumor tissue in vivo through secretion of CCN1. Collectively, these results demonstrate that DGCs contribute to GSC-dependent tumor progression by shaping a mesenchymal microenvironment via CCN1-mediated macrophage infiltration. This study provides new insight into the complex GBM microenvironment consisting of heterogeneous cells.

The usefulness of ultrasound molecular imaging with αvβ3 integrin-targeted microbubbles for detecting tumor angiogenesis has been demonstrated. Recently, we developed αvβ3 integrin-targeted microbubbles by modifying clinically available microbubbles (Sonazoid, Daiichi-Sankyo Pharmaceuticals, Tokyo, Japan) with a secreted glycoprotein (lactadherin). The aims of our present study were to simplify the preparation of lactadherin-bearing Sonazoid and to examine the diagnostic utility of lactadherin-bearing Sonazoid for αvβ3 integrin-expressing tumor vessels by using SK-OV-3-tumor–bearing mice. By incubating 1.2 × 107 Sonazoid microbubbles with 1.0 µg lactadherin, the complicated washing and centrifugation steps during the microbubble preparation could be omitted with no significant reduction in labeling ratio of lactadherin-bearing Sonazoid. In addition, the number of Sonazoid microbubbles accumulated in the SK-OV-3 tumor was significantly increased by modifying Sonazoid with lactadherin. Our data suggest that the lactadherin-bearing Sonazoid is an easily prepared and potentially clinically translatable targeted microbubble for αvβ3 integrin-expressing vessels.

Although electrical activation of the carotid sinus baroreflex (baroreflex activation therapy) is being explored as a device therapy for resistant hypertension, possible effects on baroreflex dynamic characteristics of interaction between electrical stimulation and pressure inputs are not fully elucidated. To examine whether the electrical stimulation of the baroreceptor afferent nerve impedes normal short-term arterial pressure (AP) regulation mediated by the stimulated nerve, we electrically stimulated the right aortic depressor nerve (ADN) while estimating the baroreflex dynamic characteristics by imposing pressure inputs to the isolated baroreceptor region of the right ADN in nine anesthetized rats. A Gaussian white noise signal with a mean of 120 mmHg and standard deviation of 20 mmHg was used for the pressure perturbation. A tonic ADN stimulation (2 or 5 Hz, 10 V, 0.1-ms pulse width) decreased mean sympathetic nerve activity (367.0 ± 70.9 vs. 247.3 ± 47.2 arbitrary units, P < 0.01) and mean AP (98.4 ± 7.8 vs. 89.2 ± 4.5 mmHg, P < 0.01) during dynamic pressure perturbation. The ADN stimulation did not affect the slope of dynamic gain in the neural arc transfer function from pressure perturbation to sympathetic nerve activity (16.9 ± 1.0 vs. 14.7 ± 1.6 dB/decade, not significant). These results indicate that electrical stimulation of the baroreceptor afferent nerve does not significantly impede the dynamic characteristics of the arterial baroreflex concomitantly mediated by the stimulated nerve. Short-term AP regulation by the arterial baroreflex may be preserved during the baroreflex activation therapy.

Although the pulsatility of an input pressure is an important factor that determines the arterial baroreflex responses, whether the difference in the input waveforms can meaningfully affect the baroreflex function remains unknown. This study aimed to compare baroreflex responses between two distinct pressure waveforms: a forward saw wave (FSW) and a backward saw wave (BSW). In seven anesthetized rats, carotid sinus pressure was exposed to the FSW or the BSW with a mean of 120 mmHg, pulse pressure of 40 mmHg, and pulse frequency of 1 Hz. Changes in efferent sympathetic nerve activity (SNA) and arterial pressure (AP) during six consecutive saw wave trials (FSW1, BSW1, FSW2, BSW2, FSW3, and BSW3) were examined. The steady-state SNA value during FSW1 was 91.1 ± 1.9%, which was unchanged during FSW2 and FSW3 but significantly increased during BSW1 (106.6 ± 3.4%, P < 0.01), BSW2 (110.6 ± 2.5%, P < 0.01), and BSW3 (111.6 ± 2.3%, P < 0.01). The steady-state AP value during FSW1 was 98.2 ± 8.1 mmHg, which was unchanged during FSW2 and FSW3 but significantly increased during BSW1 (106.7 ± 7.4 mmHg, P < 0.01), BSW2 (105.6 ± 7.8 mmHg, P < 0.01), and BSW3 (103.8 ± 7.2 mmHg, P < 0.05). In conclusion, the FSW was more effective than the BSW in reducing mean SNA and AP. The finding could be applied to designing an artificial pulsatile pressure such as that generated by left ventricular assist devices. NEW & NOTEWORTHY This study examined whether the waveforms of an input pressure alone can affect the baroreflex function by using a forward saw wave and a backward saw wave with the same mean pressure, pulse pressure, and pulse frequency. The forward saw wave was more effective than the backward saw wave in reducing sympathetic nerve activity and arterial pressure. The finding could be applied to designing an artificial pulsatile pressure such as that generated by left ventricular assist devices.

Desipramine (DMI) is a blocker of neuronal norepinephrine (NE) uptake transporter. Although intravenous DMI has been shown to cause centrally-mediated sympathoinhibition and peripheral NE accumulation, its parasympathetic effect remains to be elucidated. We hypothesized that intravenous DMI activates the cardiac vagal nerve via an α2-adrenergic mechanism. Using a cardiac microdialysis technique, changes in myocardial interstitial acetylcholine (ACh) levels in the left ventricular free wall in response to intravenous DMI (1mg·kg-1) were examined in anesthetized rats. In rats with intact vagi (n=7), intravenous DMI increased ACh from 1.67±0.43 to 2.48±0.66nM (P

This study examined the mechanism of release of endogenous acetylcholine (ACh) in rabbit renal cortex by applying a microdialysis technique. In anesthetized rabbits, a microdialysis probe was implanted into the renal cortex and perfused with Ringer’s solution containing high potassium concentration, high sodium concentration, a Na+/K+-ATPase inhibitor (ouabain), or an epithelial Na+ channel blocker (benzamil). Dialysate samples were collected at baseline and during exposure to each agent, and ACh concentrations in the samples were measured by high-performance liquid chromatography. High potassium had no effect on renal ACh release. High sodium increased dialysate ACh concentrations significantly. Ouabain increased dialysate ACh concentration significantly. Benzamil decreased dialysate ACh concentrations significantly both at baseline and under high sodium. The finding that high potassium-induced depolarization does not increase ACh release suggests that endogenous ACh is released in renal cortex mainly by non-neuronal mechanism. Sodium ion transport may be involved in the non-neuronal ACh release.

Ticks are blood‐feeding ectoparasites that transmit a variety of pathogens to host animals and humans, causing severe infectious diseases such as Lyme disease. In a certain combination of animal and tick species, tick infestation elicits acquired immunity against ticks in the host, which can reduce the ability of ticks to feed on blood and to transmit pathogens in the following tick infestations. Therefore, our understanding of the cellular and molecular mechanisms of acquired tick resistance (ATR) can advance the development of anti‐tick vaccines to prevent tick infestation and tick‐borne diseases. Basophils are a minor population of white blood cells circulating in the bloodstream and are rarely observed in peripheral tissues under steady‐state conditions. Basophils have been reported to accumulate at tick‐feeding sites during re‐infestation in cattle, rabbits, guinea pigs and mice. Selective ablation of basophils resulted in a loss of ATR in guinea pigs and mice, illuminating the essential role of basophils in the manifestation of ATR. In this review, we discuss the recent advance in the elucidation of the cellular and molecular mechanisms underlying basophil recruitment to the tick‐feeding site and basophil‐mediated ATR.

Boron neutron capture therapy (BNCT) requires pharmaceutical innovations and molecular-based evidence of effectiveness to become a standard cancer therapeutic in the future. Recently, in Japan, 4-borono-L-phenylalanine (BPA) was approved as a boron agent for BNCT against head and neck (H&amp, N) cancers. H&amp, N cancer appears to be a suitable target for BPA-BNCT, because the expression levels of L-type amino acid transporter 1 (LAT1), one of the amino acid transporters responsible for BPA uptake, are elevated in most cases of H&amp, N cancer. However, in other types of cancer including malignant brain tumors, LAT1 is not always highly expressed. To expand the possibility of BNCT for these cases, we previously developed poly-arginine peptide (polyR)-conjugated mercaptoundecahydrododecaborate (BSH). PolyR confers the cell membrane permeability and tumor selectivity of BSH. However, the molecular determinants for the properties are not fully understood. In this present study, we have identified the cluster of differentiation 44 (CD44) protein and translational machinery proteins as a major cell surface target and intracellular targets of BSH-polyR, respectively. CD44, also known as a stem cell-associated maker in various types of cancer, is required for the cellular uptake of polyR-conjugated molecules. We showed that BSH-polyR was predominantly delivered to a CD44High cell population of cancer cells. Once delivered, BSH-polyR interacted with the translational machinery components, including the initiation factors, termination factors, and poly(A)-biding protein (PABP). As a proof of principle, we performed BSH-polyR-based BNCT against glioma stem-like cells and revealed that BSH-polyR successfully induced BNCT-dependent cell death specifically in CD44High cells. Bioinformatics analysis indicated that BSH-polyR would be suitable for certain types of malignant tumors. Our results shed light on the biochemical properties of BSH-polyR, which may further contribute to the therapeutic optimization of BSH-BNCT in the future.

An α2A-adrenergic agonist guanfacine improves autonomic imbalance in attention-deficit hyperactivity disorder, suggesting that it may be useful to correct autonomic imbalance in chronic heart failure (CHF) patients. To investigate the effects of guanfacine on cardiac autonomic nerve activities, a microdialysis technique was applied to anesthetized rabbit heart. Acetylcholine (ACh) and norepinephrine (NE) concentrations in atrial dialysates were measured as indices of cardiac autonomic nerve activities. Guanfacine at a dose of 100 μg/kg significantly decreased heart rate and increased dialysate ACh concentration without decreasing sympathetic NE release. Guanfacine may be useful for vagal activation therapy in CHF patients.

BACKGROUND There is ongoing controversy over whether neural or peripheral factors are the predominant cause of hypertension. The closed-loop negative feedback operation of the arterial baroreflex hampers understanding of how arterial pressure (AP) is determined through the interaction between neural and peripheral factors. METHODS AND RESULTS: A novel analysis of an isolated open-loop baroreceptor preparation to examine sympathetic nervous activity (SNA) and AP responses to changes in carotid sinus pressure (CSP) in adult spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) was conducted. In the neural arc (CSP-SNA relationship), the midpoint pressure (128.9±3.8 vs. 157.9±8.1 mmHg, P

The recent development of computer technology has made it possible to simulate the hemodynamics of congenital heart diseases on a desktop computer. However, multi-scale modeling of the cardiovascular system based on computed tomographic and magnetic resonance images still requires long simulation times. The lumped parameter model is potentially beneficial for real-time bedside simulation of congenital heart diseases. In this review, we introduce the basics of the lumped parameter model (time-varying elastance chamber model combined with modified Windkessel vasculature model) and illustrate its usage in hemodynamic simulation of congenital heart diseases using examples such as hypoplastic left heart syndrome and Fontan circulation. We also discuss the advantages of the lumped parameter model and the problems for clinical use.

There are some debate as to dynamic-state applicability and cause-and-effect relationship between variables in Guyton9s circulatory equilibrium model. The work of Moller PW et al. () supports the dynamic-state applicability in the venous return property of Guyton9s model. State-space representation clearly depicts function structure of cardiovascular system; inputs to the system firstly affect internal unmeasureable properties of system (total stressed blood volume, pump function, systemic arterial resistance) and as a result measurable variables (cardiac output, venous return, RAP, LAP, systemic arterial pressure) were determined simultaneously as circulatory equilibrium. Accordingly, there is no cause-and-effect relationship among measurable variables.

A hybrid procedure combining bilateral pulmonary artery banding with ductal stenting has recently been used as stage I palliation for hypoplastic left heart syndrome. However, the advantage of the hybrid procedure over the Norwood procedure on ventricular energetics remains unclear. To clarify this, we performed a computational analysis with a combination of time-varying elastance chamber model and modified three-element Windkessel vascular model. Although mean pulmonary artery (PA) pressure, pulmonary flow, and oxygen saturation were almost equivalent with the Norwood procedure, the hybrid procedure delivered higher systolic and lower diastolic systemic arterial pressures compared to the Norwood procedure with right ventricle (RV) to PA shunt. As a result, the hybrid procedure yielded increased systolic pressure-volume area and impaired mechanical efficiency. Therefore, the hybrid procedure has probably no advantage on ventricular energetics compared to the Norwood procedure with a RV-PA shunt.

Aim To examine whether sympathetic afferent stimulation (SAS) inhibits central vagal activation induced by α2-adrenergic stimulation. Methods In anaesthetized Wistar-Kyoto rats, a cardiac microdialysis technique was applied to the left ventricle, and the effect of α2-adrenergic stimulation by medetomidine on myocardial interstitial acetylcholine (ACh) levels was examined in the absence (n = 6) or the presence (n = 6) of SAS delivered from the left stellate ganglion. The effect of electrical vagal efferent stimulation on myocardial interstitial ACh release was also examined in the absence or the presence of SAS (n = 6). Results Intravenous medetomidine (0.1 mg kg−1) significantly increased myocardial interstitial ACh levels in the absence of SAS (from 1.95 ± 0.79 to 3.36 ± 1.61 nm, P

Recent clinical trials in patients with drug-resistant hypertension indicate that electrical activation of the carotid sinus baroreflex can reduce arterial pressure (AP) for more than a year. To examine whether the electrical stimulation from one baroreflex system impedes normal short-term AP regulation via another unstimulated baroreflex system, we electrically stimulated the left aortic depressor nerve (ADN) while estimating the dynamic characteristics of the carotid sinus baroreflex in anesthetized normotensive Wistar-Kyoto (WKY; n = 8) rats and spontaneously hypertensive rats (SHR; n = 7). Isolated carotid sinus regions were perturbed for 20 min using a Gaussian white noise signal with a mean of 120 mmHg for WKY and 160 mmHg for SHR. Tonic ADN stimulation (2 Hz, 10 V, and 0.1-ms pulse width) decreased mean sympathetic nerve activity (73.4 ± 14.0 vs. 51.6 ± 11.3 arbitrary units in WKY, P = 0.012; and 248.7 ± 33.9 vs. 181.1 ± 16.6 arbitrary units in SHR, P = 0.018) and mean AP (90.8 ± 6.6 vs. 81.2 ± 5.4 mmHg in WKY, P = 0.004; and 128.6 ± 9.8 vs. 114.7 ± 10.3 mmHg in SHR, P = 0.009). The slope of dynamic gain in the neural arc transfer function from carotid sinus pressure to sympathetic nerve activity was not different between trials with and without the ADN stimulation (12.55 ± 0.93 vs. 13.03 ± 1.28 dB/decade in WKY, P = 0.542; and 17.37 ± 1.01 vs. 17.47 ± 1.64 dB/decade in SHR, P = 0.946). These results indicate that the tonic ADN stimulation does not significantly modify the dynamic characteristics of the carotid sinus baroreflex.

To examine whether moderate efferent vagal nerve stimulation (VNS) attenuates the carotid sinus baroreflex-mediated arterial pressure (AP) regulation via its antagonism to the sympathetic system.Carotid sinus baroreceptor regions were isolated from the systemic circulation in eight anesthetized and vagotomized rats. A staircase-wise input was imposed on carotid sinus pressure (CSP) with or without efferent VNS (20Hz, 2ms, 1-4V), while the responses in AP, heart rate (HR), and splanchnic sympathetic nerve activity (SNA) were measured.A multiple linear regression analysis indicated that VNS decreased the minimum HR in the CSP-HR relationship by 58.2±4.9 beats/min (P0.01) from its reference value of 387.0±5.8 beats/min. Although VNS significantly decreased an intercept of the SNA-AP relationship, it did not affect parameters of the CSP-AP relationship or the CSP-SNA relationship significantly. The operating-point AP of the baroreflex was decreased by 2.8±1.0mmHg (P0.01) during VNS, which was less than 3% of the reference value of 117.7±1.2mmHg.VNS, at an intensity of decreasing HR by approximately 13%, does not acutely attenuate the baroreflex-mediated sympathetic AP regulation.

We have reported that minute ventilation [ $$ \dot{V}_{\text{E}} $$ ] and end-tidal CO2 tension [ $$ P_{{{\text{ETCO}}_{ 2} }} $$ ] are determined by the interaction between central controller and peripheral plant properties. During exercise, the controller curve shifts upward with unchanged central chemoreflex threshold to compensate for the plant curve shift accompanying increased metabolism. This effectively stabilizes $$ P_{{{\text{ETCO}}_{ 2} }} $$ within the normal range at the expense of exercise hyperpnea. In the present study, we investigated how endurance-trained athletes reduce this exercise hyperpnea. Nine exercise-trained and seven untrained healthy males were studied. To characterize the controller, we induced hypercapnia by changing the inspiratory CO2 fraction with a background of hyperoxia and measured the linear $$ P_{{{\text{ETCO}}_{ 2} }} - \dot{V}_{\text{E}} $$ relation [ $$ \dot{V}_{\text{E}} = S\, (P_{{{\text{ETCO}}_{2} }} - {\rm B}) $$ ]. To characterize the plant, we instructed the subjects to alter $$ \dot{V}_{\text{E}} $$ voluntarily and measured the hyperbolic $$\dot{V}_{\text{E}} - P_{{{\text{ETCO}}_{ 2} }} $$ relation ( $$ P_{{{\text{ETCO}}_{ 2} }} = A/\dot{V}_{\text{E}} + C $$ ). We characterized these relations both at rest and during light exercise. Regular exercise training did not affect the characteristics of either controller or plant at rest. Exercise stimulus increased the controller gain (S) both in untrained and trained subjects. On the other hand, the $$ P_{{{\text{ETCO}}_{ 2} }} $$ -intercept (B) during exercise was greater in trained than in untrained subjects, indicating that exercise-induced upward shift of the controller property was less in trained than in untrained subjects. The results suggest that the additive exercise drive to breathe was less in trained subjects, without necessarily a change in central chemoreflex threshold. The hyperbolic plant property shifted rightward and upward during exercise as predicted by increased metabolism, with little difference between two groups. The $$ \dot{V}_{\text{E}} $$ during exercise in trained subjects was 21% lower than that in untrained subjects (P

We examined the transfer function of autonomic heart rate (HR) control in anesthetized sedentary and exercise-trained (16 wk, treadmill for 1 h, 5 times/wk at 15 m/min and 15-degree grade) rats for comparison to HR variability assessed in the conscious resting state. The transfer function from sympathetic stimulation to HR response was similar between groups (gain, 4.2 ± 1.5 vs. 4.5 ± 1.5 beats·min−1·Hz−1; natural frequency, 0.07 ± 0.01 vs. 0.08 ± 0.01 Hz; damping coefficient, 1.96 ± 0.55 vs. 1.69 ± 0.15; and lag time, 0.7 ± 0.1 vs. 0.6 ± 0.1 s; sedentary vs. exercise trained, respectively, means ± SD). The transfer gain from vagal stimulation to HR response was 6.1 ± 3.0 in the sedentary and 9.7 ± 5.1 beats·min−1·Hz−1 in the exercise-trained group ( P = 0.06). The corner frequency (0.11 ± 0.05 vs. 0.17 ± 0.09 Hz) and lag time (0.1 ± 0.1 vs. 0.2 ± 0.1 s) did not differ between groups. When the sympathetic transfer gain was averaged for very-low-frequency and low-frequency bands, no significant group effect was observed. In contrast, when the vagal transfer gain was averaged for very-low-frequency, low-frequency, and high-frequency bands, exercise training produced a significant group effect ( P < 0.05 by two-way, repeated-measures ANOVA). These findings suggest that, in the frequency domain, exercise training augments the dynamic HR response to vagal stimulation but not sympathetic stimulation, regardless of the frequency bands.

Non-technical summary The arterial baroreflex is a closed-loop, negative feedback control system that senses baroreceptor pressure and controls systemic arterial pressure (AP) to attenuate perturbations in AP. The total arc of the baroreflex consists of two subsystems: the neural (baroreceptor pressure input to sympathetic nerve activity (SNA)) and peripheral (SNA input to AP) arcs. We show that although the spontaneous baroreflex transfer function obtained by closed-loop analysis has been believed to represent the neural arc function, it is inappropriate for system identification of the neural arc but is essentially appropriate for the peripheral arc under resting condition, when compared with open-loop transfer functions that have good predictabilities of time-series output dynamics from input signals. Our results indicate that in the spontaneous baroreflex system under closed-loop conditions, the peripheral arc (feedforward) function predominates over the neural arc (feedback) function, probably because of the SNA component that is independent of the baroreceptor pressure input. Abstract Although the dynamic characteristics of the baroreflex system have been described by baroreflex transfer functions obtained from open-loop analysis, the predictability of time-series output dynamics from input signals, which should confirm the accuracy of system identification, remains to be elucidated. Moreover, despite theoretical concerns over closed-loop system identification, the accuracy and the predictability of the closed-loop spontaneous baroreflex transfer function have not been evaluated compared with the open-loop transfer function. Using urethane and α-chloralose anaesthetized, vagotomized and aortic-denervated rabbits (n= 10), we identified open-loop baroreflex transfer functions by recording renal sympathetic nerve activity (SNA) while varying the vascularly isolated intracarotid sinus pressure (CSP) according to a binary random (white-noise) sequence (operating pressure ± 20 mmHg), and using a simplified equation to calculate closed-loop-spontaneous baroreflex transfer function while matching CSP with systemic arterial pressure (AP). Our results showed that the open-loop baroreflex transfer functions for the neural and peripheral arcs predicted the time-series SNA and AP outputs from measured CSP and SNA inputs, with r2 of 0.8 ± 0.1 and 0.8 ± 0.1, respectively. In contrast, the closed-loop-spontaneous baroreflex transfer function for the neural arc was markedly different from the open-loop transfer function (enhanced gain increase and a phase lead), and did not predict the time-series SNA dynamics (r2; 0.1 ± 0.1). However, the closed-loop-spontaneous baroreflex transfer function of the peripheral arc partially matched the open-loop transfer function in gain and phase functions, and had limited but reasonable predictability of the time-series AP dynamics (r2, 0.7 ± 0.1). A numerical simulation suggested that a noise predominantly in the neural arc under resting conditions might be a possible mechanism responsible for our findings. Furthermore, the predictabilities of the neural arc transfer functions obtained in open-loop and closed-loop conditions were validated by closed-loop pharmacological (phenylephrine and nitroprusside infusions) pressure interventions. Time-series SNA responses to drug-induced AP changes predicted by the open-loop transfer function matched closely the measured responses (r2, 0.9 ± 0.1), whereas SNA responses predicted by closed-loop-spontaneous transfer function deviated greatly and were the inverse of measured responses (r, −0.8 ± 0.2). These results indicate that although the spontaneous baroreflex transfer function obtained by closed-loop analysis has been believed to represent the neural arc function, it is inappropriate for system identification of the neural arc but is essentially appropriate for the peripheral arc under resting conditions, when compared with open-loop analysis.

Although baroreceptors are known to reset to operate in a higher pressure range in spontaneously hypertensive rats (SHR), the total profile of dynamic arterial pressure (AP) regulation remains to be clarified. We estimated open-loop transfer functions of the carotid sinus baroreflex in SHR and Wistar Kyoto (WKY) rats. Mean input pressures were set at 120 (WKY120 and SHR120) and 160 mmHg (SHR160). The neural arc transfer function from carotid sinus pressure to efferent splanchnic sympathetic nerve activity (SNA) revealed derivative characteristics in both WKY and SHR. The slope of dynamic gain (in decibels per decade) between 0.1 and 1 Hz was not different between WKY120 (10.1 ± 1.0) and SHR120 (10.4 ± 1.1) but was significantly greater in SHR160 (13.2 ± 0.8, P < 0.05 with Bonferroni correction) than in SHR120. The peripheral arc transfer function from SNA to AP showed low-pass characteristics. The slope of dynamic gain (in decibels per decade) did not differ between WKY120 (−34.0 ± 1.2) and SHR120 (−31.4 ± 1.0) or between SHR120 and SHR160 (−32.8 ± 1.3). The total baroreflex showed low-pass characteristics and the dynamic gain at 0.01 Hz did not differ between WKY120 (0.91 ± 0.08) and SHR120 (0.84 ± 0.13) or between SHR120 and SHR160 (0.83 ± 0.11). In both WKY and SHR, the declining slope of dynamic gain was significantly gentler for the total baroreflex than for the peripheral arc, suggesting improved dynamic AP response in the total baroreflex. In conclusion, the dynamic characteristics of AP regulation by the carotid sinus baroreflex were well preserved in SHR despite significantly higher mean AP.

The internal thoracic artery (ITA) is harvested by either the pedicled or the skeletonized technique in coronary artery bypass grafting (CABG), with no clear advantage of one technique over the other. We compared graft flow between the pedicled and skeletonized ITA grafts while varying myocardial oxygen demand. CABG was performed to the left anterior descending artery in five anesthetized dogs using a pedicled ITA graft and the graft was subsequently skeletonized. Graft flow was measured during stepwise electrical stimulation of the stellate ganglion. The baseline graft flow before sympathetic stimulation was higher in skeletonized (27.8 ± 1.9 ml/min) than that in pedicled ITA grafts (22.6 ± 2.7 ml/min) (P < 0.05). In both ITA grafts, however, graft flow increased to a similar level during sympathetic stimulation that doubled the double product, correlating with the double product. Based on these results, we conclude that metabolic demand can override the potential difference in sympathetic vasoconstriction in both pedicled and skeletonized ITA grafts.

We estimated the transfer function of autonomic heart rate (HR) control by using random binary sympathetic or vagal nerve stimulation in anaesthetized rats. The transfer function from sympathetic stimulation to HR response approximated a second-order, low-pass filter with a lag time (gain, 4.29 ± 1.55 beats min−1 Hz−1; natural frequency, 0.07 ± 0.03 Hz; damping coefficient, 1.96 ± 0.64; and lag time, 0.73 ± 0.12 s). The transfer function from vagal stimulation to HR response approximated a first-order, low-pass filter with a lag time (gain, 8.84 ± 4.51 beats min−1 Hz−1; corner frequency, 0.12 ± 0.06 Hz; and lag time, 0.12 ± 0.08 s). These results suggest that the dynamic characteristics of HR control by the autonomic nervous system in rats are similar to those of larger mammals.

We estimated open-loop dynamic characteristics of the carotid sinus baroreflex in normal control rats and chronic heart failure (CHF) rats after myocardial infarction. First, the neural arc transfer function from carotid sinus pressure to splanchnic sympathetic nerve activity (SNA) and its corresponding step response were examined. Although the steady-state response was attenuated in CHF, the negative peak response and the time to peak did not change significantly, suggesting preserved neural arc dynamic characteristics. Next, the peripheral arc transfer function from SNA to arterial pressure (AP) and its corresponding step response were examined. The steady-state response and the initial slope were reduced in CHF, suggesting impaired end-organ responses. In a simulation study based on the dynamic and static characteristics, the percent recovery of AP was reduced progressively as the size of disturbance increased in CHF, suggesting that a reserve for AP buffering is lost in CHF despite relatively maintained baseline AP.

To directly monitor vagal acetylcholine (ACh) release into the sinoatrial node, which regulates heart rate, we implanted a microdialysis probe in the right atrium near the sinoatrial node and in the right ventricle of anesthetized rabbits, and perfused with Ringer's solution containing eserine. (1) Electrical stimulation of right or left cervical vagal nerve decreased atrial rate and increased dialysate ACh concentration in the right atrium in a frequency-dependent manner. Compared to left vagal stimulation, right vagal nerve stimulation decreased atrial rate to a greater extent at all frequencies, and increased dialysate ACh concentration to a greater extent at 10 and 20 Hz. However, dialysate ACh concentration in the right atrium correlated well with atrial rate independent of whether electrical stimulation was applied to the right or left vagal nerve (atrial rate=304-131 x log[ACh], R(2)=0.77). (2) Right or left vagal nerve stimulation at 20 Hz decreased atrial rate and increased dialysate ACh concentrations in both the right atrium (right, 17.9+/-4.0 nM; left, 7.9+/-1.4 nM) and right ventricle (right, 0.9+/-0.3 nM; left, 1.0+/-0.4 nM). However, atrial dialysate ACh concentrations were significantly higher than ventricular concentrations, while ventricular dialysate ACh concentrations were not significantly different between right and left vagal nerve stimulation. (3) The response of ACh release to right and left vagal nerve stimulation was abolished by intravenous administration of a ganglionic blocker, hexamethonium bromide. In conclusion, ACh concentration in dialysate from the right atrium, sampled by microdialysis, is a good marker of ACh release from postganglionic vagal nerves to the sinoatrial node.

To better understand the pathophysiological role of angiotensin II (ANG II) in the dynamic autonomic regulation of heart rate (HR), we examined the effects of intravenous administration of ANG II (10 μg·kg−1·h−1) on the transfer function from vagal or sympathetic nerve stimulation to HR in anesthetized rabbits with sinoaortic denervation and vagotomy. In the vagal stimulation group ( n = 7), we stimulated the right vagal nerve for 10 min using binary white noise (0–10 Hz). The transfer function from vagal stimulation to HR approximated a first-order low-pass filter with pure delay. ANG II attenuated the dynamic gain from 7.6 ± 0.9 to 5.8 ± 0.9 beats·min−1·Hz−1 (means ± SD; P < 0.01) without affecting the corner frequency or pure delay. In the sympathetic stimulation group ( n = 7), we stimulated the right postganglionic cardiac sympathetic nerve for 20 min using binary white noise (0–5 Hz). The transfer function from sympathetic stimulation to HR approximated a second-order low-pass filter with pure delay. ANG II slightly attenuated the dynamic gain from 10.8 ± 2.6 to 10.2 ± 3.1 beats·min−1·Hz−1 ( P = 0.049) without affecting the natural frequency, damping ratio, or pure delay. The disproportional suppression of the dynamic vagal and sympathetic regulation of HR would result in a relative sympathetic predominance in the presence of ANG II. The reduced high-frequency component of HR variability in patients with cardiovascular diseases, such as myocardial infarction and heart failure, may be explained in part by the peripheral effects of ANG II on the dynamic autonomic regulation of HR.

Background: Autonomic neural intervention is a promising tool for modulating the circulatory system thereby treating some cardiovascular diseases. Methods and Results: In 8 pentobarbital-anesthetized cats, it was examined whether the arterial pressure (AP) could be controlled by acupuncture-like hind-limb electrical stimulation (HES). With a 0.5-ms pulse width, HES monotonically reduced AP as the stimulus current increased from 1 to 5 mA, suggesting that the stimulus current could be a primary control variable. In contrast, the depressor effect of HES showed a nadir approximately 10 Hz in the frequency range between 1 and 100 Hz. Dynamic characteristics of the AP response to HES approximated a second-order low-pass filter with dead time (gain: -10.2 ±1.6 mmHg/mA, natural frequency: 0.040 ±0.004 Hz, damping ratio 1.80 ±0.24, dead time: 1.38 ±0.13 s, mean ± SE). Based on these dynamic characteristics, a servo-controlled HES system was developed. When a target AP value was set at 20 mmHg below the baseline AP, the time required for the AP response to reach 90% of the target level was 38 ±10 s. The steady-state error between the measured and target AP values was 1.3 ±0.1 mmHg. Conclusions: Autonomic neural intervention by acupuncture-like HES might provide an additional modality to quantitatively control the circulatory system. (Circ J 2009; 73: 851 - 859)

Although the muscle mechanoreflex is one of the pressor reflexes during exercise, its interaction with dynamic characteristics of the arterial baroreflex remains to be quantitatively analyzed. In anesthetized, vagotomized, and aortic-denervated rabbits ( n = 7), we randomly perturbed isolated carotid sinus pressure (CSP) using binary white noise while recording renal sympathetic nerve activity (SNA) and arterial pressure (AP). We estimated the transfer functions of the baroreflex neural arc (CSP to SNA) and peripheral arc (SNA to AP) under conditions of control and muscle stretch of the hindlimb (5 kg of tension). The muscle stretch increased the dynamic gain of the neural arc while maintaining the derivative characteristics [gain at 0.01 Hz: 1.0 ± 0.2 vs. 1.4 ± 0.6 arbitrary units (au)/mmHg, gain at 1 Hz: 1.7 ± 0.6 vs. 2.7 ± 1.4 au/mmHg; P < 0.05, control vs. stretch]. In contrast, muscle stretch did not affect the peripheral arc. In the time domain, muscle stretch augmented the steady-state response at 50 s (−1.1 ± 0.3 vs. −1.7 ± 0.7 au; P < 0.05, control vs. stretch) and negative peak response (−2.1 ± 0.5 vs. −3.1 ± 1.5 au; P < 0.05, control vs. stretch) in the SNA step response. A simulation experiment using the results indicated that the muscle mechanoreflex would accelerate the closed-loop AP regulation via the arterial baroreflex.

Although an importance of vasoconstrictor skin sympathetic nerve activity (SNA) in control of cutaneous circulation is widely recognized, the decoding rule that translate dynamic fluctuations of vasoconstrictor skin SNA into skin blood flow is not fully understood. In 10 male subjects who rested in supine position under normothermic condition, we measured skin blood flow index (by laser-Doppler flowmetry) at the dorsum pedis, and vasoconstrictor skin SNA (by microneurography) that was confirmed to innervate the same region as the flow index. We determined the transfer and coherence functions from the neural activity input to the flow and quantified the contribution and predictability from the input to output by system engineering technique. The results showed that in frequency-domain analysis, the transfer function from vasoconstrictor skin SNA to skin blood flow had low-pass filter characteristics with 3.6 ± 0.1 s of pure time delay. The coherence function was approximately 0.5 between 0.01 and 0.1 Hz and less above 0.1 Hz. In time-domain analysis, the predictability from the SNA to the skin blood flow was approximately 50%. These findings indicate that at normothermic rest, the decoding rule from vasoconstrictor skin SNA to skin blood flow of skin is characterized by low-pass filter with 3–4 s of pure time delay, and that the vasoconstrictor skin SNA contributes to a half of fluctuation of skin blood flow in the condition. The incomplete dependence of skin blood flow on vasoconstrictor skin SNA may confirm nonneural mechanisms to control cutaneous circulation even at normothermic rest.

Maintenance of arterial pressure (AP) under orthostatic stress against gravitational fluid shift and pressure disturbance is of great importance. One of the mechanisms is that upright tilt resets steady-state baroreflex control to a higher sympathetic nerve activity (SNA). However, the dynamic feedback characteristics of the baroreflex system, a hallmark of fast-acting neural control, remain to be elucidated. In the present study, we tested the hypothesis that upright tilt resets the dynamic transfer function of the baroreflex neural arc to minify the pressure disturbance in total baroreflex control. Renal SNA and AP were recorded in ten anesthetized, vagotomized and aortic-denervated rabbits. Under baroreflex open-loop condition, isolated intracarotid sinus pressure (CSP) was changed according to a binary white noise sequence at operating pressure +/- 20 mmHg, while the animal was placed supine and at 60 degrees upright tilt. Regardless of the postures, the baroreflex neural (CSP to SNA) and peripheral (SNA to AP) arcs showed dynamic high-pass and low-pass characteristics, respectively. Upright tilt increased the transfer gain of the neural arc (resetting), decreased that of the peripheral arc, and consequently maintained the transfer characteristics of total baroreflex feedback system. A simulation study suggests that postural resetting of the neural arc would significantly increase the transfer gain of the total arc in upright position, and that in closed-loop baroreflex the resetting increases the stability of AP against pressure disturbance under orthostatic stress. In conclusion, upright tilt resets the dynamic transfer function of the baroreflex neural arc to minify the pressure disturbance in total baroreflex control.

Vagal nerve stimulation has been suggested to ameliorate left ventricular (LV) remodeling in heart failure. However, it is not known whether and to what degree vagal nerve stimulation affects matrix metalloproteinase (MMP) and tissue inhibitor of MMP (TIMP) in myocardium, which are known to play crucial roles in LV remodeling. We therefore investigated the effects of electrical stimulation of efferent vagal nerve on myocardial expression and activation of MMPs and TIMPs in a rabbit model of myocardial ischemia-reperfusion (I/R) injury. Anesthetized rabbits were subjected to 60 min of left coronary artery occlusion and 180 min of reperfusion with (I/R-VS, n = 8) or without vagal nerve stimulation (I/R, n = 7). Rabbits not subjected to coronary occlusion with (VS, n = 7) or without vagal stimulation (sham, n = 7) were used as controls. Total MMP-9 protein increased significantly after left coronary artery occlusion in I/R-VS and I/R to a similar degree compared with VS and sham values. Endogenous active MMP-9 protein level was significantly lower in I/R-VS compared with I/R. TIMP-1 mRNA expression was significantly increased in I/R-VS compared with the I/R, VS, and sham groups. TIMP-1 protein was significantly increased in I/R-VS and VS compared with the I/R and sham groups. Cardiac microdialysis technique demonstrated that topical perfusion of acetylcholine increased dialysate TIMP-1 protein level, which was suppressed by coperfusion of atropine. Immunohistochemistry demonstrated a strong expression of TIMP-1 protein in cardiomyocytes around the dialysis probe used to perfuse acetylcholine. In conclusion, in a rabbit model of myocardial I/R injury, vagal nerve stimulation induced TIMP-1 expression in cardiomyocytes and reduced active MMP-9.

Grb2-associated binder (Gab) family of scaffolding adaptor proteins coordinate signaling cascades downstream of growth factor and cytokine receptors. In the heart, among EGF family members, neuregulin-1beta (NRG-1beta, a paracrine factor produced from endothelium) induced remarkable tyrosine phosphorylation of Gab1 and Gab2 via erythroblastic leukemia viral oncogene (ErbB) receptors. We examined the role of Gab family proteins in NRG-1beta/ErbB-mediated signal in the heart by creating cardiomyocyte-specific Gab1/Gab2 double knockout mice (DKO mice). Although DKO mice were viable, they exhibited marked ventricular dilatation and reduced contractility with aging. DKO mice showed high mortality after birth because of heart failure. In addition, we noticed remarkable endocardial fibroelastosis and increase of abnormally dilated vessels in the ventricles of DKO mice. NRG-1beta induced activation of both ERK and AKT in the hearts of control mice but not in those of DKO mice. Using DNA microarray analysis, we found that stimulation with NRG-1beta upregulated expression of an endothelium-stabilizing factor, angiopoietin 1, in the hearts of control mice but not in those of DKO mice, which accounted for the pathological abnormalities in the DKO hearts. Taken together, our observations indicated that in the NRG-1beta/ErbB signaling, Gab1 and Gab2 of the myocardium are essential for both maintenance of myocardial function and stabilization of cardiac capillary and endocardial endothelium in the postnatal heart.

Cavopulmonary assist (CPA) for failing Fontan patients remains a challenging issue in the clinical setting. To evaluate the effectiveness of a partial CPA from the inferior vena cava (IVC) to the pulmonary artery (PA), we performed a theoretical analysis using a computational model of the Fontan circulation. Cardiac chambers and vascular systems were described as the time-varying elastance model and the modified three-element Windkessel model, respectively. A rotational pump described as a non-linear function was inserted between the IVC and the PA. When pulmonary vascular resistance index varied from 2.1 to 5.9 Wood units m(2), the partial CPA maintained cardiac index as efficiently as total CPA and markedly reduced the IVC pressure compared with total CPA. However, the partial CPA increased the superior vena cava pressure substantially. The modification from total to partial CPA is potentially an effective alternative in failing Fontan patients suffering from high IVC pressure.

Although an axoplasmic Ca2+ increase is associated with an exocytotic acetylcholine (ACh) release from the parasympathetic postganglionic nerve endings, the role of voltage-dependent Ca2+ channels in ACh release in the mammalian cardiac parasympathetic nerve is not clearly understood. Using a cardiac microdialysis technique, we examined the effects of Ca2+ channel antagonists on vagal nerve stimulation- and ischemia-induced myocardial interstitial ACh releases in anesthetized cats. The vagal stimulation-induced ACh release [22.4 nM (SD 10.6), n = 7] was significantly attenuated by local administration of an N-type Ca2+ channel antagonist ω-conotoxin GVIA [11.7 nM (SD 5.8), n = 7, P = 0.0054], or a P/Q-type Ca2+ channel antagonist ω-conotoxin MVIIC [3.8 nM (SD 2.3), n = 6, P = 0.0002] but not by local administration of an L-type Ca2+ channel antagonist verapamil [23.5 nM (SD 6.0), n = 5, P = 0.758]. The ischemia-induced myocardial interstitial ACh release [15.0 nM (SD 8.3), n = 8] was not attenuated by local administration of the L-, N-, or P/Q-type Ca2+ channel antagonists, by inhibition of Na+/Ca2+ exchange, or by blockade of inositol 1,4,5-trisphosphate [Ins( 1 , 4 , 5 )P3] receptor but was significantly suppressed by local administration of gadolinium [2.8 nM (SD 2.6), n = 6, P = 0.0283]. In conclusion, stimulation-induced ACh release from the cardiac postganglionic nerves depends on the N- and P/Q-type Ca2+ channels (with a dominance of P/Q-type) but probably not on the L-type Ca2+ channels in cats. In contrast, ischemia-induced ACh release depends on nonselective cation channels or cation-selective stretch activated channels but not on L-, N-, or P/Q type Ca2+ channels, Na+/Ca2+ exchange, or Ins( 1 , 4 , 5 )P3 receptor-mediated pathway.

Objectives We examined how repolarization and depolarization abnormalities contribute to the development of extrasystoles and subsequent ventricular fibrillation (VF) in a model of the Brugada syndrome. Background Repolarization and depolarization abnormalities have been considered to be mechanisms of the coved-type ST-segment elevation (Brugada-electrocardiogram [ECG]) and development of VF in the Brugada syndrome. Methods We used high-resolution (256 × 256) optical mapping techniques to study arterially perfused canine right ventricular wedges (n = 20) in baseline and in the Brugada-ECG produced by administration of terfenadine (5 μmol/l), pinacidil (2 μmol/l), and pilsicainide (5 μmol/l). We recorded spontaneous episodes of phase 2 re-entrant (P2R)-extrasystoles and subsequent self-terminating polymorphic ventricular tachycardia (PVT) or VF under the Brugada-ECG condition and analyzed the epicardial conduction velocity and action potential duration (APD) restitutions in each condition. Results Forty-one episodes of spontaneous P2R-extrasystoles in the Brugada-ECG were successfully mapped in 9 of 10 preparations, and 33 of them were originated from the maximum gradient of repolarization (GR max : 176 ± 54 ms/mm) area in the epicardium, leading to PVT (n = 12) or VF (n = 5). The epicardial GR max was not different between PVT and VF. Wave-break during the first P2R-extrasystole produced multiple wavelets in all VF cases, whereas no wave-break or wave-break followed by wave collision and termination occurred in PVT cases. Moreover, conduction velocity restitution was shifted lower and APD restitution was more variable in VF cases than in PVT cases. Conclusions Steep repolarization gradient in the epicardium but not endocardium develops P2R-extrasystoles in the Brugada-ECG condition, which might degenerate into VF by further depolarization and repolarization abnormalities.

Despite accumulating data of muscle sympathetic nerve activity (SNA) measured by human microneurography, whether neural discharges of muscle SNA correlates and coheres with those of other SNAs controlling visceral organs remains unclear. Further, how the baroreflex control of SNA affects the relations between these SNAs remains unknown. In urethane and alpha-chloralose anesthetized, vagotomized, and aortic-denervated rabbits, we recorded muscle SNA from the tibial nerve using microneurography and simultaneously recorded renal and cardiac SNAs. After isolating the carotid sinuses, we produced a baroreflex closed-loop condition by matching the isolated intracarotid sinus pressure (CSP) with systemic arterial pressure (CLOSE). We also fixed CSP at operating pressure (FIX) or altered CSP widely (WIDE: operating pressure +/- 40 mmHg). Under these conditions, we calculated time-domain and frequency-domain measures of the correlation between muscle SNA and renal or cardiac SNAs. At CLOSE, muscle SNA resampled at 1 Hz correlated with both renal (r(2) = 0.71 +/- 0.04, delay = 0.10 +/- 0.004 s) and cardiac SNAs (r(2) = 0.58 +/- 0.03, delay = 0.13 +/- 0.004 s) at optimal delays. Moreover,muscle SNA at CLOSE strongly cohered with renal and cardiac SNAs(coherence0.8) at the autospectral peak frequencies, and weakly (0.4-0.5) at the remaining frequencies. Increasing the magnitude of CSP change from FIX to CLOSE and further to WIDE resulted in corresponding increases in correlation and coherence functions at nonpeak frequencies, and the coherence functions at peak frequencies remained high (0.8). In conclusion, muscle SNA correlates and coheres approximately with renal and cardiac SNAs under closed-loop baroreflex conditions. The arterial baroreflex is capable of potently homogenizing neural discharges of these SNAs by modulating SNA at the nonpeak frequencies of SNA autospectra.

Sympathetic activation during orthostatic stress is accompanied by a marked increase in low-frequency (LF, approximately 0.1-Hz) oscillation of sympathetic nerve activity (SNA) when arterial pressure (AP) is well maintained. However, LF oscillation of SNA during development of orthostatic neurally mediated syncope remains unknown. Ten healthy subjects who developed head-up tilt (HUT)-induced syncope and 10 age-matched nonsyncopal controls were studied. Nonstationary time-dependent changes in calf muscle SNA (MSNA, microneurography), R-R interval, and AP (finger photoplethysmography) variability during a 15-min 60 degrees HUT test were assessed using complex demodulation. In both groups, HUT during the first 5 min increased heart rate, magnitude of MSNA, LF and respiratory high-frequency (HF) amplitudes of MSNA variability, and LF and HF amplitudes of AP variability but decreased HF amplitude of R-R interval variability (index of cardiac vagal nerve activity). In the nonsyncopal group, these changes were sustained throughout HUT. In the syncopal group, systolic AP decreased from 100 to 60 s before onset of syncope; LF amplitude of MSNA variability decreased, whereas magnitude of MSNA and LF amplitude of AP variability remained elevated. From 60 s before onset of syncope, MSNA and heart rate decreased, index of cardiac vagal nerve activity increased, and AP further decreased to the level at syncope. LF oscillation of MSNA variability decreased during development of orthostatic neurally mediated syncope, preceding sympathetic withdrawal, bradycardia, and severe hypotension, to the level at syncope.

Accurate prediction of cardiac output (CO), left atrial pressure (PLA), and right atrial pressure (PRA) is a prerequisite for management of patients with compromised hemodynamics. In our previous study (Uemura et al. Am J Physiol Heart Circ Physiol 286: H2376–H2385, 2004), we demonstrated a circulatory equilibrium framework, which permits the prediction of CO, PLA, and PRA once the venous return surface and integrated CO curve are known. Inasmuch as we also showed that the surface can be estimated from single-point CO, PLA, and PRA measurements, we hypothesized that a similar single-point estimation of the CO curve would enable us to predict hemodynamics. In seven dogs, we measured the PLA-CO and PRA-CO relations and derived a standardized CO curve using the logarithmic function CO = SL[ln(PLA − 2.03) + 0.80] for the left heart and CO = SR[ln(PRA − 2.13) + 1.90] for the right heart, where SL and SR represent the preload sensitivity of CO, i.e., pumping ability, of the left and right heart, respectively. To estimate the integrated CO curve in each animal, we calculated SL and SR from single-point CO, PLA, and PRA measurements. Estimated and measured CO agreed reasonably well. In another eight dogs, we altered stressed blood volume (−8 to +8 ml/kg of reference volume) under normal and heart failure conditions and predicted the hemodynamics by intersecting the surface and the CO curve thus estimated. We could predict CO [ y = 0.93 x + 6.5, r 2 = 0.96, standard error of estimate (SEE) = 7.5 ml·min−1·kg−1], PLA ( y = 0.90 x + 0.5, r 2 = 0.93, SEE = 1.4 mmHg), and PRA ( y = 0.87 x + 0.4, r 2 = 0.91, SEE = 0.4 mmHg) reasonably well. In conclusion, single-point estimation of the integrated CO curve enables accurate prediction of hemodynamics in response to extensive changes in stressed blood volume.

Since humans are under ceaseless orthostatic stress, the mechanism to maintain arterial pressure (AP) under orthostatic stress against gravitational fluid shift is of great importance. We hypothesized that (1) orthostatic stress resets the arterial baroreflex control of sympathetic nerve activity (SNA) to a higher SNA, and (2) resetting of the arterial baroreflex contributes to preventing postural hypotension. Renal SNA and AP were recorded in eight anaesthetized, vagotomized and aortic-denervated rabbits. Isolated intracarotid sinus pressure (CSP) was increased stepwise from 40 to 160 mmHg with increments of 20 mmHg (60 s for each CSP level) while the animal was placed supine and at 60 deg upright tilt. Upright tilt shifted the CSP–SNA relationship (the baroreflex neural arc) to a higher SNA, shifted the SNA–AP relationship (the baroreflex peripheral arc) to a lower AP, and consequently moved the operating point to marked high SNA while maintaining AP. A simulation study suggests that resetting in the neural arc would double the orthostatic activation of SNA and increase the operating AP in upright tilt by 10 mmHg, compared with the absence of resetting. In addition, upright tilt did not change the CSP–AP relationship (the baroreflex total arc). A simulation study suggests that although a downward shift of the peripheral arc could shift the total arc downward, resetting in the neural arc would compensate this fall and prevent the total arc from shifting downward to a lower AP. In conclusion, upright tilt increases SNA by resetting the baroreflex neural arc. This resetting may compensate for the reduced pressor responses to SNA in the peripheral cardiovascular system and contribute to preventing postural hypotension.

An intermittent exposure to artificial hypergravity with physical exercise by a human centrifuge may provide a countermeasure against various physiological problems after space flight. To test the effects of hypergravity with ergometric exercise on dynamic regulation of heart rate during weightlessness, we quantified autonomic cardiovascular control before and after head-down-tilt bed rest (HDBR) with and without the countermeasure. Twelve male subjects underwent a 14-day period of HDBR. Six of them were exposed to a hypergravity (+1.2 Gz acceleration at heart level) for 30 min with ergometric exercise (60 W, n=4; 40 W, n=2) as a countermeasure on day 1, 2, 3, 5, 7, 9, 11, 12, 13 and 14, during HDBR (CM group). The remaining six were not exposed to a hypergravity exercise during HDBR (control group). Blood pressure and ECG were recorded at a supine position before and after HDBR. The high frequency power of R-R interval (HFRR; 1,008+/-238 to 353+/-56 ms(2) P

A novel framework of circulatory equilibrium was developed by extending Guyton's original concept. In this framework, venous return (COV) for a given stressed volume (V) was characterized by a flat surface as a function of right atrial pressure (PRA) and left atrial pressure (PLA) as follows: COV= V /W − GSPRA− GPPLA, where W, GS, and GPdenote linear parameters. In seven dogs under total heart bypass, COV, PRA, PLA, and V were varied to determine the three parameters in each animal with use of multivariate analysis. The coefficient of determination ( r2= 0.92–0.99) indicated the flatness of the venous return surface. The averaged surface was COV= V/0.129 − 19.61PRA− 3.49PLA. To examine the invariability of the surface parameters among animals, we predicted the circulatory equilibrium in response to changes in stressed volume in another 12 dogs under normal and heart failure conditions. This was achieved by equating the standard surface with the individually measured cardiac output (CO) curve. In this way, we could predict CO [ y = 0.90 x + 5.6, r2= 0.95, standard error of the estimate (SEE) = 8.7 ml·min−1·kg−1], PRA( y = 0.96 x, r2= 0.98, SEE = 0.2 mmHg), and PLA( y = 0.89 x + 0.5, r2= 0.98, SEE = 0.8 mmHg) reasonably well. We conclude that the venous return surface accurately represents the venous return properties of the systemic and pulmonary circulations. The characteristics of the venous return surface are invariable enough among animals, making it possible to predict circulatory equilibrium, even if those characteristics are unknown in individual animals.

We studied the effects of 14 days of 6 degrees head-down bed rest (HDBR) in 16 healthy male subjects to examine the functional changes in the autonomic nervous system and cardiac baroreceptor reflex response with an emphasis on dynamic changes during HDBR. Beat-by-beat RR intervals (RRIs) and systolic arterial pressures (SAPs) were measured non-invasively from simultaneous, continuous recordings of ECG and arterial pressure waves in supine resting postures. A power spectrum analysis by the fast Fourier transform was applied to a data set composed of interpolated 512 RRIs and 512 SAPs (256 s in duration). Three indices of cardiac baroreceptor reflex sensitivity (BRS) were obtained by applying a sequence technique and a cross-spectrum analysis technique to the spontaneous RRIs and SAPs. The high-frequency band power of RRI variability (HF(RRI)) decreased significantly in the latter part of HDBR and persisted until the initial stage of the post-HDBR period (POST). The low-frequency band power of SAP variability decreased significantly only during the mid-part of HDBR. The BRS(sequence) obtained by the sequence technique showed a significant increase temporarily on the initial day of HDBR. The BRS(sequence) and the estimate of BRS obtained by the cross-spectrum analysis handling the high-frequency band were both significantly decreased on the initial day of POST. Each of the BRS estimates correlated negatively with heart rate and positively with HF(RRI) during HDBR and POST. These results suggest the following: (1) cardiac spontaneous baroreceptor reflex sensitivity might be transiently increased at the initial stage of HDBR, (2) the reduction in vagal modulation on the sinus node occurs from the latter part of HDBR to the initial stage of POST, (3) sympathetic vasomotor control is probably slightly inhibited during the mid-part of HDBR, and (4) the enhancement in cardiac sympathetic modulation and the impairment in cardiac spontaneous baroreceptor reflex sensitivity may occur in the initial stage of POST.

Neuronal uptake is the most important mechanism by which norepinephrine (NE) is removed from the synaptic clefts at sympathetic nerve terminals. We examined the effects of neuronal NE uptake blockade on the dynamic sympathetic regulation of the arterial baroreflex because dynamic characteristics are important for understanding the system behavior in response to exogenous disturbance. We perturbed intracarotid sinus pressure (CSP) according to a binary white noise sequence in anesthetized rabbits, while recording cardiac sympathetic nerve activity (SNA), arterial pressure (AP), and heart rate (HR). Intravenous administration of desipramine (1 mg/kg) decreased the normalized gain of the neural arc transfer function from CSP to SNA relative to untreated control (1.03 ± 0.09 vs. 0.60 ± 0.08 AU/mmHg, mean ± SE, P < 0.01) but did not affect that of the peripheral arc transfer function from SNA to AP (1.10 ± 0.05 vs. 1.08 ± 0.10 mmHg/AU). The normalized gain of the transfer function from SNA to HR was unaffected (1.01 ± 0.04 vs. 1.09 ± 0.12 beats·min−1·AU−1). Desipramine decreased the natural frequency of the transfer function from SNA to AP by 28.7 ± 7.0% (0.046 ± 0.007 vs. 0.031 ± 0.002 Hz, P < 0.05) and that of the transfer function from SNA to HR by 64.4 ± 2.2% (0.071 ± 0.003 vs. 0.025 ± 0.002 Hz, P < 0.01). In conclusion, neuronal NE uptake blockade by intravenous desipramine administration reduced the total buffering capacity of the arterial baroreflex mainly through its action on the neural arc. The differential effects of neuronal NE uptake blockade on the dynamic AP and HR responses to SNA may provide clues for understanding the complex pathophysiology of cardiovascular diseases associated with neuronal NE uptake deficiency.

The effects of the muscle mechanoreflex on the arterial baroreflex neural control have not previously been analyzed over the entire operating range of the arterial baroreflex. In anesthetized, vagotomized, and aortic-denervated rabbits ( n = 8), we isolated carotid sinuses and changed intracarotid sinus pressure (CSP) from 40 to 160 mmHg in increments of 20 mmHg every minute while recording renal sympathetic nerve activity (SNA) and arterial pressure (AP). Muscle mechanoreflex was induced by passive muscle stretch (5 kg of tension) of the hindlimb. Muscle stretch shifted the CSP-SNA relationship (neural arc) to a higher SNA, whereas it did not affect the SNA-AP relationship (peripheral arc). SNA was almost doubled [from 63 ± 15 to 118 ± 14 arbitrary units (au), P < 0.05] at the CSP level of 93 ± 8 mmHg, and AP was increased ∼50% by muscle stretch. When the baroreflex negative feedback loop was closed, muscle stretch increased SNA from 63 ± 15 to 81 ± 21 au ( P < 0.05) and AP from 93 ± 8 to 109 ± 12 mmHg ( P < 0.05). In conclusion, the muscle mechanoreflex resets the neural arc to a higher SNA, which moves the operating point towards a higher SNA and AP under baroreflex closed-loop conditions. Analysis of the baroreflex equilibrium diagram indicated that changes in the neural arc induced by the muscle mechanoreflex might compensate for pressure falls resulting from exercise-induced vasodilatation.