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Background Pulse rate (PR) indicates heart beat rhythm and contains various intrinsic characteristics of peripheral regulation. Pulse rate variability (PRV) is a reliable method to assess autonomic nervous system function quantitatively as an effective alternative to heart rate variability. However, the frequency range of PRV is limited by the temporal resolution of PR based on heart rate and it is further restricted the exploration of optimal autoregulation frequency based on spectral analysis. Methods Recently, a new novel method, called instantaneous PRV (iPRV), was proposed. iPRV breaks the limitation of temporal resolution and extends the frequency band. Moreover, iPRV provides a new frequency band, called very high frequency band (VHF; 0.4-0.9Hz). Results The results showed that the VHF indicated the influences of respiratory maneuvers (paced respiration at 6-cycle and 30-cycle) and the nonstationary condition (head-up tilt; HUT). Conclusions VHF is as a potential indication of autoregulation in higher frequency range and with peripheral regulation. It helps for the frequency exploration of cardiovascular autoregulation. [ABSTRACT FROM AUTHOR]

Background: The frequency of jugular venous reflux (JVR) is higher in patients with transient monocular blindness (TMB). We hypothesize that JVR influences ocular venous outflow, and resulting disturbances in cerebral and ocular venous circulation might be a cause of TMB. To substantiate this hypothesis, we aimed to demonstrate that: (1) TMB patients have vasculature changes in their retinal venules, and (2) JVR could influence ocular venous outflow, as revealed by dilated retinal venules. Methods: This study has 2 parts. The case-control study included 31 TMB patients and 31 age/gender-matched normal individuals, who all received fundus photography for retinal venule diameter comparisons. The Valsalva maneuver (VM) experiment included 30 healthy volunteers who received both color Doppler imaging of the internal jugular vein and fundus photography for retinal venule diameter measurement. Results: In the case-control study, TMB patients had a wider retinal venule diameter (184.5 ± 17.5 vs. 174.3 ± 16.2 μm, right eye, p = 0.023; 194.20 ± 24.6 vs. 176.6 ± 19.5 μm, left eye, p = 0.017), especially TMB patients with JVR. The VM experiments showed that the presence of JVR was associated with a greater increase in retinal venule diameters during VM in the subjects’ right eye (14.27 ± 11.16 vs. 2.75 ± 3.51%, JVR vs. non-JVR, p = 0.0002) and left eye (10.06 ± 6.42 vs. 1.80 ± 2.03%, p = 0.0003). Conclusions: These findings provide evidence that frequently occurring JVR associated with TMB impedes ocular venous outflow, and the subsequent disturbances in ocular venous circulation may be a cause of TMB. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

pH-stating is a common technique for monitoring kinetics of various biochemical reactions that involve the generation of hydrogen or hydroxyl ions. In this work, we describe a reagentless electrochemical micro-pH-stat where the titrant of acid or base is produced by water electrolysis on the rotating sample system (RSS) platform. RSS originated from the authors' laboratory as a convective platform to support different analytical techniques in microliter-sized samples. As water electrolysis induces no volume change and the current that generates the reagent can be precisely measured even at low levels, very small samples in the microliter range become accessible for pH-stating: a reduction of more than an order of magnitude in specimen size relative to the most sensitive conventional methods. Nearly 100% current efficiency has been achieved with this system using a 250 μm Pt minidisc working electrode for electrolysis. The developed micro-pH-stat has been validated by the determination of the activity of erythrocyte acetylcholinesterase as a function of substrate concentration and pH. The optimal pH and activity profile obtained are in good agreement with those determined with standard techniques. The micro-pH-stat has the potential for applications for enzyme assays, reagentless pH control, acidity/alkalinity, and buffer capacity measurements in very small samples of biomedical and environmental origin. [ABSTRACT FROM AUTHOR]

Background: The reliability of critical closing pressure (CrCP) estimates derived from peripheral blood pressure (BP) measurements is unclear. We attempted to evaluate the influences of peripheral circulation on determining CrCP. Methods: Twenty-five young healthy volunteers were studied. BP waves were obtained with plethysmography (Portapres) and carotid applanatory tonometry, respectively, for analysis. Transcranial Doppler was used to monitor cerebral flow velocity. Using linear regression analysis, beat-to-beat CrCP was calculated at rest, during voluntary hyperventilation and during 5% CO2 inhalation. Results: Twenty of 25 participants demonstrating satisfactory tonometric tracings for both tests were included in the analysis. The systolic BP measured using plethysmography was higher than that derived from tonometry (139.4 ± 24.7 vs. 105.5 ± 29.6, p < 0.001). CrCP values derived from tonometry were all positive and higher than CrCP values derived from plethysmography (62.9 ± 19.9 vs. 11.1 ± 17.8, p < 0.001). The changes in CrCP induced by 5% CO2 inhalation and hyperventilation had a correlation between two BP monitoring methods (r = 0.52, p = 0.001). Conclusions: Pressure waveform is an important determinant in calculating CrCP by linear regression analysis. The relative changes in CrCP induced by hemodynamic challenges remained a relevant indicator of cerebrovascular regulation regardless of the methods used for non-invasive BP recording. Copyright © 2005 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Objective Panic disorder (PD) is characterized by panic attacks accompanied with respiratory symptoms. Internal jugular vein (IJV) alters its hemodynamics in response to respiration and which might cause cerebral blood flow (CBF) changes. In the present study, we compared (1) respiratory-related IJV hemodynamics and (2) CBF changes during Valsalva maneuver (VM) between PD and normal subjects. Methods 42 PD patients and age/gender-matched controls (14 men; 52.3 ± 11.4 years) were recruited. Duplex ultrasonography measured time-averaged mean velocity (TAMV) and lumen in IJV at baseline and deep inspiration. Lumen area <0.10 cm2 at deep inspiration was defined as IJV collapse. CBF changes during VM were recorded by transcranial Doppler (TCD). Results Compared with normal group, PD patients had significantly higher frequency of IJV collapse at deep inspiration (Left: 40.0% vs. 7.0%, p = 0.0003, Right: 17.0% vs. 0%, p = 0.0119). IJV collapse was associated with symptoms of respiratory subtype in our PD patients. PD group also had smaller lumen (Left: 0.53 ± 0.29 vs. 0.55 ± 0.26 cm2, p = 0.8296, Right: 0.63 ± 0.36 vs. 0.93 ± 0.45 cm2, p = 0.0014) and slower TAMV of IJV at baseline (Left: 11.8 ± 8.43 vs. 20.6 ± 16.5 cm/s, p = 0.0003, Right: 15.9 ± 9.19 vs. 24.1 ± 15.7 cm/s, p = 0.0062). PD patients with inspiration-induced IJV collapse had more decreased CBF during VM compared with the other PD patients and normal individuals respectively. Interpretation We are the first to show that PD have less IJV flow at baseline and more frequent collapse at deep inspiration. Inspiration-induced IJV collapsed was associated with CBF decrement during VM in PD patients. These results suggest that venous drainage impairment might play a role in the pathophysiology of PD by influencing CBF. [ABSTRACT FROM AUTHOR]

Background: Jugular venous reflux (JVR) has been reported to cause cough syncope via retrograde-transmitted venous hypertension and consequently decreased cerebral blood flow (CBF). Unmatched frequencies of JVR and cough syncope led us to postulate that there should be additional factors combined with JVR to exaggerate CBF decrement during cough, leading to syncope. The present pilot study tested the hypothesis that JVR, in addition to an increased level of plasma endothelin-1 (ET-1), a potent vasoconstrictor, is involved in the pathophysiology of cough syncope. Methods: Seventeen patients with cough syncope or pre-syncope (Mean[SD] = 74.63(12.37) years; 15 males) and 51 age/gender-matched controls received color-coded duplex ultrasonography for JVR determination and plasma ET-1 level measurements. Results: Multivariate logistic analysis showed that the presence of both-side JVR (odds ratio [OR] = 10.77, 95% confident interval [CI] = 2.40-48.35, p = 0.0019) and plasma ET-1 > 3.43 pg/ml (OR = 14.57, 95% CI = 2.95-71.59, p = 0.001) were independently associated with the presence of cough syncope/ pre-syncope respectively. There was less incidence of cough syncope/ pre-syncope in subjects with the absence of both-side JVR and a plasma ET-1 ≦3.43 pg/ml. Presence of both side JVR and plasma ET-1 level of > 3.43 pg/ml, increased risk for cough syncope/pre-syncope (p < 0.001). Conclusions: JVR and higher plasma levels of ET-1 are associated with cough syncope/ pre-syncope. Although sample size of this study was small, we showed a synergistic effect between JVR and plasma ET-1 levels on the occurrence of cough syncope/pre-syncope. Future studies should confirm our pilot findings. [ABSTRACT FROM AUTHOR]

To explore the mechanisms underlying the phase lag between oscillations in arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV), ABP and CBFV signals were recorded noninvasively from normal volunteers who lay quietly in a supine position. Mean ABP (MAP) and CBFV (MFV) were calculated beat-to-beat by means of integration. Cerebral vascular resistance (CVR) was calculated by dividing MAP with MFV. Frequency domain analysis of MAP, MFV and CVR signals revealed very-low frequency (VLF, 0.016-0.04 Hz), low-frequency (LF, 0.04-0.15 Hz), and high-frequency (HF, 0.15-0.4 Hz) components. The transfer phase of MAP-CVR coupling in the LF and HF range was frequency-dependent, which is equivalent to a time delay of 2 s. However, the transfer phase differed in the CVR-MFV coupling in that the phase was distributed around 180° across the LF and HF ranges. Cross-correlation analysis revealed a positive relationship between MAP-CVR coupling, with MAP leading by 2 s, and a negative relationship between CVR- MFV coupling, with CVR leading by 0.3 s. We concluded that the phase lag between oscillations in ABP and CBFV was chiefly contributed to by the starting latency of cerebral autoregulation (i.e. cerebral vasomotion, revealed by MAP-CVR coupling). Moreover, the negative correlation of the CVR-MFV coupling could offer a different explanation for the physiologic significance of the phase lead of CBFV-ABP oscillations. [ABSTRACT FROM AUTHOR]