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Objectives: To assess the feasibility of computed tomography (CT) based thermometry during interstitial laser heating in the bovine liver.Methods: Four freshly exercised cylindrical blocks of bovine tissue were heated using a continuous laser of Nd:YAG (wavelength: 1064 nm, active length: 30 mm, power: 10-30 W). All tissues were imaged at least once before and 7 times during laser heating using CT and temperatures were simultaneously measured with 5 calibrated thermal sensors. The dependency of the average CT numbers as a function of temperature was analysed with regression analysis and a CT thermal sensitivity was derived.Results: During laser heating, the growing hypodense area was observed around the laser source and that area showed an increase as a function of time. The formation of hypodense area was caused by declining in CT numbers at increasing temperatures. The regression analysis showed an inverse linear dependency between temperature and average CT number with -0.65 ± 0.048 HU/°C (R(2) = 0.75) for the range of 18-85°C in bovine liver.Conclusions: The non-invasive CT based thermometry during interstitial laser heating is feasible in the bovine liver. CT based thermometry could be further developed and may be of potential use during clinical LITT of the liver. [ABSTRACT FROM AUTHOR]

BACKGROUND: In preterm infants with respiratory distress syndrome (RDS) nasal continuous positive airway pressure (nCPAP) with the 'InSurE' procedure (intubation, surfactant, extubation) is increasingly used. However, its effect on cerebral oxygenation and brain function is not known. OBJECTIVE: To evaluate the effects of the 'InSurE' procedure in infants with RDS on regional cerebral oxygen saturation (rScO(2)) and relative cerebral fractional tissue oxygen extraction (cFTOE) using near infrared spectroscopy and on electrical brain activity using amplitude-integrated electroencephalography (aEEG). METHODS: Sixteen infants with RDS, treated with the 'InSurE' procedure, and 16 matched controls with nCPAP, were monitored for mean arterial blood pressure (MABP), arterial oxygen saturation (SaO(2)), rScO(2), cFTOE and aEEG. Ten-minute periods were selected and averaged at 120 and 20 minutes before, during the procedure and at 30 minutes, 1, 2, 6, 12 and 24 h after the start of the 'InSurE' procedure. aEEG was analysed by quantitative and qualitative (Burdjalov score) methods. RESULTS: MABP was not different between groups on all time points. rScO(2) and cFTOE were comparable between groups, but there was a trend towards lower rScO(2) and higher cFTOE 30 minutes after opioid administration in the 'InSurE' infants compared with controls (62% (SD 11) vs 68% (SD 10) and 0.30 (SD 0.10 ) vs 0.28 (SD 0.11), respectively). aEEG amplitudes and Burdjalov scores were significantly lower in 'InSurE' infants from 30 minutes after opioid administration up to 24 h after the start of the procedure (p<0.05). CONCLUSION: In the present study, the 'InSurE' procedure did not induce perturbation of cerebral oxygen delivery and extraction, whereas electrical brain activity decreased for a prolonged period of time. [ABSTRACT FROM AUTHOR]

Aims: First, the aim of the study was to determine whether irreversible electroporation (IRE) is associated with heat generation in the liver and pancreas at clinical (≤1,500 V/cm) and supraclinical (>1,500 V/cm) electroporation settings; second, to assess the risk of thermal tissue damage in and adjacent to the treated volume in highly perfused versus moderately perfused parts of both organs; third, to investigate the influence of perfusion and of the presence and the orientation of a metal stent on the maximal thermal elevation (ΔT Session,max ) in the tissue during an IRE session at fixed IRE settings, and finally, to determine whether the maximum temperature elevation within the IRE-subjected organ during an IRE treatment (single or multiple sessions) is reflected in the organ's surface temperature., Methods: The aims were investigated in 12 case studies conducted in five female Landrace pigs. Several IRE settings were applied for lateral (2), triangular (3), and rectangular (4) electrode configurations in the liver hilum, liver periphery, pancreas head, and pancreas tail. IRE series of 10-90 pulses were applied with pulse durations that varied from 70 μs to 90 μs and electric field strengths between 1,200 V/cm and 3,000 V/cm. In select cases, a metal stent was positioned in the bile duct at the level of the liver hilum. Temperatures were measured before, during, and after IRE in and adjacent to the treatment volumes using fiber optical temperature probes (temperature at the nucleation centers) and digital thermography (surface temperature). The occurrence of thermal damage was assumed to be at temperatures above 50 °C (ΔT Session,max ≥ 13 °C relative to body temperature of 37 °C). The temperature fluctuations at the organ surface (ΔT LocSurf ) were compared to the maximum temperature elevation during an IRE treatment in the electroporation zone. In select cases, IRE was applied to tissue volumes encompassing the portal vein (PV) and a constricted and patent superior mesenteric vein (SMV) to determine the influence of the heatsink effect of PV and SMV on ΔT Session,max ., Results: The median baseline temperature was 31.6 °C-36.3 °C. ΔT Session,max ranged from -1.7 °C to 25.5 °C in moderately perfused parts of the liver and pancreas, and from 0.0 °C to 5.8 °C in highly perfused parts. The median ΔT LocSurf of the liver and pancreas was 1.0 °C and 10.3 °C, respectively. Constricting the SMV in the pancreas head yielded a 0.8 °C higher ΔT Session,max . The presence of a metal stent in the liver hilum resulted in a ΔT Session,max of 19.8 °C. Stents parallel to the electrodes caused a ΔT Session,max difference of 4.2 °C relative to the perpendicular orientation., Conclusions: Depending on IRE settings and tissue type, IRE is capable of inducing considerable heating in the liver and pancreas that is sufficient to cause thermal tissue damage. More significant temperature elevations are positively correlated with increasing number of electrode pairs, electric field strength, and pulse number. Temperature elevations can be further exacerbated by the presence and orientation of metal stents. Temperature elevations at the nucleation centers are not always reflected in the organ's surface temperature. Heat sink effects caused by large vessels were minimal in some instances, possibly due to reduced blood flow caused by anesthesia., Relevance for Patients: Appropriate IRE settings must be chosen based on the tissue type and the presence of stents to avoid thermal damage in healthy peritumoral tissue and to protect anatomical structures [Table: see text]., (Copyright © 2020, Whioce Publishing Pte. Ltd.)

Adequate assessment of burn wounds is crucial in the management of burn patients. Thermography, as a noninvasive measurement tool, can be utilized to detect the remaining perfusion over large burn wound areas by measuring temperature, thereby reflecting the healing potential (HP) (i.e., number of days that burns require to heal). The objective of this study was to evaluate the clinimetric properties (i.e., reliability and validity) of thermography for measuring burn wound HP. To evaluate reliability, two independent observers performed a thermography measurement of 50 burns. The intraclass correlation coefficient (ICC), the standard error of measurement (SEM), and the limits of agreement (LoA) were calculated. To assess validity, temperature differences between burned and nonburned skin (?T) were compared to the HP found by laser Doppler imaging (serving as the reference standard). By applying a visual method, one ?T cutoff point was identified to differentiate between burns requiring conservative versus surgical treatment. The ICC was 0.99, expressing an excellent correlation between two measurements. The SEM was calculated at 0.22°C, the LoA at ?0.58°C and 0.64°C. The ?T cutoff point was ?0.07°C (sensitivity 80%; specificity 80%). These results show that thermography is a reliable and valid technique in the assessment of burn wound HP.

Purpose: Irreversible electroporation (IRE) uses high-voltage electric fields to achieve cell death. Although the mechanism of IRE is mainly designated as nonthermal, development of secondary Joule heating is inevitable. The study purpose was to gain understanding of temperature development and distribution during IRE., Materials and Methods: IRE was performed in a transparent polyacrylamide gel resembling soft tissue. Mechanical effects, changes in temperature gradient, and absolute temperature changes were measured with three different optical techniques (high-speed, color Schlieren, and infrared imaging) to investigate the effect on temperature of variations in voltage, pulse length, active tip length (ATL), interelectrode distance, electrode configuration (parallel, convergent, and divergent), and sequential pulsing (pulse delivery interrupted by breaks). The total delivered energy was calculated., Results: A temperature gradient, starting at the tips of both electrodes and expanding toward each other, developed immediately with pulse delivery. Temperatures increased with increasing voltage (by 2.5°C-40.4°C), pulse length (by 5.3°C-9.8°C), ATL (by 5.9°C-17.6°C), and interelectrode distance (by 7.6°C-21.5°C), in accordance with higher energy delivery. Nonparallel electrode placement resulted in heterogeneous temperature distribution with the peak temperature focused in the area with the shortest interelectrode distance. Sequential pulse delivery significantly reduced the temperature increase compared with continuous pulsing (4.3°C vs 11.7°C)., Conclusions: Voltage, pulse length, interelectrode distance, ATL, and electrode configuration each have a strong effect on temperature development and distribution during IRE. Sequential pulsing reduces the extent and volume of thermal distribution and may prove beneficial with respect to procedural safety., (Copyright © 2016 SIR. Published by Elsevier Inc. All rights reserved.)

Purpose: Irreversible electroporation (IRE) uses short duration, high-voltage electrical pulses to induce cell death via nanoscale defects resulting from altered transmembrane potential. The technique is gaining interest for ablations in unresectable pancreatic and hepatobiliary cancer. Metal stents are often used for palliative biliary drainage in these patients, but are currently seen as an absolute contraindication for IRE due to the perceived risk of direct heating of the metal and its surroundings. This study investigates the thermal and tissue viability changes due to a metal stent during IRE., Methods: IRE was performed in a homogeneous tissue model (polyacrylamide gel), without and with a metal stent placed perpendicular and parallel to the electrodes, delivering 90 and 270 pulses (15-35 A, 90 μsec, 1.5 cm active tip exposure, 1.5 cm interelectrode distance, 1000-1500 V/cm, 90 pulses/min), and in-vivo in a porcine liver (4 ablations). Temperature changes were measured with an infrared thermal camera and with fiber-optic probes. Tissue viability after in-vivo IRE was investigated macroscopically using 5-triphenyltetrazolium chloride (TTC) vitality staining., Results: In the gel, direct stent-heating was not observed. Contrarily, the presence of a stent between the electrodes caused a higher increase in median temperature near the electrodes (23.2 vs 13.3°C [90 pulses]; p = 0.021, and 33.1 vs 24.8°C [270 pulses]; p = 0.242). In-vivo, no temperature difference was observed for ablations with and without a stent. Tissue examination showed white coagulation 1mm around the electrodes only. A rim of vital tissue remained around the stent, whereas ablation without stent resulted in complete tissue avitality., Conclusion: IRE in the vicinity of a metal stent does not cause notable direct heating of the metal, but results in higher temperatures around the electrodes and remnant viable tissue. Future studies should determine for which clinical indications IRE in the presence of metal stents is safe and effective.

Background: Although radiofrequency ablation (RFA) is promising for the local treatment of breast cancer, burns are a frequent complication. The safety and efficacy of a new technique with a bipolar RFA electrode was evaluated., Methods: Dosimetry was assessed ex vivo in bovine mammary tissue, applying power settings of 5-15 W with 10-20 min exposure and 3.0-12.0 kJ to a 20-mm active length bipolar internally cooled needle-electrode. Subsequently, in 15 women with invasive breast carcinoma ≤2.0 cm diameter ultrasound-guided RFA was performed followed by immediate resection., Results: An ablation zone of 2.5 cm was reached in the ex vivo experiments at 15 W at 9.0 kJ administered energy. Histopathology revealed complete cell death in 10 of 13 patients (77%); in 3 patients partial ablation was due to inaccurate probe positioning. In 1 patient a pneumothorax was caused by the probe placement, treated conservatively. No burns occurred., Conclusions: Ultrasound-guided RFA with a bipolar needle-electrode appears to be a safe local treatment technique for invasive breast cancer up to 2 cm. Ways to improve placement of the probe and direct monitoring of the ablation-effect should be the aim of further research., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Objective: To determine the impact of radiofrequency ablation (RFA) in pancreas after two-week follow-up., Background: RFA is a novel treatment strategy in patients with unresectable locally advanced pancreatic cancer. The histological effect and risk of postoperative complications has not been systematically addressed in an in-vivo animal model., Methods: In a porcine model (n = 6), RFA was performed via laparotomy with previously determined optimal settings using a bipolar probe with 30 mm active length, at 30 W until a total energy of 15 KJ was administered. The probe was inserted in the pancreas at 10 mm distance from duodenum and portomesenteric vessels (PMV). RFA nearby duodenum was performed under continuous duodenal cooling using 100 ml/min saline of 5 °C. During two weeks the clinical condition was evaluated daily including blood analyses. After two weeks, total pancreatoduodenectomy was performed and the obtained tissue histopathologically assessed., Results: No mortality occurred during or after RFA. Two animals had a serum amylase increase more than threefold the pre-intervention value without clinical manifestations. Histopathologic assessment showed total ablation within the ablation zone, with loss of normal pancreatic acinar cell outlines and necrosis. In one animal, focal necrosis of duodenal submucosa was seen and in another animal focal fibrosis in the muscular layer of the superior mesenteric vein without clinical manifestations., Conclusion: No major morbidity and no mortality was seen during a period of two weeks after RFA with previously validated RFA settings including duodenal cooling and 10 mm distance to PMV. Future clinical studies should confirm safety of RFA using the settings established here., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Objective: To determine the short-term outcome of radiofrequency ablation (RFA) of pancreatic tissue near the duodenum and portomesenteric vessels (PMV) in a porcine model with and without intraluminal duodenal cooling., Background: RFA has been proposed as a new treatment strategy in patients with unresectable locally advanced pancreatic cancer. RFA may cause thermal damage to the duodenum and vascular structures, but these risks and potential protective measures have never been systematically addressed. Intraluminal duodenal cooling during RFA could prevent thermal damage to the duodenum., Methods: RFA was performed in 11 pigs during laparotomy with a bipolar probe of 30 mm active length at a power of 30 W until a total energy of 15 kJ was administered. The RFA probe was inserted in the pancreas at 5 or 15 mm from the duodenum, PMV, and in the pancreatic tail. RFA near the duodenum was performed with and without intraluminal duodenal cooling using 100 mL/min saline of 5°C. Histopathologic assessment was performed., Results: The maximum RFA-induced temperature was 92°C. RFA with one single probe induced adequate ablation lesions with a diameter of 20 mm over a length of 30 mm. Without duodenal cooling, RFA induced duodenal thermal damage, whereas with duodenal cooling, no damage was observed. RFA at 15 mm from the PMV resulted in minimal superficial focal vascular damage, without thrombosis or hemorrhage., Conclusions: RFA provides adequate ablation zones in the pancreas of the porcine. Thermal damage to the duodenum can be prevented by intraluminal duodenal cooling without loss of ablation effectivity., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Even though there are indications that stress influences body temperature in humans, no study has systematically investigated the effects of stress on core and peripheral body temperature. The present study therefore aimed to investigate the effects of acute psychosocial stress on body temperature using different readout measurements. In two independent studies, male and female participants were exposed to a standardized laboratory stress task (the Trier Social Stress Test, TSST) or a non-stressful control task. Core temperature (intestinal and temporal artery) and peripheral temperature (facial and body skin temperature) were measured. Compared to the control condition, stress exposure decreased intestinal temperature but did not affect temporal artery temperature. Stress exposure resulted in changes in skin temperature that followed a gradient-like pattern, with decreases at distal skin locations such as the fingertip and finger base and unchanged skin temperature at proximal regions such as the infra-clavicular area. Stress-induced effects on facial temperature displayed a sex-specific pattern, with decreased nasal skin temperature in females and increased cheek temperature in males. In conclusion, the amplitude and direction of stress-induced temperature changes depend on the site of temperature measurement in humans. This precludes a direct translation of the preclinical stress-induced hyperthermia paradigm, in which core temperature uniformly rises in response to stress to the human situation. Nevertheless, the effects of stress result in consistent temperature changes. Therefore, the present study supports the inclusion of body temperature as a physiological readout parameter of stress in future studies.

Obtaining access to blood vessels can be difficult, especially in children. Visualization of subsurface blood vessels might be a solution. Ultrasound and visible light have been used to this purpose, but have some drawbacks. Near-infrared light might be a better option since subsurface blood vessels can be visualized in high contrast due to less absorption and scattering in tissue as compared to visible light. Our findings with a multispectral imaging system support this theory. A device, the VascuLuminator, was developed, based on transillumination of the puncture site with near-infrared light. The VascuLuminator was designed to meet the requirements of compact and safe use. A phantom study showed that the maximum depth of visibility (5.5mm for a 3.6mm blood vessel) is sufficient to visualize blood vessels in typical locations for peripheral venous and arterial access. A quantitative comparison of the VascuLuminator and to two other vessel imaging devices, using reflection of near-infrared light instead of transillumination, was conducted. The VascuLuminator is able to decrease failure at first attempt in blood withdrawal in pediatric patients from 10/80 (13%) to 1/45 (2%; P=.05)., (Copyright © 2012 IPEM. Published by Elsevier Ltd. All rights reserved.)

Background: The next step in breast-conserving surgery for small breast carcinomas could be local ablation. In this study, the feasibility of ultrasound-guided laser-induced thermal therapy (LITT) is evaluated., Methods: Patients with large-core needle biopsy-proven invasive, palpable breast carcinoma (clinically or=2 cm in size (P = .026)., Conclusions: Successful LITT of invasive breast cancer seems to be feasible when confined to small (<2 cm) nonlobular carcinomas without surrounding extensive in-situ component and angioinvasion. However, to implement LITT in a curative setting, improvements in imaging to more reliably preoperatively assess tumor size and monitoring of fiber tip placement and treatment affect are essential.

Objectives: To evaluate whether application of a transducer on the anterior fontanelle during cranial ultrasound (US) examination effects cerebral hemodynamics and oxygenation in preterm infants. STUDY DESIGN*: During cranial US examination, changes in cerebral blood oxygenation (cHbD) and cerebral blood volume (CBV) were assessed using near infrared spectrophotometry (NIRS) in 76 infants (GA 30.7 (4.1)wk, BW 1423 (717)g) within two days after birth. Ten of these infants (GA 29.1 (1.6)wk, BW 1092 (455)g) were studied again at a postnatal age of one week. RESULTS*: We obtained stable and consistent NIRS registrations in 54 infants within the first two days after birth. Twenty-eight of these infants showed a decrease in cHbD (0.59 (0.54) micromol/100g) during the scanning procedure while CBV did not change. Twenty-four infants showed no changes in NIRS and 2 infants showed an atypical NIRS response during cranial US examination. At the postnatal age of one week, stable and consistent NIRS registrations were obtained in 7 infants. None of these infants showed changes in NIRS variables during cranial US examination., Conclusions: Application of an US transducer on the anterior fontanelle causes changes in cerebral oxygenation and hemodynamics in a substantial number of preterm infants. ( *values are expressed as median (interquartile range)).

The aim of our study was to assess consecutive changes in cerebral oxygenation and hemodynamics after serial cerebrospinal fluid (CSF) drainage from a subcutaneous ventricular catheter reservoir (SVCR) in infants with PHVD. Infants with PHVD were studied during CSF drainage from a SVCR on the day of SVCR placement, half a week and one week after SVCR placement. Changes in cHbD and CBV were assessed using near infrared spectrophotometry. Time averaged peak flow velocity (TAPFV), end diastolic flow velocity (EDFV), peak systolic flow velocity (PSFV) and pulsatility index (PI) were measured before (baseline) and after CSF drainage using Doppler ultrasound. Longitudinal data analysis was performed using linear mixed models. Seven patients (GA 26.7-40.4 weeks, BW 800-4575 g) were studied. CSF drainage resulted in a statistically significant increase in CBV during each measurement. The change in CBV was maximal on the day of SVCR placement. A significant increase in cHbD and EDFV, and decrease in PI was observed after CSF drainage only on the day of SVCR placement. Baseline values of all Doppler variables improved consecutively after serial CSF removal in the first week after SVCR placement. Frequent CSF drainage results in consecutive improvement of cerebral perfusion and oxygenation in infants with PHVD.

Background: Midazolam sedation and morphine analgesia are commonly used in ventilated premature infants., Objectives: To evaluate the effects of midazolam versus morphine infusion on cerebral oxygenation and hemodynamics in ventilated premature infants., Methods: 11 patients (GA 26.6-33.0 weeks, BW 780-2,335 g) were sedated with midazolam (loading dose 0.2 mg/kg, maintenance 0.2 mg/kg/h) and 10 patients (GA 26.4-33.3 weeks, BW 842-1,955 g) were sedated with morphine (loading dose 0.05 mg/kg, maintenance 0.01 mg/kg/h). Changes in oxyhemoglobin (Delta cO2Hb) and deoxyhemoglobin (Delta cHHb) were assessed using near infrared spectrophotometry. Changes in cHbD (= Delta cO(2)Hb - Delta cHHb) reflect changes in cerebral blood oxygenation and changes in concentration of total hemoglobin (Delta ctHb = Delta cO2Hb + Delta cHHb) represent changes in cerebral blood volume (DeltaCBV). Changes in cerebral blood flow velocity (DeltaCBFV) were intermittently measured using Doppler ultrasound. Heart rate (HR), mean arterial blood pressure (MABP), arterial oxygen saturation (saO2) and transcutaneous measured pO2 (tcpO2) and pCO2 (tcpCO2) were continuously registered. Statistical analyses were carried out using linear mixed models to account for the longitudinal character study design., Results: Within 15 min after the loading dose of midazolam, a decrease in saO2, tcpO2 and cHbD was observed in 5/11 infants. In addition, a fall in MABP and CBFV was observed 15 min after midazolam administration. Immediately after morphine infusion a decrease in saO2, tcpO2 and cHbD was observed in 6/10 infants. Furthermore, morphine infusion resulted in a persistent increase in CBV., Conclusions: Administration of midazolam and morphine in ventilated premature infants causes significant changes in cerebral oxygenation and hemodynamics, which might be harmful., (Copyright 2006 S. Karger AG, Basel.)

Background: Sodium bicarbonate (NaHCO3) is often used for correction of metabolic acidosis in preterm infants. The effects of NaHCO3 administration on cerebral hemodynamics and oxygenation are not well known. Furthermore, there is no consensus on infusion rate of NaHCO3., Objectives: To evaluate the effects of rapid versus slow infusion of NaHCO3 on cerebral hemodynamics and oxygenation in preterm infants., Methods: Twenty-nine preterm infants with metabolic acidosis were randomized into two groups (values are mean +/-SD): In group A (GA 30.5 +/- 1.7 weeks, b.w. 1,254 +/- 425 g) NaHCO3 4.2% was injected as a bolus. In group B (GA 30.3 +/- 1.8 weeks, b.w. 1,179 +/- 318 g) NaHCO3 4.2% was administered over a 30-min period. Concentration changes of oxyhemoglobin (cO2Hb) and deoxyhemoglobin (cHHb) were assessed using near infrared spectrophotometry. Changes in HbD (= cO2Hb - cHHb) represent changes in cerebral blood oxygenation and changes in ctHb (= cO2Hb + cHHb) reflect changes in cerebral blood volume. Cerebral blood flow velocity was intermittently measured using Doppler ultrasound. Longitudinal data analysis was performed using linear mixed models (SAS procedure MIXED), to account for the fact that the repeated observations in each individual were correlated., Results: Administration of NaHCO3 resulted in an increase of cerebral blood volume which was more evident if NaHCO3 was injected rapidly than when infused slowly. HbD and cerebral blood flow velocity did not show significant changes in either group., Conclusion: To minimize fluctuations in cerebral hemodynamics, slow infusion of sodium bicarbonate is preferable to rapid injection., (Copyright 2006 S. Karger AG, Basel.)

The objective of this study is to correlate regional cerebral blood concentration measurements made with near infrared spectroscopy to simultaneous local measurements of ultrasound contrast agent (CA) densitometry. Experiments were performed with piglets (7 kg) under general anesthesia. The cerebral blood flow (CBF) and volume (CBV) were changed by inducing various degrees of hypercapnia. NIRS measurements were performed with a quasi-continuous wave system, using an optode distance of 3-6 cm. The concentration changes in oxygenated and deoxygenated hemoglobin and their sum and difference (cO2Hb, cHHb, ctHb, cHbD) were continuously calculated. Ultrasound contrast agent (SF6) was administered as a short intra-venous bolus. Ultrasound equipment was used in pulse inversion second harmonic gray scale imaging mode at low transmit power setting. Three regions-of-interest (0.25 cm2) were analyzed in each image. Wash-in curves were constructed as spatial mean gray level vs. time. The variables collected with both methods changed according to the induced changes in the physiological condition. Changes in the PaCO2, pH and carotid flow induced highly correlated changes in cO2Hb, cHHb, ctHb and cHbD, and in the variables derived from CA analyses. NIRS and CA methods measure regional, respectively, local changes in CBV and CBF. Moreover, NIRS can yield complementary information about the cerebral oxygenation.

The influence of skin on the bias and reproducibility of regional cerebral oxygenation measurements is investigated using cw near-infrared spectroscopy (NIRS). Receiving optodes are placed over the left and right hemispheres of a piglet (C3, C4 EEG placement code) and one transmitting optode centrally (Cz position). Optical densities (OD) are measured during stable normo, mild, and deep hypoxemia. This is done for skin condition 1: all optodes on the skin; skin condition 2: transmitting optode on the skin and one receiving optode on the skull; and skin condition 3: all optodes on the skull. Absolute changes of oxy- (cO2Hb), deoxyhemoglobin (cHHb), and total hemoglobin (ctHb) concentrations [micromolL] are calculated from the ODs. These absolute changes are calculated for each skin condition with respect to normoxic condition. Additionally, for skin condition 2, the difference of concentration changes between receiver 1 (skull) and receiver 2 (skin) is calculated. The effect of skin removal is an average increase of attenuation changes by a factor of 1.66 (=0.51 OD) and of the concentration changes due to the arterial oxygen saturation steps by 23%. We conclude that skin significantly influences regional oxygenation measurements. Nevertheless, it is hypothesized that the estimated concentration changes are dominated by changes of the oxygenation in the brain.

A double-ring sensor was applied in photoacoustic tomographic imaging of artificial blood vessels as well as blood vessels in a rabbit ear. The peak-to-peak time (tau(pp)) of the laser (1064 nm) induced pressure transient was used to estimate the axial vessel diameter. Comparison with the actual vessel diameter showed that the diameter could be approximated by 2ctau(pp), with c the speed of sound in blood. Using this relation, the lateral diameter could also precisely be determined. In vivo imaging and monitoring of changes in vessel diameters was feasible. Finally, acoustic time traces were recorded while flushing a vessel in the rabbit ear with saline, which proved that the main contribution to the laser-induced pressure transient is caused by blood inside the vessel and that the vessel wall gives only a minor contribution.

Objective: In neonates, initially a ductal shunt is often observed during veno-arterial extracorporeal membrane oxygenation (ECMO). Depending on the degree of pulmonary hypertension in these patients, the ductal shunt will be right to left (R-L), left to right (L-R), or bidirectional. A ductal L-R shunt will possibly lead to pulmonary hyperperfusion and interact with ECMO weaning. The aim of this study was to give more insight in this ductal L-R shunt during ECMO by quantification of this shunt in relation to cardiac output and ECMO flow., Methods: In 7 lambs, closure of the duct was prevented by infiltration of the ductal wall with 10% formaline. This patent duct could be closed using a vesselloop around the duct. Ultrasound flowprobes were installed around the pulmonary artery, ascending aorta, and around the ECMO circulation tube. Right and left ventricular output and ECMO flow were measured. Ductus flow was defined as ductal left to right shunt (Qduct L-R) = flow in ascending aorta (Qao) - flow in central pulmonary artery (Qpa) and Qduct R-L = Qpa = Qao., Results: In 6 of 7 lambs a ductal L-R shunt was observed with a mean shunt of 44% (range, 11 to 79) of left ventricular output (Qduct L-R/Qao). Comparison with ECMO flow (Qduct L-R/Qecmo) showed a mean shunt of 76% (range 15 to 230). When compared with the total systemic circulating volume (Qpa + flow in the ECMO circuit [Qecmo]), the mean ductal L-R shunt showed a percentage of 51% (range, 7% to 142%)., Conclusions: During ECMO, mostly a ductal L-R shunt is observed in this lamb model. This ductal shunt is hemodynamically important. The percentages of this shunt in comparison with left ventricular output, and total circulating volume will support the idea that a ductal L-R shunt during ECMO could be another deteriorating factor in the often critical circulation of the neonate on veno-arterial ECMO.

This paper describes the simultaneous use of two, noninvasive, near-infrared techniques near-infrared spectroscopy (NIRS) and a continuous wave NIR laser Doppler flow system (LDF) to measure changes in the blood oxygenation, blood concentration and blood flow velocity in the brain. A piglet was used as animal model. A controlled change in the arterial CO2 pressure (PaCO2) was applied for achieving changes in the listed cerebrovascular parameters. The time courses of blood concentration parameters (NIRS) and RMS blood flow velocity (LDF) were found to correspond closely with those of carotid blood flow and arterial carbon dioxide pressure (PaCO2). This result shows the additional value of LDF when combined with NIRS, preferably in one instrument. Development of pulsed LDF for regional blood flow measurement is indicated.

This study tested the hypothesis that changes in the blood concentration, and possibly in the perfusion, of different areas in the brain can be assessed by the use of ultrasound contrast agent (CA) and (linear) echo densitometry. The experiments were performed with piglets (n=3) under general anesthesia and artificial ventilation. Ultrasound CA was administered through a femoral vein as a short bolus. First passage wash-in curve was measured from image gray level during continuous low level (mechanical index<0.2) ultrasound imaging. This curve was obtained from 1-cm2 areas of the cortex (surface), the brain stem (inner) and the left carotid artery (vessel). Cerebral hemoglobin concentration changes were measured with near-infrared spectroscopy (NIRS). This approach enabled a cross-validation of these techniques. The measurements were repeated under conditions of normocapnia, mild hypercapnia and deep hypercapnia. Several physiologic signals, as well as the carotid blood flow, were measured simultaneously and related to gray level by linear regression analysis. The most significant results found were a high R2-statistic of the regression of the percentage change of the peak of the surface and inner wash-in curves with the arterial carbon dioxide pressure (R2=0.63 and R2=0.70, respectively), the blood pH (R2=0.79 and R2=0.81), the carotid flow (R2=0.75 and R2=0.72) and the partial arterial oxygen pressure (R2=0.47 and R2=0.55). Finally, a high correlation of peak gray level with total hemoglobin concentration change, independently measured by NIRS, was found (R2=0.69). In conclusion, these experiments show a reasonable intersubject variability of various relative measures derived from gray level ultrasound wash-in curves. High sensitivity to physiologic changes related to hypercapnia was observed for the peak contrast of wash-in curves. For up-slope and area-under-the-curve (first passage) this was lower but still highly significant. The gray-level ultrasound measures are highly correlated to changes in regional hemoglobin concentration in brain tissue assessed by NIRS.

Objectives: in vitro assessment of the reproducibility and the optimal separation and position of the optodes in continuous wave (CW-) NIRS measurement of local inhomogeneities in absorption and/or scattering., Methods: a CW- NIRS system (OXYMON) was used with laser diodes at wavelengths of 767 nm, 845 nm, 905 nm, 945 nm and 975 nm. For practical considerations (dimensions of neonatal head) the measurements were performed on a cylindrical tissue-equivalent phantom (70 mm diameter of base material with mua = 0.01 mm(-1) (800 nm) and mu's = 1.00 mm(-1) (800 nm)), containing rods with 10 x absorption, or 10 x scattering, and 5 x both Monte Carlo simulations were carried out of a cylinder with transport scattering coefficient mu's = 0.525 mm(-1) and absorption coefficient mua = 0.075 mm(-1) and two optode positions., Results: reproducibility of repeated measurements (n = 10) was +/- 0.005 OD. Maximum OD in case of absorbing rod, and of absorbing + scattering rod was measured with optodes separated by 90 degrees and rod position angle symmetrically (45 degrees ) in between. Minimum OD for these rods was obtained with optodes at 150 degrees angle and rod position at 240 degrees (i.e. relative to transmitting optode position at 0 degrees ). A second maximum OD was obtained at an optode angle 180 degrees and rod position at 180 degrees. Maximum OD (i.e. attenuation) for the scattering rod was at optode separation angle of 90 degrees and rod at 0 degrees. Minimum OD for this case was obtained with optode angle of 180 degrees and rod positions around 80 degrees and 280 degrees. Maximum OD changes by absorbing rod were in the order of +0.12 OD and -0.04 OD, respectively. Simulations at an optode separation angle of 90 degrees showed a spatial sensitivity path enclosing the rod position at maximum absorption found experimentally., Conclusions: when considering the phantom as a realistic geometrical model for the neonatal head, it can be concluded that the optode position at 90 degrees angle would be optimal for detecting an inhomogeneity at 15 mm depth, i.e. the location of the periventricular white matter. Since the rods are relatively strongly different from the base material the question remains to be answered whether local ischemia, which might lead to irreversible brain damage, can be detected by CW-NIRS

Noninvasive determination of pulmonary hemodynamics is important for the management of congenital heart disease complicated by pulmonary hypertension. Flow deceleration is less influenced by right ventricular function and would allow more accurate estimation of pulmonary hemodynamics than acceleration. Respiratory influences on pulmonary blood flow are exaggerated by mechanical ventilation. Doppler-derived pulmonary artery (PA) blood flow velocity characteristics were therefore compared with pulmonary hemodynamic parameters in 42 mechanically ventilated children, aged 0.2 to 14.8 years (mean +/- SD 6.7 +/- 4.9). Mean PA pressure ranged from 11 to 47 mm Hg (21 +/- 9 mm Hg). Pulmonary hypertension was present in 14 patients. Significant differences were found between patients with and without pulmonary hypertension in maximal velocity (1.03 +/- 0.22 vs 0.88 +/- 0.18 m/s), acceleration time (119 +/- 39 vs 136 +/- 29 ms), maximal acceleration (17.6 +/- 6.4 vs 13.1 +/- 4.0 m/s2), mean acceleration (9.3 +/- 2.6 vs 6.7 +/- 2.0 m/s2), and mean deceleration (4.5 +/- 1.0 vs 3.8 +/- 0.8 m/s2). In contrast to our hypothesis of the deceleration phase-derived parameters, only maximal deceleration correlated with PA pressure. Acceleration parameters showed closer relations with PA pressures, but correlations were generally low and did not permit accurate prediction of PA pressure (SEE 5 to 11 mm Hg), PA resistance (SEE 1.14 U. m2) or PA driving force (SEE 7 mm Hg). An analysis that took respiratory phase into account did not improve correlations. Measurement of mean acceleration, maximal deceleration, and rate-corrected preejection period permitted for accurate discrimination between the presence or absence of pulmonary hypertension, with positive and negative predictive values being 92% and 90%. In mechanically ventilated children with congenital heart disease, accurate noninvasive PA pressure assessment is not possible. Accurate predictions for the presence of pulmonary hypertension can be made by measurement of both acceleration and deceleration parameters.

The objective of this study was to compare the effect of extracorporeal membrane oxygenation (ECMO) on cerebral oxygenation and hemodynamics in normoxemic and hypoxemic piglets. Six hypoxemic and six normoxemic piglets were put on venoarterial ECMO after cannulation of the right common carotid artery and external jugular vein with careful priming to avoid hemodilution. Changes in cerebral concentrations of oxyhemoglobin (cO2Hb), deoxyhemoglobin (cHHb), (oxidized-reduced) cytochrome aa3 (cCyt.aa3), and blood volume (CBV) were continuously measured by near infrared spectrophotometry. Heart rate, arterial O2 saturation (SaO2), arterial blood pressure, pulsatility ratio of systemic circulation (calculated as systolic-diastolic/mean arterial blood pressure), central venous pressure, intracranial pressure, and left common carotid artery blood flow (LCaBF) were simultaneously measured. We found that the cannulation procedure resulted in increased CBV, cHHb, and LCaBF in both groups. At 60 and 120 min after starting ECMO, the values of cO2Hb, CBV, and LCaBF in both groups were significantly higher than precannulation values, while the pulsatility ratio decreased. In the hypoxemic groups cHHb decreased and SaO2 increased as well. No significant changes of other variables were found. Between hypoxemic and normoxemic groups no significant differences in the response of CBV and LCaBF at 60 and 120 min were found. We conclude that in piglets cannulation for ECMO resulted in cerebral venous congestion and compensated increase in LCaBF. After starting ECMO, the cerebral O2 supply increased due to increased arterial O2 content. It was accompanied by similar increase of CBV in both groups, probably as a result of hyperperfusion, which seems to be related to the ECMO procedure itself.

The objective of this study was to investigate changes of cerebral oxygenation and hemodynamics related to opening of the bypass bridge during veno-arterial extracorporeal membrane oxygenation (ECMO). Ten newborn infants and 12 piglets were studied during opening of the bridge for 10 and 1 s, respectively. Changes in cerebral concentration of oxyhemoglobin (cO2Hb), deoxyhemoglobin (cHHb), (oxidized-reduced) cytochrome aa3 (cCyt.aa3), and blood volume (CBV) were continuously measured by near infrared spectrophotometry. Heart rate, arterial O2 saturation (saO2), and mean arterial blood pressure (MABP) were measured simultaneously. In the piglets, central venous pressure (CVP), intracranial pressure (ICP), and left common carotid artery blood flow (CaBF) were also measured. Opening of the bridge for 10 s in the infants resulted in a significant decrease in MABP, saO2, and cO2Hb, whereas cHHb increased. CBV did not change significantly. In piglets biphasic changes were observed for MABP, CaBF, cO2Hb, and CBV, showing an initial decrease followed by a smaller increase. cHHb and CVP showed reverse biphasic changes. ICP increased but saO2 was unchanged. In all cases heart rate and cCyt.aa3 did not change significantly. Opening of the bridge for 1 s resulted in minor changes in only a few variables. In conclusion, opening of the bridge resulted in a decrease of CBV and cerebral O2 supply due to a decrease of cerebral blood flow, followed by a compensatory increase of cerebral O2 extraction and vasodilatation. The return of oxygenated blood after reclosing resulted in an increase of CBV with overcompensation of cerebral O2 supply.