Regional transcranial oximetry with near infrared spectroscopy (NIRS) in comparison with measuring oxygen saturation in the jugular bulb in infants and children for monitoring cerebral oxygenation]

Using a dual channel near infrared (NIR) in vivo optical spectroscopy (INVOS) system (INVOS 3100A, Somanetics Corp. Troy, MI, USA) we investigated the relationship between jugular venous oxygen saturation (SjvO2) and regional cerebral oxygen saturation (rSO2) in 30 infants and children (mean age 4.5 years) with congenital heart disease undergoing cardiac catheterisation. The NIRS-SomaSensor (emitter and dual receiver probe) was applied at a standardised right fronto-temporal location (over the right frontal cortex) on the infant's head and covered with an adhesive flexible bandage. Using NIR light (730 and 810 nm) and two source-detector spacings (3 and 4 cm from the transmitter), percentage values of rSO2 were calculated from detected haemoglobin saturations. Simultaneously, jugular venous oxygen saturation (SjvO2) monitoring was performed via a catheter placed in the right internal jugular vein with its tip positioned in the jugular bulb, as verified by fluoroscopy. To compare the reliability of NIRS measurement characteristics, jugular venous blood was analysed for SjvO2 as a reference measure of global cerebral oxygenation, by co-oximetry (OSM3-Hemoximeter, Radiometer Copenhagen, Denmark). Other measured variables included pulse oximetry, arterial blood pressure, and venous and arterial oxygen saturations. Over a jugular venous oxygen saturation range of 31-83%, a significant positive linear correlation was found between rSO2 (NIRS measurement) and SjvO2 (jugular bulb oximetry) (r = 0.93, p < 0.001). No significant correlation was observed between rSO2 values and arterial blood saturation or pulse oximetry. The quantitative correlation between rSO2 (haemoglobin oxygenation in a small hemi-elliptical area of the brain) and reference SjvO2 measurement (method for monitoring global cerebral oxygenation) suggests that NIRS measurement with subtraction algorithm should identify predominantly intracranial saturation in the pediatric age group, and will tend to reflect global oxygenation under physiological conditions. Transcranial oximetry using dual receiving channel NIRS offers a noninvasive, real-time, reliable and practicable means of monitoring cerebral haemoglobin oxygenation changes infants and children with cyanotic and noncyanotic congenital heart disease.     

Accuracy of fiberoptic central venous saturation catheter below 50%

The fiberoptic central venous flotation catheter has gained widespread clinical acceptance for continuous monitoring of mixed venous oxyhemoglobin saturation. There are obvious research applications to this device, especially in monitoring very low central venous saturations in response to hypoxic challenge and cardiopulmonary exercise testing. However, the accuracy of this device has not been established in such low saturation ranges in humans. This study examines the tracking characteristics of the Opticath (Oximetrix, Mountain View, CA) pulmonary arterial catheter in comparison to simultaneously drawn blood specimens in which oxyhemoglobin saturation was determined by direct spectrophotometric oximetry. The results show that the catheter follows saturation established by bench oximetry quite closely between 50 and 80%, the range most commonly encountered in the clinical setting. However, at saturations below this range, the catheter consistently underestimates direct spectrophotometry. Since accuracy is extremely important for research purposes, two equations that can be used to correct catheter readings for mixed venous saturations less than 50% are presented.     

The influence of hepatic venous oxygen saturation on the liver's synthetic response to metabolic stress.

Hepatic oxygen consumption (HVO2) and hepatic venous oxygen saturation (ShvO2) were assessed in the isolated perfused rat liver under conditions that mimic critical illness in an effort to assess their utility in predicting the functional status of the liver. Flow rates were adjusted over the physiologic range of oxygen transport as indicated by the hepatic venous O2 saturation range of 10%-75%. HVO2 was found to be transport (HDO2) dependent only when perfusate conditions contained an increased counterregulatory hormone (glucagon, epinephrine, dexamethasone) stimulus or a high lactate concentration. In the absence of a metabolic load, (substrate and hormone-free perfusate), HVO2 was transport independent even at an ShvO2 as low as 10%. Although transport dependency of HVO2 is frequently used to infer tissue ischemia, hepatic oxygen consumption was poorly correlated with synthetic function under all conditions. In contrast, hepatic albumin production was directly related to ShvO2 at all levels of HDO2 and under all perfusion conditions indicating that this metabolic process is particularly sensitive to reductions in oxygen availability, which is more reliably predicted by venous saturation measurements. However, glucose and urea synthesis were almost independent of ShvO2. These findings indicate that various hepatic processes are affected differentially by stress conditions and flow alterations that may exist during critical illness, and protein synthesis is particularly sensitive to oxygen deprivation. Additionally, hepatic venous oxygen saturation measurement, but not HVO2, serves as a useful surrogate marker for hepatic albumin production suggesting that regional venous oximetry may play an important role in the detection of hepatic functional impairment.     

Monitoring the bovine fetus during stage II of parturition using pulse oximetry

Measurement of oxygen saturation using pulse oximetry is an established method of continuous monitoring of the well-being of the human fetus during parturition. In veterinary medicine, pulse oximetry has been used almost exclusively in intensive care and anesthesiology. The goal of the present study was to investigate the physiological changes in oxygen saturation of the bovine fetus during stage II of parturition and to determine whether the findings can be used to predict postnatal acidosis. The correlation between the oxygen saturation (SpO(2)) measured via pulse oximetry and the oxygen saturation (SaO(2)) of arterial blood measured via blood gas analysis was determined in 23 newborn calves. In addition, the oxygen saturation was monitored continuously via pulse oximetry (FSpO(2)) in 33 bovine fetuses during stage II of parturition. Correlations between the FSpO(2) values during the last 30 and 5min of stage II of parturition and the postpartum values for pH, partial pressures of oxygen and carbon dioxide, bicarbonate concentration, BE, SaO(2) and lactate concentration in arterial blood were determined. There was a high correlation between SpO(2) and SaO(2) postpartum (r=0.923). The FSpO(2) values correlated moderately with the pH and BE and weakly with the lactate concentration postpartum; calves with a pH<7.2, a BE<-3mM/L or a lactate concentration of >5.4mM/L had significantly lower FSpO(2) values than non-acidotic calves. FSpO(2) values <30% for a period of at least 2min had the highest predictive value for a calf born with a pH<7.2. Pulse oximetry is a novel method of monitoring the bovine fetus during parturition; however, technical modifications are required to improve its usefulness.     

Acute Variations in Retinal Vascular Oxygen Content in a Rabbit Model of Retinal Venous Occlusion

Purpose

To study the variation in intravascular oxygen saturation (oximetry) during an acute retinal vein occlusion (RVO) using hyperspectral computed tomographic spectroscopy based oximetry measurements.

Methods

Thirty rabbits were dilated and anesthetized for experiments. Baseline oximetry measurements were made using a custom-made hyperspectral computed tomographic imaging spectrometer coupled to a fundus camera. RVO were induced using argon green laser following an intravenous injection of Rose Bengal. RVO induction was confirmed by fluorescein angiography. Retinal oximetry measurements were repeated in arterial and venous branches one hour after RVO induction and up to 4 weeks afterwards. Comparison of retinal oximetry before and after vein occlusion was made using the Student T-test.

Results

One hour after RVO induction, we observed statistically significant reductions in the intravascular oxygen saturation in temporal retinal arteries (85.1±6.1% vs. 80.6±6.6%; p<0.0001) and veins (71.4±5.5% vs. 64.0±4.7%; p<0.0001). This decrease was reversible in animals that spontaneously recannulated the vein occlusion. There were no statistically significant differences in oxygen saturation in the nasal control arteries and veins before and after temporal vein RVO induction.

Conclusions

We demonstrate, for the first time, acute changes in the intravascular oxygen content of retinal vessels 1 hour after RVO. These changes are reversible upon spontaneous recannulation of retinal vessels. This study demonstrates that hyperspectral computer tomographic spectroscopy based oximetry can detect physiological variations in intravascular retinal oxygen saturation. The study also provides the first qualitative and quantitative evidence of the variation in retinal vascular oxygen content directly attributable to an acute retinal vein occlusion.     

FloTrac/Vigileo 系统在围手术期血流动力学监测中的应用

FloTrac传感器和Vigileo监护仪(爱德华生命科学公司)是一个基于动脉压力波形分析技术的微创心排量测定系统,可以连续的计算心排量。除了心排量(心指数),FloTrac/Vigileo系统还可以监测每搏变异量。如果提供中心静脉压数据,则可以计算全身血管阻力及其指数。利用仪器特别设计的中心静脉导管(Precep),可以持续监测中心静脉血氧饱和度。这个设备已由美国食品及药物管理局(FDA)批准应用于成人,目前有大量的文献描述了该设备应用于多种重症疾病的临床治疗中。本文为这一新技术作一综述以及讨论它的临床应用和局限性。     

Hyperspectral computed tomographic imaging spectroscopy of vascular oxygen gradients in the rabbit retina in vivo

Diagnosis of retinal vascular diseases depends on ophthalmoscopic findings that most often occur after severe visual loss (as in vein occlusions) or chronic changes that are irreversible (as in diabetic retinopathy). Despite recent advances, diagnostic imaging currently reveals very little about the vascular function and local oxygen delivery. One potentially useful measure of vascular function is measurement of hemoglobin oxygen content. In this paper, we demonstrate a novel method of accurately, rapidly and easily measuring oxygen saturation within retinal vessels using in vivo imaging spectroscopy. This method uses a commercially available fundus camera coupled to two-dimensional diffracting optics that scatter the incident light onto a focal plane array in a calibrated pattern. Computed tomographic algorithms are used to reconstruct the diffracted spectral patterns into wavelength components of the original image. In this paper the spectral components of oxy- and deoxyhemoglobin are analyzed from the vessels within the image. Up to 76 spectral measurements can be made in only a few milliseconds and used to quantify the oxygen saturation within the retinal vessels over a 10-15 degree field. The method described here can acquire 10-fold more spectral data in much less time than conventional oximetry systems (while utilizing the commonly accepted fundus camera platform). Application of this method to animal models of retinal vascular disease and clinical subjects will provide useful and novel information about retinal vascular disease and physiology.     

A comparison of oxygen saturation in white-tailed deer estimated by pulse oximetry and from arterial blood gases

Physiologic monitoring is important when chemically immobilizing wildlife. Blood oxygenation is usually monitored by pulse oximetry in the field; however, there is some question whether this technique accurately reflects oxygen saturation in wild white-tailed deer (Odocoileus virginianus). We evaluated different doses of medetomidine (125, 150, 175, or 200 μg/kg) mixed with ketamine (1.5 mg/kg), and tiletamine-zolazepam (1.0 mg/kg) in 22 female white-tailed deer at the University of Georgia Whitehall Deer Research Facility in Athens, Georgia on 14-15 and 21 May 2009. Deer were hand-injected intramuscularly while physically restrained in a squeeze chute, and then they were released into a pen for monitoring. Hemoglobin saturation estimated using pulse oximetry (SpO(2)) was compared with hemoglobin saturation value from arterial blood gases (SaO(2)) at 0, 10, and 20 min postimmobilization with deer in a sternal position. We made 56 simultaneous comparisons of oxygen saturation using SpO(2) (range, 54-95%) and SaO(2) (range, 60-95%). We used a Bland-Altman analysis for determining agreement between the two methods. Hemoglobin saturation estimated using SpO(2) was generally greater than SaO(2) when the mean of the two measurements was >80%. At mean values <80% oxygen saturation, there is not sufficient agreement between the techniques. Multiple readings over time may help recognition of outliers.     

Hypoxémies sévère en cours de CEC : démarches diagnostiques et conduite à tenir

The occurring of hypoxemia during CPB is a potentially serious event that requests emergency correction. Hypoxemia can be documented by repeated arterial blood gases, either systematic, or performed because of a dark red coloration of arterial blood or a drop in venous oxygen saturation, pulse oximetry or near infrared spectroscopy. The continuous surveillance of PaO₂, if available, will provide the earliest diagnosis. Except hypoxemia due to operating troubles (low flow on a canulation problem, acute haemorrhage, insufficient anaesthesia, etc.), hypoxemia during CPB is linked either to a defect in the administering of gases at the oxygenator, or to a deficient oxygenator. The analysis of the fraction of oxygen at the oxygenator exit (FeoO₂) will prove the defect in the administering of gases. The treatment consists in the use of a spare oxygen cylinder in case of hospital supply failure, the use of the accessory anaesthesia circuit in case of a flaw in the flow meter, or the identification and repair of leaks. In case of a deficient oxygenator, the measure of resistances will differentiate an obstruction associated to a shunt (caused by a lack in anticoagulation, or by platelet activation phenomenon, whether transitional or not) from a loss in the membrane transfer properties, which will most often request a replacement of the oxygenator.     

基于卷积神经网络-长短期记忆神经网络模型利用光学体积描记术重建动脉血压波信号

目的 直接动脉血压（arterial blood pressure,ABP）连续监测是侵入式的,传统袖带式的间接血压测量法无法实现连续监测。既往利用光学体积描记术（photoplethysmography,PPG）实现了连续无创血压监测,但其为收缩压和舒张压的离散值,而非ABP波的连续值,本研究期望基于卷积神经网络-长短期记忆神经网络（CNN-LSTM）利用PPG信号波重建ABP波信号,实现连续无创血压监测。方法 构建CNN-LSTM混合神经网络模型,利用重症监护医学信息集（medical information mart for intensive care,MIMIC）中的PPG与ABP波同步记录信号数据,将PPG信号波经预处理降噪、归一化、滑窗分割后输入该模型,重建与之同步对应的ABP波信号。结果 使用窗口长度312的CNN-LSTM神经网络时,重建ABP值与实际ABP值间误差最小,平均绝对误差（mean absolute error,MAE）和均方根误差（root mean square error,RMSE）分别为2.79 mmHg和4.24 mmHg,余弦相似度最大,重建ABP值与实际ABP值一致性和相关性情况良好,符合美国医疗器械促进协会（Association for the Advancement of Medical Instrumentation,AAMI）标准。结论 CNN-LSTM混合神经网络可利用PPG信号波重建ABP波信号,实现连续无创血压监测。     

Accuracy of pulse oximetry during intense exercise under severe hypoxic conditions

There is a growing need to measure arterial oxygen saturation with a non-invasive method during heavy exercise under severe hypoxic conditions. Although the accuracy of pulse oximetry has been challenged by several authors, it has not been done under extreme conditions. The purpose of this study was to evaluate the accuracy of a pulse oximeter (Satlite, Datex, Finland) during exercise under hypoxic conditions where arterial oxygen saturation was below 75%, simulating exercise at extreme altitude. Ten healthy non-smoking men performed two exercise studies of 30 min under normoxia and under hypoxia on two consecutive days. The exercise intensity was 80% of maximal O₂ consumption of O_2max. Arterial oxygen saturation measured by pulse oximetry was corrected (S _pO_2[corr]) according to previously published equations and was compared to arterial oxygen saturation (S _aO₂) in blood samples taken simultaneously from the radial artery. Reference arterial saturation values ranged from 57.2 to 97.6% for the whole data set. This data set was split according to low (S _aO₂ ≤ 75%) and high (S _aO₂ > 75%) S _aO₂ values. The error of pulse oximetry (S _pO_2[corr]− S _aO₂) was 2.05 (0.87)% [mean (SD)] and 1.80 (1.81)% for high and low S _aO₂ values, respectively. S _pO_2[corr] and S _aO₂ were highly correlated (r = 0.93, SEE = 1.8) for low values. During high-intensity constant workload under severe hypoxic conditions, once corrected, pulse oximetry provides an estimate of S _aO₂ with a mean error of 2%. Thus, the correction previously described for S _pO₂ values above 75% saturation applies also to S _pO₂ values in the range of 57–75% during exercise under hypoxic conditions. Accepted: 27 February 1997     

Skin sensors for continuous oxygen monitoring of newborns

Since the introduction of the technique of cutaneous1 pO2 measurement by directly heated oxygen sensors in 1972, the clinical applications and limitations of this new method have been extensively investigated. The method has proven to be of particular value in monitoring of high risk newborns as it affords the possibility of continuously monitoring clinically significant changes in the oxygenation state of the newborn. In this paper, methodological criteria for the assessment of the reliability of cutaneous pO2 monitoring are discussed. Particular consideration is given to the oxygen and temperature profiles in the vicinity of the skin sensor and to the response time of the sensor. In view of the fact that the cutaneous pO2 reflects the oxygen partial pressure at the level of arterialized cutaneous tissue, the method has limitations if it is used as an indirect determinant of arterial pO2.     

Myocardial oxygenation in isolated hearts predicted by an anatomically realistic microvascular transport model

An anatomically realistic model for oxygen transport in cardiac tissue is introduced for analyzing data measured from isolated perfused guinea pig hearts. The model is constructed to match the microvascular anatomy of cardiac tissue based on available morphometric data. Transport in the three-dimensional system (divided into distinct microvascular, interstitial, and parenchymal spaces) is simulated. The model is used to interpret experimental data on mean cardiac tissue myoglobin saturation and to reveal differences in tissue oxygenation between buffer-perfused and red blood cell-perfused isolated hearts. Interpretation of measured mean myoglobin saturation is strongly dependent on the oxygen content of the perfusate (e.g., red blood cell-containing vs. cell-free perfusate). Model calculations match experimental values of mean tissue myoglobin saturation, measured mean myoglobin, and venous oxygen tension and can be used to predict distributions of intracellular oxygen tension. Calculations reveal that approximately 20% of the tissue is hypoxic with an oxygen tension of <0.5 mmHg when the buffer is equilibrated with 95% oxygen to give an arterial oxygen tension of over 600 mmHg. The addition of red blood cells to give a hematocrit of only 5% prevents tissue hypoxia. It is incorrect to assume that the usual buffer-perfused Langendorff heart preparation is adequately oxygenated for flows in the range of < or =10 ml. min-1. ml tissue-1.     

Pulse arrival time is not an adequate surrogate for pulse transit time as a marker of blood pressure

Pulse transit time (PTT) is a proven, simple to measure, marker of blood pressure (BP) that could potentially permit continuous, noninvasive, and cuff-less BP monitoring (after an initial calibration). However, pulse arrival time (PAT), which is equal to the sum of PTT and the pre-ejection period, is gaining popularity for BP tracking, because it is even simpler to measure. The aim of this study was to evaluate the hypothesis that PAT is an adequate surrogate for PTT as a marker of BP. PAT and PTT were estimated through the aorta using high-fidelity invasive arterial waveforms obtained from six dogs during wide BP changes induced by multiple interventions. These time delays and their reciprocals were evaluated in terms of their ability to predict diastolic, mean, and systolic BP (DBP, MBP, and SBP) per animal. The root mean squared error (RMSE) between the BP parameter predicted via the time delay and the measured BP parameter was specifically used as the evaluation metric. Taking the reciprocals of the time delays tended to reduce the RMSE values. The DBP, MBP, and SBP RMSE values for 1/PAT were 9.8 ± 5.2, 10.4 ± 5.6, and 11.9 ± 6.1 mmHg, whereas the corresponding values for 1/PTT were 5.3 ± 1.2, 4.8 ± 1.0, and 7.5 ± 2.2 mmHg (P < 0.05). Thus tracking BP via PAT was not only markedly worse than via PTT but also unable to meet the FDA BP error limits. In contrast to previous studies, our results quantitatively indicate that PAT is not an adequate surrogate for PTT in terms of detecting challenging BP changes.     

Quantification of cerebral oxygenation by full-spectrum near-infrared spectroscopy using a two-point method

The aim of this study was to quantify the relative concentrations of oxyhemoglobin and deoxyhemoglobin within the light path of the brain and to estimate cerebral hemoglobin (Hb) oxygen saturation using full-spectrum near-infrared spectroscopy (fsNIRS). For this purpose, we developed a novel exponential correction equation as well as a two-point spectroscopy method to estimate the relative concentrations of Hb and Hb oxygen saturation in biological tissues. The results of evaluation of measurements using an in vitro model indicated that our fsNIRS method enables accurate and non-invasive measurements of Hb content and saturation in a highly scattered medium such as the human brain. According to the results of analysis using a hypoxic piglet model, the mean cerebral Hb oxygen saturation (SbO(2)) of newborn piglets at an inspired oxygen gas concentration of 0.21 was estimated to be 63+/-4% (mean+/-S.D.). Umbilical arterial and left internal jugular venous Hb oxygen saturation were simultaneously estimated to be 96+/-2% and 52+/-11%, respectively. SbO(2) and arterial Hb oxygen saturation values had a linear relationship. The average oxygenation state of cerebral tissue is comparable with that of the cerebral vein. The results of this study showed that our method can be used to monitor Hb oxygen saturation in the neonatal brain at the bedside in an intensive care unit.     

Lactate uptake by the fetal sheep liver

Lactate is produced by the sheep placenta and is an important metabolic substrate for fetal sheep. However, lactate uptake and release by the fetal liver have not been assessed directly. We measured lactate flux across the liver in 16 fetal sheep at 129 (120-138) days gestation that had catheters chronically maintained in the fetal descending aorta, inferior vena cava, right or left hepatic vein, and umbilical vein. Lactate and hemoglobin concentrations and oxygen saturation were measured in blood drawn from all vessels. Umbilical venous, portal venous, and hepatic blood flow were measured by injecting radionuclide-labeled microspheres into the umbilical vein while obtaining a reference sample from the descending aorta. We found net hepatic uptake of lactate (5.0 +/- 4.4 mg/min per 100 g liver). A large quantity of lactate was delivered to the liver (94.2 +/- 78.1 mg/min per 100 g), so that the hepatic extraction of lactate was only 7.7 +/- 6.5%. Hepatic oxygen consumption was 3.18 +/- 3.3 ml/min per 100 g, and the hepatic lactate/oxygen quotient was 2.07 +/- 1.54. There was no significant correlation between hepatic lactate uptake and hepatic lactate or glucose delivery, hepatic oxygen consumption, hepatic blood flow, hepatic glucose flux, total body oxygen consumption, arterial pH, oxygen content, or oxygen saturation. There was, however, a significant correlation between hepatic lactate uptake and umbilical lactate uptake (r = 0.74, P less than 0.005) such that net hepatic lactate uptake was nearly equivalent to that produced across the umbilical-placental circulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Normative Values of Retinal Oxygen Saturation in Rhesus Monkeys: The Beijing Intracranial and Intraocular Pressure (iCOP) Study

Objective

To study the normal values of the retinal oxygen saturation in Rhesus monkeys and to evaluated repeatability and reproducibility of retinal oxygen saturation measurements.

Methods

Eighteen adult Rhesus macaque monkeys were included in this experimental study. An Oxymap T1 retinal oximeter (Oxymap, Reykjavik, Iceland) was used to perform oximetry on all subjects. Global arterial (SaO₂) and venous oxygen saturation (SvO₂), arteriovenous difference in SO₂ were measured. In the first examination, each eye was imaged three times. At the following two examinations, each eye was imaged once. All examinations were finished in one month. P values were calculated to evaluate the difference between the measurements during three visits by performing an ANOVA. Intra-visit and inter-visit intraclass correlation coefficient (ICC) was determined.

Results

At baseline, the average SaO₂ and SvO₂ were 89.48 ± 2.64% and 54.85 ± 2.18%, respectively. The global A-V difference was 34.63 ± 1.91%. The difference between the three visits was not significant (p>0.05). The highest A-V difference in SO₂ and lowest saturations were found in the inferotemporal quadrant. Intra-session and inter-visit repeatability were both high. For all oxygen saturation parameters, the ICC values of the intra-session repeatability ranged between 0.92 and 0.96. As found previously, a relatively high ICC value for inter-visit repeatability also was found for all oxygen saturation measurements, ranging between 0.86 and 0.94, with the lowest values in the infero-nasal quadrant.

Conclusions

Our study is the first to describe retinal SO₂ in healthy Rhesus monkeys. In normal monkey eyes, the reproducibility and repeatability of retinal oximetry oxygen saturation measurements were high in the retinal arterioles and venules. Our results support that Oxymap T1 retinal oximetry is a suitable and reliable technique in monkey studies.     

Biochemical markers for clinical monitoring of tissue perfusion

The assessment and monitoring of the tissue perfusion is extremely important in critical conditions involving circulatory shock. There is a wide range of established methods for the assessment of cardiac output as a surrogate of oxygen delivery to the peripheral tissues. However, the evaluation of whether particular oxygen delivery is sufficient to ensure cellular metabolic demands is more challenging. In recent years, specific biochemical parameters have been described to indicate the status between tissue oxygen demands and supply. In this review, the authors summarize the application of some of these biochemical markers, including mixed venous oxygen saturation (S_vO₂), lactate, central venous–arterial carbon dioxide difference (PCO₂ gap), and PCO₂ gap/central arterial-to-venous oxygen difference (C_a–vO₂) for hemodynamic assessment of tissue perfusion. The thorough monitoring of the adequacy of tissue perfusion and oxygen supply in critical conditions is essential for the selection of the most appropriate therapeutic strategy and it is associated with improved clinical outcomes.

     

Blood lactate dehydrogenase activity in newborn children

Arterial and venous blood samples from babies' umbilical cord vessels before lung breath beginning were used to measure arterial-venous difference between lactate dehydrogenase activity, pH and oxygen blood saturation (sO2). Enzyme activity was 735.4 +/- 90.8 U/L in venous blood and 672.0 +/- 108.1 U/L in arterial one, pH 7.21 +/- 0.06 and 7.32 +/- 0.06, sO2 32.9 +/- 12.7 and 56.5 +/- 18.3%, respectively. Reverse correlation between enzyme activity, pH and sO2 was found.     

An electron paramagnetic resonance investigation of the oxygen dependence of the arterial-venous gradient of nitrosyl hemoglobin in blood circulation

Whether there is a nitrosyl hemoglobin (HbNO) gradient between the venous and the arterial parts of the circulatory system is a very controversial issue in nitric oxide research. We have carefully evaluated the measurement of HbNO concentration in blood using EPR generated in vivo by the NO donor DEANO under various oxygen tensions. We found that the absolute concentrations of HbNO in venous and arterial blood were the same within experimental error, independent of hemoglobin saturation; only the ratios of 5-coordinate and 6-coordinate HbNO differed. The HbNO concentration increased when the oxygen concentration breathed by the rats decreased in a manner that was linear in hemoglobin saturation. These results do not support the existence of an arterial-venous gradient of HbNO under our experimental conditions.