Cerebral HbO2 Research Articles

A Biphasic Change of Regional Blood Volume in the Frontal Cortex during Non-Rapid Eye Movement Sleep: A Near-Infrared Spectroscopy Study.

Current knowledge on hemodynamics in sleep is limited because available techniques do not allow continuous recordings and mainly focus on cerebral blood flow while neglecting other important parameters, such as blood volume (BV) and vasomotor activity. Observational study. Continuous measures of hemodynamics over the left forehead and biceps were performed using near-infrared spectroscopy (NIRS) during nocturnal polysomnography in 16 healthy participants in sleep laboratory. Temporal dynamics and mean values of cerebral and muscular oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (HHb), and BV during different sleep stages were compared. A biphasic change of cerebral BV was observed which contrasted a monotonic increase of muscular BV during non-rapid eye movement sleep. A significant decrement in cerebral HbO2 and BV accompanied by an increase of HHb was recorded at sleep onset (Phase I). Prior to slow wave sleep (SWS) HbO2 and BV turned to increase whereas HHb began to decrease in subsequent Phase II suggested increased brain perfusion during SWS. The cerebral HbO2 slope correlated to BV slope in Phase I and II, but it only correlated to HHb slope in Phase II. The occurrence time of inflection points correlated to SWS latencies. Initial decrease of brain perfusion with decreased blood volume (BV) and oxygenated hemoglobin (HbO2) together with increasing muscular BV fit thermoregulation process at sleep onset. The uncorrelated and correlated slopes of HbO2 and deoxygenated hemoglobin indicate different mechanisms underlying the biphasic hemodynamic process in light sleep and slow wave sleep (SWS). In SWS, changes in vasomotor activity (i.e., increased vasodilatation) may mediate increasing cerebral and muscular BV.

The relationship between exercise intensity, cerebral oxygenation and cognitive performance in young adults.

To assess the relationship between exercise intensity, cerebral HbO2 and cognitive performance (Executive and non-Executive) in young adults. We measured reaction time (RT) and accuracy, during a computerized Stroop task, in 19 young adults (7 males and 12 females). Their mean ± SD age, height, body mass and body mass index (BMI) were 24 ± 4 years, 1.67 ± 0.07 m, 72 ± 14 kg and 25 ± 3 kg m(-2), respectively. Each subject performed the Stroop task at rest and during cycling at exercise of low intensity [40% of peak power output (PPO)], moderate intensity (60% of PPO) and high intensity (85% of PPO). Cerebral oxygenation was monitored during the resting and exercise conditions over the prefrontal cortex (PFC) using near-infrared spectroscopy (NIRS). High-intensity exercise slowed RT in both the Naming (p = 0.04) and the Executive condition (p = 0.04). The analysis also revealed that high-intensity exercise was associated with a decreased accuracy when compared to low-intensity exercise (p = 0.021). Neuroimaging results confirm a decrease of cerebral oxygenation during high-intensity exercise in comparison to low- (p = 0.004) and moderate-intensity exercise (p = 0.003). Correlations revealed that a lower cerebral HbO2 in the prefrontal cortex was associated with slower RT in the Executive condition only (p = 0.04, g = -0.72). Results of the present study suggest that low to moderate exercise intensity does not alter Executive functioning, but that exercise impairs cognitive functions (Executive and non-Executive) when the physical workload becomes heavy. The cerebral HbO2 correlation suggests that a lower availability of HbO2 was associated with slower RT in the Executive condition only.

Cerebral oxygenation with different nasal continuous positive airway pressure levels in preterm infants

ObjectivesThis study evaluates the effect of varying nasal continuous positive airway pressure (NCPAP) level on cerebral blood flow (CBF) and oxygenation in preterm infants.MethodsOxy-haemoglobin (HbO2) and total haemoglobin (HbTot), as...

Electromyographic, cerebral, and muscle hemodynamic responses during intermittent, isometric contractions of the biceps brachii at three submaximal intensities.

This study examined the electromyographic, cerebral and muscle hemodynamic responses during intermittent isometric contractions of biceps brachii at 20, 40, and 60% of maximal voluntary contraction (MVC). Eleven volunteers completed 2 min of intermittent isometric contractions (12/min) at an elbow angle of 90° interspersed with 3 min rest between intensities in systematic order. Surface electromyography (EMG) was recorded from the right biceps brachii and near infrared spectroscopy (NIRS) was used to simultaneously measure left prefrontal and right biceps brachii oxyhemoglobin (HbO2), deoxyhemoglobin (HHb), and total hemoglobin (Hbtot). Transcranial Doppler ultrasound was used to measure middle cerebral artery velocity (MCAv) bilaterally. Finger photoplethysmography was used to record beat-to-beat blood pressure and heart rate. EMG increased with force output from 20 to 60% MVC (P < 0.05). Cerebral HbO2 and Hbtot increased while HHb decreased during contractions with differences observed between 60% vs. 40% and 20% MVC (P < 0.05). Muscle HbO2 decreased while HHb increased during contractions with differences being observed among intensities (P < 0.05). Muscle Hbtot increased from rest at 20% MVC (P < 0.05), while no further change was observed at 40 and 60% MVC (P > 0.05). MCAv increased from rest to exercise but was not different among intensities (P > 0.05). Force output correlated with the root mean square EMG and changes in muscle HbO2 (P < 0.05), but not changes in cerebral HbO2 (P > 0.05) at all three intensities. Force output declined by 8% from the 1st to the 24th contraction only at 60% MVC and was accompanied by systematic increases in RMS, cerebral HbO2 and Hbtot with a leveling off in muscle HbO2 and Hbtot. These changes were independent of alterations in mean arterial pressure. Since cerebral blood flow and oxygenation were elevated at 60% MVC, we attribute the development of fatigue to reduced muscle oxygen availability rather than impaired central neuronal activation.

Seven-year outcome of pulmonary valve autograft replacement of the mitral valve in an infant

in HbO2 concentrations could be explained by a compensatory arterial dilation. We demonstrate that multichannel optical topographic analysis can provide information on regional cerebral hemodynamics and oxygenation in patients supported by ECMO. Simultaneous measurement of systemic and cerebral HbO2 and HHb concentrations can help elucidate mechanisms related to the response of the brain during changes in ECMO and cardiopulmonary bypass flows.

Brain olfactory activation measured by near-infrared spectroscopy in humans

In recent years, near-infrared spectroscopy (NIRS) has been used to study functional activation of various areas of the brain. This is based on the assumption that an increase in the recorded oxygenated haemoglobin (HbO2) concentration represents an increase in blood flow, which in turn reflects neuronal activation. The aim of this preliminary study was to use NIRS to monitor the activity of the olfactory cortex, as mirrored by the haemodynamic response, when subjects were exposed to olfactory stimuli. A NIRO 300 (Hamamatsu Photonics, Hamamatsu, Japan) device was used. The optodes were placed on the right forehead and right temporal, parietal and occipital regions. Changes in the concentration of HbO2 and deoxygenated haemoglobin during olfactory stimulation were monitored. Olfactory stimulation was performed with vanilla essence, strawberry essence and scatol. During olfactory stimulation, cerebral HbO2 concentration increased over the frontal region. However, in the temporal, parietal and occipital regions, little or no HbO2 changes were recorded. This study shows that human brain cortical activation following olfactory stimulation can be recorded by NIRS. This NIRS analysis may therefore provide the basis for future development of an objective olfactory test in humans.

Influence of Intravenous Sildenafil on Cerebral Oxygenation Measured by Near-Infrared Spectroscopy in Infants After Cardiac Surgery

Sildenafil (Viagra) has been shown to be an effective pulmonary vasodilator and is increasingly used in patients with pulmonary hypertension. Its effects on the cerebral circulation are unclear and have not yet been described. We investigated the effect of i.v. sildenafil treatment on cerebral oxygenation in 13 children with elevated pulmonary vascular resistance due to congenital heart defects after cardiac surgery using near-infrared spectroscopy (NIRS). Median age was 4.5 mo, and median weight was 5.5 +/- 1.8 kg. Sildenafil was administered in three steps of 15 min each with cumulative doses of 0.025, 0.1, and 0.25 mg/kg. We examined the changes of oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (HHb), total hemoglobin (tHb) concentration, cytochrome oxidase (CytOx) oxygenation, and cerebral tissue oxygenation index (TOI) in 13 children. A significant increase in cerebral HbO2 and tHb at the beginning of i.v. sildenafil administration with a decrease in HHb was observed. These changes led to a significant elevation in cerebral TOI from 63.4 +/- 2.5% to 65.7 +/- 2.8%, whereas mean systemic arterial pressure and arterial oxygen partial pressure tended to decrease. In conclusion, we observed a reversible increase of HbO2, tHb, and hemoglobin oxygen saturation in the scanned tissue section after i.v. sildenafil administration. These findings may be clinically relevant because they indicate that after cardiac surgery, sildenafil may increase cerebral blood flow (CBF), probably due to general endothelial dysfunction after cardiopulmonary bypass (CPB).

Cerebral hemoglobin concentration and oxygen saturation measured by intensity modulated optical spectroscopy in the human fetus during labor.

To quantify hemoglobin concentration and oxygen saturation in the human fetal brain using intensity modulated optical spectroscopy during labor. A specially designed probe was applied to the fetal scalp in 20 women during uncomplicated labor at term. Optical fibres transmitted near infra-red light to and from an intensity modulated optical spectrometer (IMOS), which detected changes in the optical parameters of the infra-red light source. Using novel off-line analytic techniques, these changes were converted into absolute measurements of oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb). Summing Hb and HbO2 gives total hemoglobin concentration (HbT) and HbO2/HbT x 100% provided measurements of cerebral saturation (SmcO2). Of 20 fetuses studied, data from 10 fetuses were suitable for analysis. Over three consecutive uterine contractions, the mean (+/- SD) absolute cerebral concentrations of Hb and HbO2 were 30 +/- 18 and 46 +/- 21 mumol/l, respectively. This gave a mean cerebral HbT of 77 +/- 29 mumol/l and a mean SmcO2 of 59 +/- 12%. In the other ten fetuses insufficient light was detected to allow chromophore quantification. These are the first absolute measurements of cerebral Hb and HbO2 in human fetuses during labor. The values of total hemoglobin are similar to those obtained in neonates with hypoxia-ischemia and the measurements of fetal cerebral oxygen saturation are similar to previously published values.

NIRS: dose dependency of local changes of cerebral HbO2 and Hb with pCO2 in parietal cortex.

Regional cerebral oxygenated hemoglobin and total hemoglobin increased systematically with increasing depth of hypercapnia, but the concentration of deoxygenated hemoglobin remained relatively constant. Relative mean changes of oxygenated and total hemoglobin increased nearly linearly, corresponding to the characteristic increase of the cerebral vascular dilation with increasing depth of hypercapnia.

Comparison of changes in cerebral blood flow and cerebral oxygen saturation measured by near infrared spectroscopy (NIRS) after acetazolamide.

The present study compares the change of cerebral blood flow and HbO2 measured by near-infrared spectroscopy (NIRS) after administration of 1000 mg acetazolamide intravenously. CBF studies in 21 patients with ischaemic cerebrovascular disease were performed routinely with the 133Xenon technique. Additionally the local HbO2 was recorded by NIRS. A rest study was followed by a second study after the administration of 1000 mg acetazolamide. In 18 patients we observed an increase of 30.8% of CBF and 4.7% of HbO2, 3 patients showed a decrease of CBF and 2 patients a simultaneous decrease of HbO2. We did not find a correlation between the absolute values of CBF and HbO2 at rest or after stimulation. However, a positive correlation (r = 0.71, p < 0.05) between the change of CBF and HbO2 could be detected. Assuming a threshold value of normal CBF reactivity of 30% and 4% HbO2 reactivity we found for NIRS a sensitivity of 0.88 and a specificity of 0.75. The results demonstrate that changes of CBF can be detected with NIRS and the algorithm of the used monitor is able to calculate the intracranial part of the signal. So, NIRS can be used as non-invasive screening method to test the cerebrovascular reserve capacity.

Reduction of Cytochrome aa3 Measured by Near-Infrared Spectroscopy Predicts Cerebral Energy Loss in Hypoxic Piglets

Near-infrared spectroscopy is a noninvasive monitoring technique that allows quantitative measurement of changes in cerebral oxygenated Hb (HbO2), deoxygenated Hb (Hb), total Hb, and oxidized cytochrome aa3 (CytO2). Changes in cerebral Hb oxygenation and CytO2 have been measured in human neonates and infants under a variety of conditions. However, the association of these measurements with cerebral high-energy phosphate loss is not known. We studied simultaneous changes in cerebral HbO2, Hb, total Hb, and CytO2 by near-infrared spectroscopy and changes in nucleoside triphosphate (NTP, mostly ATP) and phosphocreatine (PC) concentrations and intracellular pH by in vivo 31P-labeled magnetic resonance spectroscopy. Four-wk-old piglets (n = 8) underwent sequential hypoxic episodes of increasing severity (inspired O2 concentration, 12, 8, 6, 4, and 0%). Animals were anesthetized and mechanically ventilated. At all levels of hypoxia, cerebral HbO2 decreased, and Hb increased. Loss of PC or NTP was not observed until inspired O2 concentration was decreased to less than 12%. With such severe hypoxia, hypotension, intracellular acidosis, and increasingly severe PC and NTP depletions occurred. Decreases in PC and NTP correlated closely with decreased CytO2 and arterial blood pressure (p < 0.0001) but not with changes in HbO2 and Hb. In conclusion, cerebral hypoxemia is readily detected by near-infrared spectroscopy as a decrease in HbO2 and an increase in Hb. However, relative changes in cerebral HbO2 and Hb have low predictive value for cerebral energy failure. Reduction of CytO2 is highly correlated with decreased brain energy state and may indicate impending cellular injury.