Short-term microgravity effects simulation does not affect fNIRS measures of cerebral oxygenation changes induced by cognitive load

Changes in cerebral oxygenation and hemodynamics during cranial ultrasound in preterm infants

Perioperative analgesia during thoracotomy is often achieved by combining paravertebral block (PVB) with general anesthesia (GA). Functional near-infrared spectroscopy (NIRS) can detect changes in cerebral oxygenation resulting from nociceptive stimuli in the awake state or under sedation. We used NIRS to measure changes in cerebral blood flow provoked by thoracotomy incision made under GA and determine how these changes were influenced by supplementation of GA with PVB. Thirty-four patients undergoing elective thoracotomy were enrolled. Patients were randomly assigned to a group receiving only GA, or GA combined with PVB (GA+PVB). Changes in cerebral oxygenated hemoglobin (ΔO2Hb), deoxygenated-Hb (ΔHHb), and total-Hb (ΔtotalHb) were evaluated by NIRS as surgery began. In the GA group, ΔO2Hb was significantly higher in the hemisphere contralateral to the side of surgery when the incision was made and 2min after incision compared with the ipsilateral side (start of surgery, P<0.01; 2min, P<0.05). In contrast, there were no significant changes in the ΔO2Hb at any of the time points in the GA+PVB group. Comparable with ΔO2Hb, the concentration of ΔtotalHb was significantly higher in the contralateral hemisphere in the GA group at the start of surgery (P<0.05). Changes in the cerebral O2Hb concentration were detected by NIRS immediately after surgical incision under GA, but not in the presence of a PNB. NIRS could be used to monitor surgical pain. PVB inhibited changes in oxygenation induced by incision-provoked pain.

The assessment of cerebral oxygenation during carotid endarterectomy utilising near infrared spectroscopy

Patients with autonomic failure suffer severe postural hypotension that may be associated with symptoms of cerebral hypoperfusion. This study utilized near-infrared spectroscopy (NIRS) to measure changes in cerebral oxygenation and haemodynamics during the head-up tilt table test in 18 patients with autonomic failure and 10 healthy age-matched volunteers. Heart rate, blood pressure (MAP), oxygen saturation, cerebral tissue oxygen index (TOI) and total cerebral haemoglobin concentration [HbT] were measured continuously. In patients with autonomic failure there was a mean (SD) reduction in MAP of 46.7 (26.5) mmHg (p < 0.005) associated with a reduction in TOI of 8.6 (6.2)% (p < 0.005) during the head-up tilt table test. In healthy volunteers mean (SD) MAP rose by 12.3 (8.0) mmHg (p < 0.005) and TOI fell by 2.6 (3.2)% (p < 0.05). There was a mean (SD) reduction in [HbT] of 3.09 (2.82) µmol l−1 (p < 0.005) in patients, equivalent to a decrease in cerebral blood volume of 0.2 (0.18) ml/100 g. There were no changes in [HbT] in the healthy volunteers. Postural hypotension in patients with autonomic failure is associated with a substantial decrease in absolute cerebral oxygenation measured by NIRS and this might reflect a critical reduction in cerebral oxygen delivery.

382 Effects of a 4-Months High-Intensity Interval Training Associated With Resistance Training Program on Cognitive Performance, Cerebral Oxygenation, Exercise Capacity and Cardiac Output in Middle-Aged Overweight Subjects: A Pilot Study

Observation on the effect of acupoint stimulation on regional cerebral blood flow using near-infrared spectroscopy technology

The Richalet hypoxia sensitivity test (RT), which quantifies the cardiorespiratory response to acute hypoxia during exercise at an intensity corresponding to a heart rate of ~130 bpm in normoxia, can predict susceptibility of altitude sickness. Its ability to predict exercise performance in hypoxia is unknown. Investigate: (1) whether cerebral blood flow (CBF) and cerebral tissue oxygenation (O2Hb; oxygenated hemoglobin, HHb; deoxygenated hemoglobin) responses during RT predict time-trial cycling (TT) performance in severe hypoxia; (2) if subjects with blunted cardiorespiratory responses during RT show greater impairment of TT performance in severe hypoxia. Thirteen men [27 ± 7 years (mean ± SD), Wmax: 385 ± 30 W] were evaluated with RT and the results related to two 15 km TT, in normoxia and severe hypoxia (FIO2 = 0.11). During RT, mean middle cerebral artery blood velocity (MCAv: index of CBF) was unaltered with hypoxia at rest (p > 0.05), while it was increased during normoxic (+22 ± 12 %, p < 0.05) and hypoxic exercise (+33 ± 17 %, p < 0.05). Resting hypoxia lowered cerebral O2Hb by 2.2 ± 1.2 μmol (p < 0.05 vs. resting normoxia); hypoxic exercise further lowered it to -7.6 ± 3.1 μmol below baseline (p < 0.05). Cerebral HHb, increased by 3.5 ± 1.8 μmol in resting hypoxia (p < 0.05), and further to 8.5 ± 2.9 μmol in hypoxic exercise (p < 0.05). Changes in CBF and cerebral tissue oxygenation during RT did not correlate with TT performance loss (R = 0.4, p > 0.05 and R = 0.5, p > 0.05, respectively), while tissue oxygenation and SaO2 changes during TT did (R = -0.76, p < 0.05). Significant correlations were observed between SaO2, MCAv and HHb during RT (R = -0.77, -0.76 and 0.84 respectively, p < 0.05 in all cases). CBF and cerebral tissue oxygenation changes during RT do not predict performance impairment in hypoxia. Since the changes in SaO2 and brain HHb during the TT correlated with performance impairment, the hypothesis that brain oxygenation plays a limiting role for global exercise in conditions of severe hypoxia remains to be tested further.

Background: We have shown before that blood sampling from umbilical artery catheters induces a decrease in cerebral oxygenation and cerebral blood volume (CBV) in VLBW infants. The aim of the present study was to assess, if heel lance and venepuncture effect cerebral oxygenation as well. Methods: Seventeen preterm infants (birth weight 355–1280 g, median 790 g; gestational age 24–32 weeks, median 27 weeks) were studied. In 11 cases, heel lance and venepuncture blood sampling were analyzed, in 3 heel lance, and in 3 venepuncture only. Using near infrared spectroscopy changes in oxygenated cerebral hemoglobin (O2Hb) and deoxygenated hemoglobin were measured and changes in cerebral oxygenation (HbD) and CBV were calculated. Arterial oxygen saturation, heart rate, blood pressure and tcPCO2 were registered simultaneously. Results: Blood sampling induced a decrease in cerebral O2Hb (heel lance: −3.1 micromol/L; p = 0.004; venepuncture: −1.7 micromol/L; p = 0.06) and HbD (heel lance: −4.4 micromol/L; p = 0.008; venepuncture: −3.3 micromol/L; p = 0.02) compared to baseline levels which was more pronounced after heel lance. CBV decreased significantly after heel lance blood sampling only. Simultaneously, arterial oxygen saturation as measured by pulse oximetry dropped significantly (from 92.5% to 88.7% during heel lance; p = 0.03; from 92.3% to 89.6% during venepuncture; p = 0.05). Small but significant changes of heart rate and blood pressure were observed. Conclusion: Heel lance and venepuncture for blood sampling induce a decrease in cerebral oxygenation. The decrease is more pronounced and lasting in heel lance compared to venepuncture and it is even of greater magnitude than the decrease during blood sampling from umbilical artery catheters. We speculate that the decrease in cerebral oxygenation during blood sampling from umbilical artery catheters is caused by acute volume loss, whereas the decrease during heel lance and venepuncture might be caused by a stress induced decrease in arterial oxygen saturation.

To test the hypothesis that racial biases in opioid prescribing would be more likely under high levels of cognitive load, defined as the amount of mental activity imposed on working memory, which may come from environmental factors such as stressful conditions, chaotic workplace, staffing insufficiency, and competing demands, one's own psychological or physiological state, as well as from demands inherent in the task at hand. Two (patient race: White vs Black) by two (cognitive load: low vs high) between-subjects factorial design. Ninety-eight primary care physicians from the Veterans Affairs Healthcare System. Web-based experimental study. Physicians were randomly assigned to read vignettes about either a Black or White patient, under low vs high cognitive load, and to indicate their likelihood of prescribing opioids. High cognitive load was induced by having physicians perform a concurrent task under time pressure. There was a three-way interaction between patient race, cognitive load, and physician gender on prescribing decisions (P = 0.034). Hypotheses were partially confirmed. Male physicians were less likely to prescribe opioids for Black than White patients under high cognitive load (12.5% vs 30.0%) and were more likely to prescribe opioids for Black than White patients under low cognitive load (30.8% vs 10.5%). By contrast, female physicians were more likely to prescribe opioids for Black than White patients in both conditions, with greater racial differences under high (39.1% vs 15.8%) vs low cognitive load (28.6% vs 21.7%). Physician gender affected the way in which patient race and cognitive load influenced decisions to prescribe opioids for chronic pain. Future research is needed to further explore the potential effects of physician gender on racial biases in pain treatment, and the effects of physician cognitive load on pain treatment.

Auditory-evoked cerebral oxygenation changes in hypoxic-ischemic encephalopathy of newborn infants monitored by near infrared spectroscopy.

We have shown previously that blood sampling via umbilical artery catheters decreases cerebral oxygenation and cerebral blood volume in preterm infants. To evaluate alternative methods, we assessed the effects of blood sampling via umbilical vein catheters in a cohort of preterm infants. Twenty neonates (median birth weight 900 g [range 410-1900 g], median gestational age 27 weeks [24-31 weeks]) were studied during routine blood sampling via umbilical vein catheters by near-infrared spectroscopy. Tissue oxygenation index and changes in concentrations of cerebral oxygenated and deoxygenated haemoglobin were measured and changes in cerebral oxygenation and cerebral blood volume were calculated. Oxygen saturation and heart rate were recorded simultaneously. There was a significant drop of cerebral oxygenation (-2.135 +/- 0.532 micromol/L) and cerebral blood volume (-0.037 +/- 0.019 mL/100 g tissue) during umbilical vein blood sampling. Although peripheral arterial oxygen saturation remained unchanged, cerebral tissue oxygenation index decreased from 64.8 +/- 2.5% to 62.4 +/- 2.6% (p < 0.01), accompanied by a slight increase in heart rate (from 140 +/- 2.9 to 144 +/- 2.9 beats/min, p < 0.01). Umbilical vein blood sampling reduces cerebral oxygenation and cerebral blood volume. The magnitude of the effects is similar to those during umbilical artery blood sampling.

Background: The transitional period, defined as the first 72 h after preterm birth, is often characterized by a significant hemodynamic instability, which represents an important risk factor for such neurological complications of prematurity as intraventricular hemorrhage (IVH). The impairment of cerebral autoregulation plays a key role in the pathogenesis of IVH, whose incidence is highest during the transitional period. This pilot study aimed to evaluate whether patterns of cerebral autoregulation and oxygenation differ in relation to IVH development in very preterm infants during the transitional period.Methods: Infants <32 weeks' gestation were enrolled within 12 h from birth. A simultaneous monitoring of cerebral oxygenation (CrSO2) by near-infrared spectroscopy and of heart rate and peripheral oxygen saturation by pulse oximetry was performed over the first 72 h. Cerebral fractional oxygen extraction (cFTOE) and tissue oxygenation-heart rate reactivity index (TOHRx), which represents a marker of cerebrovascular reactivity, were calculated. Daily cranial and cardiac ultrasound scans were performed, in order to assess the hemodynamic status and to detect a possible IVH onset. CrSO2 and cFTOE, clustered on 6-hour epochs, were compared between infants who developed IVH during the study period and those who did not. A between-group comparison of TOHRx before and after IVH detection was also performed.Results: Twenty preterm infants with a median gestational age of 27 weeks (interquartile range, IQR: 25-30 weeks) and median birth weight of 895 g (IQR: 822-1208 g) were enrolled. Of these, 8 developed IVH. The median age at IVH detection was 40 h (IQR: 30-48 h). Pre-IVH TOHRx was significantly higher compared to matched control periods (p <0.001). CrSO2 was significantly lower from 12 to 30 h and from 42 h onwards in cases compared to controls; however, a temporary CrSO2 rise preceded IVH detection. Similarly, cFTOE was significantly higher in IVH infants from 12 to 30 h and from 48 to 72 h, with a transient decrease between the two periods.Conclusions: In preterm infants during the transitional period, the development of IVH is preceded by transient changes in cerebral oxygenation and oxygen extraction which, in turn, may underlie an early impairment of cerebral autoregulation. Larger studies are needed to confirm these preliminary findings.

This review focuses on the clinical use of near infrared spectroscopy (NIRS) to assess brain oxygenation by the tissue oxygenation index (TOI), and monitoring regional cerebral oxygen saturation (rScO₂), cerebral fractional tissue oxygen extraction (cFTOE), which is derived from rScO₂, and systemic oxygen saturation. Its precision and pitfalls are discussed. At this stage, it is clear that NIRS-monitored oxygenation of the brain by rScO₂ or TOI lacks the precision required to be used as a robust quantitative variable to monitor cerebral oxygenation. Intra- and especially interpatient variability are too large for this aim. On the other hand, when used merely as a trend monitor in the individual patient, substantial changes in rScO₂ or TOI and consequently of cFTOE, larger than the limits of agreement, can yield important clinical information that suggest an intervention. Since neonatal intensive care is for a substantial part ‘brain orientated’ this approach seems conceivable. This gives rise to the conclusion that NIRS-monitored TOI, rScO₂ and cFTOE increasingly will have a role in clinical practice as semiquantitative indicators of changes in cerebral oxygenation and oxygen extraction. Combination with other (cerebral) parameters such as amplitude-integrated EEG and blood pressure seems promising for further optimization of monitoring the immature brain.

Changes in cerebral oxygenation in response to various stimuli in newborns as measured by functional near-infrared spectroscopy

Deep hypothermic circulatory arrest is a widely used technique in pediatric cardiac surgery that carries a risk of neurologic injury. Previous work in neonates identified distinct changes in cerebral oxygenation during surgery. This study sought to determine whether the intraoperative changes in cerebral oxygenation vary between neonates, infants, and children and whether the oxygenation changes are associated with postoperative cerebral dysfunction. The study included eight neonates, ten infants, and eight children without preexisting neurologic disease. Cerebrovascular hemoglobin oxygen saturation (SCO2), an index of brain oxygenation, was monitored intraoperatively by near-infrared spectroscopy. Body temperature was reduced to 15 degrees C during cardiopulmonary bypass (CPB) before commencing circulatory arrest. Postoperative neurologic status was judged as normal or abnormal (seizures, stroke, coma). Relative to preoperative levels, the age groups experienced similar changes in SCO2 during surgery: SCO2 increased 30 +/- 4% during deep hypothermic CPB, it decreased 62 +/- 5% by the end of arrest, and it increased 20 +/- 5% during CPB recirculation (all P < 0.001); after rewarming and removal of CPB, SCO2 returned to preoperative levels. During arrest, the half-life of SCO2 was 9 +/- 1 min in neonates, 6 +/- 1 min in infants, and 4 +/- 1 min in children (P < 0.001). Postoperative neurologic status was abnormal in three (12%) patients. The SCO2 increase during deep hypothermic CPB was less in these patients than in the remaining study population (3 +/- 2% versus 33 +/- 4%, P < 0.001). There were no other significant SCO2 differences between outcome groups. Brain oxygenation changed at distinct points during surgery in all ages, reflecting fundamental cerebral responses to hypothermic CPB, ischemia, and reperfusion. However, the changes in SCO2 half-life with age reflect developmental differences in the rate of cerebral oxygen utilization during arrest, consistent with experimental work in animals. Certain intraoperative cerebral oxygenation patterns may be associated with postoperative cerebral dysfunction and require further study.