Prefrontal cortex oxygenation during a mentally fatiguing task in normoxia and hypoxia.

Mental fatigue (MF) and hypoxia impair cognitive performance through changes in brain hemodynamics. We want to elucidate the role of prefrontal cortex (PFC)-oxygenation in MF. Twelve participants (22.9 ± 3.5 years) completed four experimental trials, (1) MF in (normobaric) hypoxia (MF_HYP) (3.800 m; 13.5%O2), (2) MF in normoxia (MF_NOR) (98 m; 21.0%O2), (3) Control task in HYP (CON_HYP), (4) Control in NOR (CON_NOR). Participants performed a 2-back task, Digit Symbol Substitution test and Psychomotor Vigilance task before and after a 60-min Stroop task or an emotionally neutral documentary. Brain oxygenation was measured through functional Near Infrared Spectroscopy. Subjective feelings of MF and physiological measures (heart rate, oxygen saturation, blood glucose and hemoglobin) were recorded. The Stroop task resulted in increased subjective feelings of MF compared to watching the documentary. 2-back accuracy was lower post task compared to pre task in MF_NOR and CON_NOR, while no differences were found in the other cognitive tasks. The fraction of inspired oxygen did not impact feelings of MF. Although performing the Stroop resulted in higher subjective feelings of MF, hypoxia had no effect on the severity of self-reported MF. Additionally, this study could not provide evidence for a role of oxygenation of the PFC in the build-up of MF.

The Effects of Head Elevation on Intracranial Pressure, Cerebral Perfusion Pressure, and Cerebral Oxygenation Among Patients with Acute Brain Injury: A Systematic Review and Meta-Analysis.

BACKGROUND: Head elevation is recommended as a tier zero measure to decrease high intracranial pressure (ICP) in neurocritical patients. However, its quantitative effects on cerebral perfusion pressure (CPP), jugular bulb oxygen saturation (SjvO2), brain tissue partial pressure of oxygen (PbtO2), and arteriovenous difference of oxygen (AVDO2) are uncertain. Our objective was to evaluate the effects of head elevation on ICP, CPP, SjvO2, PbtO2, and AVDO2 among patients with acute brain injury. METHODS: We conducted a systematic review and meta-analysis on PubMed, Scopus, and Cochrane Library of studies comparing the effects of different degrees of head elevation on ICP, CPP, SjvO2, PbtO2, and AVDO2. RESULTS: A total of 25 articles were included in the systematic review. Of these, 16 provided quantitative data regarding outcomes of interest and underwent meta-analyses. The mean ICP of patients with acute brain injury was lower in group with 30° of head elevation than in the supine position group (mean difference [MD] - 5.58 mm Hg; 95% confidence interval [CI] - 6.74 to - 4.41 mm Hg; p < 0.00001). The only comparison in which a greater degree of head elevation did not significantly reduce the ICP was 45° vs. 30°. The mean CPP remained similar between 30° of head elevation and supine position (MD - 2.48 mm Hg; 95% CI - 5.69 to 0.73 mm Hg; p = 0.13). Similar findings were observed in all other comparisons. The mean SjvO2 was similar between the 30° of head elevation and supine position groups (MD 0.32%; 95% CI - 1.67% to 2.32%; p = 0.75), as was the mean PbtO2 (MD - 1.50 mm Hg; 95% CI - 4.62 to 1.62 mm Hg; p = 0.36), and the mean AVDO2 (MD 0.06 µmol/L; 95% CI - 0.20 to 0.32 µmol/L; p = 0.65).The mean ICP of patients with traumatic brain injury was also lower with 30° of head elevation when compared to the supine position. There was no difference in the mean values of mean arterial pressure, CPP, SjvO2, and PbtO2 between these groups. CONCLUSIONS: Increasing degrees of head elevation were associated, in general, with a lower ICP, whereas CPP and brain oxygenation parameters remained unchanged. The severe traumatic brain injury subanalysis found similar results.

Maximizing the Reliability and Precision of Measures of Prefrontal Cortical Oxygenation Using Frequency-Domain Near-Infrared Spectroscopy.

Frequency-domain near-infrared spectroscopy (FD-NIRS) has been used for non-invasive assessment of cortical oxygenation since the late 1990s. However, there is limited research demonstrating clinical validity and general reproducibility. To address this limitation, recording duration for adequate validity and within- and between-day reproducibility of prefrontal cortical oxygenation was evaluated. To assess validity, a reverse analysis of 10-min-long measurements (n = 52) at different recording durations (1-10-min) was quantified via coefficients of variation and Bland-Altman plots. To assess within- and between-day within-subject reproducibility, participants (n = 15) completed 2-min measurements twice a day (morning/afternoon) for five consecutive days. While 1-min recordings demonstrated sufficient validity for the assessment of oxygen saturation (StO2) and total hemoglobin concentration (THb), recordings ≥4 min revealed greater clinical utility for oxy- (HbO) and deoxyhemoglobin (HHb) concentration. Females had lower StO2, THb, HbO, and HHb values than males, but variability was approximately equal between sexes. Intraclass correlation coefficients ranged from 0.50-0.96. The minimal detectable change for StO2 was 1.15% (95% CI: 0.336-1.96%) and 3.12 µM for THb (95% CI: 0.915-5.33 µM) for females and 2.75% (95%CI: 0.807-4.70%) for StO2 and 5.51 µM (95%CI: 1.62-9.42 µM) for THb in males. Overall, FD-NIRS demonstrated good levels of between-day reliability. These findings support the application of FD-NIRS in field-based settings and indicate a recording duration of 1 min allows for valid measures; however, data recordings of ≥4 min are recommended when feasible.

Depression in systemic lupus erythematosus: A manifestation of microcirculation dysfunction?

OBJECTIVES: Depression is highly prevalent among systemic lupus erythematosus (SLE) patients. Brain hypoperfusion in neuropsychiatric SLE patients might be associated with emotional difficulties. However, no previous study examined possible associations of depression with brain oxygenation during a mild physical stress in non-neuropsychiatric SLE patients. Our study aimed to identify possible differences in cerebral oxygenation during exercise in SLE patients with and without depressive symptoms using near-infrared spectroscopy (NIRS) and examine possible underlying mechanisms through evaluation of vascular cell adhesion molecule 1 (VCAM-1) levels. METHODS: SLE patients without a known neuropsychiatric history or treatment with antidepressants or antipsychotic drugs were enrolled. Participants were assigned into groups based on Beck's Depression Inventory I (BDI-I). Patients with BDI-I score ≥10 comprised the SLE-depression group and those with BDI-I score <9 the SLE-non-depression group. All participants underwent a protocol involving a seated rest, a 3-min handgrip exercise (at 30% of maximal strength), and a 3-min recovery. NIRS was used to monitor changes in cerebral oxygenated hemoglobin (O2Hb), deoxygenated (HHb), and total hemoglobin (tHb). VCAM-1 levels were measured in serum samples. RESULTS: Twenty-three patients were enrolled. During exercise, the SLE-depression group exhibited a significantly lower increase in cerebral O2Hb [(peak-O2Hb (p = 0.039); O2Hb-area under the curve, AUC, p = 0.027) vs. SLE-non-depression group. BDI-I score was inversely correlated with AUC (rho = -0.493, p = 0.017) and positively correlated with VCAM-1 levels (rho = 0.501, p = 0.034). CONCLUSION: This study suggests a possible association between emotional abnormalities and microvascular impairment (cerebral oxygenation and endothelial dysfunction) in SLE However, larger studies are needed to confirm these results.

"THE MANTLE" bundle for minimizing cerebral hypoxia in severe traumatic brain injury.

To ensure neuronal survival after severe traumatic brain injury, oxygen supply is essential. Cerebral tissue oxygenation represents the balance between oxygen supply and consumption, largely reflecting the adequacy of cerebral perfusion. Multiple physiological parameters determine the oxygen delivered to the brain, including blood pressure, hemoglobin level, systemic oxygenation, microcirculation and many factors are involved in the delivery of oxygen to its final recipient, through the respiratory chain. Brain tissue hypoxia occurs when the supply of oxygen is not adequate or when for some reasons it cannot be used at the cellular level. The causes of hypoxia are variable and can be analyzed pathophysiologically following "the oxygen route." The current trend is precision medicine, individualized and therapeutically directed to the pathophysiology of specific brain damage; however, this requires the availability of multimodal monitoring. For this purpose, we developed the acronym "THE MANTLE," a bundle of therapeutical interventions, which covers and protects the brain, optimizing the components of the oxygen transport system from ambient air to the mitochondria.

Association of intraplacental oxygenation patterns on dual-contrast MRI with placental abnormality and fetal brain oxygenation.

OBJECTIVES: Most human in-vivo placental imaging techniques are unable to distinguish and characterize various placental compartments, such as the intervillous space (IVS), placental vessels (PV) and placental tissue (PT), limiting their specificity. We describe a method that employs T2* and diffusion-weighted magnetic resonance imaging (MRI) data to differentiate automatically placental compartments, quantify their oxygenation properties and identify placental lesions (PL) in vivo. We also investigate the association between placental oxygenation patterns and fetal brain oxygenation. METHODS: This was a prospective study conducted between 2018 and 2021 in which dual-contrast clinical MRI data (T2* and diffusion-weighted MRI) were acquired from patients between 20 and 38 weeks' gestation. We trained a fuzzy clustering method to analyze T2* and diffusion-weighted MRI data and assign placental voxels to one of four clusters, based on their distinct imaging domain features. The new method divided automatically the placenta into IVS, PV, PT and PL compartments and characterized their oxygenation changes throughout pregnancy. RESULTS: A total of 27 patients were recruited, of whom five developed pregnancy complications. Total placental oxygenation level and T2* did not demonstrate a statistically significant temporal correlation with gestational age (GA) (R2 = 0.060, P = 0.27). In contrast, the oxygenation level reflected by T2* values in the placental IVS (R2 = 0.51, P = 0.0002) and PV (R2 = 0.76, P = 1.1 × 10-7 ) decreased significantly with advancing GA. Oxygenation levels in the PT did not show any temporal change during pregnancy (R2 = 0.00044, P = 0.93). A strong spatial-dependent correlation between PV oxygenation level and GA was observed. The strongest negative correlation between PV oxygenation and GA (R2 = 0.73, P = 4.5 × 10-7 ) was found at the fetal-vessel-dominated region close to the chorionic plate. The location and extent of the placental abnormality were automatically delineated and quantified in the five women with clinically confirmed placental pathology. Compared to the averaged total placental oxygenation, placental IVS oxygenation level best reflected fetal brain oxygenation level during fetal development. CONCLUSION: Based on clinically feasible dual-MRI, our method enables accurate spatiotemporal quantification of placental compartment and fetal brain oxygenation across different GAs. This information should improve our knowledge of human placenta development and its relationship with normal and abnormal pregnancy. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Streamlined quantitative BOLD for detecting visual stimulus-induced changes in oxygen extraction fraction in healthy participants: toward clinical application in human glioma.

OBJECTIVE: Monitoring brain oxygenation is critical in brain tumors, as low oxygenation influences tumor growth, pathological angiogenesis, and treatment resistance. This study examined the ability of the streamlined quantitative (sq)BOLD MRI technique to detect oxygenation changes in healthy individuals, as well as its potential application in a clinical setting. METHODS: We used the asymmetric spin echo (ASE) technique with FLAIR preparation, along with model-based Bayesian inference to quantify the reversible transverse relaxation rate (R2') and oxygen extraction fraction (OEF) across the brain at baseline and during visual stimulation in eight healthy participants at 3T; and two patients with glioma at rest only. RESULTS: Comparing sqBOLD-derived parameters between baseline and visual stimulation revealed a decrease in OEF from 0.56 ± 0.09 at baseline to 0.54 ± 0.07 at the activated state (p = 0.04, paired t test) within a functional localizer-defined volume of interest, and a decline in R2' from 6.5 ± 1.3s-1 at baseline to 6.2 ± 1.4s-1 at the activated state (p = 0.006, paired t test) in the visual cortex. CONCLUSION: The sqBOLD technique is sensitive enough to detect and quantify changes in oxygenation in the healthy brain and shows potential for integration into clinical settings to provide valuable information on oxygenation in glioma.

Hybrid Convolutional Neural Network (hCNN) for Image Reconstruction in Near-Infrared Optical Tomography.

Near-infrared optical tomography (NIROT), a promising imaging modality for early detection of oxygenation in the brain of preterm infants, requires data acquisition at the tissue surface and thus an image reconstruction adaptable to cephalometric variations and surface topologies. Widely used model-based reconstruction methods come with the drawback of huge computational cost. Neural networks move this computational load to an offline training phase, allowing much faster reconstruction. Our aim is a data-driven volumetric image reconstruction that generalises well to different surfaces, increases reconstruction speed, localisation accuracy and image quality. We propose a hybrid convolutional neural network (hCNN) based on the well-known V-net architecture to learn inclusion localisation and absorption coefficients of heterogenous arbitrary shapes via a joint cost function. We achieved an average reconstruction time of 30.45 s, a time reduction of 89% and inclusion detection with an average Dice score of 0.61. The CNN is flexible to surface topologies and compares well in quantitative metrics with the traditional model-based (MB) approach and state-of-the-art neuronal networks for NIROT. The proposed hCNN was successfully trained, validated and tested on in-silico data, excels MB methods in localisation accuracy and provides a remarkable increase in reconstruction speed.

Brain oxygenation during multiple sets of isometric and dynamic resistance exercise of equivalent workloads: Association with systemic haemodynamics.

Brain function relies on sufficient blood flow and oxygen supply. Changes in cerebral oxygenation during exercise have been linked to brain activity and central command. Isometric- and dynamic-resistance exercise-(RE) may elicit differential responses in systemic circulation, neural function and metabolism; all important regulators of cerebral circulation. We examined whether (i) cerebral oxygenation differs between isometric- and dynamic-RE of similar exercise characteristics and (ii) cerebral oxygenation changes relate to cardiovascular adjustments occurring during RE. Fourteen men performed, randomly, an isometric-RE and a dynamic-RE of similar characteristics (bilateral-leg-press, 2-min×4-sets, 30% of maximal-voluntary-contraction, equivalent tension-time-index/workload). Cerebral-oxygenation (oxyhaemoglobin-O2Hb; total haemoglobin-tHb/blood-volume-index; deoxyhemoglobin-HHb) was assessed by NIRS and beat-by-beat haemodynamics via photoplethysmography. Cerebral-O2Hb and tHb progressively increased from the 1st to 4th set in both RE-protocols (p < 0.05); HHb slightly decreased (p < 0.05). Changes in NIRS-parameters were similar between RE-protocols within each exercise-set (p = 0.91-1.00) and during the entire protocol (including resting-phases) (p = 0.48-0.63). O2Hb and tHb changes were not correlated with changes in systemic haemodynamics. In conclusion, cerebral oxygenation/blood-volume steadily increased during multiple-set RE-protocols. Isometric- and dynamic-RE of matched exercise characteristics resulted in similar prefrontal oxygenation/blood volume changes, suggesting similar cerebral haemodynamic and possibly neuronal responses to maintain a predetermined force.

Functional reserve and sex differences during exercise to exhaustion revealed by post-exercise ischaemia and repeated supramaximal exercise.

KEY POINTS: Females have lower fatigability than males during single limb isometric and dynamic contractions, but whether sex-differences exist during high-intensity whole-body exercise remains unknown. This study shows that males and females respond similarly to repeated supramaximal whole-body exercise, and that at task failure a large functional reserve remains in both sexes. Using post-exercise ischaemia with repeated exercise, we have shown that this functional reserve depends on the glycolytic component of substrate-level phosphorylation and is almost identical in both sexes. Metaboreflex activation during post-exercise ischaemia and the O2 debt per kg of active lean mass are also similar in males and females after supramaximal exercise. Females have a greater capacity to extract oxygen during repeated supramaximal exercise and reach lower PETCO2 , experiencing a larger drop in brain oxygenation than males, without apparent negative repercussion on performance. Females had no faster recovery of performance after accounting for sex differences in lean mass. ABSTRACT: The purpose of this study was to ascertain what mechanisms explain sex differences at task failure and to determine whether males and females have a functional reserve at exhaustion. Exercise performance, cardiorespiratory variables, oxygen deficit, and brain and muscle oxygenation were determined in 18 males and 18 females (21-36 years old) in two sessions consisting of three bouts of constant-power exercise at 120% of V̇O2max until exhaustion interspaced by 20 s recovery periods. In one of the two sessions, the circulation of both legs was occluded instantaneously (300 mmHg) during the recovery periods. Females had a higher muscle O2 extraction during fatiguing supramaximal exercise than males. Metaboreflex activation, and lean mass-adjusted O2 deficit and debt were similar in males and females. Compared to males, females reached lower PETCO2 and brain oxygenation during supramaximal exercise, without apparent negative consequences on performance. After the occlusions, males and females were able to restart exercising at 120% of V̇O2max , revealing a similar functional reserve, which depends on glycolytic component of substrate-level phosphorylation and its rate of utilization. After ischaemia, muscle O2 extraction was increased, and muscle V̇O2 was similarly reduced in males and females. The physiological response to repeated supramaximal exercise to exhaustion is remarkably similar in males and females when differences in lean mass are considered. Both sexes fatigue with a large functional reserve, which depends on the glycolytic energy supply, yet females have higher oxygen extraction capacity, but reduced PETCO2 and brain oxygenation.

A hyperspectral imaging system for mapping haemoglobin and cytochrome-c-oxidase concentration changes in the exposed cerebral cortex.

We present a novel hyperspectral imaging (HSI) system using visible and near-infrared (NIR) light on the exposed cerebral cortex of animals, to monitor and quantify in vivo changes in the oxygenation of haemoglobin and in cellular metabolism via measurement of the redox states of cytochrome-c-oxidase (CCO). The system, named hNIR, is based on spectral scanning illumination at 11 bands (600, 630, 665, 784, 800, 818, 835, 851, 868, 881 and 894 nm), using a supercontinuum laser coupled with a rotating Pellin-Broca prism. Image reconstruction is performed with the aid of a Monte Carlo framework for photon pathlength estimation and post-processing correction of partial volume effects. The system is validated on liquid optical phantoms mimicking brain tissue haemodynamics and metabolism, and finally applied in vivo on the exposed cortex of mice undergoing alternating oxygenation challenges. The results of the study demonstrate the capacity of hNIR to map and quantify the haemodynamic and metabolic states of the exposed cortex at microvascular levels. This represents (to the best of our knowledge) the first example of simultaneous mapping and quantification of cerebral haemoglobin and CCO in vivo using visible and NIR HSI, which can potentially become a powerful tool for better understanding brain physiology.

Not Removing the Glossy White Cover from Adhesive INVOS Neonatal Sensors Affects the Oxygenation Measurement.

The randomized clinical trial, SafeBoosC III, evaluates the effect of treatment guided by cerebral tissue oximetry monitoring in extremely preterm infants. Treatment should be considered, when cerebral oxygen saturation (StO2) drops below a predefined hypoxic threshold. This threshold value differs between different brands of instruments. To achieve high external validity, in this pragmatic trial all commercially available cerebral tissue oximeters have been accepted, provided their specific hypoxic threshold value has been determined in phantom studies. Since most companies produce sensors with an adhesive surface on the patient-contacting side, in the phantom studies these sensors were applied according to the specifications, i.e., the glossy cover was removed from the sensor. However, since the skin of preterm infants is particularly fragile, some neonatologists keep this cover on the adhesive sensors, to avoid the risk of skin injury when removing the sensor. Therefore, the aim of this study was to determine whether keeping this cover on leads to different StO2 values. To evaluate the effect of the cover, we performed multiple deoxygenations in a blood-lipid phantom and compared an INVOS neonatal sensor (Medtronic), with and without the cover, to a reference oximeter (OxiplexTS, ISS). As expected, the relationship of the StO2 between the INVOS neonatal sensor and OxiplexTS was linear (r2 = 0.999) with and without cover, but the cover influenced the linear equation: StO2_INVOS_cover = 1.133*StO2_ISS + 7.1 as opposed to StO2_INVOS_nocover = 1.103*StO2_ISS + 12.0. Furthermore, the hypoxic SafeBoosC III threshold differed as well: 60.3% with cover and 63.8% without cover. In conclusion, keeping the adhesive cover on an INVOS neonatal sensor results in lower measured values. At the hypoxic threshold, this is more than 3% (from 60.3% to 63.8%), and therefore, if clinicians keep the cover on the sensor, they need to be aware of this difference.

Analysis of the Association Between Lung Function and Brain Tissue Oxygen Tension in Severe Traumatic Brain Injury.

INTRODUCTION: Low brain tissue oxygen tension (PbtO2) has been shown to be an independent factor associated with unfavourable outcomes in traumatic brain injury (TBI). Although PbtO2 provides clinicians with an understanding of ischaemic and non-ischaemic derangements of brain physiology, the value alone can be the result of several factors, including partial arterial oxygenation pressure (PaO2), haemoglobin levels (Hb) and cerebral perfusion pressure (CPP). METHODS: This chapter presents a single-centre, retrospective cohort study of 70 adult patients with severe TBI who were admitted to the Neurocritical Care Unit (NCCU) at Addenbrooke's Hospital (Cambridge, UK) between October 2014 and December 2017. A total of 303 simultaneous measurements of different variables that included (but were not limited to) intracranial pressure (ICP), PaO2, PbtO2, CPP and the fraction of inspired oxygen (FiO2) were considered in this work. We conducted a correlation analysis between all of the variables. We also implemented a longitudinal data analysis of the PbtO2 and PaO2/FiO2 ratio (PF ratio). RESULTS: There were strong and independent correlations between PbtO2 and the PF ratio, and between PbtO2 and PaO2, with adjusted p values of <0.001 for both correlations. After adjustment for ICP, age, sex and the Glasgow Coma Scale (GCS) score, a PF ≤ 330 was shown to be an independent risk factor for a compromised PbtO2 value of <20, with an adjusted odds ratio of 1.94 (95% confidence interval 1.12-3.34) and a p value of 0.02. CONCLUSION: Brain and lung interactions in patients with TBI patients have complex interrelationships. Our results confirm the importance of employing lung-protective strategies to prevent brain hypoxia in patients with TBI.

A method for modelling the oxyhaemoglobin dissociation curve at the level of the cerebral capillary in humans.

NEW FINDINGS: What is the central question of this study? Can the change in haemoglobin's affinity for oxygen in the human cerebral circulation be modelled in vivo? What is the main finding and its importance? We provide a novel method for modelling the oxyhaemoglobin dissociation curve at the cerebral capillary level in humans, so that the cerebral capillary and mitochondrial oxygen tensions can reliably be estimated. This may be useful in future human-experimental studies on cerebral oxygen transport. ABSTRACT: We provide a method for modelling the oxyhaemoglobin dissociation curve (ODC) in the cerebral capillary in humans. In contrast to most previous approaches, our method involves the construction of an averaged ODC based on paired arterial-jugular venous blood gas values, which enables the estimation of oxygen parameters in cerebral capillary blood. The method was used to determine the mean cerebral capillary oxygen saturation and tension from data previously collected from 30 healthy volunteers. The averaged ODC provided systematically higher capillary oxygen tensions than when assuming a 'fixed' standard arterial ODC. When the averaged and measured arterial ODC were used for constructing the capillary ODC, similar values were obtained during resting breathing, but not when the arterial ODC was modulated by hypocapnia. The findings suggest that our method for modelling the cerebral capillary ODC provides robust and physiologically reliable estimates of the cerebral capillary oxygen tension, which may be of use in future studies of cerebral oxygen transport in humans.

Measurement and Changes in Cerebral Oxygenation and Blood Flow at Rest and During Exercise in Normotensive and Hypertensive Individuals.

PURPOSE OF REVIEW: Summarize the methods used for measurement of cerebral blood flow and oxygenation; describe the effects of hypertension on cerebral blood flow and oxygenation. RECENT FINDINGS: Information regarding the effects of hypertension on cerebrovascular circulation during exercise is very limited, despite a plethora of methods to help with its assessment. In normotensive individuals performing incremental exercise testing, total blood flow to the brain increases. In contrast, the few studies performed in hypertensive patients suggest a smaller increase in cerebral blood flow, despite higher blood pressure levels. Endothelial dysfunction and increased vasoconstrictor concentration, as well as large vessel atherosclerosis and decreased small vessel number, have been proposed as the underlying mechanisms. Hypertension may adversely impact oxygen and blood delivery to the brain, both at rest and during exercise. Future studies should utilize the newer, noninvasive techniques to better characterize the interplay between the brain and exercise in hypertension.

Reference Value of Brain Tissue Oxygen Saturation in Newborns Immediately After Birth.

The Consensus on Resuscitation Science and Treatment Recommendations indicate the target SpO2 values during the first 10 min of life. There are a few studies of values of brain regional saturation of oxygen (rSO2) in newborns, conventional instruments are large and not suitable for measuring in the delivery room. The purpose of this study was to develop reference values for brain rSO2 up to 10 min after birth and to review the changes in cerebral oxygenation in late preterm and term newborn infants immediately after birth. METHOD: We evaluated both brain rSO2 and SpO2 at 1, 3, 5 and 10 min after birth in 100 neonates. rSO2, was measured at the forehead using a finger-mounted oximeter. This is 1/100 the size of conventional NIRS and can be carried. To measure SpO2, a Radical-7 was used. This study was approved by the institutional review board at our hospital. RESULTS: The gestational age and birth weight were 37.9 ± 1.2 weeks and 2825 ± 429 g, respectively. Eighty-seven infants and 13 infants were term and late preterm infants, respectively, and there were 21 vaginal deliveries and 79 cesarean sections. In all cases, rSO2 levels were measured at 1, 3, 5, and 10 min after birth. For the SpO2 measurements, nine cases at 1 min, 40 cases at 3 min, 81 cases at 5 min and 93 cases at 10 min were available. The median rSO2 level was 43% at 1 min after birth, 48% at 3 min, 52% at 5 min and 57% at 10 min. CONCLUSION: We used a finger-mounted oximeter to observe changes in brain rSO2 values of 100 normal transition infants. It was easier to detect rSO2 in comparison to the peripheral oxygen saturation monitored by our pulse oximeter. Brain rSO2 values might be useful to evaluate oxygenation immediately after birth.

Clinical Usefulness of Transcranial Doppler as a Screening Tool for Early Cerebral Hypoxic Episodes in Patients with Moderate and Severe Traumatic Brain Injury.

BACKGROUND: Brain tissue oxygenation (PbtO2) in traumatic brain injury (TBI) is known to be dependent on cerebral blood flow (CBF) which remains difficult to assess during the very early phase of TBI management. This study evaluates if blood flow velocity measurement with 2D color-coded transcranial Doppler (TCD) can predict cerebral hypoxic episodes in moderate-to-severe TBI measured with a PbtO2 probe. METHODS: This is a prospective observational study of serial TCD measurements to assess blood flow velocity and its association with PbtO2. Measurements were done bilaterally on the middle cerebral artery (MCA) early after the insertion of PbtO2 monitoring, daily for 5 days and during dynamic challenge tests. Physiological parameters affecting PbtO2 and Doppler velocities were collected simultaneously (PaO2, PaCO2, hemoglobin [Hb] level, intracranial pressure, and cerebral perfusion pressure [CPP]). RESULTS: We enrolled 17 consecutive patients with a total of 85 TCD studies. Using 2D color-coded TCD, signal acquisition was successful in 96% of the cases. Twenty-nine (34%) TCD measures were performed during an episode of cerebral hypoxia (PbtO2 ≤ 20 mmHg). For early episodes of cerebral hypoxia (occurring ≤ 24 h from trauma), all Vmean < 40 cm/s were associated with an ipsilateral PbtO2 ≤ 20 mmHg (positive predictive value 100%). However, when considering all readings over the course of the study, however, we found no correlation between PbtO2 and MCA's mean blood flow velocity (Vmean). Vmean is also positively correlated with PaCO2, whereas PbtO2 is also correlated with PaO2, CPP, and Hb level. CONCLUSIONS: Early TCD measurements compatible with low CBF (mean velocity < 40 cm/s) detect brain tissue hypoxia early after TBI (≤ 24 h) and could potentially be used as a screening tool before invasive monitoring insertion to help minimize time-sensitive secondary injury. Various factors influence the relationship between Vmean and PbtO2, affecting interpretation of their interaction after 24 h.

In vivo validation of T2- and susceptibility-based Sv O2 measurements with jugular vein catheterization under hypoxia and hypercapnia.

PURPOSE: To investigate the mutual agreement of T2-based and susceptibility-based methods as well as their agreement with jugular catheterization, for quantifying venous oxygen saturation (Sv O2 ) at a broad range of brain oxygenation levels. METHODS: Sv O2 measurements using T2-relaxation-under-spin-tagging (TRUST) and susceptibility-based oximetry (SBO) were performed in 13 healthy subjects under room air, hypoxia, and hypercapnia conditions. Agreement between TRUST and SBO was quantitatively evaluated. In two of the subjects, TRUST and SBO were compared against the clinical gold standard, co-oximeter measurement via internal jugular vein catheterization. RESULTS: Absolute Sv O2 measurements using TRUST and SBO were highly correlated across a range of saturations from 45% to 84% (Pearson r = 0.91, P < .0001). Sv O2 -TRUST was significantly lower than Sv O2 -SBO under hypoxia and room air conditions, but the two were comparable under hypercapnia. TRUST demonstrated a larger Sv O2 increase under hypercapnia than SBO and had good agreement with jugular catheterization under hypercapnia but significantly underestimated Sv O2 under room air and hypoxia. The agreement between Sv O2 -SBO and the reference did not depend on the physiological state. CONCLUSION: A systematic bias was observed between T2-based and susceptibility-based methods that depended on the oxygenation state. In vivo validation with jugular catheterization indicated potential underestimation of TRUST under room air and hypoxia conditions. Our findings suggested that caution should be employed in comparison of absolute Sv O2 measurements using either TRUST or SBO.

Cerebral metabolism is not affected by moderate hyperventilation in patients with traumatic brain injury.

BACKGROUND: Hyperventilation-induced hypocapnia (HV) reduces elevated intracranial pressure (ICP), a dangerous and potentially fatal complication of traumatic brain injury (TBI). HV decreases the arteriolar diameter of intracranial vessels, raising the risk of cerebral ischemia. The aim of this study was to characterize the effects of moderate short-term HV in patients with severe TBI by using concomitant monitoring of cerebral metabolism, brain tissue oxygen tension (PbrO2), and cerebral hemodynamics with transcranial color-coded duplex sonography (TCCD). METHODS: This prospective trial was conducted between May 2014 and May 2017 in the surgical intensive care unit (ICU) at the University Hospital of Zurich. Patients with nonpenetrating TBI older than 18 years of age with a Glasgow Coma Scale (GCS) score < 9 at presentation and with ICP monitoring, PbrO2, and/or microdialysis (MD) probes during ICU admission within 36 h after injury were included in our study. Data collection and TCCD measurements were performed at baseline (A), at the beginning of moderate HV (C), after 50 min of moderate HV (D), and after return to baseline (E). Moderate HV was defined as arterial partial pressure of carbon dioxide 4-4.7 kPa. Repeated measures analysis of variance was used to compare variables at the different time points, followed by post hoc analysis with Bonferroni adjustment as appropriate. RESULTS: Eleven patients (64% males, mean age 36 ± 14 years) with an initial median GCS score of 7 (IQR 3-8) were enrolled. During HV, ICP and mean flow velocity (CBFV) in the middle cerebral artery decreased significantly. Glucose, lactate, and pyruvate in the brain extracellular fluid did not change significantly, whereas PbrO2 showed a statistically significant reduction but remained within the normal range. CONCLUSION: Moderate short-term hyperventilation has a potent effect on the cerebral blood flow, as shown by TCCD, with a concomitant ICP reduction. Under the specific conditions of this study, this degree of hyperventilation did not induce pathological alterations of brain metabolites and oxygenation. TRIAL REGISTRATION: NCT03822026 . Registered on 30 January 2019.

Breathe Easy, Speak Easy: Pulmonary Function and Language Performance in Aging.

BACKGROUND: This study explored the association between pulmonary function (PF) and older adults' language performance accuracy. Study rationale was anchored in aging research reporting PF as a reliable risk factor affecting cognition among the elderly. METHODS: 180 adult English native speakers aged 55 to 84 years participated in the study. PF was measured through forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC ratio (FFR). Language performance was assessed with an action naming test and an object naming test, and two tests of sentence comprehension, one manipulating syntactic complexity and the other, semantic negation. Greater PF was predicted to be positively associated with all tasks. RESULTS: Unadjusted models revealed FVC and FEV1 effects on language performance among older adults. Participants with higher FVC showed better naming on both tasks and those with higher FEV1 had better object naming only. In covariate-adjusted models, only a positive FVC-object naming association remained. CONCLUSION: Findings were discussed in terms of brain oxygenation mechanisms, whereby good PF may implicate efficient oxygenation, supporting neurotransmitter metabolism that protects against neural effects of cerebrovascular risk. Effects on object naming were linked to putative differential oxygenation demands across language tasks.