Quantification of cerebral hemoglobin as a function of oxygenation using near-infrared time-resolved spectroscopy in a piglet model of hypoxia

Conflicting findings on the effectiveness of hydrogen therapy for ameliorating vascular leakage in a 5-day post hypoxic-ischemic survival piglet model

Neonatal hypoxic-ischemic encephalopathy (HIE) is a major cause of morbidity and mortality in newborns in both high- and low-income countries. The important determinants of its pathophysiology are neural cells and vascular components. In neonatal HIE, increased vascular permeability due to damage to the blood-brain barrier is associated with seizures and poor outcomes in both translational and clinical studies. In our previous studies, hydrogen gas (H₂) improved the neurological outcome of HIE and ameliorated the cell death. In this study, we used albumin immunohistochemistry to assess if H₂ inhalation effectively reduced the cerebral vascular leakage. Of 33 piglets subjected to a hypoxic-ischemic insult, 26 piglets were ultimately analyzed. After the insult, the piglets were grouped into normothermia (NT), H₂ ventilation (H₂), therapeutic hypothermia (TH), and H₂ combined with TH (H₂-TH) groups. The ratio of albumin stained to unstained areas was analyzed and found to be lower in the H₂ group than in the other groups, although the difference was not statistically significant. In this study, H₂ therapy did not significantly improve albumin leakage despite the histological images suggesting signs of improvement. Further investigations are warranted to study the efficacy of H₂ gas for vascular leakage in neonatal HIE.

Relationship of cerebral blood volume with arterial and venous flow velocities in extremely low-birth-weight infants

Unstable cerebral blood flow is theorised to contribute to the occurrence of intraventricular haemorrhage (IVH) in extremely low-birth-weight infants (ELBWIs), which can be caused by increased arterial flow, increased venous pressure, and impaired autoregulation of brain vasculature. As a preliminary step to investigate such instability, we aimed to check for correlations of cerebral blood volume (CBV), as measured using near-infrared spectroscopy, with the flow velocities of the anterior cerebral artery (ACA) and internal cerebral vein (ICV), as measured using Doppler ultrasonography. Data were retrospectively analysed from 30 ELBWIs uncomplicated by symptomatic patent ductus arteriosus, which can influence ACA velocity, and severe IVH (grade ≥ 3), which can influence ICV velocity and CBV. The correlation between tissue oxygen saturation (StO₂₎ and mean blood pressure was also analysed as an index of autoregulation. CBV was not associated with ACA velocity; however, it was significantly correlated with ICV velocity (Pearson R = 0.59 [95% confidence interval: 0.29-0.78], P = 0.00061). No correlation between StO₂ and mean blood pressure was observed, implying that autoregulation was not impaired.    Conclusion: Although our findings are based on the premise that cerebral autoregulation was unimpaired in the ELBWIs without complications, the same result cannot be directly applied to severe IVH cases. However, our results may aid future research on IVH prediction by investigating the changes in CBV when severe IVH occurs during ICV velocity fluctuation. What is Known: • The pathogenesis of IVH includes unstable cerebral blood flow affected by increased arterial flow, increased venous pressure, and impaired cerebral autoregulation. • The approaches that can predict IVH are under discussion. What is New: • ACA velocity is not associated with CBV, but ICV velocity is significantly correlated with CBV. • CBV measured using NIRS may be useful in future research on IVH prediction.

Impact of hydrogen gas inhalation during therapeutic hypothermia on cerebral hemodynamics and oxygenation in the asphyxiated piglet

We previously reported the neuroprotective potential of combined hydrogen (H2) gas ventilation therapy and therapeutic hypothermia (TH) by assessing the short-term neurological outcomes and histological findings of 5-day neonatal hypoxic-ischemic (HI) encephalopathy piglets. However, the effects of H2 gas on cerebral circulation and oxygen metabolism and on prognosis were unknown. Here, we used near-infrared time-resolved spectroscopy to compare combined H2 gas ventilation and TH with TH alone. Piglets were divided into three groups: HI insult with normothermia (NT, n = 10), HI insult with hypothermia (TH, 33.5 ± 0.5 °C, n = 8), and HI insult with hypothermia plus H2 ventilation (TH + H2, 2.1-2.7%, n = 8). H2 ventilation and TH were administered and the cerebral blood volume (CBV) and cerebral hemoglobin oxygen saturation (ScO2) were recorded for 24 h after the insult. CBV was significantly higher at 24 h after the insult in the TH + H2 group than in the other groups. ScO2 was significantly lower throughout the 24 h after the insult in the TH + H2 group than in the NT group. In conclusion, combined H2 gas ventilation and TH increased CBV and decreased ScO2, which may reflect elevated cerebral blood flow to meet greater oxygen demand for the surviving neurons, compared with TH alone.

Cerebral hemodynamic response during the resuscitation period after hypoxic-ischemic insult predicts brain injury on day 5 after insult in newborn piglets

Perinatal hypoxic-ischemic brain injury of neonates remains a significant problem worldwide. During the resuscitation period, changes in cerebral hemoglobin oxygen saturation (ScO₂) have been identified by near-infrared spectroscopy (NIRS). However, in asphyxiated neonates, the relationship between these changes and brain injury is not known. Three-wavelength near-infrared time-resolved spectroscopy, an advanced technology for NIRS, allows for the estimation of ScO₂ and cerebral blood volume (CBV). Here, we studied changes in ScO₂ and CBV during the resuscitation period after hypoxic-ischemic insult and the relationship between these changes after insult and histopathological brain injuries on day 5 after insult using an asphyxiated piglet model. Of 36 newborn piglets subjected to hypoxic-ischemic insult, 29 were analyzed. ScO₂ and CBV were measured 0, 5, 10, 15, and 30 min after the insult. Brain tissue was histologically evaluated on day 5. ScO₂ and CBV increased immediately after the insult, reached a peak, and then maintained a consistent value. The increase in CBV 5 to 30 min after the insult was significantly correlated with histopathological injury scores. However, there was no correlation with ScO₂. In conclusion, an increase in CBV within 30 min after hypoxic-ischemic insult reflects the histopathological brain injury on day 5 after insult in a piglet model.

Cerebral hemoglobin oxygenation in children with congenital heart disease

BACKGROUND

It is important to identify the pathological characteristics of cerebral circulation and oxygen metabolism at the bedside in children with congenital heart disease (CHD) to prevent neurodevelopmental impairments. The brain regional oxygen saturation index (rSO₂ ) can be easily obtained at the bedside with near-infrared spectroscopy and has been widely used in the management of children with CHD in recent years.

METHODS

To determine if the rSO₂ before or after CHD surgery is a good predictor of cerebral oxygen metabolism, we investigated the impact of different clinical variables on the correlation between rSO₂ and reference values under steady ratios of hemoglobin oxygen saturation in the internal jugular vein (SjvO₂ ) or femoral artery (SaO₂ ) (0.75:0.25, 0.66:0.34, and 0.50:0.50) in 186 children with CHD undergoing cardiac catheterization.

RESULTS

In three patient groups-double ventricles before surgery, double ventricles after surgery, and single ventricle before surgery-there were significant relationships between rSO₂ and the reference values of SO₂ under all three steady ratios of SjvO₂ and SaO₂ . No relationship with the reference values was found for the single ventricle after surgery group.

CONCLUSIONS

Regional oxygen saturation index is useful for assessing cerebral oxygenation in children with CHD, but knowledge of the underlying cardiac pathology in CHD, especially in the case of a single ventricle after surgery, is important for the correct interpretation of rSO₂ measurements obtained using near-infrared spectroscopy.

Cerebral blood volume increment after resuscitation measured by near-infrared time-resolved spectroscopy can estimate degree of hypoxic-ischemic insult in newborn piglets

Neonatal hypoxic–ischemic encephalopathy is a notable cause of neonatal death and developmental disabilities. To achieve better outcomes, it is important in treatment strategy selection to categorize the degree of hypoxia ischemia and evaluate dose response. In an asphyxia piglet model with histopathological brain injuries that we previously developed, animals survived 5 days after insult and showed changes in cerebral blood volume (CBV) that reflected the severity of injuries. However, little is known about the relationship between changes in CBV during and after insult. In this study, an HI event was induced by varying the amount and timing of inspired oxygen in 20 anesthetized piglets. CBV was measured using near-infrared time-resolved spectroscopy before, during, and 6 h after insult. Change in CBV was calculated as the difference between the peak CBV value during insult and the value at the end of insult. The decrease in CBV during insult was found to correlate with the increase in CBV within 6 h after insult. Heart rate exhibited a similar tendency to CBV, but blood pressure did not. Because the decrement in CBV was larger in severe HI, the CBV increment immediately after insult is considered useful for assessing degree of HI insult.

Clinical and Technical Limitations of Cerebral and Somatic Near-Infrared Spectroscopy as an Oxygenation Monitor

Cerebral and somatic near-infrared spectroscopy monitors are commonly used to detect tissue oxygenation in various circumstances. This form of monitoring is based on tissue infrared absorption and can be influenced by several physiological and non-physiological factors that can induce error in the interpretation. This narrative review explores those clinical and technical limitations and proposes solutions and alternatives in order to avoid some of those pitfalls.

Effect of differential muscle activation patterns on muscle deoxygenation and microvascular haemoglobin regulation

NEW FINDINGS

What is the central question of this study? Does the presence and extent of heterogeneity in the ratio of O2 delivery to uptake across human muscles relate specifically to different muscle activation patterns? What is the main finding and its importance? During ramp incremental knee-extension and cycling exercise, the profiles of muscle deoxygenation (deoxy[haemoglobin + myoglobin]) and diffusive O2 potential (total[haemoglobin + myoglobin]) in the vastus lateralis corresponded to different muscle activation strategies. However, this was not the case for the rectus femoris, where muscle activation and deoxygenation profiles were dissociated and might therefore be determined by other structural and/or functional attributes (e.g. arteriolar vascular regulation and control of red blood cell flux).

ABSTRACT

Near-infrared spectroscopy has revealed considerable heterogeneity in the ratio of O2 delivery to uptake as identified by disparate deoxygenation {deoxy[haemoglobin + myoglobin] (deoxy[Hb + Mb])} values in the exercising quadriceps. However, whether this represents a recruitment phenomenon or contrasting vascular and metabolic control, as seen among fibre types, has not been established. We used knee-extension (KE) and cycling (CE) incremental exercise protocols to examine whether differential muscle activation profiles could account for the heterogeneity of deoxy[Hb + Mb] and microvascular haemoconcentration (i.e. total[Hb + Mb]). Using time-resolved near-infrared spectroscopy for the quadriceps femoris (vastus lateralis and rectus femoris) during exhaustive ramp exercise in eight participants, we tested the following hypotheses: (i) the deoxy[Hb + Mb] (i.e. fractional O2 extraction) would relate to muscle activation levels across exercise protocols; and (ii) KE would induce greater total[Hb + Mb] (i.e. diffusive O2 potential) at task failure (i.e. peak O2 uptake) than CE irrespective of muscle site. At a given level of muscle activation, as assessed by the relative integrated EMG normalized to maximal voluntary contraction (%iEMGmax ), the vastus lateralis deoxy[Hb + Mb] profile was not different between exercise protocols. However, at peak O2 uptake and until 20% iEMGmax for CE, rectus femoris exhibited a lower deoxy[Hb + Mb] (83.2 ± 15.5 versus 98.2 ± 19.4 μm) for KE than for CE (P < 0.05). The total[Hb + Mb] at peak O2 uptake was not different between exercise protocols for either muscle site. These data support the hypothesis that the contrasting patterns of convective and diffusive O2 transport correspond to different muscle activation patterns in vastus lateralis but not rectus femoris. Thus, the differential deoxygenation profiles for rectus femoris across exercise protocols might be dependent upon specific facets of muscle architecture and functional haemodynamic events.

Evaluation of hyperspectral NIRS for quantitative measurements of tissue oxygen saturation by comparison to time-resolved NIRS

Near-infrared spectroscopy (NIRS) is considered ideal for brain monitoring during preterm infancy because it is non-invasive and provides a continuous measure of tissue oxygen saturation (StO2). Hyperspectral NIRS (HS NIRS) is an inexpensive, quantitative modality that can measure tissue optical properties and oxygen saturation (StO2) by differential spectroscopy. In this study, experiments were conducted using newborn piglets to measure StO2 across a range of oxygenation levels from hyperoxia to hypoxia by HS and time-resolved (TR) NIRS for validation. A strong correlation between StO2 measurements from the two techniques was observed (R2 = 0.98, average slope of 1.02 ± 0.28); however, the HS-NIRS estimates were significantly higher than the corresponding TR-NIRS values. These regression results indicate that HS NIRS could become a clinically feasible method for monitoring StO2 in preterm infants.

Measurement of the Absolute Value of Cerebral Blood Volume and Optical Properties in Term Neonates Immediately after Birth Using Near-Infrared Time-Resolved Spectroscopy: A Preliminary Observation Study

The aim of this study was to use near-infrared time-resolved spectroscopy (TRS) to determine the absolute values of cerebral blood volume (CBV) and cerebral hemoglobin oxygen saturation (ScO2) during the immediate transition period in term neonates and the changes in optical properties such as the differential pathlength factor (DPF) and reduced scattering coefficient (μs’). CBV and ScO2 were measured using TRS during the first 15 min after birth by vaginal delivery in term neonates who did not need resuscitation. Within 2–3 min after birth, CBV showed various changes such as increases or decreases, followed by a gradual decrease until 15 min and then stability (mean (SD) mL/100 g brain: 2 min, 3.09 (0.74); 3 min, 3.01 (0.77); 5 min, 2.69 (0.77); 10 min, 2.40 (0.61), 15 min, 2.08 (0.47)). ScO2 showed a gradual increase, then kept increasing or became a stable reading. The DPF and μs’ values (mean (SD) at 762, 800, and 836 nm) were stable during the first 15 min after birth (DPF: 4.47 (0.38), 4.41 (0.32), and 4.06 (0.28)/cm; μs’: 6.54 (0.67), 5.82 (0.84), and 5.43 (0.95)/cm). Accordingly, we proved that TRS can stably measure cerebral hemodynamics, despite the dramatic physiological changes occurring at this time in the labor room.

Time-Domain Near-Infrared Spectroscopy and Imaging: A Review

This article reviews the past and current statuses of time-domain near-infrared spectroscopy (TD-NIRS) and imaging. Although time-domain technology is not yet widely employed due to its drawbacks of being cumbersome, bulky, and very expensive compared to commercial continuous wave (CW) and frequency-domain (FD) fNIRS systems, TD-NIRS has great advantages over CW and FD systems because time-resolved data measured by TD systems contain the richest information about optical properties inside measured objects. This article focuses on reviewing the theoretical background, advanced theories and methods, instruments, and studies on clinical applications for TD-NIRS including some clinical studies which used TD-NIRS systems. Major events in the development of TD-NIRS and imaging are identified and summarized in chronological tables and figures. Finally, prospects for TD-NIRS in the near future are briefly described.

Hydrogen ventilation combined with mild hypothermia improves short-term neurological outcomes in a 5-day neonatal hypoxia-ischaemia piglet model

Despite its poor outcomes, therapeutic hypothermia (TH) is the current standard treatment for neonatal hypoxic-ischaemic encephalopathy (HIE). In this study, due to its antioxidant, anti-inflammatory, and antiapoptotic properties, the effectiveness of molecular hydrogen (H₂) combined with TH was evaluated by means of neurological and histological assessments. Piglets were divided into three groups: hypoxic-ischaemic insult with normothermia (NT), insult with hypothermia (TH, 33.5 ± 0.5 °C), and insult with hypothermia with H₂ ventilation (TH-H₂, 2.1–2.7%). H₂ ventilation and TH were administered for 24 h. After ventilator weaning, neurological assessment was performed every 6 h for 5 days. On day 5, the brains of the piglets were harvested for histopathological analysis. Regarding the neurological score, the piglets in the TH-H₂ group consistently had the highest score from day 2 to 5 and showed a significantly higher neurological score from day 3 compared with the NT group. Most piglets in the TH-H₂ group could walk at day 3 of recovery, whereas walking ability was delayed in the two other groups. The histological results revealed that TH-H₂ tended to improve the status of cortical gray matter and subcortical white matter, with a considerable reduction in cell death. In this study, the combination of TH and H₂ improved short-term neurological outcomes in neonatal hypoxic-ischaemic piglets.

Relationship between prolonged neural suppression and cerebral hemodynamic dysfunction during hypothermia in asphyxiated piglets

OBJECTIVES

Hypothermia (HT) improves the outcome of neonatal hypoxic-ischemic encephalopathy. Here, we investigated changes during HT in cortical electrical activity using amplitude-integrated electroencephalography (aEEG) and in cerebral blood volume (CBV) and cerebral hemoglobin oxygen saturation using near-infrared time-resolved spectroscopy (TRS) and compared the results with those obtained during normothermia (NT) after a hypoxic-ischemic (HI) insult in a piglet model of asphyxia. We previously reported that a greater increase in CBV can indicate greater pressure-passive cerebral perfusion due to more severe brain injury and correlates with prolonged neural suppression during NT. We hypothesized that when energy metabolism is suppressed during HT, the cerebral hemodynamics of brains with severe injury would be suppressed to a greater extent, resulting in a greater decrease in CBV during HT that would correlate with prolonged neural suppression after insult.

METHODS

Twenty-six piglets were divided into four groups: control with NT (C-NT, n = 3), control with HT (C-HT, n = 3), HI insult with NT (HI-NT, n = 10), and HI insult with HT (HI-HT, n = 10). TRS and aEEG were performed in all groups until 24 h after the insult. Piglets in the HI-HT group were maintained in a hypothermic state for 24 h after the insult.

RESULTS

There was a positive linear correlation between changes in CBV at 1, 3, 6, and 12 h after the insult and low-amplitude aEEG (<5 µV) duration after insult in the HI-NT group, but a negative linear correlation between these two parameters at 6 and 12 h after the insult in the HI-HT group. The aEEG background score and low-amplitude EEG duration after the insult did not differ between these two groups.

DISCUSSION AND CONCLUSION

A longer low-amplitude EEG duration after insult was associated with a greater CBV decrease during HT in the HI-HT group, suggesting that brains with more severe neural suppression could be more prone to HT-induced suppression of cerebral metabolism and circulation.

The effect of dietary nitrate supplementation on the spatial heterogeneity of quadriceps deoxygenation during heavy-intensity cycling

This study investigated the influence of dietary inorganic nitrate (NO₃⁻) supplementation on pulmonary O₂ uptake (V˙O₂) and muscle deoxyhemoglobin/myoglobin (i.e. deoxy [Hb + Mb]) kinetics during submaximal cycling exercise. In a randomized, placebo‐controlled, cross‐over study, eight healthy and physically active male subjects completed two step cycle tests at a work rate equivalent to 50% of the difference between the gas exchange threshold and peak V˙O₂ over separate 4‐day supplementation periods with NO₃⁻‐rich (BR; providing 8.4 mmol NO₃⁻∙day⁻¹) and NO₃⁻‐depleted (placebo; PLA) beetroot juice. Pulmonary V˙O₂ was measured breath‐by‐breath and time‐resolved near‐infrared spectroscopy was utilized to quantify absolute deoxy [Hb + Mb] and total [Hb + Mb] within the rectus femoris, vastus lateralis, and vastus medialis. There were no significant differences (P > 0.05) in the primary deoxy [Hb + Mb] mean response time or amplitude between the PLA and BR trials at each muscle site. BR significantly increased the mean (three‐site) end‐exercise deoxy [Hb + Mb] (PLA: 91 ± 9 vs. BR: 95 ± 12 μmol/L, P < 0.05), with a tendency to increase the mean (three‐site) area under the curve for total [Hb + Mb] responses (PLA: 3650 ± 1188 vs. BR: 4467 ± 1315 μmol/L sec⁻¹, P = 0.08). The V˙O₂ slow component reduction after BR supplementation (PLA: 0.27 ± 0.07 vs. BR: 0.23 ± 0.08 L min⁻¹, P = 0.07) correlated inversely with the mean increases in deoxy [Hb + Mb] and total [Hb + Mb] across the three muscle regions (r² = 0.62 and 0.66, P < 0.05). Dietary NO₃⁻ supplementation increased O₂ diffusive conductance across locomotor muscles in association with improved V˙O₂ dynamics during heavy‐intensity cycling transitions.

Protein kinase D2: a versatile player in cancer biology

Protein kinase D2 (PKD2) is a serine/threonine kinase that belongs to the PKD family of calcium-calmodulin kinases, which comprises three isoforms: PKD1, PKD2, and PKD3. PKD2 is activated by many stimuli including growth factors, phorbol esters, and G-protein-coupled receptor agonists. PKD2 participation to uncontrolled growth, survival, neovascularization, metastasis, and invasion has been documented in various tumor types including pancreatic, colorectal, gastric, hepatic, lung, prostate, and breast cancer, as well as glioma multiforme and leukemia. This review discusses the versatile functions of PKD2 from the perspective of cancer hallmarks as described by Hanahan and Weinberg. The PKD2 status, signaling pathways affected in different tumor types and the molecular mechanisms that lead to tumorigenesis and tumor progression are presented. The latest developments of small-molecule inhibitors selective for PKD/PKD2, as well as the need for further chemotherapies that prevent, slow down, or eliminate tumors are also discussed in this review.

Joint blood flow is more sensitive to inflammatory arthritis than oxyhemoglobin, deoxyhemoglobin, and oxygen saturation

Joint hypoxia plays a central role in the progression and perpetuation of rheumatoid arthritis (RA). Thus, optical techniques that can measure surrogate markers of hypoxia such as blood flow, oxyhemoglobin, deoxyhemoglobin, and oxygen saturation are being developed to monitor RA. The purpose of the current study was to compare the sensitivity of these physiological parameters to arthritis. Experiments were conducted in a rabbit model of RA and the results revealed that joint blood flow was the most sensitive to arthritis and could detect a statistically significant difference (p<0.05, power = 0.8) between inflamed and healthy joints with a sample size of only four subjects. Considering that this a quantitative technique, the high sensitivity to arthritis suggests that joint perfusion has the potential to become a potent tool for monitoring disease progression and treatment response in RA.

Muscle deoxygenation in the quadriceps during ramp incremental cycling: Deep vs. superficial heterogeneity

Muscle deoxygenation (i.e., deoxy[Hb + Mb]) during exercise assesses the matching of oxygen delivery (Q̇O2) to oxygen utilization (V̇O2). Until now limitations in near-infrared spectroscopy (NIRS) technology did not permit discrimination of deoxy[Hb + Mb] between superficial and deep muscles. In humans, the deep quadriceps is more highly vascularized and oxidative than the superficial quadriceps. Using high-power time-resolved NIRS, we tested the hypothesis that deoxygenation of the deep quadriceps would be less than in superficial muscle during incremental cycling exercise in eight males. Pulmonary V̇O2 was measured and muscle deoxy[Hb + Mb] was determined in the superficial vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF-s) and the deep rectus femoris (RF-d). deoxy[Hb + Mb] in RF-d was significantly less than VL at 70% (67.2 ± 7.0 vs. 75.5 ± 10.7 μM) and 80% (71.4 ± 11.0 vs. 79.0 ± 15.4 μM) of peak work rate (WR(peak)), but greater than VL and VM at WR(peak) (87.7 ± 32.5 vs. 76.6 ± 17.5 and 75.1 ± 19.9 μM). RF-s was intermediate at WR(peak) (82.6 ± 18.7 μM). Total hemoglobin and myoglobin concentration and tissue oxygen saturation were significantly greater in RF-d than RF-s throughout exercise. The slope of deoxy[Hb + Mb] increase (proportional to Q̇O2/V̇O2) in VL and VM slowed markedly above 70% WR(peak), whereas it became greater in RF-d. This divergent deoxygenation pattern may be due to a greater population of slow-twitch muscle fibers in the RF-d muscle and the differential recruitment profiles and vascular and metabolic control properties of specific fiber populations within superficial and deeper muscle regions.

Monitoring of Cerebrovascular Reactivity for Determination of Optimal Blood Pressure in Preterm Infants

OBJECTIVE

To define levels of mean arterial blood pressure (MABP) where cerebrovascular reactivity is strongest in preterm infants (ie, optimal MABP, or MABPOPT) and correlate deviations from MABPOPT with mortality and intraventricular hemorrhage (IVH).

STUDY DESIGN

A total of 60 preterm infants born at median gestational age 26 ± 2 weeks (23 ± 2 to 32 ± 1) with indwelling arterial catheter were studied at a median 34 hours (range 5-228) of age. Tissue oxygenation heart rate (HR) reactivity index, which estimates cerebrovascular reactivity, was calculated as the moving correlation coefficient between slow waves of tissue oxygenation index, measured with near-infrared spectroscopy, and HR. MABPOPT was defined by dividing MABP into 2-mm Hg bins and averaging the tissue oxygenation HR reactivity index within those bins. A measurement of divergence from MABPOPT was calculated as the absolute difference between mean MABP and mean MABPOPT.

RESULTS

Individual MABPOPT was defined in 81% of the patients. A measurement of divergence from MABPOPT was greater in those patients who died (mean 4.2 mm Hg; 95% CI 3.33-4.96) compared with those who survived (mean 2.1 mm Hg; 95% CI 1.64-2.56), P = .013. Patients who had MABP lower than MABPOPT by 4 mm Hg or more had a greater rate of mortality (40%) than those with MABP close to or above MABPOPT (13%), P = .049. Patients with MABP greater than MABPOPT by 4 mm Hg had greater IVH scores, P = .042.

CONCLUSIONS

Continuous monitoring of cerebrovascular reactivity allows the determination of MABPOPT in preterm neonates. Significant deviation below MABPOPT was observed in infants who died. Deviation of MABP above optimal level was observed in infants who developed more severe IVH.

Validation of a high-power, time-resolved, near-infrared spectroscopy system for measurement of superficial and deep muscle deoxygenation during exercise

Near-infrared assessment of skeletal muscle is restricted to superficial tissues due to power limitations of spectroscopic systems. We reasoned that understanding of muscle deoxygenation may be improved by simultaneously interrogating deeper tissues. To achieve this, we modified a high-power (∼8 mW), time-resolved, near-infrared spectroscopy system to increase depth penetration. Precision was first validated using a homogenous optical phantom over a range of inter-optode spacings (OS). Coefficients of variation from 10 measurements were minimal (0.5-1.9%) for absorption (μa), reduced scattering, simulated total hemoglobin, and simulated O2 saturation. Second, a dual-layer phantom was constructed to assess depth sensitivity, and the thickness of the superficial layer was varied. With a superficial layer thickness of 1, 2, 3, and 4 cm (μa = 0.149 cm(-1)), the proportional contribution of the deep layer (μa = 0.250 cm(-1)) to total μa was 80.1, 26.9, 3.7, and 0.0%, respectively (at 6-cm OS), validating penetration to ∼3 cm. Implementation of an additional superficial phantom to simulate adipose tissue further reduced depth sensitivity. Finally, superficial and deep muscle spectroscopy was performed in six participants during heavy-intensity cycle exercise. Compared with the superficial rectus femoris, peak deoxygenation of the deep rectus femoris (including the superficial intermedius in some) was not significantly different (deoxyhemoglobin and deoxymyoglobin concentration: 81.3 ± 20.8 vs. 78.3 ± 13.6 μM, P > 0.05), but deoxygenation kinetics were significantly slower (mean response time: 37 ± 10 vs. 65 ± 9 s, P ≤ 0.05). These data validate a high-power, time-resolved, near-infrared spectroscopy system with large OS for measuring the deoxygenation of deep tissues and reveal temporal and spatial disparities in muscle deoxygenation responses to exercise.

Cerebral blood volume measurement using near-infrared time-resolved spectroscopy and histopathological evaluation after hypoxic-ischemic insult in newborn piglets

The aim of this study was to assess the relationship between the cerebral blood volume (CBV) measured by near-infrared time-resolved spectroscopy (TRS) and pathological change of the brain in a hypoxic-ischemic (HI) piglet model. Twenty-one anesthetized newborn piglets, including three sham controls, were studied. An HI event was induced by low inspired oxygen. CBV was measured using TRS (Hamamatsu TRS-10). Data were collected before, during, and 6h after the insult. CBV was calculated as the change from the end of the insult. The piglets were allowed to recover from anesthesia for 6h after the insult. At the age of 5 days, the brains of the piglets were perfusion-fixed, and histologic evaluations of brain tissue were performed. The extent of histopathological damage was graded in 0.5-unit intervals on a 9-step scale. CBV increments were well correlated with histopathological scores, especially at 1 and 3h after resuscitation. Spearman's rank-correlation coefficients at 1, 3, and 6h after resuscitation in the gray matter were 0.9016, 0.9127, and 0.6907, respectively. We conclude that an increased CBV after HI insult indicates more marked histological brain damage. CBV measurement immediately after resuscitation provides a more precise prediction of the histological outcome.

Modified Beer-Lambert law for blood flow

We develop and validate a Modified Beer-Lambert law for blood flow based on diffuse correlation spectroscopy (DCS) measurements. The new formulation enables blood flow monitoring from temporal intensity autocorrelation function data taken at single or multiple delay-times. Consequentially, the speed of the optical blood flow measurement can be substantially increased. The scheme facilitates blood flow monitoring of highly scattering tissues in geometries wherein light propagation is diffusive or non-diffusive, and it is particularly well-suited for utilization with pressure measurement paradigms that employ differential flow signals to reduce contributions of superficial tissues.

Novel method for early signs of clinical shock detection by monitoring blood capillary/vessel spatial pattern

The ability to monitor capillary/vessel spatial patterns and local blood volume fractions is critical in clinical shock detection and its prevention in Intensive Care Units (ICU). Although the causes of shock might be different, the basic abnormalities in pathophysiological changes are the same. To detect these changes, we have developed a novel method based on both spectrally and spatially resolved diffuse reflectance spectra. The preliminary study has shown that this method can monitor the spatial distribution of capillary/vessel spatial patterns through local blood volume fractions of reduced hemoglobin and oxyhemoglobin. This method can be used as a real-time and non-invasive tool for the monitoring of shock development and feedback on the therapeutic intervention.

Relationship between early changes in cerebral blood volume and electrocortical activity after hypoxic-ischemic insult in newborn piglets

BACKGROUND

Early changes in cerebral hemodynamics and depressed electrocortical activity have been reported after a hypoxic-ischemic (HI) insult. However, the relationship between these two parameters is unclear. This study aimed to examine the relationship between changes in cerebral blood volume (CBV) and cerebral Hb oxygen saturation (ScO2) after a HI insult and the low amplitude-integrated electroencephalography (aEEG) duration concomitantly observed.

METHODS

Sixteen newborn piglets obtained within 24h of birth were used (n=3 controls). Thirteen piglets were subjected to a HI insult of 20-min low-amplitude aEEG (<5 μV, LAEEG), after which a low mean arterial blood pressure (<70% of baseline) was maintained for 10 min. We measured changes in CBV and ScO2 using near-infrared time-resolved spectroscopy (TRS) and cerebral electrocortical activities using aEEG until 6h after the insult.

RESULTS

A positive correlation was observed between the LAEEG duration and CBV increase, but not ScO2, after the insult.

CONCLUSION

These results suggest that a larger increase in CBV reflected a more severe failure in cerebral circulation to maintain cell membrane action potentials, which induced a more extended recovery period of electrocortical activity after the insult. We conclude that an early increase in CBV and longer LAEEG indicate severe brain injury.

Evaluation of cerebral circulation and oxygen metabolism in infants using near-infrared light

Bedside monitoring of cerebral circulation or oxygen metabolism in infants to appropriately manage circulation and establish the oxygen dose, aiming at improving the neurological prognosis, is needed in general clinical practice. Near-infrared spectroscopy is used for measurements of neonatal cerebral Hb oxygen saturation, cerebral blood volume, cerebral blood flow and cerebral metabolic rate of oxygen. Near-infrared time-resolved spectroscopy is particularly useful for bedside evaluation of cerebral circulation and oxygen metabolism because of its simple measurement procedure. Combined evaluation of cerebral blood volume and cerebral Hb oxygen saturation is expected to contribute to treatment centering on the brain in neonatal medical care.

Comparison of a layered slab and an atlas head model for Monte Carlo fitting of time-domain near-infrared spectroscopy data of the adult head

Near-infrared spectroscopy (NIRS) estimations of the adult brain baseline optical properties based on a homogeneous model of the head are known to introduce significant contamination from extracerebral layers. More complex models have been proposed and occasionally applied to in vivo data, but their performances have never been characterized on realistic head structures. Here we implement a flexible fitting routine of time-domain NIRS data using graphics processing unit based Monte Carlo simulations. We compare the results for two different geometries: a two-layer slab with variable thickness of the first layer and a template atlas head registered to the subject's head surface. We characterize the performance of the Monte Carlo approaches for fitting the optical properties from simulated time-resolved data of the adult head. We show that both geometries provide better results than the commonly used homogeneous model, and we quantify the improvement in terms of accuracy, linearity, and cross-talk from extracerebral layers.

Cerebral blood volume combined with amplitude-integrated EEG can be a suitable guide to control hypoxic/ischemic insult in a piglet model

INTRODUCTION

The purposes of this study are to compare two hypoxic/ischemic (H/I) insults using amplitude-integrated EEG (aEEG), alone or combined with cerebral blood volume (CBV), as a guide to control hypoxia and to determine which protocol most effectively produces a consistent degree of survivable neuropathological damage in a newborn piglet model of perinatal asphyxia.

METHODS

Eighteen piglets were subjected to H/I insult of 20-min low aEEG (LAEEG). After the 20-min, the aEEG group was maintained with low mean arterial blood pressure for 10min. The procedure for the aEEG plus CBV group was stopped if CBV became the rated value after 20min of LAEEG. We measured changes in CBV using a near-infrared time-resolved spectroscopy (TRS) and cerebral electrocortical activity using aEEG until 6h post-insult. At 5days post insult, the piglets' brains were perfusion-fixed and stained with hematoxylin/eosin. Piglets were grouped as undamaged or damaged; piglets that did not survive to 5days were grouped separately as dead.

RESULTS

Among surviving piglets, CBV combined with aEEG resulted in significantly greater percentage of damaged piglets than aEEG alone.

CONCLUSIONS

We conclude that combining CBV with aEEG may be a more effective guide to control H/I insult in a newborn piglet model than aEEG alone.

Methodological validation of the dynamic heterogeneity of muscle deoxygenation within the quadriceps during cycle exercise

The conventional continuous wave near-infrared spectroscopy (CW-NIRS) has enabled identification of regional differences in muscle deoxygenation following onset of exercise. However, assumptions of constant optical factors (e.g., path length) used to convert the relative changes in CW-NIRS signal intensity to values of relative concentration, bring the validity of such measurements into question. Furthermore, to justify comparisons among sites and subjects, it is essential to correct the amplitude of deoxygenated hemoglobin plus myoglobin [deoxy(Hb+Mb)] for the adipose tissue thickness (ATT). We used two time-resolved NIRS systems to measure the distribution of the optical factors directly, thereby enabling the determination of the absolute concentrations of deoxy(Hb+Mb) simultaneously at the distal and proximal sites within the vastus lateralis (VL) and the rectus femoris muscles. Eight subjects performed cycle exercise transitions from unloaded to heavy work rates (>gas exchange threshold). Following exercise onset, the ATT-corrected amplitudes (Ap), time delay (TDp), and time constant (τp) of the primary component kinetics in muscle deoxy(Hb + Mb) were spatially heterogeneous (intersite coefficient of variation range for the subjects: 10–50 for Ap, 16–58 for TDp, 14–108% for τp). The absolute and relative amplitudes of the deoxy(Hb+Mb) responses were highly dependent on ATT, both within subjects and between measurement sites. The present results suggest that regional heterogeneity in the magnitude and temporal profile of muscle deoxygenation is a consequence of differential matching of O2 delivery and O2 utilization, not an artifact caused by changes in optical properties of the tissue during exercise or variability in the overlying adipose tissue.

Comparison of time-resolved and continuous-wave near-infrared techniques for measuring cerebral blood flow in piglets

A primary focus of neurointensive care is monitoring the injured brain to detect harmful events that can impair cerebral blood flow (CBF), resulting in further injury. Since current noninvasive methods used in the clinic can only assess blood flow indirectly, the goal of this research is to develop an optical technique for measuring absolute CBF. A time-resolved near-infrared (TR-NIR) apparatus is built and CBF is determined by a bolus-tracking method using indocyanine green as an intravascular flow tracer. As a first step in the validation of this technique, CBF is measured in newborn piglets to avoid signal contamination from extracerebral tissue. Measurements are acquired under three conditions: normocapnia, hypercapnia, and following carotid occlusion. For comparison, CBF is concurrently measured by a previously developed continuous-wave NIR method. A strong correlation between CBF measurements from the two techniques is revealed with a slope of 0.79±0.06, an intercept of -2.2±2.5 ml∕100 g∕min, and an R2 of 0.810±0.088. Results demonstrate that TR-NIR can measure CBF with reasonable accuracy and is sensitive to flow changes. The discrepancy between the two methods at higher CBF could be caused by differences in depth sensitivities between continuous-wave and time-resolved measurements.

Lawrence K. Using near-infrared spectroscopy to measure cerebral metabolic rate of oxygen under multiple levels of arterial oxygenation in piglets

Improving neurological care of neonates has been impeded by the absence of suitable techniques for measuring cerebral hemodynamics and energy metabolism at the bedside. Currently, near-infrared spectroscopy (NIRS) appears to be the technology best suited to fill this gap, and techniques have been proposed to measure both cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2). We have developed a fast and reliable bolus-tracking method of determining CMRO2 that combines measurements of CBF and cerebral venous oxygenation [venous oxygen saturation (CSvO2)]. However, this method has never been validated at different levels of arterial oxygenation [arterial oxygen saturation (SaO2)], which can be highly variable in the clinical setting. In this study, NIRS measurements of CBF, CSvO2, and CMRO2 were obtained over a range of SaO2 in newborn piglets ( n = 12); CSvO2 values measured directly from sagittal sinus blood samples were collected for validation. Two alternative NIRS methods that measure CSvO2 by manipulating venous oxygenation (i.e., head tilt and partial venous occlusion methods) were also employed for comparison. Statistically significant correlations were found between each NIRS technique and sagittal sinus blood oxygenation ( P < 0.05). Correlation slopes were 1.03 ( r = 0.91), 0.73 ( r = 0.73), and 0.73 ( r = 0.81) for the bolus-tracking, head tilt, and partial venous occlusion methods, respectively. The bolus-tracking technique displayed the best correlation under hyperoxic (SaO2 = 99.9 ± 0.03%) and normoxic (SaO2 = 86.9 ± 6.6%) conditions and was comparable to the other techniques under hypoxic conditions (SaO2 = 40.7 ± 9.9%). The reduced precision of the bolus-tracking method under hypoxia was attributed to errors in CSvO2 measurement that were magnified at low SaO2 levels. In conclusion, the bolus-tracking technique of measuring CSvO2, and therefore CMRO2, is accurate and robust for an SaO2 > 50% but provides reduced accuracy under more severe hypoxic levels.

Diffuse optical monitoring of hemodynamic changes in piglet brain with closed head injury

We used a nonimpact inertial rotational model of a closed head injury in neonatal piglets to simulate the conditions following traumatic brain injury in infants. Diffuse optical techniques, including diffuse reflectance spectroscopy and diffuse correlation spectroscopy (DCS), were used to measure cerebral blood oxygenation and blood flow continuously and noninvasively before injury and up to 6 h after the injury. The DCS measurements of relative cerebral blood flow were validated against the fluorescent microsphere method. A strong linear correlation was observed between the two techniques (R=0.89, p<0.00001). Injury-induced cerebral hemodynamic changes were quantified, and significant changes were found in oxy- and deoxy-hemoglobin concentrations, total hemoglobin concentration, blood oxygen saturation, and cerebral blood flow after the injury. The diffuse optical measurements were robust and also correlated well with recordings of vital physiological parameters over the 6-h monitoring period, such as mean arterial blood pressure, arterial oxygen saturation, and heart rate. Finally, the diffuse optical techniques demonstrated sensitivity to dynamic physiological events, such as apnea, cardiac arrest, and hypertonic saline infusion. In total, the investigation corraborates potential of the optical methods for bedside monitoring of pediatric and adult human patients in the neurointensive care unit.

Relationship between cerebral oxygenation and phosphorylation potential during secondary energy failure in hypoxic-ischemic newborn piglets

The aim of this study was to evaluate the hypothesis that cerebral hemoglobin (Hb) oxygenation is related to phosphorylation potential during primary and secondary cerebral energy failure in newborn infants who have experienced birth asphyxia. We subjected newborn piglets to severe transient cerebral hypoxic-ischemia followed by resuscitation and examined cerebral energy metabolism by 31P-magnetic resonance spectroscopy and evaluated changes in cerebral Hb oxygen saturation (ScO2) using full-spectrum near-infrared spectroscopy before, during, and up to 54 h after the hypoxic-ischemic insult. ScO2 was significantly decreased during the hypoxic-ischemic insult compared with baseline values. During secondary energy failure, piglets were separated based on the relationship between the ratio of phosphocreatine to inorganic phosphate and ScO2; those with a negative correlation were less injured than those with a positive correlation. These results indicate that changes in ScO2 as measured by near-infrared spectroscopy are related to phosphorylation potential during secondary energy failure in asphyxiated infants.

Changes in breast hemodynamics in breastfeeding mothers

The purpose of the present study was to measure changes in blood volume and the oxygenation state of breast tissue during breastfeeding with the use of near-infrared time-resolved spectroscopy (TRS) as a noninvasive method. Forty breastfeeding mothers were divided into 2 groups in which measurements were made in the contralateral breast (group A) and in the ipsilateral breast (group B). The tissue concentrations of oxyhemoglobin, deoxyhemoglobin, and total hemoglobin and the hemoglobin oxygen saturation were measured in the breast by using TRS during a breastfeed. In both groups A and B, the values of all parameters decreased significantly after the start of breastfeeding compared with the pre-breastfeeding values. The values of all parameters fluctuated cyclically after the beginning of the breastfeed. Time-resolved spectroscopy is an effective noninvasive method for investigating the hemodynamics of the breast during breastfeeding.

[Transfusion in neurosurgery]

In neurosurgery, the question of the optimal transfusion "trigger" remains a controversial matter. Regarding the brain, the current data are still incomplete, justifying the continuation of experimental and clinical studies. The existing expert advices are based on these rather poor data and would probably evolve after the completion of clinical studies in progress. In spine surgery, the situation is simpler and the transfusional stakes are quite similar to those of orthopedics and traumatology. With regard to hemostasis, standardized recommendations exist depending on the laboratory test results or the anticoagulant treatments of the patient.

A non-invasive, in vivo technique for monitoring vascular status of glioblastoma during angiogenesis

The growth of solid tumors dependent on the process of angiogenesis in which growth factors secreted by tumor and stromal cells promote endothelial cell proliferation, migration, and maturation. This process generates a tumor-specific vascular supply and enables small or dormant tumors to grow rapidly with exponential increases in tumor volume. Determination of tumor oxygenation at the microvascular level will provide important insight into tumor growth, angiogenesis, necrosis, and therapeutic response, and will facilitate to develop protocols for studying tumor behavior. A non-invasive multi-modality approach based on near infrared spectroscopy (NIRS) technique, namely: Steady State Diffuse Optical Spectroscopy (SSDOS) along with Magnetic Resonance Imaging (MRI) is applied for monitoring the concentration of oxyhemoglobin, deoxyhemoglobin and water within tumor region and for studying the vascular status of tumor and the patho-physiological changes that occur during angiogenesis. Since, the growth of solid tumors depends on the formation of new blood vessels, an association between intramural microvessel density (MVD) and tumor oxygenation is also investigated. The relative decrease in oxygenation value with tumor growth indicates that though blood vessels infiltrate and proliferate the tumor region, a hypoxic trend is clearly present.

A noninvasive multimodal technique to monitor brain tumor vascularization

Determination of tumor oxygenation at the microvascular level will provide important insight into tumor growth, angiogenesis, necrosis and therapeutic response and will facilitate to develop protocols for studying tumor behavior. The non-ionizing near infrared spectroscopy (NIRS) technique has the potential to differentiate lesion and hemoglobin dynamics; however, it has a limited spatial resolution. On the other hand, magnetic resonance imaging (MRI) has achieved high spatial resolution with excellent tissue discrimination but is more susceptible to limited ability to monitor the hemoglobin dynamics. In the present work, the vascular status and the pathophysiological changes that occur during tumor vascularization are studied in an orthotopic brain tumor model. A noninvasive multimodal approach based on the NIRS technique, namely steady state diffuse optical spectroscopy (SSDOS) along with MRI, is applied for monitoring the concentrations of oxyhemoglobin, deoxyhemoglobin and water within tumor region. The concentrations of oxyhemoglobin, deoxyhemoglobin and water within tumor vasculature are extracted at 15 discrete wavelengths in a spectral window of 675-780 nm. We found a direct correlation between tumor size, intratumoral microvessel density and tumor oxygenation. The relative decrease in tumor oxygenation with growth indicates that though blood vessels infiltrate and proliferate the tumor region, a hypoxic trend is clearly present.

Is near-infrared spectroscopy living up to its promises?

The first clinical application of near-infrared spectroscopy (NIRS) was made 20 years ago on the head of newborn infants under intensive care. Since then NIRS has yielded much credible and some important clinical research data. The most important results have been obtained using the cumbersome but quantitative techniques for measuring cerebral blood flow, cerebral blood volume, or venous oxygen saturation with manipulation of FiO(2) or impeding venous outflow from the brain. The continuous nature of NIRS has been combined with monitoring of arterial pressure to obtain measures of cerebrovascular regulation, but this method has not been applied on a larger scale. Second-generation instruments allow a running estimate of vascular haemoglobin oxygen saturation, named the tissue oxygenation index (TOI), in absolute terms. Applied to the head, this is a surrogate measure of cerebro-venous saturation, an important variable in neuro-intensive care. The precision, however, is insufficient to be useful.

IN CONCLUSION

clinical application is not in sight.

Development and validation of a multiwavelength spatial domain near-infrared oximeter to detect cerebral hypoxia-ischemia

Detection of cerebral hypoxia-ischemia in infants remains problematic, as current monitors in clinical practice are impractical, insensitive, or nonspecific. Our study develops a multiwavelength spatial domain construct for near-infrared spectroscopy (NIRS) to detect cerebral hypoxia-ischemia and evaluates the construct in several models. The NIRS probe contains photodiode detectors 2, 3, and 4 cm from a three-wavelength, light-emitting diode. A construct determines cerebral O(2) saturation based on spatial domain principles. Device performance and construct validity are examined in in-vitro models simulating the brain, and in piglets subjected to hypoxia, hypoxia-ischemia, and hyperoxic conditions using a weighted average of arterial and cerebral venous O(2) saturation measured by CO-oximetry. The results in the brain models verify key equations in the construct and demonstrate reliable performance of the device. In piglets, the device measures cerebral O(2) saturation with bias +/-4% and precision +/-8%. In conclusion, this NIRS device accurately detects cerebral hypoxia-ischemia and is of a design that is practical for clinical application.

Feasibility of Intravascular Near-Infrared Spectroscopy in Off-Pump Myocardial Revascularization

Objectives

The intravascular application of near-infrared spectroscopy was previously evaluated in acute ischemia-reperfusion studies in animal experiments. The objective of our study was to assess the technical feasibility and clinical reliability of an online myocardial ischemia monitoring by using intravascular near-infrared spectroscopy during off-pump coronary bypass surgery.

Methods

Intravascular near-infrared spectroscopy of coronary sinus blood was performed in 10 elective patients selected for off-pump coronary bypass surgery. Light signals were transferred through a fiberoptic catheter for emission and collection from the coronary sinus blood. Spectrometric analyses were performed before and after revascularization with internal thoracic artery and saphenous vein grafts. Changes in spectroscopic data were compared with hemodynamic parameters and electrocardiographic, transesophageal echocardiographic, and laboratory findings.

Results

All of the operations were finished as off-pump procedures. No remarkable intraoperative myocardial ischemia was observed in the patient group, as indicated by electrocardiography and transesophageal echocardiography. Reproducible absorption spectra of coronary sinus blood were obtained at every defined step of the surgical procedure. Clear ischemia-related changes were detected in none of the patients.

Conclusions

Our initial results showed that intravascular near-infrared spectroscopic ischemia monitoring is technically feasible. However, the method must be further evaluated and standardized under varying conditions to determine the role of near-infrared spectroscopy as an ischemia monitoring tool in off-pump coronary bypass surgery.

Developmental changes of optical properties in neonates determined by near-infrared time-resolved spectroscopy

Near-infrared spectroscopy has been used for measurement of changes in cerebral Hb concentrations in infants to study cerebral oxygenation and hemodynamics. In this study, measurements by time-resolved spectroscopy (TRS) were performed in 22 neonates to estimate the values of light absorption coefficient and reduced scattering coefficient (mu'(s)), cerebral Hb oxygen saturation (SCO2), cerebral blood volume (CBV), and differential pathlength factor (DPF), and the relationships between postconceptional age and mu'(s), SCO2, CBV, and DPF were investigated. A portable three-wavelength TRS system with a probe attached to the head of the neonate was used. The mean mu'(s) values at 761, 795, and 835 nm in neonates were estimated to be (mean +/- SD) 6.46 +/- 1.21, 5.90 +/- 1.15 and 6.40 +/- 1.16/cm, respectively. There was a significant positive relationship between postconceptional age and mu'(s) at those three wavelengths. The mean SCO2 value was calculated to be 70.0 +/- 4.6%, and postconceptional age and SCO2 showed a negative linear relationship. The mean value of CBV was 2.31 +/- 0.56 mL/100 g. There was a significant positive relationship between postconceptional age and CBV. The mean DPF values at 761, 795, and 835 nm were estimated to be 4.58 +/- 0.41, 4.64 +/- 0.46, and 4.31 +/- 0.42, respectively. There was no relationship between postconceptional age and DPF at those three wavelengths. The results demonstrated that our near-infrared TRS method can be used to monitor mu'(s), SCO2, CBV, and DPF in the neonatal brain at the bedside in an intensive care unit.