Near-infrared spectroscopy measurements of cerebral blood flow and oxygen consumption following hypoxia-ischemia in newborn piglets

Dissociated coupling between cerebral oxygen metabolism and perfusion in the prefrontal cortex during exercise: a NIRS study

Purpose: The present study used near-infrared spectroscopy to investigate the relationships between cerebral oxygen metabolism and perfusion in the prefrontal cortex (PFC) during exercises of different intensities. Methods: A total of 12 recreationally active men (age 24 ± 6 years) were enrolled. They performed 17 min of low-intensity exercise (ExL), followed by 3 min of moderate-intensity exercise (ExM) at constant loads. Exercise intensities for ExL and ExM corresponded to 30% and 45% of the participants' heart rate reserve, respectively. Cardiovascular and respiratory parameters were measured. We used near-infrared time-resolved spectroscopy (TRS) to measure the cerebral hemoglobin oxygen saturation (ScO2) and total hemoglobin concentration ([HbT]), which can indicate the cerebral blood volume (CBV). As the cerebral metabolic rate for oxygen (CMRO2) is calculated using cerebral blood flow (CBF) and ScO2, we assumed a constant power law relationship between CBF and CBV based on investigations by positron emission tomography (PET). We estimated the relative changes in CMRO2 (rCMRO2) and CBV (rCBV) from the baseline. During ExL and ExM, the rate of perceived exertion was monitored, and alterations in the subjects' mood induced by exercise were evaluated using the Profile of Moods Scale-Brief. Results: Three minutes after exercise initiation, ScO2 decreased and rCMRO2 surpassed rCBV in the left PFC. When ExL changed to ExM, cardiovascular variables and the sense of effort increased concomitantly with an increase in [HbT] but not in ScO2, and the relationship between rCMRO2 and rCBV was dissociated in both sides of the PFC. Immediately after ExM, [HbT], and ScO2 increased, and the disassociation between rCMRO2 and rCBV was prominent in both sides of the PFC. While blood pressure decreased and a negative mood state was less prominent following ExM compared with that at rest, ScO2 decreased 15 min after exercise and rCMRO2 surpassed rCBV in the left PFC. Conclusion: Dissociated coupling between cerebral oxidative metabolism and perfusion in the PFC was consistent with the effort required for increased exercise intensity and associated with post-exercise hypotension and altered mood status after exercise. Our result demonstrates the first preliminary results dealing with the coupling between cerebral oxidative metabolism and perfusion in the PFC using TRS.

Early changes in cerebral metabolism after perinatal hypoxia-ischemia: a study in normothermic and hypothermic piglets

Introduction

Hypoxic ischemic encephalopathy (HIE) after a perinatal insult is a dynamic process that evolves over time. Therapeutic hypothermia (TH) is standard treatment for severe to moderate HIE. There is a lack of evidence on the temporal change and interrelation of the underlying mechanisms that constitute HIE under normal and hypothermic conditions. We aimed to describe early changes in intracerebral metabolism after a hypoxic-ischemic insult in piglets treated with and without TH and in controls.

Methods

Three devices were installed into the left hemisphere of 24 piglets: a probe measuring intracranial pressure, a probe measuring blood flow and oxygen tension, and a microdialysis catheter measuring lactate, glucose, glycerol, and pyruvate. After a standardized hypoxic ischemic insult, the piglets were randomized to either TH or normothermia.

Results

Glycerol, a marker of cell lysis, increased immediately after the insult in both groups. There was a secondary increase in glycerol in normothermic piglets but not in piglets treated with TH. Intracerebral pressure, blood flow, oxygen tension, and extracellular lactate remained stable during the secondary increase in glycerol.

Conclusion

This exploratory study depicted the development of the pathophysiological mechanisms in the hours following a perinatal hypoxic-ischemic insult with and without TH and controls.

Cognitive fatigue due to exercise under normobaric hypoxia is related to hypoxemia during exercise

We previously found that a 10-min bout of moderate-intensity exercise (50% maximal oxygen uptake) under normobaric and hypoxic conditions (fraction of inspired oxygen [[Formula: see text]] = 0.135) reduced executive performance and neural activity in the left dorsolateral prefrontal cortex (DLPFC). To examine whether this cognitive fatigue is due to a decrease in SpO₂ during exercise, we compared executive performance and related prefrontal activation between two experimental conditions, in which the participants inhaled normobaric hypoxic gas ([Formula: see text]= 0.135) (hypoxic exercise [HE]) or hypoxic gas adjusted so that SpO₂ during exercise remained at the resting level (milder hypoxic exercise [ME]). ME condition showed that reaction time in executive performance decreased (t[13] = 2.228, P < 0.05, d = 0.34, paired t-test) and left DLPFC activity increased (t[13] = -2.376, P < 0.05, d = 0.63, paired t-test) after exercise compared with HE condition. These results showed that the HE-induced reductions in the left DLPFC activity and executive performance were both suppressed in the ME condition, supporting the hypothesis that exercise-induced cognitive fatigue under hypoxic environment is due to hypoxemia during exercise. This may lead to the development of a method of coping with cognitive fatigue due to exercise that causes hypoxemia.

Duraplasty in Traumatic Thoracic Spinal Cord Injury: Impact on Spinal Cord Hemodynamics, Tissue Metabolism, Histology, and Behavioral Recovery Using a Porcine Model

After acute traumatic spinal cord injury (SCI), the spinal cord can swell to fill the subarachnoid space and become compressed by the surrounding dura. In a porcine model of SCI, we performed a duraplasty to expand the subarachnoid space around the injured spinal cord and evaluated how this influenced acute intraparenchymal hemodynamic and metabolic responses, in addition to histological and behavioral recovery. Female Yucatan pigs underwent a T10 SCI, with or without duraplasty. Using microsensors implanted into the spinal cord parenchyma, changes in blood flow (ΔSCBF), oxygenation (ΔPO₂), and spinal cord pressure (ΔSCP) during and after SCI were monitored, alongside metabolic responses. Behavioral recovery was tested weekly using the Porcine Injury Behavior Scale (PTIBS). Thereafter, spinal cords were harvested for tissue sparing analyses. In both duraplasty and non-animals, the ΔSCP increased ∼5 mm Hg in the first 6 h post-injury. After this, the SCP appeared to be slightly reduced in the duraplasty animals, although the group differences were not statistically significant after controlling for injury severity in terms of impact force. During the first seven days post-SCI, the ΔSCBF or ΔPO₂ values were not different between the duraplasty and control animals. Over 12 weeks, there was no improvement in hindlimb locomotion as assessed by PTIBS scores and no reduction in tissue damage at the injury site in the duraplasty animals. In our porcine model of SCI, duraplasty did not provide any clear evidence of long-term behavioral or tissue sparing benefit after SCI.

Physiological function and application of dietary fiber in pig nutrition: A review

Dietary fiber (DF), divided into soluble dietary fiber (SDF) and insoluble dietary fiber (IDF), has attracted increasing attention in the field of pig nutrition. Although DF reduces nutrient digestibility and inhibits energy deposition in most cases, fiber-rich feeds have been widely used in pig diets. This is not only because of lower feed costs, but also from the continuous discovery about the nutritional value of DF, mainly including the improvement of piglet intestinal health and sow reproductive performance. The addition timing has also been further considered, which potentially enables the nutritional value of DF to be accurately used in applicable pig models. Furthermore, fiber degrading enzymes have been shown to alleviate the anti-nutritional effects of DF and have ensured the improvement effect of fiber on intestinal health in young piglet models. However, the regulatory effect of fiber on pork quality is still unclear, which requires consideration of the wide range of fiber sources and the complexity of the basic diet composition, as well as the impact of pig breeds. Taken together, future research needs to gain more insight into the combined effects of SDF and IDF, processing methods, and addition timing to improve the nutritional value of DF, and further explore the physiological functions and regulatory mechanisms of DF fermentation products short-chain fatty acids in pigs.

Combined vEEG and Cerebral Oximetry Results to Determine the Severity of Hypoxic–Ischemic Encephalopathy

The objectives of the study were to evaluate the prognostic utility of bedside monitoring tools for hypoxic–ischemic encephalopathy (HIE) outcome and develop a prognostic predictive model. This retrospective study reviewed neonatal HIE treated with hypothermia between 2013 and 2016. Continuous video electroencephalography (vEEG) recordings scored for background electrocerebral activity, seizure, and sleep–wake cycles, and rSO2 data were stratified by magnetic resonance imaging (MRI) severity. The vEEG and rSO2 were combined in a predictive model. The analysis included 38 patients. The rSO2 was significantly higher in the severe group. vEEG showed early and persistent maximal suppression in the severe group. The predictive correlation of the rSO2 improves when combined with the vEEG.

Using a multimodal near-infrared spectroscopy and MRI to quantify gray matter metabolic rate for oxygen: A hypothermia validation study

Non-invasive quantitative imaging of cerebral oxygen metabolism (CMRO₂) in small animal models is crucial to understand the role of oxidative metabolism in healthy and diseased brains. In this study, we developed a multimodal method combining near-infrared spectroscopy (NIRS) and MRI to non-invasively study oxygen delivery and consumption in the cortex of mouse and rat models. The term CASNIRS is proposed to the technique that measures CMRO₂ with ASL and NIRS. To determine the reliability of this method, CMRO₂ values were compared with reported values measured with other techniques. Also, the sensitivity of the CASNIRS technique to detect changes in CMRO₂ in the cortex of the animals was assessed by applying a reduction in core temperature, which is known to reduce CMRO₂. Cerebral blood flow (CBF) and CMRO₂ were measured in five mice and five rats at a core temperature of 37 °C followed by another measurement at 33 °C. CMRO₂ was 7.8 ± 1.8 and 3.7 ± 0.9 (ml/100 g/min, mean ± SD) in mice and rats respectively. These values are in good agreement with reported values measured by ¹⁵O PET, ¹⁷O NMR, and BOLD fMRI. In hypothermia, we detected a significant decrease of 37% and 32% in CMRO₂ in the cortex of mice and rats, respectively. Q10 was calculated to be 3.2 in mice and 2.7 in rats. In this study we showed that it is possible to assess absolute values of metabolic correlates such as CMRO₂, CBF and oxygen extraction fraction (OEF) noninvasively in living brain of mice and rats by combining NIRS with MRI. This will open new possibilities for studying brain metabolism in patients as well as the many mouse/rat models of brain disorders.

Lawrence K, Amendolia O, Quattrone F, Balu R, Kofke WA, Yodh AG. Noninvasive continuous optical monitoring of absolute cerebral blood flow in critically ill adults

We investigate a scheme for noninvasive continuous monitoring of absolute cerebral blood flow (CBF) in adult human patients based on a combination of time-resolved dynamic contrast-enhanced near-infrared spectroscopy (DCE-NIRS) and diffuse correlation spectroscopy (DCS) with semi-infinite head model of photon propogation. Continuous CBF is obtained via calibration of the DCS blood flow index (BFI) with absolute CBF obtained by intermittent intravenous injections of the optical contrast agent indocyanine green. A calibration coefficient ( γ ) for the CBF is thus determined, permitting conversion of DCS BFI to absolute blood flow units at all other times. A study of patients with acute brain injury ( N = 7 ) is carried out to ascertain the stability of γ . The patient-averaged DCS calibration coefficient across multiple monitoring days and multiple patients was determined, and good agreement between the two calibration coefficients measured at different times during single monitoring days was found. The patient-averaged calibration coefficient of 1.24 × 10 9    ( mL / 100    g / min ) / ( cm 2 / s ) was applied to previously measured DCS BFI from similar brain-injured patients; in this case, absolute CBF was underestimated compared with XeCT, an effect we show is primarily due to use of semi-infinite homogeneous models of the head.

Lawrence K, Diop M. Simultaneous monitoring of cerebral perfusion and cytochrome c oxidase by combining broadband near-infrared spectroscopy and diffuse correlation spectroscopy

Preterm infants born with very low birth weights are at a high risk of brain injury, in part because the premature brain is believed to be prone to periods of low cerebral blood flow (CBF). Tissue damage is likely to occur if reduction in CBF is sufficient to impair cerebral energy metabolism for extended periods. Therefore, a neuromonitoring method that can detect reductions in CBF, large enough to affect metabolism, could alert the neonatal intensive care team before injury occurs. In this report, we present the development of an optical system that combines diffuse correlation spectroscopy (DCS) for monitoring CBF and broadband near-infrared spectroscopy (B-NIRS) for monitoring the oxidation state of cytochrome c oxidase (oxCCO) - a key biomarker of oxidative metabolism. The hybrid instrument includes a multiplexing system to enable concomitant DCS and B-NIRS measurements while avoiding crosstalk between the two subsystems. The ability of the instrument to monitor dynamic changes in CBF and oxCCO was demonstrated in a piglet model of neonatal hypoxia-ischemia (HI). Experiments conducted in eight animals, including two controls, showed that oxCCO exhibited a delayed response to ischemia while CBF and tissue oxygenation (StO2) responses were instantaneous. These findings suggest that simultaneous neuromonitoring of perfusion and metabolism could provide critical information regarding clinically significant hemodynamic events prior to the onset of brain injury.

Neural basis for reduced executive performance with hypoxic exercise

While accumulating evidence suggests positive effects of exercise on executive function, such effects vary with environment. In particular, exercise in a hypoxic environment (hypobaric or normobaric hypoxia), leading to decreased oxygen supply, may dampen or cancel such effects. Thus, we further explore the relation between the effects of hypoxic exercise on executive function and their underlying neural mechanisms by monitoring changes of cortical activation patterns using functional near-infrared spectroscopy (fNIRS). Fifteen healthy participants performed color-word Stroop tasks (CWST) before and after a 10 min bout of moderate-intensity exercise (50%V̇O_2peak) under normoxic and hypoxic conditions (fraction of inspired oxygen (FIO₂) = 0.135). During the CWST, we monitored prefrontal activation using fNIRS. CWST performance under hypoxic conditions decreased compared with normoxic conditions. In addition, CWST-related activation in the left dorsolateral prefrontal cortex (DLPFC) was reduced after a bout of hypoxic exercise. There was statistically significant association between decreased CWST performance and activation in the left DLPFC. These results suggest that moderate exercise under normobaric hypoxic conditions has negative effects on executive function by reducing task-related activations in the DLPFC.

Investigating the Role of Near-Infrared Spectroscopy in Neonatal Medicine

Near-infrared spectroscopy (NIRS) is a clinical tool that provides a bedside method of noninvasively measuring continuous, "real-time" oxygen consumption and monitoring for potential ischemia of somatic tissues, particularly the brain, kidneys, and intestine in neonates. Although the concept of NIRS seems promising, its implementation into clinical practice has been inconsistent for various reasons, including difficulty in interpreting regional oxygen saturation (rSO2), the wide variation in types of NIRS monitors and probes, the cost of new equipment, different monitoring modalities, large discrepancies in both intra- and interindividual use, a lack of defined universal normative values, and little to no data on outcomes or potentially harmful interventions made based on rSO2 readings. We combine findings from previously published informational articles and studies on the use of NIRS in neonatal medicine to provide a comprehensive overview of this tool and identify potential indications for clinical use.

Modelling Blood Flow and Metabolism in the Preclinical Neonatal Brain during and Following Hypoxic-Ischaemia

Hypoxia-ischaemia (HI) is a major cause of neonatal brain injury, often leading to long-term damage or death. In order to improve understanding and test new treatments, piglets are used as preclinical models for human neonates. We have extended an earlier computational model of piglet cerebral physiology for application to multimodal experimental data recorded during episodes of induced HI. The data include monitoring with near-infrared spectroscopy (NIRS) and magnetic resonance spectroscopy (MRS), and the model simulates the circulatory and metabolic processes that give rise to the measured signals. Model extensions include simulation of the carotid arterial occlusion used to induce HI, inclusion of cytoplasmic pH, and loss of metabolic function due to cell death. Model behaviour is compared to data from two piglets, one of which recovered following HI while the other did not. Behaviourally-important model parameters are identified via sensitivity analysis, and these are optimised to simulate the experimental data. For the non-recovering piglet, we investigate several state changes that might explain why some MRS and NIRS signals do not return to their baseline values following the HI insult. We discover that the model can explain this failure better when we include, among other factors such as mitochondrial uncoupling and poor cerebral blood flow restoration, the death of around 40% of the brain tissue.

In vivo Monitoring of Cerebral Hemodynamics in the Immature Rat: Effects of Hypoxia-Ischemia and Hypothermia

BACKGROUND

Neonatal hypoxic-ischemic (HI) encephalopathy occurs in 1-4 per 1,000 live term births and can cause devastating neurodevelopmental disabilities. Currently, therapeutic hypothermia (TH) is the only treatment with proven efficacy. Since TH is associated with decreased cerebral metabolism and cerebral blood flow (CBF), it is important to assess CBF at the bedside. Diffuse correlation spectroscopy (DCS) has emerged as a promising optical modality to noninvasively assess an index of CBF (CBFi) in both humans and animals. In this initial descriptive study, we employ DCS to monitor the evolution of CBFi following HI with or without TH in immature rats. We investigate potential relationships between CBF and subsequent cerebral damage.

METHODS

HI was induced on postnatal day 10 or 11 rat pups by right common carotid artery ligation followed by 60-70 min hypoxia (8% oxygen). After HI, the pups recovered for 4 h under hypothermia (HI-TH group, n = 23) or normothermia (HI-N group, n = 23). Bilateral measurements of hemispheric CBFi were made with DCS in unanesthetized animals at baseline, before HI, and 0, 1, 2, 3, 4, 5, and 24 h after HI. The animals were sacrificed at either 1 or 4 weeks, and brain injury was scored on an ordinal scale of 0-5 (0 = no injury).

RESULTS

Carotid ligation caused moderate bilateral decreases in CBFi. Following HI, an initial hyperemia was observed that was more prominent in the contralateral hemisphere. After initiation of TH, CBFi dropped significantly below baseline levels and remained reduced for the duration of TH. In contrast, CBFi in the HI-N group was not significantly decreased from baseline levels. Reductions in CBFi after 4 h of TH were not associated with reduced damage at 1 or 4 weeks. However, elevated ipsilateral CBFi and ipsilateral-to-contralateral CBFi ratios at 24 h were associated with worse outcome at 1 week after HI.

CONCLUSIONS

Both HI and TH alter CBFi, with significant differences in CBFi between hypothermic and normothermic groups after HI. CBFi may be a useful biomarker of subsequent cerebral damage.

Regional changes in cerebral blood flow oxygenation can indicate global changes in cerebral blood flow during coronary artery occlusion in juvenile pigs

Near infrared spectroscopy (NIRS) is a widely employed method for assessment of regional cerebral oxygenation (RcStO2). RcStO2 values are expected to vary with changes in the relative amount of oxyhaemoglobin. The present experimental study aimed to assess the response of RcStO2 to controlled alterations of carotid blood flow (CQ). Landrace pigs were anesthetized followed by surgical preparation. Cyclic variations in cardiac output were accomplished by intermittently occluding the main stem of the left coronary artery. A flow measurement probe for assessing CQ was placed around the left carotid artery. One NIRS probe was placed on the left ipsilateral forehead to assess regional cerebral oximetry. Simultaneous registration of CQ and RcStO2 was conducted. There was a strong correlation for variation in CQ and RcStO2 signal values. Based on coherence analysis the fraction of power of the RcStO2 that was coherent with the CQ signal reached 0.84 ± 0.12 (P < 0.05) for frequencies lower than 0.1 Hz. The agreement of the sample-to-sample co-variation, as assessed by the Pearson correlation coefficient, was 0.83 ± 0.08 (P < 0.05). One explanatory component for variations in cerebral oxygenation verified by NIRS should be attributed to variations in the cerebral blood flow.

A tale of two methods: combining near-infrared spectroscopy with MRI for studies of brain oxygenation and metabolism

Combining magnetic resonance imaging (MRI) with near-infrared spectroscopy (NIRS) leads to excellent synergies which can improve the interpretation of either method and can provide novel data with respect to measuring brain oxygenation and metabolism. MRI has good spatial resolution, can detect a range of physiological parameters and is sensitive to changes in deoxyhemoglobin content. NIRS has lower spatial resolution, but can detect, and with specific technologies, quantify, deoxyhemoglobin, oxyhemoglobin, total hemoglobin and cytochrome oxidase. This paper reviews the application of both methods, as a multimodal technology, for assessing changes in brain oxygenation that may occur with changes in functional activation state or metabolic rate. Examples of hypoxia and ischemia are shown. Data support the concept of reduced metabolic rate resulting from hypoxia/ischemia and that metabolic rate in brain is not close to oxygen limitation during normoxia. We show that multimodal MRI and NIRS can provide novel information for studies of brain metabolism.

Quantifying cerebral blood flow in an adult pig ischemia model by a depth-resolved dynamic contrast-enhanced optical method

Dynamic contrast-enhanced (DCE) near-infrared (NIR) methods have been proposed for bedside monitoring of cerebral blood flow (CBF). These methods have primarily focused on qualitative approaches since scalp contamination hinders quantification. In this study, we demonstrate that accurate CBF measurements can be obtained by analyzing multi-distance time-resolved DCE data with a combined kinetic deconvolution optical reconstruction (KDOR) method. Multi-distance time-resolved DCE-NIR measurements were made in adult pigs (n=8) during normocapnia, hypocapnia and ischemia. The KDOR method was used to calculate CBF from the DCE-NIR measurements. For validation, CBF was measured independently by CT under each condition. The mean CBF difference between the techniques was -1.7 mL/100 g/min with 95% confidence intervals of -16.3 and 12.9 mL/100 g/min; group regression analysis revealed a strong agreement between the two techniques (slope=1.06±0.08, y-intercept=-4.37±4.33 mL/100 g/min, p<0.001). The results of an error analysis suggest that little a priori information is needed to recover CBF, due to the robustness of the analytical method and the ability of time-resolved NIR to directly characterize the optical properties of the extracerebral tissue (where model mismatch is deleterious). The findings of this study suggest that the DCE-NIR approach presented is a minimally invasive and portable means of determining absolute hemodynamics in neurocritical care patients.

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.

Does treatment of patent ductus arteriosus with cyclooxygenase inhibitors affect neonatal regional tissue oxygenation?

The effect of patent ductus arteriosus (PDA) treatment with cyclooxygenase (COX) inhibitors (indomethacin [INDO] and ibuprofen [IBU]) on regional oxygenation requires further clarification. The authors hypothesized that both INDO and IBU reduce regional tissue oxygenation in preterm neonates with PDA but that the risk is not uniform for different tissues and other factors may contribute. Regional cerebral (rSO(2-C)), renal (rSO(2-R)), and mesenteric (rSO(2-M)) tissue oxygenation measured by near-infrared spectroscopy and peripheral arterial oxygen saturation measured by pulse oximetry were recorded simultaneously before, during, and after treatment with the first dose of INDO or IBU in very preterm-born infants with PDA. Tissue-specific fractional oxygen extraction (FOE) was calculated using the rSO(2-C), rSO(2-R), rSO(2-M), and corresponding SpO(2) measurements. The findings showed a significant reduction in rSO(2-C), rSO(2-R), and rSO(2-M) and an increase in regional FOE after treatment with COX inhibitors in approximately one third of the 38 enrolled infants, which were associated with increased baseline regional tissue oxygen saturation (p < 0.01). However, the infants with posttreatment reduction of tissue oxygenation had significantly lower baseline rSO(2-C) (66.7 ± 8.1 vs 69.7 ± 8.1 %), rSO(2-R) (55.2 ± 10.8 vs 62.7 ± 11.8 %) and especially rSO(2-M) (37.8 ± 11.4 vs 46.7 ± 16.0 %) than the neonates with unchanged or increased tissue oxygenation. The two groups did not differ in terms of the risk for posttreatment reduction in regional tissue oxygenation with respect to either INDO or IBU treatment and their respective blood levels. Treatment of PDA with either INDO or IBU is associated with a 30-40 % risk for a reduction in regional tissue oxygenation, which is more pronounced in mesenteric tissue than in cerebral or renal tissue. Despite the inconsistency, reduction of regional tissue oxygenation in preterm infants with PDA is more likely associated with the administration of INDO than with the administration of IBU.

Quantification of compensatory processes of postnatal hypoxia in newborn piglets applying short-term nonlinear dynamics analysis

Background

Newborn mammals suffering from moderate hypoxia during or after birth are able to compensate a transitory lack of oxygen by adapting their vital functions. Exposure to hypoxia leads to an increase in the sympathetic tone causing cardio-respiratory response, peripheral vasoconstriction and vasodilatation in privileged organs like the heart and brain. However, there is only limited information available about the time and intensity changes of the underlying complex processes controlled by the autonomic nervous system.

Methods

In this study an animal model involving seven piglets was used to examine an induced state of circulatory redistribution caused by moderate oxygen deficit. In addition to the main focus on the complex dynamics occurring during sustained normocapnic hypoxia, the development of autonomic regulation after induced reoxygenation had been analysed. For this purpose, we first introduced a new algorithm to prove stationary conditions in short-term time series. Then we investigated a multitude of indices from heart rate and blood pressure variability and from bivariate interactions, also analysing respiration signals, to quantify the complexity of vegetative oscillations influenced by hypoxia.

Results

The results demonstrated that normocapnic hypoxia causes an initial increase in cardiovascular complexity and variability, which decreases during moderate hypoxia lasting one hour (p < 0.004). After reoxygenation, cardiovascular complexity parameters returned to pre-hypoxic values (p < 0.003), however not respiratory-related complexity parameters.

Conclusions

In conclusion, indices from linear and nonlinear dynamics reflect considerable temporal changes of complexity in autonomous cardio-respiratory regulation due to normocapnic hypoxia shortly after birth. These findings might be suitable for non-invasive clinical monitoring of hypoxia-induced changes of autonomic regulation in newborn humans.

Regional tissue oxygenation in preterm born infants in association with echocardiographically significant patent ductus arteriosus

OBJECTIVE

To analyze the levels of regional tissue oxygenation in preterm infants in association with echocardiographically significant patent ductus arteriosus (PDA).

STUDY DESIGN

Preterm infants with gestational age less than 32 week were enrolled before the first dose of the pharmacological treatment for the PDA. Non-invasive near-infrared spectroscopy (NIRS) technology was utilized to measure cerebral (rSO(2)-C), renal (rSO(2)-R) and mesenteric (rSO(2-M)) tissue oxygenation for approximately 60 min. Regional fractional oxygen extraction (FOE) was calculated using simultaneously measured arterial saturation (SaO(2)). We analyzed regional tissue oxygenation and oxygen extraction, hemodynamic parameters, and demographic and clinical information in association with the size of the PDA (moderate vs large).

RESULT

Among the 38 enrolled infants, the majority were diagnosed with a large (63.2%, n=24) and the rest with a moderate-sized PDA. Infants with large and moderate PDA were comparable in terms of gestational age, study age and weight, mode of delivery and hemodynamic parameters. A significantly higher proportion of infants with a moderate PDA were mechanically ventilated as compared with those with a large PDA. We found no significant differences in the rSO(2)-C and rSO(2)-R, irrespective of the type of respiratory support. However, in infants with a large PDA on continuous nasal positive airway pressure (NCPAP), the rSO(2)-M was lower and mesenteric FOE was higher than that in mechanically ventilated neonates with a large PDA, and in those with moderate PDA irrespective of the type of respiratory support.

CONCLUSION

The PDA size did not affect cerebral and renal tissue oxygenation, but the mesenteric tissue oxygenation was decreased in infants with a large PDA on NCPAP.

Continuous monitoring of absolute cerebral blood flow by near-infrared spectroscopy during global and focal temporary vessel occlusion

Treatment of intracranial aneurysms by surgical clipping carries a risk of intraoperative ischemia, caused mainly by prolonged temporary occlusion of cerebral arteries. The objective of this study was to develop a near-infrared spectroscopy (NIRS) technique for continuous monitoring of cerebral blood flow (CBF) during surgery. With this approach, cerebral hemodynamics prior to clipping are measured by a bolus-tracking method that uses indocyanine green as an intravascular contrast agent. The baseline hemodynamic measurements are then used to convert the continuous Hb difference (HbD) signal (HbD = oxyhemoglobin - deoxyhemoglobin) acquired during vessel occlusion to units of CBF. To validate the approach, HbD signal changes, along with the corresponding CBF changes, were measured in pigs following occlusion of the common carotid arteries or a middle cerebral artery. For both occlusion models, the predicted CBF change derived from the HbD signal strongly correlated with the measured change in CBF. Linear regression of the predicted and measured CBF changes resulted in a slope of 0.962 (R(2) = 0.909) following carotid occlusion and 0.939 (R(2) = 0.907) following middle cerebral artery occlusion. These results suggest that calibrating the HbD signal by baseline hemodynamic measurements provides a clinically feasible method of monitoring CBF changes during neurosurgery.

Effects of selective head cooling on cerebral blood flow and metabolism in newborn piglets after hypoxia-ischemia

AIM

the effect of selective head cooling on cerebral blood flow (CBF) and cerebral metabolism rate (CMR) was investigated in newborn piglets.

METHODS

seven days old newborn piglets were randomly assigned to one of the following three groups: Selective head cooling in normal piglets (n=4), selective head cooling after HI (n=6) and normal temperature after HI (n=6). CBF was measured with color microspheres. Cerebral oxygenation metabolism rate (CMRO(2)), Cerebral glucose consumption (CMR(Glu)) and Cerebral lactate production (CMR(lac)) were calculated.

RESULT

in normal piglets, CBF, CMRO(2) and CMR(glu) were significantly decreased at both 35°C (P<0.05) and 32°C (P<0.01), while CMR(lac) did not change. Compared to baseline, CBF and CMRO(2) were significantly reduced (P<0.05), while CMR(glu) and CMR(lac) were significantly increased (P<0.01), AVDO(2) was decreased (P<0.05), while AVD(glu) and AVD(lac) were significantly increased (P<0.01 respectively) in HI piglets with normal temperature respectively. Compared to normal temperature after HI, selective head cooling after HI significantly reduced CMR(glu) and CMR(lac), and AVDO(2), AVD(glu), AVD(lac) were improved at 35°C.

CONCLUSION

selective head cooling not only reduced energy consumption, but also improve brain oxygen metabolism in newborn after HI.

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.

Lawrence K. Cerebral metabolic rate of oxygen and amplitude-integrated electroencephalography during early reperfusion after hypoxia-ischemia in piglets

The therapeutic window following perinatal hypoxia-ischemia is brief, and early clinical signs of injury can be subtle. Electroencephalography (EEG) represents the most promising early diagnostic of hypoxia-ischemia; however, some studies have questioned the sensitivity and specificity of EEG. The present study investigated the use of both near-infrared spectroscopy (NIRS) measurements of the cerebral metabolic rate of oxygen (CMRO2) and amplitude-integrated EEG (aEEG) to detect the severity of hypoxia-ischemia after 1 h of reperfusion in newborn piglets (10 insult, 3 control). The CMRO2 was measured before and after 1 h of reperfusion from hypoxia-ischemia, the duration of which was varied from piglet to piglet with a range of 3–24 min, under fentanyl/nitrous oxide anesthesia to mimic awake-like levels of cerebral metabolism. EEG data were collected throughout the study. On average, the CMRO2 and mean aEEG background signals were significantly depressed following the insult ( P < 0.05). Mean CMRO2 and mean aEEG background were 2.61 ± 0.11 ml O2·min−1·100 g−1 and 20.4 ± 2.7 μV before the insult and 1.58 ± 0.09 ml O2·min−1·100 g−1 and 11.8 ± 2.9 μV after 1 h of reperfusion, respectively. Both CMRO2 and aEEG displayed statistically significant correlations with duration of ischemia ( P < 0.05; r = 0.71 and r = 0.89, respectively); however, only CMRO2 was sensitive to milder injuries (<5 min). This study highlights the potential for combining NIRS measures of CMRO2 with EEG in the neonatal intensive care unit to improve early detection of perinatal hypoxia-ischemia.

A broadband continuous-wave multichannel near-infrared system for measuring regional cerebral blood flow and oxygen consumption in newborn piglets

Near-infrared spectroscopy (NIRS) is a promising technique for assessing brain function in newborns, particularly due to its portability and sensitivity to cerebral hemodynamics and oxygenation. Methods for measuring cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO(2)) have been developed based on broadband continuous-wave NIRS. However, broadband NIRS apparatus typically have only one detection channel, which limits their applicability to measuring regional CBF and CMRO(2). In this study, a relatively simple multiplexing approach based on electronically controlled mechanical shutters is proposed to expand the detection capabilities from one to eight channels. The tradeoff is an increase in the sampling interval; however, this has negligible effects on CBF measurements for intervals less than or equal to 1 s. The ability of the system to detect focal brain injury was demonstrated in piglets by injecting endothelin-1 (ET-1) into the cerebral cortex. For validation, CBF was independently measured by computed tomography (CT) perfusion. The average reduction in CBF from the source-detector pair that interrogated the injured region was 51%+/-9%, which was in good agreement with the CBF reduction measured by CT perfusion (55%+/-5%). No significant changes in regional CMRO(2) were observed. The average regional differential pathlength prior to ET-1 injection was 8.4+/-0.2 cm (range of 7.1-9.6 cm) and did not significantly change after the injury.

Assessing the severity of perinatal hypoxia-ischemia in piglets using near-infrared spectroscopy to measure the cerebral metabolic rate of oxygen

Reduced cerebral function after neonatal hypoxia-ischemia is an early indicator of hypoxic-ischemic encephalopathy. Near-infrared spectroscopy offers a clinically relevant means of detecting impaired cerebral metabolism from the measurement of the cerebral metabolic rate of oxygen (CMRO2). The purpose of this study was to determine the relationship between postinsult CMRO2 and duration of hypoxia-ischemia in piglets. Twelve piglets were subjected to randomly selected durations of hypoxia-ischemia (5-28 min) and five animals served as controls. Measurements of CMRO2 were taken before and for 24 h after hypoxia-ischemia. Histology was carried out in nine piglets (six insults, three controls) to estimate brain injury. In the first 4 h after the insult, average CMRO2 of the insult group was significantly depressed (33 +/- 3% reduction compared with controls) and by 8 h, a significant correlation developed, which persisted for the remainder of the study, between CMRO2 and the duration of ischemia. Histologic staining suggested little brain damage resulted from shorter insult durations and considerable damage from more prolonged insults. This study demonstrated that near-infrared spectroscopy could detect early changes in CMRO2 after hypoxia-ischemia for a range of insult severities and CMRO2 could be used to distinguish insult severity by 8 h after the insult.

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 cerebral oxygen consumption and high-energy phosphates during early recovery in hypoxic-ischemic piglets: a combined near-infrared and magnetic resonance spectroscopy study

Near-infrared spectroscopy (NIRS) offers the ability to assess brain function at the bedside of critically ill neonates. Our group previously demonstrated a persistent reduction in the cerebral metabolic rate of oxygen (CMRO(2)) after hypoxia-ischemia (HI) in newborn piglets. The purpose of this current study was to determine the causes of this reduction by combining NIRS with magnetic resonance spectroscopy (MRS) to measure high-energy metabolites and diffusion-weighted imaging to measure cellular edema. Nine piglets were exposed to 30 min of HI and nine piglets served as controls. Proton and phosphorous MRS spectra, apparent diffusion coefficient (ADC) maps, and CMRO(2) measurements were collected periodically before and for 5.5 h after HI. A significant decrease in CMRO(2) (26 +/- 7%) was observed after HI. Incomplete recovery of nucleotide triphosphate concentration (8 +/- 3% <controls) and reduced ADC (16 +/- 5%) suggested mitochondrial dysfunction. However, CMRO(2) did not correlate with any metabolite concentration during the last 3 h of the recovery period, and no significant changes were found in phosphocreatine and lactate levels. Therefore, the CMRO(2) decrease is likely a combination of impaired mitochondrial function and reduced energy demands during the acute phase, which has been previously observed in the mature brain.

Neuroprotective effects of the nonpsychoactive cannabinoid cannabidiol in hypoxic-ischemic newborn piglets

To test the neuroprotective effects of the nonpsychoactive cannabinoid cannabidiol (CBD), piglets received i.v. CBD or vehicle after hypoxia-ischemia (HI: temporary occlusion of both carotid arteries plus hypoxia). Nonhypoxic-ischemic sham-operated piglets remained as controls. Brain damage was studied by near-infrared spectroscopy (NIRS) and amplitude-integrated electroencephalography (aEEG) and by histologic assessment (Nissl and FluoroJadeB staining). In HI+vehicle, HI led to severe cerebral hemodynamic and metabolic impairment, as reflected in NIRS by an increase in total Hb index (THI) and a decrease in the fractional tissue oxygenation extraction (FTOE); in HI+CBD the increase of THI was blunted and FTOE remained similar to SHAM. HI profoundly decreased EEG amplitude, which was not recovered in HI+vehicle, indicating cerebral hypofunction; seizures were observed in all HI+vehicle. In HI+CBD, however, EEG amplitude recovered to 46.4 7.8% baseline and seizures appeared only in 4/8 piglets (both p < 0.05). The number of viable neurons decreased and that of degenerating neurons increased in HI+vehicle; CBD reduced both effects by more than 50%. CBD administration was free from side effects; moreover, CBD administration was associated with cardiac, hemodynamic, and ventilatory beneficial effects. In conclusion, administration of CBD after HI reduced short-term brain damage and was associated with extracerebral benefits.