Cerebral monitoring in newborn infants by magnetic resonance and near infrared spectroscopy

Sickle cell microvascular paradox-oxygen supply-demand mismatch

We have previously demonstrated that sickle cell disease (SCD) patients maintain normal global systemic and cerebral oxygen delivery by increasing cardiac output. However, ischemic end-organ injury remains common suggesting that tissue oxygen delivery may be impaired by microvascular dysregulation or damage. To test this hypothesis, we performed fingertip laser Doppler flowmetry measurements at the base of the nailbed and regional oxygen saturation (rSO₂ ) on the dorsal surface of the same hand. This was done during flow mediated dilation (FMD) studies in 26 chronically transfused SCD, 75 non-transfused SCD, and 18 control subjects. Chronically transfused SCD patients were studied prior to and following a single transfusion and there was no acute change in rSO₂ or perfusion. Laser Doppler estimates of resting perfusion were 76% higher in non-transfused and 110% higher in transfused SCD patients, compared to control subjects. In contrast, rSO₂ was 12 saturation points lower in non-transfused SCD patients, but normal in the transfused SCD patients. During cuff occlusion, rSO₂ declined at the same rate in all subjects suggesting similar intrinsic oxygen consumption rates. Upon cuff release, laser doppler post occlusive hyperemia was blunted in SCD patients in proportion to their resting perfusion values. Transfusion therapy did not improve the hyperemia response. FMD was impaired in SCD subjects but partially ameliorated in transfused SCD subjects. Taken together, non-transfused SCD subjects demonstrate impaired conduit artery FMD, impaired microcirculatory post-occlusive hyperemia, and resting hypoxia in the hand despite compensated oxygen delivery, suggesting impaired oxygen supply-demand matching. Transfusion improves FMD and oxygen supply-demand matching but not microcirculation hyperemic response.

Cardiac Surgery-Associated Kidney Injury in Children and Renal Oximetry

OBJECTIVES

Cardiac surgery-associated acute kidney injury is common in children and associates with negative outcomes. Novel interventions to reduce cardiac surgery-associated acute kidney injury require knowledge of its pathophysiology. States of altered perfusion, oxygen delivery, and energy consumption occur during cardiopulmonary bypass and could protect against or contribute to renal cellular injury and recovery. Near-infrared spectroscopy is noninvasive technology for monitoring regional blood flow and tissue oxygenation. This study evaluated the relationship between renal regional oxygen saturation and cardiac surgery-associated acute kidney injury, using near-infrared spectroscopy monitoring before, during, and after cardiopulmonary bypass in children.

DESIGN

Prospective cohort study.

SETTING

Single-center, tertiary care pediatric hospital (Stollery Children's Hospital, Edmonton, AB, Canada).

PATIENTS

Children less than or equal to 10 kg undergoing congenital heart disease repair with cardiopulmonary bypass. Heart transplant, preoperative dialysis, sepsis, extracorporeal life support, congenital renal disease, and preoperative nephrotoxins were exclusions.

INTERVENTIONS

Renal regional near-infrared spectroscopy monitoring before, during, and after cardiopulmonary bypass.

MEASUREMENTS AND MAIN RESULTS

Outcome measure was cardiac surgery-associated acute kidney injury (defined according to Kidney Disease: Improving Global Outcomes criteria). Regional oxygen saturation was measured continuously using near-infrared spectroscopy (INVOS 5100C Cerebral/Somatic Oximeter; Medronic, Troy, MI) from time of anesthesia to time of transfer to intensive care. Cardiac surgery-associated acute kidney injury occurred in 65%. Lower baseline (precardiopulmonary bypass) regional oxygen saturation was associated with decreased risk of cardiac surgery-associated acute kidney injury (p = 0.01); children with baseline regional oxygen saturation in the highest tertile were 7.14 times more likely to get cardiac surgery- associated acute kidney injury (vs lowest tertile). Area under the curve for ability of baseline regional oxygen saturation to predict cardiac surgery-associated acute kidney injury was 0.73 (95% CI, 0.60-0.85). Children with lower baseline glomerular filtration rate had lower mean renal regional oxygen saturation.

CONCLUSIONS

Findings demonstrate that preoperative oxygen supply/demand balance is an important predictor of cardiac surgery-associated acute kidney injury, suggesting lower preoperative (and intraoperative) renal blood flow may be protective. There is not yet a definite link between remote ischemic preconditioning and prevention of cardiac surgery-associated acute kidney injury; however, renal protective effects of sublethal ischemia should continue to be explored.

Functional near infra-red spectroscopy (fNIRS) in schizophrenia: A review

The research on the alterations in functional connectivity in schizophrenia has been facilitated by development of an array of functional neuroimaging techniques. Functional Near Infra Red Spectroscopy (fNIRS) is a novel diffuse optical neuromonitring method with its own advantages and limitations. The advantages of fNIRS have made it to be frequently used as a research tool by medical community in different settings. In fNIRS the property of haemoglobin to absorb near infrared light is used to measure brain activity. It provides the indirect measurement of the neuronal activity in the areas of interest. The advantage of fNIRS being less restrictive has made it to be used more commonly in the research of psychiatric disorders in general, schizophrenia in particular. The fNIRS studies on patients with schizophrenia have shown haemodynamic hypo activation primarily in the prefrontal cortex during various cognitive tasks. In this review, initially we have briefly explained the basic principles of fNIRS followed by detailed review of fNIRS findings in patients with schizophrenia.

Somatic stimulation causes frontoparietal cortical changes in neonates: a functional near-infrared spectroscopy study

Palmar and plantar grasp are the foremost primitive neonatal reflexes and functions. Persistence of these reflexes in infancy is a sign of evolving cerebral palsy. Our aims were to establish measurement feasibility in a clinical setting and to characterize changes in oxyhemoglobin (HbO) and deoxyhemoglobin (HbD) concentration in the bilateral frontoparietal cortex in unsedated neonates at the crib-side using functional near-infrared spectroscopy (fNIRS). We hypothesized that bilateral concentration changes will occur upon somatic central and peripheral somatic stimulation. Thirteen preterm neonates (five males) underwent time 1, and six (two males) returned for time 2 (mean [Formula: see text] and 47.0 weeks, respectively). Signals from a total of 162 somatic stimuli responses were measured. Response amplitude, duration, and latency were log-transformed and compared between palmar, plantar, and oromotor stimuli using linear mixed models, adjusted for cap, electroencephalogram abnormality, time (1 versus 2), and Sarnat score, if necessary. The oromotor stimulus resulted in a 50% greater response than the palmar or plantar stimuli for HbO left and right hemisphere duration ([Formula: see text]). There were no other statistically significant differences between stimuli for any other outcome ([Formula: see text]). Utilizing fNIRS in conjunction with occupational and physical therapy maneuvers is efficacious to study modifiable and restorative neurophysiological mechanisms.

Review of transcranial photobiomodulation for major depressive disorder: targeting brain metabolism, inflammation, oxidative stress, and neurogenesis

We examined the use of near-infrared and red radiation (photobiomodulation, PBM) for treating major depressive disorder (MDD). While still experimental, preliminary data on the use of PBM for brain disorders are promising. PBM is low-cost with potential for wide dissemination; further research on PBM is sorely needed. We found clinical and preclinical studies via PubMed search (2015), using the following keywords: "near-infrared radiation," "NIR," "low-level light therapy," "low-level laser therapy," or "LLLT" plus "depression." We chose clinically focused studies and excluded studies involving near-infrared spectroscopy. In addition, we used PubMed to find articles that examine the link between PBM and relevant biological processes including metabolism, inflammation, oxidative stress, and neurogenesis. Studies suggest the processes aforementioned are potentially effective targets for PBM to treat depression. There is also clinical preliminary evidence suggesting the efficacy of PBM in treating MDD, and comorbid anxiety disorders, suicidal ideation, and traumatic brain injury. Based on the data collected to date, PBM appears to be a promising treatment for depression that is safe and well-tolerated. However, large randomized controlled trials are still needed to establish the safety and effectiveness of this new treatment for MDD.

Optical Measurement of Tissue Oxygen Saturation

Advances in opto-electronic systems have meant that optical spectroscopy can now be used for noninvasive measurements in tissue in patients. A number of techniques have evolved over the last 15 years that make use of the characteristic differences in the absorption spectrum of deoxygenated and oxygenated hemoglobin to measure oxygen saturation. This article summarizes, in particular, those techniques that may prove to be applicable to measurements relating to lower extremity wounds. A short introduction is given about existing electrode methods before describing applications of near infrared and visible wavelength spectroscopy to measurements in tissue. The advantages and limitations of these methods are discussed. An example of an area where tissue spectroscopy is now in routine clinical use for tissue healing viability assessment is presented.

Direct estimation of evoked hemoglobin changes by multimodality fusion imaging

In the last two decades, both diffuse optical tomography (DOT) and blood oxygen level dependent (BOLD)-based functional magnetic resonance imaging (fMRI) methods have been developed as noninvasive tools for imaging evoked cerebral hemodynamic changes in studies of brain activity. Although these two technologies measure functional contrast from similar physiological sources, i.e., changes in hemoglobin levels, these two modalities are based on distinct physical and biophysical principles leading to both limitations and strengths to each method. In this work, we describe a unified linear model to combine the complimentary spatial, temporal, and spectroscopic resolutions of concurrently measured optical tomography and fMRI signals. Using numerical simulations, we demonstrate that concurrent optical and BOLD measurements can be used to create cross-calibrated estimates of absolute micromolar deoxyhemoglobin changes. We apply this new analysis tool to experimental data acquired simultaneously with both DOT and BOLD imaging during a motor task, demonstrate the ability to more robustly estimate hemoglobin changes in comparison to DOT alone, and show how this approach can provide cross-calibrated estimates of hemoglobin changes. Using this multimodal method, we estimate the calibration of the 3 tesla BOLD signal to be -0.55%+/-0.40% signal change per micromolar change of deoxyhemoglobin.

The Application of Near-infrared Oximetry to Cerebral Monitoring During Aneurysm Embolization: A Comparison With Intraprocedural Angiography

Near-infrared spectroscopy (NIRS) has been used to monitor regional cerebral oxygen saturation (rSO2) in patients at risk of cerebral desaturation during surgical and neurointerventional procedures. However, the quantitative capabilities of the method have been questioned, as has its validation compared with jugular bulb oximetry. Here, we compare NIRS data acquired during coil embolization procedures with incidence of vasospasm as detected from angiography. Thirty-two subarachnoid hemorrhage patients underwent embolization. Bilateral SomaSensor strips (Invos 4100, Somanetics) were affixed to the forehead at constant anatomic positions, avoiding frontal sinuses and scalp hair. Mean arterial pressure, SaO2, end-tidal pCO2, temperature and Hb were held within a narrow range during the procedure. Ipsilateral angiography was performed every 10 to 15 minutes. An independent neuroradiologist classified any vasospasm in the parent vessel as mild (25% baseline), moderate (50%), severe (75%), or total (100%). Of all, 15/32 (46.9%) patients developed spasm; in 2 it was severe or total. There was no significant association between World Federation of Neurological Surgeons grade and baseline rSO2 signal (either ipsilateral or contralateral to the side of the aneurysm) (P=0.598). There was no significant association between side of aneurysm and baseline rSO2 signal (P=0.243). However, episodes of angiographic spasm were strongly associated with reduction in trend ipsilateral NIRS signal (P<0.001); furthermore, the degree of spasm (especially more than 75% vessel diameter reduction) was associated with a greater reduction in same-side NIRS signal (P<0.001) (2-level random effects regression model, Stata 8.2, Stata Corp, TX). NIRS may have a useful role to play in the detection of cerebral desaturation secondary to vasospasm during neuroendovascular procedures.

Cerebral intravascular oxygenation correlates with mean arterial pressure in critically ill premature infants

OBJECTIVES

Premature infants experience brain injury, ie, germinal matrix-intraventricular hemorrhage (GMH-IVH) and periventricular leukomalacia (PVL), in considerable part because of disturbances in cerebral blood flow (CBF). Because such infants are susceptible to major fluctuations in mean arterial blood pressure (MAP), impaired cerebrovascular autoregulation would increase the likelihood for the changes in CBF that could result in GMH-IVH and PVL. The objectives of this study were to determine whether a state of impaired cerebrovascular autoregulation could be identified reliably and conveniently at the bedside, the frequency of any such impairment, and the relation of the impairment to the subsequent occurrence of severe GMH-IVH and PVL.

PATIENTS AND METHODS

To monitor the cerebral circulation continuously and noninvasively, we used near-infrared spectroscopy (NIRS) to determine quantitative changes in cerebral concentrations of oxygenated hemoglobin (HbO(2)) and deoxygenated hemoglobin (Hb) from the first hours of life. Our previous experimental study showed a strong correlation between a measure of cerebral intravascular oxygenation (HbD), ie, HbD = HbO(2) - Hb, determined by NIRS, and volemic CBF, determined by radioactive microspheres. We studied 32 very low birth weight premature infants (gestational age: 23-31 weeks; birth weight: 605-1870 g) requiring mechanical ventilation, supplemental oxygen, and invasive blood pressure monitoring by NIRS from 1 to 3 days of age. MAP measured by arterial catheter pressure transducer and arterial oxygen saturation measured by pulse oximetry were recorded simultaneously. The relationship of MAP to HbD was quantitated by coherence analysis.

RESULTS

Concordant changes (coherence scores >. 5) in HbD and MAP, consistent with impaired cerebrovascular autoregulation, were observed in 17 of the 32 infants (53%). Eight of the 17 infants (47%) developed severe GMH-IVH or PVL or both. Of the 15 infants with apparently intact autoregulation, ie, coherence scores <.5, only 2 (13%) developed severe ultrasonographic lesions. Thus, for the entire study population of 32 infants, 8 of the 10 with severe lesions exhibited coherence scores >.5.

CONCLUSIONS

We conclude that NIRS can be used in a noninvasive manner at the bedside to identify premature infants with impaired cerebrovascular autoregulation, that this impairment is relatively common in such infants, and that the presence of this impairment is associated with a high likelihood of occurrence of severe GMH-IVH/PVL.

Intracerebral hemodynamics probed by near infrared spectroscopy in the transition between wakefulness and sleep

Previous imaging studies have shown that cerebral metabolism is gradually reduced at the beginning of sleep. Few studies have examined the sleep state transition periods from wakefulness to sleep and sleep to wakefulness. The current study used the Near Infrared Spectroscopy (NIRS) technique to describe the intracerebral hemodynamics at the frontal pole in the circumscribed period between wakefulness and sleep. Nine healthy young adults were studied during afternoon naps. Optical probes were placed on the forehead and EEG electrodes on the scalp. At sleep onset oxygenated hemoglobin (oxy-Hb) was reduced (P<0.01) and deoxygenated hemoglobin (deoxy-Hb) showed a near significant reduction (P<0.063). At sleep offset there were increases in oxy-Hb (P<0.005) and deoxy-Hb (P<0.05). In 18 of 26 transitions to sleep there was a coordinated fall in both NIRS parameters, we call the Switch Point, that lasted a mean of 3.6 s. In 32 of 36 transitions to wakefulness there was an analogous Switch Point that lasted a mean of 3.4 s. Before and after the Switch Point, changes were small and the relationship between oxy-Hb and deoxy-Hb was a combination of parallel and reciprocal fluctuations. A synchronized, parallel and short-lived change in oxy-Hb and deoxy-Hb is a discrete event in the transition period between wakefulness and sleep. The concentration of these light absorbing molecules is abruptly set to a new level at sleep-wake transitions and probably reflects the different perfusion demands of these states.

Reduced vasomotor reactivity in cerebral microangiopathy : a study with near-infrared spectroscopy and transcranial Doppler sonography

BACKGROUND AND PURPOSE

Reduction of cerebral blood flow and vasomotor reactivity (VMR) are thought to play an important role in the pathogenesis of cerebral microangiopathy. The aim of our study was to determine whether near-infrared spectroscopy (NIRS) can detect a reduced VMR in patients with microangiopathy, whether NIRS reactivities correlate with VMR assessed by transcranial Doppler sonography (TCD), and whether the differing extents of patients' microangiopathy demonstrated on MRI or CT can be distinguished by both noninvasive techniques.

METHODS

We compared the VMR of 46 patients with cerebral microangiopathy with 13 age-matched control subjects. Patients were classified with the Erkinjuntti scale. We monitored cerebral blood flow velocity (CBFV) in both middle cerebral arteries by TCD, changes in concentration of oxyhemoglobin (HbO(2)), deoxyhemoglobin (Hb) and blood volume (HbT) by NIRS, mean arterial blood pressure, and end-tidal CO(2) (EtCO(2)) during normocapnia and hypercapnia. VMRs were calculated as percent change of CBFV (NCR) and as absolute change in concentration of HbO(2), Hb, and HbT per 1% increase in EtCO(2) (CR-HbO(2), CR-Hb, CR-HbT).

RESULTS

NCR and NIRS reactivities were significantly reduced in patients with cerebral microangiopathy. CR-HbO(2) and CR-Hb showed a close correlation with NCR, and NCR and NIRS reactivities were related to the severity of cerebral microangiopathy according to the Erkinjuntti scale. Validity of NCR and NIRS reactivities were similar.

CONCLUSIONS

VMR is reduced in patients with cerebral microangiopathy and can be noninvasively assessed in basal arteries (with TCD) and brain parenchyma (with NIRS). Reduction of CO(2)-induced VMR, as measured by NIRS and TCD, may indicate the severity of microangiopathy.

Cerebral oxygenation during paediatric cardiac surgery: identification of vulnerable periods using near infrared spectroscopy

OBJECTIVE

Neurologic sequelae remain a well recognised complication of paediatric cardiac surgery. Monitoring of cerebral oxygenation may be a useful technique for identifying vulnerable periods for the development of neurologic injury. We sought to measure regional cerebral oxygenation in children undergoing cardiac surgery using near infrared spectroscopy to ascertain such vulnerable periods.

METHODS

Observational study of 18 children (median age 1.3 years) undergoing cardiac surgery (17 with cardiopulmonary bypass, 8 with circulatory arrest). Regional cerebral oxygenation was monitored using the INVOS 3100 cerebral oximeter and related to haemodynamic parameters at each stage of the procedure.

RESULTS

Prior to the onset of bypass, 10 patients had a decrease in regional cerebral oxygenation of > or = 15% points, reaching an absolute haemoglobin saturation less than 35% in 5 cases. The most common cause was handling and dissection around the heart prior to and during caval cannulation. With institution of bypass, regional cerebral oxygenation increased by a mean 18% points to a mean maximum of 75%. During circulatory arrest regional cerebral oxygenation decreased with rate of decay influenced by temperature at onset of arrest (0.25%/min at < 20 degrees C; 2%/min at > 20 degrees C). Reperfusion caused an immediate increase in regional cerebral oxygenation followed by a decrease during rewarming. Discontinuation of bypass caused a precipitous decrease in regional cerebral oxygenation in 5 patients, reaching less than 50% in 3 patients.

CONCLUSIONS

These observations suggest that the pre- and early post-bypass periods are vulnerable times for provision of adequate cerebral oxygenation. Near infrared spectroscopy is a promising tool for monitoring O2 supply/demand relationships especially during circulatory arrest.

Comparison of 13 published cytochrome c oxidase near-infrared spectroscopy algorithms

Conflicting patterns of change in cytochrome c oxidase (Cyt a,a3) redox status have been obtained between different near-infrared spectrophotometers when making measurements during tissue ischaemia. This study identifies possible sources of error that could be the cause of the discrepancy. A single set of optical density data was repeatedly analysed using each of the absorption spectra from 13 publications. In addition, changes in Cyt a,a3 redox status were calculated from the data set using three numerical methods, five computer software routines, eight displacements in wavelength, and ten incremental changes in the value of absorption or concentration coefficients. All Cyt a,a3 absorption spectra resulted in algorithms yielding similar patterns of change, regardless of the numerical method or computer process employed (0.9996 average r2, coefficient of correlation). However, a significantly different pattern of change in Cyt a,a3 redox status, resembling that reported by Piantadosi [Piantadosi CA (1993) Methods Toxicol. 2:107-126], was obtained when either the wavelengths, and/or the absorption values were altered to simulate erroneous values. This implies that all of the present algorithms are valid (including those of Piantadosi), but that microchip encoding errors may exist in the instrument used by Piantadosi.

Higher hematocrit improves cerebral outcome after deep hypothermic circulatory arrest

BACKGROUND

Various degrees of hemodilution are currently in clinical use during deep hypothermic circulatory arrest to counteract deleterious rheologic effects linked with brain injury by previous reports.

MATERIAL AND METHODS

Seventeen piglets were randomly assigned to three groups. Group I piglets (n = 7) received colloid and crystalloid prime (hematocrit < 10%), group II piglets (n = 5) received blood and crystalloid prime (hematocrit 20%), group III piglets (n = 5) received blood prime (hematocrit 30%). All groups underwent 60 minutes of deep hypothermic circulatory arrest at 15 degrees C with continuous magnetic resonance spectroscopy and near-infrared spectroscopy Neurologic recovery was evaluated for 4 days (neurologic deficit score 0, normal, to 500, brain death; overall performance category 1, normal, to 5, brain death). Neurohistologic score (0, normal, to 5+, necrosis) was assessed after the animals were euthanized on day 4.

RESULTS

Group I had significant loss of phosphocreatine and intracellular acidosis during early cooling (phosphocreatine in group I, 86.3% +/- 26.8%; group II, 117.3% +/- 8.6%; group III, 110.9% +/- 2.68%; p = 0.0008; intracellular pH in group I, 6.95 +/- 0.18; group II, 7.28 +/- 0.04; group III, 7.49 +/- 0.04; p = 0.0048). Final recovery was the same for all groups. Cytochrome aa3 was more reduced in group I during deep hypothermic circulatory arrest than in either of the other groups (group I, -43.6 +/- 2.6; group II, -16.0 +/- 5.2; group III, 1.3 +/= 3.1; p < 0.0001). Neurologic deficit score was best preserved in group III (p < 0.05 group II vs group III) on the first postoperative day, although this difference diminished with time and all animals were neurologically normal after 4 days. Histologic assessment was worst among group I in neocortex area (group I, 1.33 +/- 0.3; group II, 0.22 +/- 0.1; group III, 0.40 +/- 0.2, p < 0.05, group I vs group II; p = 0.0287, group I vs group III).

CONCLUSION

Extreme hemodilution during cardiopulmonary bypass may cause inadequate oxygen delivery during early cooling. The higher hematocrit with a blood prime is associated with improved cerebral recovery after deep hypothermic circulatory arrest.

Recent developments in cerebral monitoring--near-infrared light spectroscopy. An overview

A recent development has been the resurgence of interest in the concept of near-infrared light spectroscopy as a method of monitoring cerebral perfusion. Although this technique has been in use for 40 years, the principle has been primarily employed in peripheral pulse oximetry. Infrared light of wavelengths 600-1300 nanometres (nm) penetrate human tissue to a depth of several centimetres. Within the human brain this light is attenuated by the chromophores oxyhaemoglobin, deoxyhaemoglobin and also oxidised cytochrome a3. Positioning a near-infrared light source and a photodetector in a side by side configuration detects light attenuated and reflected in a parabolic path through the scalp, skull and brain tissue.

Cerebral Monitoring by Near-Infrared Spectroscopy

Near-infrared spectroscopy (NIRS) is a noninvasive optical monitoring technology that can provide information on relative cerebral oxyhemoglobin, deoxyhemoglobin, and oxidized cytochrome aa3 concentrations. Unlike other bedside clinical monitoring technologies, NIRS provides direct information on cerebral hemoglobin oxygenation and blood volume changes. NIRS recordings have documented changes in cerebral oxygenation in fetuses during labor, critically ill premature infants, cardiopulmonary bypass patients, and adult surgical patients. This information may improve understanding of the causes of brain injury and allow detection of inadequate oxygen delivery before brain injury occurs. Future developments in NIRS technology are likely to produce practical, quantitative bedside monitors of global and regional cerebral oxygenation.

Validation in volunteers of a near-infrared spectroscope for monitoring brain oxygenation in vivo

Cerebral oximeters based on near-infrared spectroscopy may provide a continuous, noninvasive assessment of cerebral oxygenation. We evaluated a prototype cerebral oximeter (Invos 3100; Somanetics, Troy, MI) in 22 conscious, healthy volunteers breathing hypoxic gas mixtures. Using the first 12 subjects (training group), we developed an algorithm based on the mathematic relationship that converts detected light from the field surveyed by the probe to cerebral hemoglobin oxygen saturation (CSfO2). To develop the algorithm, we correlated the oximeter result with the estimated combined brain hemoglobin oxygen saturation (CScombO2, where CScombO2 = SaO2 x 0.25 + SjO2 x 0.75 and SjO2 = jugular venous saturation). We then validated the algorithm in the remaining 10 volunteers (validation group). A close association (r2 = 0.798-0.987 for individuals in the training group and r2 = 0.794-0.992 for individuals in the validation group) existed between CSfO2 and CScombO2. We conclude that continuous monitoring with cerebral oximetry may accurately recognize decreasing cerebral hemoglobin oxygen saturation produced by systemic hypoxemia.

Amputation level assessment using lightguide spectrophotometry

The aim of this experimental study was to investigate whether lightguide spectrophotometry in the visible wavelength range in skin could be used to predict stump healing viability in patients with critical lower limb ischaemia. Remission spectra recorded at two sites (medial and lateral) on the line of a proposed trans-tibial amputation (TTA) and at 10mm intervals along the leg were analysed to give haemoglobin oxygenation (SO2). Degree of tissue hypoxia (DTH) along the leg was defined as the percentage of values along the leg less than 10% SO2. DTH and mean SO2 values were compared with skin blood flow values ((I125) 4-Iodoantipyrine clearance technique) and clinical outcome of trans-tibial amputation, (TTA) or trans-femoral amputation (TFA), in 41 patients. SO2 histograms were also measured in 12 normal subjects for comparison. The results of the study allowed the establishment of criteria for the accurate prediction of flap healing potential. Successful TTAs all displayed a minimum mean SO2 at the medial and lateral measurement sites of 30%, together with a maximum degree of tissue hypoxia of 15% along the limb. The combination of these criteria gave a sensitivity and selectivity of 1.0 for prediction of a successful outcome of TTA.

A comparison of two systems for assessing cerebral venous oxyhaemoglobin saturation during cardiopulmonary bypass in humans

The Somanetics Invos 3,100 cerebral oximeter is a new noninvasive device which measures the regional oxygen saturation of haemoglobin within the cerebral microvasculature by infrared spectroscopy. It was used in nine patients undergoing elective cardiac surgery and its results were compared with measurements of jugular venous bulb saturations obtained by the Oximetrix Opticath oximetry system. The index value of jugular venous bulb saturation was obtained by analysis of jugular bulb blood in an Il282 cooximeter. The cerebral oximeter was less accurate and precise (standard deviation of difference 14.1%) than the Oximetrix system (standard deviation of the difference 2.65%) and also demonstrated a systematic error in bias unrelated to cerebral perfusion pressure. The cerebral oximeter may therefore be less useful than jugular venous bulb saturation in the clinical management of patients undergoing cardiopulmonary bypass.

Near-infrared spectroscopic localization of intracranial hematomas

Near-infrared spectroscopy (NIRS) of the cerebral hemispheres, applied transcranially through the intact scalp and skull, was evaluated for its ability to detect the presence of an intracranial hematoma in 46 head-injured patients. In 40 patients intracranial hematomas (22 subdural, 10 epidural, eight intracerebral) were identified on computerized tomography (CT); in all 40 cases, NIRS demonstrated greater absorption of light at 760 nm on the side of the hematoma. The mean difference in optical density (OD) between the hemisphere with the hematoma and the normal hemisphere was 0.99 +/- 0.30 for epidural hematomas, 0.87 +/- 0.31 for subdural hematomas, but only 0.41 +/- 0.11 for intracerebral hematomas. In 36 patients, the asymmetry in OD resolved after surgical evacuation of the hematoma or with spontaneous resorption of the hematoma. Four patients who developed postoperative or delayed hematomas exhibited persistence of the asymmetry in OD. Six patients had only diffuse injuries and exhibited only minor differences in OD between the hemispheres, similar to 10 patients in the control group with no head injury. It appears that NIRS is useful in the initial examination of the head-injured patient, as an adjunct to CT, and in following patients postoperatively in the intensive care unit.

Human visual cortical function during photic stimulation monitoring by means of near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) was used to monitor human visual cortical function during and after photic stimulation (PS) in five adult volunteers. Cerebral blood volume (CBV) increased on the occipital surface during PS, but NIRS parameters did not change on the frontal surface. The increase in CBV was caused by a rapid increase in oxyhemoglobin with but a small increase in deoxyhemoglobin, suggesting cerebral vascular dilatation with decreased oxygen consumption. After PS stopped, CBV promptly decreased and then slightly increased again. Cytochrome aa3 did not show any change during and after PS. These phenomena reappeared following repeated PS in all five subjects. These results may represent the first step in the development of NIRS imaging.

Spectrophotometric measurements of haemoglobin saturation and concentration in skin during the tuberculin reaction in normal human subjects

A non-invasive technique employing light-guide spectrophotometry is described for the measurement of haemoglobin concentration and oxygenation in human skin. Measurements were carried out in the visible wavelength range (500-620 nm) and a series of experiments were carried out in vitro and in vivo in order to calibrate the system. Indices were derived for the measurement of relative haemoglobin concentration and absolute oxygen saturation. The technique was applied to measure the changes in these parameters occurring during the course of the tuberculin reaction in human skin. The results are compared with those from laser Doppler flowmetry and transcutaneous oxygen measurements which were carried out concurrently. Divergence between the intracapillary and tissue oxygenation during the course of the reaction provides evidence for the existence of increased diffusion resistance for oxygen; a model is proposed. The study demonstrates the potential clinical usefulness of light-guide spectrophotometry for the non-invasive investigation of tissue oxygen supply.

Noninvasive methods for estimating in vivo oxygenation

Clinical signs of hypoxia and hyperoxia are nonspecific and unreliable, yet both are potentially injurious. Noninvasive methods of oxygen assessment fill the gap between clinical observation and invasive tests, helping physicians deliver sufficient oxygen with minimum toxicity. Potential sites for oxygen measurement vary between the blood and the mitochondria; each method measures at a different site and detects different types of hypoxia and hyperoxia. Thus, values obtained by two different methods are not equivalent, giving each method unique strengths and weaknesses. We review two clinical methods (pulse oximetry and transcutaneous oximetry), as well as four experimental methods (near-infrared spectrophotometry, magnetic resonance spectroscopy, magnetic resonance saturation imaging, and time-of-flight absorbance spectrophotometry). The principles of each method and the clinical situations in which each succeeds or fails are discussed. A fundamental understanding of each method can help in deciding which methods, if any, are appropriate for a given patient and how best to correct observed oxygenation problems once they are discovered.

A method for measuring the rate of oxygen release from single microvessels

A system determining the rate of oxygen release from erythrocytes flowing in single microvessels was constructed with an inverted microscope by connecting 1) a scanning/grating spectrophotometer equipped with a photon-counting detector through a thin light guide, to obtain the visible absorption spectrum of a spot (5 microns in diameter) focused on a microvessel, 2) two photomultipliers (connected to a microcomputer via an analog-to-digital converter) through two light guides, to determine the flow velocity of erythrocytes by calculating the cross correlation between the light-intensity changes of two spots (3 microns in diameter, 5 microns apart from each other) focused on the microvessel, and 3) an image processor through a video camera, to estimate the diameter of microvessel from the digitized video images. The rate of oxygen release from single microvessels 7-25 microns in diameter in rat mesentery was measured under the superfusion of deoxygenated solution: 1) The maximal rate was obtained in capillaries, and the rate in arterial microvessels was larger than that in venous microvessels, when similar diameters were compared. 2) The rate was maximum at pH 7.0-7.2, and it decreased in more acidic and alkaline pH values. 3) The rate decreased with a decrease in temperature. The reliability of the measurement using the present apparatus was tested in detail.

Intracerebral penetration of infrared light. Technical note

Near infrared transmission spectroscopy of the human cerebrum may allow noninvasive evaluation of cerebral hemoglobin saturation in humans. The emerging spectroscopy configuration for this application is a side-by-side source-receiver construct. The ability of this spectroscopy paradigm to detect changes in intracerebral attenuation by selective injection of the infrared tracer indocyanine green into the internal and external carotid arteries during endarterectomy is evaluated in five adult patients. In all five, simultaneous two-channel infrared transmission spectroscopy over the ipsilateral hemisphere documented tracer bolus transit with a signal-to-noise ratio greater than 100:1. In addition, the two channels could be configured to achieve depth resolution of the collected spectra.

Effects of age on the metabolic, ionic and electrical responses to anoxia in the newborn dog brain in vivo

The interrelation between brain energy metabolism, electrical activity and ion homeostasis developing under experimental anoxia in animals of different ages is of significant value in the understanding of brain damage occurring under similar conditions of clinical neuropathology. The purpose of the present study was to compare brain energy states and extracellular ion homeostasis during anoxia in newborn puppies of various ages. We have developed and used a multiparametric monitoring device by which various functions of the brain can be recorded in a real-time mode from a 5 mm diameter area on the surface of the cortex. Intracellular oxygen balance was evaluated in newborn puppies of various ages by monitoring the intramitochondrial NADH redox state using a fluorescence technique. The electrical activity was measured by recording the spontaneous ECoG (electrocorticogram) and DC (direct current) steady potential. Ion homeostasis was evaluated using surface potassium and calcium mini-electrodes. Newborn puppies were anesthetized, the dura mater was removed and the multiprobe assembly was placed on the brain and cemented to the skull. Five groups of puppies (0-1, 2-7, 8-14, 15-21 days and 3-24 weeks) were exposed to 5 minutes of complete O2 deprivation (100% nitrogen exposure) and were monitored during the recovery period until all parameters returned to baseline values. The results may be summarized as follows: 1. Resting baseline levels of extracellular K+ were in the same range as described for other young and adult mammals (2.9 +/- 0.05 mM). 2. Extracellular Ca2+ levels were higher than those published for other mammals (1.6 +/- 0.07 mM). 3. During 5 minutes of anoxia, a significant increase in K+ levels was recorded. This increase was not accompanied by measurable changes in extracellular Ca2+. 4. The effect of age on the length of time to the elevation of the extracellular K+ concentration and on the rate of K+ accumulation from the onset of the anoxic condition was significant, i.e., the younger the animal the longer the time and the lower the rate. 5. The rate of energy depletion was age dependent as indicated by the rate of NADH accumulation during anoxia. However, no significant effect of age on the basal aerobic metabolism was found as measured by the maximum percent increase of NADH during anoxia.(ABSTRACT TRUNCATED AT 400 WORDS)

Cerebral oxygen monitoring with near infrared spectroscopy: clinical application to neonates

Near infrared spectroscopy is a new noninvasive optical method for bedside monitoring of cerebral oxygenation. It uses differential absorbance of near infrared light to assess relative changes in the oxidation-reduction state of cytochrome aa3, as well as changes in the amounts of oxyhemoglobin, deoxyhemoglobin, and blood volume in the monitored field. Although this technique is applicable to all ages and sizes of patients and to multiple clinical settings, the majority of clinical studies to date have focused on the neonate. These studies have demonstrated its potential for advancing neonatal care and in understanding how diseases and therapies affect cerebral oxygenation. This paper reviews the near infrared spectroscopy technique and summarizes its potential applications in the field of neonatal intensive care.

Regional cerebrovascular oxygen saturation measured by optical spectroscopy in humans

Regional cerebrovascular oxygen saturation, a quantitative measure of hemoglobin saturation in the combined arterial, venous, and microcirculatory compartments of the brain, can be measured noninvasively with near infrared spectroscopy. We assessed the sensitivity of this aggregate saturation to cerebral hypoxia during transient cerebral hypoxic hypoxia in seven human subjects. Regional cerebrovascular oxygen saturation measured over the middle frontal gyrus and analog electroencephalogram were recorded. We compared the time to achieve two end points: the earliest paroxysmal burst of theta-delta background slowing and a cerebrovascular oxygen saturation of less than 55%. Saturation fell below 55% prior to the electroencephalographic change (p less than 0.05). In a related effort, we also compared spectroscopically measured regional cerebrovascular oxygen saturation with an estimate of this value calculated from arterial and cerebral mixed venous saturation in nine patients. A positive linear relation (n = 68, R2 = 0.55, s = 4.2) was noted.

Near-infrared spectroscopy in peripheral vascular disease

Near-infrared spectroscopy has been performed on the calf muscles of 38 subjects, 21 normal controls without vascular disease and 17 patients with peripheral vascular disease. Oxygen consumption was measured in the calf by calculating the rate of conversion of oxyhaemoglobin to deoxyhaemoglobin during a period of tourniquet-induced ischaemia. Postischaemic reoxygenation was also measured. Median oxygen consumption in patients with peripheral vascular disease was 0.10 ml 100 g tissue-1 min-1, while in the control group it was 0.20 ml 100 g tissue-1 min-1 (P less than 0.03, Mann-Whitney U test). The median time taken to reach maximum oxyhaemoglobin levels after ischaemia was 40 s in patients with peripheral vascular disease and 20 s in controls (P less than 0.02). The results indicate that oxygen consumption is reduced in peripheral vascular disease. Near infrared spectroscopy is a non-invasive method for assessing metabolic improvement resulting from surgical or pharmacological treatment.

New noninvasive techniques for assessing brain oxygenation and hemodynamics

Infants who require intensive care are at considerable risk of death or long-term neurodevelopmental disability. Therefore, noninvasive methods have been sought for assessing the structure and function of the brain in the immediate newborn period. The major aims are to investigate the prevalence and mechanisms of brain-damaging lesions, to test preventive strategies and treatment, and to assign the prognosis of the infants. Several methods have proved their worth, e.g., ultrasound imaging, electroencephalography, including the testing of evoked potentials, and Doppler ultrasonography for measuring flow velocity in intracerebral vessels.

Estimation of optical pathlength through tissue from direct time of flight measurement

Quantitation of near infrared spectroscopic data in a scattering medium such as tissue requires knowledge of the optical pathlength in the medium. This can now be estimated directly from the time of flight of picosecond length light pulses. Monte Carlo modelling of light pulses in tissue has shown that the mean value of the time dispersed light pulse correlates with the pathlength used in quantitative spectroscopic calculations. This result has been verified in a phantom material. Time of flight measurements of pathlength across the rat head give a pathlength of 5.3 +/- 0.3 times the head diameter.

Intracellular monitoring of experimental respiratory failure. Collaborative Group on Intracellular Monitoring

The view that intracellular changes during oxygen depletion are the primary cause of abnormal function and altered physiology was originally proposed by Paul Bert. From that time it remains a basic assumption that hypoxia in intact animals produces alterations of cell and organ function, and that by measuring the intensity of these disturbances or the intensity of the functional impairment produced by these disturbances, a clearer understanding of the impact and consequences of oxygen depletion should emerge. At present, intracellular changes are inferred from the measurement of extracellular signals such as blood pressure, arterial oxygen tension and pH, or hemoglobin saturation, which provide mean values of changes occurring over the entire body. However, cells and organs in different parts of the body respond differently to a given degree of hypoxia or ischemia, and measurements of extracellular variables cannot provide precise information about abnormalities in any specific organ. Extracellular variables also do not reflect adaptive responses of a specific organ such as autoregulation of its blood flow and the ability to alter energy demand in response to changes in energy production. Other factors include differences in metabolic rates and dependence upon oxidative and glycolytic reactions, cell heterogeneities within a tissue or organ, redistribution of blood flow to various organs during hypoxia, or other insults, and other, yet unknown, cell-specific changes that result in a range of survival capabilities among organs. These considerations suggest the importance of direct monitoring of intracellular changes produced by cardiovascular or respiratory diseases.(ABSTRACT TRUNCATED AT 250 WORDS)