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

Directed physiological networks in the human prefrontal cortex at rest and post transcranial photobiomodulation

Cerebral infra-slow oscillation (ISO) is a source of vasomotion in endogenic (E; 0.005-0.02 Hz), neurogenic (N; 0.02-0.04 Hz), and myogenic (M; 0.04-0.2 Hz) frequency bands. In this study, we quantified changes in prefrontal concentrations of oxygenated hemoglobin (Δ[HbO]) and redox-state cytochrome c oxidase (Δ[CCO]) as hemodynamic and metabolic activity metrics, and electroencephalogram (EEG) powers as electrophysiological activity, using concurrent measurements of 2-channel broadband near-infrared spectroscopy and EEG on the forehead of 22 healthy participants at rest. After preprocessing, the multi-modality signals were analyzed using generalized partial directed coherence to construct unilateral neurophysiological networks among the three neurophysiological metrics (with simplified symbols of HbO, CCO, and EEG) in each E/N/M frequency band. The links in these networks represent neurovascular, neurometabolic, and metabolicvascular coupling (NVC, NMC, and MVC). The results illustrate that the demand for oxygen by neuronal activity and metabolism (EEG and CCO) drives the hemodynamic supply (HbO) in all E/N/M bands in the resting prefrontal cortex. Furthermore, to investigate the effect of transcranial photobiomodulation (tPBM), we performed a sham-controlled study by delivering an 800-nm laser beam to the left and right prefrontal cortex of the same participants. After performing the same data processing and statistical analysis, we obtained novel and important findings: tPBM delivered on either side of the prefrontal cortex triggered the alteration or reversal of directed network couplings among the three neurophysiological entities (i.e., HbO, CCO, and EEG frequency-specific powers) in the physiological network in the E and N bands, demonstrating that during the post-tPBM period, both metabolism and hemodynamic supply drive electrophysiological activity in directed network coupling of the prefrontal cortex (PFC). Overall, this study revealed that tPBM facilitates significant modulation of the directionality of neurophysiological networks in electrophysiological, metabolic, and hemodynamic activities.

Directed physiological networks in the human prefrontal cortex at rest and post transcranial photobiomodulation

Cerebral infra-slow oscillation (ISO) is a source of vasomotion in endogenic (E; 0.005-0.02 Hz), neurogenic (N; 0.02-0.04 Hz), and myogenic (M; 0.04-0.2 Hz) frequency bands. In this study, we quantified changes in prefrontal concentrations of oxygenated hemoglobin ( Δ [ H b O ] ) and redox-state cytochrome c oxidase ( Δ [ C C O ] ) as hemodynamic and metabolic activity metrics, and electroencephalogram (EEG) powers as electrophysiological activity, using concurrent measurements of 2-channel broadband near-infrared spectroscopy and EEG on the forehead of 22 healthy participants at rest. After preprocessing, the multi-modality signals were analyzed using generalized partial directed coherence to construct unilateral neurophysiological networks among the three neurophysiological metrics (with simplified symbols of HbO, CCO, and EEG) in each E/N/M frequency band. The links in these networks represent neurovascular, neurometabolic, and metabolicvascular coupling (NVC, NMC, and MVC). The results illustrate that the demand for oxygen by neuronal activity and metabolism (EEG and CCO) drives the hemodynamic supply (HbO) in all E/N/M bands in the resting prefrontal cortex. Furthermore, to investigate the effect of transcranial photobiomodulation (tPBM), we performed a sham-controlled study by delivering an 800-nm laser beam to the left and right prefrontal cortex of the same participants. After performing the same data processing and statistical analysis, we obtained novel and important findings: tPBM delivered on either side of the prefrontal cortex triggered the alteration or reversal of directed network couplings among the three neurophysiological entities (i.e., HbO, CCO, and EEG frequency-specific powers) in the physiological network in the E and N bands, demonstrating that during the post-tPBM period, both metabolism and hemodynamic supply drive electrophysiological activity in directed network coupling of the PFC. Overall, this study revealed that tPBM facilitates significant modulation of the directionality of neurophysiological networks in electrophysiological, metabolic, and hemodynamic activities.

Prefrontal cortical connectivity and coupling of infraslow oscillation in the resting human brain: a 2-channel broadband NIRS study

The resting-state infraslow oscillation (ISO) of the cerebral cortex reflects the neurophysiological state of the human brain. ISO results from distinct vasomotion with endogenic (E), neurogenic (N), and myogenic (M) frequency bands. Quantification of prefrontal ISO in cortical hemodynamics and metabolism in the resting human brain may facilitate the identification of objective features that are characteristic of certain brain disorders. The goal of this study was to explore and quantify the prefrontal ISO of the cortical concentration changes of oxygenated hemoglobin (Δ[HbO]) and redox-state cytochrome c oxidase (Δ[CCO]) as hemodynamic and metabolic activity metrics in all 3 E/N/M bands. Two-channel broadband near-infrared spectroscopy (2-bbNIRS) enabled measurements of the forehead of 26 healthy young participants in a resting state once a week for 5 weeks. After quantifying the ISO spectral amplitude (SA) and coherence at each E/N/M band, several key and statistically reliable metrics were obtained as features: (i) SA of Δ[HbO] at all E/N/M bands, (ii) SA of Δ[CCO] in the M band, (iii) bilateral connectivity of hemodynamics and metabolism across the E and N bands, and (iv) unilateral hemodynamic–metabolic coupling in each of the E and M bands. These features have promising potential to be developed as objective biomarkers for clinical applications in the future.

Interplay between up-regulation of cytochrome-c-oxidase and hemoglobin oxygenation induced by near-infrared laser

Photobiomodulation, also known as low-level laser/light therapy (LLLT), refers to the use of red-to-near-infrared light to stimulate cellular functions for physiological or clinical benefits. The mechanism of LLLT is assumed to rely on photon absorption by cytochrome c oxidase (CCO), the terminal enzyme in the mitochondrial respiratory chain that catalyzes the reduction of oxygen for energy metabolism. In this study, we used broadband near-infrared spectroscopy (NIRS) to measure the LLLT-induced changes in CCO and hemoglobin concentrations in human forearms in vivo. Eleven healthy participants were administered with 1064-nm laser and placebo treatments on their right forearms. The spectroscopic data were analyzed and fitted with wavelength-dependent, modified Beer-Lambert Law. We found that LLLT induced significant increases of CCO concentration (Δ[CCO]) and oxygenated hemoglobin concentration (Δ[HbO]) on the treated site as the laser energy dose accumulated over time. A strong linear interplay between Δ[CCO] and Δ[HbO] was observed for the first time during LLLT, indicating a hemodynamic response of oxygen supply and blood volume closely coupled to the up-regulation of CCO induced by photobiomodulation. These results demonstrate the tremendous potential of broadband NIRS as a non-invasive, in vivo means to study mechanisms of photobiomodulation and perform treatment evaluations of LLLT.

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

Objectives

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

Methods

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

Results

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

Conclusions

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

Ischemia monitoring in off-pump coronary artery bypass surgery using intravascular near-infrared spectroscopy

BACKGROUND

In off-pump coronary artery bypass surgery, manipulations on the beating heart can lead to transient interruptions of myocardial oxygen supply, which can generate an accumulation of oxygen-dependent metabolites in coronary venous blood. The objective of this study was to evaluate the reliability of intravascular near-infrared spectroscopy as a monitoring method to detect possible ischemic events in off-pump coronary artery bypass procedures.

METHODS

In 15 elective patients undergoing off-pump myocardial revascularization, intravascular near-infrared spectroscopic analysis of coronary venous blood was performed. NIR signals were transferred through a fiberoptic catheter for signal emission and collection. For data analysis and processing, a miniature spectrophotometer with multivariate statistical package was used. Signal acquisition and analysis were performed before and after revascularization. Spectroscopic data were compared with hemodynamic parameters, electrocardiogram, transesophageal echocardiography and laboratory findings.

RESULTS

A conversion to extracorporeal circulation was not necessary. The mean number of grafts per patient was 3.1 +/- 0.6. An intraoperative myocardial ischemia was not evident, as indicated by electrocardiogram and transesophageal echocardiography. Continuous spectroscopic analysis showed reproducible absorption spectra of coronary sinus blood. Due to uneventful intraoperative courses, clear ischemia-related changes could be detected in none of the patients.

CONCLUSION

Our initial results show that intravascular near-infrared spectroscopy can reliably be used for an online intraoperative ischemia monitoring in off-pump coronary artery bypass surgery. However, the method has to be further evaluated and standardized to determine the role of spectroscopy in off-pump coronary artery bypass surgery.

Brain, spine, and muscle cytochrome Cu-A redox patterns of change during hypothermic circulatory arrest in swine

Past near infrared spectroscopy (NIRS) studies have reported different changes in cytochrome C oxidase (Cyt) redox status during similar interventions that cause tissue ischaemia. We investigated whether there were distinctive differences when NIRS signals were obtained simultaneously from different tissues during total circulatory arrest. Forty-two healthy 10 kg commercial swine (Sus scrofa) on cardiopulmonary bypass, each underwent 2 to 8 sequential periods of hypothermic circulatory arrest for 7.5 min. Prior to each arrest, key physiologic variables were adjusted to 1 of 81 combinations of high, normal, or low levels of core temperature, hematocrit, pH, and serum glucose. Each combination was repeated at least twice. Simultaneous NIRS monitoring yielded 202 brain, 191 spine, and 199 muscle Cyt data sets, which were then classified into 13 distinctive patterns of change. The data sets always differed between tissues in the same arrest trial and subject. Typically, brain Cyt rapidly became more reduced at the start of arrest and changed little thereafter, muscle Cyt behaved comparably to brain Cyt but continued to become reduced throughout the arrest, and spine Cyt either did not change status or gradually became more reduced over the course of arrest. The spine pattern's mean rate of change was 12 times slower than those of the brain or muscle. The Cyt patterns of change were classified into 13 groups which were significantly related to core temperature in the brain and spine, and hematocrit in muscle. The respiratory response in mitochondria during systemic circulatory arrest differs between brain, spine and muscle tissues in the same subject.

Temperature, hematocrit, pH, and glucose 4-way ANOVA of cytochrome C oxidase redox status during systemic cold circulatory arrest in swine

Various investigators using near infrared spectroscopy (NIRS) have reported differing patterns of cytochrome C oxidase (cytochrome a,a3) redox status in similar brain oxygenation studies. We investigated whether distinctive differences could be due to combinations of variations in temperature, hematocrit, pH, and glucose.

METHODS

Thirty-six healthy 10 kg commercial juvenile swine on cardiopulmonary bypass underwent 2-8 sequential periods of circulatory arrest. Prior to each arrest, key physiological variables were adjusted to match a random selection of one of 81 combinations of high, normal, or low levels of hypothermia, hematocrit, pH, and serum glucose. In the course of the study, the combinations were repeated twice to yield 162 NIRS data sets.

RESULTS

The mean rate of change in net oxidized minus reduced cytochrome a,a3 redox status in the brain following 7.5 min of ischemia was 0.49 +/- 0.26 micromol L(-1) min(-1), and, the corresponding mean magnitude of change was -1.23 +/- 0.57 micromol L(-1). The rate of change was influenced by temperature but not by hematocrit, pH, or glucose, either singly or in combination.

CONCLUSION

The respiratory response in mitochondria during systemic circulatory arrest is significantly influenced by temperature.

Comparison of two spatially resolved NIRS oxygenation indices

We compared the percentage haemoglobin oxygenation indices from two near infrared spectrophotometers (NIRS) to determine whether the devices reported similar changes in response to induced changes in oxygenation.

METHODS

24 healthy juvenile swine undergoing cardiac bypass surgery had INVOS 5100 and NIRO-300 sensors applied to the brow. Induced events included circulatory arrest, altered blood flow rate, core cooling, and re-warming.

RESULTS

The average data collection was 4 hours 36 minutes and had an r = 0.82 mean correlation between the INVOS and NIRO. The total resting baseline collection from all trials (8,590 pairs) had a correlation of r = 0.62. The average relationship between the INVOS and NIRO was non-linear: an INVOS regional oxygen saturation index (rSO2) of 0% was equivalent to a NIRO tissue oxygenation index (TOI) of 36.2%; values were equal at 56.8%; and an (rSO2) of 100% was equivalent to a TOI 85.9%. There was good or excellent agreement (r > 0.5) between the (rSO2) and TOI patterns of change during induced events in 96% of trials. The INVOS and NIRO were most closely correlated when an attenuation filter was used to obtain identical emitter/detector separations.

CONCLUSIONS

There was close agreement between the INVOS 5100 and NIRO-300 in response to major physiological change, although absolute values of (rSO2) and TOI were not identical. There was less agreement during baseline measurements or minimal physiologic change.

Near infrared spectroscopy for intraoperative monitoring of the spinal cord

STUDY DESIGN

Animal model study of three healthy commercial pigs was conducted.

OBJECTIVE

To determine whether near infrared spectroscopic monitoring of the spinal cord is feasible, and whether changes in near infrared spectroscopy correlate with changes in blood flow to the cord or operative maneuvers.

SUMMARY OF BACKGROUND DATA

Near infrared spectroscopy is a noninvasive continuous monitoring tool capable of measuring absolute changes in the concentration of three chromophores: oxygenated hemoglobin, deoxygenated hemoglobin, and cytochrome aa3, the terminal enzyme in the electron transfer chain and a measure of cellular energy equilibrium. Near infrared spectroscopy has been used to monitor the brain intraoperatively in multiple circumstances. The authors hypothesized that near infrared spectroscopy could be used to monitor the spinal cord's cellular energy equilibrium during spinal surgery (i.e., that vascular compromise could be identified before irreversible damage occurred).

METHODS

The posterior elements of the spine were exposed, and near infrared spectroscopy optodes (fiberoptic bundles) were sutured to either the lamina or the spinous processes of T9, T10, or both and directed toward the spinal cord. Interventions included manipulation of oxygen saturation and distraction of the T9-T10 disc space.

RESULTS

With reduced oxygen delivery (lower arterial oxygen saturation and blood flow), oxygenated hemoglobin concentration decreased and deoxygenated hemoglobin concentration increased. With distraction, blood volume (oxygenated hemoglobin plus deoxygenated hemoglobin) decreased, and cytochrome aa3 became more oxidized. Changes were apparent within 1 second of the intervention beginning, and recovery to the baseline of near infrared spectroscopy occurred with relief of each intervention.

CONCLUSIONS

This near infrared spectroscopy technique monitors changes in oxygenation of the spinal cord, and therefore appears capable of intraoperative warning about impending vascular compromise of the spinal cord.

Intravascular Detection of Ischemia by Near-Infrared Spectroscopy

The interruption of myocardial oxygen supply in acute ischemia alters the O2 content of coronary venous blood. The oxygenation status of coronary sinus blood was assessed by intravascular application of near-infrared spectroscopy in 10 domestic pigs under in-vivo conditions. Calibration of the catheter was performed in vitro by perfusion of blood with gas mixtures of various O2 concentrations. The catheter was placed into the coronary sinus, and anterior wall ischemia was induced by temporary occlusion of the left anterior descending coronary artery. Spectroscopic and hemodynamic data were obtained. The main differences between oxygenated and deoxygenated hemoglobin were found with O2 concentrations < 30%, corresponding to the coronary sinus blood O2 content. Spectrographs showed variations related to CO2 concentration, pH, and temperature. Spectral analysis showed significant differences between pre-ischemia and ischemia. Variations in spectrographs could be observed in both in-vitro and in-vivo experiments. The intravascular application of near-infrared spectroscopy is technically feasible and can be used as a reliable tool in detection and follow-up of tissue deoxygenation, particularly in acute myocardial ischemia.

C/C++ Coding for Matrix Pseudo Inverses in Clinical Near Infrared Spectroscopy

Near infrared spectroscopy is used clinically to investigate patterns of change in cerebral oxygenation. We have shown that differences reported between authors are likely the result of computer encoding errors in the manipulation of matrices. Current methods compute the inverse of a non-square matrix to derive chromophore concentration values, and solution of another non-square matrix to derive polynomial coefficients of a least squares best fit curve from which the first derivative can be used to estimate blood flow values. Encoding of these pseudo inverses involves too many nested looping steps to easily identify encoding errors. We have given C/C++ source code along with sample numerical values at the termination of each loop within the algorithm. This provides counter checking for future software development by other programmers, and also permits other investigators to report whether the software used for their experiments agrees with previously published material.

Effects of propofol on cerebral oxygenation during cardiopulmonary bypass in children

PURPOSE

Neurologic complications occur following cardiopulmonary bypass surgery. We conducted a randomized, controlled, single-blind study to determine the effect of propofol on the redox status of cytaa3, and to evaluate its potential for decreasing neurologic complications.

METHODS AND MATERIALS

Twenty-four children (median age: 3.3 yr; median weight: 14.4 kg) scheduled for elective cardiopulmonary bypass surgery were assigned to either the experimental group (Group P, given sufficient propofol to eliminate brain electrical activity as measured on EEG (i.e. burst suppression)) or the control group (Group C, no propofol). Near infrared spectroscopy data were collected at one-second intervals throughout the surgical procedures. Pre- and postoperative neurologic examinations were completed by a physician blinded to the group to which the patient was assigned. Change in cytochrome aa3 data at 10-min intervals (10, 20, 30, 40 min) following start of bypass were compared between groups by repeated measures analysis of variance.

RESULTS

The patterns of change in redox state of cytochrome were different between the two groups (P < 0.002). The pattern of change within Group P was similar to that in hypothermic patients in Group C. There were correlations between change in cytaa3 redox status and temperature in the control subjects. There were no gross neurologic complications in either group.

CONCLUSIONS

Propofol appears to stabilize the energy supply/demand equilibrium of the brain during cardiopulmonary bypass surgery and thus theoretically could reduce the incidence or severity of neurologic complications.

Measurement of cerebral oxygen consumption in the human neonate using near infrared spectroscopy: cerebral oxygen consumption increases with advancing gestational age

Measurements of cerebral oxygen consumption (CVO2) may improve our understanding of cerebral oxygenation, but there are few published data for sick neonates. Although cerebral maturation is associated with an increase in cerebral glucose consumption, the relationship between CVO2 and increasing gestational age has not previously been assessed in humans. The aims of this study were to evaluate a noninvasive method for the estimation of CVO2 in the neonate using near infrared spectroscopy, and to investigate the relationship between gestational age and CVO2. Twenty babies who were undergoing intensive care in the neonatal period were studied. Cerebral hemoglobin flow (CHbF) and cerebral venous oxyhemoglobin saturation (CSVO2) were measured using near infrared spectroscopy. Arterial oxyhemoglobin saturation was measure by pulse oximetry (SpO2). CVO2 was calculated from the equation: CVO2=CHbF x (SpO2 - SvO2 x 4. The median (range) CVO2 was 0.9 (0.52-1.76) mL x 100 g(-1) min(-1). There was an increase in CVO2 with advancing gestational age (n=20, p=0.55, p=0.014). We conclude that CVO2 can be estimated in sick neonates using noninvasive optical methods. The values obtained are similar to those obtained in other studies by more invasive methods, and are in agreement with values which would be expected from the known rate of cerebral glucose consumption in neonates. Mean (SD) CVO2 at 24-26 wk was 0.5 (0.18) mL x 100 g(-1) min(-1) and rose with increasing gestation to term by 0.03 mL x 100 g(-1) min(-1) per wk.