Liquid light guides versus fiber light guides in clinical near-infrared spectroscopy.

New commercial liquid light guides have an advantage over fiberoptic bundles regarding breakage during clinical handling. We investigate the quality of clinical data collection using liquid versus fiber bundles as receivers. A four-wavelength NIRO-500 near-IR spectrophotometer is used with single-terminal fiber bundles, multiterminal fiber bundles, or a single-terminal liquid light guide as receivers. Repeated 3-min trials are done using a stable phantom, an unstable phantom, and the human forearm. A least-squares linear best-fit line and its root mean square error (RMSE), a measure of signal noise, are derived for each wavelength of each trial. The mean and standard deviations for the RMSEs of the single-terminal fiber optic receiving cable are derived for comparison standards. The liquid light guides have 51 to 174% greater signal noise with RMSEs 2 to 12 standard deviations above the mean of the single-terminal fiber bundle. The multiterminal fiber bundles have 49% less to 32% greater signal noise and had RMSEs within 1 to 4 standard deviations above the mean of the single-terminal fiber bundle. These comparisons suggest fiber optic bundles are preferable for clinical near-IR spectroscopy (NIRS) applications requiring low signal noise.

Correlation of near-infrared spectroscopy with perfusion parameters at the hepatic and systemic levels in an endotoxemic shock model.

BACKGROUND: To determine the correlation of near-infrared spectrophotometry (NIRS) readings from the liver surface with invasive measurements of blood flow and tissue perfusion parameters in an animal model of endotoxemic shock. MATERIAL/METHODS: Laparotomy was performed in 12 Yorkshire piglets, and ultrasound blood flow probes were placed on the hepatic artery and portal vein. Hepatic vein, portal vein, and femoral artery catheters were inserted for intermittent blood sampling, and a pulmonary artery catheter was inserted via the jugular vein for cardiac output measurements. Near-infrared spectrophotometry optodes were placed across the right hepatic lobe. Endotoxemic shock was induced by continuous infusion of Escherichia coli lipopolysaccharide 055: B5. Pearson correlations were calculated between the perfusion parameters and the near-infrared spectrophotometry (NIRS) readings. RESULTS: After endotoxemic shock induction, liver blood flow decreased from 144 +/- 36 to 62 +/- 24 ml*min(-1)*100 g(-1) and oxygen delivery to the liver decreased from 20 +/- 6 to 7 +/- 4 ml*min(-1)*100 g(-1). Near-infrared spectrophotometry readings of oxyhemoglobin concentration decreased by 11.7+/-15.1 micromol*L(-1), and readings of deoxyhemoglobin concentration increased by 12.3 +/- micromol*L(-1). There were significant correlations (p < 0.05 for r2 > 0.11) between the oxyhemoglobin readings and liver oxygen delivery (r2 = 0.58), liver blood flow (r2 = 0.73) and cardiac output (r2 = 0.80). Deoxyhemoglobin readings highly correlated (p < 0.05 for r2 > 0.11) with mixed venous lactate (r2 = 0.87) and with hepatic vein lactate (r2 = 0.82). CONCLUSIONS: Noninvasive near-infrared spectrophotometry measurements of hepatic oxyhemoglobin and deoxyhemoglobin correlate with liver hemodynamics as well as with global and specific organ perfusion parameters and may serve, in the future, as a useful tool to monitor tissue perfusion in septic patients.

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

UNLABELLED: 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.

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.

Cerebral oxygenation during defibrillator threshold testing of implantable cardioverter defibrillators.

BACKGROUND: The induction of ventricular fibrillation (VF) during defibrillator threshold testing of implantable cardioverter defibrillators (ICD) provokes global cerebral hypoperfusion and impaired oxygen delivery. Limited data are available on the neurophysiological effects of defibrillator threshold testing. Near infrared spectroscopy (NIRS) can noninvasively measure changes in specific chromophores, which reflect cerebral oxygenation at the intravascular and mitochondrial levels. We performed a prospective trial using NIRS to analyze cerebral cortical oxygenation during defibrillator threshold testing. METHODS: Eleven patients (men = 9; age = 64 +/- 11 years: LVEF = 44 +/- 11%) underwent subpectoral ICD implantation and defibrillator threshold testing under general anesthesia. A NIRO 300 spectrometer was used to measure the absolute changes in the concentrations of oxyhemoglobin, de-oxyhemoglobin, and cytochrome c oxidase copper moiety during each procedure. The mean arterial blood pressure was monitored simultaneously. RESULTS: The mean number of defibrillator threshold tests was two (range 2-6). Twenty-six episodes of VF (duration 13.1 +/- 9.7 seconds; cycle length 230.2 +/- 20.8 ms) and two episodes of VT (duration 15 +/- 2.8 seconds; cycle length 320 +/- 11.3 ms) were induced. Each episode of VF and VT resulted in a decrease in the mean arterial blood pressure to 23.9 +/- 7.5 mmHg (p < or = 0.05) and oxyhemoglobin (-4.2 +/- 1.7 micromol/L; p < or = 0.05) and an increase in de-oxyhemoglobin (2.7 +/- 1.4 micromol/L). There was no change in the cytochrome c oxidase copper moiety redox status (0.09 +/- 0. 30 micromol/L). CONCLUSION: Our results suggest that impaired oxygen delivery during induced VF and VT does not affect oxygen availability at the cellular intra-mitochondrial level.

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.

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.

Comparison of two spatially resolved NIRS oxygenation indices.

UNLABELLED: 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.