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B Chance

Publications and source records attributed to B Chance.

At least 73 records · Page 4Linked to original sources
PubMed1994

A method to estimate the ratio of absorption coefficients of two wavelengths using phase modulated near infrared light spectroscopy.

Near infrared spectroscopy provides a very useful tool to monitor the oxygen saturation of the living tissue non-invasively. We can calculate the hemoglobin oxygen saturation within the tissue, using the ratio of the absorption coefficient (mu a) at two different wave lengths of light. Biological tissue has a very high effective scattering factor (mu s), which elongates an optical path length and makes it difficult to compute the mu a by the conventional method using continuous light. Phase Modulated Spectroscopy (PMS) measures the path length which is a complex function of the mu a and mu s. To get the ratio of the mu a, we have to eliminate the effects of the mu s from the obtained value by the PMS method. In this report, we present a theory and an experimental result which show that the inverse of the squared ratio of two phase angle differences at two different separations obtained by two different light wavelengths provides a good estimate of the ratio at these wavelength.

Algorithms↗
PubMed1994

Ethanol stimulates chemiluminescence from neutrophils in the liver.

The production of free radicals in tissues can be continually monitored by measurement of low-level chemiluminescence. In these experiments the effects of ethanol on luminol (1 microM)-enhanced chemiluminescence were recorded in isolated perfused livers from control rats, and from rats that had undergone a 30-min period of ischemia, followed by 3 h of reinstitution of blood flow. Our previous experiments showed considerable neutrophil accumulation at this time. A routine concentration of 100 mM ethanol added after 20 min of perfusion with Krebs-Henseleit solution caused an increase in chemiluminescence of about 2000 cpm above the resting level (1600 cpm) in both control livers and livers from rats after 3 h of ischemia reperfusion in vivo. However, if ethanol was added to the perfusing medium of the isolated liver after at least 1 h of in vitro perfusion, then the magnitude of the response was very much greater (peak approximately 27000 cpm) in livers that had undergone ischemia reperfusion than in control livers (peak approximately 7000 cpm). Experiments combining addition of ethanol and the potent neutrophil stimulator, phorbol myristate acetate (PMA), plus the use of rat antineutrophil serum have shown conclusively that the very large chemiluminescent response to ethanol after prolonged in vitro perfusion is due to stimulation of neutrophil radical production.

Animals↗
PubMed1994

Reactive oxygen inducing vasoconstriction in the isolated perfused rat liver.

The effect of reactive oxygen generation on intact livers was studied. Production of reactive oxygen species in perfused livers isolated from normal and endotoxin-treated rats was measured using chemically enhanced chemiluminescence. The resting state chemiluminescence of the livers increased on endotoxin administration and was maximal about 6 h after treatment. Chemiluminescence from the livers was further stimulated severalfold by inclusion of phorbol myristate acetate in the perfusion medium, reaching maximum intensity 3 h after endotoxin treatment. Oxygen consumption by the endotoxin-treated liver showed a transient increase followed by a significant decrease on phorbol myristate acetate stimulation, which was inhibited by dexamethasone. These results are consistent with the occurrence of a respiratory burst followed by oxygen-radical-species-induced vasoconstriction in the intact perfused liver. The evaluation of reactive oxygen species by resident and accumulated macrophages in the intact liver is made possible by these studies, and related effects on the liver could be conveniently and quantitatively followed using this model.

Animals↗
PubMed1994

Contribution of the mitochondrial compartment to the optical properties of the rat liver: a theoretical and practical approach.

The purpose of this work was to analyze the contribution of the mitochondria to the optical properties, i.e., light absorption and scattering, of the blood-free rat liver. Firstly, a theoretical model of the reduced scattering coefficient of the liver was performed by using the Mie theory, the Rayleigh-Debye-Gans approximation, and the electron microscopy descriptions of the liver ultrastructure. Compared with the hepatocyte volume, the nucleus and the peroxisomes, the mitochondria compartment, accounting for 22% of the liver cell volume, seemed to be the predominant factor for the light scattering of the liver. Second, by using time-resolved spectroscopy and a sample substitution method, we have measured the absorption and reduced scattering coefficients of blood-free perfused rat livers, isolated hepatocyte suspensions, and isolated mitochondria suspensions. A subsequent extrapolation of the isolated mitochondria data to the in vivo mitochondrial content and a comparison with the whole liver measurements lead to the following conclusions: 1) the mitochondria account for about 50% of the liver absorption coefficient at 780 nm (mu a = 0.25 cm-1 extrapolated from isolated mitochondria vs. 0.53 +/- 0.05 cm-1 measured for the liver); and 2) the mitochondrial compartment is the primary factor for the light scattering in the rat liver (mu s' = 15.5 cm-1 extrapolated from the isolated mitochondria versus 15.9 +/- 2.4 cm-1 measured for the liver), demonstrating the relevancy of our preliminary theoretical study.

Animals↗
PubMed1994

Non-invasive approaches to tissue bioenergetics.

It is clear that continuous light affords a very limited window of opportunity for quantitative spectrophotometry of brain tissue. However, the number of qualitative applications which are available exemplify how this extremely simple technique can be applied to important medical problems. The development of devices which can measure directly the oxygen saturation of the brain is more complicated yet affords the essential data necessary for clinical decisions on the degree of hypoxia which may be critical for neuronal survival. We can predict that such devices will be available for reliable operation shortly and will complement the existing continuous-light devices. The information from time- and frequency-domain equipment can be employed in two ways, either directly to give saturation of haemoglobin by the dual-wavelength algorithms or to provide path-length information continuously to the continuous-light devices, as many of these are commercially available and afford realistically only trend information. Thus, quantitative brain oximetry can be obtained from continuous light devices with the input of pathlength information from time- and frequency-domain systems.

Animals↗
PubMed1994

Quantitative measurement of optical parameters in the breast using time-resolved spectroscopy. Phantom and preliminary in vivo results.

RATIONALE AND OBJECTIVES: Although many optical approaches have been investigated to diagnose breast cancers, optical parameters have never been standardized in phantom experiments; thus, the detectabilities in the various approaches could not be compared. The authors measured optical properties of the breast quantitatively using time-resolved reflectance spectroscopy to optimize the optical condition of the phantom. METHODS: A time-correlated single-photon counting method was used to obtain time-response curves of a phantom and human breasts. The optical parameters were analyzed by fitting the curves to the diffusion equation. RESULTS: The parameters could be quantified within approximately 10% error in the finite breast phantom. In vivo preliminary results showed significant individual differences. CONCLUSIONS: The authors were able to measure the optical parameters quantitatively using time-resolved spectroscopy. This optical information will contribute to the investigation of photon migration in the breast.

Adult↗
PubMed1994

The high-spin cytochrome o' component of the cytochrome bo-type quinol oxidase in membranes from Escherichia coli: formation of the primary oxygenated species at low temperatures is characterized by a slow 'on' rate and low dissociation constant.

Cytochromes b and o in membrane vesicles from aerobically grown Escherichia coli were readily reduced by succinate; one cytochrome, which we propose should be called cytochrome o', reacted with CO in the Fe(II) state to give a photodissociable CO adduct. The photodissociation spectrum (photolysed minus pre-photolysis) at sub-zero temperatures had a relatively high gamma/alpha absorbance ratio, indicating a high-spin haem, which, in the reduced state, probably contributes little to the sharp alpha absorbance of the oxidase complex in membranes. Reaction with oxygen of the unliganded high-spin haem between -132 degrees C and -95 degrees C following photolytic activation gave a product that is identified as the oxygenated form, being spectrally similar to, but not identical with, the CO adduct. In membranes, the forward velocity constant at -95 degrees C was 61 M-1s-1, and the dissociation constant was 1.6 x 10(-5) M O2, as it is in intact cells. These data clearly distinguish the oxygen-trapping strategy of the cytochrome o' in this oxidase from that of cytochrome a3 and also suggest that the presence of the soluble flavohaemoglobin (Hmp) in intact cells is without effect on such measurements of the primary oxygen reaction. In view of recent findings that this oxidase complex contains predominantly one mole of haem O and one of haem B, a revised nomenclature for the oxidase complex is proposed, namely, cytochrome bo'.

Carbon Monoxide↗
PubMed1994

Simultaneous in vivo measurements of HbO2 saturation and PCr kinetics after exercise in normal humans.

Simultaneous measurements of phosphocreatine (PCr) and oxyhemoglobin (HbO2) saturation were made during recovery from exercise in calf muscles of five male subjects. PCr was measured using magnetic resonance spectroscopy in a 2.0-T 78-cm-bore magnet with a 9-cm-diam surface coil. Relative HbO2 saturation was measured as the difference in absorption of 750- and 850-nm light with use of near-infrared spectroscopy. The light source and detectors were 3 cm apart. Exercise consisted of isokinetic plantar flexion in a supine position. Two 5-min submaximal protocols were performed with PCr depletion to 60% of resting values and with pH values of > 7.0. Then two 1-min protocols of rapid plantar flexion were performed to deplete PCr values to 5-20% of resting values with pH values of < 6.8. Areas of PCr peaks (every 8 s) and HbO2 saturation (every 1 s) were fit to a monoexponential function, and a time constant was calculated. The PCr time constant was larger after maximal exercise (68.3 +/- 10.5 s) than after submaximal exercise (36.0 +/- 6.5 s), which is consistent with the effects of low pH on PCr recovery. HbO2 resaturation approximated submaximal PCr recovery and was not different between maximal (29.4 +/- 5.5 s) and submaximal (27.6 +/- 6.0 s) exercise. We conclude that magnetic resonance spectroscopy measurements of PCr recovery and near-infrared spectroscopy measurements of recovery of HbO2 saturation provide similar information as long as muscle pH remains near 7.0.

Adult↗
PubMed1994

Validation of near-infrared spectroscopy in humans.

Near-infrared (NIR) spectroscopy is a noninvasive technique that uses the differential absorption properties of hemoglobin to evaluate skeletal muscle oxygenation. Oxygenated and deoxygenated hemoglobin absorb light equally at 800 nm, whereas at 760 nm absorption is primarily from deoxygenated hemoglobin. Therefore, monitoring these two wavelengths provides an index of deoxygenation. To investigate whether venous oxygen saturation and absorption between 760 and 800 nm (760-800 nm absorption) are correlated, both were measured during forearm exercise. Significant correlations were observed in all subjects (r = 0.92 +/- 0.07; P < 0.05). The contribution of skin flow to the changes in 760-800 nm absorption was investigated by simultaneous measurement of skin flow by laser flow Doppler and NIR recordings during hot water immersion. Changes in skin flow but not 760-800 nm absorption were noted. Intra-arterial infusions of nitroprusside and norepinephrine were performed to study the effect of alteration of muscle perfusion on 760-800 nm absorption. Limb flow was measured with venous plethysmography. Percent oxygenation increased with nitroprusside and decreased with norepinephrine. Finally, the contribution of myoglobin to the 760-800 nm absorption was assessed by using 1H-magnetic resonance spectroscopy. At peak exercise, percent NIR deoxygenation during exercise was 80 +/- 7%, but only one subject exhibited a small deoxygenated myoglobin signal. In conclusion, 760-800 nm absorption is 1) closely correlated with venous oxygen saturation, 2) minimally affected by skin blood flow, 3) altered by changes in limb perfusion, and 4) primarily derived from deoxygenated hemoglobin and not myoglobin.

Absorption↗
PubMed1994

In vivo magnetic resonance spectroscopy measurement of deoxymyoglobin during exercise in patients with heart failure. Demonstration of abnormal muscle metabolism despite adequate oxygenation.

BACKGROUND: Skeletal muscle metabolic abnormalities have been described in patients with heart failure that are independent of total limb perfusion, histochemical changes, and muscle mass. However, these skeletal muscle metabolic abnormalities may result from tissue hypoxia caused by maldistribution of flow. Myoglobin is an O2 binding protein that can indirectly assess tissue hypoxia. METHODS AND RESULTS: In vivo measurement of deoxymyoglobin was performed by use of proton (1H) magnetic resonance spectroscopy in 16 heart failure (HF) (left ventricular ejection fraction = 20 +/- 6%; VO2 = 14.5 +/- 5.1 mL/kg per minute) and 7 healthy (Nl) subjects. Simultaneous phosphorus (31P) magnetic resonance spectroscopy and near-infrared spectroscopy also were obtained to examine muscle metabolism and oxygenation. Supine calf plantarflexion was performed every 4 seconds. Incremental steady-state work was performed. A second exercise protocol studied rapid incremental (RAMP) exercise with plantarflexion every 2 seconds. Arterial occlusion at end exercise provided physiological calibration for myoglobin and hemoglobin signals. With steady-state exercise, the work slope, ie, inorganic phosphorus to phosphocreatine ratios versus work, was significantly greater in patients with heart failure (Nl: 0.18 +/- 0.08; HF: 0.40 +/- 0.32 W-1; P < .05). Intracellular pH was reduced significantly at end exercise in patients but not healthy subjects. Despite these metabolic abnormalities, muscle oxygenation derived from 760- to 850-nm absorption was comparable in both groups throughout exercise. The relation of inorganic phosphorus/phosphocreatine (P1/PCr) ratio and muscle oxygenation was shifted upward in patients with heart failure such that at the same muscle oxygenation, Pi/PCr ratio in these patients was increased. No deoxymyoglobin signals were observed at rest. At maximal exercise, 4 of the healthy subjects and 3 of the patients exhibited deoxymyoglobin (P = NS). With RAMP exercise, the work slope was again significantly greater in patients with heart failure (Nl: 0.21 +/- 0.10; HF: 0.57 +/- 0.32 W-1; P < .05). Intracellular pH again was significantly decreased at end exercise in patients but not healthy subjects. Five of the healthy subjects and 3 of the heart failure patients had deoxymyoglobin signal (P = NS). With arterial occlusion, deoxymyoglobin was seen in all subjects. CONCLUSION: Abnormal skeletal muscle metabolism in patients with heart failure usually occurs in the absence of myoglobin deoxygenation, suggesting that the abnormalities are not a result of cellular hypoxia during exercise with minimal cardiovascular stress.

Aged↗
PubMed1994

In vivo detection of radicals in biological reactions.

In vivo detection of free radicals on a quantitative basis is essential for an establishment of their role in membrane, protein, and cell and tissue damage. This article compares optical methods, including chemiluminescence, electron paramagnetic resonance (EPR) and NMR methods for the study of free radicals and free radical damage, especially reperfusion injury neutrophil accumulation 6 hr after the ischemia/reperfusion insult. The chemiluminescence method is applied to an evaluation of the improved resistance to free radical stress due to transfection of creatine kinase in the mouse liver.

Animals↗
PubMed1993

Highly sensitive object location in tissue models with linear in-phase and anti-phase multi-element optical arrays in one and two dimensions.

Based upon previous observations of low-frequency photon diffusion waves within highly scattering tissue, this paper explores the "near-field" phenomena of such waves of approximately 10-cm wavelength with 200-MHz phase modulation equipment. Multiple-element source arrays consist of laser diode sources modulated at 180 degrees out of phase with respect to the other sources. The diffusing waves originating from the out-of-phase sources give, in the midplane, an amplitude null and a sharp phase transition. These may be observed in a highly scattering intralipid medium simulating the breast or brain (0.5% intralipid), 3-5 cm from the transmitting laser diodes. In the plane containing the array, there is a high sensitivity for a small volume of a hidden absorber (indocyanine green) deep within a highly scattering medium; 20 pmol in a volume of 70 microliters can be detected. Two-dimensional arrays consisting of four or more elements in two orthogonal planes give sensitivity on both axes similar to the one-dimensional array. Measurements show that in the presence of a light-absorbing object, the amplitude null and the interference plane becomes a curved surface which is deflected toward the heterogeneity. The degree of deflection is related to the volume and the absorption characteristics of the heterogeneity and provides detection of the heterogeneity, and thereby may provide localization information for the detection of small tumors within the human breast, or stroke volumes, aneurysms, and tumors in the human brain.

Brain↗
PubMed1993

Cognition-activated low-frequency modulation of light absorption in human brain.

Animal model studies indicate light-absorption changes of the exposed animal brain in response to visual stimulation. Here we report observations of red-light absorbance changes, attributable to repetitive blood concentration changes in response to stimulation in the human brain frontal region by a cognitive process. These responses are observed as low-frequency recurrence of changes by Fourier transform analysis and are attributed to blood concentration change stimulated by the increased metabolic rate of brain tissue in cognitive function. A simple, portable dual wavelength spectrophotometer was attached noninvasively to the human forehead to measure the low frequency and power spectra of fluctuations of absorbances attributed to variations of brain blood concentration in the frontal region. The responses are associated with brain activity in responses to problem solving of analogies presented visually that require an associative function in the frontal region. The method of subtraction of test -rest Fourier transforms minimizes the arterial pulse frequency contributions and identifies specific frequencies--for example, 0.8, 1.6, 1.8 Hz in 24 of 28 tests of nine individuals (85%). Tests in which no increased brain activity was elicited (rest-rest) showed small differences. It is concluded that low-frequency recurrences of brain activity linked to blood concentration increases can be detected in human subjects with an optical device of potentially for simplified tests of cognitive function in the 0- to 3-Hz region and with modifications for wider band recordings in localized tissue volumes by time-resolved spectroscopy.

Adolescent↗
PubMed1993

A method to estimate the ratio of absorption coefficients of two wavelengths using phase-modulated near infrared light spectroscopy.

Near infrared spectroscopy is a very useful tool for monitoring the oxygen saturation of living tissue noninvasively. We can calculate the hemoglobin oxygen saturation within tissue, using the ratio of the absorption coefficients (mua) at two different wave lengths of light. Biological tissue has a very high effective scattering factor (mu's), which elongates an optical path length and makes it difficult to compute the mua by the conventional method using continuous light. Phase-modulated spectroscopy (PMS) measures the path length which is a complex function of the mua and mu's. To obtain the ratio for mua, we have to eliminate the effects of the mu's from the obtained value by the PMS method. In this report, we present a theory and an experimental result which show that the inverse of the squared ratio of two phase angle differences at two different separations obtained by two different light wavelengths provides a good estimate of the ratio at these wavelengths.

Algorithms↗
PubMed1993

NMR visibility studies of N-delta proton of proximal histidine in deoxyhemoglobin in lysed and intact red cells.

Recent in vivo 1H MRS studies of muscle oxygen levels by means of myoglobin (Mb) oxygenation have necessitated an investigation of the possible contamination from deoxy-hemoglobin (Hb). To determine the contribution of Hb in these NMR measurements, we studied the NMR visibility of histidyl N-delta proton of Hb in lysed and intact RBC (red blood cell) suspensions. We found that the visibility of deoxy-Hb was significantly lower in intact RBCs (ca. 16%) than the solution form at an equivalent concentration of beta heme-iron, even though the visibility of deoxy-Hb from lysed RBC and deoxy-Mb was almost identical. Our study also shows that visibility increases with RBC swelling. Based on the difference in concentration and compartmentation, we conclude that less than 17% contribution from Hb is expected in Mb measurements in vivo. The possible mechanisms which cause the low visibility of Hb in RBCs are discussed.

Erythrocytes↗
PubMed1993

Characterization of absorption and scattering properties of small-volume biological samples using time-resolved spectroscopy.

With time-resolved spectroscopy, we develop an experimental approach by sample substitution to measure the absorption (mu a) and reduced scattering (mu's) coefficients of small-volume biological samples. To investigate the method, small-volume control samples are substituted into a large-size host medium during increases in the absorber (or scatterer) concentration of the host. By characterizing the deviation of the spectra taken with and without the sample, we determine the matching points where the sample and surrounding medium are optically identical. We show that this method can result in correct values of the mu a and mu's for the sample within 6% error if the matching conditions for both the mu a and mu's are fully realized. The results also indicate that this method can give approximate values of the mu a and mu's in a reasonable range if either the mu a or the mu's matching between the two media is realized. This method has been applied to the studies of absorption properties of a human finger and of scattering properties of yeast.

Absorption↗