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Biomedical subjects

B Chance

Publications and source records attributed to B Chance.

At least 55 records · Page 3Linked to original sources
PubMed1995

Effects of hypercapnia on ECoG and oxidative metabolism in neonatal dog brain.

The effects of hypercapnia on cerebral electrical activity and mitochondrial oxidative phosphorylation were studied in the anesthetized neonatal dog by using the electrocorticogram (ECoG) and 31P-magnetic resonance spectroscopy. Three levels of hypercapnia with arterial PCO2 values of approximately 70, 100, and 140 Torr reduced the intracellular pH of the brain from 7.11 to 6.99, 6.87, and 6.76, respectively. These levels of hypercapnia also reduced ADP concentration ([ADP]) from 21.5 to 18.1, 14.8, and 12.9 microM as well as the average ECoG power output by 20, 30, and 40%. A Michaelis-Menten relationship for the mitochondrial respiratory enzymes was fitted with [ADP] and the change in the average ECoG. The result suggests that mitochondrial respiration is regulated by [ADP] and that the in vivo Michaelis-Menten constant for ADP was 21 microM, a value close to the in vitro value. The mitochondrial maximal reaction velocity was reduced by only 10% during hypercapnia and showed no relationship with the degree of acidosis, suggesting that mitochondrial respiratory enzymes are not responsible for the inhibition of the brain electrical activity.

Adenosine Diphosphate↗
PubMed1995

Early detection of delayed traumatic intracranial hematomas using near-infrared spectroscopy.

Delayed intracranial hematomas are an important treatable cause of secondary brain injury in patients with head trauma. Early identification and treatment of these lesions, which appear or enlarge after the initial computerized tomography (CT) scan, may improve neurological outcome. Serial examinations using near-infrared spectroscopy (NIRS) to detect the development of delayed hematomas were performed in 167 patients. The difference in absorbance of light (delta OD) at 760 nm between the normal and the hematoma side was measured serially during the first 3 days after injury. Twenty-seven (16%) of the patients developed a type of late hematoma: intracerebral hematoma in eight, extracerebral hematoma in six, and postoperative hematoma in 13 patients. Eighteen of the delayed hematomas caused significant mass effect and required surgical evacuation. The hematomas appeared between 2 and 72 hours after admission. In 24 of the 27 patients, a significant increase (> 0.3) in the delta OD occurred prior to an increase in intracranial pressure, a change in the neurological examination, or a change on CT scan. A favorable outcome occurred in 67% of the patients with delayed hematomas, which suggests that early diagnosis using NIRS may allow early treatment and reduce secondary injury caused by delayed hematomas.

Adolescent↗
PubMed1994

Scattering of diffuse photon density waves by spherical inhomogeneities within turbid media: analytic solution and applications.

We present an analytic solution for the scattering of diffuse photon density waves by spherical inhomogeneities within turbid media. The analytic result is compared to experimental measurements. Close agreement between theory and experiment permits the use of the theory to determine the properties of unknown sphere-like objects embedded in turbid media. The analytic solution is extended to encompass several problems of practical interest in imaging, including the influence of multiple sources, multiple objects, and boundaries on the characterization of spherical inhomogeneities. We also extend the solution to encompass time-domain measurements.

Algorithms↗
PubMed1994

Spectroscopic, electrochemical, and ligand binding properties of the horse heart metmyoglobin His64-Tyr variant.

The distal histidine (E7) of horse heart myoglobin (Mb) has been replaced by tyrosine using site-specific mutagenesis. The resulting green Mb variant (His64-Tyr) was expressed in Escherichia coli JM101, isolated and purified to homogeneity. Spectrophotometric pH titrations of the variant exhibit a change in spectrum that occurs with a pKa of 4.7 (25 degrees C). The midpoint reduction potential of the variant is 20 mV (vs. SHE at pH 7, 25 degrees C). Cyanide and azide binding measurements indicate that the oxidized variant binds these anionic ligands with much greater affinity at pH 4.0 than at neutral pH. Extended X-ray absorption fine structure (EXAFS) spectroscopy establishes that the variant is six coordinate at pH 7.0 and pH 4.2. Higher shell contributions to the iron EXAFS observed at pH 7.0 are attributed to tyrosine. These contributions are absent at pH 4.2. Thus, the sixth heme iron ligand of the oxidized variant Mb at pH 7.0 is attributed to oxygen from the hydroxyl group of tyrosine and the sixth ligand present at pH 4.2 is attributed to the oxygen atom of a coordinated water. The EXAFS spectra, electronic absorption spectra, and ligand binding properties of the His64-Tyr Mb variant are consistent with the binding of Tyr-64 as the sixth heme iron ligand between pH 5 and 12 and with the replacement of Tyr-64 by a water molecule at low pH with a pKa of 4.7.

Animals↗
PubMed1994

Bilateral carotid artery occlusion causes periventricular leukomalacia in neonatal dogs.

At 14 days of age, seven mongrel puppies were anesthetized and bilateral carotid arteries, not only the common but also the external and internal carotid arteries, were ligated with sutures. Seven sham-operated littermates served as controls. They were sacrificed at 3 months of age, and their brains were examined macro- and microscopically. Neuropathological examination revealed dilated posterior communicating and basilar arteries in bilateral carotid artery occlusion (BCAO) animals. Six out of 7 BCAO brains had uni- or multiloculated cysts in the periventricular white matter which were surrounded by a band of GFAP-positive glial cells. Scattered small areas of gliosis were found in all experimental animals. Four BCAO brains also showed ventricular dilatation. Although the cerebral cortex seemed to be intact, the periventricular white matter and the corpus callosum were reduced in width in experimental animals. Myelination in the white matter was significantly reduced in BCAO animals compared with the controls. This study directly demonstrates that cerebral hypoperfusion alone can produce periventricular leukomalacia in neonatal dogs.

Animals↗
PubMed1994

Kinetics of ligand binding of cytochrome oxidases: a comparative study.

The plethora of microbial oxidases revealed by photochemical action spectra (Chance, B. (1989)) Biochim. Biophys. Acta 1000, 345-347) has led to detailed identification, purification and overproduction in many species, to the point where kinetic comparison of properties seems to allow structure/function deductions. This work compares the carbon monoxide recombination of five types of oxidases obtained from various organisms. The results are plotted in an Arrhenius-type plot and suggest that the carbon monoxide ligation is a sensitive indicator of the heme environment specific for an oxidase expressed under a given oxygen concentration. This survey of the carbon monoxide recombination kinetics of naturally occurring cytochrome oxidases in whole cells shows evidence for structural control of the reaction kinetics.

Animals↗
PubMed1994

Structure of the binuclear heme iron-copper site in the quinol-oxidizing cytochrome aa3 from Bacillus subtilis.

Cytochrome aa3-600 is a terminal quinol oxidase of Bacillus subtilis, belonging to the large family of structurally and functionally related respiratory enzymes to which the mitochondrial cytochrome c oxidase also belongs. However, the CuA center typical of the cytochrome c oxidases is lacking from cytochrome aa3-600. The presence of only one copper, viz. CuB of the binuclear heme iron-copper site, makes cytochrome aa3-600 especially suitable for XAS analysis of this structure. Cu and Fe XAS data for fully oxidized cytochrome aa3-600 indicate a structure for the binuclear site similar to that previously reported for mitochondrial cytochrome c oxidase (see Powers et al. (1981) Biophys. J. 34, 465-468). Heme Fea3 has a proximal histidine nitrogen ligand 2.10 +/- 0.02 A from the iron, and a distal S or Cl ligand at 2.36 +/- 0.03 A. The latter is also a ligand of CuB (2.21 +/- 0.02 A), and apparently forms a bridge between the two metals which are 3.70 +/- 0.06 A apart. CuB has two more close-lying ligands at 1.95 +/- 0.02 A, which are likely histidine nitrogens. The similarity between EXAFS of CuB and type 1 'blue' copper is contrasted to EPR and optical spectroscopic properties of CuB, and the nature of the bridging ligand is discussed.

Bacillus subtilis↗
PubMed1994

An oxidative defect in metabolic myopathies: diagnosis by noninvasive tissue oximetry.

Metabolic myopathies due to a variety of enzymatic deficiencies are well recognized. The dynamics of oxygen delivery and utilization during exercise have not been observed previously in these disorders. We used a noninvasive optical technique to measure oxygen consumption in the exercising limb in normal subjects and patients with metabolic myopathies. We measured near-infrared spectra of hemoglobin in the gastrocnemius muscle during treadmill exercise in 10 normal subjects, 1 patient with cytochrome c oxidase deficiency, 2 patients with myophosphorylase deficiency, 3 patients with phosphofructokinase deficiency, and 2 patients with carnitine palmityl transferase deficiency. All normal subjects demonstrated a sustained deoxygenation during exercise, indicating an efficient utilization of delivered oxygen. The patient with cytochrome c oxidase deficiency demonstrated consistent oxygenation during exercise, indicating an underutilization of delivered oxygen. In the patients with myophosphorylase or phosphofructokinase deficiency, abnormal oxygenation during exercise indicated an oxidative defect due to a lack of pyruvate production. In the patients with myophosphorylase deficiency, changes in oxidation coincident with glucose utilization and "the second wind phenomenon" were observed. Patients with carnitine palmityl transferase deficiency demonstrated a normal deoxygenation during exercise. Noninvasive tissue oximetry during exercise demonstrates specific abnormalities in a variety of metabolic myopathies, indicating abnormal oxygen utilization, and will be a useful addition to the clinical investigation of exercise intolerance.

Adult↗
PubMed1994

Optical imaging of human breast cancer.

Since an increasing number of breast cancers have been reported in recent years, there is a need for improving techniques for early detection of the breast cancer. Here we tested a time gated optical imaging technique as a tool for imaging human breast. Pulsed laser light at wavelengths of 780 and 830 nm are transmitted through human breast tissues and time spectra of the diffused light through the tissue are recorded over nanoseconds. Data from different locations are acquired and used to reconstruct a two dimensional image as a set of spectra in pixel form. The imaging consists of absorption and scattering coefficients, and the absorption coefficients at the two wavelengths are related to oxygen concentration and blood volume. The analysis of these coefficients is based upon the early arrival photons, therefore allowing construction of a better image than those from the current diaphanography. We demonstrate images of breast cancer, cysts created after lumpectomy, and consequences of radiation therapy. Results show that time gated optical imaging can image oxygen concentration in the cancerous and fibrotic breasts. Resolution of the imaging for smaller tumor size needs to be improved.

Adult↗
PubMed1994

Near-infrared optical imaging of tissue phantoms with measurement in the change of optical path lengths.

Using 2-D Monte Carlo simulations, we have demonstrated that values of delta < L > at varying delta t, T1 and T2 can contain significant information concerning the presence and location of a light absorbing volume in scattering media such as tissue. Specifically, we have illustrated that relationships exist between ZPW measured in x,y reflectance geometries and the absorber x,y,z position. These relationships are predictable yet can be expected to furthermore vary with (i) absorber z-dimensions, (ii) the optical properties of the surrounding media, and (iii) the source/detector separation, rho. In addition, while we have reported absorber positions located within 1 cm of tissue thickness for rho = 2 cm, One can expect interrogation of absorbers located at greater tissue thicknesses with greater rho 4. Most importantly, it is noteworthy that there exists greater opportunity to monitor specific population of photons in time-domain PMI than in frequency-domain PMI. Therefore, time-domain localization may be more sensitive than in the frequency-domain. From comparison to PMI, Figure 8 illustrates the values of delta I* computed from equation (1) versus absorber position for the same values T1 and T2 as in Figure 3. Upon inspection of Figures 3 and 8, one can see that it is easier to infer the relationship between the PSV and the absorber position from delta < L > than from delta I*. As a consequence, the measurement of delta < L > may enable creation of an inverse localization algorithm for photon migration imaging.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomedical Engineering↗
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↗