Search PubMed⌕ Search

Biomedical subjects

B Chance

Publications and source records attributed to B Chance.

At least 721 records · Page 40Linked to original sources
PubMedDate not supplied

Antepartum, transabdominal near infrared spectroscopy: feasibility of measuring photon migration through the fetal head in utero.

OBJECTIVE: We report the feasibility of measuring photon migration through the fetal head in utero using antepartum, transabdominal, near infrared (NIR) spectroscopy. METHODS: We developed a continuous wave (CW) spectrometer that incorporates a halogen light source, silicon photodetectors, and a differential processing circuit for antepartum, transabdominal, NIR spectroscopy. By placement of the light source and photodetector on the midline of the maternal abdomen above the fetal head at a separation (approximately 10 cm) large enough for the light to propagate through maternal and fetal tissues via multiple scattering events before being detected at the surface and the use of filtered illumination and detection at wavelengths (760 nm, 850 nm), which coincide with the absorption bands of oxygenated and deoxygenated hemoglobin in the NIR window, we performed studies to evaluate whether antepartum, transabdominal NIR spectroscopy can measure photon migration through the fetal head in utero. RESULTS: The results demonstrate that the CW spectrometer we developed can be employed to make NIR measurements from the maternal abdomen at a 10 cm source-detector separation, with an excellent signal-to-noise ratio. Furthermore, a variety of antepartum, transabdominal NIR measurements that we performed on patients undergoing a routine nonstress test demonstrate the feasibility of measuring photon migration through the fetal head in utero. CONCLUSIONS: Preliminary assessment of transabdominal NIR spectroscopy suggests that this technique can enable photon migration through the fetal head in utero. This is an important step towards the development of this technique for measuring and quantifying fetal cerebral blood oxygenation in utero.

Feasibility Studies↗
PubMedDate not supplied

31P NMR and enzymatic analysis of cytosolic phosphocreatine, ATP, Pi and intracellular pH in the isolated working perfused rat heart.

Hearts from fed male Wistar rats (200-350 g) were perfused at low and high workloads with Pi-free Krebs-Henseleit medium containing either 10 mM glucose or 10 mM glucose plus 15 mU/mL insulin. The intracellular pH by 31P NMR ranged between 6.99 and 7.02 and agreed to within 0.1 pH unit of estimates calculated using enzymatically determined total tissue HCO3-/CO2 contents. At high work, where the tissue contents of phosphocreatine (PCr) and ATP were determined on the same heart as NMR areas (n = 16), the proportionality factors, defined as the 31P NMR area units divided by the total enzymatically determined tissue content (area units/mumol/g dry wt), were 112 +/- 8 for PCr, 99 +/- 4 for gamma-ATP, 138 +/- 9 for alpha-ATP and 100 +/- 4 for beta-ATP. These values were normalized by taking beta-ATP as 100 area units/mumol/g dry wt. Since the proportionality factor for PCr and gamma- and beta-ATP were not statistically different (p less than 0.05), it was concluded that each was equally visible by 31P NMR and that no significant breakdown of PCr occurred during freezing or tissue acid extraction procedures. The cytosolic Pi estimated from NMR in glucose plus insulin perfused hearts at low and high work was 4.92 +/- 0.67 and 6.33 +/- 0.42 mumol/g dry wt. Using the near-equilibrium expression of KCK/KG + G and the metabolite levels in heart extracts, the calculated cytosolic Pi was 13.08 +/- 1.83 and 16.17 +/- 3.08 mumol/g dry wt, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMedDate not supplied

Highly scattering optical system identification via frequency response analysis of NIR-TRS spectra.

Frequency response analysis via pulse testing is often used for the characterization of engineering systems. Near infrared-time resolved spectroscopy (NIR-TRS) is a frequently used technique for the analysis of biological system properties. Since the TRS input is a very sharp photon pulse, a well designed TRS input pulse can produce a multi-frequency response over the useful frequency range for the system identification. This new approach for analyzing NIR-TRS provides new optical system parameters (e.g., magnitude ratio and phase shift at multi-frequencies, system time constant, system order, and steady state gain) that are not available by traditional TRS spectra analysis. In this paper, the basic theory of pulse reduction is introduced for the multi-modulation frequency response of TRS spectra. Homogeneous system response with various absorption and scattering properties were analyzed for the multi-system parameters. In heterogeneous systems, the position of the localized absorber is correlated with the multi-parameters, which can ultimately be used to enhance medical imaging.

Absorption↗
PubMedDate not supplied

Characterization of absorption and scattering properties for various yeast strains by time-resolved spectroscopy.

An understanding of the optical properties of biological media and cells is essential to the development of noninvasive optical studies of tissues. Unicellular organisms offer a unique opportunity to investigate the factors affecting light propagation, since they can be manipulated in ways impossible for more complex biological samples. In this study, we examined optical absorption and scattering properties of strongly multiple scattering yeast suspensions by means of near-infrared (NIR) time-resolved spectroscopy (TRS) and a sample substitution method. We determined the critical parameters for photon migration by varying the cell organelle content, the cell ploidy, the cell size, and the concentration of suspended cells. The results indicate that the photon absorption is insensitive to cell differentiation and that the cell volume is the primary factor determining light-scattering property.

Cell Count↗
PubMedDate not supplied

Multiple structures and functions of cytochrome oxidase.

X-ray absorption studies have been used to investigate the structure of the four redox centers (2Fe, 2Cu) of the terminal enzyme in the respiratory chain, cytochrome c oxidase in the resting oxidized form as well as in the functional intermediates that are freeze-trapped. Methods of x-ray fluorescence detection for these low-concentration samples together with low-temperature cryostats and simultaneous optical monitoring were developed to ensure good signal-to-noise data and sample integrity. The resting oxidized form contains a sulfur bridge between the copper and iron of the active site which are separated by approximately 3.8 A. This separation of the active site metal atoms was uniquely identified by comparison of both the iron and copper EXAFS data and iron EXAFS of the copper-depleted enzyme. In the reduced state, the CO or O2 is bound to the active site iron having a structure identical to CO or oxy hemoglobin while the sulfur remains with the active site copper. Little change in structure is observed for the other iron and copper. It is the sulfur bridged active site form that is isolated by the Yonetani and Caughy methods with greater than or equal to 85% homogeneity but not the Hartzell-Beinert or similar methods. Another form observed in the redox cycle is also fully oxidized but lacks the sulfur bridged active site with the iron of the active site having a structure identical to that of the peroxidases. This form exhibits peroxidase as well as oxidase activity, and a stable intermediate is formed with hydrogen and ethylhydrogen peroxide in which the iron of the active site is structurally similar to that of the peroxidase intermediate. The active site copper, however, does not participate in the peroxidatic role and the structures of the other iron and copper are identical to those of the sulfur bridged resting oxidized form. Thus this unique enzyme has peroxidase activity which may serve to safeguard its main oxidase function.

Animals↗
PubMedDate not supplied

Localization of a fluorescent object in highly scattering media via frequency response analysis of near infrared-time resolved spectroscopy spectra.

Frequency response analysis via pulse testing for engineering systems and near infrared (NIR) time resolved spectroscopy (TRS) for biological system characterization involve identical principles: the system of interest is disturbed by an input pulse and the output response is observed. Since a sharp pulse, such as the Dirac delta function, contains the information of multimodulation frequencies (theoretically from 0 to infinity in frequency) a narrow pulse TRS input can produce a wide range frequency response for identifying any system of interest. Currently used NIR-TRS spectral analyses either fit the spectra with a known theoretical solution or use photon mean time-of-flight. Transforming the system time domain representation to the frequency domain generates five system parameters that can be valuable for process identification utility: steady state gain, time constant, system order, and magnitude ratio and phase shift over a wide frequency range. Optical contrast agents or fluorescent agents can be used to enhance the capability of optical instruments in detecting biological heterogeneities. In this article, magnitude ratio, phase shift, and other system parameters derived from the transfer function of systems with both a fluorescent absorber and a regular absorber are correlated with the position of the absorber. This technique is important in that ultimately it can be used to enhance optical medical imaging.

Artifacts↗
PubMedDate not supplied

Investigation of the nonlinear aspects of imaging through a highly scattering medium.

The edge-spread function that is expected when imaging a sharp edge in a highly scattering medium using a time-of-flight imaging system has been investigated. Experimental results have been compared with computer simulations. The effect of scattering is to broaden the image of the edge, accompanied by an offset of the midpoint (50% transmission) of the edge. Small random errors in the measurement of the time of flight results in an increase in the offset of the edge position at very short times of flight. The offset in the midpoint of the edge is evidence of the nonlinear nature imaging process, in view of which we conclude that nonlinear algorithms will be necessary to maximize the image information available from measured intensities.

Algorithms↗
PubMedDate not supplied

Kinetic analysis of ATP-synthetase and ATPase in regenerating rabbit liver.

The activities of ATP-synthetase and ATPase in rabbit liver were evaluated by kinetic analysis of rapid changes in ATP during alteration of oxygen supply, and were compared between normal and hepatectomized rabbits. Velocity constants of ATP-synthetase and ATPase were computed on the assumption that ATP-synthetase and ATPase follow the pseudo-first order reaction of ADP and ATP, respectively. The velocity constant of ATPase increased from the control value of 0.21 to 0.48 (min-1) in the remnant rabbit liver at 24 h after 70% hepatectomy. The velocity constant of ATP-synthetase increased from the control value of 4.05 to 5.24 (min-1) after the hepatectomy. These results indicate that both ATP-synthetase and ATPase are accelerated due to liver regeneration.

ATP Synthetase Complexes↗
PubMedDate not supplied

Multiparametric evaluation of brain functions in the Mongolian gerbil in vivo.

We have developed the multiprobe assembly (MPA) by which metabolic, ionic and electrical activities can be monitored from the surface of the brain. In the present study we included optical fibers for the monitoring of intracapillary hemoglobin oxygenation by use of the Erlangen Microlight Guide Spectrophotometer (EMPHO-I) from the surface of the gerbil brain. The newly developed MPA provides simultaneous information about oxygen delivery (oxydeoxy Hb), tissue pO2 level, as well as the intracellular oxygen balance (intramitochondrial redox state). The ionic homeostasis was evaluated by monitoring extracellular K+ and Ca2+ activities reflecting the permeability changes of cation channels as well as the activities of Na+,K(+)-ATPase and other ion linked transport processes. The electrical activities were monitored by a bipolar electrocortical surface probe and DC steady potential. The subjects of the present study were Mongolian gerbils (Meriones unguiculatus) anesthetized and operated according to our routine techniques. After 30 min of recovery from the operation each gerbil was exposed to a short anoxia, graded hypoxia, ischemia as well as spreading depression. The results can be summarized as follows: 1. A clear correlation was recorded between the changes in oxydeoxy Hb spectra, tissue pO2 level and oxidation-reduction state of intramitochondrial NADH under oxygen deficiency situations (hypoxia, ischemia). 2. Blood volume changes under various perturbations monitored by various probes (366 reflectance and EMPHO-I) correlated very well with each other. 3. The degree of inhibition of Na+,K(+)-ATPase induced by oxygen deficiency could be interpreted by changes in extracellular levels of K+ measured by the surface mini-electrode. 4. Brain stimulation induced by spreading depression mechanism led to transient changes in ionic homeostasis and increase in energy requirements. The major HbO2 response was an increase in oxygenation due to the large CBF increase as monitored by the laser Doppler flowmeter. 5. Changes in oxy-deoxy Hb under fast scanning of 500-600 nm during 2-3 seconds of bilateral carotid arterial occlusion provided an indirect index for tissue O2 consumption.

Animals↗
PubMedDate not supplied

In vivo flavoprotein redox measurements of rabbit corneal normoxic-anoxic transitions.

Reversible normoxic-anoxic transitions from in vivo rabbit corneas were measured and displayed as mitochondrial flavoprotein fluorescence histograms. The flavoproteins were excited with a Helium-Cadmium laser at 441.6 nm, and the fluorescence was detected in the region of 550 nm. The laser excitation light was incident at the apex of the cornea perpendicular to the optic axis, and the emission was detected along the optic axis. Artifacts due to the motion of the globe and fluorescence from the iris and the lens were not significant. These studies demonstrate the feasibility of non-invasive in vivo monitoring of corneal anoxia-normoxia, and suggest its future applications to studies with contact lens and corneal wound healing.

Animals↗