Biomedical subjects

W R Riddle

Publications and source records attributed to W R Riddle.

7 recordsLinked to original sources

PubMed1995

Brain proton magnetic resonance spectroscopy studies in recently abstinent alcoholics.

Chronic alcohol-dependent patients have reduced brain volumes and concomitant neurobehavioral deficits that may recover during abstinence. In 10 chronic alcoholic patients, using localized proton magnetic resonance spectroscopy, we found reliable increases during the first 3-4 weeks of abstinence in the concentrations within the superior cerebellar vermis of choline (Cho)-containing compounds relative to the neuronal marker, N-acetylaspartate (NAA). Lesser changes were observed following 1 month of abstinence, and in one of the patients studied longitudinally over 3 months, a marked reduction in the Cho/NAA ratio was associated with relapse. After detoxification, the Cho/NAA ratio correlated with a composite clinical impression of brain functions. The lowest Cho/NAA was observed in a patient with persisting alcoholic dementia, in striking contrast to reduced relative concentrations of NAA reported in dementia of the Alzheimer's type. Possible molecular explanations for these brain metabolic changes are discussed.

Adult↗

PubMed1993

Dissecting and implementing STEAM spectroscopy.

A rapid, simple method for constructing a site-specific STEAM sequence from a basic Hahn three-pulse sequence is presented. The method assures maximum signal available from the hardware.

Image Enhancement↗

PubMed1992

Evaluating flux of labeled albumin into the pulmonary interstitium of sheep lungs.

A noninvasive method was used to measure the movement of 131I-labeled albumin across the pulmonary microvascular barrier of a blood-perfused in situ sheep lung lymph preparation. After injection of labeled albumin into the blood, external measurements of gamma activity were taken for 2 h. The interstitial concentrations were calculated by applying the external activities and sampled lung lymph concentrations to a mass transport model. For the external activities and lymph activities to yield the same quantitative results, two modifications were necessary. First, lymph concentrations were corrected for transport delay from the lymphatic system. Second, externally detected radioactivity had to be corrected for the contribution of unbound nuclide. Application of a mathematical model to the data indicated the extravascular distribution volume for albumin was 79% of the pulmonary blood volume, and the extravascular distribution volume for radiolabeled iodide was 4.42 times greater than the pulmonary blood volume. The permeability-surface area product for iodide in the lung was estimated to be 0.274 ml.min-1.g blood-free dry lung wt-1. The transport delay in the lymphatic system was approximately 30-45 min and represented a volume of 1.44-2.80 ml.

Albumins↗

PubMed1990

Modeling flux of free and protein-bound radioisotopes into the pulmonary interstitium.

Several groups of investigators are using external detection of radiolabeled protein to study the flux of protein from plasma into the pulmonary interstitium. A basic assumption for these studies has been that the unbound (free) tracer concentration is small and insignificant. The purpose of this study is to evaluate how free tracer influences the determination of normalized slope index. A five-compartment model for the lung was used with transport equations for both unbound and bound nuclide flux. Parameters of the unbound and bound transport equations were varied to evaluate the sensitivity of normalized slope index to each parameter. The model was also compared with published protein flux data to investigate the validity of the transport model. Application of the model to external scan data provides a sensitive method for evaluating the flux of bound and unbound tracers into the pulmonary interstitium. We conclude that because the distribution volume for unbound tracer is large with respect to protein distribution volume, even a small amount of unbound tracer (2-5%) can create large errors in the determination of normalized slope index.

Animals↗

PubMed1990

Fluid balance in sheep lungs before and after extracorporeal perfusion.

Lung fluid balance was studied in sheep under the following conditions: 1) unanesthetized, standing in a metabolic cage; 2) anesthetized, in a supine position; 3) 1 h after extracorporeal perfusion; and 4) either 4-6 h after extracorporeal perfusion (i.e., control experiments) or 1.5 h after left atrial pressure was increased by 15 cmH2O. Lung lymph flow rate (QL), plasma and lymph concentrations for nine protein fractions, urea permeability-surface area product (PS), urea effective diffusivity (D1/2S), and extravascular lung water (VE) were measured under each condition. Bloodless wet and dry lung weights were measured at the end of each experiment. QL increased and lymph-to-plasma concentration ratio for total proteins (L/P) decreased after the sheep were anesthetized and placed in a supine position. This possibly resulted from an increase in microvascular pressure induced by anesthesia and/or reorientation of the lungs. PS, D1/2S, and VE decreased, indicating a decrease in perfused surface area associated with a decreased cardiac output or alteration in lung orientation. After 90 min of extracorporeal perfusion, no significant differences were found in QL, PS, and D1/2S compared with those measured during the anesthetized period. No changes in PS or D1/2S could be detected after an average of 4.2 h of extracorporeal perfusion. The average bloodless wet-to-dry lung weight ratio [(W-D)/D] was 3.77 +/- 0.12, well within the range for normal sheep lungs. An increase in venous pressure of 15 cmH2O produced a response similar to that observed in the unanesthetized sheep lung lymph preparation: QL increased, L/P decreased, PS and D1/2S did not increase, and VE and (W-D)/D increased slightly.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗

PubMed1989

Analysis of noninvasive macromolecular transport measurements in the lung.

Several groups of investigators are measuring transcapillary protein flux in the lung using noninvasive methods. Results from these studies are reported using several different protein transport indexes, including pulmonary transvascular transfer coefficient, relative extravascular protein, pulmonary transcapillary escape rate, protein leak index, lung transferrin index, slope index, and lung-to-heart count ratios. The purpose of this study is to discover the relationships between these indexes by employing a two-compartment theory of protein transcapillary transport in the lung. We found that all the above indexes can be related to a single index, which we call the normalized slope index. This index is the time rate of change of radioactivity originating from protein in lung interstitium divided by radioactivity arising from protein in lung plasma, normalized by this ratio at time 0, and corrected for blood volume changes. In particular the normalized slope index is shown to be the same as pulmonary transcapillary escape rate under normal sampling conditions and is relatively unaffected by changes in interstitial volume. The response of the normalized slope index to changes in microvascular pressure and microvascular permeability is explored by applying a two-pore model of the microvascular barrier. Results indicate that the normalized slope index is relatively insensitive to changes in microvascular pressure but is greatly affected by changes in microvascular permeability (i.e., changes in large-pore size or number). Since all published leak indexes are related, we would encourage all investigators in the field to adopt a single leak index. We recommend that when a two-compartment model is applied to external detection data, the results be expressed as pulmonary transcapillary escape rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Lung↗

PubMedDate not supplied

Removing effects of eddy currents in proton MR spectroscopy.

The use of pulsed gradients to define a volume of interest for localized magnetic resonance spectroscopy produces magnetic field perturbations which distort both the free induction decay and the spectrum after Fourier transformation. A technique is presented that removes the artifacts from eddy currents from a sampled free induction decay. To linearize the phase, the nonlinear phase of a reference free induction decay is subtracted from the phase of a sample free induction decay. Next, to move the frequency to resonance and perform a zero-order phase correction, the line fit from a linear regression is subtracted from the phase. After reconstructing the free induction decay, the resulting frequency spectra are sorted into absorption mode and dispersion mode components.

Artifacts↗