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Biomedical subjects

L D Homer

Publications and source records attributed to L D Homer.

At least 55 records · Page 3Linked to original sources
PubMed1984

Pulmonary oxygen toxicity in awake dogs: metabolic and physiological effects.

Because the pulmonary endothelium is sensitive to O2-induced damage, we studied in vivo angiotensin-converting enzyme (ACE) activity in the lungs of 14 catheterized unanesthetized dogs exposed either to air or continuous 100% O2 at 1 ATA. For 5 days, or until the dog died, we measured physiological variables and lung ACE activity. The metabolic data were analyzed with a model that accounted for the effect of changes in cardiac output. Nine dogs breathing O2 lived 88 +/- 21.8 (SD) h and except for blood O2 tensions were indistinguishible from controls until development of a terminal response lasting only a few hours. Hemodynamic instability preceded a precipitous terminal change in blood gas tensions which resulted in impairment of arterial oxygenation, hypercapnia, and acidosis. Plasma renin activity increased. The metabolic capacity of the pulmonary endothelium of O2-exposed animals decreased with time so that after 96 h it was 50% of the control. That of five control animals did not change with time. Thus changes in lung ACE activity preceded alterations in hemodynamics or gas exchange, and the contributions of each are discussed.

Angiotensin I↗
PubMed1983

Diffusion of oxygen in slices of rat brain.

A new method for the joint determination in tissue slices of the diffusion coefficient of oxygen (D) and the fluorescence-quenching coefficient (K') of pyrenebutyric acid (PBA) is introduced. Values of D and K' in rat brain at temperatures (Tc) from 20 to 40 degrees C were determined and referred to the values in water. D = DH2O (0.72 - 0.0074 Tc) +/- 0.079 X 10(-5) cm2/s for 80-microns slices. D = DH2O (1.01 - 0.0074 Tc) +/- 0.12 X 10(-5) cm2/s for 160-microns slices. K' = K'H2O (0.72 + 0.025 Tc) +/- 0.56 X 10(-4) mmHg-1. The temperature dependence of both these parameters in tissue is different from their temperature dependence, and comparison with parameter values obtained with other methods leads us to conclude that factors affecting the diffusion of oxygen in tissue are heterogenous rather than homogenous. The variation in the different parameters, D and K', probably exceeds a twofold range.

Animals↗
PubMed1983

Transient solutions of equations for countercurrent capillary exchange.

A model for passive countercurrent capillary exchange is presented, and solutions for transient responses are obtained. The model is applied to an analysis of hydrogen gas exchange in the renal medulla. Estimates of medullary flow per gram tissue are in reasonable agreement with estimates obtained with vascular tracers and similar to the values for whole kidney. Semilog plots of tissue washout curves appear nearly linear but will overestimate flow if the countercurrent process is inefficient and will underestimate flow if the countercurrent exchange is efficient. Analysis of the countercurrent process also provides some insights into the importance of tracer exchange between capillaries in vascular beds not arranged in orderly countercurrent networks. Capillaries in other vascular beds that are close enough together to permit considerable exchange of inert gas tracers may simulate countercurrent effects if some of the adjacent capillaries are in countercurrent or staggered cocurrent arrangements.

Animals↗
PubMed1982

Homogeneous nucleation of gas bubbles in vivo.

Several current theories of decompression sickness (DCS) presume the preexistence of gas bubble nuclei in tissue, because the de novo nucleation of gas bubbles in the body is thought to be theoretically impossible. Reexamination of nucleation theory reveals the overwhelming importance of two parameters: gas supersaturation and tissue surface tension (gamma). For the high gamma of pure water nucleation theoretically requires more than 1,000 ATA supersaturation. Lower values of gamma allow nucleation to occur with vastly smaller supersaturations. Application of homogeneous nucleation theory can provide reasonable fits to both rat and human pressure-reduction data with values of gamma within the range reported for biological fluids (below 5 dyn/cm). The initial bubble sizes predicted are 0.1 micron or less. The presence of heterogeneous sites, for example crevices and lipid surfaces, makes nucleation even more likely.

Decompression Sickness↗
PubMed1981

Distribution of xenon gas exchange rates in dogs.

The kinetics of xenon gas uptake and elimination in seven anesthetized dogs were studied by simultaneous external recording of gas concentrations in several thousand anatomic sites during 7-h experiments. The data were analyzed by a previously described method of extracting moments of the distribution of gas residence times. Mean residence times (first moment) varied by more than a factor of 50 within a single animal: the fastest exchange was in the lungs (under 2 min), and progressively slower exchange occurred in the brain, spinal cord, ears, peripheral joints, and shoulder (over 2 h). Variance of the residence time (second moment) was found to approximate four times the mean residence time squared. This ratio was nearly the same throughout the body. Indications of unexpectedly high xenon solubility in the ear and joint regions were also found.

Animals↗
PubMed1980

Comparison of two- and four-magnetometer methods of measuring ventilation.

Two computerized methods of measuring ventilation from four pairs magnetometers placed anteroposteriorly (AP) and laterally on the rib cage and abdomen were compared with a method that employs two pairs of magnetometers placed AP on the rib cage and abdomen. This comparison showed that the most accurate method of measuring ventilation employed four-magnetometer pairs and a model that assumes that the rib cage and abdomen may be approximated by elliptical cylinders. In 10 subjects of widely varying body habitus, this method predicted lung volume change accurately during quiet breathing (R greater than 0.98) and during vital capacity maneuvers (R greater than 0.97). With this technique, we have confirmed that the rib cage contributes the majority (74%) of the volume change in the upright position. Additionally, we have shown that this method is sufficiently accurate to be used as a method of monitoring ventilation under a wide variety of tidal volumes, postures, and exercise states.

Abdomen↗
PubMed1980

Solubility of inert gases in biological fluids and tissues: a review.

Data have been tabulated from more than 150 references on the solubility of inert gases in fluids and tissues of biological interest. Thirty-two gases have been studied in blood with measured solubility ranging from 0.005 to 16 ml of gas at 37 degrees C per ml of blood per ATA (Ostwald coefficient). For most gases, solubility in other tissues such as muscle or brain is between 60% and 300% of blood solubility. Measured solubilities in biological tissues do not correspond well to solubility in water and oil. Most gases decrease in solubility by 1%-6% for each degree C rise in temperature. The effect of pressure on solubility has not been well studied, and only crude estimates can be obtained by using methods of chemical thermodynamics.

Humans↗
PubMed1979

An explanation of impaired solute mixing in extracellular fluid after hemorrhagic hypotension.

A theory is presented suggesting that the slowed rate of solute dispersion in the extracellular fluid (ECF) space during or after hemorrhagic shock is largely due to a depressed cardiac output, and that mixing may be improved by any fluid therapy that decreases the mean recirculation time for the solute. This theory was tested by comparing solute mixing rates after treatment of shocked anesthetized dogs with either protein-free Ringer solution with Ringer solution containing 5% albumin. The rate of mixing was determined by computer analysis of the disappearance of an ECF tracer from plasma. Compared with Ringer-treated dogs, the albumin-treated group had a faster rate of tracer equilibration, larger cardiac plasma output, and smaller, approximately normal ECF volume. It was concluded that the abnormal dispersion of solute within the ECF space seen during or after hypotension can be corrected simply by restoring the cardiac output, and that albumin-containing fluid may be more effective in this regard than crystalloid solution alone.

Animals↗
PubMed1979

Stochastic description of inert gas exchange.

Data from experiments measuring the rate of uptake and elimination of nonmetabolic gas in living organs are usually analyzed by several exponential time constants or their equivalent half-times (i.e, exponential series analysis). To avoid the limitations of this technique, we have formulated a method that combines analysis by moments of distribution with transfer function techniques, which makes the analysis independent of any mechanistic model. This method is an improvement over previous methods because it allows better comparison of gas exchange experiments and better prediction of gas exchange in the formulation of diver decompression schedules. Measurements of radioxenon uptake and elimination in two areas of a dog are presented. Analysis of the same organ response by both methods showed a fivefold variation in derived exponential time constants compared with less than 10% variation among moment descriptors.

Animals↗
PubMed1978

The influence of pH on the sex-related differences in renal organic ion transport.

The stimulating effects of elevated medium pH and androgen on in vitro transport of p-aminohippurate and N-methylnicotinamide (NMN) were additive, although the androgenic effect was pH-dependent only in the case of NMN. The similarity of response of the 2 systems supports the idea of a common passive efflux pathway for organic anions and cations.

Aminohippuric Acids↗
PubMed1978

Hemorrhagic shock treatment with hot intravenous fluid in dogs.

In hot climates, only high temperature fluids (are greater than 100 F) may be available for treatment of blood loss shock in combat casualties. Can the hot fluid be used safely and effectively? We compared hot Ringer's lactate (51.7% C/125 F) resuscitation (n=10) to body-temperature (100 F) fluid resuscitation (n=10) in a hemorrhagic shock dog model. One liter of 125 F fluid, as part of the resuscitation, did not cause hyperthermia, red blood cell hemolysis, or any significantly different response in the cardiovascular system when compared to body-temperature fluid. All animals in both groups survived. These findings suggest that battlefield use of hot fluids in controlled amounts can be safe and effective for treatment of blood loss shock in human combat casualties.

Animals↗