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Biomedical subjects

L D Longo

Publications and source records attributed to L D Longo.

At least 163 records · Page 9Linked to original sources
PubMed1978

Water exchange in the placenta: a mathematical model.

To better understand the complicated interplay of forces affecting human placental water exchange, we developed a system of differential equations describing the flows of water, glucose, bicarbonate ion, amino acids, CO2, O2, passive cations (such as Na+ and K+), and chloride ion transplacentally and across the erythrocytes. The equations are based largely on the flux equations of irreversible thermodynamics, although Goldman's hypothesis and equation are employed to treat the ionic currents across the erythrocyte membrane. Bicarbonate ion and dissolved carbon dioxide were found to be major forces acting early in capillary transit to produce a large flow of water toward the fetus. Near the end of the capillary an almost equal amount of water returns to the mother, an effect due predominantly to the effect of glucose. For small deviations from accepted normal values, water transfer is most sensitive to changes in passive cations and chloride, followed by bicarbonate and CO2, plasma solutes (including lactate and glucose), hydrostatic pressure, and amino acids. A simple equation is given to summarize the model's results for water transfer when many factors change simultaneously. Uneven distribution of maternal-to-fetal blood flows tends to favor fetal water acquisition.

Cell Membrane Permeability↗
PubMed1977

Survival in the fetal rabbit exposed to intermittent hypoxia.

To investigate the time course and mechanisms of fetal O2 deprivation, we exposed 93 near-term, pregnant rabbits and their fetuses in utero to intermittent hypoxia. We administered a gas mixture containing 3, 4, 5 or 6 per cent O2 in N2 to a rabbit for 0.5, 1, 2, or 3 minutes, alternately with a recovery period of air breathing of 0.5, 1, 2, or 3 minutes. A given cyclical pattern was continued for 2 hours and fetal survival recorded 1 hour thereafter. Fetal survival decreased significantly at lower O2 levels, longer durations of exposure, and shorter durations of recovery intervals between exposures. Chances for survival were significantly greater among fetuses located at either end of the uterine horn.

Animals↗
PubMed1977

Carbon monoxide exchanges between the human fetus and mother: a mathematical model.

A mathematical model was developed to calculate maternal and fetal carboxyhemoglobin concentrations, [HbCO], as functions of time during and after exposure of the mother to various inspired CO concentrations. Effects of variation in alveolar ventilation rates, pulmonary and placental fiffusing capacities, cardiac output, endogenous carbon monoxide production and other factors were studied. Following a change in the inspired CO concentration, fetal HbCO lags behind maternal HbCO by several hours. During CO uptake, fetal HbCO eventually overtakes maternal, and approaches an equilibrium value as much as 10% higher than the mother's. During CO washout the fetal levels again lag behind the mothers. Results indicate that treatment of pregnant women who have elevated HbCO levels with 100% oxygen reduces the time necessary to reduce the maternal HbCO level as expected, but that the rate of fetal CO elimination is not increased as much as that of the mother. Changes in maternal and fetal HbCO were also calculated for a representative exposure to changing inspired CO levels produced by fluctuating levels of air pollution. Finally, the effects of carboxyhemoglobin on fetal oxygenation were studied, including the effects of high altitude and exercise.

Carbon Monoxide↗