Purpose: The reported magnitude of plasma volume increase (∆%PV) following heat acclimation (HA) varies widely. Variations may result from differences in measurement techniques, season and subjects' fitness. This report compares direct and indirect measurements of ∆%PV after 10 days of HA from studies in winter (WIN, n = 8) and summer (SUM, n = 10) in men, age 21-43 yr, at two fitness levels (VO 2 max: 35 and 51 ml/min/kg). Direct measurements were made before and after HA (cycling at 30% of VO 2 max at 50 °C, for 100 min/day) by carbon monoxide (CO) rebreathing and compared with indirect estimates from changes in hematocrit, hemoglobin and plasma protein concentration. Results: Overall, ∆%PV by CO was small (2.9%) and greater in SUM than WIN (5.0 vs. 0.3%). Red cell, blood and plasma volumes/kg lean body mass increased in SUM and decreased in WIN, the difference being significant, and ∆%PV by CO was similar for high and low VO 2 max. Conclusion: Overall, indirect estimates of ∆%PV by hemoglobin and hematocrit were similar to CO, but tended to differentiate by fitness and not season. The difference in THb increase in SUM and decrease in WIN was significant. This probably accounts for the differences from the seasonal and fitness results by the direct CO method.
The effects of pentoxifylline on pulmonary hemodynamics were studied in anesthetized dogs during acute alveolar hypoxia. In Series A, 7 dogs received pentoxifylline orally (18 mg/kg/day) for 11 wk and 7 untreated dogs served as control animals. During anesthesia and controlled ventilation, acute alveolar hypoxia was induced (10 to 13% inspired O2) and pulmonary and systemic hemodynamic and blood rheologic measurements were compared with normoxia. In control dogs, cardiac index did not change during hypoxia, but pulmonary vascular resistance index (PVRI) increased 79%, erythrocyte filterability decreased significantly (p less than 0.05), and relative viscosity of blood corrected for hematocrit did not change. In the pentoxifylline-treated dogs, cardiac index increased 28% and PVRI increased only 20%; in contrast to the control dogs, relative viscosity of blood was decreased by 18% and no significant changes in filterability were observed. The increase in PVRI in relation to the drop in arterial O2 saturation was significantly larger (p less than 0.05) in the control dogs. Pentoxifylline also increased P50 by 2.8 mm Hg (p less than 0.05). In Series B, hemodynamic measurements were made during variations in blood flow (induced by restricting venous return) in 3 treated (26 mg/kg/day for 3 wk) and 3 control dogs. In these experiments, pulmonary artery pressure was significantly lower at comparable flows during both normoxia and hypoxia. In both studies, the hemodynamic effects of the drug on the systemic circulation were less than on the pulmonary circulation.(ABSTRACT TRUNCATED AT 250 WORDS)
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