Acute Normobaric Hypoxia Does Not Increase Blood Or Plasma Viscosity

BACKGROUND: It has previously been reported that chronic hypoxia increases blood viscosity. The increase is usually attributed to polycythemia-induced increases in hematocrit. However, the effect of acute hypoxia in humans on blood viscosity is unknown.OBJECTIVE: Therefore, the purpose of this study was to determine the effect of acute hypoxia, independent of changes in hematocrit, on blood and plasma viscosity.METHODS: Nine healthy volunteers breathed room air for 30 min, followed by 30 min of breathing 15% oxygen. Blood samples were collected at the end of both the normoxic and hypoxic conditions. Blood viscosity, plasma viscosity, and hematocrit were measured in each sample.RESULTS: The mean +/- SD hemoglobin oxygen saturation significantly (P < 0.05) decreased from 98 +/- 1% during normoxia to 87 +/- 2% during hypoxia. Hematocrit was essentially identical for the two conditions (42.1% vs. 42.0%). Blood viscosity was not significantly different for the two conditions with a mean of 2.89 +/- 0.17 cP during normoxia and 2.83 +/- 0.19 cP during hypoxia. Likewise, plasma viscosity was not significantly different for the two conditions with a mean of 1.19 +/- 0.04 cP during normoxia and 1.19 +/- 0.05 cP during hypoxia.CONCLUSION: Such results suggest that acute normobaric hypoxia, independent of changes in hematocrit, does not increase blood or plasma viscosity.