The threshold of the intermittent hypoxic exposure period to elicit polycythemia in rats.

ABSTRACT

It is not yet clear whether there is an intermittent hypoxia (IHx) threshold to elicit polycythemia and blood pressure elevation, and whether blood hemoglobin concentration ([Hb]) increases with an increase in the hypoxic exposure period. We have previously shown that repetitive exposure to 10% O2 for 60 min/day for up to 5 weeks does not produce polycythemia. In the present study, we evaluated the effect of IHx of 10% O2, 120 min/day for 1, 2, 3 and 4 weeks on [Hb], arterial blood pressure, heart rate and arterial blood gases in the rat. IHx of 10% O2, 120 min/day induced polycythemia at 1 week and produced a time-dependent increase in [Hb] from 0 week to 4 weeks. Arterial blood pressure significantly increased during IHx exposure for 4 weeks probably due to a combination of an increased sympathetic activity as well as increased blood viscosity. The IHx threshold for polycythemia might exist between 60 min/day and 120 min/day in this level of hypoxia.