Daytime blood pressure elevation after nocturnal hypoxia

The purpose of this study was to investigate whether nocturnal hypoxia caus es daytime blood pressure (BP) elevation. We hypothesized that overnight ex posure to hypoxia leads the next morning to elevation in BP that outlasts t he hypoxia stimulus. We studied the effect on BP of two consecutive night e xposures to hypobaric hypoxia in 10 healthy normotensive subjects. During t he hypoxia nights, subjects slept for 8 h in a hypobaric chamber at a simul ated altitude of 4,000 m (barometric pressure = 462 mmHg). Arterial O-2 sat uration and electrocardiogram were monitored throughout the night. For 30 m in before the nocturnal simulated ascent and for 4 h after return to baseli ne altitude the next morning, BP was measured every 5 min while the subject was awake. The same measurements were made before and after 2 normoxic nig hts of sleep in the hypobaric chamber at ambient barometric pressure (745 m mHg). Principal components analysis was applied to evaluate patterns of BP response after the second night of hypoxia and normoxia. A distinct pattern of diastolic BP (DBP) elevation was observed after the hypoxia night in 9 of the 10 subjects but in none after the normoxia night. This pattern showe d a mean increase of 4 mmHg in DBP compared with the presleep-awake baselin e in the first 60 min and a return to baseline by 90 min. We conclude that nocturnal hypoxia leads to a carryover elevation of daytime DBP.