Blood pressure and heart rate during periodic breathing while asleep at high altitude

The ventilatory and arterial blood pressure (ABP) responses to isocapnic hy poxia during wakefulness progressively increased in normal subjects staying 4 wk at 5,050 m (Insalaco CT, Romano S, Salvaggio A, Braghiroli A, Lanfran chi P, Patruno V, Donner CF, and Bonsignore G; J Appl Physiol 80: 1724-1730 , 1996). In the same subjects (n = 5, age 28-34 yr) and expedition, nocturn al polysomnography with ABP and heart rate (HR) recordings were obtained du ring the Ist and 4th week to study the cardiovascular effects of phasic (i. e., periodic breathing-dependent) vs. tonic (i.e., acclimatization-dependen t) hypoxia during sleep. Both ABP and HR fluctuated during non-rapid eye mo vement sleep periodic breathing. None of the subjects exhibited an ABP incr ease during the ventilatory phases that correlated with the lowest arterial oxygen saturation of the preceding pauses. Despite attenuation of hypoxemi a, ABP and HR behaviors during sleep in the 4th wk were similar to those in the Ist wk. Because ABP during periodic breathing in the ventilatory phase increased similarly to the ABP response to progressive hypoxia during wake fulness, ABP variations during ventilatory phases may reflect ABP responsiv eness to peripheral chemoreflex sensitivity rather than the absolute value of hypoxemia, suggesting a major tonic effect of hypoxia on cardiorespirato ry control at high altitude.