THE EFFECT OF HYPOXIA ON BAROREFLEXES AND PRESSOR SENSITIVITY IN SLEEP-APNEA AND HYPERTENSION

Many persons with sleep apnea are hypertensive. Forty-two subjects of similar age and weight were divided into four groups of hypertensives and normotensives with and without sleep apnea. All subjects had heart rate, blood pressure (BP), baroreflex sensitivity and presser sensiti vity to phenylephrine measured while breathing room air or 15% oxygen. Hypoxia raised heart rate and lowered BP in all groups (p < 0.001), w ith the greatest hypotensive effect among hypertensives. Hypertensives had blunted baroreflex sensitivity, and breathing a hypoxic mixture l owered baroreflex sensitivity of all four groups (p = 0.008). The apne ic subjects tended to lower their baroreflex sensitivity more in respo nse to hypoxia and also had an enhanced presser response to phenylephr ine, whether breathing room air or 15% oxygen. Episodes of sleep apnea lead to hypoxia, an initial period of hypotension and a subsequent in crease in sympathetic nervous activity. Our studies suggest that apnei cs could have an exaggerated pressor sensitivity to norepinephrine. Th ey might also have difficulty returning BP to normal levels, because h ypoxia impaired baroreflexes.