DEPRESSED BAROREFLEX SENSITIVITY IN PATIENTS WITH OBSTRUCTIVE SLEEP-APNEA

Muscle nerve sympathetic activity (MSA), the interval between two R-wa ves in the ECC, or the interbeat interval (RR-interval), and blood pre ssure (BP) were recorded in 10 awake patients with obstructive sleep a pnea (OSA) and in nine sex- and age-matched controls. Changes in RR-in terval and MSA, evoked by sodium nitroprusside-induced reduction of BP , were used to quantitate baroreflex sensitivity. Both the cardiac (ex pressed as the RR-interval versus mean arterial BP slope) and the musc le sympathetic (mean MSA area versus diastolic BP slope) baroreflex se nsitivity were depressed in patients as compared with controls. Cardia c baroreflex slope sensitivity (expressed as a regression coefficient) was 5.5 +/- 1.2 (mean +/- SEM) in patients and 9.6 +/- 0.96 in contro ls (p < 0.05), The corresponding figures for the sympathetic slope sen sitivity were -4.9 +/- 0.9 and -13.1 +/- 2.3, respectively (p < 0.05). Differences remained after stepwise correction for age, body mass ind ex (BMI), and to some extent BP. Resting MSA correlated with cardiac ( r = 0.67, p < 0.003) and sympathetic (r = 0.56, p < 0.025) baroreflex sensitivity in the entire study group. We conclude that OSA patients e xhibit an impaired baroreflex sensitivity to a hypotensive stimulus, w hich may represent an adaptive response to changes in BP or hypoxemia occurring in association with nocturnal apneas. Baroreflex adaptation may also contribute to the augmentation of resting MSA observed in OSA patients in this as well as in a previous study.