A CHEMOREFLEX MODEL OF RELATION BETWEEN BLOOD-PRESSURE AND HEART-RATEIN SLEEP-APNEA SYNDROME

In obstructive sleep apnea syndrome (OSAS), pronounced low-frequency ( LF) oscillations of blood pressure and interbeat interval (I) occur du ring recurrent apneas. We investigated the time relations between LF o scillations of diastolic pressure (D) and I in 12 patients with OSAS b y means of spectral analysis. A high coherency between I and D was fou nd, allowing a description of the relation by gain and phase. Oscillat ions in I and D were almost in counterphase in the LF range. Simple ph ysiological models were implemented to interpret the observed features of LF oscillations. Model 1 describes the vagal and sympathetic influ ence by the carotid body chemoreflex on the circulation. From derivati on of the frequency response of this model, gain and phase relations w ere obtained as would be expected from the action of the chemoreflex. We found that a range of phase relations can be induced by this reflex , depending on the relative vagal and sympathetic efferent influence o n the circulation. This range of phase relations was indeed observed i n 10 patients. Extended models that also included the orienting reflex (model 1a) or the baroreflex and a mechanical influence of breathing on the circulation (model 2) could not fit the data without a major co ntribution of the chemoreflex. We conclude that the relation between L F oscillations in I and D in OSAS can be explained by assuming that st imulation of the carotid body chemoreflex is the main source of these oscillations.