HEART-RATE DURING OBSTRUCTIVE SLEEP-APNEA DEPENDS ON INDIVIDUAL HYPOXIC CHEMOSENSITIVITY OF THE CAROTID-BODY

Background In patients with obstructive sleep apnea syndrome (OSAS). t here are cyclic fluctuations in heart rate (HR). that is, bradycardia during apnea followed by abrupt tachycardia on resumption of ventilati on. Although a previous study suggested that the degree of bradycardia observed during central apnea at high altitude was determined by indi vidual hypoxic chemosensitivity of the carotid body, it is not known w hether this is true for subjects with obstructive sleep apnea syndrome . Methods and Results First. we examined apnea-associated HR changes i n II subjects with OSAS and analyzed the relationship of the HR change during apnea (Delta HR, defined as the difference between the values at the beginning and the end of apnea) and apnea-induced nadir SaO(2) in each subject. Second. we conducted an apnea-simulation study in 7 s ubjects to examine whether the individual pattern of Delta HR could be simulated while they held their breath under different levels of arte rial oxygenation, The Delta HR was highly variable among subjects: 2 s howed an increase in HR Juring apnea, 6 a decrease, and the other 3 a borderline-type response. The slope factor of the nadir of the SaO(2)- Delta HR line obtained from each subject had a significant correlation with the HR change during breath-holding conducted under normoxia (Sp earman's rank correlation coefficient. rs=.69. P<.05) or hypoxia (rs=. 81, P<.05) but not under hyperoxia. Finally, we evaluated hypoxic chem osensitivity of the carotid body by measuring the ventilatory response to isocapnic progressive hypoxia in all subjects. The magnitude of th e ventilatory response ranged from 0.05 to 1.89 L.min(-1).%SaO(2) fall (-1) and showed a significant correlation with the slope factor of the nadir of the Sao(2)-Delta HR line (rs=-.64, P<.05). Conclusions The i ntersubject variation of the HR changes during sleep apnea can be expl ained in large part by individual hypoxic chemosensitivity of the caro tid body regardless of the type of apnea.