CONTRIBUTIONS OF HYPOXIA AND RESPIRATORY DISTURBANCE INDEX TO SYMPATHETIC ACTIVATION AND BLOOD-PRESSURE IN OBSTRUCTIVE SLEEP-APNEA SYNDROME

Hypertension is a common finding among obstructive sleep apnea (OSA) p atients, and is thought, to be caused by sympathetic hyperactivity. Th e present study compares the contributions of the respiratory disturba nce index (RDT) as a reflection of sleep fragmentation, and the magnit ude of: oxygen desaturation, to sympathetic activation as indexed by u rinary norepinephrine concentrations, as well as to morning and evenin g blood pressure in sleep apnea syndrome patients. Data (polysomnograp hy, blood pressure [BP], and urine catecholamines) of 38 consecutive O SA patients (age, 46 +-/ 14.5 years) were analyzed, Stepwise logistic regression analysis revealed that minimal oxygen saturation level (SaO (2)min) was a significant predictor of both morning and evening norepi nephrine levels, and that 37% of morning systolic BP variance could be accounted for by a combination of age and norepinephrine, while 20% o f the diastolic BP variance was accounted for by SaO(2)min alone. In c ontrast, RDI entered the prediction equation only when minimal oxygen saturation was rejected first. Our results indicate that the degree of nocturnal hypoxia is more closely associated with the level of sympat hetic activation and with daytime level of blood pressure than with sl eep fragmentation. (C) 1998 American Journal of Hypertension, Ltd.