ROLE OF DAYTIME HYPOXEMIA IN THE PATHOGENESIS OF RIGHT HEART-FAILURE IN THE OBSTRUCTIVE SLEEP-APNEA SYNDROME

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Abstract
Although right heart failure is a recognized complication of obstructive sleep apnea, the incidence and pathogenesis of this complication has not been established. Patients (50) with obstructive sleep apnea were studied to determine the incidence of right heart failure and the factors involved in its development. Six patients (12%) had right heart failure. There were no differences in the number of apneas between those with right heart failure (mean .+-. SE, 30 .+-. 10 per h sleep) and those without right heart failure (33 .+-. 4 per h sleep). Mean nocturnal O2 saturation was lower in patients with right heart failure (76 .+-. 3%) than in those without right heart failure (90 .+-. 1%; P < 0.001). Patients with right heart failure also had a substantially lower awake arterial PO2 [partial pressure O2] (52 .+-. 4 mmHg vs. 75 .+-. 2 mmHg; P < 0.001) and a higher PCO2 (51 .+-. 2 mmHg vs. 36 .+-. 1 mmHg; P < 0.001) than those without right heart failure. Severe nocturnal hypoxemia in the absence of diurnal hypoxemia was not associated with right heart failure. Daytime hypoxemia in the patients with right heart failure was associated with a higher residual volume (P < 0.001) and lower forced expiratory volume in 1 s (P < 0.001) than in the patients without right heart failure. Sustained hypoxemia and/or hypercapnia over a 24-h period is a necessary prerequisite for the development of right heart failure in patients with obstructive sleep apnea, and that diffuse airway obstruction plays a major role in causing such hypoxemia.