ASSOCIATION OF LOW PACO2 WITH CENTRAL SLEEP-APNEA AND VENTRICULAR ARRHYTHMIAS IN AMBULATORY PATIENTS WITH STABLE HEART-FAILURE

Background: Central sleep apnea frequently occurs in patients with hea rt failure. Because it is not practical to perform sleep studies on al l patients, readily available laboratory tests that predict sleep apne a would be clinically useful. Arterial PCO2 has a profound influence o n breathing during sleep: When it decreases below a certain threshold, apnea occurs. Objective: To study the value of a low PaCO2 while pati ents are awake in predicting central sleep apnea in patients with stab le, treated heart failure. Design: Prospective study. Setting: Referra l sleep laboratory of a Department of Veterans Affairs Medical Center. Participants: 59 patients with left ventricular ejection fractions of 45% or less. Measurements: Arterial blood gases and hydrogen ion conc entrations were measured, and cardiac radionuclide ventriculography, H olter monitoring, and polysomnography were done. Results: Patients wer e classified as eucapnic (PaCO2 > 35 and < 44 mm Hg [n = 41]) or hypoc apnic (PaCO2 less than or equal to 35 mm Hg [n = 18]). The mean (+/- S D) hourly episodes of apnea or hypopnea (36 +/- 25 and 20 +/- 27; P = 0.015), the prevalence of central sleep apnea (78% and 39%; P = 0.01), and the mean hourly occurrences of ventricular tachycardia (Z +/- 3 a nd 0.1 +/- 0.1; P = 0.003) were significantly greater in hypocapnic pa tients than in eucapnic patients. Conclusion: Data on patients with he art failure in this study are consistent with the physiologic notion t hat a low PaCO2 results in ventilatory instability and central apnea d uring sleep. The positive predictive value of a low PaCO2 for central sleep apnea is 78%. The prevalence of ventricular tachycardia was 20 t imes greater in hypocapnic patients than in eucapnic patients.