Am. J. Respir. Crit. Care Med., Volume 164, Number 5, September 2001, 807-812

Cardiac Autonomic Control in Obstructive Sleep Apnea
Effects of Long-term CPAP Therapy

MICHAEL C. K. KHOO, VASILY BELOZEROFF, RICHARD B. BERRY, and CATHERINE S. H. SASSOON

Biomedical Engineering Department, University of Southern California, Los Angeles, California; Department of Medicine, University of Florida, Gainesville, Florida; and Department of Medicine, University of California-Irvine/VA Medical Center, Long Beach, California

To determine how long-term treatment with continuous positive airway pressure (CPAP) affects cardiac autonomic function, we measured R-R interval (RRI), respiration, and blood pressure in 13 awake patients with moderate-to-severe obstructive sleep apnea (OSA) in both supine and standing postures, before and after 3 to 9 mo of home therapy. Using visual feedback, the subjects controlled their respiration to track a randomized breathing pattern. From the RRI spectrum, we computed high-frequency power and the ratio of low-frequency to high-frequency power (LHR). To correct for differences in breathing, the average transfer gain relating respiration to RRI changes (G_RSA) and the modified low-frequency to high-frequency ratio (MLHR) were also derived. CPAP therapy did not change the conventional spectral indices of heart rate variability (HRV). However, G_RSA increased with average nightly CPAP use in supine (p < 0.01) and standing (p < 0.03) postures, whereas MLHR decreased with CPAP compliance during standing (p < 0.03). Supine mean heart rate decreased with compliance (p < 0.03). None of the estimated parameters was correlated with duration of therapy when actual CPAP use was not taken into account. These results suggest that CPAP treatment improves vagal heart rate control in patients with OSA and that the degree of improvement varies directly with compliance level.

Keywords: heart rate variability; autonomic nervous system; spectral analysis; sleep-disordered breathing; cardiovascular control

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