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To determine the acute effects of continuous positive airway pressure (CPAP) on baroreceptor reflex sensitivity (BRS) for heart rate during sleep in congestive heart failure (CHF) patients with obstructive sleep apnea (OSA).In eight CHF patients with OSA not previously treated with CPAP, spontaneous BRS was assessed during overnight polysomnography prior to the onset of sleep, and during stage 2 non-rapid eye movement sleep (NREM) before, during and after application of CPAP.CPAP alleviated OSA and acutely increased the slope of BRS (median, 25%,75%) [from 3.9 (3.5, 4.8) to 6.2 (4.6, 26.2) ms/mmHg, P < 0.05]. Increases in the slope of BRS persisted following withdrawal of CPAP [4.9 (4.3, 6.9) ms/mmHg, P < 0.05]. CPAP also lowered heart rate (from 81.3 ± 4.9 to 76.0 ± 5.7 bpm, P < 0.05), an effect which persisted after its withdrawal (76.7 ± 5.7 bpm, P < 0.05). Systolic blood pressure at the midpoint of the pressure range of BRS sequences fell while on CPAP (from 139 ± 8 to 120 ± 7 mmHg, P < 0.05), and remained lower following CPAP withdrawal (124 ± 9 mmHg, P < 0.05).In CHF patients with OSA, CPAP increases acutely BRS during sleep, lowers heart rate and resets the operating point for BRS to a lower blood pressure. These effects of CPAP persist after its withdrawal, suggesting that nocturnal CPAP therapy may cause sustained improvement in the neural control of heart rate.