Clin Sci (Lond). 2007 Sep 10; [Epub ahead of print]

Continuous positive airway pressure increases heart rate variability in heart failure patients with obstructive sleep apnoea.

Patients with heart failure or obstructive sleep apnoea (OSA) have reduced high frequency heart rate variability, indicating reduced cardiac vagal modulation, a marker of poor prognosis. Continuous positive airway pressure (CPAP) abolishes OSA in patients with heart failure, but effects on daytime high frequency heart rate variability have not been determined. We hypothesized that, in heart failure patients, treatment of coexisting OSA by CPAP would increase morning high frequency heart rate variability. In 19 patients with heart failure (left ventricular ejection fraction <45%) and OSA (>/=20 apnoeas and hypopnoeas/hr of sleep), high frequency heart rate variability was quantified before and 1 month after randomization to a control or CPAP treated group. In the control group (n=7), there were no changes in high frequency heart rate variability over the 1 month study during wakefulness in the morning. In the CPAP treated group (n=12) high frequency heart rate variability increased significantly during wakefulness in the morning (from 2.43+/-0.55 to 2.82+/-0.50 log[ms 2/Hz], P=0.002) due to an increase in transfer function between changes in lung volume and changes in high frequency heart rate variability (92.37+/-96.03 to 219.07+/-177.14 ms/L, P=0.01). In conclusion, treatment of coexisting OSA by nocturnal CPAP in heart failure patients increases high frequency heart rate variability during morning wakefulness indicating improved vagal modulation of heart rate. This may contribute to improved prognosis.

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