Continuous positive airway pressure therapy lowers vagal tone in patients with obstructive sleep apnoea-hypopnoea syndrome.

INTRODUCTION: Sleep apnoea, which constitutes a major social problem because of its high prevalence and its emerging association with cardiovascular morbidity and mortality, is known to affect autonomic nervous system activity. We assessed the hypothesis that treatment of sleep apnoea patients with continuous positive airway pressure (CPAP) alters the indices of heart rate variability (HRV) that reflect sympathetic and parasympathetic autonomic nervous system activity. METHODS: We studied 26 patients (18 men, aged 49.2 +/- 7.6 years) with obstructive sleep apnoea-hypopnoea syndrome. In all patients, a 24-hour Holter recording was obtained one week before initiation of CPAP treatment and another one two months later. From these recordings we assessed the time domain indices of HRV (pNN50, rMSSD, SDNN, SDANN, SD) during the day (08:00-23:00) and during the night hours (23:00-08:00) as well as their post-treatment changes. The same HRV indices were also assessed in a group of 19 age and sex matched controls, without sleep apnoea. RESULTS: No significant differences in the HRV indices were observed during the daytime hours, while during the night both pNN50 and rMSSD were significantly higher in patients compared to controls (19.5 +/- 12.5 vs. 13.8 +/- 9.7, p=0.001, for pNN50 and 54.7 +/- 23.1 vs. 44.0 +/- 15.9, p=0.001, for rMSSD, for patients and controls respectively). No such differences were observed in any of the monitored indices following CPAP treatment. CONCLUSIONS: The indices that reflect parasympathetic activity are increased during the night in patients with obstructive sleep apnoea syndrome. CPAP treatment reduces the night time vagal indices of HRV to resemble those of normal controls. The reduction of parasympathetic activity may be one of the mechanisms responsible for the alleviation of bradyarrhythmic episodes following the initiation of CPAP therapy.

Atrial overdrive pacing for the obstructive sleep apnea-hypopnea syndrome.

BACKGROUND: The role of atrial overdrive pacing (AOP) in sleep apnea remains uncertain. We prospectively evaluated the effect of AOP after 24 hours and after one month in patients with the obstructive sleep apnea-hypopnea syndrome and compared it with the use of nasal continuous positive airway pressure (n-CPAP). METHODS: We studied 16 patients with a moderate or severe case of the obstructive sleep apnea-hypopnea syndrome (baseline mean apnea-hypopnea index, 49) and normal left ventricular systolic function in whom a dual-chamber pacemaker had been implanted. After 48 hours, the patients were randomly assigned to AOP (pacing at 15 bpm above the spontaneous mean nocturnal heart rate) or backup atrial pacing (pacing at a heart rate below 40 bpm); the latter group began n-CPAP therapy one day later. After one month, the two groups switched therapies and were followed for an additional month. Polysomnographic studies were performed at baseline, on the first night after randomization, at crossover, and at the end of the study. RESULTS: During AOP, no significant changes were observed in any of the respiratory variables measured. The change in the apnea-hypopnea index at one month with AOP was +0.2 (95 percent confidence interval, -2.7 to +2.3; P=0.87). In contrast, all variables improved significantly after one month of n-CPAP (change in the apnea-hypopnea index, -46.3; 95 percent confidence interval, -56.2 to -36.5; P<0.001). CONCLUSIONS: Nasal continuous positive airway pressure therapy is highly effective for the treatment of the obstructive sleep apnea-hypopnea syndrome, whereas AOP has no significant effect.