Reduced cardiac sympathetic autonomic tone after long-term nasal continuous positive airway pressure in obstructive sleep apnoea syndrome

The increased sympathetic activation that occurs in obstructive sleep apnoe a (OSA) may play an important role in associated morbidity. We investigated the effect of long-term (3 month) nasal continuous positive airway pressur e (CPAP) on the autonomic nervous system assessed by heart rate variability (HRV). Fourteen patients (12 men), mean age 61.4 +/- 8.1 years, with OSA u nderwent continuous synchronized electrocardiographic and polysomnographic monitoring The apnoea/hypopnoea index (AHI) decreased from 50.6 +/- 13.7 to 2.2 +/- 2.5 events h(-1) after CPAP. HRV analysis showed significant decre ases in low frequency (LF; from 7.12 +/- 1.06 to 6.22 +/- 1.18 In ms(2) Hz( -1); P < 0.001), high frequency (HF; from 5.91 +/- 0.87 to 5.62 +/- 0.92 In ms(2) Hz(-1); P<0.05) and LF/HF (from 1.21 +/- 0.12 to 1.11 +/- 0.15 ln ms (2) Hz(-1); P<0.001) when the patients were asleep. The decrease in LF/HF w as prolonged into the daytime (from 1.33 +/- 0.22 to 1.24 +/- 0.21 ln ms(2) Hz(-1); P<0.001). Treatment of OSA by CPAP significantly reduced the param eters of cardiac sympathetic tone, a favourable effect.