Résumé : BACKGROUND: Cardiac vagal predominance increases the RR interval and RR high-frequency (HF) variability during non-rapid eye movement (non-REM) sleep (stages I through IV) in young subjects. Aging suppresses deep sleep, but effects of age-related changes in sleep architecture on RR are unknown. Whether mechanical effects of changes in the breathing pattern on the sinus node during sleep affect RR variability is unclear. METHODS AND RESULTS: Polygraphic sleep recordings and RR and RR spectral profiles were determined in 8 young (22.5+/-3.3 years) and 8 older (55.0+/-7.3 years) healthy volunteers. HF oscillations in RR of 8 cardiac-denervated heart transplant recipients determined mechanical effects of respiration on the sinoatrial node during sleep. Transition from wakefulness to non-REM sleep increased the RR interval in young and older subjects and increased the HF variability of RR in the young (P:<0.05) but not in the older subjects. Older subjects disclosed a faster RR (P:<0.01) and a lower HF variability (P:<0.05) during non-REM sleep than the young subjects. Aging did not affect light and REM sleep but decreased deep sleep (stage IV) from 39+/-23 to 6+/-6 minutes (P:<0.001). Reduction in sleep stage IV with aging blunted the increase in RR and in RR HF variability during non-REM sleep (r>0.55, P:<0.05). Transition from wakefulness to non-REM sleep doubled the markedly reduced HF variability of RR in the heart transplant recipients (P:<0.05). CONCLUSIONS: Disappearance of deep sleep with aging impairs nocturnal increase in cardiac vagal activity. Mechanical effects of changes in breathing pattern during sleep favor increases in HF oscillations of the RR interval during non-REM sleep.