Table 1.

Relative changes of parameters during the various stages of sleep.

Parameter	Wakefulness	Light sleep (N1 and N2)	Deep sleep (N3)
Heart rate	1.06	0.98	0.99
Heart rate variability (HRV)	1.15	0.97	0.93
Respiratory rate	1.02	0.95	0.92
Strength of RSA	0.90	1.33	1.37
Strength of Synchronization	1.6	2.7	4.2

The mean values for each sleep phase have been normalized to the corresponding value in REM sleep. While mean heart rate, HRV, and respiratory rate increase during wakefulness as compared with REM sleep, they drop during non-REM sleep (light and deep sleep). The opposite dependence is observed for the strength of respiratory sinus arrhythmia (RSA). In contrast, the strength of cardio-respiratory synchronization is weakest during REM sleep. Furthermore, a greater sensitivity with respect to transitions between stages of sleep is seen for synchronization—greater by a factor of ten than for RSA. This demonstrates that sleep regulation influences both aspects of cardiopulmonary coupling in different ways.