Table 2: Frequency-domain Variable Ranges and the Components of the Autonomic Nervous System They Reflect.

Event		Per minute	Hertz (per second)	Autonomic nervous system
Heart beat		60 (range 40–200)	1 (1.4–0.67)	Sympathetic and parasympathetic
Respiration (respiratory sinus arrhythmia)	High frequency	15 (range 10–20)	0.25 (0.17–0.33)	Vagal, parasympathetic
Baroreflex activity	Low frequency	6 (range 4–10)	0.1 (0.07–0.17)	Sympathetic and parasympathetic (with slow respiration)
Thermoregulation	Very low frequency	2 (range 4–0.1)	0.03 (0.07–0.002)	Probably circadian, neuroendocrine and thermoregulation