Sleep and control of heart rate.

The heart rate in normal humans is determined by many factors. Assuming a normal hemoglobin concentration, left ventricular function, and metabolic rate, respiration, and its effects, along with autonomic nervous activity, appear to influence heart rate the most. Hypoxia and hypercapnia both increase heart rate during wakefulness and probably do the same during sleep. The hypoxic response is dependent on information from lung inflation and the carotid bodies. Respiratory rate, within limits, will determine the amplitude of the well-known (respiratory) sinus arrhythmia. During sleep, a distinct pattern of heart rate response and its respiratory arrhythmia are seen for each stage of sleep and are related to the level of autonomic nervous system activity during wakefulness. Blood pressure follows the same trend as heart rate during sleep, and changes in cardiac output and total peripheral vascular resistance are variable during sleep, but there is no consensus of opinion about the direction of these changes. Rhythm disturbances are predominantly those of bradyarrhythmias, exaggerated sinus arrhythmias, and transient AV block, which are probably occurring in REM sleep.