William Shakespeare, in "Macbeth," spoke of the "sleep that knits up the ravelled sleave of care." It is a time of restoration when your body and mind slow down, a time for your heart to lower its pace to match your diminished need for strength and energy and to repair itself. But some parts of sleep are surprisingly active, and your heart will follow suit. There is no usual and constant sleeping heart rate.
From Awake to Asleep
The sleep research team at Tel Aviv University in Israel, in 2006, discovered your body changes from its waking physiology to a different state as sleep approaches. Your vagus nerve---which slows your heart---becomes more active during sleep onset. Simultaneously, your excitatory or adrenergic nervous system is suppressed.
In 2001, Dr. K. Krauch, reporting in "Neuropsychopharmacology," observed heart rates of sleep study volunteers dropped by about 8 percent during sleep onset. He also noted heart rates begin falling at "lights out," suggesting a psychological component.
Calculate 92 percent of your awake heart rate to estimate your heart rate when light, continuous sleep, also called stage 1, begins.
Stages 1 through 4
Normal sleep is cyclic after onset. Stage 1 within a few minutes progresses to stage 2, the most common sleep stage. Stage 3 and 4 follow, the deepest, physically most relaxing stage---about 25 percent of sleep in adults but almost absent in the seventh and later decades of life. When relaxation deepens, your body temperature might drop slightly, and your heart rate might slow a few extra percent. But your general physical condition, previous day's work load and even diet can make exact predictions of heart rate imprecise if not impossible.
REM Sleep
Dreaming activates your eyes. Rapid-eye-movements (REM) under your eyelids show you are watching your dreams about 20 percent to 25 percent of a normal night. During REM sleep, your nervous system switches physiological states again. Respiratory and heart rates become unrestrained, speeding and slowing unpredictably. Rates might exceed your waking normal.
Stages 1 through 4 are followed by REM, then back to stage 1 in 90-minute cycles. Your heart rate changes all night long.
Sleep Apnea
Some people suffer periodic upper-airway collapse while sleeping---obstructive sleep apnea, also called OSA. People with heart disease or after a stroke might periodically "forget" to breathe, which is central sleep apnea, or CSA. Breaths can be missed from five to 200 times in an hour. REM sleep is the most common time for this. Resultant oxygen starvation and cardiac stress can change heart rates. There is no normal sleeping heart rate for sleep apnea patients.
After a Heart Attack
The leader of the University of Oklahoma Cardiovascular Research Team, Dr. Emilio Vanoli, says sleep is different after a heart attack---a myocardial infarction, or MI. A patient's vagus nerve, which normally slows the heart, becomes inactive during sleep onset, but the excitatory, adrenergic nervous system remains active. This loss of the vagus nerve's slowing or braking effect on heart rate makes post-MI sleeping heart rates more variable, more susceptible to speeding up, and it contributes to sleeping heart attacks and death.
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