Does physical exercise following lack of sleep increase the risk of sudden cardiac death (SCD)?
Sleep is an important aspect of our life. Sleep disorders are acute due to their effects in physiological and mental health of a person.Sleep occupies nearly 30% of our daily life and people were gradually decreasing the sleep time in order to adjust their busy schedule. According to the United States National Sleep Foundation, adults need to sleep 7-9 hours each night. The decrease in sleep time contribute mostly towards cardiovascular disease, including hypertension, coronary artery disease(CAD),risk of arrhythmia, stroke etc.
The circadian and dirurnal rhythms influence the neural circulatory control causing the changes in heart rate, vascular tone and blood pressure. The REM(Rapid Eye Movement)sleep and nonREM sleep affects the cardiovascular system. Researchers found it important that normal sleep is a complex and dynamic process with profound effects on cardiovascular homeostasis.
Insufficient sleep is a stress stimulator that acts through the sympathetic nervous system elicit changes in blood pressure, heart rate and barroreflex setpoint.
Sleep deprivation is a state of having less or no sleep which is a major reason for cardiovascular diseases.Which may cause
Inflammation
Cardiovascular disease is mainly driven by atherothrombosis, which is an inflammatory process. Increased levels of C-reactive protein(CRP) and interleukin-6(IL6) have been implicated as the predictors of cardiovascular disease risk.Both CRP and IL6 have been found elevated in both totally and partially sleep-deprived subjects.Inflammatory cells such as monocytes and neutrophils were also found to be elevated during acute sleep deprivation, supporting that sleep deprivation is an inflammatory process.
Endothelial Dysfunction
Endothelial Dysfunction has been reported after a combination of sleep deprivation and stress, also increased heart rate, blood pressure are reported in sleep deprived subjects may result in Endothelial Dysfunction.
Hypertension and Stress
Hyper tension and stress hormones are released by the body when lack of sleep occurs, this results in elevated bloop pressure and may lead to CAD.
CardioArtery Disease
The American Cancer Society , the Almeda County study and Partinen also showed an increased risk of CAD in subjects who reported sleeping 4-6 hours a day.
Diabetes Mellitus(DM)
Diabetes Mellitus is a major risk factor for CAD and it has been underlined from several studies across past decades that sleeplessness can result in DM.

A sudden cardiac death is highly probable for a person who follows increased physical exercise and decreased sleep durations. For a sleep deprived person the risk of cardiac diseases are so high, then for some one who spend lot of time exercising can cause chronic cardiac problems. Physical exercise and over training can cause more stress hormones and increased heart rates, these factors along with prolonged sleep deprivation can cause serious cardiac diseases or even sudden cardiac death.


Levels of cortisol (the &quot;stress&quot; hormone) are elevated for long periods of time.
The body spends more time in a catabolic state than an anabolic state (perhaps as a result of elevated cortisol levels).
Excessive strain to the nervous system during training.
http://en.wikipedia.org/wiki/Overtraining

References

Critical Care Nursing: Synergy for Optimal Outcomes - Roberta Kaplow
Sleep Deprivation and Disease: Effects on the Body, Brain and Behavior - Matt T. Bianchi