HEART RATE VARIABILITY DURING SLEEP
Keywords:
heart rate, spectral analysis, sleep stages, restoration of functional state of cardiovascular functionAbstract
Heart rate (HR), stroke (SV) and cardiac output (CO) were investigated at individual sleep stages, as well as during active orthostatic test (AOT) at evening before sleep and morning-after sleep in 42 healthy subjects (HSs) and 184 ischemic heart disease patients (IHDpts). HR variability was analyzed using HR power spectrum with calculation of three main frequency components: very low (VLFC), low (LFC) and high frequency component (HFC). There was shown, that constant CO during changes of sleep stages was reached due to increase of SV following HR increase during non-REM and by a decrease of SV with increasing HR frequency during REM sleep for HSs. IHD pts demonstrated reduced responses of both HR and hemodynamics, less able to reach constancy of CO during sleep. Decrease of CO was sun at transition from wakefulness to light sleep due to lowering SV and decreasing HR frequency. Decrease of HR was followed by slight increase of SV and CO during sleep non-REM sleep did not enabling to read the level of hemodynamics at wakefulness. During REM sleep there was seen markedly diminished CO due to lowered SV, which was not compensated by reduced HR increase.
HR power spectrum analysis demonstrated an increase of HFC and decrease of LFC and VLFC during sleep non-REM sleep, pointier to increase of parasympathetic and decreased sympathetic impact to HR control. Marked decrease at of HFC and increase of VLFC, LFC during REM sleep was due to depression of parasympathetic and increase of sympathetic control.
Sleep, due to its cyclic activity, was promoting restoration of functional reserve of cardiovascular function, what was rejected by HR decrease and a tendency to increase of SV and CO in HSs. While restoration of cardiovascular function was going on in HSs mainly due to decrease of HR frequency, e. g. due to increase of parasympathetic control, in IHD pts restoration was related more to improving hemodynamics, e. g. due to decreasing peripheral vascular tone, what was sun by means of decrease of total peripheral resistance and systolic blood pressure at morning time, as composed to evening.
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