Heart Rate Variability as the Indicator of Cardiovascular Function Restoration during Sleep

Introduction: Autonomic heart rate (HR) control evaluated by means of HR variability measures has been widely accepted as important information of cardiovascular function being a marker of sudden death. Methods: Polysomnography was performed in 405 CAD pts (mean age 60.7 yr.) pts, including 200 pts with CHF (mean age 63.4 yr.). Sleep apnea syndrome (SAS) was observed in 46 pts (mean age 64.2 yr.), including 24 pts with CHF (mean age 65.4 yr.). Computerized HR analysis was performed by Poincare plots of RR intervals recorded during sleep as well as during active orthostatic test (AOT) just before and after sleep. Minimal (RRmax) and maximal (RRmin) HR frequencies, the difference between of them as maximal HR response (DRRr), maximal HR variability (DRRt) as maximal width between of tangential lines of square, parallel to diagonal, general HR variability (P) as the plot of all square were measured. Results: Patients with CHF, as compared with pts without CHF, at evening-time during AOT demonstrated significantly reduced maximal HR response (DRRr 349 & 393 ms) due to higher minimal HR frequency (RRmax 1108 & 1146 ms) and significantly reduced HR variability evaluated as maximal and general HR variability (DRRt 94 & 103 ms and P 20700 & 24166 ms2). Maximal HR response and HR variability remained significantly reduced during sleep in CHF pts, as compared with pts without CHF. The difference between maximal HR response during AOT at morningand evening-time was significantly lower in pts with CHF reflecting more reduced restoration of autonomic HR control.SAS pts demonstrated inability of restoration of cardiovascular function during sleep: maximal HR response to AOT did not differ significantly at eveningand morning-time. CHF pts with SAS, as compared without SAS, demonstrated significantly reduced maximal HR variability (DRRt 77 & 96 ms) during AOT at evening-time. During sleep minimal and maximal HR frequency was significantly lower (RRmax 1309 & 1237 ms and RRmin 746 & 711 ms) and general HR variability was higher in SAS pts, as compared with pts without SAS. In CHF pts with SAS, as compared without SAS, HR variability characteristics during sleep did not differed significantly. Sleep efficiency (85.0% & 88.9%), stage 4 (1.2% & 2.2%), and REM sleep (11.5% & 13.5%) were significantly decreased in CHF pts, as compared without CHF. Sleep structure was more disturbed in SAS pts, as compared without SAS, as well as in CHF pts demonstrating SAS, as compared without SAS, due to significantly decreased slow wave sleep and REM sleep in both group. Conclusions: CHF patients demonstrated reduced restoration of autonomic HR control due to depressed tonic and reflex control, especially parasympathetic one and disturbed sleep. Inability to restore cardiovascular function during sleep was observed in patients demonstrating SAS.