Objective: Heart rate variability (HRV) is an universally accepted method for assessing the heart autonomic balance (HAB). At the same time HRV is a highly specific method, but with a low sensitivity to the cardiovascular diseases (CVD). We found that HRV indices may be applied to obtain differentiated characteristics of the HAB for individual CVD.
Methods: We assessed the changes taking place in the circadian characteristic of the autonomic balance, which has a definite profile with and without the principal CVD. We proposed adequate time-related autonomic balance indicator (TRABI) for evaluating the changes in the circadian nature of HAB by comparing the values of the HRV indices during rest and upon vegetative nervous system stimulation during two intervals in the 24-hour period in which there is a physiologically determined difference in the balance.
Results: The normal circadian characteristic of HAB is distinguished by a slight prevalence of the circadian nature of the parasympathetic component. The mean value of the assessments of the HRV indices using TRABI in healthy individuals, according to data from the study during rest and with the handgrip test is 0.100, according to data from the study during rest and with the Valsalva maneuver is 0.141. The mean values of the scores of the indices for HRV using TRABI in the comparative studies during rest and with the two stimulation tests are accordingly: with hypertension- 0.132 and 0.047; with morning myocardial infarction incidents- 0.177 and 0.107; with non-morning myocardial infarction incidents- 0.082 and 0.053. The patients with unstable angina in the population studied have a good long-term prognosis and the mean values in this case in the two comparative studies are 0.180 and 0.211.
Conclusions: Cardiovascular diseases have a characteristic abnormal circadian nature of the autonomic balance. In our opinion, the proposed time-related autonomic balance indicator broadens, the opportunities for using HRV for HAB assessment. The method for evaluating the circadian changes in HAB through the HRV indices during rest and with stimulation during different time intervals is convenient and accessible for clinical use.