Heart rate fluctuations in the low frequency (LF) range (0-0.05 Hz) may be divided into non-periodic and periodic components. The non-periodic fluctuations may be related to physiological or emotional activities. The LF periodic fluctuations have been observed in cardiopulmonary disorders and have been considered signs of loss of homeostatic activity. A method or assessing periodic LF fluctuations of heart rate variability (HRV) based on calculation of the bandwidth of the LF power spectrum (PS) has been developed in the present study. This method was tested in a group of 109 patients without evidence of cardiac disease and found to distinguish between patients with and without significant LF periodic fluctuation. Compared with these patients with no evidence of cardiac disease, a higher prevalence of periodic LF fluctuations was found in groups of cardiac patients and also in a group of obese patients.
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