DIFFERENTIATION OF PERIODIC FROM NONPERIODIC LOW-FREQUENCY HEART-RATEFLUCTUATIONS

Periodic low-frequency (LF) fluctuations of heart rate (HR) may be of diagnostic and prognostic value in diverse pathologic cardiopulmonary conditions. Two principal components of LF HR rate variations may be d istinguished: periodic fluctuations and nonperiodic, nonstationary cha nges. The frequency content of these two components may overlap consid erably. In order to avoid a tedious work-intensive visual analysis an efficient computer-based method for detection, differentiation, and qu antitation of these signals is required. Two methods for separating pe riodic from nonperiodic KR changes are presented, namely, detrending a nd bandwidth (BW) calculation. A group of healthy individuals was eval uated in order to assess these methods in individuals with significant LF periodic episodes (15 patients) contrasted to those without LF per iodic episodes (94 patients). The commonly used method of detrending c onsists of a fitted polynomial which by subtraction removes low freque ncies originating from nonstationary changes without affecting periodi c fluctuations. We found, however, that the frequencies involved in no nstationary and periodic fluctuations often overlap and thus the detre nding method may not be highly efficient. In a second method we postul ated different shapes for power spectrum curves of periodic and nonper iodic episodes. This latter method is based on BW calculation of the L F component of the R-R power spectrum and proved to be more efficient in detecting periodic episodes. It showed higher significance levels f or the difference between the periodic and nonperiodic groups when the BW or the ratio between peak power and BW in the LF range was used. T his new, alternative detection method may be employed in further studi es which seek to elucidate the clinical relevance of the LF range and, in particular, the mechanisms for such long-wavelength periodic fluct uations. (C) 1994 Academic Press, Inc.