engleski

Comparison of Linear and Nonlinear Analyses of Cardiac R-R intervals

Linear and nonlinear properties are involved in the genesis of heart rate variability (HRV). They are determined by complex interactions of haemodynamics, electrophysiological and humoral variables, as well as by autonomic and central nervous regulations. Therefore, the aim of this study was to compare changes in linear and nonlinear cardiac parameters during working and non-working daily periods in shift workers. Ten middle-aged nurses participated in this study, whose cardiac R-R intervals were continuously recorded from 7, 00 hours to 21, 00 hours for two days, which included different shifts, the morning shift in one case, and the afternoon shift in the other. For the purpose of this study, R-R intervals were recorded during fourteen hours the two days, divided into 5 minute periods and analysed. Spectral analyses of the data (five minutes periods) included calculation of spectral densities at different frequency bands (low and high frequency) expressed in normalised units. The ratio between low and high frequency spectral density seems to have reflected sympathetic modulation of HRV during the working daily periods. This effect was significantly larger during the morning shift, than the afternoon shift, which is, most likely, the result of the differences in workload. The parameters which used to measure nonlinear properties of HRV included the largest Lyapunov exponents (LLE) and the correlation dimension (D2). The results indicated the existence of the chaotic dynamic in HRV during both working and equivalent non-working daily periods, since the chaotic dynamic was more obvious in non-working periods. The differences in chaotic dynamics between two equivalent daily periods (working and non-working) are most probably due to the effects of the parasympathetic modulation of HRV which is more prominent during non-working periods, than equivalent daily working periods. Generally speaking, it seems that increased sympathetic modulation of HRV during working periods caused a reduction in the dimensionality of underlying system dynamics.

shiftwork; HRV; linear and nonlinear parameters

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