Multiscale-Multifractal Assessment of Heart Rate Variability in Shift Workers by Detrended Fluctuation Analysis

Alteration of the circadian rhythm of the sleep-wake cycle is observed in shift workers, causing sleep disorders and changes in the cardiac autonomic nervous system. The multifractal-multiscale structure of inter-beat intervals (IBI) during sleep was analyzed in healthy shift working females by the multiscale-multifractal detrended fluctuation analysis (MMF-DFA) method. The MMF-DFA was applied to estimate the self-similarity coefficients $$\alpha (q,\tau )$$ considering moment orders q between $$-5$$ and $$+5$$ , and scales $$\tau $$ between 8 and 150 s. During daytime sleep, for $$q > 2$$ , the $$\alpha (q,\tau )$$ coefficients were very similar to those of nighttime sleep along $$\tau $$ . However, significantly higher scaling coefficients were observed during daytime sleep than during nighttime sleep, at small scales $$44\le \tau \le 68$$ for $$1 \le q \le 2$$ , and at large scales $$219 \le \tau \le 414$$ for negative moment orders q. The results suggest an alteration in the autonomic nervous system of shift workers, which could increase the risk of cardiovascular disease. Also, multifractal surface assessment of scale coefficients during sleep could be a tool to complement and improve the assessment of HRV alterations due to shift work.