detrended fluctuation analysis Detrended fluctuation analysis 4 Heart 4 Heart rate variability 4 Sleep research 4 Acoustic wave velocity 3 Breathing disorders 3 Entropy 3 HRV 3 Multiscale entropy 3 Photoplethysmography 3 Polysomnography 3 SampEn 3 Sampen 3 Self-similarities 3 Sleep monitoring 3 Sleep studies 3 Spectrum analysis 3 Tachograms 3 Wave propagation 3 Wearable technology 3 breathing disorders 3 multiscale entropy 3 polysomnography 3 self-similarity 3 sleep 3 spectral analysis 3 Apnea detection 1 Cepstrum 1 Cepstrum coefficient 1