A methodology for evaluating the influence of the respiratory component in measuring the complexity of heart rate variability

The process responsible for the heart rate variability (HRV) is influenced by a variety of physiological factors and, especially under particular conditions, the respiratory sinus arrhythmia is a very important one. To understand whether and up to what extent the respiratory sinus arrhythmia interferes with the dimensional characterization of the cardiovascular dynamics the authors investigated the approximate dimension and entropy of the HRV in six healthy subjects under controlled conditions. During these sessions the respiratory signal was recorded together with the electrocardiogram (ECG), noninvasive blood pressure and skin resistance. A recursive least squares adaptive filter was used to cancel the respiratory component from the RR series and then the approximate dimension and entropy of HRV were measured before and after filtering. The results over this small sample of a population indicated no significant difference in dimension and entropy before and after filtering