Correlation properties and regularity of heart period time series: influence of posture and heart disease.

Nonlinear measures of heart period variability (HPV) were determined in supine rest and standing posture in children and young adults with heart disease and compared to the control. The aim was to study influence of posture and heart disease on heart period dynamics. It was found that standing increases short-term scaling exponent in all subjects and decreases sample entropy in healthy and less severely ill patients. Severely ill patients compared to control have higher short-term scaling exponent in supine. Changes in nonlinear measures of HPV upon standing are more pronounced in healthy than diseased subjects due to different vagal activity.