Short-term complexity of cardiovascular oscillations during orthostatic change in aging

Complexity of R-R intervals (RR) and systolic arterial pressure (SAP) variability were computed to detect the aging process influence over cardiovascular control in resting supine (REST) and standing position (STAND). One hundred healthy subjects were divided into five groups (n=20 for each), according to age: 21-30; 31-40; 41-50; 51-60; 61-70. The RR and SAP series were recorded for 15 minutes at REST and STAND. Short sequences of RR and SAP were analyzed by conditional entropy. At REST, RR complexity showed reduction with age in 61-70, and SAP complexity decreased, starting from 31-40. Changes in cardiovascular control complexity, induced by STAND, reveal the difficulty of elderly individuals in dealing with sympathetic stressors.