Effect of the postural challenge on the dependence of the cardiovascular control complexity on age

Short-term complexity of heart period (HP) and systolic arterial pressure (SAP) was computed to detect age and gender influences over cardiovascular control in resting supine condition (REST) and during standing (STAND). Healthy subjects (n = 110, men = 55) were equally divided into five groups (21-30; 31-40; 41-50; 51-60; and 61-70 years of age). HP and SAP series were recorded for 15 min at REST and during STAND. A normalized complexity index (NCI) based on conditional entropy was assessed. At REST we found that both NCI_HP and NCI_SAP decreased with age in the overall population, but only women were responsible for this trend. During STAND we observed that both NCI_HP and NCI_SAP were unrelated to age in the overall population, even when divided by gender. When the variation of NCI in response to STAND (ΔNCI = NCI at REST-NCI during STAND) was computed individually, we found that ΔNCI_HP progressively decreased with age in the overall population, and women were again responsible for this trend. Conversely, ΔNCI_SAP was unrelated to age and gender. This study stresses that the complexity of cardiovascular control and its ability to respond to stressors are more importantly lost with age in women than in men.