Gender differences in cardiovascular and cardiorespiratory coupling in healthy subjects during head-up tilt test by Joint Symbolic Dynamics

Gender related-differences in the autonomic regulation of the cardiovascular and cardiorespiratory systems have been studied mainly by hemodynamic responses during different physical stressors. In this study, the influence of gender on the autonomic response to an orthostatic challenge was investigated by obtaining the cardiovascular and cardiorespiratory coupling using the nonlinear technique known as joint symbolic dynamics (JSD) representation. This study includes 24 healthy young subjects. Males (N = 12) and age-matched females (N = 12) were enrolled in a head-up tilt (HUT) test, breathing normally, including 5 minutes of supine position (baseline) and 25-40 minutes of 70 orthostatic phase. The cardiovascular and cardiorespiratory couplings were obtained at baseline, early and middle orthostatic phases. Although in baseline there were some gender differences, parameters from JSD showed highly significant (p = 0.0004) differences in specific cardiovascular coupling patterns in the early tilt phase. Furthermore, JSD analysis revealed that in males, due to increased sympathetic activity, exist a lower degree of cardiovascular coupling accompanied with an increased occurrence of tachycardic patterns. On the other hand, the cardiorespiratory coupling revealed only very few slightly significant differences in all three phases.