Information-Theoretic Assessment of Cardiovascular Variability During Postural and Mental Stress

This study was aimed at investigating the individual and combined effects of postural and mental stress on short-term cardiovascular regulation. To this end, we applied measures taken from the emerging framework of information dynamics on the beat-to-beat spontaneous variability of RR interval and systolic arterial pressure (SAP) measured from healthy subjects in the resting supine position and during the separate and simultaneous execution of experimental protocols performing head-up tilt (HUT) and mental arithmetics (MA). The information stored in RR interval variability, a measure inversely related to the complexity of the time series, increased significantly during HUT and HUT+MA compared with the rest and MA conditions, reflecting the activation of the sympathetic nervous system induced by the orthostatic stress. The information transferred from SAP to RR, a measure reflecting the strength of the directed effects between two time series, decreased during MA and increased during HUT and HUT+MA, documenting a differential involvement of the cardiac baroreflex during the administration of mental and orthostatic stressors. These results suggest that information-theoretic measures are useful tools to assess the complex picture of cardiovascular dynamics and interactions in physiological conditions, as well as to quantify the specific modifications of these dynamics induced by different types of stress.