The baroreflex contribution to human cardiovascular control: Insight from passive exercise studies

Abstract

The present thesis examined the affect of passive exercise on spontaneous baroreflex sensitivity (BRS) and cardiac syrnpathovagal balance. Other cardiovascular variables such heart rate (HR) and blood pressure (BP) were also assessed.

Study 1 revealed that during passive exercise spontaneous BRS is decreased, the cardiac syrnpathovagal balance is shifted as a result a vagal withdrawal, and HR and BP increase in parallel. Study 2 investigated the interaction between postural shift and passive exercise on baroreflex control and HR. At rest, the postural shift from upright to supine resulted increased BRS and elicited bradycardia, while during both upright and supine passive exercise decreased BRS and elicited tachycardia. Study 3 showed that after passive exercise the cardiac vagal traffic was increased and HR was attenuated compared with pre-exercise. While, total peripheral resistance (TPR) increased, resulting in BP elevation. Study 4 showed that during passive exercise the local muscle tissue oxygenation increases despite the augmentation in oxygen uptake.

In conclusion, the overall findings demonstrate that during passive exercise spontaneous BRS is decreased and the cardiac sympathovagal balance is shifted due to vagal withdrawal. The effects of passive exercise on BRS and HR override those of postural shift. After passive exercise cardiac vagal activity is enhanced and HR is reduced, while TPR and BP are elevated, presumably caused by increased vasoconstriction, as Q did not change. Also during passive exercise both muscle oxygenation and oxygen uptake increase.