Cardiovascular responses during recovery from exercise and thermal stress

Although the central cardiovascular adjustments to exercise in the heat have been identified, little is known about the post-exercise hemodynamics during recovery from exercise and heat stress. This study examined heart rate (HR), stroke index (SI), cardiac index (CI), systemic vascular resistance (SVR), systolic (SBP) and diastolic (DBP) blood pressure in 8 males during 15 min of passive seated recovery preceded by 30 min of cycle ergometry (60% VO2max) on two separate occasions: under control (C) and heat stress (HS) conditions. During both recovery conditions, SI significantly declined (p < 0.05) to below pre-exercise values. No differences were observed between groups with respect to SI. The decrease in recovery HR was slower (p < 0.05) in HS than C. The greater elevation in HR during HS accounted for the relative increase in CI above that observed prior to exercise. The estimated SVR measured immediately following exercise in both groups was lower (p < 0.05) than pre-exercise values. By 5 min of C recovery, SVR returned to baseline values but remained significantly depressed (p < 0.05) for the entire HS condition. These results indicate that the pressor responses were attenuated during HS; however, CI was maintained above pre-exercise levels due to higher HR responses compensating for the reduction in SI. Stimulation of the baroreceptor reflex and increased myocardial contractility could possibly explain the maintenance of output at a time when preload and afterload were reduced.