Systemic cardiovascular and carotid baroreflex support of arterial pressure during recovery from passive heat stress in young and older adults

We evaluated the systemic cardiovascular and carotid baroreflex support of arterial pressure during recovery from whole-body, passive heating in young and older adults. Supine mean arterial pressure (MAP), cardiac output (Q; acetylene washin), systemic vascular conductance (SVC), heart rate (HR), and stroke volume (SV) were evaluated in 16 young (8F, 18-29 years) and nine older (6F, 61-73 years) adults at normothermic baseline and for 60-min passive heating and 120-min normothermic recovery. Externally applied neck pressure was used to evaluate HR, brachial vascular conductance, and MAP responses to carotid baroreceptor unloading. MAP was reduced with heating in young adults (p < 0.001) and similar to baseline within 30 min recovery in both age groups. Heating-induced Q, SVC, HR, and SV responses returned to baseline within 60 min recovery in both age groups. Heating attenuated HR and brachial vascular responses to neck pressure in young adults (both p < 0.01), but these responses did not differ from baseline throughout recovery in either age cohort. MAP responses to neck pressure were not impacted by heating in either age group but increased after 90 min recovery in young adults (p < 0.05). The systemic cardiovascular and carotid baroreflex responses accompanying passive heating do not persist beyond 30 min of post-heating recovery in young or older adults.