CAROTID ARTERIAL BAROREFLEX REGULATION OF BLOOD PRESSURE DURING RECOVERY FROM EXERCISE

Abstract

1214 This study examined the involvement of altered autonomic blood pressure control in post-exercise hypotension. Carotid arterial baroreflex function was compared before an incremental cycling test to exhaustion and during recovery(5 and 30 min after exercise) in eight male subjects using the variable pressure neck chamber method. The protocol was repeated on two separate occasions (seated baseline/recovery versus supine baseline/recovery). Blood pressure was measured non-invasely from the digital artery (Finapres) and the carotid sinus baroreflex was challenged with both negative (-20, -40, -60,-80, -100 mmHg) and positive (+20, +40, +60 mmHg) neck pressures. Arterial pressure (AP) and heart rate (HR) were expressed relative to carotid sinus pressure (CSP) and neck chamber pressure (NCP) to investigate changes in baroreceptor sensitivity and blood pressure stimulus response relationship. Relative to baseline, AP and CSP were unchanged following exercise at 5(AP=-3.5 mmHg) and 30 min (AP=+1.5 mmHg) in both postures. In contrast, there was a significant increase (P < 0.05) in baroreflex HR gain throughout seated recovery, that was not evident in the supine position. On closer inspection, four subjects presented with significant (P < 0.05) hypotension after 5 min of recovery (-12.3±3.2 vs +4.3±3.1 mmHg for hypotensives and non-hypotensives). With supine and seated data pooled for the hypotensives, there were significant reductions (P < 0.05) in AP and CSP for all neck pressures used. This suggests that the post-exercise hypotension was associated with a downward and lateral displacement of the stimulus-response function encompassing both threshold and saturation regions, indicating that there was a transient resetting of the baroreflex to a lower arterial pressure immediately following maximal exercise.