Group III/IV muscle afferents are important for the pressor response to dynamic exercise in healthy humans (1165.9)

Abstract

The onset of dynamic exercise typically exhibits a triphasic blood pressure (BP) response, consisting of an initial rise (0‐3s) followed by a transient drop below resting levels (4‐10s) and then a sustained increase (>10s). We investigated the role of skeletal muscle afferents in modulating the dynamics of BP at the onset of exercise. Beat‐to‐beat BP (brachial artery), heart rate (HR), stroke volume (SV), cardiac output (CO) were continuously monitored in 8 healthy men (28±3 yr) while performing leg cycling exercise (80W) under control (CTRL) and lumbar intrathecal fentanyl (FENT) (impairing cephalad projection of opioid receptor sensitive muscle afferents). To evaluate whether cephalad migration of fentanyl affected cardiovascular control centers, we assessed the pressor response to handgrip exercise in both conditions. At the exercise onset, mean BP increased from baseline in the first 3s (+5±1 mmHg, P<0.05) and decreased to a nadir at 10s (‐4±3 mmHg, P<0.05). Fentanyl did not affect BP response during the first 10s, but blunted its increase thereafter (CTRL: +9±3 vs. FENT: 0±2 mmHg at 50s; P<0.05). HR, SV and CO responses to exercise were not affected by fentanyl. Similar mean BP responses to static handgrip in both conditions indicated that cephalad migration of fentanyl was avoided. Our findings demonstrate an important contribution of group III/IV muscle afferent fibers to BP response to leg cycling exercise.Grant Funding Source: Supported by the Brazilian Science Without Borders Program