Global Reach 2018: sympathetic neural and hemodynamic responses to submaximal exercise in Andeans with and without chronic mountain sickness

Andeans with chronic mountain sickness (CMS) and polycythemia have similar maximal oxygen uptakes to healthy Andeans. Therefore, this study aimed to explore potential adaptations in convective oxygen transport, with a specific focus on sympathetically mediated vasoconstriction of nonactive skeletal muscle. In Andeans with (CMS , n = 7) and without (CMS+, n = 9) CMS, we measured components of convective oxygen delivery, hemodynamic (arterial blood pressure via intra-arterial catheter), and autonomic responses [muscle sympathetic nerve activity (MSNA)] at rest and during steady-state submaximal cycling exercise [30% and 60% peak power output (PPO) for 5 min each]. Cycling caused similar increases in heart rate, cardiac output, and oxygen delivery at both workloads between both Andean groups. However, at 60% PPO, CMS had a blunted reduction in Dtotal peripheral resistance (CMS+, -10.7 ± 3.8 vs. CMS , -4.9 ± 4.1 mmHg L-1 min-1; P = 0.012; d = 1.5) that coincided with a greater Dforearm vasoconstriction (CMS+, -0.2 ± 0.6 vs. CMS , 1.5 ± 1.3 mmHg mL-1 min-1; P = 0.008; d = 1.7) and a rise in Ddiastolic blood pressure (CMS+, 14.2 ± 7.2 vs. CMS , 21.6 ± 4.2 mmHg; P = 0.023; d = 1.2) compared with CMS+. Interestingly, although MSNA burst frequency did not change at 30% or 60% of PPO in either group, at 60% Dburst incidence was attenuated in CMS (P = 0.028; d = 1.4). These findings indicate that in Andeans with polycythemia, light intensity exercise elicited similar cardiovascular and autonomic responses compared with CMS+. Furthermore, convective oxygen delivery is maintained during moderateintensity exercise despite higher peripheral resistance. In addition, the elevated peripheral resistance during exercise was not mediated by greater sympathetic neural outflow, thus other neural and/or nonneural factors are perhaps involved.