Aerobic fitness and sympathetic responses to spontaneous muscle sympathetic nerve activity in young males
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RESEARCH ARTICLE
Aerobic fitness and sympathetic responses to spontaneous muscle sympathetic nerve activity in young males Myles W. O’Brien1 · Diane Ramsay1 · William Johnston1 · Derek S. Kimmerly1 Received: 29 July 2020 / Accepted: 18 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Purpose Lower aerobic fitness increases the risk of developing hypertension. Muscle sympathetic nerve activity (MSNA) is important for the beat-by-beat regulation of blood pressure. Whether the cardiovascular consequences of lower aerobic fitness are due to augmented transduction of MSNA into vascular responses is unclear. We tested the hypothesis that aerobic fitness is inversely related to peak increases in total peripheral resistance (TPR) and mean arterial pressure (MAP) in response to spontaneous MSNA bursts in young males. Methods Relative peak oxygen consumption ( VO2peak, indirect calorimetry) was assessed in 18 young males (23 ± 3 years; 41 ± 8 ml/kg/min). MSNA (microneurography), cardiac intervals (electrocardiogram) and arterial pressure (finger photoplethysmography) were recorded continuously during supine rest. Stroke volume and cardiac output (CO) were estimated via the ModelFlow method. TPR was calculated as MAP/CO. Changes in TPR and MAP were tracked for 12 cardiac cycles following heartbeats associated with or without spontaneous bursts of MSNA. Results Overall, aerobic fitness was inversely correlated to the peak ΔTPR (0.8 ± 0.7 mmHg/l/min; R = − 0.61, P = 0.007) and ΔMAP (2.3 ± 0.8 mmHg; R = − 0.69, P
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