Muscle Sympathetic Nerve Activity Responses to Hypercapnia in Exercise Trained and Sedentary Adults

Abstract

Elevated activity of the sympathetic nervous system at rest and sympathetic hyperreactivity to stress have been shown to be predictors for the development of cardiovascular diseases, such as hypertension. Previous studies have shown that there is no difference in resting muscle sympathetic nerve activity (MSNA) with exercise in young adults; however, the effects of exercise on the sympathoexcitatory response to chemical stimuli, such as hypercapnia, have not been studied. The purpose of this study was to compare MSNA responses to hypercapnia in young exercise trained and sedentary adults. Twenty‐nine young healthy adults were evaluated including 16 exercise trained (EX: M/F = 7/9; age = 27 ± 5 years; BMI = 23 ± 2 kg/m2) and 13 sedentary controls (CON: M/F = 7/6; age = 28 ± 4 years; BMI = 25 ± 2 kg/m2). Mean arterial pressure (MAP), heart rate (HR) and MSNA were measured continuously throughout the protocol. After baseline measurements were recorded, participants underwent a stepped hypercapnic protocol increasing to 6% CO2. Results are reported as mean ± SE. MAP was not different between groups at baseline (EX: 95 ± 4 mmHg vs. CON: 91 ± 5 mmHg; p>0.05) and during 6% CO2 (EX: 96 ± 4 mmHg vs. CON: 101 ± 5 mmHg; p>0.05). Both the change in MAP (EX: 1 ± 4 mmHg vs. CON: 11 ± 5 mmHg; p<0.05) and % change in MAP (EX: 2 ± 4 % vs. CON: 13 ± 5 %; p<0.05) were greater in the CON group compared with the EX group. HR was greater in the CON group compared with the EX group at baseline (EX: 50 ± 1 bpm vs. CON: 59 ± 3 mmHg; p<0.05) and during 6% CO2 (EX: 57 ± 2 bpm vs. CON: 68 ± 3 bpm; p<0.05). Both the change in HR (EX: 8 ± 1 bpm vs. CON: 9 ± 2 mmHg; p>0.05) and % change in HR (EX: 16 ± 3 % vs. CON: 16 ± 4 %; p>0.05) were not different between groups. MSNA was not different at baseline (EX: 16 ± 1 bursts/min vs. CON: 18 ± 2 bursts/min; p>0.05) and during 6% CO2 (EX: 17 ± 2 bursts/min vs. CON: 20 ± 2 bursts/min; p>0.05). The change in MSNA was greater in the CON group compared with the EX group (EX: 0.5 ± 0.4 bursts/min vs. CON: 2.4 ± 0.9 bursts/min; p<0.05) and the percent change in MSNA was non‐significant but tended to be higher in the CON group compared with the EX group (EX: 4 ± 2 % vs. CON: 16 ± 6 %; p=0.057). The sympathetic response to hypercapnia was lower in young exercise‐trained adults compared with sedentary adults. Taken together, these results suggest that hypercapnia‐induced sympathoexcitation may be altered with exercise training status, even in young healthy adults.Support or Funding InformationNIH HL118154This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.