Rapid Onset Vasodilation: Impact of Cardiorespiratory Fitness

Abstract

IntroductionHigher cardiorespiratory fitness is associated with greater vascular function that leads to improved regulation of skeletal muscle blood flow during exercise. Rapid onset vasodilation (ROV) describes the immediate increase in blood flow following a single contraction, which is integral to support greater blood flow during exercise. As such, blood flow regulation during exercise hyperemia is important. However, it is unclear if cardiorespiratory fitness plays a role in ROV of small muscle mass in young, healthy individuals.PurposeTo investigate the relationship of cardiorespiratory fitness on ROV following a single handgrip (HG) contraction in young, healthy adults.MethodsCardiorespiratory fitness (VO2peak) was assessed during a maximal cycle ergometer test in 14 volunteers (M/F, 6/8; 28 ± 5yrs; 24.8 ± 4.1kg/m2). Brachial velocity and diameter were measured using duplex Doppler ultrasound for 10 cardiac cycles prior to and 20 cardiac cycles following the first cardiac cycle after a single 30% of maximal voluntary handgrip contraction. Brachial artery blood flow (FBF) was calculated for each cardiac cycle: (diameter2/2)*π*velocity*60. Peak forearm (brachial) blood flow (FBFpeak) was determined as the maximal FBF from baseline following the first cardiac cycle after the single HG contraction. Time to peak blood flow response was determined as the time to reach FBFpeak and heart rate was measured using a three‐lead ECG. The relationship between FBFpeak and time to peak blood flow was tested using a multivariate regression analysis with cardiorespiratory fitness and sex as independent variables.ResultsCardiorespiratory fitness (VO2peak: 30.6 ± 8.0mL/kg/min); β for VO2peak= 0.162 [0.003, 0.327]) was the only predictor of time to peak blood flow response, F(1,12)= 4.602, p= 0.05, R2= 0.217, r= 0.526, while sex (β for time to peak= ‐106.5 [‐156.9, ‐56.2]) was the only predictor of FBFpeak, F(1,12)= 21.245, p<0.001, R2= 0.609, r= 0.799, indicating that females had a lower FBFpeakoverall.ConclusionOur data suggests blood flow responsiveness (e.g., time to peak) is positively associated with cardiorespiratory fitness and these data contribute to our understanding of potential mechanisms between improved blood flow regulation commonly associated with greater cardiorespiratory fitness. More research is necessary to fully elucidate the role biological sex has on these relationships, but our data suggest there may be sex differences in certain blood flow responses.