Author(s): RIBEIRO, I., BAPTISTA, M.E., SANTOS, L.P., SANTINI, M.H., IRAHA, A.Y., BARTELS, R., PRADO, D.M.L., GUALANO, B., ROSCHEL, H., PEÇANHA, T. , Institution: FACULDADE DE MEDICINA DA UNIVERSIDADE DE SÃO PAULO - FM/USP, Country: BRAZIL, Abstract-ID: 1394

INTRODUCTION:
The assessment of muscle blood flow during whole-body dynamic exercise can offer valuable information about the mechanisms underlying exercise tolerance and fatigue in different populations. However, costs (e.g., magnetic resonance imaging) and/or invasiveness (e.g., intravenous cannulation/contrast injection) are challenging obstacles to wider application, warranting the development of practical, non-invasive, low-cost alternative methods. Objectives: To test the initial validity of a non-invasive ultrasound-based protocol developed to measure muscle blood flow responses during cycle ergometer exercise.
METHODS:
Twelve healthy participants (7 males/5 females; 28.9±1.4 years) attended the laboratory for a progressive square wave test on an upright cycle ergometer. The test consisted of 4-min stages at each of the four following intensity domains: 1) moderate (36±9% of maximal workload [WLmax]); 2) moderate-to-heavy (46±10% WLmax); 3) heavy (67±7% WLmax); 4) maximal (100% WLmax). After each stage, participants stopped pedalling and stayed still for 60s for the assessment of the right common femoral artery blood flow (CFBF) using a Doppler ultrasound (Logiq E, GE Medical System, China). Additionally, quadriceps oxygenation (oxy-, deoxy- and total haemoglobin [HbO2, HHb, THb], and tissue saturation index [TSI]) were assessed via Near-infrared spectroscopy. Cardiorespiratory variables were evaluated using a metabolic cart. Mean CFBF responses at baseline and after each stage were compared using a One-way repeated measures ANOVA. The associations between CFBF and cardiorespiratory and NIRS responses (changes from baseline) were performed using aggregated data from all participants across all exercise stages using repeated measures correlation analysis (rmcorr, Stata v18.0). Strength of the linear association between the variables tested were calculated via the rmcorr coefficient (rrm). Significance was set at P<0.05.
RESULTS:
CFBF increased following a "quasi-linear" pattern (baseline=0.26±0.15 L/min; moderate=2.28±1.15 L/min; moderate-to-heavy=2.42±1.39 L/min; heavy=3.93±2.11 L/min; maximal=4.16±2.17; P<0.001). CFBF responses to exercise were strongly and linearly correlated with exercise workload (rrm=0.69, P<0.01) and with HHb (rrm=0.68, P<0.01), VO2 (rrm=0.69, P<0.01) and heart rate (rrm=0.70, P<0.01). Additionally, CFBF responses were moderately or weakly correlated to THb, TSI and oxygen pulse (rrm=0.4-0.59 and P<0.05).
CONCLUSION:
The results of this study indicate that the proposed protocol may be a valid approach to investigate lower limb muscle blood flow responses during cycle ergometer exercise. This approach can provide a practical and non-invasive alternative to assess muscle blood flow in an applied context.