Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA168

Poster Communications

Effect of period during sinusoidal leg cycling exercise on the blood flow dynamics of the brachial artery in humans

Y. Fukuba1, K. Miura1, H. Kashima1, M. Endo1, A. Ooue2, A. Kondo1, S. Watanabe1, Y. Fukuoka3, S. Koga4

1. Exercise Science and Physiology, Prefectural University of Hiroshima, Hiroshima, Japan. 2. Food and Nutrition Science, Toyo University, Gunma, Japan. 3. Health and Sports Science, Doshisha University, Kyoto, Japan. 4. Applied Physiology, Kobe Design University, Kobe, Japan.

BACKGROUND and PURPOSE: Recent human studies have indicated the increased blood flow (BF) to inactive muscles during exercise (e.g., Padilla et al., 2011). This seems to be the key factor for endothelial adaptation of the inactive limb (the upper limb) beyond the active muscles (the lower exercising limb) (e.g., Green et al., 2017). However, the dynamic property of BF to the inactive arm (through the biracial artery; BA-BF) with respect to the non-steady state change in the work rate (WR) during leg exercise remains unclear. We first quantified the dynamics of BA-BF during leg cycling exercise using a sinusoidal WR forcing with a 4-min period and found that the sinusoidally changing BA-BF response showed an anti-phasic delay (~180°), unlike other cardiorespiratory variables (Fukuba et al., 2017). However, since this anti-phasic response was observed in the BA-BF in the 4-min period, it should be clarified as to whether sinusoidal WR forcing with other periods would induce the similar phasic response. We, therefore, measured the dynamics of BA-BF in response to sinusoidal WR leg cycling exercises of 6-, 4-, and 2-min periods. METHODS: Seven healthy, young, male subjects (19-22 years) performed upright leg ergometer exercise with a constant WR (mean of the sinusoidal WR) for 30 min followed by three different periods of sinusoidal WR exercises (number of the repetitions); 6-min (3), 4-min (4) and 2-min (7), where the WR fluctuated in the range of 20 W to peak WR, corresponding to the 60% of VO2max. During protocols, we continuously measured the pulmonary gas exchange, heart rate (HR), mean arterial blood pressure, stroke volume, blood velocity and cross sectional area of the BA, and forearm skin BF (SBF) and sweating rate (SR). The measured and calculated variables: y(t) were fitted as y(t) = M + A*sin((2π/T)*t-θ), where t: time, M: mean level, A/M: relative amplitude, T: period (of sinusoidal WR), θ: phase. RESULTS: All variables traced as the sinusoid form adequately. The phases and A/Ms of the variables for gas exchange and central circulation, such as VO2 and HR, to WR forcing were similar (e.g., HR, phase [°]: 6-min, 37 ± 8, 4-min, 45 ± 10, 2-min, 60 ± 7; A/M (%): 6-min, 12.3 ± 2.8; 4-min, 10.3 ± 2.4; 2-min, 8.0 ± 1.1, mean ± SD). Similar to previous studies with sinusoidal WR forcing (e.g., Casaburi et al., 1977), a longer period showed a shorter phase and larger amplitude of responses. In contrast, the response of BA-BF showed an approximately anti-phase (165-195°) and a relatively constant A/M (~28%) regardless of the period, while the forearm SBF and SR were similar to those with the gas exchange and central circulation. CONCLUSION: The BF in the non-active limb is out of phase relative to the active muscle, reflecting a redistribution of BF and oxygen transport.

Where applicable, experiments conform with Society ethical requirements