Kinetics of estimated human muscle capillary blood flow during recovery from exercise

Abstract

The kinetic characteristics of muscle capillary blood flow ( Q̇cap) during recovery from exercise are controversial (e.g. one versus two phases). Furthermore, it is not clear how the overall Q̇cap kinetics are temporally associated with muscle oxygen uptake (V̇O2m) kinetics. To address these issues, we examined the kinetics of Q̇cap estimated from the rearrangement of the Fick equation (Q̇cap = V̇O2m/C(a-v)O2) using the kinetics of pulmonary V̇O2 (V̇O2p, primary component) and deoxy-haemoglobin concentration ([HHb]) as indices of V̇O2m and C(a-v)O2 (arterio-venous oxygen difference) kinetics, respectively. V̇O2p (1min-1) was measured breath by breath and [HHb] (μm) was measured by near infrared spectroscopy during moderate (M; below lactate threshold, LT) and heavy exercise (H, above LT) in nine subjects. The kinetics of Q̇cap were biphasic, with an initial fast phase (τI; M = 9.3 ± 4.9 s and H = 6.0 ± 3.8 s) followed by a slower phase 2 (τp; M = 29.9 ± 8.6 s and H = 47.7 ± 26.0 s). For moderate exercise, the overall kinetics of Q̇cap (mean response time [MRT], 36.1 ± 8.6 s) were significantly slower than the kinetics of V̇O2p (τp; 27.8 ± 5.3 s) and [HHb] (MRT for [HHb]; 16.2 ± 6.3 s). However, for heavy exercise, there was no significant difference between MRT-[HHb] (34.7 ± 10.4 s) and τp for V̇O2p (32.3 ± 6.7 s), while MRT for Q̇cap (48.7 ± 21.8 s) was significantly slower than MRT for [HHb] and τp for V̇O2p. In conclusion, during recovery from exercise the estimated Q̇cap kinetics were biphasic, showing an early rapid decrease in blood flow. In addition, the overall kinetics of Q̇cap were slower than the estimated VO2m kinetics. © The Physiological Society 2005.