Does postexercise modelled capillary blood flow accurately reflect cardiovascular effects by different exercise...

Blood flow (BF) in exercising muscles is an important factor for exercise capacity. Recently, a non-invasive method to estimate capillary BF (Q_cap ) was introduced. Using this method, the Fick principle is re-arranged by using relative differences in deoxygenated haemoglobin (ΔHHb) as a surrogate for arteriovenous O₂ difference and pulmonary oxygen uptake (VO₂ ) instead of muscular oxygen uptake. The aim of this study was to examine (I) the relationship between Q_cap and exercise intensity during and following exercise, and (II) to critically reflect the Q_cap approach. Seventeen male subjects completed six bouts of cycling exercise with different exercise intensities (40-90% peak oxygen uptake, VO_2peak ) in randomized order. VO₂ and ΔHHb were monitored continuously during the trail. Q_cap was modelled bi-exponentially, and mean response time (MRT) was calculated during recovery as well as the dissociation of modelled VO₂ and Q_cap recovery kinetics (MRT/τVO₂ ). End-exercise Q_cap increased continuously with exercise intensity. This also applied to MRT. Postexercise MRT/τVO₂ increased from 40 to 60% VO_2peak but remained stable thereafter. The results show that Q_cap response to exercise is linearly related to exercise intensity. This is presumably due to vasoactive factors like shear-stress or endothelial-mediated vasodilation. MRT/τVO₂ shows that postexercise Q_cap is elevated for a longer period than VO₂ , which is representative for metabolic demand following exercise ≥70% VO_2peak . This is a hint for prolonged local vasodilation. According to previous studies, Q_cap could not be modelled properly in some cases, which is a limitation to the method and therefore has to be interpreted with caution.