Relationship Between Blood Flow in Brachial Artery and Basilic Vein During Increasing Forearm Flexor Muscle Work
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Background: Cardiac output (Q) is thought to be one of the main factors determining maximal oxygen consumption (VO2max) during whole- body exercise. During exercise with a reduced volume of active muscles, Q becomes less and less important for peak oxygen consumption (VO2peak). This suggests that Q may be eliminated as the main factor limiting VO2peak when working with a small muscle mass. Peripheral factors such as blood flow (BF), O2 diffusion and extraction are more important factors for VO2peak. BF in small muscle mass is usually studied in the lower extremities, because there are only one main artery-vein coupling. Since venous BF is found to reflect arterial BF in lower extremities, it is interesting to investigate if this is the same for the forearm flexor muscles at rest and during exercise with different workloads measured with ultrasound Doppler. This is though more complicated because the forearm flexor muscles consist of more than one artery- vein coupling. Purpose: The aim of this study was to investigate if basilic venous BF is a valid reflection of brachial arterial BF during increasing forearm flexor muscle work. Methods: Eight young males participated in this study, performing six submaximal tests with the forearm flexor muscles, each test of three minutes duration. The tests consisted one arterial and one venous test at 40, 60 and 80% of maximal workload measured with ultrasound Doppler. Results: Venous BF reflected arterial BF at rest and during steady state handgrip exercise at 40, 60 and 80% of maximal workload. Both arterial and venous BF increased significant (P<0.01) with work intensity up to 60% of maximal workload, with no further increase due to vasoconstriction. Arterial diameter was significant greater (P<0.05) during exercise compared to resting diameter. Both arterial and venous BF and diameter during muscle relaxation was significant higher (P<0.01) than during muscle relaxation- contraction. Conclusion: This study shows that it is possible to continuously measure arterial inflow and venous outflow during rest and exercise with different work intensities with ultrasound Doppler. Basilic venous BF is a valid reflection of brachial arterial BF at rest and during increasing forearm flexor muscle work. For BF and diameters in the forearm to be expressed best possible during exercise, measurement should be done during muscle relaxation-contraction.