Assessment of continuous skeletal muscle blood flow during exercise in humans

The ability to measure regional blood flow from exercising skeletal muscles is of great interest. However, noninvasive techniques such as venous occlu sion plethysmography and pulsed Doppler duplex ultrasonography only allow d etermination of blood now at rest. The aim of our study was to investigate the influence of position on continuous measured skeletal muscle blood now response in the upright and supine positions during graded maximal exercise by means of the local (133)Xenon washout technique with portable CdTe(Cl) detectors. Fifteen healthy subjects (8 women and 7 men, mean age 46 +/- 11 years) performed graded maximal bicycle exercise in both supine and upright positions in random order on 2 subsequent days. Blood flow in the musculus tibialis anterior was measured using the local (133)Xenon washout techniqu e. A total of 55-110 MBq of (133)Xenon dissolved in isotonic saline was inj ected intramuscularly and the gamma emission was registered by light-weight portable CdTe(CI) detectors. During supine exercise skeletal muscle blood flow increased continuously with increasing work load. However, during upri ght exercise blood flow increased only at the initial three work loads, the n it decreased gradually. Immediately after exercise blood now returned to preexercise values for both positions. The skeletal muscle blood now at max imum work load for each subject was 74% (relative flow values) (P < 0.05) h igher in the supine compared with the upright position. There was no signif icant difference in absolute or relative blood flow values at similar time points. Exercise time was longer in the supine (1345 +/- 548 s) compared wi th the upright position (1148 +/- 453 s) (P < 0.005). The local (133)Xenon washout technique with portable CdTe(Cl) detectors allows continuous determ ination of skeletal muscle blood flow during graded bicycle exercise in sup ine and upright positions. Furthermore, blood flow at maximum work load and exercise time was increased in supine compared with upright exercise. (C) 2000 Academic Press.