[Intramuscular pressure and muscle blood flow during and after contraction (author's transl)]

In order to investigate the effects of intramuscular pressure on muscle blood flow changes during and after isometric contraction, experiments were conducted in anesthetized rabbits. Simultaneous measurements of muscle blood flow with a heated thermocouple technique and intramuscular pressure with a 'multi-hole wick catheter' connected to a transducer were done in the quadriceps muscle. The muscle contraction was caused by stimulating the femoral nerve using supramaximal square voltage pulses (7-9V, 0.1 msec). Intramuscular pressure increased linearly in response to various levels of stimulation frequency. At the low levels of frequency in stimuli (1-17 Hz), muscle blood flow during contraction increased continuously and intramuscular pressure was lower than the level of arterial blood pressure. But at the levels of frequency above 25 Hz, intramuscular pressure reached to or exceeded the level of systolic arterial blood pressure and muscle blood flow during contraction decreased continuously. It was suggested that increased intramuscular pressure disturbed muscle blood flow by collapsing the vessels within the muscle. Postcontraction peak flow appeared immediately after contraction caused by high frequent stimuli. This peak flow was not related to the duration of the contraction. Postcontraction hyperemia persisting long after contraction increased proportional to the intensity and duration of the contraction. These findings suggested the postcontraction peak flow was related to mechanical factor, whereas postcontraction hyperemia was to the other mechanism, such as metabolic products.