Effects of limb elevation and increased intramuscular pressure on human tibialis anterior muscle blood flow.

The effects of limb elevation and increased intramuscular pressure (IMP) on blood flow in the tibialis anterior muscle and leg neuromuscular function were studied in eight healthy subjects. Muscle blood flow (MBF) was measured by photoplethysmography using a custom-designed probe. IMP was elevated bilaterally by vein obstruction (60-65 mmHg) lasting 30 min induced by a thigh tourniquet of casted legs. Skin sensibility of the feet and the amplitude and area of the compound muscle action potentials from the extensor digitorum brevis muscle were evaluated. The subject kept one leg elevated 32 cm above heart level and the contralateral leg at heart level. All recordings were made before, during and after vein obstruction. IMP increased to 40 mmHg in the vein-obstructed casted legs. Perfusion pressure decreased from [mean (SD)] 42 (5.8) mmHg to 17 (6.4) mmHg in the elevated leg and from 65 (9.9) mmHg to 43 (8.4) mmHg in the non-elevated leg. MBF decreased by 50% in the elevated leg and by 42% in the non-elevated leg. Subjects experienced sensory dysfunction and muscular weakness in the elevated leg. In conclusion, increased IMP, induced by venous obstruction of a casted leg, reduced perfusion pressure and MBF, and resulted in a diminished amplitude and area of the compound muscle action potentials. Limb elevation above heart level combined with venous stasis of a casted leg further reduced perfusion pressure and MBF, and induced sensory dysfunction and muscular weakness.