Pain and changes in peripheral resistance at high vascular transmural pressure in the human forearm

A hydrostatic rise in forearm vascular transmural pressure may be associated with an increase in forearm blood flow (FBF) that causes pain. To test this hypothesis, forearm vascular transmural pressure was elevated in eight male volunteers by a series of 1-min hypobaric exposures of the left arm to incrementing differential pressures of 40, 80, 120, 140, 160 and 200 mmHg. The series was repeated after a 30-min interval. Forearm venous pressure (FVP) was measured in the median antecubital vein, and FBF was determined by ultrasound Doppler in the axillary artery. Pain level was recorded by numerical rating scale. In all subjects, an increase in FBF and forearm vascular conductance (FVC) occurred (P < 0.05) at high FVP (mean ± SE, 184 ± 8 mmHg). Pain was linearly related to the increase in FVC. In the second series of exposures, increases in FBF, FVC and pain occurred at a lower transmural pressure (FVP 152 ± 15 mmHg, P < 0.01). It is concluded that intense forearm pain is associated with a failure of autoregulation in the peripheral vascular bed and is worsened on repeated exposure to high transmural pressure. This may explain the overt forearm pain experienced by the crews of high performance military aircraft during manoeuvring.