Effect of increased compartment pressure on the microcirculation of skeletal muscle

To determine the changes in capillary perfusion, which occur with elevated tissue pressure, and to highlight the relationship between systemic blood pressure and compartment pressure, we designed an experiment that allowed direct observation of the microcirculation of skeletal muscle under normal and increased compartment pressures. In each of 10 anesthetized rats, the cremaster muscle was exposed and suspended in a transparent pressure chamber. In vivo videomicroscopy was then performed and blood pressure was monitored via left carotid artery cannulation. Two sets of data for each animal were obtained: deltaP (mean arterial pressure compartment pressure) at which the muscle capillary blood flow was completely arrested, and the number of capillaries per 10,000 square micrometers of skeletal muscle with blood flowing at compartment pressures of 0, 15, 30, 45, and 60 mm Hg. Capillary blood flow stopped at a deltaP of 25.5 mm Hg +/- 14.3 SD. We found that capillary blood flow, as measured by the number of capillaries with blood flow per 10,000 square micrometers, decreased significantly (P < 0.05) as compartment pressure reached 15, 30, 45, and 60 mm Hg, when compared to 0 mm Hg; there was no vessel collapse at these pressures. These data show that increasing compartment pressure reduces the number of perfused capillaries per unit area, and that there is complete cessation of muscle capillary blood flow when the compartment pressure is within about 25 mm Hg of the mean arterial pressure.