Bone hemodynamic responses to changes in external pressure.

Adequate blood supply and circulation to the bones is required to maintain a healthy skeleton. Inadequate blood perfusion is associated with numerous bone pathologies and a decrease in bone mineral density, yet bone hemodynamics remains poorly understood. This study aims to 1) quantify bone hemodynamic responses to changes in external pressure, and 2) identify the predominant mechanisms regulating bone hemodynamic responses to pressure changes. Photoplethysmography was used to measure bone and skin perfusion in response to changes in external pressure. Single-limb pressure chamber experiments were performed over a pressure range of -50 to +50mmHg. Bone perfusion is decreased at all negative pressures, and larger decrements in perfusion are observed at the more extreme pressure differences. At positive pressures we observed an initial increase in perfusion followed by activation of intramuscular pressure receptors at +30mmHg, which overrides the initial response and results in decreased perfusion at the highest positive pressure levels. The myogenic effect is observed and is shown to be the predominant control mechanism in bone over a wide range of pressure exposures. Greater understanding of these hemodynamic mechanisms may be important in developing new drugs and therapies to treat various bone disorders.