Shear vs pressure as causative factors in skin blood flow occlusion.

An instrument was developed to measure the external pressure, shear, and pulsatile arteriolar blood flow existent at a given portion of the anatomy. Application of this device to the thenar eminence of 4 healthy subjects showed that externally applied pressure was approximately twice as effective as shear in reducing pulsatile arteriolar blood flow. The combination of pressure plus shear was found particularly effective in promoting blood flow occlusion. At a sufficiently high level of shear (roughly 100 g/cm2) the pressure necessary to produce occlusion was half that required when little shear was present.