The profile of the fall in hydrostatic pressure along the various vascular elements between the heart and capillaries has been determined in numerous studies. There is general agreement that there is relatively little pressure loss within the large conduit arteries and that although the pressure profile varies somewhat between studies and for different vascular beds (Figure 2), 7 the drop in pressure occurs predominantly in precapillary vessels ranging from 10 to 300 μm in diameter. It has been suggested that differences in methodology may be responsible for at least some of the variation between studies. 5 In particular, the use of exteriorized muscles may underestimate the pressures delivered to the microcirculation. Pressures recorded with minimal surgical intervention have indicated that as much as 70% to 90% of the systemic pressure is delivered to the microcirculation in many skeletal muscles. 8