To the Editor.—I read with interest "Non-Invasive Assessment of the Peripheral Vascular System" (Arch Surg 112:679-683, 1977) by Van De Water et al.
The two-coordinate display relating systolic pressure (P) and pulsatile perfusion (PFz) to clinical findings (ischemia, claudication, normal) suggested containment of a clinical situation within concentric circles. Mathematically, this relationship is a< √ P2 + (PFz)2 < b where a and b are indices categorizing clinical severity. The authors also recount the basic law of fluid dynamics: pressure equals flow times resistance (P = Q x R).
Two "ischemia" points, roughly 66.7 and 8.44, are abandoned outside their "circle," and several "claudication" points ingress into "ischemia." The data presented are more suggestive of an inverse relationship of pressure to pulsatile perfusion within a clinical category, a < P X (PFz) < b. This, in turn, suggests an analogy to another pressure/flow system: the electric curcuit,