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. Author manuscript; available in PMC: 2012 Oct 24.
Published in final edited form as: Compr Physiol. 2012 Jan 1;2(1):711–741. doi: 10.1002/cphy.c100091

Figure 1.

Figure 1

Starling resistor model to explain the concept of closing pressure within a circulatory system. Flow (Q) is determined by the gradient between an inflow pressure, or mean pulmonary artery pressure (Ppa), and an outflow pressure which is either closing pressure (Pc) or left atrial pressure (Pla). When Pla > Pc, the (Ppa – Pla)/Q relationship crosses the origin (A curve) and PVR is constant. When Pc > Pla, the (Ppa - Pla)/Q relationship has a positive pressure intercept (B and C curves), and PVR decreases curvilinearly with increasing Q. The B and C curves are curvilinear a low flow representing recruitment. Also shown are possible misleading PVR calculations: PVR, the slope of (Ppa-Pla)/Q may remain unchanged in the presence of a vasoconstriction (from 1 to 2) or decrease (from 1 to 3) with no change in the functional state of the pulmonary circulation (unchanged pressure/flow line). Adapted from reference 155. Permission pending.