Pulmonary Physiology, Pulmonary Circulation, Dr. D. Penney

Figure 6.02. Pulmonary vascular resistance (PVR) falls as the very compliant (distensible) vessels are subjected to higher distending pressures.

PVR falls sharply in exercise, since even though pulmonary arterial and venous pressures increase somewhat, flow increases very much more, and computed resistance is a function of change in pressure over change in flow. Keep in mind that the pulmonary circulation carries the entire cardiac output. This is essential because the right heart is a low-pressure pump, and fails easily when subjected to high pressures / resistances.

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