Figure 1 Relationship between lung volume and pulmonary vascular resistance. At low lung

Figure 1 Relationship between lung volume and pulmonary vascular resistance. At low lung volumes, the extra-alveolar vessels have less traction forces to distend them and resistance rises. At high lung volumes, resistance in pulmonary capillaries (alveolar vessels) is compromised by high alveolar pressures. Lowest pulmonary vascular resistance occurs at intermediate lung volumes. The figure assumes constant blood flow independent of lung volume.