Pulmonary pressures at high flows in the intact pulsatile flow perfused lung

Pulmonary pressure-flow curves can be easily generated in the intact animal by using a combination of systemic arteriovenous (a-v) fistulas and inferior vena cava (IVC) occlusion. By combining this technique with pulmonary artery occlusion, pulmonary pressure-flow curves may be studied over a broader range of pressures than has been previously been done in the intact, resting animal using pulsatile flow. Pressure-flow curves were generated by varying flow through opening and closing of the a-v fistulas in conjunction with inflating and deflating a balloon in the inferior vena cava. The pressure-flow curves were done under two conditions; (1) with both lungs perfused; (2) with the right lung excluded from the circulation (PA occlusion). PA occlusion resulted in no change in alveolar arterial oxygen tension gradient. The pressure-flow relationships for one lung and two lungs were well described by linear equations (r2 = 0.83 +/- 0.03 and 0.82 +/- 0.04 respectively). The slope of the equations increased with PA occlusion (3.6 +/- 0.4 mmHg.L-1 to 5.9 +/- 0.9 mmHg.L-1). There was no change in the pressure axis intercept with PA occlusion (8.34 +/- 0.8 mmHg pre-occlusion and 8.9 +/- 1.3 mmHg post-occlusion). It is concluded that the pulmonary pressure-flow relationship is well described by a linear function above a mean pulmonary artery pressure (PAP) of 10-12 mmHg.