[Studies on pressure-flow relationships in the pulmonary vascular bed, during antegrade and retrograde pulsatile perfusion of an excised canine lung lobe preparation].

Pulsatile pressure-flow relationships were studied in order to clarify the mechanical property of the pulmonary vascular bed. The left or right lower lobe of the dog was excised. Then, its pulmonary artery, pulmonary vein and bronchus were attached to a perfusion system. The lobe was perfused either via pulmonary artery (antegrade perfusion) or via pulmonary vein (retrograde perfusion) employing Harvard 1405 pulsatile pump. Positive pressure ventilation was maintained by a respirator throughout the experiment. From the pressure and flow wave, pulmonary vascular input impedance and total hydrauric power were computed by means of Fourier analysis. Pulmonary vascular resistance during retrograde perfusion was lower than that obtained during antegrade perfusion in a high flow state. The data suggests that the pulmonary vascular bed shows more passively distensible character during retrograde perfusion compared with antegrade perfusion. In the control flow state (inflow pressure of 15 mmHg and outflow pressure of 5 mmHg), however, above mentioned relationship was reversed (statistically significant). As outflow pressure was elevated, also, pulmonary vascular bed showed more remarkable distensibility during retrograde perfusion than during antegrade perfusion. With regard to the input impedance modulus and phase, there is no difference between the antegrade and retrograde perfusion of an excised lung lobe. Therefore, pulmonary arterial tree and pulmonary venous tree have a similar mechanical property, which determines the pulmonary vascular impedance. The rate of pulsatile power (Wp)/total hydrauric power (Wt) was 15-25% during antegrade perfusion, and Wp/Wt had minimum value at an inflow pressure of 14.5-15.5 mmHg. It may be stated that this value indicates the best condition for the pulmonary arterial smooth muscle.