Influence of lung volume and alveolar pressure on reverse pulmonary venous blood flow

Abstract

We have reported that left atrial blood refluxes through the pulmonary veins to gas-exchanging tissue after pulmonary artery ligation. This reverse pulmonary venous flow (Qrpv) was observed only when lung volume was changed by ventilation. This was believed to drive Qrpv by alternately distending and compressing the alveolar and extra-alveolar vessels. Because lung and pulmonary vascular compliances change with lung volume, we studied the effect of positive end-expiratory pressure (PEEP) on the magnitude of Qrpv during constant-volume ventilation. In prone anesthetized goats (n = 8), using the right lung to maintain normal blood gases, we ligated the pulmonary and bronchial arterial inflow to the left lung and ventilated each lung separately. A solution of SF6, an inert gas, was infused into the left atrium. SF6 clearance from the left lung was determined by the Fick principle at 0, 5, 10, and 15 and again at 0 cmH2O PEEP and was used to measure Qrpv. Left atrial pressure remained nearly constant at 20 cmH2O because the increasing levels of PEEP were applied to the left lung only. Qrpv was three- to fourfold greater at 10 and 15 than at 0 cmH2O PEEP. At these higher levels of PEEP, there were greater excursions in alveolar pressure for the same ventilatory volume. We believe that larger excursions in transpulmonary pressure during tidal ventilation at higher levels of PEEP, which compressed alveolar vessels, resulted in the reflux of greater volumes of left atrial blood, through relatively noncompliant extra-alveolar veins into alveolar corner vessels, and more compliant extra-alveolar arteries.

Effect of ventilation on vascular permeability and cyclic nucleotide concentrations in ischemic sheep lungs

“…The effect of ventilation on the movement of pulmonary vascular blood and the potential delivery of nutrients during ischemia depends on the type of ventilation, the vascular pressure, and the patency of the pulmonary artery and vein (32). For example, Obermiller et al (32) showed that positive-pressure ventilation caused reverse pulmonary venous blood flow in an in situ ischemic dog lung with patent pulmonary veins by cyclic ventilatory compression of alveolar capillaries. We reasoned that ventilating by lowering the surface pressure of the lung and keeping alveolar pressure constant relative to vascular pressure would minimize this effect, because the tidal emptying and filling of the alveolar vessels would be eliminated (39).…”

Acute Lung Injury and Pulmonary Vascular Permeability: Use of Transgenic Models

“…The lung apparently also can receive significant oxygenation through reverse perfusion through the pulmonary veins after pulmonary artery occlusion when the lung is ventilated. This provides distending mechanical forces on the veins to move blood into the alveolar capillaries from the left atrium (339,340). Hamvas et al (28) found that transcapillary albumin flux was only increased in static lungs inflated with oxygen but not in lungs ventilated with either oxygen, pure nitrogen, or a nitrogen -5% CO 2 mixture.…”

Soluble gas exchange in the pulmonary airways of sheep

“…A potential problem with interpretation of our data is the presence of a reflux flow from the pulmonary venous circulation (4). This reflux flow may contribute a small amount of inert gas to the alveolar vessels in an amount dependent on ventilation (8,9). We studied two additional animals to determine the contribution of alveolar exchange in the left lung both before and after left pulmonary artery occlusion, using MIGET.…”