Effects of coronary flow reduction on lung vascular tissue transport in sheep

This study was performed to measure the effects of a sustained reduction in coronary flow on lung lymph flow and protein content. Ten halothane-anesthetized sheep with cannulated lymphatic vessels were provided with a carotid-to-left anterior descending coronary artery cannula containing an electromagnetic flowmeter. One group of five animals was observed at base line and after coronary flow was reduced to 38% of base line. A second group of five animals acted as controls and was observed at base line, for 111 min of increased left atrial pressure, and a second period of normal pressures. Sustained coronary flow reduction led to significant increases in pulmonary arterial pressure, left atrial pressure, lymph flow, total protein lymph-to-plasma concentration ratio (L/P), and protein lymph clearance (L/P X lymph flow). Analysis of the pressure, lymph, protein, and indicator data with a two-pore model of the microvascular barrier showed that the observations were consistent with the concept that coronary flow reduction decreased functioning lung capillary surface but increased the size of the large pore and the number of small pores relative to the number of larger pores. Control studies showed increases in lymph flow and decreases in L/P with increased pressure but no significant changes in any variable between the first and second period of normal pressures. We conclude that coronary flow reduction increases lung vascular-tissue transport by decreasing the resistance of the microvascular barrier to protein and fluid movement. However, increased pressure secondary to left ventricular dysfunction plays a role in the magnitude of this response.