Effect of furosemide on pulmonary blood flow distribution in resting and exercising horses

We determined the spatial distribution of pulmonary blood flow (PBF) with 1 5-mu m fluorescent-labeled microspheres during rest and exercise in five Th oroughbred horses before and 4 h after furosemide administration (0.5 mg/kg iv). The primary finding of this study was that PBF redistribution occurre d from rest to exercise, both with and without furosemide. However, there w as less blood flow to the dorsal portion of the lung during exercise postfu rosemide compared with prefurosemide. Furosemide did alter the resting perf usion distribution by increasing the flow to the ventral regions of the lun g; however, that increase in flow was abated with exercise. Other findings included 1) unchanged gas exchange and cardiac output during rest and exerc ise after vs. before furosemide, 2) a decrease in pulmonary arterial pressu re after furosemide, 3) an increase in the slope of the relationship of PBF vs. vertical height up the lung during exercise, both with and without fur osemide, and 4) a decrease in blood flow to the dorsal region of the lung a t rest after furosemide. Pulmonary perfusion variability within the lung ma y be a function of the anatomy of the pulmonary vessels that results in a p redominantly fixed spatial pattern of flow distribution.