Pulmonary vascular response to digoxin in newborn lambs.

The effects of digoxin on pulmonary vascular resistance (PVR) were evaluated in normoxic (N) and hypoxic (H) newborn lambs with normal and elevated PVR, respectively. Lambs were anesthetized and instrumented to enable continuous measurement of mean pulmonary arterial pressure (PPA), mean left atrial pressure (PLA), mean pulmonary blood flow (Qp), and mean aortic pressure (PAO). Digoxin (10-20 micrograms/kg) was injected via central venous catheters in 11 N lambs and 4 H lambs. Under N conditions, baseline PVR was equal to 0.12 mm Hg/ml/min/kg, PPA was 33 mm Hg, PLA was 6 mm Hg, Qp was 235 ml/min/kg, and PAO was 69 mm Hg. Following digoxin, mean PVR increased by 24% (P less than 0.001) and PPA increased by 23% (P less than 0.001) for an average duration of 199 sec while QP increased by 5% (P less than 0.02) and PLA was constant suggesting a direct vasoconstrictive effect. Under H conditions, baseline PVR was equal to 0.26 mm Hg/ml/min/kg, PPA was 58 mm Hg, PLA was 4 mm Hg, Qp was 208 ml/min/kg, and PAo was 65 mm Hg. Following digoxin, mean PVR, Qp, PLA, and PAo did not change appreciably although PPA had a uniform increase of 5% (P less than 0.001). The blunted response may suggest that either the pulmonary vascular bed was maximally constricted or that digoxin and hypoxia share a common mechanism. In conclusion, digoxin has a direct pulmonary vasoconstrictor action in newborn lambs. Because of its short duration, this action probably should not alter the clinical use of this drug in newborn humans.