124: HEMODYNAMIC EFFECTS OF SUBMAXIMAL TREADMILL EXERCISE IN LAMBS WITH AN AORTOPULMONARY SHUNT (S)

Abstract

We showed that S lambs at rest could maintain their systemic blood flow (SBF) at the expense of an increased heart rate (HR). Therefore we wondered whether a diminished reserve in HR would limit the S lambs to perform strenuous exercise. We studied 6 7-week-old lambs (12±1 kg; mean±SD) with a Goretex O graft between aorta (ao) and pulmonary artery (pa) (PBF: SBF ratio =3). Six lambs without graft served as controls (C). Variables were recorded at the end of a 10 min. treadmill run at 75% of predetermined VO2max. During exercise HR increased more in C (108±23 to 239±31 bpm) than in S lambs (169±32 to 238±32). Total left ventricular stroke volume (SVlv) did not change in both groups (S: 2.0±0.3 to 2. 0±0.3; d 1.1±0.3 to 1.1±0.1 ml/kg), but the fraction of total SVlV through the shunt decreased per heart beat so that the fraction contributing to SBF (effective SVlv) increased significantly (S: 0.7±0.2 to 0.9±0.3). This enabled S lambs to increase SBF (118±20 to 216±40 ml/min/kg) to such an extent that it was not significantly different from SBF in C lambs (116±10 to 260±20). We conclude that S lambs adapt well to exercise by increasing their effective SVlV.