To determine how much myocardial O2 consumption (VO2) would increase during an additional load on the heart in shunt as compared with control lambs, we studied 12 7-wk-old lambs with an aortopulmonary left-to-right shunt (59 +/- 3% of left ventricular output, mean +/- SE) and 11 control lambs during exercise at 80% of their predetermined peak VO2 (VO2peak), at 12 +/- 1 days after surgery. During exercise, systolic aortic pressure increased by 25% in the two groups. Left atrial pressure and left ventricular stroke volume did not change significantly and remained considerably higher in shunt than in control lambs. Heart rate, however, increased less in shunt than in control lambs (163 +/- 8 to 235 +/- 8 vs. 107 +/- 7 to 230 +/- 8 beats/min). The same was true for left ventricular myocardial blood flow (245 +/- 19 to 391 +/- 27 vs. 128 +/- 10 to 320 +/- 45 ml.min-1 x 100 g-1) and myocardial VO2 (847 +/- 101 to 1,692 +/- 136 vs. 528 +/- 58 to 1,579 +/- 178 mumol O2 x min-1 x 100 g-1). We conclude that, despite the volume load, myocardial VO2 of shunt lambs does not increase to a greater extent than in control lambs during a considerable additional load on the heart.
Anastomosis, Surgical Animals