The end-systolic pressure-volume relationship in young animals using the conductance technique

Evaluation of ventricular performance by the end-systolic pressure-volume relationship (ESPVR) has been extensively performed in the adult heart using the conductance technique. We undertook this study to validate the conductance technique and to generate ESPVRs in the small heart. To validate the technique, we simultaneously measured left ventricular volume by the conductance catheter and biplane cineangiography in nine piglets during changes in volume and contractility. Raw conductance volumes correlated highly with cineangiographic volumes (R = 0.97), and the slope was near identity (1.11 +/- 0.04). However, 'alpha Vc-corrected' volumes correlated less well (R = 0.85), probably because of errors induced by the saline technique for alpha Vc. We evaluated the ESPVR in nine lambs by inferior vena cava (IVC) occlusion, aortic occlusion, and volume infusion at rest and during changes in contractility. Reliable and linear ESPVRs were obtained in almost all IVC and aortic occlusions but not in volume infusions. Neither slope (Ees) nor position (V14) significantly changed over time or with dobutamine, but both changed after propranolol, supporting studies showing a limited contractile reserve in the newborn. However, Ees was 25% less steep when generated by IVC occlusion as compared to aortic occlusion. We conclude that the ESPVR can be reliably generated in the small heart using the conductance technique, but that it is sensitive to the loading technique.