Hypervolaemia improves global and local function and efficiency in postischaemic myocardium

1. In the present study, we investigated the effects of blood volume on postischaemic function and efficiency. In 14 anaesthetized dogs, following recovery from a period of 15 min occlusion of the left anterior descending coronary artery, the effects of hypervolaemia (HYPER; 15% increased volume produced by fast infusion of Hespan; B Braun Medical, Irvine, CA, USA), normovolaemia (NORMO) and hypovolaemia (HYPO) were studied. 2. Although myocardial O2 consumption was not significantly increased by volume (6.37+/-0.94 vs 6.89+/-1.1 mL/min per 100 g for HYPO and HYPER, respectively), local work of the stunned myocardium was markedly elevated (8.8+/-1.7 vs 22.5+/-3.5 g.mm/ beat, for HYPO and HYPER, respectively; P < 0.05). External work of the heart was also significantly improved (71.8+/-12.7 vs 139.5+/-16.2 mmHg.L/min for HYPO and HYPER, respectively). These data indicate markedly improved efficiency produced by volume, because work was increased with no change in myocardial O2 consumption. 3. Local dysfunction was characterized by several parameters, including systolic bulge, end-diastolic length, delay to onset of shortening, end shortening time delay (EST) and tail work ratio. Hypervolaemia reduced EST compared with hypovolaemia (98.6+/-18.3 vs 110.7+/-14.9 msec, respectively; P < 0.05) and improved tail work ratio (28.0+/-7.0 vs 36.0+/-7.0%, respectively; P < 0.05), with no effects on systolic bulge, end-diastolic length and delay to onset of shortening. 4. Thus, even in the postischaemic myocardium, increasing work by volume is energetically efficient and is accompanied by partial improvement of local dysfunction.