title: Circulatory effects of acute normovolaemic haemodilution in rats with healed myocardial infarction.
abstract: This study evaluated the haemodynamic response to different degrees of acute normovolaemic haemodilution with hetastarch at rest and during preload and afterload stress in 123 anaesthetised Sprague-Dawley rats divided according to cardiac status (sham operated, n = 46; no myocardial infarction, n = 47; large myocardial infarction, n = 30). Histological infarct size was 41 (SEM 2)%. Cardiac output was recorded using an electromagnetic flow probe. The preload test was achieved by rapid infusion of blood adjusted for packed cell volume, while the afterload test was achieved by an aortic clamp technique. Prior to haemodilution, rats with large myocardial infarction had lower (p less than 0.05) cardiac index, stroke volume index, left ventricular dp/dt, and oxygen delivery, and higher left ventricular end diastolic pressure compared with sham operated rats and rats with no myocardial infarction. Haemodilution to a haematocrit of 30% in all three groups resulted in a similar significant (p less than 0.05) rise in cardiac index and stroke volume index such that blood pressure was maintained despite the decrease (p less than 0.05) in peripheral resistance. Compared with sham operated rats, rats with large myocardial infarcts haemodiluted to packed cell volume of 20% had a more limited rise in cardiac index of 14 (SEM 6) v 45(12)%, p less than 0.05, and a greater fall in oxygen delivery of 50(5) v 28(9)%, p less than 0.05 which was associated with a higher left ventricular end diastolic pressure of 6.6(1.0) v 3.7(0.4) mm Hg, p less than 0.05. Following preload and afterload stress, rats with large myocardial infarcts had lower (p less than 0.05) left ventricular developed pressure, peak cardiac index and peak stroke volume index compared with sham operated rats and rats with no myocardial infarction, independent of packed cell volume. The data suggest that large myocardial infarctions impaired the ability of the left ventricle to pump blood and generate pressure. This diminished left ventricular performance was most apparent in response to preload and afterload stress and at the lowest level of haemodilution employed (packed cell volume 20%).
authors.affiliation: Department of Heart and Hypertension, Cleveland Clinic Foundation, Ohio 44195-5076.
authors.forename: H
authors.initials: H
authors.lastname: Kobayashi
authors.forename: C E
authors.initials: CE
authors.lastname: Smith
authors.forename: F M
authors.initials: FM
authors.lastname: Fouad-Tarazi
authors.forename: P
authors.initials: P
authors.lastname: Wicker
authors.forename: G F
authors.initials: GF
authors.lastname: Estafanous
mesh_terms: D000818:Animals; D003331:Coronary Vessels / Q000601:surgery; D006438:Hemodilution; D006439:Hemodynamics / Q000502:physiology*; D008297:Male; D009203:Myocardial Infarction / Q000503:physiopathology*; D011184:Postoperative Period; D051381:Rats; D011919:Rats, Inbred Strains