Heart performance of lambs and its relation to muscle volume and body surface

Electrocardiography-gated dynamic magnetic resonance imaging (MRI) methodology was developed for the in vivo examination of sheep heart characteristics. By combining noninvasive determination of skeletal muscle mass, we studied the relationship between total body skeletal muscle content and heart performance. Measurements were carried out on male Merino lambs using 1.5 T field strength equipment. Average left ventricular volumes were determined and stroke volume was estimated during image postprocessing. Ejection fraction was calculated (73 +/- 1.8%) and the cardiac output (CO) value was estimated (2.75 +/- 0.16 L/min). After measuring left ventricular wall thickness, contraction values were determined at the septum (62%), anterior (69%), lateral (54%), and posterior (58%) walls. Ventricular mass was also calculated. Body composition measurement was performed immediately after MRI examination by computerized tomography (CT) during the same narcosis. Relative CO value was developed from the interpretation of the functional MRI and volumetric CT results, expressing the relationship between heart performance and total body skeletal muscle volume. Finally, CO value relating to body surface was estimated (18.3 +/- 3.1 dm(2)/(L min(-1))) to characterize the metabolic rate.