Myocardial blood flow and hemodynamic responses to exercise training in dogs

Abstract

Left ventricular (LV) hemodynamics and myocardial blood flow (MBF) were examined under acute pressure (P) and volume (V) load states in 6 exercise-trained (T) and 6 nontrained (NT) dogs. MBF was measured with 9-.mu.m radioactive microspheres. Training by 8 wk of treadmill running was verified by increased gastrocnemius cytochrome oxidase (T, 282 .+-. 20 .mu.l O2/min .cntdot. g; NT, 209 .+-. 18; P < 0.025) and reduced heart response to submaximal exercise. Phenylephrine infusion doubled stroke work in T and NT groups and caused a significant rise in left atrial pressure (Pla) in the T group. Dextran and NaCl infusion produced a 50% rise in Pla in both groups and increased stroke work in T. The volume needed to raise Pla by 50% was higher in the T group (NT, 12.9 .+-. 1.9; T, 17.7 .+-. 3.1 ml/kg; P < 0.05). Total LVMBF increased with P and V loads in the T group only. Resting (R) LVMBF (ml/min per 100 g) was lower in T (NT, 114 .+-. 57; T, 83 .+-. 26; P < 0.10). Endocardial to epicardial flow ratio was unchanged in the T group with loading (R, 1.16 .+-. 0.04; P, 1.13 .+-. 0.12; NS [not significant]; V, 1.26 .+-. 0.03; NS), in the NT group this ratio was increased (R, 1.15 .+-. 0.03; P, 1.26 .+-. 0.07; P < 0.05; V, 1.26 .+-. 0.03; P < 0.01). Heart-to-body wt. ratio was increased in the T group (NT, 6.31 .+-. 0.22 g/gk; T, 6.97 .+-. 0.23; P < 0.05). Exercise training results in an altered left atrial pressure response to acute V loading and unchanged MBF under load compared to the untrained state.