Background: Cardiovascular conditioning reduces resting myocardial oxygen demand by lowering systolic blood pressure and heart rate. Lower myocardial oxygen demand at rest would be expected to be associated with a decrease in resting myocardial blood flow and, consequently, an increase in myocardial flow reserve as the ratio of hyperemic to resting blood flow. However, the effect of controlled exercise together with a low-lipid diet on myocardial blood flow and flow reserve has not been examined in humans.
Methods and results: Myocardial blood flow at rest and after dipyridamole-induced hyperemia (0.56 mg/kg i.v.) was quantified with [13N]ammonia and positron emission tomography in 13 volunteers before and upon completion of a 6-week program of cardiovascular conditioning and a low-fat diet. Exercise capacity and serum lipid profiles were also assessed at the start and finish of the program. Eight normal volunteers of similar age not participating in the conditioning program served as a control group. Cardiovascular conditioning lowered the resting rate-pressure product (8859 +/- 2128 versus 7450 +/- 1496, P < .001), serum cholesterol (217 +/- 36 versus 181 +/- 26 mg/dL), LDL cholesterol (140 +/- 32 versus 114 +/- 24 mg/dL), and triglycerides (145 +/- 53 versus 116 +/- 33 mg/dL, all P < .05). Exercise tolerance (metabolic equivalent of the task, METs) improved significantly from 10.0 +/- 3.0 to 14.4 +/- 3.6 (P < .01). Resting blood flow decreased (0.78 +/- 0.18 versus 0.69 +/- 0.14 mL.g-1.min-1, P < .05), whereas hyperemic blood flow increased (2.06 +/- 0.35 versus 2.25 +/- 0.40 mL.g-1.min-1, P < .05), resulting in an improved myocardial flow reserve (2.82 +/- 1.07 versus 3.39 +/- 0.91, P < .05). Overall, the myocardial flow reserve was significantly related to exercise performance (METs). In the control group, no changes in resting rate-pressure product, serum cholesterol levels, exercise performance, resting or hyperemic myocardial blood flow, or flow reserve were observed.
Conclusions: Short-term cardiovascular conditioning together with a low-fat diet results in an improved myocardial flow reserve by lowering resting blood flow and increasing coronary vasodilatory capacity. These changes are associated with an improved exercise capacity and may offer a protective effect in patients with coronary artery disease.