Noninvasive determination of myocardial blood flow, oxygen consumption andefficiency in normal humans by carbon-11 acetate positron emission tomography imaging

The aims of this study were: (1) to measure noninvasively and near simultan eously myocardial blood flow, oxygen consumption, and contractile function and (2) to analyze myocardial energy expenditure and efficiency at rest and during dobutamine stress in normal humans. Dynamic and gated carbon-11 ace tate positron emission tomography (PET) imaging was performed in 11 normal subjects. The initial uptake of C-11-acetate was measured to estimate myoca rdial blood flow. Oxygen consumption was derived from the monoexponential s lope of the C-11-clearance curve recorded during myocardial washout. EGG-ga ted systolic and diastolic images were acquired during the peak myocardial C-11 activity to measure left ventricular radius, myocardial wall thickness , and long axis length. Myocardial oxygen consumption and parameters of car diac geometry were used to determine myocardial energetics and cardiac effi ciency by tension-area area analysis. Myocardial blood flow averaged 0.8+/- 0.06 ml min(-1) g(-1) at rest and 1.48+/-0.15 ml min(-1) g(-1) during dobut amine stress. Oxygen delivery and consumption were 151+/-13 and 88+/-15 mu l O-2 min(-1) g(-1) at rest and increased to 291+/-31 and 216+/-31 mu l O-2 min(-1) g(-1) respectively, during pharmacological stress (P<0.001). Oxyge n extraction increased from 59%+/-8% at rest to 76%+/-9% during stress (P<0 .001). Mechanical efficiency was 29%+/-6% at rest and 32%+/-6% during dobut amine stress (P=NS) while external work efficiency was 16%+/-6% at rest and increased to 21%+/-4% (P<0.01) during dobutamine stress. Stepwise linear r egression analysis identified rate-pressure product and external cardiac wo rk as major correlates of oxygen consumption. In summary, rapid dynamic and gated PET C-11 acetate imaging provides the unique capability to study non invasively determinants of myocardial energy delivery, expenditure, and eff iciency.