Radionuclide Ventriculography in Normal Volunteers Performing Graded Supine Bicycle Exercise

We used the radionuclide ventriculogram (RVG) to study the left ventricular (LV) ejection fraction (LVEF) response to supine bicycle exercise. The study involved 20 normal volunteers exercising to an end-point of exhaustion. Heart rate (HR), blood pressure (BP), left ventricular ejection fraction, LV end-diastolic volume (number of pixels of LVED), peak ejection rate (PER), peak filling rate (PFR), time to PER and time to PFR were obtained at rest and during each stage of exercise. As expected, mean HR, BP, PER and PFR significantly and continuously increased, while time to PER and time to PFR decreased. The LVEF was initially significantly increased, from baseline to stage 1. LVEF did not increase from stage 1 to stage 2; however, it increased continuously from stage 2 to stage 5. The LVEF increased in all individuals of both sexes, except when the baseline LVEF was high, or where the exercise performance was submaximal. LVED volume did not show any significant change. The proportional increase in exercise PFR was steeper than that of the PER. In summary: (1) the LVEF response during supine exercise is biphasic with an early plateau followed by continuously increasing values; (2) the LVEF response to exercise is independent of sex but is dependent on baseline EF and the intensity of the exercise protocol; (3) no significant changes in LVED dimension occurred; the Frank-Starling mechanism is not employed during supine bicycle exercise, and (4) the increase in PFR appears to be independent of the increase in PER.