DETERMINATION OF LEFT-VENTRICULAR CARDIAC VOLUME BY SIMULTANEOUS RADIONUCLIDE ANGIOGRAPHY AND MEASUREMENT OF OXYGEN-CONSUMPTION AT REST ANDDURING MAXIMAL EXERCISE - A COMPARISON OF 2 NONINVASIVE ISOTOPIC PROCEDURES

The investigation of left ventricular contractile reserve usually requ ires the determination of left ventricular volume, but its measurement with radionuclide angiography is difficult. The aim of this study was to determine left ventricular volume directly during exercise by the simultaneous measurement of peak exercise left ventricular ejection fr action (LVEF) and oxygen consumption (V over dot O-2max) and to compar e the results with another geometric method. In the absence of lung di sease, the systemic arteriovenous oxygen difference (DAV(max)) during maximal exercise converges to 0.13-0.14 ml O-2 per ml blood. The measu rement of V over dot O-2max allows maximal cardiac output (COmax) to b e calculated as V over dot O-2max = COmax. DAV(max). By simultaneously determining LVEF(ex), exercise end-diastolic volume (EDV(ex)) can the n be expressed as a linear function of V over dot O-2max, maximal hear t rate (HR(max)), DAV(max) and LVEF(ex). Then, the relationship betwee n end-diastolic counts and true volume can be derived at rest. The two methods were closely correlated (r = 0.91, P < 0.001), despite the ge ometric method being less accurate when applied to low counting statis tic acquisitions. We conclude that rest and exercise left ventricular volume can be determined non-invasively by the simultaneous measuremen t of V over dot O-2max and LVEF(ex). Furthermore, this method provides additional prognostic information which is clinically relevant in the staging of patients with heart failure.