Left ventricular performance in normal subjects: a comparison of the responses to exercise in the upright and supine positions.

Left ventricular (LV) performance at rest and during multilevel exercise in the supine and up- right positions was studied in seven normal subjects with equilibrium radionuclide ventriculography. The mean left ventricular end-diastolic volume (LVEDV) during supine rest was 107 4 10 ml ( SEM) and 85 6 ml (p < 0.02) in the upright position; the mean resting left ventricular end-systolic volumes (LVESV) were not diSferent in the upright and supine positions. The LV ejection fraction (LVEF) tended to be slightly higher in the supine (76 2%) than in the upright position (72 4%). The resting hpart rate was 89 + 5 beats/min up- right, compared with 71 6 beats/min supine (p < 0.05). Multilevel exercise testing was carried out at a low work load of 300 kpm/min, an intermediate work load of 600-750 kpm/min and a peak work load of 1092 66 kpm/min supine and 946 146 kpm/min upright (p < 0.05). With peak exercise, supine LVEDV increased significantly, to 135 13 ml (27%), but LVESV did not change. LVEF increased from 76 2% to 84 i 2% (p < 0.05). With upright exercise, LVEDV increased 39% above the resting level, to 116 8 ml (p < 0.02), but remained lower than the supine LVEDVs at intermediate (p < 0.05) and peak work loads. LVESV decreased significantly by 41%, to 19 3 ml, and was significantly smaller than the corresponding supine volume at intermediate and peak exercise (p < 0.05). LVEF increased from 72 4% to 91 2% (p < 0.05), which was significantly higher than peak supine LVEF (p < 0.05). Heart rates at rest and during exercise were higher in the upright position (p < 0.05), but arterial pressures and double products did not differ significantly.