UNDERSTANDING RIGHT AND LEFT-VENTRICULAR SYSTOLIC FUNCTION AND INTERACTIONS AT REST AND WITH EXERCISE IN PRIMARY PULMONARY-HYPERTENSION

The effort limitation in primary pulmonary hypertension (PPH) is thoug ht to result from an inability to increase cardiac output with exercis e. The precise mechanism, however, is unknown. We studied right ventri cular (RV) and left ventricular (LV) function and interactions in 16 p atients with PPH with electron beam competed tomography (EBCT) at rest and during supine bicycle exercise. RV and LV volumes and masses were measured at systole and diastole, and election fraction and cardiac i ndex computed. Resting RV end-diastolic volume (215 +/- 72 ml) and mas s (110 +/- 45 g) were increased, whereas stroke volume (65 +/- 26 ml) and ejection fraction (31 +/- 8%) were decreased. LV end-diastolic vol ume (80 +/- 31 ml) was decreased, whereas ejection fraction remained n ormal (66 +/- 9%). Cardiac index was at the lower limit of normal (2.2 6 +/- 0.72 L/min/m(2)). During exercise, RV end-diastolic volume was u nchanged (196 +/- 63 ml, p = NS) but stroke volume (52 +/- 29 ml, p <0 .05) and election fraction (26 +/- 10%, p = 0.08) decreased. LV end-di astolic (52 +/- 22 ml, p <0.001), end-systolic (17 +/- 8 ml, p <0.001) , and stroke volumes (35 +/- 20 ml, p <0.001) decreased, whereas elect ion fraction (65 +/- 15%, p = NS) and cardiac index remained unchanged (2.17 +/- 0.93 L/min/m(2), p = NS). The ratio of RV/LV stroke volume at rest (1.21 +/- 1.06) increased with exercise (1.74 +/- 1.13, p = 0. 09). Patients with PPH have increased RV volume and reduced systolic f unction with reduced LV volume and normal systolic function. During ex ercise, RV failure manifested by reduced election fraction and worseni ng tricuspid regurgitation limits cardiac output. LV volume is further reduced due to underfilling rather than direct RV compression.