Effects of a natural volume overload state (pregnancy) on left ventricular performance in normal human subjects.

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Abstract
To assess the effects of a natural volume overload state (pregnancy) on left ventricular function echocardiograms were recorded each trimester (TM) and 4-12 wk postpartum. Heart rate increased from 77 .+-. 2 (SEM, standard error of the mean) to 88 .+-. 2 beats/min (TM 1 vs. TM 3, P < 0.01) and declined to 69 .+-. 2.0 beats/min postpartum (P < 0.05 vs. TM 3). Despite these changes, end-diastolic dimension increased from 46.3 .+-. 0.7 to 50.7 .+-. 0.7 mm (TM 1 vs. TM 3, P < 0.01) and decreased postpartum to 47.5 .+-. 0.7 mm (P < 0.01 vs. TM 3). Calculated stroke volume and cardiac index changed correspondingly, but ejection fraction, percent of fractional shortening and mean normalized rate of internal diameter shortening were not significantly altered. Left ventricular wall mass increased during gestation but decreased between TM 3 and postpartum (162 .+-. 8.3 vs. 143 .+-. 6.2 g, P < 0.05). The ratio of posterior wall thickness to left ventricular radius decreased from 0.32 .+-. 0.01 to 0.29 .+-. 0.01 (TM 1 vs. TM 3, P < 0.05), indicating progressive eccentric left ventricular enlargement. A temporary volume overload state in normal humans results in hemodynamic adjustments often observed in cardiac decompensation (increased heart rate and size). Left ventricular function, although not augmented, is well-preserved, leading to an increase in minute output. Despite progressive left ventricular enlargement the shortening characteristics of the left ventricle remain unimpaired.