Left ventricular size, output, and structure during guinea pig pregnancy

We investigated left ventricular (LV) hemodynamics, pressure-volume relations, and morphometry to determine what cardiac changes characterize pregnancy in the guinea pig. Time-bred virgin guinea pigs were paired by weight with unbred controls. Hemodynamic studies and LV pressure-volume relations were obtained on days 59-68 of the 68-day gestation. Weight of control sows increased from 817 to 902 g (P<0.01) and pregnant sows from 810 to 1,251 g (P<0.01). LV weights were no different. When indexed for maternal weight minus uterus and contents, pregnancy produced increases in O₂ consumption, +48% (P<0.01); cardiac output, +32% (P<0.05); and stroke volume, +46% (P<0.025). Passive LV pressure-volume curves (dP/dV) were shifted to the right (P<0.025), but dP/dV at constant pressure was unchanged. Using a thin-walled spherical model, elastic modulus at constant stress was not different. The percent LV inter- and intracellular volumes and myocyte myofibril and organelle volumes were unchanged during pregnancy. In the guinea pig, pregnancy increases LV, output, stroke volume, and size without changes in LV mass, morphometry, or elastic modulus.