A longitudinal study of cardiac output in unstressed pregnant guinea pigs.

A previous study in pregnant guinea pigs failed to demonstrate any increase in cardiac output when a group of pregnant animals was compared with four nonpregnant animals. In the current study an increase in cardiac output of 35 +/- 14 (SE) ml/min, a 13% increase, was observed during an average 2-wk interval between 44 and 58 days of pregnancy (P less than 0.05, term 68 days, n = 8). A significant increase in placental blood flow of 14.8 +/- 6.2 ml/min (42% increase, P less than 0.05) was also observed during this interval without significant change in the percentage of cardiac output going to the uterus. The data on cardiac output and its distribution to the uteroplacental circulations are consistent with reports in other mammalian species; to accommodate the increased demands of the uteroplacental circulation, cardiac output increases as pregnancy advances. These data demonstrate that multiple observations in the same animal describe cardiac output and its distribution more accurately than a single observation.