Cardiac systolic time intervals in fetal monkeys: pre-ejection period.

The systolic time intervals of the fetal cardiac cycle were studied by means of simultaneous recordings of electrocardiogram (ECG) and ultrasound Doppler cardiogram (DCG) in chronic preparations of fetal rhesus monkeys. Recordings were made under physiologic conditions as well as during various experimental stresses. The pre-ejection period (PEP) showed no significant relationship with heart rate in the unstressed fetuses, but the acceleration of heart rate induced by epinephrine was accompanied by shortening of PEP. The PEP increased with advancing fetal age. The PEP was inversely correlated with left ventricular end-diastolic pressure and arterial pulse pressure, but showed a positive correlation with both systolic and diastolic arterial blood pressure. The PEP also exhibited strong negative correlation with arterial blood pH. the prolongation was essentially the same whether acidosis was of respiratory or metabolic origin. The PEP increased slightly but significantly during nonacidemic hypoxemia; however, there was no correlation between Pao2 and PEP Epinephrine shortened the PEP significantly, whereas the effect of atropine was inconsistent. Alteration of the plasma glucose level by injection of insulin or glucose did not affect PEP. These findings demonstrate that the PEP may be a useful indicator of fetal cardiac performance, reflecting both myocardial contractility and the hemodynamic state of the cardiovascular system.