Cardiac output in adult and neonatal rats utilizing impedance cardiography

Impedance cardiography (IC) has the potential to be applied to very small animals for the measurement of cardiac output (Q). To evaluate this, Q measured by impedance (ZQ) and thermal dilution (TDQ) were compared in adult Sprague-Dawley rats. Absolute values for TDQ were comparable with ZQ (e.g., 29.7 vs. 26.0 ml.min-1.100 g-1), and both equally followed the change in Q caused by hemorrhage and reinfusion of blood. IC was also evaluated in neonatal rats (1 and 7 day old). Control ZQ values were 113 ml.min-1.100 g-1 for the 1-day-old rats, and 104 ml.min-1.100 g-1 for 7-day-old rats. Both stroke volume and Q decreased with head-up tilt and increased with head-down tilt for both ages. Therefore, in the neonate, ZQ decreased appropriately with age and with preload reduction. From these results, it is concluded that IC can be utilized to evaluate cardiac function in neonatal and adult rats.