Echocardiographic detection of pulmonary hypertension in anesthetized rats

Evaluation of pulmonary arterial pressure in small laboratory animals requires surgical catheter implantation. However, even this modest surgical procedure is known to retard weight gain, alter various biochemical parameters and may exert other deleterious actions which could complicate data interpretation. To obviate these adverse effects of surgery and to permit better staging of experimental procedures, a method for non-invasive detection of pulmonary hypertension would be desirable. The present study examined the utility of m-mode echocardiography to detect increased pulmonary arterial pressure and right ventricular hypertrophy in rats with monocrotaline-induced pulmonary hypertension. At various times after administration of monocrotaline (105 mg/kg), rats were anesthetized lightly with sodium pentobarbital (30 mg/kg) and m-mode echocardiograms were generated using a 7 mHz transducer with the animals in the supine position. Mean pulmonary arterial pressure was then determined by closed-chest catheterization of the pulmonary artery. At sacrifice, the extent of right ventricular hypertrophy was determined as the ratio of the weight of the right ventricular free wall to that of the left ventricle plus septum. Right ventricular systolic time intervals, determined from the echocardiogram, correlated significantly with the extent of right ventricular hypertrophy (p = 0.05; r2 = 0.39) but not with mean pulmonary arterial pressure (p = 0.2; r2 = 0.14). Echocardiography may provide a simple, non-invasive means to detect cardiopulmonary abnormalities in rats and may thus be useful in staging subsequent experimental procedures without need for prior surgical catheter implantation.