Evaluation of a new method using telemetry for monitoring the left ventricular pressure in free-moving rats

Left ventricular pressure (LVP) in free-moving rats was continuously measured for 2 weeks by a telemetry blood pressure measurement system. Prior to LVP measurement, a dummy transmitter was used to determine whether organ weights, including that of the heart and the lungs, or the stiffness of the left ventricular chamber were affected by the catheterization of the LV chamber. Organ weights did not increase, and no functional abnormalities were observed in the left ventricular pressure-volume relationship. The LVP transmitter was implanted in the left ventricle, and systolic LVP, end-diastolic LVP, LV dP/dt max, and heart rate were measured. All parameters were essentially stable during the 2-week observation period after implantation, and the values, especially the heart rate, in the dark phase tended to be higher than those in the light phase. Microscopic examination of the left ventricular wall revealed that implantation of the dummy or LVP transmitter caused no histological damage. We confirmed that LVP in free-moving rats can be measured continuously for 2 weeks without any harmful effect on cardiac function and that this telemetry system should be useful in pharmacological and toxicological studies.