An approach to measuring cardiac output with Doppler flow probes in conscious rats.

The continuous measurement of cardiac output in conscious rats is difficult. Previously, Doppler flow probes have been applied to the ascending aorta by means of silicone cuffs. The placement of these cuffs can conceivably introduce errors engendered by the destruction of nerve fibers that are important in cardiac autonomic innervation. We report a novel method of Doppler flow-probe attachment directly to the ascending aorta by means of a polyacrylic cement. When we compared the response with baroreceptor activation with methoxamine and nitroprusside in conscious rats equipped either with probes attached via cuffs or directly via cement, we observed that animals equipped with cuffs failed to give the expected cardiac output and heart rate responses after nitroprusside administration. In contrast, animals that had their probes attached with cement displayed the expected responses. The data not only show that probes applied with cement give a result superior to probes attached with cuffs but also verify the suspicion that the ascending aorta is associated with nerve fibers that are important in mediating baroreceptor responses.