MEASUREMENT OF CARDIAC-OUTPUT IN STANDING HORSES BY DOPPLER-ECHOCARDIOGRAPHY AND THERMODILUTION

Measurements of cardiac output by Doppler echocardiography were compar ed to simultaneous measurements by thermodilution in 9 conscious horse s. In the Doppler technique, mean blood flow velocities for estimation of cardiac output were recorded from the aorta and pulmonary artery, The flow area of each vessel was calculated from the vessel diameter, measured from a 2-dimensional ultrasound image. Differences in the sit e and method of measuring the vessel diameter altered the estimation o f cardiac output by the Doppler method, Cardiac output was modified by the i.v. infusion of 4 mu g/kg bwt/min dopamine and 4 mu g/kg bwt/min dobutamine and by the i.v. administration of 10 mu g/kg bwt detomidin e and 20 mu g/kg bwt butorphanol, Doppler measurements of cardiac outp ut correlated closely with measurement by thermodilution. Measurements from the aortic outflow correlated more closely with thermodilution, than those from the pulmonary artery (r = 0.89 and r = 0.77, respectiv ely), Doppler measurements agreed most closely with thermodilution mea surements when the mean flow velocity was recorded from the aorta and the flow area was measured from the ascending aorta using the leading edge method, There was no significant bias between the 2 techniques wh en Doppler flow velocities were recorded by this method and the limits of agreement were narrow (+/- 12.26 l/min). The differences between t he 2 methods increased with increasing cardiac output. Doppler echocar diography is a safe noninvasive method of measuring cardiac output in horses, The agreement between Doppler echocardiography and thermodilut ion in this study is similar to that reported in man and is similar to that reported between thermodilution and other techniques in man.