The ratio of cardiopulmonary blood volume to stroke volume as an index of cardiac function in horses.

A method was developed for determining the ratio of cardiopulmonary blood volume to stroke volume, in horses. The radioisotope 99 Tc (technetium 99m pertechnetate) was injected into the jugular vein as a bolus, which was then detected in the right and left ventricles consecutively by a scanning device consisting of a Na I crystal, a collimator, an amplifier and a discriminator. The radiocardiogram (RCG) and the ECG were recorded simultaneously by a two-channel writing device. The ratio of cardiopulmonary blood volume to stroke volume (cardiopulmonary flow index = CPFI) was then determined from the RCG and ECG tracings. Five categories of horses were examined, viz. Thoroughbreds in training, showjumpers in training, horses not in training, horses with cardiovascular disease and horses with chronic lung disease. The mean CPFI of the above categories were respectively 7.0 +/- 0.39, 7.3 +/- 0.45, 6.7 +/- 0.61, 9.8 +/- 1.30 and 6.2 +/- 0.47. The mean CPFI of the subjects with heart disease was significantly greater than the mean values of the other four categories (P less than 0.001). It was concluded that the CPFI was a reproducible physiological parameter in horses and that the value was significantly increased in our series of subjects with heart disease.