Cardiac output determination by use of lithium dilution during exercise in horses.

The research investigates the accuracy of the lithium dilution method (LiDCO) in measuring cardiac output (CO), especially during high-intensity exercise in Thoroughbred horses. The researchers used the widely accepted Fick principle for comparison, testing both methods over two separate exercise studies involving 13 horses.

Research Methods

• The first part of the investigation involved five horses which performed a warm-up and then an intense exercise test. During the test, CO measurements were taken using both the Fick principle and LiDCO methods at 60-second intervals, resulting in seven total measurements.
• The second part of the investigation included eight separate horses. These horses also performed a warm-up routine, followed by an intense exercise test involving three measurements.

Results of the Study

• The results indicated that the cardiac output increased significantly as the speed of exercise increased. This was evident with both the Fick principle and LiDCO measurements.
• In the first part of the experiment, it was noted that the LiDCO method significantly overestimated the CO when compared to the Fick principle. This overestimation increased as the intensity of exercise and number of lithium injections increased. On average, the bias was 246 +/- 264 mL of blood/min/kg.
• In the second part of the investigation, three lithium injections resulted in less overestimation of CO (a bias of 67 +/- 100mL of blood/kg/min) than seven injections did in the first part.

Conclusions from the Research

• The study concluded that lithium dilution can act as an acceptable alternative to the Fick principle in measuring the cardiac output in horses during intense exercise. This conclusion relies on the provision that the number of lithium injections is limited, as increasing doses resulted in greater overestimation of CO.