Comparison of thermal dilution and electrical impedance dilution methods for measurement of cardiac output in standing and exercising horses.

The research paper details the comparison of thermal dilution and electrical impedance dilution methods for the measurement of cardiac output in standing and exercising horses. The study finds that thermal dilution provides a larger estimate of cardiac output while electrical impedance dilution is deemed reliable over a large range of values.

Research Subject

• The study was carried out using fit and clinically normal Standardbreds, a breed of horses, aged between 2 and 5 years, as the subjects.

Methodology

• The researchers used two separate methods of measuring cardiac output, thermal dilution and electrical impedance dilution.
• Impromptu changes in blood temperature and electrical impedance were instigated by bolus injections of saline hypertonic solutions which were of 6% and 9% NaCl concentration.
• Cardiac output was computed by applying Stewart-Hamilton principles to the transients of the indicator dilution.
• The measurements were taken during sequential exercise episodes on a level treadmill over approximately an eight-fold range of cardiac output values.

Results

• The researchers observed a congruence between cardiac outputs determined via electrical impedance dilution at the pulmonary artery and carotid artery.
• It was noticed that cardiac output derived from thermal dilution measured at the carotid artery exceeded that measured at the pulmonary artery.
• Thermal dilution technique resulted in a higher-value cardiac output than the electrical impedance dilution technique at both locations.

Conclusions

• The electrical impedance indicator is conserved on the first transit, hence, the cardiac output measured by electrical impedance dilution at the carotid artery is trustworthy over a broad range of values.
• As compared to the electrical impedance dilution technique, the thermal dilution method provides a larger estimate of cardiac output, likely due to a loss of indicator.
• The study concludes by suggesting that the transpulmonary electrical impedance dilution technique might hold potential for clinical application, particularly in animals where catheterization of the pulmonary artery might not be appropriate or when blood loss needs to be minimized.