Comparison of methods to calculate cardiac output using the CO2 rebreathing method

Area of Science:

• Physiology
• Cardiovascular Research

Background:

• The indirect CO2 Fick procedure is a method for calculating cardiac output.
• Accurate estimation of arterial and mixed venous PCO2 is crucial for this calculation.
• Variations in CO2 dissociation curves can affect results.

Purpose of the Study:

• To compare different methods for calculating cardiac output using the indirect CO2 Fick equilibrium method.
• To evaluate alternative calculations for PCO2 and gas tension to content conversion.
• To identify the most accurate approach for determining cardiac output.

Main Methods:

• Comparison of indirect CO2 Fick procedure with dye dilution method.
• Testing alternative calculations for arterial PCO2, mixed venous PCO2, and gas tension to content.
• Utilizing the Bohr equation for arterial PCO2 estimation during exercise.
• Evaluating different CO2 dissociation curves for calculating veno-arterial CO2 content difference.

Main Results:

• Cardiac output values using a "corrected" equilibrium PCO2 approximated mixed venous PCO2 and closely matched dye dilution results.
• Arterial PCO2 was best estimated using the Bohr equation with literature-based dead space prediction equations for the study population.
• Significant differences were observed among CO2 dissociation curves.

Conclusions:

• A "corrected" equilibrium PCO2 method offers improved accuracy for cardiac output calculation via the indirect CO2 Fick procedure.
• The Bohr equation provides a reliable method for estimating arterial PCO2 in exercise.
• Selection of an appropriate CO2 dissociation curve is critical for accurate veno-arterial CO2 content difference determination.