Cardiac output determined by the CO2 rebreathing method during arm exercise

Area of Science:

• Exercise Physiology
• Cardiovascular Physiology
• Respiratory Physiology

Background:

• Arm exercise impacts respiratory muscles, necessitating evaluation of CO2 rebreathing for cardiac output (Q) determination.
• Accurate measurement of cardiac output is crucial for understanding physiological responses to exercise.
• Existing methods for measuring Q during arm exercise require validation.

Purpose of the Study:

• To compare three methods for determining arterial carbon dioxide tension (PaCO2) during arm exercise.
• To verify the linearity of the relationship between cardiac output (Q) and oxygen uptake (VO2) during arm exercise.
• To assess the accuracy of the CO2 rebreathing method for determining Q during arm exercise.

Main Methods:

• Sixty male subjects performed arm-cranking exercise at 20%, 40%, and 60% of maximal load.
• Cardiac output (Q) was measured using the CO2 rebreathing method, with PaCO2 estimated via modified Bohr formula, arterialized blood, and end-expiratory CO2.
• Carbon dioxide output (VCO2) and mixed venous CO2 tension (PvCO2) were measured; comparisons were made with direct Fick measurements.

Main Results:

• High correlation (P < 0.01) was found among the three methods for estimating PaCO2.
• A linear relationship (P < 0.01) was confirmed between cardiac output (Q) and oxygen uptake (VO2).
• CO2 rebreathing method showed good agreement with direct Fick measurements and other established methods.

Conclusions:

• The CO2 rebreathing method is accurate for determining cardiac output (Q) during submaximal arm exercise.
• Validated methods for PaCO2 estimation support the reliability of the CO2 rebreathing technique.
• The linear Q-VO2 relationship during arm exercise is consistent with findings from other exercise modalities.