Comparison between PtCO₂ and PaCO₂ and Derived Parameters in Heart Failure Patients during Exercise: A Preliminary...

Area of Science:

• Cardiopulmonary physiology
• Exercise intolerance in heart failure
• Non-invasive monitoring techniques

Background:

• Assessing arterial carbon dioxide pressure (PaCO2) and dead space to tidal volume ratio (VD/VT) during exercise is crucial for understanding exercise limitation causes in heart failure (HF).
• Current methods involving arterial or ear lobe capillary blood sampling can be invasive and cumbersome.
• Non-invasive monitoring offers a potentially more practical alternative for evaluating these parameters.

Purpose of the Study:

• To evaluate transcutaneous PCO2 (PtCO2) as a non-invasive method to estimate PaCO2 in heart failure patients during cardiopulmonary exercise tests (CPET).
• To assess the correlation between PtCO2 and PaCO2, and their derived parameters like VD/VT, during incremental exercise.
• To develop and validate a correction method for PtCO2 to improve its accuracy at higher exercise intensities.

Main Methods:

• 29 cardiopulmonary exercise tests (CPET) were conducted on a bicycle ergometer with a ramp protocol.
• PaCO2 and PtCO2 measurements were taken at rest and every 2 minutes during exercise.
• The error between PtCO2 and PaCO2 was analyzed, and a multiple regression model was used to correct PtCO2 values based on measurement time.
• VD/VT changes were evaluated before and after PtCO2 correction.

Main Results:

• PtCO2 measurements showed decreasing accuracy compared to PaCO2 at higher exercise intensities, with a median error of 2.45 at 10 minutes.
• A mathematical correction model significantly reduced the error, with a median error of 0.50 at 10 minutes (p > 0.05).
• The correction improved the estimation of both PaCO2 and VD/VT changes, making PtCO2 a reliable measure across different exercise intensities.

Conclusions:

• Transcutaneous PCO2 (PtCO2) is a reliable non-invasive method for estimating PaCO2 and VD/VT at rest and low exercise intensities in heart failure patients.
• At high exercise intensities, PtCO2 accuracy decreases but can be significantly improved using a time-based mathematical correction model.
• This corrected non-invasive approach facilitates accurate assessment of exercise limitation in heart failure patients without repeated invasive sampling.