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

Mauro Contini,Andrea Aliverti,Calogero Claudio Tedesco,Giovanni Berna,Paola Gugliandolo,Alessandra Angelucci,Simona Romani,Piergiuseppe Agostoni,Beatrice Pezzuto

doi:10.3390/s21196666

Abstract

Evaluation of arterial carbon dioxide pressure (PaCO2) and dead space to tidal volume ratio (VD/VT) during exercise is important for the identification of exercise limitation causes in heart failure (HF). However, repeated sampling of arterial or arterialized ear lobe capillary blood may be clumsy. The aim of our study was to estimate PaCO2 by means of a non-invasive technique, transcutaneous PCO2 (PtCO2), and to verify the correlation between PtCO2 and PaCO2 and between their derived parameters, such as VD/VT, during exercise in HF patients. 29 cardiopulmonary exercise tests (CPET) performed on a bike with a ramp protocol aimed at achieving maximal effort in ≈10 min were analyzed. PaCO2 and PtCO2 values were collected at rest and every 2 min during active pedaling. The uncertainty of PCO2 and VD/VT measurements were determined by analyzing the error between the two methods. The accuracy of PtCO2 measurements vs. PaCO2 decreases towards the end of exercise. Therefore, a correction to PtCO2 that keeps into account the time of the measurement was implemented with a multiple regression model. PtCO2 and VD/VT changes at 6, 8 and 10 min vs. 2 min data were evaluated before and after PtCO2 correction. PtCO2 overestimates PaCO2 for high timestamps (median error 2.45, IQR −0.635–5.405, at 10 min vs. 2 min, p-value = 0.011), while the error is negligible after correction (median error 0.50, IQR = −2.21–3.19, p-value > 0.05). The correction allows removing differences also in PCO2 and VD/VT changes. In HF patients PtCO2 is a reliable PaCO2 estimation at rest and at low exercise intensity. At high exercise intensity the overall response appears delayed but reproducible and the error can be overcome by mathematical modeling allowing an accurate estimation by PtCO2 of PaCO2 and VD/VT.

Highlights

Assessment of dead space/tidal volume ratio (VD /VT ) and PaCO2 during exercise is of paramount importance for identification of exercise limitation at cardiopulmonary exercise testing (CPET) in the setting of several cardiovascular and pulmonary diseases, including heart failure (HF)
The aim of our study was to verify the correlation between PtCO2 and PaCO2 and between VD /VT derived from PtCO2 and that derived from PaCO2 during a maximal exercise test in patients with stable heart failure
The present study shows that in patients with severe but stable heart failure PtCO2 without any further correction is a reliable estimation of

Summary

Introduction

Assessment of dead space/tidal volume ratio (VD /VT ) and PaCO2 during exercise is of paramount importance for identification of exercise limitation at cardiopulmonary exercise testing (CPET) in the setting of several cardiovascular and pulmonary diseases, including heart failure (HF). VD /VT value during exercise is calculated through simultaneous measurement of PaCO2 and mean expiratory PCO2 (PE CO2 ) [1]. VD /VT is used to assess ventilation/perfusion mismatch [2,3] and it is elevated in case of concomitant pulmonary hypertension and/or respiratory disease. PaCO2 value during the isocapnic buffering period is a recognized index of reflex ventilation regulation [4,5]. The end tidal CO2 —arterial CO2 pressure gradient (∆PetCO2 − PaCO2 ) during exercise is another parameter useful to assess ventilation perfusion mismatch in the lung [6]

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