Transcutaneous carbon dioxide threshold during exercise.

BACKGROUND

To study the possible use of transcutaneous carbon dioxide pressure measurements to estimate ventilatory threshold during exercise.

EXPERIMENTAL DESIGN

comparative study.

SETTINGS

Institutional practice, ambulatory care. Patients and measures: seventy-nine subjects.

INTERVENTION

incremental exercise tests with simultaneous recordings of breath by breath gas exchange and transcutaneous carbon dioxide pressure.

MEASURES

Six reviewers determined the ventilatory threshold using both the graphs for the carbon dioxide excretion to oxygen consumption relationship: V slope technique (VTa), and the ventilatory equivalent for oxygen uptake changes over time: (VTb), the respiratory compensation point (RCP) on ventilatory equivalent for carbon dioxide, and the transcutaneous threshold (Ttc) on the transcutaneous carbon dioxide pressure changes over time respectively.

RESULTS

A Ttc could be defined by all observers in 85% of the subjects. Correlation between Ttc and VT expressed as oxygen consumption absolute values ranged from 0.971 to 0.975 on the mean values of six observers. Using the Bland-Altmann approach, differences (mean +/- SD) were 13 +/- 215, -40 +/- 204, 231 +/- 221 ml.min-1 between Ttc and VTa, RCP respectively. A difference of 38 +/- 173 ml.min-1 was found between VTa and VTb. This suggests that Ttc shows little difference with VT but not with RCP.

CONCLUSIONS

We suggest that a carbon dioxide transcutaneous threshold can be found close to the ventilatory threshold. Potential clinical use of transcutaneous device are vast.