Transcutaneous PCO -based dead space ventilation at submaximal exercise accurately discriminates healthy controls from patients with chronic obstructive pulmonary disease.

BACKGROUND

Increased physiological dead space ventilation (V /V ) at exercise reflects pulmonary gas exchange impairment and is a sensitive marker of cardio-respiratory disease. V /V is typically not measured during routine cardiopulmonary exercise testing (CPET) because its calculation requires arterial blood gas analysis for determination of PaCO . Instead, dead space ventilation is indirectly evaluated as a determinant of the ventilation (VE)/VCO relationship, which also depends on the PaCO set point. We hypothesized that V /V calculations based on non-invasive transcutaneous PCO (PtcCO ) measurement had better diagnostic characteristics than the VE/VCO slope for the discrimination of healthy subjects from patients with COPD, a common disease associated with impaired pulmonary gas exchange.

METHODS

Retrospective study of 19 healthy controls and 24 COPD patients who underwent CPET with continuous PtcCO monitoring. Areas under receiver operating characteristics curves (AUC) were calculated to assess diagnostic accuracy of CPET measurement for the discrimination of COPD and Controls.

RESULTS

The AUC for PtcCO -based V /V at VT1 (0.977) was significantly higher than for the VE/VCO slope (0.660), SpO at peak exercise (0.913), decrease in inspiratory capacity (0.719), and ventilatory reserve (0.708). At a threshold of 0.24, the sensitivity and specificity of PtcCO -based V /V for the discrimination of COPD patients and healthy Controls were 100% and 84%, respectively. All Control subjects had PtcCO -based V /V  ≤ 0.25.

CONCLUSIONS

PtcCO -based V /V was the most accurate measurement to discriminate healthy controls from subjects with COPD, a chronic lung disease associated with altered pulmonary gas exchange. Non-invasive monitoring of PtcCO may be useful for routine CPET.