Transcutaneous PCO₂ -based dead space ventilation at submaximal exercise accurately discriminates healthy controls...

Increased physiological dead space ventilation (V_D /V_T ) at exercise reflects pulmonary gas exchange impairment and is a sensitive marker of cardio-respiratory disease. V_D /V_T is typically not measured during routine cardiopulmonary exercise testing (CPET) because its calculation requires arterial blood gas analysis for determination of PaCO₂ . Instead, dead space ventilation is indirectly evaluated as a determinant of the ventilation (VE)/VCO₂ relationship, which also depends on the PaCO₂ set point. We hypothesized that V_D /V_T calculations based on non-invasive transcutaneous PCO₂ (PtcCO₂ ) measurement had better diagnostic characteristics than the VE/VCO₂ slope for the discrimination of healthy subjects from patients with COPD, a common disease associated with impaired pulmonary gas exchange.

Retrospective study of 19 healthy controls and 24 COPD patients who underwent CPET with continuous PtcCO₂ monitoring. Areas under receiver operating characteristics curves (AUC) were calculated to assess diagnostic accuracy of CPET measurement for the discrimination of COPD and Controls.

The AUC for PtcCO₂ -based V_D /V_T at VT1 (0.977) was significantly higher than for the VE/VCO₂ slope (0.660), SpO₂ 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 PtcCO₂ -based V_D /V_T for the discrimination of COPD patients and healthy Controls were 100% and 84%, respectively. All Control subjects had PtcCO₂ -based V_D /V_T  ≤ 0.25.

PtcCO₂ -based V_D /V_T 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 PtcCO₂ may be useful for routine CPET.