Transcutaneous PCO for Exercise Gas Exchange Efficiency in Chronic Obstructive Pulmonary Disease.

Gas exchange inefficiency and dynamic hyperinflation contributes to exercise limitation in chronic obstructive pulmonary disease (COPD). It is also characterized by an elevated fraction of physiological dead space (V/V). Noninvasive methods for accurate V/V assessment during exercise in patients are lacking. The current study sought to compare transcutaneous PCO (TcPCO) with the gold standard-arterial PCO (PaCO)-and other available methods (end tidal CO and the Jones equation) for estimating V/V during incremental exercise in COPD. Ten COPD patients completed a symptom limited incremental cycle exercise. TcPCO was measured by a heated electrode on the ear-lobe. Radial artery blood was collected at rest, during unloaded cycling (UL) and every minute during exercise and recovery. Ventilation and gas exchange were measured breath-by-breath. Bland-Altman analysis examined agreement of PCO and V/V calculated using PaCO, TcPCO, end-tidal PCO (PCO) and estimated PaCO by the Jones equation (PaCO-Jones). Lin's Concordance Correlation Coefficient (CCC) was assessed. 114 measurements were obtained from the 10 COPD subjects. The bias between TcPCO and PaCO was 0.86 mmHg with upper and lower limit of agreement ranging -2.28 mmHg to 3.99 mmHg. Correlation between TcPCO and PaCO during rest and exercise was r=0.907 ( < 0.001; CCC = 0.941) and V/V using TcPCO vs. PaCO was r=0.958 ( < 0.0001; CCC = 0.967). Correlation between PaCO-Jones and PCO vs. PaCO were r=0.755, 0.755, ( < 0.001; CCC = 0.832, 0.718) and for V/V calculation (r=0.793, 0.610;  < 0.0001; CCC = 0.760, 0.448), respectively. The results support the accuracy of TcPCO to reflect PaCO and calculate V/V during rest and exercise, but not in recovery, in COPD patients, enabling improved accuracy of noninvasive assessment of gas exchange inefficiency during incremental exercise testing.