Prediction and types of dead-space fraction during exercise in male chronic obstructive pulmonary disease patients

A high dead space (V_D) to tidal volume (V_T) ratio during peak exercise (V_D/V_Tpeak) is a sensitive and consistent marker of gas exchange abnormalities; therefore, it is important in patients with chronic obstructive pulmonary disease (COPD). However, it is necessary to use invasive methods to obtain V_D/V_Tpeak, as noninvasive methods, such as end-tidal PCO₂ (P_ETCO_2peak) and P_ETCO₂ adjusted with Jones’ equation (P_JCO_2peak) at peak exercise, have been reported to be inconsistent with arterial PCO₂ at peak exercise (P_aCO_2peak). Hence, this study aimed to generate prediction equations for V_D/V_Tpeak using statistical techniques, and to use P_ETCO_2peak and P_JCO_2peak to calculate the corresponding V_D/V_Tpeaks (i.e., V_D/V_TpeakETV_D/V_TpeakJ).A total of 46 male subjects diagnosed with COPD who underwent incremental cardiopulmonary exercise tests with P_aCO₂ measured via arterial catheterization were enrolled. Demographic data, blood laboratory tests, functional daily activities, chest radiography, two-dimensional echocardiography, and lung function tests were assessed.In multivariate analysis, diffusing capacity, vital capacity, mean inspiratory tidal flow, heart rate, and oxygen pulse at peak exercise were selected with a predictive power of 0.74. There were no significant differences in the PCO_2peak values and the corresponding V_D/V_Tpeak values across the three types (both p = NS).In subjects with COPD, V_D/V_Tpeak can be estimated using statistical methods and the P_ETCO_2peak and P_JCO_2peak. These methods may have similar predictive power and thus can be used in clinical practice.