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 PCO(2) (P(ET)CO(2peak)) and P(ET)CO(2) adjusted with Jones’ equation (P(J)CO(2peak)) at peak exercise, have been reported to be inconsistent with arterial PCO(2) at peak exercise (P(a)CO(2peak)). Hence, this study aimed to generate prediction equations for V(D)/V(Tpeak) using statistical techniques, and to use P(ET)CO(2peak) and P(J)CO(2peak) to calculate the corresponding V(D)/V(Tpeak)s (i.e., V(D)/V(TpeakET)V(D)/V(TpeakJ)). A total of 46 male subjects diagnosed with COPD who underwent incremental cardiopulmonary exercise tests with P(a)CO(2) 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(ET)CO(2peak) and P(J)CO(2peak). These methods may have similar predictive power and thus can be used in clinical practice.