Small airway dysfunction predicts excess ventilation and dynamic hyperinflation during exercise in patients with COPD

Abstract

Introduction

Small airway dysfunction (SAD) is a pathophysiological characteristic of chronic obstructive pulmonary disease (COPD). Excess ventilation and dynamic hyperinflation (DH) are two main pathophysiological traits and limiting factors of COPD patients while exercising. We aimed to ascertain whether or not SAD, assessed by the multiple breath nitrogen washout (MBNW), may predict exercise ventilatory inefficiency and DH.

Methods

Fifty stable COPD patients were prospectively studied and underwent MBNW and incremental cardio-pulmonary exercise test (CPET). Indices of conductive (S_cond) and acinar (S_acin) ventilation heterogeneity as well as minute ventilation/CO₂ production (V_E/VCO₂) linear relationship and the change in inspiratory capacity (IC) were analyzed.

Results

S_acin was significantly and directly related to V_E/VCO₂ slope and inversely related to IC change and to peak O₂ uptake (p < 0.01 for all correlations). No significant correlation was found between S_cond and CPET parameters. The regression equation generated by stepwise multiple regression analysis for the V_E/VCO₂ slope and IC change, as dependent variables, included only S_acin, as independent variable. This model accounted for 31% and 36% of the total variance for the V_E/VCO₂ slope and IC change, respectively.

Conclusion

Our study shows the value of the SAD as determinant of the excess ventilation and DH during exercise in patients with stable COPD.