The analysis of components that lead to increased work of breathing in chronic obstructive pulmonary disease patients

Abstract

Background: This study is to explore the components and related mechanism responsible for the increase of work of breathing (WB) in chronic obstructive pulmonary disease (COPD) patients.

Methods: Eight COPD patients and eight healthy volunteers were recruited in the study. The rebreathing method was used to increase end-tidal CO2 partial pressure (PetCO2) and stimulate the increase in ventilation (VE). The increase in VE, WB, and changes in the compositions of WB were observed and analyzed. The WB and its components were calculated using the Campbell diagram.

Results: The inspiratory work (Wi) of breathing, a major component of total work of breathing (Wtot), in the COPD group was significantly higher than the control group during quiet breathing (P<0.05). As the minute VE increased, Wtot and Wi increased in a linear manner, and the slope of increase was significantly higher in the COPD group as compared to the normal group (P<0.05). The analyses of changes in overcoming airway resistance (Wrs) and lung/chest-wall elastance (Wel) indicated that the slope of increase (response to VE increase) of Wrs was not significantly different between the two groups (P>0.05) although the Wrs in the COPD group was always higher than the normal group (P<0.05). However, as the VE increased, the slope of the increase in Wel was significantly higher in the COPD group than the normal group. Work done to overcome the intrinsic PEEP (WPEEPi), a component of the Wel, was not observed in the control group. However, WPEEPi increased gradually as VE increased and accounted for 56% of Wel at the end of rebreathing trial in COPD group.

Conclusions: Airway resistance was the main cause for increased WB during quiet breathing. As the VE increased, an increase of WPEEPi became an important part of increased WB in COPD patients, so it is important to reduce dynamic hyperinflation in COPD patients.

Keywords: Work of breathing (WB); chronic obstructive pulmonary disease (COPD); intrinsic PEEP (PEEPi); lung elastance.

Conflict of interest statement

The authors have no conflicts of interest to declare.

Figures

Figure 1

Campbell diagram and the work of breathing calculation. (A) Pressure and lung volume changes during breathing. CL represents for compliance of lung and Ccw for compliance of chest wall; (B) Wi = Wrs (dot area) + Wel (horizontal line area); (C) Wex was the vertical line area on the right of the Ccw; (D) the area inside the network was the work done to overcome intrinsic PEEP (WPEEPi). Wi, inspiratory work; Wrs, work to overcome airway resistance; Wel, work to overcome elestance; Wex, expiratory work; CL, compliance of lung; Ccw, compliance of chest wall.

Figure 2

Wtot at different levels of PetCO2. Wtot, total work of breathing; PetCO2, end-tidal CO2 partial pressure.

Figure 3

Work of breathing and its components in response to increased ventilation. VE, ventilation.