PARTITIONING OF THE ELASTIC WORK OF INSPIRATION IN PATIENTS WITH COPDDURING EXERCISE

During exercise, dynamic hyperinflation-induced intrinsic positive end -expiratory pressure (PEEPi) and decreased dynamic lung compliance (CL ,dyn) of patients with chronic obstructive pulmonary disease (COPD) in crease the elastic work of inspiration (Wi) more than would be predict ed from the increase in tidal volume (VT). This contributes significan tly to their exertional breathlessness, In 10 stable patients with COP D, the dynamic Wi was measured during incremental bicycle exercise to exhaustion, The total Wi was then partitioned into the portion require d to overcome PEEPi (Wi,PEEPi) and nonPEEPi elastic load (Wi,nonPEEPi) . The latter is used to overcome the increase in the total respiratory system elastance during inflation, From resting breathing to peak exe rcise, Wi more than doubled (p<0.001). This increase tvas largely due to Wi,PEEPi, which significantly rose from 1.7+/-03 to 5.3+/- 0.8 L.cm H(2)O(-1) (p<0.001), In comparison, Wi,nonPEEPi increased from only 3. 0+/-0.4 to 5.1+/-05 L.cmH(2)O(-1) (p<0.01), Consequently; Wi,PEEPi as a fraction of total Wi increased from 35.5+/-5.6 to 51.0+/-3.3% (p<0.0 2), In addition, the measured Wi,nonPEEPi at peak exercise, when expre ssed as a percentage of its value during resting breathing, was 25% mo re than that predicted from the increase in VT alone, Assuming a const ant chest wall compliance, this can be attributed to the exercise-indu ced decrease in CL,dyn, which was 0.27+/-0.04 and 0.17+/-0.02 L.cmH(2) O(-1) (p<0.01), respectively, during resting breathing and peak exerci se, In conclusion, the dynamic hyperinflation-induced intrinsic positi ve end-expiratory pressure is more important than the increase in tida l volume in raising the work of inspiration during exercise in patient s with chronic obstructive pulmonary disease; the decrease in dynamic lung compliance plays a definite but less important role.