BREATHING EFFICIENCY DURING INSPIRATORY THRESHOLD LOADING IN PATIENTSWITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Patients with chronic obstructive pulmonary disease (COPD) demonstrate an increased oxygen cost of breathing. It is as yet unclear whether t his is related to a decreased breathing efficiency. The aim of the pre sent study was to compare breathing efficiency in 16 patients with COP D (II men, five women) and 16 healthy elderly subjects (seven men, nin e women), and to investigate a possible relationship between breathing efficiency and resting energy expenditure (REE). REE was measured usi ng a ventilated hood system. Breathing efficiency was assessed by meas uring oxygen consumption (V'O-2), mean inspiratory mouth pressure (MIP ) and flow during breathing at rest and subsequently during breathing against an inspiratory threshold (40% of maximal inspiratory pressure) . During loaded breathing there was a significant increase in V'o(2), MIP, and external work of breathing compared with unloaded breathing i n both groups. As intended, ventilation did not increase significantly during the breathing efficiency test in the patients with COPD. The b reathing efficiency (median, range) of the patients with COPD was simi lar (3.7%, 1.4-8.7%) to that of the healthy elderly subjects (3.2%, 1. 7-8.3%). Breathing efficiency was not correlated with REE in either gr oup. In the present study, in which dynamic hyperinflation was probabl y prevented, no difference in breathing efficiency was found between h ealthy elderly subjects and COPD patients when breathing against an ex ternal inspiratory threshold. Furthermore, breathing efficiency was no t related to REE in both groups.