Imposed Work of Breathing during Sustained Maximal Inspiration: Comparison of Six Incentive Spirometers

The designs of incentive spirometers (IS) differ considerably, and we generally distinguish flow-oriented from volume-oriented devices. Neither type of IS provides an estimate of the inspiratory effort required from the patient. Therefore, we evaluated the inspiratory imposed work of breathing (WOB_imp) associated with the use of six models of disposable IS (three flow-oriented and three volume-oriented) at their lowest (minimum) available flow adjustment. MATERIALS AND METHODS: We used a test lung that incorporates a spontaneous breathing mode. The incentive spirometer and its tubing were connected via a one-way valve and a pneumotachograph to the lung model. The inspiratory pressure was measured between the tubing and the flowmeter. Tidal volume was determined by breath-to-breath integration of the flow signal from the pneumotachograph. WOB_imp was calculated from tidal volume and inspiratory pressure change by a pulmonary function computer. RESULTS: Despite comparable flow adjustment, we observed significant differences in the minimum WOB_imp required from patients when different IS were used: Airx 0.11 J/L, Voldyne 5000 0.33 J/L, Coach 0.35 J/L, Triflo II 0.54 J/L, Lung Volume Exerciser 0.60 J/L, and Coach Jr 0.60 J/L (p < 0.05). CONCLUSION: Differences in minimum WOB_imp by different IS may be clinically important in patients at risk for developing inspiratory muscle fatigue. In order to maximize lung expansion in patients with impaired breathing mechanics, we recommend incentive spirometers associated with a low WOB_imp.