Piirila P, Smith HJ, Hodgson U and Sovijärvi AR
Objectives: Body plethysmography is a lung function testing method usually applied for determination of thoracic gas volume and airways resistance, but option to measure work of breathing is available in most models. Although the method has been known over fifty years, assessment of work of breathing with it has not yet systematically studied in obesity. The aim of the study was to evaluate the relevance of work of breathing measured by body plethysmography in obese subjects and to compare the results with those of healthy controls and patients with pulmonary diseases of different pulmonary mechanics. Methods: Altogether sixty-two adults were studied prospectively: healthy non-smoking obese subjects (BMI > 30, N = 15), patients with interstitial lung disease (ILD) (N =15), emphysematic COPD (emphysema) (N = 16) and healthy non-smoking controls (controls) (N = 16). Inspiratory, expiratory and total work of breathing (WOBin, WOBex and WOB) and specific work of breathing (sWOBin, sWOBex and sWOB) were measured. Results: In obese subjects, WOB, WOBin (p < 0.001) and WOBex (p = 0.002) were elevated in comparison to controls. Also in ILD, WOB was significantly higher than in controls (p < 0.006). sWOBin, sWOBex and SWOB were significantly higher in emphysema than in the controls (p < 0.001). Conclusions: In obesity and ILD WOB whereas in emphysematic COPD sWOB differed significantly from controls, which is caused by differences in lung mechanics and lung volumes. The results concerning COPD correspond earlier study, but the present results suggest that body plethysmography is suitable for the assessment of work of breathing also in obesity.
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