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Diaphragm Ultrasonography as an Alternative to Whole-Body Plethysmography in Pulmonary Function Testing

Centre for Exercise Science and Medicine, Institute of Biomedical and Life Sciences, Glasgow University, Glasgow, Scotland (S.S., M.M., N.G.M.); Department of Respiratory Medicine, Glasgow Royal Infirmary, Glasgow, Scotland (J.P.F., R.C.); and Department of Medical Cardiology, Western Infirmary, Glasgow, Scotland (M.M.).

Address correspondence to Niall G. MacFarlane, PhD, University of Glasgow, Room 354, West Medical Building, Glasgow G12 8QQ, Scotland. E-mail: N.MacFarlane{at}bio.gla.ac.uk

Objective. Whole-body plethysmography is a common method of measuring pulmonary function. Although this technique provides a sensitive measure of pulmonary function, it can be problematic and unsuitable in some patients. The development of more accessible techniques would be beneficial. Methods. A prospective study was performed to validate diaphragm ultrasonography as an alternative to whole-body plethysmography in patients referred for pulmonary function testing. Diaphragm movement and position were assessed by ultrasonography after standard pulmonary function testing using whole-body plethysmography. Results. A wide range of lung function was observed. Standard lung volumes were as follows: total lung capacity, 5.57 ± 1.31 L, residual volume, 2.27 ± 0.56 L; and vital capacity, 3.30 ± 0.98 L (mean ± SD). The ratio of forced expiratory volume in 1 second to forced vital capacity was calculated as 0.69 ± 0.08. Ultrasonography showed that mean diaphragm excursion values were 11.1 ± 3.8 mm (2-dimensional), 14.7 ± 4.1 mm during quiet breathing (M-mode), and 14.8 ± 3.9 mm during a maximal sniff (M-mode). The velocity of diaphragm movement rose sharply during the sniff maneuver from 15.2 ± 5.8 mm/s during quiet breathing to 104.0 ± 33.4 mm/s. Static 2-dimensional measures of diaphragm position at the end of quiet inspiration or expiration correlated with standard measures of lung volume on plethysmography (eg, a correlation coefficient of 0.83 was obtained with end inspiration and vital capacity). All measures of diaphragm movement (whether by 2-dimensional or M-mode techniques) were poorly correlated with any lung volumes measured. Conclusions. These data suggest that dynamic measurements using diaphragm ultrasonography provide a relatively poor measure of pulmonary function in relation to whole-body plethysmography.

Key Words: diaphragm • plethysmography • ultrasonography

Abbreviations: FEV₁, forced expiratory volume in 1 second • FVC, forced vital capacity • PA, posterior-anterior • TLC, total lung capacity • 2D, 2-dimensional • VC, vital capacity

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