Breath-by-breath measurement of the volume displaced by diaphragm motion

Abstract

To develop an accurate method to measure the volume displaced by diaphragm motion (ΔVdi) breath by breath, we compared ΔVdi measured by a previously evaluated biplanar radiographic method (Singh B, Eastwood PR, and Finucane KE. J Appl Physiol 91: 1913–1923, 2001) at several lung volumes during vital capacity inspirations in 10 healthy and nine hyperinflated subjects with 1) ΔVdi measured from the same chest X-rays by two previously described uniplanar methods (Petroll WM, Knight H, and Rochester DF. J Appl Physiol 69: 2175–2182, 1990; Verschakelen JA, Deschepper K, and Demendts M. J Appl Physiol 72: 1536–1540, 1992) and a proposed method that considered actual cross-sectional shape of the rib cage and spinal volume (ΔVdiS); and 2) ΔVdiS measured by lateral fluoroscopy in the same 10 healthy subjects. Relative to biplanar ΔVdi, ΔVdiS values from lateral chest X-rays and fluoroscopy were not different, whereas ΔVdi values of Petroll et al. and Verschakelen et al. were increased by (means ± SD) 1.98 ± 1.59 and 1.16 ± 0.82 liters, respectively (both P< 0.001). During quiet breathing, ΔVdiS by lateral fluoroscopy was 66 ± 16% of tidal volume and similar to that between functional residual capacity and one-half inspiratory capacity by the biplanar radiographic method. We conclude that accurate breath-by-breath measurements of ΔVdi can be made by using lateral fluoroscopy.