Three-dimensional reconstruction of the in vivo human diaphragm shape at different lung volumes

Abstract

The ability of the diaphragm to generate pressures at different lung volumes (VLs) in humans may be determined by the following factors: 1) its in vivo three-dimensional shape, radius of curvature, and tension according to Laplace law; 2) the relative degree to which it is apposed to the rib cage (i.e., zone of apposition) and lungs (i.e., diaphragm dome); and 3) its length-force properties. To gain more insight into these factors we have reconstructed from nuclear magnetic images the three-dimensional shape of the diaphragm of four normal subjects under supine relaxed conditions at four different VLs: residual volume, functional residual capacity, functional residual capacity plus one-half of the inspiratory capacity, and total lung capacity. Under our experimental conditions the shape of the diaphragm changes substantially in the anteroposterior plane but not in the coronal one. Multivariate regression analysis indicates that the zone of apposition is dependent on both diaphragm shortening and lower rib cage widening with lung inflation, although much more on the first of these two factors. Because of the changes in anteroposterior shape and expansion of the insertional origin at the costal margin with lung inflation, the data therefore suggest that the diaphragm may be more accurately modeled by a "widening piston" (Petroll's model) than a simple "piston in a cylinder" model. A significant portion of the muscular surface is lung apposed, suggesting that diaphragmatic force has radial vectors in the dome and vectors along the body axis in the zone of apposition. The muscular surface area of the diaphragm decreased linearly by approximately 41% with VL from residual volume to total lung capacity. Diaphragmatic fibers may shorten under physiological conditions more than any other skeletal muscle. The large changes in fiber length combined with limited shape changes with lung inflation suggest that the length-twitch force properties of the diaphragm may be the most important factor for the pressure-generating function of this respiratory muscle in response to bilateral phrenic shocks at different VLs.

Dynamic echo-planar MR imaging of the diaphragm for a 3D dynamic analysis

“…Concerning the 2D resolution, our 128×128 matrix (3.5 mm pixels) was of reasonable quality compared to similar studies where a 128×256 matrix was used [2][3][4][5]8,9]. This resolution was enough to adequately segment the diaphragmatic surfaces.…”

“…This marker was a flexible tube filled with water, taped to the skin, as previously described by Gauthier et al [2].…”

“…We used 15 sagittal slices as previous studies [2], but our acquisition protocol allowed us to arbitrarily choose this number without adding any constraints for the subject. The combination with the 15 coronal slices allowed us to over-sample the diaphragmatic surfaces in the zone of apposition.…”

“…Due to the short slice acquisition time of the FFE-EPI technique, the subject did not have to hold his breath, unlike in previous studies [1][2][3][4][5]. Moreover, in quiet breathing situation, the subject breathed with minimal effort as the synchronization flash rhythm mimicked his own respiratory rhythm.…”

“…Previous studies were restricted to various lung volumes, during breath holding and, therefore, not adequate for the study of patients with Chronic Obstructive Pulmonary Disease (COPD) [1][2][3][4][5][6].…”