Ap. Gauthier et al., 3-DIMENSIONAL RECONSTRUCTION OF THE IN-VIVO HUMAN DIAPHRAGM SHAPE AT DIFFERENT LUNG-VOLUMES, Journal of applied physiology, 76(2), 1994, pp. 495-506
The ability of the diaphragm to generate pressures at different lung v
olumes (VLs) in humans may be determined by the following factors: I)
its in vivo three-dimensional shape, radius of curvature, and tension
according to Laplace law; 2) the relative degree to which it is appose
d to the rib cage (i.e., zone of apposition) and lungs (i.e., diaphrag
m 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, fun
ctional residual capacity, functional residual capacity plus one-half
of the inspiratory capacity, and total lung capacity. Under our experi
mental conditions the shape of the diaphragm changes substantially in
the anteroposterior plane but not in the coronal one. Multivariate reg
ression analysis indicates that the zone of apposition is dependent on
both diaphragm shortening and lower rib cage widening with lung infla
tion, 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 s
uggest that the diaphragm may be more accurately modeled by a ''wideni
ng piston'' (Petroll's model) than a simple ''piston in a cylinder'' m
odel. A significant portion of the muscular surface is lung apposed, s
uggesting that diaphragmatic force has radial vectors in the dome and
vectors along the body axis in the zone of apposition. The muscular su
rface area of the diaphragm decreased linearly by similar to 41% with
VL from residual volume to total lung capacity. Diaphragmatic fibers m
ay 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 prop
erties of the diaphragm may be the most important factor for the press
ure-generating function of this respiratory muscle in response to bila
teral phrenic shocks at different VLs.