Diaphragm thickness heterogeneity at functional residual capacity and total lung capacity.

One of the determinants of muscular force is the number of myofibrils in parallel, which is approximated by thickness. To better understand the heterogeneity of diaphragm thickness, we quantified the interregional and radial patterns of thickness of nine canine diaphragms rapidly perfusion fixed in situ with glutaraldehyde at functional residual capacity (FRC) (n = 6) and total lung capacity (TLC) (n = 3). Thickness was determined gravimetrically from punch biopsies radiating from the central tendon to rib cage insertion in ventral, middle, and dorsal costal and crural regions. For comparison, the contralateral unfixed hemidiaphragm was sampled in the same fashion. The findings of this investigation include the following. 1) The costal diaphragm exhibits the same pattern of interregional heterogeneity at FRC, TLC, and in the freshly excised state. 2) The costal diaphragm is significantly thinner at FRC in situ (0.17 +/- 0.01 cm) than is the freshly excised contralateral diaphragm (0.21 +/- 0.01 cm; P < 0.05), whereas there is no significant difference between thickness at TLC and the freshly excised state. 3) There is significant, previously underscribed, radial tapering from the rib cage attachment (0.24 +/- 0.02) to the central tendon insertion (0.15 +/- 0.01 cm; P < 0.05) that is exaggerated at TLC. 4) With passive inflation from FRC to TLC, the greatest increase in thickness occurs close to the rib cage attachment for the ventral and medial costal regions but close to the central tendon in the dorsal and crural regions. We conclude that the diaphragm at FRC and TLC exhibits radial thickness heterogeneity that cannot be predicted from dimensions of the freshly excised diaphragm.(ABSTRACT TRUNCATED AT 250 WORDS)