COSTAL DIAPHRAGM CURVATURE IN THE DOG

The curvature of the midcostal region of the diaphragm in seven dogs w as determined at functional residual capacity (FRC) and end inspiratio n during spontaneous breathing and mechanical ventilation and at total lung capacity in the prone and supine positions. Metallic markers wer e attached to muscle fibers on the abdominal surface of the diaphragm, and the dog was allowed to recover from surgery. The three-dimensiona l positions of the markers were determined by biplane videofluoroscopy . A quadratic surface was fit to the bead positions. The principal axe s of the quadratic surface lie nearly along and perpendicular to the m uscle fibers. In both the supine and prone positions, the values of th e principal curvatures were similar at FRC and end inspiration during spontaneous breathing, when muscle tension and transdiaphragmatic pres sure both increase with increasing lung volume, and during mechanical ventilation and passive inflation to total lung capacity, when both de crease relative to their magnitude at FRC. No abrupt change of curvatu re, which might be expected at the edge of the zone of apposition, was apparent. The curvature along the muscle fiber was 0.35 +/- 0.07 cm-1 ; the curvature perpendicular to the muscle fiber was much smaller, 0. 06 +/- 0.01 cm-1. The costal region of the diaphragm displaces and sho rtens as lung volume increases, but its shape, as described by its cur vatures, does not change substantially.