Muscle shortening and volume displacement are critical determinants of the pressure generating capacity of the diaphragm. This study was designed to test the hypothesis that diaphragm volume displacement is heterogeneous and distribution of volume displacement is dependent on regional muscle shortening, posture and level of muscle activation. Radio opaque markers were sutured along muscle bundles of the peritoneal surface of the crural muscle, dorsal costal, mid-costal, and ventral costal regions of the left hemi-diaphragm in four dogs. The markers were followed by bi-planar video fluoroscopy during quiet spontaneous breathing, passive inflation to total lung capacity (TLC), as well as inspiratory efforts against an occluded airway at three lung volumes spanning the vital capacity (functional residual capacity (FRC), FRC + 1/2 inspiratory capacity (IC), and TLC in both the prone and supine postures. Our data show the ventral costal diaphragm had the largest volume displacement (VD) and contributed nearly 2 times to the total diaphragm VD compared to the dorsal costal portion. In addition, the ventral costal diaphragm contributed nearly half of the total VD in the prone position while it only contributed a quarter of the total VD in the supine. During efforts against occluded airway and during passive inflation to TLC in the supine position, the crural diaphragm displaced volume equivalent to that of the mid-costal portion. We conclude that regional muscle shortening closely match regional volume displacement, and the primary force generator of the diaphragm is primarily dominated by contribution of ventral costal region to its volume displacement.
- Respiratory muscle
- Chest wall mechanics
- Modeling diaphragm kinematics
- Copyright © 2016, American Journal of Physiology-Regulatory, Integrative and Comparative Physiology