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We tested the hypothesis that diaphragm muscle shortening modulates volume displacement and kinematics of the lower rib cage in dogs, and that posture and mode of ventilation affect such modulation. Radiopaque markers were surgically attached to the lower three ribs of the ribcage and to the mid-costal region of the diaphragm in six dogs of ~8 kg, and the locations of these markers were determined by biplane fluoroscopy system. Three-dimensional software modeling techniques were used to compute volume displacement and surface area of the mid-costal diaphragm and the lower three ribs during quiet spontaneous breathing, mechanical ventilation, and bilateral phrenic nerve stimulation at different lung volumes spanning the vital capacity. Volume displaced by the diaphragm relative to that displaced by the lower ribs is disproportionately greater under mechanical ventilation than during spontaneous breathing in the supine position (P<0.05). At maximal stimulation, diaphragm volume displacement grows disproportionately larger than rib volume displacement as lung volume increases (P<0.05). Surface area of both the diaphragm and the lower ribs during maximal stimulation of the diaphragm is reduced compared to that at spontaneous breathing (P<0.05). In the prone posture, mechanical ventilation results in a smaller change in diaphragm surface area than spontaneous breathing (P<0.05). Our data demonstrate that during inspiration the lower rib cage move not only through the pump- and bucket-handle motion, but also rotate around the spine. Taken together, these data support the observation that the kinematics of the lower rib cage and its mechanical interaction with the diaphragm are more complex than previously known.
This article was published in the following journal.
Name: American journal of physiology. Regulatory, integrative and comparative physiology
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A process leading to shortening and/or development of tension in muscle tissue. Muscle contraction occurs by a sliding filament mechanism whereby actin filaments slide inward among the myosin filaments.
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