Specific aims are (1) to develop techniques to measure regional elastic and contractile behavior of the diaphragm in vivo in dogs using biplane cineradiography; and (2) using these techniques, to study changes in regional function of the diaphragm in response to local impairment of blood flow or local perfusion with anemic, hypoxic, or acidotic blood without causing overall diaphragmatic failure or systemic changes in arterial blood gases or pressures. Our hypothesis is that regional elastic behavior, contractile function, directions of regional length, curvature and area changes, and regional mechanical work can be studied in the diaphragms of intact animals using high speed biplane cineradiograhy to follow the motion of surgically implanted radiopaque markers. The methods of continuum mechanics will be used to analyze the data and to address the following questions: 1. What are the regional and overall changes in diaphragmatic surface area, radii of curvature and major directions of length change as transdiaphragmatic pressure is varied by passive changes in lung volume or during active contraction of the diaphragm? 2. Does the diaphragm contract and relax homogeneously and, if not, are inhomogeneities due to local differences in mechanical properties of the muscle or differences in orientation and curvature? 3. When regional perfusion of the diaphragm is impaired what is the relationship between local reduction in blood flow and work that can be sustained by that region? 4. What maximal level of work can a region of the diaphragm sustain without regional contractile function being affected when being locally perfused with hypoxic, anemic or acidotic blood at constant perfusion pressure or at constant flow? These studies should enhance our knowledge of the geometry and contractile function of the diaphragm in vivo and provide quantitative description of some important causes of diaphragmatic fatigue.
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