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Departments of 1 Medicine and 2 Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195; 3 National Aeronautics and Space Administration-Johnson Space Center, Houston, Texas 77058; Departments of 4 Anesthesiology, 5 Physiology/Biophysics, and 6 Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana 46202
To compare the relative contributions of gravity and vascular structure to the distribution of pulmonary blood flow, we flew with pigs on the National Aeronautics and Space Administration KC-135 aircraft. A series of parabolas created alternating weightlessness and 1.8-G conditions. Fluorescent microspheres of varying colors were injected into the pulmonary circulation to mark regional blood flow during different postural and gravitational conditions. The lungs were subsequently removed, air dried, and sectioned into ~2 cm3 pieces. Flow to each piece was determined for the different conditions. Perfusion heterogeneity did not change significantly during weightlessness compared with normal and increased gravitational forces. Regional blood flow to each lung piece changed little despite alterations in posture and gravitational forces. With the use of multiple stepwise linear regression, the contributions of gravity and vascular structure to regional perfusion were separated. We conclude that both gravity and the geometry of the pulmonary vascular tree influence regional pulmonary blood flow. However, the structure of the vascular tree is the primary determinant of regional perfusion in these animals.
blood flow; microgravity; fluorescent microspheres; supine; prone
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