Journal of applied physiology
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We tested the hypothesis that features of upper airway and tracheal geometry can be inferred from acoustic reflection data recorded at the mouth. In six subjects we computed inferences of airway cross-sectional area vs. distance and compared them with measurements obtained from orthogonal radiographic projections of the trachea. The acoustic data show local area maxima at the uvula and hypopharynx and local minima at the oropharynx and the glottis. ⋯ With subjects breathing 80% He-20% O2 there was good intrasubject agreement between acoustic and radiographic data in spite of large intersubject variability. The average coefficient of variation of tracheal area determinations for five trials in all subjects was 0.16. These studies suggest that features of airway geometry between the mouth and carina can be determined accurately and noninvasively in individual subjects from high-frequency reflection data measured at the mouth.
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We have attempted to determine both experimentally and theoretically whether a significant quantity of oxygen enters the pulmonary blood before it reaches the alveolar wall capillaries. We built a microspectrophotometer that allowed us to record oxyhemoglobin saturation values with light reflected from transected frozen pulmonary arteries as small as 100 microns in diameter. We prepared anesthetized cats to provide optimal conditions for precapillary oxygenation, quickly froze their lungs with chilled liquid propane, and removed these lungs. ⋯ These data did not tell us how much this process normally contributes to total lung oxygenation because propane did not freeze the lungs fast enough to capture conditions exactly as they are in life. We therefore made several calculations to estimate the extent of precapillary oxygenation using available data on pulmonary arterial geometry and diffusing capacity. We concluded that pulmonary arterial blood may be as much as 15% oxygenated by this process at rest and as much as 100% during oxygen breathing.