Lung mechanics in sitting and horizontal postures studied by body plethysmographic methods

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Abstract
Mechanical properties of the lungs were examined in normal subjects in the sitting and supine body postures using body plethysmographic and conventional methods. At comparable lung volumes airway conductance or resistance (measured independently of esophageal pressure) was quite uninfluenced, and lung conductance or resistance (determined during high-frequency breathing, when esophageal pressure and intrapleural pressure variations are known to agree better than during ordinary breathing) was almost uninfluenced by changes in body posture. A "static" lung compliance estimated from plethysmographically measured lung volumes and the corresponding esophageal pressures was less influenced by posture than the conventionally measured "dynamic" lung compliance. Previously reported differences between lung compliance or resistance in the sitting and supine postures seem to be explained by differences in lung volumes at the measurements and probably also by the variation with posture of differences between intrapleural and esophageal pressure changes during ordinary breathing. Changing from upright to horizontal posture therefore does not seem to alter significantly the true mechanical properties of the lungs.