Airway volume, airway resistance, and work and force of breathing: theory

Abstract

Equations for optimal frequencies of breathing at which mechanical work and mean inspiratory force are minimal and which assume dead space and resistance are constant ignore possible changes in airway caliber. We assumed an inverse relationship between resistance and dead space and plotted a series of curves relating mechanical work and mean inspiratory force to frequency of breathing for various dead spaces and corresponding resistances. As dead space increases, the levels of work and inspiratory force fall to minima, then rise; the frequencies at which work and force are minimal increase, then decrease. Adding a series resistance or dead space, changing the resistance/dead space relationship, decreasing lung compliance, or increasing alveolar ventilation do not alter the general shapes of the curves, but change the values of optimal dead space. The optimal dead spaces for minimal work (0.125 liter) and for minimal inspiratory force (0.14 liter) lie within the normal range. Nervously mediated airway tone in healthy subjects may represent optimal adjustment of airway caliber. dead space, optimal; bronchial caliber Submitted on October 26, 1962