Alveolar and Total Ventilation and the Dead Space Problem

Abstract

An analysis is presented of the respiratory dead space problem, in which careful distinctions are made between the anatomical dead space, measured by anatomical means, virtual expired dead air, calculated from the Bohr formula, and virtual (cylindrical) dead space, calculated from laminar flow principles. In five normal subjects in the steady state of breathing various CO2 mixtures at rest and in exercise, ventilation, tidal volume and frequency were recorded, and inspired and expired air and arterial blood (for alveolar air) were analyzed. The experimental results support the following features of the theoretical analysis: a) the washout phenomenon may be represented in terms of virtual dead space flushed by laminar flow; b) the virtual dead space increases linearly with tidal volume; c) the expired alveolar air volume increases linearly with tidal volume, when the latter exceeds twice the virtual dead space; d) the respiratory frequency increases linearly with ventilation in exercise and CO2 inhalation; and e) the alveolar ventilation increases linearly with total ventilation. The constants for all the equations of the system can be derived from four fundamental system properties, whose normal values were estimated from the experimental data, as follows: a) for the personal standard virtual dead space (DS0), 180 cc, or 37 cc/l. of vital capacity; b) for the increase in virtual dead space with tidal volume (Kds), 23 cc/l. or DS0/8; c) for the respiratory frequency at zero ventilation (f0), 9.8 cycles/min.; d) for the increase in frequency with total ventilation (Kf), .267 cycles/min/l/min. Numerous important and useful applications of these findings are discussed. Submitted on May 22, 1956