I’d spent some time researching single-breath tests a while back and of course ran across the Fowler method for measuring anatomic dead space. It’s a relatively simple test but assessing its results as well as the results of alternate dead space measurement techniques turns out to be more complicated than I had remembered.
The official definition of anatomic dead space is that it is that part of the inhaled volume that remains in the airways at the end of inhalation and does not participate in gas exchange. An accurate estimate of this volume is important because respiratory dead space (Vd/Vt, discussed previously) is composed of both anatomical and physiological dead space. The physiological component of the respiratory dead space cannot be determined without knowing the anatomical dead space.
Anatomic dead space is usually considered to be the physical volume of the airways but static measurements of airway volume do not take into consideration the dynamic aspects of respiration. The most commonly used method for measuring anatomic dead space in a research setting is the single-breath technique developed by Fowler in 1948. In this method, after an inhalation of oxygen, the nitrogen concentration in an individual’s exhalation is plotted against exhaled volume.
