Characteristics of the washout dead space.

The dead space volume was reproducibly measured in normal and diseased lungs by analysis of an inert gas washout. This washout dead space was appreciably larger than that measured by the Fowler technique. In the patients, the washout dead space (VD(0)) formed 72% of the physiological dead space volume, while the Fowler (VD(F)) method accounted for only 50%. The VD(O) increased significantly with age in males, but not in females. VD(F) was not well related to age in this population. VD(O) and VD(F) did not relate to lung volume in these subjects. Although that portion of the dead space delivered in Phase I was significantly greater in males than in females, it was not responsible for the difference in dead space measured by the two techniques. This volume difference was found in that portion delivered late in the breath (Phase III). The nature of this volume is speculative, but may involve a parallel dead space that is measured in addition to the series dead space.