Partitioning of dead space--a method and reference values in the awake human.

Although dead space is often increased in disease, it is not frequently measured in the clinic. This may reflect that an adequate method as well as reference values are missing. Healthy males and females, n=38, age 20-61 yrs, were connected to a pneumotachograph and a fast CO2 analyser after radial artery catheterization. The physiological dead space was partitioned into airway and alveolar dead space using a delineation principle denoted the pre-interface expirate. Physiological dead space was 201+/-41 mL in males and 150+/-34 mL in females. Dead space values were depending upon parameters reflecting lung size (predicted total lung capacity), breathing pattern and age. After multiple correlation the variation decreased and differences between males and females disappeared. The residual SD was then for physiological dead space 18.9 mL. The clinical use of the new method for determination of dead space can be based upon reference values, with a more narrow range than previous data.