Chapter 16: Pulmonary Function Testing, Plethysmography, and Pulmonary Diffusing Capacity

Chapter 16. Pulmonary Function Testing, Plethysmography, and Pulmonary Diffusing Capacity

A 55-year-old man who has smoked 10 cigarettes in the preceding 90 minutes now has a measured HbCO of 10%. If his measured DL_CO on this same day is 21.4 mL·min^–1·mm Hg^–1, what is the best approximation of this patient's actual DL_CO?

a. 18.2 mL·min^–1·mm Hg^–1

b. 23.5 mL·min^–1·mm Hg^–1

c. 19.1 mL·min^–1·mm Hg^–1

d. 20.1 mL·min^–1·mm Hg^–1

e. 22.5 mL·min^–1·mm Hg^–1

The most correct answer is b.

For every % of HbCO present, the measured DL_CO is decreased by about the same amount from the actual DL_CO. In this patient with HbCO = 10%, the measured DL_CO is 21.4 mL·min^–1·mm Hg^–1. Multiplying the measured value of 21.4 by 110% will correct upward toward the actual value of 23.5 mL·min^–1·mm Hg^–1 that would have been found if this patient's HbCO had been 0%.