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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 DLCO on this same day is 21.4 mL·min–1·mm Hg–1, what is the best approximation of this patient's actual DLCO?

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 DLCO is decreased by about the same amount from the actual DLCO. In this patient with HbCO = 10%, the measured DLCO 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%.

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