A 56-year-old woman with a 75-pack-year history of smoking cigarettes visits her physician in Mumbai because of shoness of breath. The physician sends her to a pulmonary function laboratory for a complete workup. The table below shows pulmonary volumes and capacities obtained using simple spirometry and helium washout techniques. Lung volumes Amount Functional residual capacity 4.5L Inspiratory reserve volume 1.5L Inspiratory capacity 2.0L Vital capacity 3.0L What is the residual volume of this patient?
High-Yield Explanation
In this paicular problem, it is first necessary to calculate the total lung capacity (TLC) by adding the functional residual capacity and inspiratory capacity (TLC = 4.5 L + 2.0 L = 6.5 L). The residual volume is then calculated as the difference between TLC and vital capacity, i.e., 6.5 L - 3.0 L = 3.5L. The total lung capacity, functional residual capacity, and residual volume are often increased in the emphysematous lungs of patients with a long-term history of cigarette smoking.