A 34-year-old man is evaluated due to dyspnea. The patient undergoes complete pulmonary function testing as well as lung volume measurements. His pulmonary volume curve (blue line) is compared with a normal individual's curve (black line) in the illustration below: Which of the following measures is increased in this patient?

Question

A 34-year-old man is evaluated due to dyspnea.  The patient undergoes complete pulmonary function testing as well as lung volume measurements.  His pulmonary volume curve (blue line) is compared with a normal individual's curve (black line) in the illustration below:  Which of the following measures is increased in this patient?

Quizplus · Accepted Answer

11ec160b_3cdb_c5b2_9249_c7d08ba415a7_MD0001_00 The graph compares the respiration curve for a normal, healthy individual (black line) and this patient (blue line), who has chronic obstructive pulmonary disease (COPD); the tracings show resting breaths along with a maximal air intake and expulsion effort. In a resting breath, a single tidal volume (TV) is exchanged. With maximal inhalation, the curve includes both the TV and the inspiratory reserve volume (IRV), which together equal the inspiratory capacity. With maximal exhalation, the curve reflects the expulsion of the IRV and the TV, as well as the amount of additional air that can be expired, which is the expiratory reserve volume (ERV). The air remaining in the lungs following full exhalation is the residual volume (RV). COPD causes air trapping and hyperinflation of the lungs, so these patients breathe at higher baseline lung volumes (higher FRC). The absolute volume of air in the lungs that is not respired, the RV, is substantially increased. The total lung capacity (TLC) also increases but to a lesser extent than RV. Therefore, the fraction of air in the lungs that is not involved in respiration, the RV/TLC ratio, is also increased. (Choice A) ERV is decreased in obstructive lung disease, as less air can be forcefully exhaled due to obstruction. The substantial increase in RV is greater than the decrease in ERV, resulting in the overall increase in FRC. (Choices B, C, and D) Both forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) are decreased in obstructive lung disease due to airway obstruction. Because FEV1 is decreased more than FVC, the FEV1/FVC ratio is also decreased (<0.7 in COPD). Educational objective: Chronic obstructive pulmonary disease causes air trapping and hyperinflation; consequently, these patients breathe at higher baseline lung volumes (higher functional residual capacity). The absolute volume of air in the lungs that is not respired (residual volume) increases substantially, as does the fraction of air in the lungs that is not involved in respiration (residual volume/total lung capacity ratio).

A 34-Year-Old Man Is Evaluated Due to Dyspnea