Bronchoscopic lung volume reduction with valves: What should the internist know?

Pressure-volume loops while breathing at rest and during exercise in a healthy individual (A) and in a patient with chronic obstructive pulmonary disease (COPD) (B). Inspiratory capacity (maximum volume of breath that can be taken in after exhalation) increases in healthy people during exercise owing to a fall in lung volume at the end of exhalation. The volume loop during normal breathing is situated in the central linear portion of the pressure-volume relationship, which means that relatively small changes in pressure produce comparatively large changes in volume. In COPD, inspiratory capacity declines due to progressive air-trapping during exercise; thus, patients have to breathe at the upper and less compliant portion of the pressure-volume relationship. This means that increasingly higher pressures must be generated for any given breath, increasing the work of breathing.

IC = inspiratory capacity; IRV = inspiratory reserve volume; P = pressure; RV = residual volume; TLC = total lung capacity; V = volume

Used with the permission of the American Thoracic Society.