Introduction

Figure 1 – Volume-time graphic presentation of tidal breathing and vital capacity maneuver. (TLC=total lung capacity, RV=residual volume, FRC=functional residual capacity) Pulmonary function tests provide the physician with insight into the workings of the lungs, chest wall, and ventilatory muscles. They are the laboratory basis upon which we diagnose and rate the severity of restrictive and obstructive pulmonary disorders. The best way to understand and remember the patterns of abnormality seen in different disease states is to examine the physiological principles that are responsible for determining lung volumes, flows, and gas exchange. Figure 1 demonstrates a volume-time plot of normal breathing and a deep breath in to total lung capacity (TLC) followed by a complete exhalation to residual volume (RV). The difference between TLC and RV is the vital capacity (VC).