Expiratory cough flow tracings

(A) A series of cough spikes superimposed on the maximal expiratory flow volume curve. (B) An example of a patient who was unable to produce cough spikes. (C) A grossly distorted cough flow/volume curve in a bulbar patient.
This test is performed in a pulmonary function laboratory. The patient starts at total lung capacity by taking a large and deep breath and is then asked to cough sequentially without taking additional inspirations. The measured curve is superimposed on an expiratory limb of the flow volume loop (not shown in this figure).