Figure 2 Time-expanded waveform of sections of pleural friction rub. In panel A, the upper

There are other sounds that have yet to be added to this classification, including squawks, squeaks, short wheezes, and pleural friction rubs. On waveform analysis, squawks, squeaks, and short wheezes have a sinusoidal pattern and a brief duration (4080 ms). Squawks were described in bird-fancier’s lung, a form of hypersensitivity pneumo­ nitis. They are common in hypersensitivity pneumonitis and in idiopathic pulmonary fi­ brosis (IPF). They can also be found in pneumonia.