Visual lung-sound characterization using time-expanded wave-form analysis
Time amplitude plots of lung sounds are generally made in two ways: expanded or unexpanded. The unexpanded method is similar to a phonocardiographic time amplitude display. This allows an overall view of the acoustic characteristics in real time. In the time expanded analysis the time or x-axis is stretched out so that details of the acoustic phenomena can be examined more carefully. Time domain plots are illustrated in both the time unexpanded and time expanded modes. It is clear that the pattern differences between different types of lung sounds are seen more easily in the expanded mode.
Time is on the horizontal axis, and amplitude on the vertical axis. The plots on the right, reproduced here at a scale of 400 mm per second, are 0.1 sec long and are sections from the 0.8-sec-long plots on the left shown here at 50 mm per second.