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Figure 2: Identification of the start and end of inspiration. (a) A time-amplitude plot of a single channel breath sound band pass filtered between 80 Hz and 500 Hz. (b) The running average of the absolute value of the time amplitude signal. The start of inspiration was defined as the time when the signal reached 25% of its maximum level (left vertical line). The end of inspiration was defined as the time when the signal just dropped below 25% of its maximum value (right vertical line).