Automated Analysis of Crackles in Patients with Interstitial Pulmonary Fibrosis

Table 1

Individual crackle features	Definition
Number of zero line crossings (ZXS)	The number of times the crackle waveform crossed the baseline
𝑇1	First half-period, Figure 1(a)
Crackle pitch	Crackle pitch (spectral frequency) calculated from 4 half-periods: 𝑇1, 𝑇2, 𝑇3, and 𝑇4, Figure 1(a)
𝑇2/𝑇1	Ratio of the 2nd and 1st half periods
Half-period duration variability (%)	(Standard deviation {𝑇1,𝑇2,𝑇3,…,𝑇𝑛}×100%)/(mean {𝑇1,𝑇2,𝑇3,…,𝑇𝑛})
Crackle timing (timing)	Crackle timing is defined as follows: 1 for early inspiration, 2 for mid-inspiration, 3 for late inspiration, 4 for early expiration, 5 for mid-expiration, 6 for late expiration
Crackle transmission coefficient (CTC)	The degree of crackling sound transmission through the ipsilateral chest, as calculated from crackle family observation by multiple microphones. The CTC has a value of 0% in the absence of any transmission and 100% when there is equal transmission to all ipsilateral channels see [7] for detailed description and discussion.
Amplitude	Amplitude of the highest peak (arbitrary units)
𝐴2/𝐴1	See Figure 1(a)
𝐴3/𝐴1	See Figure 1(a)
Half period amplitude variability (%)	(Standard deviation {𝐴1,𝐴2,𝐴3,…,𝐴𝑛}×100%)/(Mean {𝐴1,𝐴2,𝐴3,…,𝐴𝑛})
Crackle polarity (polarity)	Direction of the highest peak, Figures 1(b) and 1(c) see [8] for detailed description and discussion