Inspiratory crackles--early and late

Crackles: recording, analysis and clinical significance

“…There has been a controversy about the clinical significance of the low frequency sounds recorded, since some researchers have suggested that the low frequencies may also originate in the lungs [56,57]. The high-pass cut-off frequency has varied markedly in recent studies: no prefiltration [56,57], >50 Hz [48], >75 Hz [44], >100 Hz [13,58], >200 Hz [59], and >600 Hz [6,7]. In several studies, different bandpass filters have been applied: 50-2,000 Hz [43], 100-3,000 Hz [10], 150-350 Hz [47], and 150-700 Hz [60].…”

“…Phonocardiographic microphones have been used in the first lung sound recording systems [6,7,40,41], but their low sensitivity and their narrow frequency response band limit their application for further lung sound analysis. DRUZGALSKI et al [42] found air-coupled condenser microphones suitable for lung sound recordings.…”

“…The first phonopneumographic recordings of crackling sounds were presented in the 1970s [5][6][7]. FORGACS [5,8] stated that pulmonary crackles were generated during inspiration as a result of sudden opening of the airways.…”

“…Therefore, the size and properties of the airways could affect the character of a crackle. Since the presentation of this theory, advanced studies on crackling sounds have been conducted using sound spectrography [9,10], phonopneumography [6,7], time-expanded waveform FORGACS [5,8]. However, their theory assumes that when an airway opens, sudden changes occur in elastic stress, i.e.…”

Objective assessment of cough

“…Phonocardiographic microphones were used in the first lung sound recording systems [63,66,67]. Their low intensity levels and frequency response characteristics limit their application to respiratory sound analysis, although they may be suitable in the detection of cough sounds in cough counting.…”