Scaling behavior in crackle sound during lung inflation

Abstract

During slow inflation of lung lobes, we measure a sequence of short explosive transient sound waves called "crackles," each consisting of an initial spike followed by ringing. The crackle time series is irregular and intermittent, with the number of spikes of size s following a power law, n(s) proportional, variants(-alpha), with alpha=2.77+/-0.05. We develop a model of crackle wave generation and propagation in a tree structure that combines the avalanchelike opening of airway segments with the wave propagation of crackles in a tree structure. The agreement between experiments and simulations suggests that (i) the irregularities are a consequence of structural heterogeneity in the lung, (ii) the intermittent behavior is due to the avalanchelike opening, and (iii) the scaling is a result of successive attenuations acting on the sound spikes as they propagate through a cascade of bifurcations along the airway tree.

Computerized Adventitious Respiratory Sounds as Outcome Measures for Respiratory Therapy: A Systematic Review

“…CRs are assumed to be caused by the sudden opening of abnormally closed airways, [39][40][41][42] and their parameters provide essential information about the function and structure of the tracheobronchial tree 41 (eg, CR recording during mechanical ventilation has been considered a simple method to monitor lung recruitment/derecruitment). 43 However, CR variables have been explored as outcome measures in only 3 studies.…”

Collective Effects in Charge Transfer within a Hybrid Organic-Inorganic System

“…An avalanche height distribution exponent of 2.7 was reported to characterize systems with avalanches following the binary tree structure. 13 This suggests that avalanches in our system may be propagating along the same pattern. The noise data indicate that charge transfer through self-assembled organic molecules occurs as correlated, uninterrupted sequences of events, avalanches, rather than acts of individual electron transfer.…”

Crackle sounds and lung recruitment

“…Additionally, as the airway opening is also associated with crackle sound generation [5,8,12,16,28,34] it may be expected that the density of crackles is highest near the lower knee in the P−V curve.…”

“…The closure of peripheral airways at low transpulmonary pressures (P L ) is exaggerated in the presence of bronchoconstrictor stimuli [11], and we argue that the recruitment during a subsequent reinflation would be accompanied by an increased crackle activity. 5 The patency of the lower airways is fundamentally maintained by the parenchymal tethering forces, and loss of elasticity in the parenchymal network would lead to increased collapsibility of the bronchi. In emphysema, which is characterized clinically by a loss of elastic recoil and significant hyperexpansion of the lungs, permanent destruction of the parenchymal structure takes place [42,43].…”

“…Overall, the recording of crackles at the airway opening results in high-quality waveforms that permit a better assessment of the underlying mechanisms. Although crackle sounds have been studied extensively in vitro in collapsed lungs [1,5,16], the potential of acoustic measurements for the detection of airway recruitment in vivo has not yet been exploited.…”