Abstract
Using pressures on the chest, chest physiotherapy (CP) is efficient but empirical, its mechanisms remain unknown. Historically, CP consisted in applying strong pressures onto the chest, with possible discomfort and risks. New techniques using low pressures on the chest at small lung volumes have emerged but remain controversial. Thus CP now needs scientific basis.
In CP, mucus movement is due to tangential constraints induced by air motion on the air/mucus interface. They are correlated positively to pressure amplitudes and negatively to bronchi volumes in a complex way, due to lung structure and deformability. Thus we evaluated the effects of pressure amplitudes for different lung volumes on mucus motion in the bronchial tree.
We set up an in silico biomechanical model of CP. We developed a model based on physical sub-models fitted with experimental data from the literature. The core elements are the lung multi-scaled geometry, bronchi and pleural cavity mechanics (quasi-static), and linearized fluid mechanics for air and mucus.
Our results show that mucus starts moving only if pressure overcome a threshold (Mauroy, B. et al, Phys Biol 2011; 8(5):056006). A given pressure has a stronger effect on mucus motion if applied at low lung volumes: 75.0% more mucus out if CP is performed at -12.3% FRC instead of -2.5% FRC. But this scenario leads to strong lung constraints (+57.3%), thus to high patient discomfort; it also leads to increased chance of bronchi closure. Thus our model suggests that to maximize its efficiency while minimizing patient discomfort, CP should use the whole range of lung's volumes and the minimal pressures to induce mucus movement. In its limit, our model can predict the minimal pressures in a patient dependent basis.
- © 2014 ERS
