Mucus clearance by two-phase gas-liquid flow mechanism: asymmetric periodic flow model

Abstract

Mucus transport by two-phase gas-liquid flow mechanism was investigated with in vitro flow models under asymmetric periodic airflow conditions with nine different liquid solutions with rheological properties similar to human sputum. The flow model was made with 1.0-cm-ID glass tube and positioned either vertically or horizontally. With a constant supply of the test liquids into the model tube (0.5 ml/min), the liquid layer transport speed (LLTS) as well as the mean liquid layer thickness at steady-state condition (hs) was measured in conjunction with various airflow patterns of different expiratory and inspiratory flow rate, breathing frequency (f), and tidal volume (VT). The flow patterns were maintained within the range of normal breathing. In the horizontal tube model, LLTS ranged from 1.14 +/- 0.02 to 3.39 +/- 0.04 cm/min at the peak expiratory flow rate (VEp) of 30-60 l/min. The inspiratory flow rate, as well as f and VT did not affect LLTS. However, LLTS increased with increasing VEp, and at the same VEp LLTS was higher with viscoelastic than with viscous liquid. In the vertical tube model, the upward transport of mucus could not be achieved at VEp lower than 30 l/min particularly with low viscosity and low elasticity fluid. However, at high values of VEp, LLTS was comparable to that in the horizontal tube model with viscoelastic fluid, whereas LLTS of viscous liquid showed 26-40% lower than that in the horizontal tube model. The value of hs was 5-20% of the tube diameter at VEp of 30-60 l/min in both models. These results indicate that effective mucus clearance can be achieved by two-phase gas-liquid flow mechanism in patients with excessive bronchial secretions with biased tidal breathing favoring the expiratory flow and that the clearance can be further promoted by changing rheological properties of mucus.

Intrapulmonary Effects of Setting Parameters in Portable Intrapulmonary Percussive Ventilation Devices

“…18 Previous in vitro and in vivo studies already demonstrated that increased expiratory flows induced by increased inspiratory time favor mucus clearance. Kim et al 19 investigated in vitro flow models with mechanical ventilation, maintaining E/I flow ratios at 1.5/1, 2/1, and 3/1. They found that mucus transport speed linearly increased with increasing E/I flow ratio.…”

Efficacy of Pursed Lips Breathing with Forced Expiration Techniques and Active Cycle of Breathing Technique on Pulmonary Mucus Clearance in Healthy Subjects

“…The cephalad mucus transport can be achieved by keeping the expiratory flow. In addition, the ratio of the expiratory to the inspiratory flow rate of 1.5 with a tidal volume of 500 ml is sufficient to transport mucus in a vertical tube model [27][28][29][30] . Therefore, we speculate that the increased mucus clearance achieved by PLB & FETs is the result of this mechanism.…”

Airways Clearance Techniques in Cystic Fibrosis: Physiology, Devices and the Future

“…In the latter, mucus transport can be achieved by expiratory airflow during forced expiration, as well as tidal breathing. The peak expiratory flow/peak inspiratory flow ratio (PEF/PIF) needs to be > 1.1 to achieve this (Kim et al, 1986;Kim et al, 1986a;Kim et al, 1987) and the frequency of oscillation needs to be between 3 -17 Hz, with the ideal frequency being around 13 Hz (Gross et al, 1985) 3. Decrease the mucus visco-elasticity in the airway, and hence improve mucus transport (App et al, 1998) (Konstan et al, 1994).…”

“…The flow rates generated by vibration would be insufficient to augment secretion clearance by annular flow, since the PEF/PIF ratio was 0.75 and needs to exceed 1.1 (Kim et al, 1987). Why the inspiratory flow bias occurred is unclear, but may be related to the way in which physiotherapists ask the patient to take a deep breath.…”

“…This is achieved because the movement of air above a layer of mucus develops a shearing force over the surface of this liquid layer. When the shearing force exceeds the surface tension in the mucous layer, the mucus starts to move in the direction of the air flow (Kim et al, 1987). As the mucus moves up the bronchial tree, it will eventually be swallowed.…”