The effect of angle and oscillation on mucous simulant speed in flexible tubes

The aim of this study was to investigate, in a tube model, how the speed of a mucous simulant was influenced by angle and different types of oscillations.

Using a repeated-measures study design, the primary outcome measure was the mucous simulant speed calculated from the time taken for the mucous simulant to travel a distance of 10 cm. Ultrasonic gel diluted to a viscosity (113 Poise), approximating human sputum, was introduced into a flexible tube similar in diameter to the human adult trachea. The tube was subjected to discrete angles of 0 degrees and 30 degrees, 60 degrees and 90 degrees downward. Symmetrical oscillation was applied in both the transverse and longitudinal directions with frequencies of 5, 15 and 25 Hz at amplitudes of 1 mm and 2 mm peak-to-peak using a commercially available oscillator. Asymmetrical oscillation was applied using repeated cycles of slow acceleration and fast deceleration in the longitudinal direction at 0 degrees and 30 degrees downward and up a 5 degrees incline using a custom-built apparatus.

Each 30 degrees angle increment of the tube from 0 degrees to 90 degrees significantly increased mucous simulant speed (p<0.001). Symmetrical oscillation did not provide an advantage over angle in terms of mucous simulant speed; however, asymmetrical oscillation increased mucous simulant speed beyond that caused by angle for all angles tested (p<0.001) and was able to drive mucous simulant up a small incline (5 degrees) in this tube model. It was found that certain types of longitudinal oscillation elongated the mucous simulant.

The present study supports the use of gravity to assist in secretion clearance. Asymmetrical oscillation is a novel technique which warrants further investigation.