Sampling Technique and Rheology of Human Tracheobronchial Mucus

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Abstract
The aims of this work were: (1) to establish a technique for the sampling of human tracheobronchial mucus not contaminated by saliva or topical anesthesia, and (2) to measure its viscoelastic properties. After local anesthesia of the hypopharynx by topical application of 4% xylocaine, a double-sleeve microbiology specimen brush was introduced into a flexible bronchoscope placed in the trachea. The brush was left in direct contact with the bronchial mucosa for 20 to 30 s to allow mucus to collect on it. The mucus sample was then scraped from the brush and immediately covered with paraffin oil. Its viscoelastic properties were determined by the magnetic microrheometer technique. Excluding the time to anesthetize, the whole procedure took less than 1 min (thus minimizing the effect of cough) and resulted in sufficient mucus for rheologic analysis in approximately 90% of trials, i.e., 2.1 ± 1.5 (SD) mg. Mucus specimens were collected from 20 fasting healthy nonsmoking subjects; 17 of them returned for a second collection several days later. Values for mucus mechanical impedance (vector sum of elasticity and viscosity) at 1 rad/s were: Control 1, 141 ± 41 (SE); Control 2, 155 ± 58 dyn/cm2. There was a large variation in mucus viscoelasticity, both between subjects (CV, 130%) and within the same subject (CV, 55%) on different days. In 7 subjects, mucus samples were collected 15 min after intravenous injection of 0.6 mg atropine. Viscoelasticity in these samples was 708 ± 147 dyn/cm2, a value significantly different from Control 1 (p < 0.05) and Control 2 (p < 0.05) values. Atropine also reduced the quantity collected by 75%. Finally, in 8 subjects, mucus viscoelasticity was measured 60 min after ingestion of 5 mg diazepam. The value obtained was 204 ± 151 dyn/cm2, a value not significantly different from either control value, indicating that the stress generated by the bronchoscopy does not appear to affect the mucus viscoelastic properties.