Tracheal Mucus Rheology in Patients Undergoing Diagnostic Bronchoscopy: Interrelations with Smoking and Cancer

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Abstract
We examined the differences in tracheal mucus rheology between nonsmokers and smokers, and between smokers with and without lung cancer. Mucus was collected from patients undergoing diagnostic bronchoscopy without atropine by holding a cytology brush in contact with the tracheal mucosa for 10 to 15 s. Samples were obtained from 43 patients 24 to 79 yr of age: nine nonsmokers, 18 current smokers, and 16 exsmokers (>6 months); 12 patients (nine smokers, three exsmokers) had lung cancer. Pulmonary function testing showed that the nonsmoker patients had significant restrictive lung disease, and the patients with cancer had significant irreversible airway obstruction. The viscoelastic properties of the mucus samples were determined by magnetic microrheometry. Two parameters are reported: G* (modulus of rigidity) and tan .delta. (loss tangent), each measured at 1 and 100 rad/s. G* is an index of overall deformability (elastic and viscous), and tan .delta. is the ratio of viscous to elastic deformability. For nonsmoker patients, the viscoelastic parameters were virtually identical to those found previously for normal volunteers. For smokers without cancer, the mucus had a lower value of tan .delta. at 1 rad/s and therefore was predicted to be more easily transportable by ciliary action; for exsmokers without cancer, ciliary transportability as calculated from viscoelasticity was even higher because of both low tan .delta. and low G*. Mucus from patients with cancer was not significantly different from that of nonsmokers; however, the mucus was predicted to be less easily clearable by ciliary action than was that from smokers and exsmokers without cancer, mainly because of a higher tan .delta. at 1 rad/s. This rheologic difference persisted even when the patients were matched for degree of obstruction, comparing the cancer group with the more obstructed smokers without cancer. In all smokers, with or without cancer, the mucus was predicted to be less easily clearable by coughing. This latter abnormality increased with the magnitude of tobacco consumption, but it was not accentuated in those with cancer. Our findings are consistent with the hypothesis that long-term impairment of mucus clearance could represent a risk factor for the development of lung cancer in smokers.