A new viscoelastometer for studying the rheological properties of bronchial mucus in clinical practice.

In clinical practice, a wide variety of drugs are given to modify the rheological properties of bronchial mucus but they are frequently not correctly chosen because there is not a simple apparatus available for the routine measurement of the mucus viscoelasticity. We designed a new viscoelastometer which is easy to operate and permit accurate measurement of the viscoelastic properties of mucus. The system has a Couette geometry and requires a sample of 1 ml. The outer cylinder is thermostated and rotates at a constant rate. The resulting torque is measured on the inner cylinder using a microdisplacement transducer. The inner cylinder is suspended by a special wire system which maintains a constant 0.75 mm gap between the two cylinders. The apparent viscosity is calculated up to 100 Pa.s. at a low shear rate (0.4 s-1) and the elasticity is analyzed by a stress relaxation method. The characteristics of the apparatus and the typical viscoelasticity behaviour of several sputum samples are reported.