How clean are your lungs?

The airways that conduct air into and out of the lung contain secretions - mucus - that trap inhaled particles. These are removed from the lung by a process called mucociliary clearance that moves the mucus, dead cells and inhaled particles and microorganisms towards the throat from where they are swallowed. 

Patients with respiratory disease such as chronic obstructive pulmonary disease (COPD) typically have more secretions and products of infections in their airways.

Mucociliary clearance, an important component of lung function, has usually been measured using a technique that determines the rate of removal of inhaled radiolabelled aerosols from the lung. However, it can only be carried out in medical facilities that have specialised equipment. 

Lucy Morgan (Department of Thoracic Medicine, Concord Hospital, Concord, Australia) and her colleagues set out to develop a simpler technique that could be used in any nuclear medicine department. This new technique uses a much lower dose of radioactivity and takes much less time and equipment.

The authors studied two groups of normal subjects: 20 people under 50 and 12 people of 50 years or more, as well as 34 patients with COPD.

The new technique involves injecting a small volume (0.1 ml) of fluid through the cricothyroid membrane, just below the trachea, after applying anaesthetic cream. The fluid contains albumen spheres (10-40 um) labelled with radioactive technetium that are deposited in the trachea. Their movement towards the larynx is detected and measured with a gamma camera.

After a 15 minute period of observation the rate of mucociliary clearance can be calculated. The technique causes minimal discomfort.

In young normal subjects this was approximately 10 mm/minute - similar to values found in previous studies. The rate of clearance was slower in older normal subjects.

The authors found that patients with COPD had a much slower clearance rate of approximately 1.5 mm/minute. This impaired clearance may be the cause and/or result of some aspects of lung disease in COPD.

Lucy Morgan believes that this new technique will be useful to study an important aspect of lung function particularly with respect to causation of disease and the effects of different therapies in treating patients.

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