[Estimation of pulmonary dust load using magnetic pneumography].

If an occupational history enables the identification of subjects at high risk from occupational disease, it yields no information on the individual dust level on account of very important inter-individual variations in pulmonary dust retention. Magnetopneumography is the only technique which enables pulmonary dust loads to be estimated on living subjects. The first measures of dust load by magnetopneumography made at the Ambroise Pare Hospital are reported. By knowing the magnetic properties of occupationally inhaled aero-contaminants, this technique is sensitive and non-invasive and enables the total pulmonary dust load to be estimated from the study of the residual magnetism in the ferromagnetic component of these aero-contaminants. A SQUID magnetometer measures this magnetism on 5 lines of the anterior surface of the thorax after overall magnetisation of the latter by an external magnetic field of 30 kA/m. Measurements were made on 18 male subjects: 5 non-exposed controls and 13 occupationally exposed subjects to these aero-contaminants. The dust load calculated was variable, 0 in the controls and between 0 and 3,065 mg in exposed subjects. For the first time measures were made in 4 dental technicians: their dust load was between 725 and 3,065 mg. The problems posed by this method are broached. Its principle objective is the surveillance of occupationally exposed population to these aero-contaminants of ferromagnetic composition. A decrease in the residual magnetic signal after the cessation of magnetisation was observed in keeping with the data of the literature. This phenomenon, recognised under the term of "relaxation", is evidence of the activity of alveolar macrophages.