Relevence of respiratory symptoms and signs to ventilatory capacity changes after exposure to grain dust and phosphate rock dust.

Ventilatory capacity was measured before and after exposure to high concentrations of wheat dust in 24 men, i8 of whom were similarly studied while working with calcium phosphate rock. Changes in venti-latory capacity were examined in relation to respiratory symptoms as commonly elicited in occupational surveys, and to the presence or absence of a productive cough on request and under observation. A significant decrease in the forced expiratory volume at one second was observed within half an hourof beginning work in the wheat dust, and this decrease was maintained throughout the work shift. A smaller significant decrease was found on exposure to phosphate rock over several hours, no significant change occurring within the first half-hour. Greater or more consistent decreases were recorded in those men who gave a history of persistent cough and sputum, and more particularly in those who had a productive cough on request, than in those without these features. A history of symptoms on exposure failed to define a group showing any more severe ventilatory reaction on exposure to wheat dust than the average. Some of the factors influencing the history of symptoms in occupational populations are reviewed, and the advantage of an objective sign, as provided by a deliberate cough, is indicated in defining an 'abnormal' group within such a population. This study of the acute effects on ventilatory capacity of grain and phosphate rock dusts in high concentration was undertaken in I96I prior to an investigation of the long-term effects of grain dust on the lungs of workers handling it frequently. In the event, no long-term effects of wheat dust were demonstrated in a survey of an entire working population (Gandevia and Ritchie, to be published), but the short-term investigation of a small group is of interest in relation to recent work on the changes in ventilatory capacity during the day in workers in a variety of occupations involving exposure to vegetable dusts. It also provides further evidence in support of a view previously expressed (Gandevia and Milne, I965a) that the objective sign of an observed productive cough defines better two subgroups of an industrial population than does a history of cough and sputum, whether these symptoms are constant or occur merely on exposure to the relevant dust.