CHANGES IN VENTILATORY CAPACITY IN A GROUP OF FLAX WORKERS IN NORTHERN IRELAND.

One-second forced expiratory volume (F.E.V.) and forced vital capacity (F.V.C.) were measured before starting work in five flax hacklers with symptoms of grade II byssinosis and in five matched controls. Similar measurements were taken in each group at the end of the day shift. A significant (P < 0·05) decline in F.E.V. was observed in the hacklers during the day on Monday, Tuesday, Wednesday, and Friday. The F.V.C. also declined significantly in the hacklers on Monday, Tuesday, and Wednesday. In the control group, ventilatory function tended to decline during the day, but this was significant only for F.E.V. on Monday. The reason for this is discussed. Variations in the dust concentrations in the mill and in outdoor air pollution are shown to be unlikely to have affected the findings. Morning values of F.E.V. and of F.V.C. were consistently lower in the byssinotic group than in the matched controls, suggesting that the inhalation of flax dust causes not only daily variations in lung function but longer-term impairment of ventilatory capacity as well. Additional evidence is given for this conclusion from two other studies.