Relationship of ventilatory capacity to hyperbaric exposure in divers

The results of divers' annual medical examinations were used to assess the effects of diving exposure independent of age, stature, and smoking on forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1). Cross-sectional analysis of records for 858 men showed a significant positive association between the maximal depth that subjects had experienced and FVC but not FEV1. There was a significant negative association for FEV1/FVC%, and this index was also positively correlated with years of diving exposure. Among a subsample of 81 men the forced expiratory flow rate at low lung volume was reduced relative to that of control subjects similarly assessed; the extent of the reduction from the reference value was significantly correlated with the diving exposure. Longitudinal analysis of results for 255 men over a minimum of 5 yr showed that the change in FVC per annum (positive or negative) was correlated with the change in maximal depth; there were no similar associations for FEV1 or FEV1/FVC%. Thus diving exposure affects the vital capacity and the forced expiratory flow rate at small lung volumes. The latter is evidence for narrowing of airways that might be secondary to diving-induced loss of lung elastic tissue; this hypothesis merits further investigation.