Flow-volume curves with air and helium, and spirometry were obtained in 423 subjects during epidemiologic health surveys; subjects were divided into 4 groups: nonsmokers and smokers not exposed to air pollutants at work, and nonsmoking and smoking grain elevator workers. The data obtained from 78 healthy nonsmokers who were not exposed to any air contaminants at work and had no respiratory symptoms were used to develop "normal" prediction equations for each of the following parameters: forced expiratory volume in one second (FEV1), maximal mid-expiratory flow, maximal expiratory flow at 50% of vital capacity while breathing air (Vmax50), the increase in Vmax50 after breathing a mixture of helium and O2 (delta Vmax50), and the volume of isoflow (VisoV). The prediction equations thus obtained from normal nonsmokers agreed with those published in the literature. The coefficient of variation was higher for delta Vmax50 (40.7%) and VisoV (57.6%) than for FEV1 (17.7%) or Vmax50 (27.7%). Comparison of results in smokers and nonsmokers who were not exposed to any air contaminants at work indicated that Vmax50 was the best test for discriminating the effect of cigarette smoking, whereas delta Vmax50 and VisoV were not significantly different. The FEV1 was the best discriminator of the effects of grain dust. There was poor concordance among FEV1, Vmax50, and delta Vmax50 or VisoV. We concluded that FEV1 and Vmax50 are more useful parameters than are delta Vmax50 and VisoV for detecting ventilatory abnormalities in a smoking, working population and in grain elevator workers. The results suggest that the addition of the more time-consuming test, the helium flow-volume curve, is unlikely to contribute any further useful information among the populations surveyed.
Air Pollutants, Occupational Forced Expiratory Flow Rates