Lung function prediction equations derived from healthy South African gold miners
- aNational Centre for Occupational Health, Johannesburg 2000, South Africa, bArum Health Research, Welkom, South Africa, cPrecious Metal Refiners, PO Box 331, Kroonsdal 0350, South Africa
- Dr Eva Hnizdo, National Institute for Occupational Safety and Health, 1095 Willowdale Rd, MS 2800, Morgantown, WV 26505, USAexhb{at}cdc.gov
- Accepted 25 May 2000
Abstract
OBJECTIVES To estimate lung function prediction equations and to identify appropriate normal reference values for the population of about 250 000 of South African gold miners.
METHODS Data from a lung function screening programme conducted at a large South African gold mine from 1994 to 1998 were used to estimate the lung function prediction equations. The most reliable period of lung function testing was identified in a previous study of a temporal pattern in reliability, and lung function tests from this period were used. Miners with a history of pulmonary tuberculosis or with radiological abnormalities were excluded from the study. The prediction equations were estimated cross sectionally on 15 772 black and 2752 white miners, and published reference equations that fitted most closely the observed data were identified.
RESULTS The estimated prediction equations for forced vital capacity (FVC) are as follows: for black men, FVC (l)=− 2.901−0.025×age+4.655×height; and for white men, FVC(l)=−4.407−0.036×age+ 5.940×height. For forced expiratory volume in one second (FEV1) these equations are: for black men, FEV1(l)=−1.654− 0.30×age+3.665×height; and for white men, FEV1(l)= −2.341− 0.038×age+4.314×height. Units are years for age and metres for height. Knudson's and the European Community of Coal and Steel (ECCS) reference values provided the closest fit to the data on lung function of white miners, but the lower limits of normal from the ECCS equations were the closest to the observed one sided lower 95% confidence intervals (95% CIs). For black miners, reference equations that fitted best were derived by Louw et alon asymptomatic black South African men unexposed to occupational dust. There were significant differences between the two groups of miners in the estimated height adjusted mean lung function values for a 40 year old 1.7 m tall man (220 ml (5.2%) for FVC and 110 ml (3.2%) for FEV1); white men had higher FVC and FEV1, but lower FEV1/FVC ratio. The ECCS reference values scaled by a conversion factor of 0.93 for the FVC and 0.95 for the FEV1provided close fits to the data for black miners, but the rate of decline with age was higher than that in the observed data. None of the linear equations provided a good fit for the 20–29 and more than 55 years old age categories.
CONCLUSION The ECCS and Knudson equations provided the best fit to the data for white miners, whereas the equations by Louw et alestimated on asymptomatic black South African bank workers provided the best fit to the data for black miners. The ECCS reference values scaled by a factor of 0.93 for FVC and by 0.95 for FEV1 provided close fits, but the rate of decline with age was higher than that in the data for black miners.
