Spirometric Reference Equations for Semi-Urban and Urban Bantu Cameroonians

Abstract

Background: Spirometric reference values vary substantially across ethnic groups, and remain largely poorly characterized among Africans. We derived spirometric reference equations for adult Cameroonians and compared their performance with those derived from other ethnic groups. Methods: Spirometric variables according to the American Thoracic Society/European Respiratory Society 2005 guidelines were acquired in voluntary healthy non-smoker subjects in Yaounde (Capital City) and Foumbot (semi-urban area in West Region), in Cameroon during November 2011 to January 2012 (Yaounde) and August 2012 (Foumbot). Reference equations were derived separately for men and women from multiple linear regressions. Results: A total of 411 subjects (206 men) met the inclusion criteria. The mean age was 39.5 ± 16.1 years (min - max: 18 - 85 years) for men and 39.2 ± 14.1 years (18 - 90 years) for women. Age and height were the only variables significantly associated with spirometric values in the final linear regression models. Derived reference values were lower than those derived from Global Lung Initiative 2012 equations for different ethnic groups, except for the forced expiratory volume in 1 second/forced vital capacity ratio (FEV1/FVC ratio). The mean FEV1/FVC ratio was 0.88 ± 0.07 for Cameroonian men and 0.89 ± 0.07 for Cameroonian women. Variations in the performance of derived models in bootstrap internal validation were marginal. Conclusion: This study highlights the importance of deriving specific predictive equations for each ethnic group. The use of adjustment factors applied to Caucasian equations when compared with the values derived in our study leads to an overestimation of the values for FEV1 and FVC.