Assessment of lung function is an essential component of both clinical practice and physiological research. However, the reference equations used to interpret spirometric data need to be aligned with the anthropometric, genetic, and environmental characteristics of the population studied. A study conducted by Ahmadial et al. (2006) provides important data on lung parameters in Iranian adolescents, highlighting the inadequacy of Western reference values—specifically, those proposed by the American Thoracic Society (ATS)—for Middle Eastern populations.
The study evaluated 302 healthy, non-smoking Iranian students (152 males and 150 females), with a mean age of approximately 20 years, and demonstrated statistically significant differences between their lung values and the reference values for Caucasians. Among the most relevant findings, the high functional residual capacity (FRC) in men stands out, which presented 110% of the predicted value, and an inspiratory capacity (IC) 14% lower than expected according to the ATS equations. These deviations are not trivial, as they directly influence the clinical interpretation of respiratory function tests, especially in the diagnosis of obstructive and restrictive disorders (Ahmadial et al., 2006).
A notable aspect is the strong correlation between height and all spirometric parameters, with emphasis on total lung capacity (TLC), which showed the most robust correlations in both sexes. On the other hand, body mass index (BMI) did not demonstrate a statistically significant correlation with respiratory parameters in men, and showed an association only with CI, FRC and reserve volumes in female data. This pattern corroborates previous findings in the literature, suggesting that BMI — especially in normal ranges — has a limited influence on lung function, unlike height, which is confirmed as a primary determinant.
The presence of ethnic and regional variations in lung physiology has been documented in several previous studies. However, the persistent use of European or North American reference values in contexts such as Iran or even Brazil may lead to misinterpretations and even inappropriate clinical conduct. Ethnicity, environmental factors, nutritional status and body development patterns directly affect respiratory physiology and should therefore be incorporated into prediction models.
It is also relevant to note that, unlike previous studies conducted in Iran, this work incorporated essential parameters such as residual volume (RV) and functional residual capacity (FRC), elements that are often neglected but fundamental for the complete characterization of ventilatory mechanics. The absence of these data in previous population studies compromised the diagnostic accuracy of subtle respiratory alterations, such as hyperinflation disorders or masked restrictive patterns.
Therefore, this study reinforces the urgency of developing and adopting regionally and ethnically adjusted reference values for lung function tests. As a researcher, I often notice this gap in genetically and socio-environmentally diverse countries, where equations based on urban Caucasian populations with high socioeconomic status still predominate. Building more representative databases, such as the one conducted by Ahmadial et al., is not only a scientific necessity, but an ethical responsibility in the face of human diversity.
Reference:
AHMADIAL, N.; KHAMNEI, S.; ABEDINZADEH, M.; NAJAFI, H.; MOHAMMADI, M. Lung function reference values in Iranian adolescents. Eastern Mediterranean Health Journal, vol. 12, no. 6, p. 834–839, 2006.
