Establishing age specific spirometry reference ranges for children/adolescents of Karachi, Pakistan: Randomized trials.

Objective: To establish age-specific normative spirometry reference range along with regression equation for children and adolescents.

Methods: The cross-sectional study was conducted from April to October 2017, and comprised children and adolescents aged 7-18 years at 8 educational institutions representing various socio-economic strata of Karachi. A modified version of the International Study of Asthma and Allergies in Childhood Questionnaire was used. Spirometry variables including forced vital capacity, forced expiratory volume in 1 second, ratio between the two, peak expiratory flow rate, forced expiratory flow between 25% and 75% expired volume were recorded and interpreted. By normal distribution curve the reference values were established, and mean}2 standard deviation values were taken as significant. Pearson's correlation coefficient and linear regression models were calculated for all pulmonary variables with age.

Results: Of the 751 subjects, 484(64.4%) were boys and 267(35.5%) were girls. The overall mean age was 12.96}2.8 years. The mean lung volume for forced vital capacity was 2.21}0.75, forced expiratory volume in 1 second 2.08}0.73, ratio between the two 92.9}4.7, peak expiratory flow 231.3 } 70.5 and forced expiratory flow between 25% and 75% expired volume was , , , 2.68}1.2. These lung volumes directly increased with age from children to adolescents (p<0.05). All variables showed a significant difference between boys and girls (p<0.05).

Conclusions: There was a linear positive correlation of age with lung function variables, while the boys presented higher values than the girls.