Introduction
The Global Lung Function Initiative (GLI), an international collaboration with the goal of developing universal reference equations for children and adults11ReferencesCooper BG, Stocks J, Hall GL, Culver B, Steenbruggen I, Carter KW, Thompson BR, Graham BL, Miller MR, Ruppel G, Henderson J, Vaz Fragoso CA, Stanojevic S. The Global Lung Function Initiative (GLI) Network: bringing the world’s respiratory reference values together. Breathe (Sheff). 2017 Sep;13(3): e56-e64., published reference equations for spirometry in 201222Quanjer PH, Stanojevic S, Cole TJ, Baur X, Hall GL, Culver BH, Enright PL, Hankinson JL, Ip MS, Zheng J, Stocks J; ERS Global Lung Function Initiative. Multi-ethnic reference values for spirometry for the 3-95-yr age range: the global lung function 2012 equations. Eur Respir J. 2012 Dec;40(6):1324-43.. These reference equations, obtained from healthy children, may potentially add to a better understanding of lung growth. A careful analysis of changes in the forced expiratory volume in the first second of the maneuver (FEV1) as a proportion of the forced vital capacity (FVC), or the FEV1/FVC ratio, with age through childhood and adolescence demonstrated a remarkable shape to the curve33Quanjer PH, Stanojevic S, Stocks J, Hall GL, Prasad KV, Cole TJ, Rosenthal M, Perez-Padilla R, Hankinson JL, Falaschetti E, Golshan M, Brunekreef B, Al-Rawas O, Kühr J, Trabelsi Y, Ip MS; Global Lungs Initiative. Changes in the FEV₁/FVC ratio during childhood and adolescence: an intercontinental study. Eur Respir J. 2010 Dec;36(6):1391-9.. Figure 1a demonstrates that the mean ratio of FEV1/FVC rapidly decreases through childhood in healthy children, at least up to about 10-12 years of age, followed by a small increase during early adolescence, before resuming an inexorable downhill decrease throughout life44Quanjer PH, Stocks J, Polgar G, Wise M, Karlberg J, Borsboom G. Compilation of reference values for lung function measurements in children. Eur Respir J Suppl. 1989 Mar; 4:184S-261S.. It is generally accepted that FEV1/FVC decreases from childhood to old age55Quanjer PH, Stocks J, Polgar G, Wise M, Karlberg J, Borsboom G. Compilation of reference values for lung function measurements in children. Eur Respir J Suppl. 1989 Mar;4:184S-261S.,falling with both age and height66Stanojevic S, Wade A, Cole TJ, Lum S, Custovic A, Silverman M, Hall GL, Welsh L, Kirkby J, Nystad W, Badier M, Davis S, Turner S, Piccioni P, Vilozni D, Eigen H, Vlachos-Mayer H, Zheng J, Tomalak W, Jones M, Hankinson JL, Stocks J; Asthma UK Spirometry Collaborative Group. Spirometry centile charts for young Caucasian children: the Asthma UK Collaborative Initiative. Am J Respir Crit Care Med. 2009 Sep 15;180(6):547-52.. The reasons for this “Shepherd’s Hook” appearance in early adolescence are not well understood. One suggestion is that this age-dependent increase in the ratio may be due to well-recognized changes in thoracic configuration, and as a result, decreased chest-wall compliance in adolescents77Merkus PJ, ten Have-Opbroek AA, Quanjer PH. Human lung growth: a review. Pediatr Pulmonol. 1996 Jun;21(6):383-97.,viii,ix,x , particularly during the adolescent growth spurt and puberty88Schrader PC, Quanjer PH, van Zomeren BC, Wise ME. Changes in the FEV1-height relationship during pubertal growth. Bull Eur Physiopathol Respir. 1984 Jul-Aug;20(4):381-8.. This might result in slower growth in measured vital capacity relative to FEV199Degroodt EG, Quanjer PH, Wise ME, et al. Changing relationships between stature and lung volumes during puberty. Respir Physiol 1986; 65: 139-153.,1010Smeets M, Brunekreef B, Dijkstra L, Houthuijs D. Lung growth of pre-adolescent children. Eur Respir J. 1990 Jan;3(1):91-6..
The primary objective of this study was to analyze the relationship between FEV1/FVC and age in children and adolescents with asthma. The cross-sectional area of the airways may not increase relative to alveolar volume in adolescents with asthma, as much as in healthy adolescents. If so, this might result in a reduced FEV1/FVC ratio. If individuals with asthma do not have this temporary adolescent growth spurt in FEV1/FVC ratio noted in healthy adolescents, the trajectory of FEV1/FVC throughout adulthood might remain permanently lower. Secondary objectives were to assess the role of gender, obesity, and measurements of lung volumes on the relationship between age and FEV1/FVC.