Copyright ©ERS Journals Ltd 2002 Lung and thorax development during adolescence: relationship with pubertal status1 Laboratory of Respiratory Physiology, and 2 Laboratory of Endocrinology, Hôpital d'Enfants Armand Trousseau, and 3 Dept of Biostatistics, Hôpital Tenon, Paris, France CORRESPONDENCE: M. Boulé, Laboratoire de Physiologie Respiratoire, Hôpital d'Enfants Armand Trousseau, Avenue du Dr Arnold Netter, 26, 75012, Paris, France. Fax: 33 1 44736336. E-mail: michele.boule@trs.aphopparis.fr Keywords: adolescence, diffusing capacity, lung growth, reference values, thoracic volume index
Received: January 29, 2001
The aim of the present study was to define reference values for lung volumes and the lung transfer factor for carbon monoxide (TL,CO) for an adolescent population using thoracic volume index (TVI) and an index of pubertal stage in order to account for the variation in growth pattern between adolescents. TVI, pubertal stage by Tanner scale (PST), time since menarche, functional residual capacity measured using the heliumdilution technique, vital capacity, total lung capacity and TL,CO measured using a steadystate method were determined in 51 males (aged 1320 yrs; PST T3T5) and 52 females (aged 1318 yrs; PST T2T4; all but three had already undergone menarche). In male adolescents, height, weight, TVI, lung volumes and TL,CO increased with age. This was not the case in female adolescents. In males, the TVI was the independent variable that best correlated with pulmonary volumes. In females, height was the independent variable that best correlated with pulmonary volumes. In both sexes, the variable that best correlated with TL,CO was PST, associated with height in males. This crosssectional study provides prediction equations for lung volumes and the lung transfer factor for carbon monoxide taking into account thoracic volume index and pubertal stage. It shows that, in adolescent males, lung and thoracic development occurs during and until the end of puberty. Conversely, in adolescent females, lung development is almost finished following menarche. Many studies have described the increase in forced expiratory flows occurring during adolescence but little is known about the increase in thoracic measurements, lung volumes and lung transfer factor for carbon monoxide (TL,CO).
It is known that lung function increases linearly with age and height until the adolescent growth spurt at The sudden change in spirometric lung function seen in males and females appears to coincide with the pubertal growth spurt observed in the Tanner chart 9. To account for the variation in growth pattern between adolescents in reference equations, in addition to height, a measure of pubertal status and an estimation of thoracic volume should be incorporated. This would allow for the fact that the growth of the lungs lag behind that of the legs and height 8, 10, 11. Extrapolation of reference values from children to an adolescent population cannot be used to predict lung volumes and TL,CO. Therefore, summary equations and limits of normal values need to be determined for use in current clinical practice. Therefore, the aim of the present study was to derive prediction equations for lung volumes and TL,CO for adolescent males and females using refined anthropometric measurements allowing determination of thoracic growth (such as thoracic volume index (TVI)) and an index of growth stage (pubertal stage).
Subjects Having obtained the authorisation of the Department of Education (Versaille, France) to ask all pupils attending two levels of a secondary school (fourth and sixth year) in Paris, France, to participate in the study, 103 pupils (51 males and 52 females) gave their oral consent and were included. Written parental consent was also obtained. Lung examination and spirometric results were normal on the day of the pulmonary function tests.
Methods
Pubertal status
Pulmonary function tests
Statistical analysis In order to determine whether or not logarithmic transformation was required, the variance of the pulmonary function data was determined 15: males and females were divided into groups on the basis of 3-cm height intervals. The mean and SD of the pulmonary function test results for each group were plotted against each other. Correlation was evaluated using the Spearman correlation coefficient (rS) as only 10 height groups were obtained 14. When SD did not increase with mean (rs>0.05), constant variance was assumed and no transformation was performed before multiple regression. When SD increased with mean, increased scatter with height was assumed and logarithmic transformation of the data was performed. After having checked that this transformation had stabilised the variance, multiple regression of the logtransformed pulmonary function test data was performed.
Multiple regression of pulmonary function parameters or logtransformed pulmonary function parameters on anthropometric data was then performed. Height was chosen in the first step 16, except in the female group when TL,CO was the dependent variable as no correlation between height and TL,CO was found. Other independent variables were included by decreasing partial rP until no further increase in R2 adjusted for the increase in the number of independent variables included in the equation (
Anthropometric data Mean male age (16 yrs, range 1320 yrs) was not significantly different from mean female age (16 yrs, range 1318 yrs, p=0.22). Males were taller (172 cm, range 150184 cm versus 163 cm, range 147176 cm, p<0.0001) and heavier (61 kg, range 4284 kg versus 53 kg, range 3968 kg, p<0.0001) than females. In males, height and weight increased with age (rP=0.45, p<0.01 and rP=0.42, p<0.01, respectively); the height increase reached a plateau at 1617 yrs. Conversely, in females, neither height nor weight increased with age (rP=0.025, NS and rP=0.05, NS, respectively).
Thoracic measurements (mean±SD and range) in males and females are reported in table 1
The correlation of thoracic measurements with anthropometric data is reported in table 2
Pubertal status No males were prepubescent (T1), 11 were in early puberty (all T3) and most in late puberty (15 in T4 and 24 in T5). No females were prepubescent, most were in early puberty (two in T2 and 20 in T3) and nine in late puberty (all T4). These Tanner scores were converted into PST as described in the Methods section. Nine of the females were in menarcheal category 1, 14 in category 2 and 12 in category 3.
Pulmonary function tests
In males, TVI was the independent variable that best correlated with pulmonary volumes: TLC=0.0006TVI+1.2, rp=0.77, R2=0.59, p=1x107; VC=0.0006TVI+1.16, rp=0.75, R2=0.56, p=2x107; and FRC=0.0004TVI+0.36, rp=0.66, R2=0.44, p=2x105. In both sexes, the variable that best correlated with TL,CO was PST, associated to height in males. In females, TL,CO=3.643PST+11.587, rp=0.50, R2=0.25, p=0.015. In males, TL,CO=4.59PST+14.96, rp=0.61, R2=0.37, p=3x105; and TL,CO=0.45H52.68, rp=0.58, R2=0.34, p=1x104.
Variance of pulmonary function test data Conversely, in males, the SD of TL,CO within a 3-cm height group increased with mean (rS=0.72, p<0.05) and the intercept did not differ from zero (p=0.28). Natural log transformation stabilised variance (rS=0.224, p>0.05). In females, the SD of FRC within a 3-cm height group increased with mean (rS=0.81, p<0.05) and could be assumed to be proportional to the mean as the intercept of the regression line did not differ significantly from zero (p=0.06). Natural log transformation stabilised variance (rS=0.51, p>0.05). For FRC in females and TL,CO in males, a similar R2 was obtained by fitting by a power or exponential function to the data. Therefore, it was decided to perform simple log transformation and regress natural logtransformed TL,CO on height in males and natural log FRC on height in females.
Multiple regression equation
Limits of normal The mean and SD of the residuals (differences between actual and predicted value) for each adolescent are presented in tables 5 and 6
The present study provides reference values for TVI, lung volumes and TL,CO for adolescent males and females. No other reports on normal values of TVI and thoracic measurements in an adolescent population could be located. Besides its importance in providing normal values for thoracic mensurations in adolescents for height and age, these reference values could be of help in quantifying the chest wall sequelae of treatments, such as radiotherapy, and the decrease in chest wall volume due to decrease in muscle strength in neuromuscular disease. In addition, this study has the advantage of providing reference values for lung volumes and TL,CO using equations that take height as well as TVI and pubertal stage into consideration, an approach allowing variation in growth pattern between adolescents to be taken into account 8, 11. Data were obtained from a group of males aged 1320 yrs whose PST ranged T3T5 and a group of females aged 1318 yrs whose PST ranged T2T4. All but three of the females had undergone menarche. Analysis of the distribution of the subjects within the Tanner rating scales shows that males and females in prepubertal or early pubertal stage (T1 and T2 in males and T1 in females) were lacking, and most females were investigated following menarche. Although the mean ages of the males and females were comparable and the group of males slightly more mature, height, weight, TVI and pulmonary function test measurements in the males continued to increase with age, whereas those in the females did not. These data, although crosssectional, suggest that, in the present group of males, lung and thoracic development was still occurring, whereas it was almost complete in the females. This is in agreement with the data of LEBOWITZ and SHERRILL 3 showing that, in males, lung and thoracic development is observed during and until the end of puberty. Conversely, in females, lung development occurs over a shorter period of time and earlier in the pubertal process. In addition, the present data show that, in females, lung development is almost complete after menarche. Analysis of the variance of the pulmonary function test data showed that the variance of TL,CO in males and FRC in females increased with the mean, i.e. the scatter increased in proportion to the predicted value. This heteroscedasticity is frequently observed in the paediatric age range 16. Logarithmic transformations stabilised the variance as anticipated. Conversely, the variance of all other pulmonary function test data did not increase with the mean. This can be explained by the fact that the present sample included a limited range of ages and heights. In females, the anthropometric parameter best correlated with pulmonary volumes was height. In males, this was the TVI. In both sexes, PST was the anthropometric parameter that best correlated with TL,CO, followed by height in males. Multiple regression equations were therefore determined, entering as independent variable height, TVI, pubertal stage for lung volumes, and height and PST for TL,CO. Compared with the data of COOK and HAMANN 17, suggested for use in the age range 518 yrs for gas dilution methods 16, the present equation predicts comparable values for TLC in males and females but slightly lower FRC and RV.
Compared with the equations of regression of FRC, VC and TL,CO with height that have been defined previously in the present authors' laboratory in younger children using the same techniques 12, 1820, a smooth transition from the equation of younger children to that of adolescents is observed for all lung volumes (FRC, VC and TLC) as a function of height in females and only for FRC in males. In males, the transition is less perfect for VC, TLC and TL,CO as a function of height as the slope increases during adolescence. This marked acceleration in the development of lung volumes, such as VC and TLC, during puberty in males compared to their linear increase from childhood to puberty in females can be related to differences in the development of muscle strength between the sexes. Indeed, muscle strength increases linearly with chronological age from early childhood to
TVI and pubertal stage were included in the prediction equations in order to maximise the variance explained by the model (
Considering the effect of sex on the prediction equations for lung volumes, as the females in the present study had probably completed most of their lung growth, factors supposed to explain lung growth and increase
In both sexes, the variable that best predicted TL,CO was PST, associated with height in males. The importance of using an index of maturity when describing the increase in TL,CO in males and females may, in part, be ascribed to the delayed development of cardiac function during the pubertal process compared to the development of lung volumes. Indeed, SEELY et al. 6 showed that sex difference in cardiac output develops late in the pubertal process, i.e. age 14 yrs in females and age 16 yrs in males. In conclusion, the present study provides reference values for thoracic measurements, thoracic volume index, lung volumes (such as vital capacity, functional residual capacity and total lung capacity) and pulmonary diffusing capacity in a group of males aged 1320 yrs and a group of females aged 1318 yrs. To date, no reference values of thoracic mensurations in adolescents have been published. The present data provide normal values for thoracic mensurations in adolescents for height and age that could be of help in quantifying the chest wall sequelae of treatments and the decrease in chest wall volume due to decrease in muscle strength in neuromuscular disease. In addition, this study has the advantage of providing reference values for lung volumes and diffusing capacity using equations which take into consideration, height, thoracic volume index and pubertal stage, an approach allowing for the variation in growth pattern between adolescents to be taken into account. Finally, the present data, although crosssectional, confirm that, in males, lung and thoracic development is observed during and until the end of puberty. They also confirm that, in females, lung growth is of short duration and occurs early in the pubertal process and show that lung development is almost finished after menarche.
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