Muhammad Asif  ( Govt. College, Muzzafar Ghar )
Ghulam Mustafa  ( Department of Pediatrics, Nishtar Medical College, Multan, )
Muhammad Aslam  ( Department of Statistics, Bahauddin Zakariya University, Multan, Pakistan. )
Saima Altaf  ( Department of Statistics, Bahauddin Zakariya University, Multan, Pakistan. )

Objective: To predict pulmonary function test values in children. Methods: This cross-sectional study was carried out at Nishtar Medical College, Multan, Pakistan, from August 2014 to March 2015, and comprised school-going children aged 5-14 years. After noting their gender, age, height and weight, the pulmonary function test measures, force vital capacity, forced expiratory volume in 1 second and peak expiratory flow rate were taken. Simple and multiple regression models were used for the prediction of pulmonary function test values. SPSS 19 was used for statistical analysis.
Results: Of the 3,275 participants, 1,809(55.2%) were boys and 1,466 (44.8%) were girls. The overall mean age was 10.27±2.41 years. The means height, weight, forced expiratory volume in 1 second, force vital capacity and peak expiratory flow rate were 137.37±13.41cm, 30.44±8.56kg, 1.56±0.58, 1.72±0.50 and 3.66±1.10, respectively. Generally, no significant difference between the mean pulmonary function test values was noted for boys and girls (p>0.05), except that the boys of age 13 and 14 had higher mean values (p<0.05). All the three variables - age, height and weight - had significant linear relationship with the pulmonary function test values (p<0.05). 
Conclusion: The pulmonary function test values tended to increase with increase in age, height and weight. 
Keywords: Forced expiratory volume in 1 second, Force vital capacity, Peak expiratory flow rate, Pulmonary function test, Spirometry. (JPMA 67: 1323; 2017)

Introduction

Pulmonary function test (PFT) performs a pivotal role in respiratory medicines. Now a days, these tests are more frequently used in the investigation of respiratory diseases as they give reliable information about status of an individual\\\'s respiratory system. Abnormality of individual\\\'s lung function is diagnosed by defining whether PFT values are within or outside the normal range. Several reference values for lung function indices of the children have been published from different parts of the globe. These values are influenced by age, sex, ethnicity and anthropometric profile of an individual.^1-6 In Pakistan, few studies are available in the literature that have tried to examine the development of lung function and to formulate the lung function prediction equations for the people of different age groups, regions and ethnicity.^7-9 However, only one study7 since 1987 has been carried out specifically for the Pakistani children about the PFT values in which regression relationship of PFT values with age, height and weight were measured for both genders to establish specific normal values. With the passage of time, the pattern of lung function growth of a population at any age changes, hence it becomes necessary that lung function norms should be updated regularly. The present study was conducted to predict PFT values in children. 

Subjects and Methods

This cross-sectional study was carried out at Nishtar Medical College, Multan, Pakistan, from August 2014 to March 2015, and comprised school-going children aged 5-14 years with different socio-economic backgrounds. The children having some respiratory symptoms or with any history of pulmonary diseases and taking treatment were excluded. Prior to all physical and PFT measurements, a written consent was taken from their parents.
A questionnaire was administered in which socio-demographic information (like age and gender status), and anthropometric and spirometric measurements of each child were recorded. Age (rounded to next year) was calculated from the date of birth provided by the parents. Body measurements of each child, including standing height (cm) and weight (kg), were measured following standard protocols while body surface area (BSA) was calculated.¹⁰
For this study, the PFT measures — forced vital capacity (FVC), forced expiratory volume 1(FEV1) and peak expiratory flow rate (PEFR) — were taken using computerised spirometry device (Spiro USB 5050), and the American Thoracic Society (ATS) guidelines^2,11 for spirometry were strictly followed. 
To study the effect of age, height and weight on the PFT values, simple and multiple regression models were applied. Following Barcala et al.,¹² the PFT values were transformed using natural logarithm due to the fact that these values were non-normally distributed.  The descriptive results were expressed as percentages and mean ± standard deviation (SD). Two-sample Student\\\'s t-test was used to compare the significant difference between mean PFT values of boys and girls. Pearson\\\'s correlation coefficient was used to measure linear relationship of the PFT measures with age, height and weight. In order to predict the stated spirometric measures using age, height and weight, simple and multiple linear regression models were used. SPSS 19 was used for statistical analysis.

Results

Of the 3,275 participants, 1,809(55.2%) were boys and 1,466 (44.8%) were girls. The overall mean age was 10.27±2.41 years and mean weight was 30.44±8.56kg. Besides, 1,323(40.4%) participants belonged to the age group of 5-9 years and 1,952(59.6%) to 10-14 years.
 
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 The mean PFT values increased with age for both boys and girls. This increase was fairly slow in the age group of 7 to 9 years, but a sharper and more variable increase was reported at the age of 10 years or after. FEV1, FVC and PEFR for boys (of age 13 and 14 years) were found to be significantly higher than those of girls.
 
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All the coefficients between different PFT values and physical measures (age, height and weight) were found to be positive, moderate to high and statistically significant
 
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To study the effect of age, height and weight on the PFT values, simple and multiple regression models were applied. Following Barcala et al.,¹² the PFT values were transformed using natural logarithm due to the fact that these values were non-normally distributed. All the estimated coefficients of the predictors (age, height and weight)were found to be positive which meant the PFT values tended to increase with increase in age, height and weight
 
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Discussion

In the present study, we found that the mean values of FEV1, FVC and PEFR increased when children got older. Although all the regression coefficients were statistically significant, but similar to previous studies,^12-14 the values of coefficient of determination R2 were not much high. Similar findings have also been reported in a few previous studies.^7,15,16 The PFT values were observed to be positively correlated with age, height and weight. However, the most significant and strong positive correlation (i.e., 0.73) was observed between FVC and height. The results are in agreement with other studies.^15,16
Simple regression models can be considered to predict the PFT values against age, height and weight. For instance, if we consider average height of 137cm, the predicted values of FVC, FEV1 and PEFR will be 1.49, 1.65 and 3.50, respectively, for boys. In the similar order, these values for girls will be 1.45, 1.62 and 3.44. The results reveal that PFT values for boys are greater than those for girls.  For discussion, we focus only on the multiple regression model to predict FVC against given age, height and weight. When rounded mean values of age (10 years), weight (30kg) and height (137cm) were considered, the predicted FVC values were found to be 1.65 and 1.57, respectively, for boys and girls. The PFT values were found to be fairly closer to those of an Indian study16 having school-going children (aged 6-15 years) as participants. For example, when the above-mentioned mean values of age, height and weight were used, the Indian study16 predicted FVC values of 1.72 and 1.59 for boys and girls, respectively. However, when the same mean values of age, height and weight were used in the equations given in a study conducted by Barcala et al.,¹² the predicted FVC values were reported to be 2.12 and 2.74 for boys and girls, respectively. 

Conclusion

Age, height and weight had statistically considerable and positive correlation with the PFT values, both for boys and girls. Height was found to be most strongly and positively correlated with the PFT values. Older boys (aged 13 and 14 years) had significantly higher PFT values than the girls of the same age group. The fitted regression equations will help to predict the PFT values for the Pakistani children at given age, height and weight.

Disclaimer: None.
Conflict of Interests: None.
Source of Funding: None

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