Pulmonary Function Tests in Obese and Overweight Children Aged 5–16 Years: A Case-Control Study
Mounika Naidu and Panyala Aparna Reddy*
Department of Pediatric Pulmonology, Rainbow Children’s Hospital & Birthright, Banjara Hills, Hyderabad, India
*Corresponding author: Panyala Aparna Reddy, Department of Pediatric Pulmonology, Rainbow Children’s Hospital & Birth right, Banjara Hills, Hyderabad, India, E-mail: email@example.com
Citation: Naidu M and Reddy PA (2019) Pulmonary Function Tests in Obese and Overweight Children Aged 5–16 Years: A Case-Control Study. J Pulmonary Medicine Respi Ther 2018: 28-44.
Received Date: 20 March, 2019; Accepted Date: 04 July, 2019; Published Date: 12 July, 2019
Background: Obesity influences respiratory mechanics, exercise intolerance, gas exchanges, control of respiratory pattern, strength and endurance of respiratory muscles, which is evident in adults but lacking in children.
Method: In this prospective case-control study, lung functions in children aged 5-16 years were evaluated and compared among normal, overweight and obese.
Results: We included 150 children 50 each in group. The median age was 114 months in normal and overweight children; 28 (56.0%) were aged >114 months in those with normal weight. Among those with overweight there was an equal distribution with 25 children each. Among those who were obese, median age was 108 months and 27 (54.0%) were aged <108 months. There was a decrease in the mean FVC, FEV1, FEV1 /FVC, PEF, Pre-test & post-test % predicted but an increase in the mean % change for all the parameters except for PEF, with an increase in body mass index (BMI). The changes in the mean FEV1/FVC-Pre-test % predicted and % change predicted with BMI were statistically insignificant; similarly, PEF post test predicted though reduced with increasing BMI, but was statistically insignificant. There was a decrease in the % change predicted for PEF with increasing BMI. Spirometry was normal in all normal weight, 30 in overweight and in 23 obese children. Lung function tests were statistically significant among normal, overweight, and obese children corelated with age. Gender wise significant differences were observed in obese children.
Conclusion: Obesity, overweight have a negative impact on pulmonary functions in children, decreasing FVC, FEV1 and FVC/FEV1.
Obesity; Overweight; Pulmonary Functions; Restrictive Changes
Overweight and obese children are likely to stay obese into adulthood and more likely to develop non-communicable diseases like diabetes, hypertension, cardiovascular diseases, premature death and disability at a younger age . Besides, these children develop other health related issues such as breathing difficulties, increased risk of fractures, and psychological effects . Obesity causes important changes in respiratory mechanics, intolerance to exercise, gas exchanges, control of the respiratory pattern and the strength and endurance of respiratory muscles [3-6]. Pulmonary function abnormalities are one of the well-defined complications of obesity in adults .
According to ventilatory mechanics and pulmonary function, the accumulation of fat may lead to restriction of diaphragm, abdominal movement and thoracic cage expansion . This may lead to changes in pulmonary functions due to the increase in respiratory effort and the compromise of gas transport [9-10]. Obesity may lead to a reduced capacity for functional exercise and to symptoms suggestive of lung disease .
Lung function abnormalities are well documented in obese adults who exhibit a reduction in pulmonary function because of reduced reserve volume and functional vital capacity, which in turn, causes reduced chest wall and lung compliance [12-14]. In contrast, the studies involving the pediatric population offer considerable diversity . The impact of obesity on respiratory functions in overweight, obese and morbidly obese children has not yet been fully determined. Available evidence, though limited, indicate negative association between obesity and lung function; the same is seen in Indian population [16-18].
Materials and Methods
This case-control study was conducted by the pediatric pulmonology department of a tertiary care pediatric hospital, after obtaining approval from the Institutional Ethics Committee. Prospective participants were identified from those attending the out-patient department of nutrition, endocrine and general pediatric clinics, screened after obtaining written informed consent from the parents/guardians, and assent from children ≥ 7 years. We included children aged 5-16 years with a normal respiratory finding on systemic examination and a baseline SpO2 of 100% (measured using non-invasive method). Children with acute or chronic respiratory tract infection or disease, chest pain, known heart disease, neurological or physical limitations (kyphosis, scoliosis), syndromes such as, Prader Willi, Laurence Moon Biedel syndrome, recent eye/abdominal/chest surgery, aneurysm in the chest, abdomen or brain were excluded. The control group consisted of children of the same age groups with normal weight. The primary objective was to study the lung functions in healthy children aged 5-16 years and comparing with that of overweight and obese children.
After a detailed clinical history, anthropometry, general physical examination and systemic examination, each subject underwent spirometric assessments to evaluate the pulmonary function.
Revised Indian Academy of Pediatrics (IAP) 2015 Growth Charts for Height, Weight and Body Mass Index (BMI) for 5 to 18-year-old Indian Children was used as reference. Accordingly, to define overweight and obesity in children from 5-16 years of age, adult equivalent of 23 and 27 cut-offs presented in BMI charts was used .
Participants were weighed (in kg) on an electronic weighing machine, manufactured by Gargee Healthcare, model – GI 120. Height (in cm) was measured to the nearest 0.1 cm with a stadiometer with a base plate. The BMI, was calculated by the formula,
BMI = weight/height2 (kg/m2)
Pulmonary function testing:
A computerised spirometer, (Royal Medisystem, S No 226421, model – EASYON PC) was used. Participants were asked to follow the instructed prerequisites and the test was conducted under standard laboratory conditions (temperature: 22-25°C, relative humidity: 55-60%).
Forced vital capacity (FVC) (L), forced expiratory volume in the first second (FEV1) (L), FEV1/FVC (%), and peak Expiratory Flow (PEF) (L/s) were measured and compared among the study groups.
After recording the baseline parameters, children were given a bronchodilator (salbutamol 200-300µg through spacer) in the form of inhaler and lung function tests were repeated after 15-20minutes. Minimum three FVC maneuvers wasrecorded for each individual; the tests and curves that met the acceptability and reproducibility criteria of the American Thoracic Society were selected . The highest of at least three was technically acceptable measurements for FEV1 and FVC & was selected. All children were assessed by person to reduce inter-observer variability
We enrolled 150, with 50 in each group. Data was collected by using a structured proforma captured on MS excel worksheets (2007) and analysed by using SPSS 19.0 version IBM USA. Qualitative data was expressed in terms of proportions. Quantitative data was expressed in terms of Mean and Standard deviation. Descriptive statistics of each variable was presented in terms of Mean, standard deviation, standard error of mean. Comparison of mean and SD between all groups was done by using one-way ANOVA test. If ANOVA was significant, then Post Hoc Tukey’s HSD test was carried out to assess the significance of mean difference between a pair of group. Mann-Whitney U test was used to compare the results of two genders and the different age groups. p<0.05 and <0.001 was considered as statistically significant and highly significant, respectively.
We included 150 children meeting the selection criteria, 50 each in group. Demographic characteristics of the study population are tabulated in (Table 1). The median age was 114 months in normal and overweight children; 28 (56.0%) were aged >114 months in those with normal weight. Among those with overweight there was an equal distribution with 25 children each. Among those who were obese, median age was 108 months and 27 (54.0%) were aged <108 months.
Table 1. Demographic characteristics of the study population.
The difference in the mean FVC, FEV1, FEV1 /FVC, PEF, of all three groups was statistically analysed and a significant difference between normal and overweight as well as between normal and obese was noted for both parameters tested. There was a decrease in the mean FVC, FEV1, FEV1 /FVC, PEF, Pre-test & post-test % predicted but an increase in the mean % change for all the parameters except for PEF, with an increase in BMI (Table 2). The changes in the mean FEV1/FVC-Pre-test % predicted and % change predicted with BMI were statistically insignificant; similarly, PEF post test predicted though reduced with increasing BMI, but was statistically insignificant. There was a decrease in the % change predicted for PEF with increasing BMI. Spirometry was normal in all normal weight children (n=50), 30 in overweight (n=50) and in 23 obese children (n=50). (Figure 1) Of 20 overweight children with abnormal spirometry, only restrictive lung functions (n=10), restrictive lung functions with an additional significant FEV1 post change (>12%post change) (n=07) were noted (Figure 1).
# Statistically not significant
Table 2. Comparison of FVC-% predicted and FEV1 predicted
Figure 1. Spirometric findings in the study group.
Lung function tests (LFT) were statistically significant among normal, overweight, and obese study group when compared agewise. However, gender wise, significant differences were observed in study group (Table 3a, 3b, 4a, 4b, 5a and 5b).
* Statistically significant
Table 3a. Comparison of lung functions in normal study groups with age
* Statistically significant
Table 3b. Comparison of lung functions in normal study groups with gender
* Statistically significant
Table 4a. Comparison of lung functions in Overweight study groups with age
* Statistically significant
Table 4b. Comparison of lung functions in Overweight study groups with gender
* Statistically significant
Table 5a. Comparison of lung functions in Obese study groups with age
* Statistically significant
Table 5b. Comparison of lung functions in obese study groups with gender
The detrimental effect of obesity on respiratory functions is well established in adults [21-23] but with a differing pattern of effect on lung functions in children . There are unconvincing, inconclusive evidences on the effect of increased body weight on respiratory funcitons in children. Few reports support the negative association between BMI lung functions resulting in reduction in lung volume and lung functions [25-32]. Mild obesity in children has not shown any significant impairment of pulmonary function [33-35]. Das D et al.  observed that thin had lower FVC, FEV1, FEV3 and overweight boys had greater FVC, FEV1, FEV3, compared to norrmal boys. Choudhuri D et al.  report a positive association between BMI and pulmonary function.
Pulmonary function tests are the most appropriate and simple clinical investigations for the evaluation of lung functions; spirometry is a non-invasive tool to assess lung functions. Spathopoulos D et al.  observed a reduction reduction in spirometric parameters in children with an increase in BMI.
There is limited data on the effect of BMI on spirometric parameters in Indian pediatric population, hence, we evaluated and assessed the same in children aged 5-16 years.
We observed that the statistically significant difference (P<0.05) in mean FVC-Pre & post-test % predicted between the study groups compared to normal; there was an inverse relationship between BMI and the parameters, with an increasing BMI, mean FVC-Pre & post-test % predicted decreased. Similar observation was observed in previous studies [39-41] where FVC was significantly lower in obese children. The difference in mean FVC-% change predicted was significant only between normal and obese (P<0.05) in our study. As BMI increased, mean FVC-% change predicted increased suggesting that the obese group has more post bronchodilator change compared to the normal weight group. There was negative correlation between BMI and FVC-Pre-test% predicted in obese group.
Similar trend was observed in mean FEV1-Pre-test % predicted when normal weight children were compared with obese and overweight (P<0.001). But the difference in mean FEV1-Post test % predicted was significant between normal and obese (P<0.05). We noted a decrease in mean FEV1-Pre &post test % predicted with an increase in BMI. Similar reports are available in the literature. However, there are differing reports on this effect of BMI; few reporting lower FEV1% in obese children [29,40-41]. While no statistically significant associations were reported by few authors [33,42-43]. There was a statistically significant difference in mean FEV1-% change predicted between normal and obese (P<0.05) children in our study; with an increasing BMI, the mean FEV1-% change predicted also increased suggesting that the obese group has more post bronchodilator change compared to those with normal weight. However, there was a negative correlation in obese children similar to that reported by Akin O et al. 
With a significant effect on FVC and FEV1, a similar trend on the effect of BMI on the mean FEV1/FVC pre &post test % predicted can be expected; however, there was no statistically significant difference was noted in the mean FEV1/FVC-pre-test % predicted and % change predicted, among all three groups, but there was significant difference in mean FEV1/FVC-Post test % predicted between normal and obese (p<0.05). Our reports are in agreement with the previous report [33, 39, 41, 43]. Though with an increase in BMI, we observed a decrease in the mean FEV1/FVC-Pre-test % predicted albeit statistically insignificant. In contrast, significant statistical relation between these two parameters was observed in previous studies [16-17, 29]. Children with high BMI had a statistically significant lower FEV1/FVC ratios [45-46]. There was negative correlation between BMI and FEV1/FVC- % change predicted among all three groups in our study.
The mean difference PEF-Pre-test % predicted between normal and obese was found to be significant (P<0.05) with the latter group having a significantly lower mean pre test % predicted. Similar reports available in the literature [17, 43]. As with other parameters, increase in BMI was associated with a decrease in the pre-test % predicted, PEF - % change, although not statistically significant. We report a negative correlation between BMI and PEF- Pre-test % predicted among overweight and obese groups. In contrast, there was a positive correlation observed by, Yao et al. .
We performed spirtomety and its interpretation as per the ATS guidelines. Normal spirtometry was seen in all our participants (100%) in the normal weight group.
Among overweight and obese children, 60% and 46.0% had normal spirometry, respectively; restrictive changes were common in those with abnormal spirometry, more pronounced in obese children (50.0%) than those who were overweight. Obstructive changes were seen in less number of patients; irreversible obstructive changes were seen in two children who were overweight and not in obese children. However, the number of children with obstructive changes are too less to arrive at a concrete conclusion. de Assuncao SNF et al.  report that in overweight and obese children, the restrictive lung functions were predominant with an additional significant FEV1 post change; obstructive pathology (32.2%), restrictive (25.4%) and mixed ventilatory disorder (6.7%) were reported.
We compared the influence of weight in all groups with age and gender; there was no significant influence of age but there was statistically significant influence on gender was noted in obese group, more in male patients. However, the number of females in normal and obese group were less (n=12 & 14, respectively) to make concrete conclusion.
Similar to our study, previous studies (cross-sectional studies) also showed negative association of BMI with lung functions (FEV1 (%), FEV1/FVC (%), PEF (P < 0.05)) [16-17]. Wafaa FA et al  reported that FVC and FEV1 were significantly lower in obese group. There was no statistically significant difference in FEV1/FVC between two groups. There was statistically significant positive correlation between FVC and waist circumference.
Previous studies on Indian pediatric population involved only certain groups like, pre-pubertal girls, adolescent boys that yielded varied results. To the best of our knowledge, this is the first case-control study in India to study the effect of overweight and obesity on lung function parameters using spirometry involving normal, overweight and obese children.
Small sample size, not excluding children who were passive smokers, not performing DLCO for confirmation of mixed and restrictive lung function were the limitations of our study.
Our observations imply that overweight and obesity adversely affects the pulmonary function parameters even in healthy children, which alarms the need for parental awareness and action against controlling childhood obesity to build a healthy society.
Adverse influence of Obesity has not spared the respiratory system. Obesity and being overweight have a negative impact on the pulmonary functions in children, decreasing FVC, FEV1 and FVC/FEV1. Restrictive pathology is more common though obstructive pathology is less significant, but un-ignorable.