This cross-sectional comparative study was conducted in the Human Physiology Laboratory of a Private University (MSU), Malaysia. Necessary ethical approval has been taken from the university ethical committee (registration No-MSU-HE 124). A total of 100 (50 obese and 50 non obese) non-smoking adolescent students of both sexes aged between 16 to 19 years were randomly selected for the study. Written consent was obtained from each participant. The study was conducted during the period from June to December 2017.

BMI of each subject was calculated as per the following formula:

Subjects having BMI greater than the 95^th percentile for age were classified as obese [11]. A total of 50 such obese boys were identified. An identical number of age-matched non-obese with BMI=18.50-24.99 kg/m² were taken as controls. Subject with symptoms of illness like fever, cough, abdominal pain, any history of pulmonary diseases, anxious, apprehensive, and uncooperative ones were excluded from the study. All subjects were explained about the procedures to be undertaken. The following measurements/tests were performed.

The body weight of the studied participants were measured by using balanced beam scale to an accuracy of ±0.1 kg with the subject wearing minimum clothing while body height was measured with the measuring rod attached to the balanced beam with an accuracy of ±0.50 cm. Waist circumference was recorded by measuring the smallest circumference between the ribs and the iliac crest to the nearest 0.1 cm, while the participant was standing with the abdomen relaxed, at the end of normal expiration. Hip circumference was recorded by measuring the maximum circumference between the iliac crest and the upper border of pubic symphysis. WHR was calculated by dividing waist circumference by hip circumference.

The dynamic pulmonary functions were recorded on a computerized spirometer (Spirobank II MIR, Del Maggiolino125, 00155 Roma, Italy). The parameters measured were FEV₁, FVC, FEV₁/FVC ratio, PEFR, FEF_25–75%. The spirometer was calibrated daily using calibration syringe of 3 Lt. All the measurements were taken in standing posture with nose clipped according to the guidelines given by the American Thoracic Society and European Respiratory Society [12]. The system was calibrated at source to read all measures at Body Temperature and Pressure Saturated with vapour (BTPS). All anthropometric measurements and pulmonary function measurements were conducted in one sitting on the same day for each subject.

The pulmonary function parameters of the obese and control groups were compared using Student’s t-test. Pearson’s product moment correlation co-efficient was calculated to determine the relationship between various measures of obesity (BMI, waist circumference, hip circumference, waist-to-hip ratio) and pulmonary function parameters. All the statistical analysis were performed using MS-Excel 2010 data analysis tool pack. The p-values less than 0.05 were considered as statistically significant.

Among 100 non-smoking healthy adolescent participants studied, 57 were female (23 obese, 34 non obese) and 43 were male (27 obese, 16 non obese). The general characteristics and anthropometric variables of the obese and control groups have been depicted in [Table/Fig-1].

Weight, waist circumference, hip circumference and BMI were found to be significantly higher in obese groups compared to control group. The comparison of observed pulmonary function parameters of the obese and control groups has been shown in [Table/Fig-2]. Mean FVC, FEV₁ and PEFR were marginally higher in obese group compared to non-obese control group, while mean FEV₁/FVC%, FEF_25-75% were marginally lower in obese subjects than age matched non obese control group. There was no significant difference in mean pulmonary function parameters between obese and non-obese control group. However, five obese subjects had mild restriction, whereas no obstructive impairment was detected in any subject of the obese and control group.

[Table/Fig-3] presents the correlation matrix between various anthropometric obesity markers and pulmonary function parameters in studied obese subjects.

In studied obese subjects, FEV1/FVC% exhibited significant (p<0.01) inverse correlation with all measured anthropometric obesity markers. FVC and FEV1 had positive significant (p<0.05) correlation with WC and HC, whereas maximum mid expiratory flow rate (FEF_25-75%) exhibited negative significant correlation with BMI and WHR. [Table/Fig-4] depicts the correlation matrix between various anthropometric obesity markers and pulmonary function parameters in studied normal weight control group.

In normal weight studied subjects, FVC and FEV1 had positive significant association with WC and WHR; however rest of the dynamic pulmonary measurements had no significant correlation with measured anthropometric obesity indices.

The present study was aimed to evaluate the effect of obesity on different dynamic pulmonary functions among Malaysian adolescent university students by comparing lung function of the obese adolescent to their age matching normal weight control group. Some studies have shown a significant reduction in spirometry parameters with obesity while others have not shown any effect [13,14]. Torun E et al., have shown in a comparative study on obese and non-obese that although there was no statistically significant difference in FEV₁, FVC, or FEV₁/FVC, a significant reduction in PEFR and FEF_25-75% was found in overweight and obese individuals [14]. The present study did not find any significant effect of obesity or overweight on dynamic lung volumes measured by spirometer, however the mean FVC was high in obese compared to non-obese control group which may be due to higher body surface area of the subjects in obese group. The mean values of FVC and FEV₁ in obese and non obese were lower than the previously reported values among Malaysians [15,16]. Similar study conducted among obese adolescent boys from a school in Baroda city, Gujarat showed that FEV₁ and FEV₁/FVC were significantly low in the obese group [17]. However, in our present study among Malaysians, adolescents showed that FVC, FEV₁ and PEFR were higher in obese subjects whereas FEV₁/FVC ratio, FEF_25-75% were lower in obese compared to age matched non obese control group, however, the difference was not statistically significant. This is supported by a study conducted on Saudi population by Al Ghobain M where he showed that there were no significant differences between the obese and non-obese subjects in FEV1, FVC, FEV1/FVC ratio and FEF_25-75% [18].

The present study was also aimed to evaluate correlation between various anthropometric obesity marker such as BMI, WC, HC, WHR and pulmonary function parameters. The present study revealed that in obese adolescent FEV1/FVC% exhibited significant inverse correlation with all measured anthropometric obesity markers, suggesting that both relative obesity and central obesity causes significant decrease in FEV1/FVC% and obese are more susceptible to obstructive pulmonary diseases. Similar negative correlation has been observed by Banerjee J et al., [9]. On the other hand, in normal weight studied subjects, FVC and FEV1 positively associated with WC and WHR; however rest of the dynamic pulmonary measurements had no significant correlation with measured anthropometric obesity indices.

Some recent studies have observed that pulmonary function shows an inverse relationship with various anthropometric markers of obesity in children and adolescent [17,19,20]. BMI, WC, HC and WHR are considered as anthropometric markers of both general and central obesity, which may influence pulmonary function in children and adolescents [21,22]. The mechanical effect of fat in restricting normal breathing is more evident if central obesity is considered instead of overall or peripheral fat [23]. The excess of fat in the abdomen and thoracic region may lead to a decrease in the compliance and resistance of respiratory system, increasing work of breathing [24]. Obesity has effects on lung function that may exaggerate the effects of existing airway disease [25]. There is no difference in the effect of obesity on the respiratory system when different abdominal obesity indicators are used, such as WC and waist-to-hip ratio, and thoracic fat indicators [25], suggesting an interdependency of these measures with respect to pulmonary function parameters.

Some studies reported that variables like ethnicity, age, weight, and height, are the prime predictors of lung function in different groups of population [26,27]. In contrast, our present study showed that in obese subjects BMI, WC, HC and WHR had inverse significant association with FEV₁/FVC%, suggesting that obese are more susceptible to obstructive pulmonary diseases. A number of hypotheses have been proposed to explain the negative correlation between pulmonary function parameters and measures of visceral adiposity. One possible mechanism is a mechanical limitation of chest expansion during the FVC maneuver. Increased abdominal mass may impede the descent of the diaphragm and increase the thoracic pressure [28]. Also, abdominal adiposity is likely to reduce expiratory reserve volume via compressing the lungs and diaphragm [29,30].

There are few limitations in the present study. A bigger sample size would have given more concrete evidence. In the present study we have only investigated the dynamic lung volumes since we did not have facilities to examine static lung volumes.

Our study concludes that there was no significant effect of obesity on dynamic pulmonary functions among non-smoker healthy adolescent students of both sexes. BMI, WC, HC and WHR exhibited inverse significant correlation with FEV1/FVC ratio, suggesting that obesity decrease FEV1/FVC ratio and obese are more prone to obstructive lung diseases.