Effect of Body Composition on Ventilation Parameters in a Group of Young Sudanese Females

Background: Lung Function Test helps (LFT) in the diagnosis and follow up of patients with pulmonary or cardiac diseases. Ignoring BMI and body composition during interpretation of LFT results may lead to wrong diagnosis and unnecessary use of drugs. Objective: This study was conducted to test the hypothesis that differences in body composition between individuals can explain some of the features of LFT that are explained by variations in age, sex, and height only.Methods: This observational analytical cross sectional study which included 150 young adult females. Those with history of amenorrhea, smoking, asthma or cardiac disease were excluded. Anthropometric measurements including: BMI, waist circumference (WC) and body fat percent calculated from skinfold thickness measurements were done. Dynamic spirometric tests were performed using digital spirometer; FEV1, FVC, FEV1% were measured. Results: Both obese and underweight subjects had a significant reduction in FEV1 (P = .002) and FVC (P = .004) compared to normal ones. FEV1% was significantly higher in the overweight and obese group compared to the other two groups (P = .02). Body weight, BMI, and WC had significant positive correlation with FEV1 and FEV1% in young healthy females. Conclusion: Increase in BMI, body weight, WC and body fat showed positive significant correlation with FEV1% and may give a restrictive pattern in LFT. Underweight subjects may show significant reduction in lung function if their BMI is not considered.


Introduction
Assessment of the lung functions (LF) helps in the diagnosis and management of patients with pulmonary or cardiac diseases.Lung volume measurements made during forced expiration are interpreted by comparing them with the expected values given the age, height and sex of the patient.Body mass index (BMI) is rarely used.This may lead to wrong diagnosis, unnecessary use of drugs, and failure to detect significant improvement in FEV 1 (forced expiratory volume in the first second) [1].Racial or ethnic differences in lung volumes have been reported.USA Blacks were found to have lower lung volumes than Whites.The differences in the body size and shape were suggested to be the reason for these differences in spirometric findings [2].
Obesity is known to affect the LF and may increase the effect of an existing airway disease [3].Obese subjects may have a decrease in lung volume and expiratory flow rates [4] and may experience dyspnea at rest [5,6].Some studies found that BMI has a strong positive association with risk of adult-onset asthma [5][6][7][8].Other studies showed that obese individuals can have dyspnea but not airway obstruction [6,9].Many obese Sudan Journal of Medical Sciences Production and Hosting by Knowledge E subjects were using bronchodilators without evidence of airflow obstruction [6].Jones and Nzekwu found that BMI has significant effects on all lung volumes [10].It has been observed that BMI improved the predictions for both volumes and flows, regardless of sex.BMI or body weight (BW) gain has been related to the decrease in FEV 1 and forced vital capacity (FVC) in adults [11][12][13].
The addition of waist circumference (WC) to BMI improved the prediction of health risk than BMI alone [14].Chen et al. reported that WC, but not BMI, is negatively associated with LF [15].Some studies suggest that upper body fat distribution [16,17] and abdominal adiposity [18] are better predictors of LF than BW or BMI.Body fat distribution also affects the LF [17].Fat% and fat free mass (FFM) index improved the descriptions of FVC and of changes in FEV 1 and FVC [14].
This study was conducted to test the hypothesis that differences in body composition between individuals can explain some of the features of LFT that are explained by variations in age, sex, and height only.

Materials and Methods
This study is an observational analytical cross sectional study, done on 150 young female university students.The main objective of the study was to determine the effect of overweight and obesity on the ventilatory parameters (FEV 1 , FVC, FEV 1 %).
The secondary objectives were: to determine the effect of BMI on each of the ventilatory parameters, and to verify the relation between BMI, percentage of body fat and waist circumference and each of the ventilatory parameters.Subjects were volunteers from the practical groups who considered themselves healthy with no history of amenorrhea, smoking, asthma or cardiac disease.Their age was between 17-23 years.All subjects had completed a questionnaire personal data and additional questions on smoking, history of asthma, other respiratory or cardiovascular disease, or any other disease that can affect the lung function.Each subject underwent complete physical examination to exclude any abnormality and signed an informed consent.Dynamic spirometric tests and anthropometric measurements including: BW, height, BMI, WC, skinfold thickness were done.
Weight (kg): was measured to the nearest 100 g using standardized digital weight scale (Beurer, Germany) with the subject in standing position wearing light clothes and without shoes.
Standing height (m) was measured without shoes with the subject's back to avertical standardized height scale (Seca, Germany) to the nearest mm.Then BMI (kg/m 2 ) was calculated as a ratio between body weight (kg) and squared height (m 2 ).
Waist circumference (cm) was measured using a tape to the nearest 0.1 cm at the end of a normal expiration from exposed relaxed abdomen, at the level of the umbilicus in standing position.
Body composition was estimated using three steps: (a) Skinfold thickness was measured in mm using Holtain skinfold caliper (Crymych Company, United Kingdom) from the triceps and subscapular region to the nearest 1 mm [19] by the same investigator.
(c) Fat Free Mass (FFM) (kg) was calculated from the body weight and BF%.
Dynamic spirometric tests were performed using Electronic spirometer (Chest Corporation, Japan) in the sitting position and with a nose clips.First subjects were instructed in the FVC maneuver then the appropriate technique was demonstrated by the investigator.Each subject inhale from FRC and then insert the breathing tube into her mouth, making sure her lips are sealed around the mouthpiece before starting the FVC maneuver.The subject must have a complete inhalation before beginning the forced exhalation.Each subject attempted to perform at least three acceptable FVC maneuvers according to the ATS (American Thoracic Society) acceptability and reproducibility criteria [21].The highest result was used for statistical analysis.FEV 1 , FVC, and FEV 1 % were measured.

Results
This study included 150 young healthy females.Subjects were classified according to BMI class into 3 groups underweight, normal, obese (include both overweight and obese BMI > 25kg/m 2 ) according to WHO classification [22].Table 1 shows means of anthropometric and spirometric measurements in different to BMI classes.
To determine the effect of overweight and obesity in lung function test ANOVA test was done to compare the means of the three BMI groups.Underweight subjects had a significantly lower FEV1 than normal BMI and obese subjects (P = 0.03) (Figure 2).FVC was significantly higher in normal BMI subjects compared to the other two groups (P = 0.01).There was no significant difference between underweight and obese subjects in FVC (Figure ??).FEV 1 % was significantly higher in the overweight and obese group compared to the other two groups (P = .02).

Discussion
In this study obese subjects had the highest mean of BF %, but they also had the highest mean of FFM as well (table 1).The increase in BW in the study group could be explained partially by the physical growth involving skeletal frame, muscles and fat.This means that subjects in the obese group were overfed females with excessive energy intake and minimal exercise, therefore they deposited more fat.They had a good nutritional status which leads to development of good muscle bulk (more FFM).

Effect of Body Composition on Ventilation Parameters
We found that the subgroup with normal BMI had the highest mean of both FEV 1 and FVC, while underweight ones had the lowest mean of both FEV 1 and FVC.Welldeveloped muscles especially of the chest wall are expected to influence all forced expiratory parameters.Being underweight with small muscle bulk may reduce the lung volumes.
FVC showed a significant positive association with BW (P = .02).The increase in BW in this young females increase in both muscle bulk and body fat with predominant effect of muscle bulk on LF.Contrary to expectations FVC had no significant association with BMI in the present sample.The effect of BMI may be clearer in older age group.BF% showed a negative correlation with FVC but it was not significant.The present results agreed partially with Lazarus et al results who found that adjusted FVC was not significantly associated with BMI, but was negatively associated with BF% in men and women [17].Therefore, it was justified to look for the FFM and its correlation with LF parameters because: the number of overweight and obese is too small to show the effect of increased BMI or body fat on LF.FVC showed positive correlation with BW and not with BMI.In addition, underweight had the lowest FVC.From the previous results muscle mass is more likely to affect the lung parameters.The results showed a highly positive association between FFM and FVC (P = .000)as shown in table 2; which agrees with Lazarus et al results [17].In Cotes et al study, this association was insignificant in women but not for women who perform much exercise [14].
Unlike the results of Chen et al in which WC, but not BMI, is negatively associated with LF [15]; there was no association between WC and FVC in this sample.This is most probably due to the opposing effects of fat and muscle in these young females.FEV 1 had highly significant positive association with BW, FFM and WC (P < .005);and a positive significant association with BMI (P = .01).This can be explained by the effect of the good muscle bulk on forced expiration.
FEV 1 % had a highly significant positive correlation with BW and BMI (P = .005),because these measures caused a significant increase in FEV 1 and a slight or no increase in FVC (table 2).In contrary to Heather et al results which showed a negative association between WC and FEV 1 % [18], there was a highly significant positive correlation between them in this study (P < .005).The increase in WC in these young females was associated with the increase in muscles mass (causing increase FEV 1 ) as well as fat (causing insignificant effect on FVC) and therefore a positive association with FEV 1 %.In addition, there was a positive highly significant association between FEV 1 % and BF% calculated from the subscapular skinfold (P = .002)and triceps skinfold (P = .02).FEV 1 % was significantly higher in the overweight and obese group compared Sudan Journal of Medical Sciences Production and Hosting by Knowledge E to the other two groups (P = .02).Thus, results of LFT in healthy obese persons may give a restrictive pattern.This may be due to the mechanical load impeding expansion of the chest wall during inspiration.Future studies may yield more conclusive results if more sensitive estimates of muscle mass are employed age group.

Effect of BMI on Ventilation Parameters
In this study BMI class had a significant effect on FEV 1 (P = .004),FVC (P = .008)and on FEV 1 % (P = .04).Underweight subjects had significantly lower FEV 1 compared to normal BMI and obese subjects.There was no significant difference in FEV 1 between obese and normal BMI subjects, which support the hypothesis that the effect of increase muscle mass is likely to offsets the effect of fatness on FEV 1 .
In agreement with previous studies which have demonstrated that a rise in BMI lowers FEV 1 and FVC [12,13]; this study showed that FVC was significantly reduced in the obese and underweight group compared to normal BMI subjects (P < .05).There was no significant difference in FVC between obese and underweight subjects.This means that both obese and underweight had a significant reduction in FVC compared to normal weight females.

Conclusion
The higher FEV 1 % in the overweight and obese group compared to the other two groups and the positive association of body fat, body weight, WC and high BMI with FEV 1 % suggests that obese subjects may show a restrictive pattern in LFT.On the other hand, underweight subjects may have a significant reduction in lung function.
We suggest that more anthropometric measurements should be taken into account for the assessment of lung function.

Ethics Approval
This study was approved by the Department of Physiology-Faculty of Medicine-University of Khartoum.Each participant signed an informed consent form.

Competing Interests
No areas of competing interest of this study.DOI 10.18502/sjms.v12i2.918 Data analysis: Data was saved and analyzed using SPSS version 10. Subjects were classified into 3 BMI groups: underweight, normal and obese (include both overweight and obese BMI > 25 kg/m 2 ) according to WHO classification [22].Descriptive statistics were calculated for all the variables according to BMI classes.Correlations of body measurements with ventilatory parameters were done using Pearson Correlation.To verify the effect of BMI class on the ventilatory parameters their mean values was compared between underweight, normal, obese groups using analysis of multiple variances (ANOVA) Test.

Figure 1 :
Figure 1: Means of FEV 1 in Different BMI Groups.

Figure 2 :
Figure 2: Means of FVC in Different BMI Groups.