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 Table of Contents  
Year : 2022  |  Volume : 11  |  Issue : 1  |  Page : 14-19

Sex differences in spirometric measures and its association with basal metabolic rate in obese and healthy normal weight middle-aged subjects

1 Department of Physiology, All India Institute of Medical Sciences, Mangalagiri, Andhra Pradesh, India
2 Department of Physiology, Navodaya Medical College and Research Center, Raichur, Karnataka, India
3 Department of Physiology, A. B. N. Seal College, Cooch Behar, West Bengal, India
4 Department of Microbiology, Datta Meghe Institute of Medical Sciences, Wardha, Maharashtra, India
5 Department of Public Health Dentistry, ESIC Dental College, Kalaburagi, Karnataka, India

Date of Submission06-Sep-2021
Date of Decision27-Oct-2021
Date of Acceptance01-Nov-2021
Date of Web Publication04-Jan-2022

Correspondence Address:
Dr. Afreen Begum H. Itagi
Department of Physiology, All India Institute of Medical Sciences, Mangalagiri, Andhra Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijrc.ijrc_116_21

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Context: Reduced basal metabolic rates (BMRs) are said to be common in obese or sedentary adults. Very few investigations have analyzed the BMR relationship with that of respiratory functions in middle-aged obese individuals. Objectives: We aimed to determine the sex differences in BMR and spirometric measures in obesity and evaluate the association of BMR with respiratory functions in middle-aged people. Methods: This analytical study was undertaken in healthy normal-weight and obese men and women (50 each) of age 35–55 years. Body mass index (BMI), percentage of body fat, fat mass, and fat-free mass were estimated and BMR was calculated using predicted equations. Spirometric measures such as forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), FEV1/FVC, peak expiratory flow rate, mean forced expiratory flow during the middle of FVC (FEF25%–75%), and maximum voluntary ventilation were assessed in both sexes. Independent two-sample t-test and Pearson's correlation were used as tests of significance with P ≤ 0.05 affirming the statistical significance. Results: BMR among men showed significantly higher mean scores than females. In obese group, most of the respiratory function parameters except FEV1/FVC ratio were significantly reduced in females compared to men. An inverse correlation existed between BMR and FEV1/FVC ratio, whereas BMR observed a positive correlation with all other respiratory function measures among both obese and nonobese. Conclusions: To study the early lung function alterations in the obese, it is necessary to take into account the sex differences, BMR, and body composition instead of BMI alone.

Keywords: Anthropometrics, basal metabolism, lung functions, obesity, sex differences

How to cite this article:
Itagi AB, Kalaskar A, Dukpa PT, Chandi DH, Yunus G Y. Sex differences in spirometric measures and its association with basal metabolic rate in obese and healthy normal weight middle-aged subjects. Indian J Respir Care 2022;11:14-9

How to cite this URL:
Itagi AB, Kalaskar A, Dukpa PT, Chandi DH, Yunus G Y. Sex differences in spirometric measures and its association with basal metabolic rate in obese and healthy normal weight middle-aged subjects. Indian J Respir Care [serial online] 2022 [cited 2022 Aug 11];11:14-9. Available from: http://www.ijrc.in/text.asp?2022/11/1/14/334802

  Introduction Top

Obesity being twenty-first century's worldwide and one of the most pressing public health concerns has approached epidemic proportions in India, with morbid obesity afflicting over 5% of the country's population.[1] The energy metabolism rate per day that an individual must endure in order to maintain the integrity of daily vital functions is referred to as the basal metabolic rate (BMR). It is a minimum required energy for sustenance of life in temperate environment neutrally when in a postabsorptive condition, taking into account the energy cost of physiological activities such as muscular contractions, breathing, and brain activity.[2] It is hypothesized that reduced BMRs are common in obese people and in sedentary adults, BMR accounts for 60% of total energy expenditure.[3] However, differential BMRs, on the other hand, are unlikely to be the cause of growing obesity rates.[4]

Obesity impedes the mobility of diaphragm and the expansion of the thoracic cage, which reduces chest compliance. Its negative impacts on energy cost/effort of breathing, respiratory mechanics, respiratory resistance, respiratory volumes and muscle functioning, gaseous exchange in lungs, and breathing control can drastically change pulmonary function and cut down exercise capacity.[5],[6] The mechanism that impacts respiratory function in obesity is still being disputed, and so is an appropriate indicator of fatness in connection to respiration in a dynamic state yet unclear.[7],[8],[9] Multiple studies have found that obese persons had inferior lung volumes, with negative relation between lung functioning and numerous indicators of fat distribution and obesity.[5],[6],[7],[8],[9],[10] Only a few investigations, however, have looked at the association between BMR and the components of ventilatory dysfunction.[11],[12],[13],[14]

To our knowledge, the relationship between obesity and BMR as a risk factor for pulmonary dysfunction has not been thoroughly investigated and documented among South Indians, who are regarded to be at higher risk of obesity-related problems. Furthermore, there is a dearth of research evidence about sex differences in BMR, spirometric measures in obesity, and also the association between BMR and ventilatory dysfunction in middle-aged people. Hence, the study aimed at investigating the BMR and its influence on spirometric measures among middle-aged obese and nonobese individuals with an emphasis on sex differences in the same.

  Methods Top

This observational research was undertaken in an institute of medical sciences and research in southern India. The apparently healthy individuals between the ages of 35 and 55 years were taken as participants. Minimum required sample (N) was estimated using the equation N = (Z/2) 2 s2/d2; considering power of 80%, error rate of 5% and taking into account the standard deviation (SD) of 9 resulted from the pilot study undertaken on 8 middle-aged obese adults, the estimated sample size was 45. However, allowing for 10% nonrespondents, the corrected sample size required in each group was 49. Detailed history of extended exposure to drugs that can lead to altered lung functions, medical issues requiring drug therapy during the last 6 months, and current clinical/systemic examination findings were recorded. Subjects with physical chest wall abnormalities, established obstructive pulmonary illness, unstable coronary syndromes, presently smokers and alcoholics were excluded. The approval of research protocol was provided by the institutional scientific review board and ethical committee. Informed as well as written consent from all subjects was obtained after satisfactorily detailing about the objectives and procedures of the study.

After a minimum of 2 h of light breakfast and according to the specified guidelines, anthropometric measures were obtained in the physiology laboratory. All spirometric measurements were obtained from 10 a. m. to 12 noon to eliminate circadian variations.[15] The estimation of BMR was done using height, age, gender, and body weight. Measuring the weight to the nearest 0.5 kilogram (kg) was done using a digital personal weighing scale (Apollo Hospitals Enterprises Ltd), while the stature was recorded by means of 150 cm standard flexible poly-fiber tape for measuring to the nearest 0.2 cm, with the subject standing against a wall and head in Frankfort horizontal plane.[16] Body mass index (BMI) was calculated as weight/height2, expressed in kilograms and square meters (m2), respectively.[17] Percentage of body fat (BF%) was calculated based on physiological differences in the males and females by using Deurenberg formula, which accounts for factors such as age, BMI, and sex.[17] BF% estimation was followed by calculation of fat mass (FM) and fat-free mass (FFM) using the standard equations.[17],[18],[19] Eventually, Cunningham's equation is used to relate the FFM with the BMR, as mentioned in [Table 1].
Table 1: Measures and formulae used for calculation of basal metabolic rate

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The pulmonary function tests were performed as per the Joint Indian Chest Society-National College of Chest Physicians (India) guidelines for spirometry. Subjects with history of forced expiration/cough-related syncope, thoracic (or) abdominal surgery in recent 4 weeks, atrial/ventricular arrhythmia, confirmed/suspected systemic or transmissible respiratory infection were excluded from participating in the study. “NDD – Easy on PC,” a portable, computerized, precalibrated, electronic, dry-type spirometer from NDD Medical Technologies, was used for recording spirometric measures. Even though the sensor of NDD – Easy on PC is based on a principle of digital measurement technique, requires calibration only once, and does not change during the sensor's lifetime, daily calibration verification of the spirometer at low, medium, and high flow along with the visual inspection of the performance of each maneuver was also undertaken by the principal investigator for quality assurance.

Spirometric measurements were recorded in a vacant area with adequate sunlight, and the subjects were made to sit comfortably/relaxed in an armed chair with straight back and were explained about the forced expiratory maneuvers before the procedure. Disposable filter mouthpiece (spirette) was used to avoid cross-contamination, and face masks and gloves were used to protect the investigator/assistants. The participants were asked to inhale atmospheric air deeply, and the nose clip was placed immediately with the spirette inside the mouth, lips tightly sealed around it, followed by blowing out the air as hard and fast as possible. The blast out for a minimum of 6 s was followed by inhalation deeply with the spirette still inside the mouth (to form a loop). Similarly, at least three appropriate maneuvers of forced vital capacity (FVC), forced 1-s expiratory volume (FEV1), mean forced expiratory flow during the middle of FVC (FEF25%–75%), peak expiratory flow rate (PEFR), and maximum voluntary ventilation (MVV) have been performed. The highest volumes of three acceptable FVCs, FEV1, PEFR, and FEV1/FVC ratio percentage were recorded. MVV was assessed by asking the subject to inhale and exhale as deeply and rapidly as possible for 15 s.

Statistical analysis

The data were analyzed using version 20.0 Statistical Package for the Social Sciences software (SPSS Inc., IBM Corporation, Chicago, Illinois, USA). Descriptive data presentation included expressing as mean ± SD or percentages. Independent two-sample t-test was used as an inferential test for measuring the difference between two measured variables. The degree of correlation was determined using the correlation coefficient (Pearson's “r”). Statistically significant was affirmed at P ≤ 0.05.

  Results Top

The estimated gender-wise mean age and anthropometric measurements of both the groups, i.e., obese (n = 50) and nonobese (n = 50), are presented in [Table 2]. In both obese and normal-weight individuals, BMR was higher in males than in females (P < 0.05). In comparison to nonobese middle-aged individuals, the BMR was significantly higher among obese group [Table 3].
Table 2: Sex differences in anthropometric measures, basal metabolic rate, and spirometric measures among obese and nonobese subjects

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Table 3: Comparison of anthropometric measures, basal metabolic rate, and spirometric measures between obese and nonobese subjects

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The spirometric evaluation showed substantial sex difference in most of the respiratory measures among obese with significant reduction in females than in males. However, except for FEF and MVV, no other respiratory measures were significantly less in normal-weight females than in nonobese males [Table 2]. The PFT parameters FVC, FEV1, and FEF25-75% were substantially lower in obese group; however, FEV1/FVC%, PEFR, and MVV were not significantly different in comparison to nonobese [Table 3]. [Table 4] shows the sex differences in the correlation of BMR with spirometric parameters. In both the obese and nonobese groups studied, a significantly positive correlation of BMR was identified with FVC and FEV1. In comparisons to obesity (r = +0.66 FVC and r = +0.62 for FEV1), the degree of correlation was higher for nonobese compared to obese (r = +0.57 FVC and r = +0.56 FEV1) [Table 4] and [Figure 1]. This positive association implies that whenever the BMR increases, the FVC and FEV1 levels will increase significantly. An inverse correlation of BMR with FEV1/FVC was observed among both obese and nonobese subjects, which was showing comparatively higher strength of relationship in obese group (r = −0.02) than the nonobese middle-aged individuals (r = −0.002). A positive correlation of BMR with PEFR, FEF25%–75%, and MVV was observed in both groups, with the strength of correlation being comparatively slightly high and significant in nonobese subjects, as shown in [Table 4] and [Figure 1].
Figure 1: Relationship of basal metabolic rate with pulmonary functions in obese subjects

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Table 4: Comparison of basal metabolic rate with relation to spirometric measures between obese and nonobese subjects

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  Discussion Top

Obesity is linked to variation of lung volume and result in various patterns of alteration to the respiratory parameters; however, it is still unclear whether the gender difference exists. The BMR accounts for 44%–70% of total daily expended energy, subjected to age and lifestyle, and is largely determined by age, gender, body size, body composition, etc., and hence, BMR is the principal focus of development and treatment of obesity.[20],[21] Spirometry is among the simplest of the tools to detect impairment in pulmonary function at an early stage so that preventive measures can be adopted. Our study evaluates the sex differences in respiratory function parameters and examines the relationship of BMR with spirometric measures among the obese and nonobese subjects of age group 35–55 years.

In the present study, BMR, FEF25%–75%, and MVV measures were significantly higher for nonobese men than the corresponding values for normal-weight women. It was found that the BMR, FVC, FEV1, PEFR, FEF, and MVV measures in obese females were substantially lower than in obese men. These findings corroborate previous data of similar studies by Mihai et al., Wang et al., Merghani et al., and Lasser et al., where comparative analysis was undertaken between obese and normal-weight individuals.[11],[20],[22],[23] In addition to smaller lung volumes and diffusion surfaces, the respiratory airways in women are usually with smaller diameter compared to their height-matched men. The lower lung function test values of female subjects in this study can be attributed to the above gender-related differences, which is evident from previous research.[24],[25]

There existed a positive correlation of pulmonary functions with BMR, which implies the higher the BMR, the higher were the levels of FVC, FEV1, and FEF25%–75% in both normal-weight and obese subjects, however, the levels of PEFR showed a nonsignificant correlation in obese subjects only. These possibly indicate that respiratory functions are more directly related to fat distribution rather than the degree of obesity. Respiratory measure variables, such as forced FEV1 and FVC, tend to decline with continuing increase in BMR.[11],[12],[21] The effect is, however, quite minimal, and in children, healthy adults, and obese individuals, FVC and FEV1 are commonly within the normal range. The FEV1-to-FVC ratio even in morbid obesity is either well maintained or increased, implying that both FEV1 and FVC are influenced equally. This outcome signifies that obesity has a substantial impact on lung volume but has no effect on airway obstruction directly.[11],[12],[13],[14],[26]

Our study shows that the level of FEF25%–75% was significantly higher in subjects with increased BMR reflecting a positive correlation. A study done on respiratory function in obese individuals with normal FEV1/FVC showed that pulmonary function is impaired only with higher degrees of obesity.[27] Similarly, other studies have shown obesity to modestly affect the total lung capacity and vital capacity.[5],[28],[29],[30] Our investigation is consistent with the results of Ofuya et al. which reported a decrease in PEFR in obesity.[31]

Harik-Khan et al., Zeng et al., and others confirmed that deposition of fat minimizes the thoracic movements and also observed reduced maximal expiratory flow rates at lower lung volumes indicating impeded peripheral airflow and resistance in obese individuals.[13],[32],[33] The harmful influence of abnormal metabolism and obesity on lung function is also affirmed in many other studies.[30],[34],[35] In line with these observations, we found BMR significantly correlated with values of respiratory function indicators. There is, however, a considerable deviation in BMR between normal weight and individuals with obesity as its calculations are based directly on participants' weight.


Among the limitations of the study, important ones to mention include the use of BMI as an obesity analysis parameter which rather cannot differentiate muscle mass from body fat. We did not investigate further the duration of obesity, potential association between changes in respiratory volumes, and obesity phenotype (i.e., central/abdominal obesity), which might account for the above sex differences. The moderate sample size of our study has limits, and it may be useful to assess maximal inspiratory and expiratory pressures, which are markers of diaphragm strength and abdominal/intercostal muscle strength, respectively, along with FVC and FEV1. FVC and FEV1 are the pulmonary variables most commonly utilized in clinical investigations and appear to be the most closely associated with fat distribution. To further validate the existence of this association, it is proposed that a more practical estimate of BMR based on direct oxygen consumption measurement be undertaken. Finally, the study population was confined to small geographical location in south India, and hence, it is uncertain whether our findings could be generalized to other populations.

  Conclusions Top

We found a significant effect of BMR on spirometric measures, and gender difference existed in detrimental effects of obesity on lung functions. Females were more susceptible to the effects than males. To our knowledge, this is one of the few studies of its kind that has sought to determine and assess the association of BMR with respiratory functioning in obese and normal-weight individuals. Although our research is not thorough, it does give a glimpse into direct relationships of BMR with pulmonary functions in middle-aged healthy subjects with obesity. The study outcomes suggest that the BMR is a stronger predictor of pulmonary function changes in normal-weight and obese people; therefore, instead of looking at BMI, it is vital to look at BMR when identifying early changes in respiratory function.

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Conflicts of interest

There are no conflicts of interest.

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  [Figure 1]

  [Table 1], [Table 2], [Table 3], [Table 4]


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