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ORIGINAL ARTICLE
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Differences in total lung capacity among Indians and Europeans


1 Department of Interdisciplinary School of Health Sciences, Savitribai Phule Pune University; Chest Research Foundation, Pune, Maharashtra, India
2 Central Government Health Scheme, Pune, Maharashtra, India
3 Chest Research Foundation, Pune, Maharashtra, India
4 Chest Research Foundation; Pure Foundation, Pune, Maharashtra, India

Date of Submission14-May-2021
Date of Decision23-Jul-2021
Date of Acceptance23-Jul-2021

Correspondence Address:
Nitin Vasant Vanjare,
Department Interdesciplinary School of Health Sciences, University, Savitribai Phule Pune University, Pune, Maharashtra
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mjdrdypu.mjdrdypu_357_21

  Abstract 


Background: Total lung capacity (TLC) is the volume of air in the lungs at the end of a maximal inhalation. TLC mainly depends on various factors/predictors such as height, age, gender, and ethnicity, and therefore, population-specific reference equations should be used. Currently, in India, we use the (European committee for coal and steel [ECCS], published in the year 1993) reference equation with no correction factor for TLC. It is recommended that the reference equation should be tested on a sample of local healthy participants, differences between the measured values and the predicted values are determined to see if the reference equation is a suitable/good fit for the population. Aim: The aim of this study was to compare the actual values of TLC from the healthy male and female volunteers from Pune city with the reference values obtained from the ECCS equations in these participants and determine the correction factor/percent differences between the mean values for different age and height groups. Design and Setting: A prospective, cross-sectional study of lung function measurements (TLC) by body plethysmography was carried out in a research center. Methodology: TLC was measured by Jaeger's Body Plethysmograph (model: Master scope) according to the recommendation of the American Thoracic Society's/European Respiratory Society's standards 2005 in a sample of 241 healthy nonsmoking volunteers (150 men and 82 women) aged 20–70 years, living in Pune city of Maharashtra, India. Statistical Analysis: The mean of actual TLC and the reference TLC were plotted against the different age groups and height groups and percentage difference was determined. Multiple linear regression was carried out to find the predictive equations for TLC parameter measured by the body plethysmography. Age, height, and weight were used as the predictors (independent variables) in the multiple regression analysis. Since sex is also a predictor of TLC, separate models were run for men and women. Results: There were statistically significant differences between the measured TLC and the reference TLC obtained from the ECCS equation in both males (5.05 L ± 0.69 vs. 6.3 L ± 0.50) and females (3.69 L ± 0.54 vs. 4.39 L ± 0.36), respectively. Males have higher TLC as compared to females of the same age and height. The mean of actual TLC and the reference TLC was plotted against different age groups and height groups, and percentage difference was determined. The percentage differences ranged from 17% to 21% in males and 13%–17% in females. Conclusion: The ECCS equation is not suitable for Pune population and may lead to misinterpretation of restrictive lung diseases and hyperinflation. A correction factor of 18.5% in males and 15% in females may be used for the ECCS equation for TLC in Pune population.

Keywords: Body plethysmography, correction factor, European committee for coal and steel, lung function tests, reference equation, restrictive lung disease, total lung capacity



How to cite this URL:
Vanjare NV, Rao P K, Jadhav S, Rasam S, Salvi S. Differences in total lung capacity among Indians and Europeans. Med J DY Patil Vidyapeeth [Epub ahead of print] [cited 2022 Nov 30]. Available from: https://www.mjdrdypv.org/preprintarticle.asp?id=339384




  Introduction Top


Total lung capacity (TLC) is the volume of air in the lungs at the end of a maximal inhalation. TLC mainly depends on various factors/predictors such as height, age, gender, and ethnicity.[1],[2],[3] TLC increases with age up to adolescence and then plateaus at around 25 years of age. Males have higher TLC than females of the same height and age, TLC increases with height.[4],[5] Europeans have higher TLC as compared to Africans.[6] TLC is influenced by the strength developed by the inspiratory muscles, lung elastic recoil, and the elastic properties of the thorax.

Body plethysmography is a standardized and an accurate technique to measure TLC. TLC may be reduced due to intrinsic (parenchymal) and extrinsic factors (extra parenchymal). TLC is reduced in diseases such as sarcoidosis, idiopathic pulmonary fibrosis, and pneumonia due to the intrinsic factors, whereas TLC is reduced in scoliosis and obesity due to the extrinsic factors. Increased TLC is indicative of obstructive lung diseases such as chronic obstructive pulmonary disease where TLC may be increased due to hyperinflation.[4] TLC measurement may also be used as a marker to indicate if a candidate is suitable for lung cancer surgery/lung resection.[7] TLC is the gold standard for the diagnosis of restrictive lung disease. Clinically, TLC measured is compared with the reference (predicted) TLC value and the percentage predicted is reported. TLC <5th percentile of predicted or <80% predicted are diagnostic of a restrictive lung disease.[8],[9] On the other hand, if TLC percent predicted is more than 120%, its indicative of hyperinflation.

Ideally, the reference/predicted TLC values should be obtained from healthy participants similar (in terms of age range, anthropometric, race/ethnic, socioeconomic, and environmental characteristics) to those participants who are tested in the laboratory. Guidelines suggest to use country-specific reference values.[5],[10]

Currently, in India, the The European community for coal and steel (ECCS) equation derived from the European sample (participants) and published in the year 1993 is the most commonly used reference equation for TLC.

It is recommended[5] that the reference equation should be tested on a sample of local healthy participants, differences between the actual values, and the predicted values are determined to see if the reference equation is a suitable/good fit for the population. If the differences between the measured values and the predicted values (residuals) are high, it suggests that the reference equation is not suitable for the population and a correction factor may be used.[10] The American Thoracic Society (ATS) prefers to choose the lung volumes published equations closest to local normal values derived from a sample of minimum 40 healthy participants.[11] For spirometry, a relatively large number of healthy participants (n = 100) are required to be assured that a significant difference between the published reference equations and the values from the local community does not exist.[10]

We determined the differences between the measured TLC (actual value) and the TLC predicted by the ECCS equation.


  Methodology Top


The study protocol was reviewed and approved by the Institutional Ethics Committee on January 20, 2016. A convenient sampling strategy was used to recruit healthy participants in the study. Relatives or attendants of the patients visiting the research center, employees of government offices, private offices, school and hospital staff, and residents of housing societies were invited to participate in this study. Written informed consent was obtained from the participants before performing any study-related activities. A clinical examination of the participants was performed by a chest physician, followed by an administration of a questionnaire.[12]

The participants were defined healthy if they were lifetime nonsmokers, healthy based on the absence of symptoms, absence of any known ailments, and normal on clinical examination by a qualified doctor. Participants who had undergone thoracic surgery or had any occupational exposures or smokers (ex and current smokers) and pregnant women were excluded from the study. The height and weight of the healthy participants were measured using calibrated equipment. Height and weight were recorded to the nearest centimeter and kilogram, respectively.

Device preparation

On the day, when TLC measurements were planned, the body plethysmograph device was checked for its accuracy, volume calibration check of the device was done using a 3 L syringe. The volume calibration was allowed in the range of ± 3.5%. Box calibration was also performed to check for leaks and thermal drifts. Box calibration was performed to check if the pressure and volume changes recorded in the body box were accurately recorded.

Subject preparation

Participants were asked to withhold from doing any strenuous exercise before the test. Alcohol consumption was prohibited before testing. The participants were asked to refrain from heavy meal within 2 h of the test. Participants were asked to avoid tea and coffee on the day of the test.

Procedure

The TLC was measured using the Jaeger's Body Plethysmograph device (Model-Master-screen Body, Manufactured in Germany). The tests were performed according to the 2005 recommendations[10] given by the European Respiratory Society (ERS) and ATS.

Body box is a glass cabinet with an airtight seal. Inside the box, there is a chair, on which the patient/participant can sit. Inside the box, there is a spirometer and a pressure transducer which can measure the flow and volume and pressure changes, respectively. The spirometer is connected to a shutter mechanism. When the shutter is open, flow, and volumes are recorded while when the shutter is closed, the pressure changes at the mouth are recorded.

The participants were trained/instructed on the procedure to perform the body plethysmography test. They were asked to sit inside the body box and the door was closed. The participants were asked to sit inside the box for at least 1 min before starting the actual test/procedure. The participants were asked to put a nose clip and to hold the mouthpiece between their teeth with lips tightly sealed around and place their hands on their cheeks and breathe tidally in the spirometer. Initially, the shutter is open and the spirometer records the flow and volume. After 30–40 s of breathing or until a plateau at the end expiration was achieved, the shutter was closed, the participants were asked to breathe against the closed shutter. (This is when the ITGV is calculated). After the shutter was opened (within few seconds), the participants were then asked to exhale out completely to residual volume, followed by a complete inhalation to TLC. Three acceptable tests were recorded. The tests were performed according to the 2005 ATS/ERS standards.[10]

Data management and statistical analysis

Epi Info software was used for data entry. Two data entry operators entered data, this data was compared, miss-match records were checked and corrections were made.

The analysis was performed using SPSS Version 22.0, (Armonk, NY: IBM Corp). The anthropometric data and TLC data were expressed descriptively. Data were presented as mean standard deviation and confidence interval. Since sex is a predictor of TLC, the data were analyzed separately for men and women. The mean of actual TLC and the reference TLC were plotted against different height groups [Figure 1] and age groups [Figure 2] and [Figure 3] and the percentage difference were determined. Multiple linear regression was also carried out to find the predictive equations for TLC parameter measured by the body plethysmography. Age, height, and weight were used as the predictors (independent variables) in the multiple regression analysis. As sex is also a predictor of TLC, separate models were run for men and women, respectively. After correlation analysis, stepwise regression was carried out. Those predictors which contributed significantly (P < 0.05) to the model were added, whereas others were removed (P > 0.05).
Figure 1: Comparison between actual total lung capacity and total lung capacity obtained by European committee for coal and steel equation in different height groups in males and females

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Figure 2: Comparison between actual TCL and total lung capacity obtained by European committee for coal and steel equation in different age groups in males and females

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Figure 3: Comparison of measured total lung capacity versus total lung capacity obtained by the European committee for coal and steel equation in males and females

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  Results Top


The study was done in 232 healthy participants out of which 150 were males and 82 were female participants. The anthropometric parameters are shown in [Table 1]. TLC in males (mean 5.05 L ± 0.76) was higher than in females (mean 3.69 L ± 0.54).
Table 1: Anthropometric and lung function characteristics of study participants

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The mean values of actual TLC were compared with the mean of TLC obtained by the ECCS equation in different height groups [Figure 1] and age groups [Figure 2] in men and women, respectively. In men, the measured TLC was 17%–21% lower as compared to the TLC obtained by the ECCS equation. While in women the measured was TLC 13%–17% lower as compared to the TLC obtained by the ECCS equation.

There was a weak negative correlation between TLC and age in both males (Pearson's correlation = ‒0.11, P = 0.176) and females (Pearson's correlation = ‒0.11, P = 0.345). A statistically significant positive correlation was observed between TLC and height in both males (Pearson's correlation = ‒0.47, P < 0.0001) and females (Pearson's correlation n = ‒0.55, P < 0.0001), respectively.

The anthropometric parameters such as height, age, gender, and weight were included as the predictor variables (independent variables) in the prediction model to derive the reference values for TLC. Nonsignificant variables were excluded one by one. Height was included in the prediction model for TLC in both males and females [Table 2].
Table 2: Local reference equation for total lung capacity in males and females

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  Discussion Top


The TLC values measured by the body plethysmography technique is lower in both men and women in different age and height groups as compared to the values obtained by the most commonly used ECCS equation. The difference between the measured TLC and the predicted TLC by ECCS is large (not closer to zero). Hence, the ECCS equation is not suitable for the population of Pune city.[10] There are differences in the TLC values between participants from Pune city and Europeans.

TLC <5th percentile of predicted or <80% predicted are diagnostic of a restrictive lung disease.[8],[9] On the other hand, if TLC percent predicted is more than 120%, its indicative of hyperinflation. If ECCS reference equation is used for TLC in Indian population, there are chances of misinterpretation of restrictive lung diseases and moreover, overestimation of restriction. The ECCS equation has many limitations-ECCS equation is not derived from a single study it is in fact, a derived summary equation from published reference equations from different studies.[2],[11] However, this method of arriving at summary equation is not ideal. Because the method by which the ECCS equation was derived/obtained is not based on the original data but on published regression equations (which may not be the best description of the data).[5] The studies from which the ECCS summary equation is derived had included smokers and are quite old, done between the year from 1960s to 1983.[2] Relying on equation derived from such old studies are prone to cohort effect. (A person of 30 years old today would be different from a person of 30 years old in 1990). Compared to the year 1993 when the ECCS equation was published the guidelines have been updated and there are more standardization techniques introduced today.

Ideally, a reference sample should be representative of the general population from which the patients come to the laboratory or hospital.[5],[10],[13] Random sample from the population is recommended. In our study, we did a random sampling by inviting volunteers from offices, hospitals (staff), schools, and housing societies to participate in the study, this may not be a perfect random sampling strategy. However, a study has reported that once hospital patients were excluded, the method for selecting the study sample used to derive the reference values had relatively little effect on either the range or mean values obtained.

In India, regional differences have been reported in forced vital capacity (FVC) and Forced expiratory volume in one second (FEV1) measured by spirometry. Aggarwal et al.[14] In their study have compared the predicted equations (FVC) and FEV1 (obtained from studies done in north, west, and south India) in interpreting spirometry reports of North Indian patients. They reported that the western equation under predicted FVC and FEV1 values when used for interpreting reports of North Indian patients. Chhabra[15] has also highlighted those considerable variations exist in FVC predicted from different regional equations in adult men in India. Considering the above studies, regional differences (within India) in TLC should also be studied. The differences between the actual TLC and the TLC obtained by the ECCS equation could be attributed to the race, environmental conditions, and nutrition also to some extent to the differences in the sample size of the healthy participants enrolled in the study.

We have also derived reference equations for TLC in males and females in a limited sample [Table 2]. However, we recommend to derive reference equations in a larger sample size. Conducting a study in a larger sample size is a big challenge. Multicenter studies can be conducted to get a representative and a large sample size. The volunteers should be healthy, non-smokers, and the equipment and the procedure should be standardized to reduce the technical variation.

A survey[16] conducted across the lung function laboratories in Ohio has shown that many doctors do not know which reference values they use for the lung function tests and there were differences observed in the interpretation of lung function tests. We speculate that the awareness about reference values in India is even poorer as compared to other countries. There is a need to spread awareness about reference values and their importance in interpretation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Pellegrino R, Viegi G, Brusasco V, Crapo RO, Burgos F, Casaburi R, et al. Interpretative strategies for lung function tests. Eur Respir J 2005;26:948-68.  Back to cited text no. 10
    
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Taussig LM, Chernick V, Wood R, Farrell P, Mellins RB. Standardization of lung function testing in children. Proceedings and recommendations of the GAP conference committee, cystic fibrosis foundation. J Pediatr 1980;97:668-76.  Back to cited text no. 12
    
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14.
Aggarwal AN, Gupta D, Jindal SK. Comparison of Indian reference equations for spirometry interpretation. Respirology 2007;12:763-8.  Back to cited text no. 14
    
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Chhabra SK. Regional variations in vital capacity in adult males in India: Comparison of regression equations from four regions and impact on interpretation of spirometric data. Indian J Chest Dis Allied Sci 2009;51:7-13.  Back to cited text no. 15
    
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Mohanka MR, McCarthy K, Xu M, Stoller JK. A survey of practices of pulmonary function interpretation in laboratories in Northeast Ohio. Chest 2012;141:1040-6.  Back to cited text no. 16
    


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