Pediatric Pulmonology 00:1–9 (2005)

Influence of Socioeconomic Status on Lung Function and Prediction Equations in Indian Children

P. Sitarama Raju, MBBS,1 K.V.V. Prasad, MSc,1 Y. Venkata Ramana, MSc, PhD,2 N. Balakrishna, MSc,3 and K.J.R. Murthy, MD

1*

Summary. The present study was carried out to assess the influence of socioeconomic status on

lung functions and to suggest prediction equations for Indian children. For this purpose, 2,616

normal, healthy schoolchildren aged between 5-15 years were recruited. Boys were classified into

three groups, i.e., high-income (HIG), middle-income (MIG), and low-income (LIG), while girls were

classified into HIG and LIG groups, based on socioeconomic status (SES). Height, weight, chest

circumference, body surface area (BSA), fat-free mass (FFM), and body fat were assessed.

Forced expiratory volume in 1 sec (FEV1), forced vital capacity (FVC), FEV1/FVC ratio, and peak

expiratory flow rate (PEFR) were measured. The results, before and after adjustment of physical

characteristics, showed that anthropometry, body composition, and lung functions were signi-

ficantly higher in HIG compared to MIG and LIG children, while in girls, no differences were ob-

served in physical characteristics after adjustments. Multiple linear regression equations were

developed to predict FEV1, FVC, and PEFR, using independent variables like age, height, fat-free

mass, and SES. It is opined that these equations could be used as Indian reference equations for

healthy children based on the SES. Pediatr Pulmonol. 2005; 00:1-9. e2005W "i^ss, Inc.

Key words: lung functions; body composition; socioeconomic status; reference equations; spirometry.

INTRODUCTION

Pulmonary function tests (PFT) are important para-

meters widely used to evaluate lung function for various

purposes.1,2 Due to ethnic differences in populations, apart

from procedural and technical aspects, equations used to

predict normal lung function are diverse. , Thus, it is

important to improvise appropriate prediction equations as

references for a given population, and the American

Thoracic Society published guidelines for making such

choices. However, the inappropriate use of control data

obtained from non-native populations regarding variations

in physical fitness and genetic factors is a major cause of

misinterpreting PFT results. Besides, probably due to

relatively small samples, many of the universally used

standardized prediction equations offer less reliability on

the extremes of status and age spectrums. These

shortcomings can be overcome by defining normal values

for different populations.

Several studies of lung functions were carried out on

children of different age groups in different parts of India

and projected the equations for predicting different lung

functions, using height, age, weight, FFM, and chest

measurements as independent variables.410 I V

Studies carried out in the US and UK reported dif-

ferences in lung functions among children of European,

Afro-Caribbean, and Indian origin, and used different in-

dependent variables for prediction of lung functions.

© 2005 Wiley-Liss, Inc.

Apart from genetic influence, the physical growth of

children depends on socioeconomic status (SES), which

influences the quality of pre- and postnatal nutrition,

thereby affecting physical growth variables like height or

weight. It is an established fact that, due to poor prenatal

nutrition, birth weights are lower in low-income popula-

tions.1516

Socioeconomic status, whether measured by

education, income, or other indices of social class, has long

been known to be associated with different diseases.17

Socioeconomic differences were shown to exist for a

number of diseases, including ischemic heart disease, many

types of cancer, and respiratory diseases. , In

addition,

Government Vemana Yoga Research Institute, Ameerpet, Hyderabad,

India.

Department of Physiology, National Institute of Nutrition, Hyderabad,

India.

Department of Statistics, National Institute of Nutrition, Hyderabad, India.

*Correspondence to: K.J.R. Murthy, M.D., Government Vemana Yoga

Research Institute, 7-1-66 Dharam Karan Road, Ameerpet, Hyderabad 500

016, India. E-mail: kvvprasad@ownmail.net

Received 19 July 2004; Revised 8 October 2004; Accepted 31 October

2004.

DOI 10.1002/ppul.20206 Published online in Wiley InterScience (www.interscience.wiley.com).

2 Raju et al.

despite a general fall in mortality during recent decades, the relative disadvantage of low socioeconomic status continues to increase.

18,20,21

Low birth weight was associated with reduced lung

function,22

and this gap may continue to widen in adult life,

as suggested by Barker et al.23

It had been reported that

lung functions are influenced by physical growth

parameters such as height and weight. Only a few studies

attempted to quantify the effect of socioeconomic status on

indices of lung function.24,25

A study conducted on

Canadian children reported differences in forced expired

volume in 1 sec (FEV1) and forced vital capacity (FVC)

between the highest and lowest socioeconomic categories

of boys only.25

Hence, in the present study, focus was

given to assess the influence of socioeconomic status on

lung functions in Indian children. The study also aimed to

elucidate which anthropometric indices have an influence

on prediction of lung functions. By using easily

measur-able physical parameters, which have a very high

pre-dictability toestimate lung functions, regression

equations were developed and are presented.

MATERIALS AND METHODS

The present study was conducted on 2,688 normal,

healthy boys (n¼1,612) and girls (n¼1,076) aged between

5–15 years. Based on our request, the District Educational

Officer had randomly selected and recom-mended five

schools in Hyderabad, India, which formed the basis of

selection criteria of the subjects in the present study. They

were categorized into three groups based on their

socioeconomic status according to a modified scale

ofKuppuswamy,26

and incomeiscorrectedtothe All India

Consumer Price Index (AICPI) of 1998. These groups are

high-income (social class I), middle-income (social class

II), and low-income (social class IV). This clas-sification

gave equal importance to education, occupation, and

family income for assessment of SES. The boys

represented all three SES groups. On the other hand, girls

were recruited only from HIG and LIG categories. This is

because of observations made on boys from the MIG and

LIG categories, where no differences were found in all

study parameters, and hence girls from the MIG category

were not recruited. Health and socioeconomic status were

recorded using a questionnaire, filled out by the parents of

subjects. Based on the questionnaire and physical

examination, the study excluded 72 children (43 boys and

29 girls) suffering from respiratory diseases or with a

recent history of respiratory infections. Thus, the final

study population was confined to 2,616 subjects. None of

the children smoked or consumed alcohol. A minimum of

40 subjects was recruited in each age group and

socio-economic category. The purpose and objectives of

the study were explained to the subjects, their parents, and

the school management, and their written consent was

obtained. The design and study protocol were approved by

the Ethics Committee of the Institute and conform to the

principles embodied in the Helsinki Declaration.

The anthropometric parameters such as height, weight,

and chest circumference (expired) were recorded. Height

and weight were measured by using a height and weight

machine (Libra, India). Heights were recoded to the nearest

millimeter, and weights to the nearest 0.1 kg were

measured with minimal clothing and after emptying the

bladder. Expired chest circumference was measured to the

nearest millimeter, using fiberglass tape. Fat-fold thickness

was measured at the triceps and subscapular regions to the

nearest 0.2 mm with skin-fold calipers (Holtain Ltd., UK).

Fat-free mass (FFM) and body fat (BF) were estimated

from the sum of the two skin-fold thickness.27

Body

surface area (BSA) was derived using the heights and

weights of the children.28

For best results, the pulmonary function test technique

was explained to each child, and three trials were conducted

a day prior to the actual measurement. Spirometry was

performed according to American Thoracic Society (ATS)

criteria to ensure quality29

Then the children were asked to

perform the test three times, and the best of three results

with less than 5% deviation from one another was used for

analysis. Forced expiratory volume per second (FEV1) and

forced vital capacity (FVC) were measured with a

spirometer (Vitalograph Ltd., UK), and peak expiratory

flow rate (PEFR) was recorded with Wright’s peak flow

meter. Values were corrected for BTPS. FEV1/FVC

percentage was then calculated. The spiro ~j eter was

calibrated every day with a 1-liter standard syringe before

measurements.

Analysis

The SPSS (Windows version 10.0) package was used to

analyze data. Values were indicated as mean ± SD, and

significance was noted at 0.05. The values of anthro-

pometry, body composition, and lung functions of the HIG,

MIG, and LIG groups were compared with each other

using one-way ANOVA and ANCOVA, with a post hoc

test of the LSD method, with and without adjusting

for variables like ag _ height, weight, and FFM. In the first

step of regression analysis, we analyzed the associations of

the study variables by correlation coefficients. In the

second step, parameters were selected that were 1) highly

correlated with lung functions, and 2) used in the devel-

opment of the predictive models for lung functions. The

remaining parameters were not considered in the analysis.

In the third step, several regression models (such as linear,

quadratic, cubic, or logarithmic) were tried for the pre-

diction of FEV1, FVC, and PEFR using age, height, and

FFM as independent variables separately. Then linear

step-wise multiple regression models were selected,

comparing the model’s R2, checking for violation of

assumptions, and

TABLE 1 — Physical Characteristics and Anthropometry in Boys1

HIG(n = 511), MIG(n = 529) LIG(n = 529) NCHS-50th centiles

Age Height Weight BSA years (n) (cm) (kg)

(M2) j

108.00

(4.92)

113.21

(5.18)

118.80

(4.83)

123.10

(6.14)

133.50

(3.44)

135.66

(5.61)

1

3

9

.

6

5

(

6

.

1

7

)

1

4

4

.

7

9

(

4

.

9

8

)

1

5

0

.

2

2

(

5

.

2

1

)

1

5

9

.

4

2

(

8

.

9

5

)

1

6

4

.

4

4

(

5

.

9

1

)

Values

expressed as mean ±

SD.

BF (%)

16.12 (2.46)

14.4

(1.41)

16.75

(4.95)

17.13

(4.24)

18.25

(7.52)

18.44

(7.22)

16.62

(5.09)

19.12

(7.13)

17.54

(8.40)

14.18

(6.44)

18.38

(7.69)

FFM (kg)

14.20

(1.70)

15.13

(1.64)

16.83

(2.47)

18.19

(2.71)

21.44

(2.01)

22.44

(3.04)

24.38

(3.10)

26.51

(3.62)

30.51

(4.82)

34.79

(5.21)

39.23

(4.44)

Chest

(cm)

50.90 (2.83) 50.87 (2.82) 53.80 (3.33) 54.8 (3.58) 57.80 (2.70) 59.27 (4.31) 60.24 (3.47) 62.85 (4.99) 64.88 (4.99) 68.57 (5.85) 72.77 (4.58)

Years (n)

5

(50) 6

(48) 7

(45) 8

(43) 9

(50) 10

(51) 11

(50) 12

(50) 13

(50) 14

(50) 15

(42)

Height

Weight

(cm)

(kg)

106

.26

(4.

34)

112

.40

(3.

76)

116

.71

(6.

88)

120

.29

(5.

90)

124

.90

(4.

43)

132

.26

(5.

66)

137

).9

3

(7.

15)

141

).9

9

(5.

70)

144

.67 (6.39)

155).57

(6.74^

161.53

(6.90)

BSA (M2)

0.69 (0.01) 0.7 (40.01)

0.79 (0.01) 0.84 (0.01) 0.89 (0.01) 0.98 (0.01) 1.06 (0.01) 1.12 (0.01) 1.14 (0.01) 1.33 (0.01) 1.46 (0.01)

BF (%)

15.80

(1.64)

14.11

(2.24)

14.27

(2.51)

15.31

(4.22)

13.84

(2.22)

14.70

(2.84)

14.11

(3.98)

15.10

(5.46)

14.88

(3.99)

14.05

(5.67)

16.44

(6.81)

FFM

(kg)

13.51 (1.24)

14.98

(1.27)

16.4

(2.80)

17.36

(2.35)

19.27

(1.93)

21.82

(3.15)

24.24

(3.82)

26.43

(4.77)

26.54

(3.48)

33.91

(4.15)

38.50

(5.65)

Chest

(cm)

49.92

(2.37)

51.55

(1.56)

52.30

(3.01)

53.74

(3.24)

55.43

(2.58)

57.73

(3.29)

59.83

(3.86)

60.54

(3.53)

61.96

(3.29)

66.38

(5.00)

71.67

(6.28)

Age Height Years (n)

(cm)

1

0

1

.

8

3

(

6

.

4

1

)

1

1

1

.

0

1 (

7

.

4

8

)

1

1

4

.

3

3

(

5

.

4

0

)

1

1

8

.

1

1

(

4

.

7

2

)

16.02

(1.61)

17.35

(1.32)

19.20

(2.72)

20.58

(3.25)

22.38

(2.39)

25.65

(4.12)

28.38

(5.27)

31.32

(6.37)

31.26

(4.46)

39.71

(6.23)

46.63

(9.48)

15.43

(1.64)

14.68

(1.48)

14.41

(2.35)

13.82

(1.98)

14.15

(2.33)

16.49

(4.96)

13.73

(2.45)

14.37

(4.22)

15.47

(4.23)

13.04

(3.98)

13.49

(5.91)

5 (40) 6 (42) 7 (40) 8 (45) 9 (40) 10 (50) 11 (52) 12 (55) 13 (44) 14 (53) 15 (50)

17.00 (2.44)

17.70

(2.08)

20.40

(3.78)

22.10

(3.91)

26.40

(3.42)

27.80

(4.87)

29.30

(4.96)

33.19

(6.28)

37.49

(7.70)

42.99

(8.84)

48.43

(6.46)

0.71

(0.02) 0.75

(0.02) 0.82

(0.02) 0.88

(0.02) 1.00

(0.02) 1.04

(0.01) 1.09

(0.01) 1.17

(0.01) 1.27

(0.02) 1.40

(0.01) 1.51

(0.01)

5 (48) 6 (44) 7 (48)

8 (50) 9 (50) 10 (50) 11 (45) 12 (46) 13 (50) 14 (50) 15 (48)

126.11 (6.04) 131.77

(5.72) 136.46 (3.98) 143.28

(7.80) 145.23 (8.45) 157.02

(8.45) 161.63 (7.42)

Weight

BSA

BF (kg)

(M2)

(%)

1

4

.

5

4

(

1

.

8

8

)

1

7

.

2

2

(

2

.

1

6

)

1

7

.

9

1

(

2

.

3

0

)

1

9

.

1

3

(

2

.

2

3

)

2

2

.

2

2

(

2

.

7

1

)

2

4

.

9

2

(

3

.

0

4

)

2

6

.

9

7

(

2

.

9

8

)

3

0

.

9

9

(

4

.

5

7

)

3

2

.

0

4

(

5

.

4

2

)

3

9

.

6

3

(

6

.

5

4

)

4

2

.

3

3

(

4

.

9

0

)

FFM

(kg)

12.29

(1.54)

14.69

(1.82)

15.31

(1.80)

16.47

(1.83)

19.65

(2.18)

20.73

(2.14)

23.25

(2.57)

26.46

(3.61)

26.98

(4.10)

34.36

(3.25)

36.50

(3.88)

Chest

(cm)

50.05

(2.43)

50.68

(2.71)

51.16

(2.60)

52.56

(2.35)

54.76

(2.43)

56.72

(2.79)

58.93

(2.84)

60.87

(3.70)

60.90

(3.67)

66.56

(4.65)

68.50

(3.83)

Height

(cm)

109.9

116.1

121.7

127.0

132.2

137.5

143.3

149.0

156.5

165.1

169.0

Weight

(kg)

18.7

20.7

22.9

25.3

28.1

31.4

35.3

39.8

45.0

50.8

56.7

en o o o' (D o o 3 o

o a> C

a> 3 a t~ c

3 (C Tl C 3

s o 3

0.64

(0.01)

0.73

(0.01)

0.76

(0.01)

0.80

(0.01)

0.89

(0.01)

0.97

(0.01)

1.03

(0.01)

1.13

(0.01)

1.16

(0.01)

1.34

(0.01)

1.41

(0.01)

3 a.

,'N

TABLE 2—Physical Characteristics and Anthropometry in Girls1

HIG(n = 515) LIG(n = 532) NCHS-50th centiles

Age Age years (n) Height (cm) Weight (kg) BSA (M2) BF (%) FFM(kg) Chest (cm) years (n) Height (cm) Weight (kg) BSA (M2) BF (%) FFM(kgM Chest (cm) Height (cm) Weight (kg)

5 107.43 15.93 0.69 18.71 12.93 49.75 5 99).24 13.80 0.60 19.11 11.15 46.93 108.4 17.7 (44) (5.37) (1.94) (0.06) (1.67) (1.45) (0.63) (50) (5.24) (1.38) (0.04) (2.11) (1.03) (0.49) 6 113.02 18.08 0.76 18.55 14.71 51.75 6 108.46 15.98 0.68 17.77 13.11 49.14 114.6 19.5 (46) (4.48) (1.89) (0.05) (1.62) (1.35) (0.62) (45) (5.35) (1.79) (0.05) (2.39) (1.26) (0.42) 7 118.35 20.21 0.80 18.15 16.48 53.51 7 114.44 18.13 0.74 17.40 14.96 51.11 120.6 21.8 (40) (5.02)

122.06 (2.93)

21.60 (0.07)

0.84 (2.64) (1.94) (0.67) (48) (4.62)

119.88 (1.84)

19.80 (0.05)

0.80 (1.76)

16.62 (1.34)

16.49 (0.50)

52.54 126.4

8 17.66 17.75 55.34 8 24.8 (43) (4.69) (2.61) (0.06) (1-99) (1.82) (0.64) (50) (3.87) (1-59) (0.04) (1.62) (1.14) (0.49) 9 126.66 23.20 0.89 16.86 19.21 56.47 9 125.44 21.99 0.86 16.17 18.40 54.41 132.2 28.5 (40) (4.88) (3.89) (0.08) (2.62) (2.55) (0.68) (42) (5.04) (2.57) (0.06) (1.81) (1.86) (0.54) 10 131.14 25.57 0.95 16.80 21.23 58.12 10 130.32 23.79 0.92 15.57 20.01 56.57 138.3 32.5 (54) (6.15) (3.32) (0.08) (1.89) (2.43) (0.57^ (52) (6.30) (3.55) (0.08) (2.85) (2.44) (0.48) 11 138.13 29.35 1.05 16.88 24.30 61.69 11 137.89 26.14 0.99 14.51 22.23 58.94 144.8 37.0 (50) (7.19) (4.66) (0.10) (2.71) (3.27) (0.60) (50) (5.18) (4.09) (0.08) (3.19) (2.68) (0.49) 12 149.27 37.63 1.23 18.51 30.59 66.75 12 144.19 31.92 1.12 16.20 26.61 ■ 62.38 151.5 41.5 (55) (4.96) (4.12) (0.08) (2.38) (2.68)^ (0.57) (56) (6.62) (5.22) (0.10) (3.23) (3.46) (0.46) 13 152.33 44.64 1.34 21.30 34.90 73.13 13 148.02 36.83 1.21 17.49 30.28 65.98 157.1 14.1 (43) (4.68) (6.80) (0.10) (3.83) (3.62) (0.64) (43) (5.25) (4.87) (0.09) (2.48) (3.30) (0.51) 14 154.89 43.55 1.34 18.99 35.09 72.23 14 149.93 38.06 1.22 17.20 31.2jfl 66.23 160.4 50.3 (55) (4.07) (5.90) (0.09) (3.42) (3.33) (0.577) (51) (6.62) (5.95) (0.20) (3.70) (3.85) (0.49) 15 153.50 42.94 1.36 18.37 34.92 72.37 15 151.16 40.75 1.26 17.05 33.34 67.56 161.8 53.7 (45) (6.00) (5.81) (0.11) (2.99) (3.78) (0.71) (45) (5.19) (6.73) (0.21) (3.52) (3.97) (0.58)

Values expressed as mean ± SD.

A

analyzing the model residuals. Finally, we computed linear

stepwise multiple regression equations separately, using age,

height, FFM, and SES as independent variables for FEV1,

FVC, and PEFR. It was observed that all four independent

variables have a highly significant impact on final regression

equations; hence, all four were used for prediction of lung

functions.

RESULTS

The physical characteristics and body composition of

children belonging to high-, middle-, and low-income

groups are presented in Table 1 (boys) and Table 2 (girls).

The study parameters of subjects between the three groups

were compared with each other to find out the influence of

SES on lung functions and physical characteristics. It was

found that the physical characteristics of the HIG group

were significantly higher than of the children from the

middle- and low-income groups. The differences in physical

characteristics before and after adjustment with age, height,

weight, and FFM are given in Table 3. The ventilatory

functions of boys and girls are given in Tables 4 and 5,

respectively, based on SES. It was observed that values of

FEV1 were lower by 14% and 16.7%, FVC by 14.1% and

16.6%, and PEFR by 9.1% and 8.4% in MIG and LIG boys

when compared to HIG boys, while in girls they were

lowerby14.4% (FEV1), 14% (FVC), and 15.6% (PEFR),

respectively, in the LIG category compared with the HIG

category. PFT parameters were significantly higher in the

HIG of both boys and girls after adjusting for physical

characteristics like age, height, weight, and FFM (Table 6).

We also observed no significant differ-ences among physical

characteristics and lung functions between middle- and

low-income boys. In view of this observation, the study on

girls did not include the MIG. Children were also compared

with National Center of Health Statistics (NCHS) US

standards, and all groups of boys and girls were found to be

lower than the 50th centile regarding height for age, weight

for age, and weight for

TABLE 3—Group Mean Values of Physical Characteristics in Children

1

SES N Age Height Weight FFM

Boys HIG 511 10.33 ± 3.15a 137.28 ± 18.515a (134.8)a 30.26 ± 11.347a (28.4)a 24.87 ± 8.888a (23.0)a MIG 529 9.99 ± 3.14a 132.16 ± 17.834 (133.1) 27.04 ±10.144 (27.6) 22.92 ±8.135 (23.5) LIG 529 10.30 ± 3.16a 131.69 ± 19.538 (133.1) 26.24 ± 9.604 (27.4) 23.43 ± 8.226 (23.5) F value 1.7 14.1 (23.6) 21.4 (21.2) 12.0 (14.3) p value NS 0.001 (0.001) 0.001 (0.001) 0.001 (0.001)

Girls HIG 515 10.07 ± 3.09a 133.89 ± 17.204a (131.2)a 29.57 ± 11.126a (27.2)a 24.03 ± 8.259a (23.4)a LIG 532 9.88 ±2.88a 128.21 ± 17.438 (130.9)a 24.85 ± 8.886 (27.2)a 20.63 ±7.148 (23.3)a F value 2.7 26.8 (1.2) 54.6 (0.01) 46.2 (1.1) p value NS 0.001 (NS) 0.001 (NS) 0.001 (NS)

Socioeconomic Status and Lung Function in Indiar=~| 5

height. A few subjects belonging to the HIG, bothooys and

girls, were comparable to or higher than the 50th centiles

of NCHS standards.

The prediction equations were calculated considering the

correlation coefficients of physical characteristics with

lung functions. It was observed that age, height, weight,

FFM, and BSAwere highly correlated with lung functions.

Highly significant R2 values were found when age, height,

and FFM were used as independent variables for lung

functions, and hence the prediction equations using these

variables were given. Since it was found that lung func-

tions were significantly different after adjustment of

physical characteristics, SES was also considered as an

independent categorical variable to develop common pre-

diction equations for entire groups of boys and girls

separately, such that the influence of SES was also used in

the predictability of lung functions. Hence, separate

equations were given with SES as an independent variable

for boys and girls, respectively. Multiple regression

equa-tions are presented using the three or four

independent variables for both boys and girls (Table 7).

DISCUSSION

Socioeconomic inequalities reflect differences in health

status and were reported to vary between countries.

Intrauterine growth retardation because of

malnourish-ment during pregnancy, associated with low

SES, is prevalent in developing countries.16

In a study

comparing mortality in manual and nonmanual workers in

two British towns, respiratory symptoms and impairment

of lung function were found to differ across social class.31

In a study of 410 male nonsmokers, it was found that the

difference in FEV1 between the highest and the lowest

social class was 400 ml. Several studies were conducted

to assess pulmonary functions in middle-aged adults, and

it is worth remembering that lung function in this age

group may be the result of several mechanisms.32

Reduced

lung function in middle age may result from a

1Values in parentheses are mean values adjusted for other physical characteristics. Superscript variations indicate significant differences of means

between groups.

I

5

6

7

8

9

10

11

12

13

14

15

0.95 0.93 (0.22) (0.20) 1.04 1.00 (0.19) (0.17) 1.25 1.20 (0.30) (0.28) 1.33 1.25 (0.21) (0.20) 1.67 1.52 (0.25) (0.21) 1.79 1.66 (0.30) (0.26) 2.02 1.87 (0.33) (0.29) 2.22 2.01 (0.37) (0.35) 2.44 2.25 (0.35) (0.37)

2.89 2.65 (0.49) (0.46) 3.35 3.10 (0.53) (0.49)

97.47 (3.61) 96.26 (5.78) 96.90

(7.96) 94.03 (3.98) 91.23 (6.61)

93.08 (5.94) 92.24 (3.87) 90.43

(5.59) 92.31 (5.66) 91.95 (4.71)

92.86 (5.26)

176.10 0.77 0.75 (36.67) (0.17) (0.16) 201.60 0.94 0.90 (30.55) (0.22) (0.20) 220.90 1.12 1.09 (56.64) (0.30) (0.22) 241.40 1.26 1.18 (48.19) (0.23) (0.18) 285.00 1.44 1.33

(.U.1SJ 298.80 1.62 1.48 (46.18) (0.29) (0.27)

319.41 1.90 1.71 (45.60) (0.32) (0.30) 338.09 2.01 1.83 (51.09) (0.29) ^0.30) 354.25 2.15 1.93 (62.56) (0.35) (0.29)

427.75 2.56 2.41 (61.54) (0.39) (0.38) 474.30 2.94 2.76 (57.99) (0.57) (0.56)

98.85

(2.60)

96.45

(4.93)

95.44

(4.89)

93.82

(6.14)

92.82

(5.13)

91.21

(4.08)

89.83

(4.15)

91.42

(7.35)

90.55

(6.89)

94.11

(4.56)

93.86

(4.94)

156.73 0.64 0.63 (38.59) (0.22) (0.22) 192.19 0.96 0.93 (38.85) (0.24) (0.21) 201.13 1.05 1.01 (42.91) (0.23) (0.20) 217.28 1.15 1.09 (35.11) (0.24) (0.22) 247.56 1.44 1.32 (38.77) (0.24) (0.22) 276.65 1.63 1.50 (42.18) (0.25) (0.22) 303.60 1.82 1.65 (61.97) (0.25) (0.25) 326.22 1.96 1.80 (47.56) (0.39) (0.35) 327.40 2.02 1.80 (44.52) (0.40) (0.35)

TABLE A—Lung Functions in Boys1

HIG(n = 511) MIG(n = 529) LIG (n = 529)

Age (years) FVC (1) FEVj (1/sec)

FEVj/FVC^c

PEFR (1/min) FVC (1) FEVj (1/sec) FEV!/FVC% PEFR (1/min) FVC (1) FEVj (1/sec) FEV!/FVC% PEFR (1/min)

416.22 2.62 2.42 (64.06) (0.48) (0.46) 458.93 2.79 2.58 (70.92) (0.40) (0.39)

98.71 (2.28)

97.16 (2.91)

95.27 (3.23)

94.83 (4.37)

91.32 (5.48)

92.36 (7.20)

90.81 (4.92)

91.87 (6.11)

89.72 (5.01)

92.33 (5.97)

92.71 (5.30)

136.42

(34.83)

181.93

(35.74)

211.77

(37.83)

212.86

(35.05)

260.52

(37.55)

274.86

(56.26)

296.11

(38.77)

338.26

(58.30)

338.28

(60.50)

420.00

(61.14)

462.35

(60.19)

Values expressed as mean ± SD.

Socioeconomic Status and Lung Function in Indiarzrn 7

TABLE 5—Lung Functions in Girls1

HIG girls (n ¼ 515) LIGgirls(n = 532)

Age

(years) FEV1 (l/sec) FVC (l) FEV1/FVC% PEFR (l/min) FEV1 (l/sec)

FVC (l) FEV1/FVC??) PEFR (l/min)

5 6 7 8 9 10 11 12 13 14 15

0.70 (0.16)

0.94 (0.18)

0.98 (0.15)

1.17 (0.17)

1.28 (0.19)

1.45 (0.23)

1.68 (0.36)

2.01 (0.34)

2.26 (0.43)

2.19 (0.39)

2.31 (0.34)

0.73 (0.18)

0.97 (0.19)

1.03 (0.16)

1.24 (0.20)

1.37 (0.20)

1.53 (0.25)

1.79 (0.38)

2.12 (0.36)

2.40 (0.45)

2.29 (0.40)

2.47 (0.38)

96.68

96.88 95.24

95.14

93.33

94.74

94.21

94.89

94.65

95.76

93.74

(7.02)

(4.54)

(7.12)

(4.81)

(4.60)

(4.72)

(3.48)

(3.87)

(4.02)

(4.04)

(3.48)

149.55

187.72

193.25

212.56

234.50

279.26

312.40

374.91

367.21

380.73

385.43

(36.79)

(35.22)

(35.26)

(32.15)

(37.75)

(43.47)

(50.17)

(35.74)

(38.39)

(41.00)

(51.53)

0.49 (0.14)

0.79 (0.18)

0.96 (0.22)

1.04 (0.17)

1.18 (0.22)

1.31 (0.20)

1.43 (0.25)

1.71 (0.36)

1.89 (0.28)

1.96 (0.31)

2.04 (0.30)

0.51 (0.15)

0.81 (0.20)

1.01 (0.25)

1.10 (0.19)

1.27 (0.23)

1.42 (0.22)

1.54 (0.26)

1.85 (0.37)

1.96 (0.29)

2.01 (0.33)

2.12 (0.36)

96.74

97.84

95.19

94.20

92.80

92.72

92.62

92.53

96.39

97.28

95.78

(8.85)

(4.30)

(4.60)

(5.68)

(7.03)

(5.62)

(5.28)

(7.44)

(4.22)

(3.64)

(4.84)

111.40

134.00

175.00

192.10

213.05

235.87

243.20

284.95

361.09

359.60

370.21

(16.51)

(28.99)

(39.52)

(38.57)

(39.13)

(34.42)

(40.26)

(57.91)

(52.50)

(49.50)

(46.89)

Values are expressed as mean ± SD.

low maximally attained lung function due to either low

lung function at birth or decreased growth of lung function

during childhood and adolescence as a consequence to low

SES.

Lung functions in children were largely overlooked

because of the difficulties in measuring them at clinical

setups, especially in developing countries like India. For

the diagnosis and follow-up of respiratory diseases in

children, lung function tests are essential and important.

Regression equations for predicting lung function tests can

be used based on simple anthropometric indices, which can

be easily measured and used for epidemiolo-gical surveys,

community health programs, and compar-ison with actual

values in clinical setups.

In India, several studies were conducted on

school-children to predict lung functions using

anthropometric variables.4–10

Most of these studies

included children of the local region, with a limited sample

size. In order to project equations applicable to most

regions of India and to the whole population at large, we

selected subjects with different linguistic backgrounds and

different SES who

were settled in Hyderabad, India. The present study com-

prised children from 11 of the 15 official Indian languages

as their mother tongue. Apart from regional variations,

considerable efforts were made to ensure that each age

group consisted of a minimum 40 subjects in each

socio-economic category, in order to get a more reliable

and accurate prediction of lung functions among the

population of the Indian subcontinent. The study on girls

was limited to only the HIG and LIG, since we found no

significant differences between MIG and LIG boys. The

impact of puberty is not considered in the present study.

The present study was undertaken to project generalized

prediction equations for Indian children based on SES. A

few Indian studies4,7,8 considered SES in their subjects.

However, none of them presented the regression equations

or results based on the SES of subjects.

Studies from the UK, China, and Malaysia did not find

any relationship between SES and lung functions in

children. A study conducted on Canadian children reported

differences in FEV1 (—8.1%) and FVC (—8.2%) only

among boys, and between the highest and lowest

TABLE 6—Group Mean Values of Lung Functions in Children1

SES N FEV1 FVC PEFR

Boys HIG 511

529 1.83 ± 0.742a (1.72)a 1.98 ± 0.816a (1.85)a 311.78 ± 102.340a (296.7)a

MIG 1.57 ±0.652 (1.61) 1.70±0711 (1.74) 283.35 ± 101.00 (289.0) LIG 529 1.52 0.653b (1.59)b 1.65 0.724b (1.72)b 285.67 106.544b (294.1)a

F value 29.3 (35.0) 28.3 (32.8) 11.8 (3.9)

p Value 0.001 (0.001) 0.001 (0.001) 0.001 (.02) Girls

HIG 515 1.56±0.615a (1.47)a 1.64 ± 0.653a (1.55)a 283.18 ±92.730a (270.3)a LIG 532 1.29 ±0.518 (1.38) 1.36 ±0.545 (1.46) 232.64 ± 90.609 (245.9)

F value 56.8 (30.4) 54.8 (28.8) 75.5 (83.9) p Value 0.001 (0.001) 0.001 (0.001) 0.001 (0.001)

1Values in parenthesis are mean values-adjusted for age, height, weight, and FFM. Superscript variations indicate

significant differences of means between groups.

8 Rajuetal.

TABLE 7—Regression Equations for Lung Functions1

Dependent variable

Boys (n¼1,569) FEV1

FVC PEFR Girls (n

¼ 1,047) FEV1 FVC

PEFR

Regression equation

1.280 + (0.04043* FFM) + (0.01404* Height) + (0.01584*Age) —

1.5870 + (0.01697* Height) + (0.03863* FFM) + (0.2507* Age)

-155.482 + (2.140* Height) + (4.652* FFM) + (5.336* Age)

1.186 + (0.01482* Height) + (0.02728* FFM) + (0.02436* Age)

-1.285 + (0.01798* Height) + (0.03077* FFM) + (0.02869* Age)

-155.195 + (2.136* Height) + (2.955* FFM) + (8.084* Age) — (12.

(0.0612* SES)

(0.0656* SES)

(0.0441* SES)

(0.0459* SES)

188* SES)

SEE

0.939 2,871 0.2399 0.942 3,064 0.2561 0.907 2,388 43.93

0.915 1,280 0.2359 0.913 1,245 0.2523 0.910 1,186 39.56

1Numbers in bold indicate significance at P<0.001; SES is HIG ¼0, MIG¼1, LIG¼2.

categories of SES, with no differences in physical

char-acteristics in boys and girls.25

Contrary to this, in the

present study, there were significantly large differences

among boys and girls in lung function values between

different categories, and they ranged from 8.4–16.7%.

Highly significant differences were also observed between

physical characteristics like height, weight, and FFM

among different SES categories in both boys and girls.

In Western and developed countries, ethnic variations

are considered for prediction equations. In view of the

large variations in anthropometric and physiological

para-meters between the three different socioeconomic

groups as elucidated in the present study, SES had to be

con-sidered for the evaluation of lung functions in Indian

children. The differences between groups, in the present

study, could be attributed to the intake of highly nutritious

food by HIG category children, which plays an important

role in physical and mental growth as well as immune

status. The lower height, FFM, and lung function indices in

MIG and LIG children may indicate lower lung strength

and may make them susceptible to infections owing to

poor immune strength when compared to HIG children.

Since the living conditions and dietary habits of the

middle- and low-income groups are comparable, no

significant differences among anthropometric and lung

function parameters were found.

The studies conducted on Indian children projected

regression equations for estimating lung function

vari-ables, using age, height, weight, FFM, chest, and BSA

as dependent variables.4–10

The studies conducted on

Western populations used height,11

sitting height,12

sta-ture, FFM/stature,2 and percentage BF

13 as dependent

variables to predict ventilatory functions. In the present

study, a significantly high correlation of lung functions

with age, height, and FFM was observed. However, we

presented regression equations using three or four

para-meters, including SES, as independent variables for

lung function estimations.

An important finding of the present study is the

in-fluence of SES of subjects on lung functions and

physical characteristics. The present study revealed

significant differences in growth variables like height,

weight, FFM,

and lung functions, before and after adjustment of physical

characteristics between the HIG and the other two groups.

Thus, the present study clearly demonstrated the impact of

SES on lung functions in children over and above physical

size. In view of significant differences in physical

characteristics and lung function parameters between high-,

middle-, and low-income groups, it is recommended that

the socioeconomic status of children be taken into account

when evaluating lung functions, especially in the Indian

context and in children of other developing nations, to

arrive at accurate values. Here the authors concur that the

measures of SES in the present study can be reproduced

and are feasible to determine. The authors infer that the

differences between SES categories in physical

characteristics and lung functions may be reduced largely

with nutritional supplementation from the prenatal stage

onward. The equations developed in the present study can

be applied in epidemiological surveys and community

health programs. Finally, we conclude that the regression

equations derived in the present study can be used as

Indian reference quations, keeping in view the large sample

size of the s ~Jy population.

ACKNOWLEDGMENTS

We express our sincere appreciation and gratitude to the

students for participating in the study, their parents, and the

school managements for continuous support and

encouragement, without which the study could not have

been completed successfully. We express our gratitude to

Mr. Gowrinath Shastry, National Institute of Nutrition,

Hyderabad, for critical suggestions in designing the study,

and we sincerely thank Mrs. Subharty for her untiring help

during data collection and preparation of records. We

express our gratitude to Mrs. TV. Phyllis, Central Institute

of English and Foreign Languages, Hyderabad, for

English-language improvements in the manuscript. We

sincerely express our appreciation for the support and

encouragement given by the Director of Vemana Yoga

Research Institute, Mr. M. Venkata Reddy, during the

study. This study was carried out at the Physiology Labo-

ratory, Government Vemana Yoga Research Institute,

A

Ameerpet, Hyderabad, India. M/s Vitalograph, UK, provided graph cards for recording lung function charts. This article does not conflict with the interests of any individuals or firms.

REFERENCES

1. Baum GL, Crapo JD, Celli BR, Carlinsky JB. Textbook of pul-monary diseases. 6th ed. Philadelphia: Lippincott-Raven; 1998;

199p.

2. Becklake M, Crapo RO. Lung function testing: selection of

reference values and interpretive strategies. Am Rev Respir Dis

1991;144:1202–1218.

3. Crapo RO. Pulmonary function testing. N Engl J Med 1994;331:

25–30.

4. Chowgule RV, Shetye VM, Parmar JR. Lung function tests in

normal Indian children. Indian Pediatr 1995;32:185–191.

5. Mallik SK, Jindal SK. Pulmonary function tests in healthy children.

Indian Pediatr 1985;22:677–681.

6. Bhattacharya AK, Banerjee S. Vital capacity in children and young

adults of India. Indian J Med Res 1966;54:62–71.

7. Sharma PP, Gupta P, Deshpande R, Gupta P. Lung function values

in healthy children (10–15 years). Indian J Pediatr 1997; 64:85–91.

8. Nair RH, Kesavachandran C, Sanil R, Srikumar R, Shashidhar S.

Prediction equation for lung functions in south Indian children. Indian

J Physiol Pharmacol 1997;41:390–396.

9. Jain SK, Ramaiah TJ. Lung volumes and mechanics of breathing in

healthy 7–14 year olds. Indian J Chest Dis 1968;10:63–68.

10. Raju PS, Prasad KVV, Ramana YV, Ahmed SK, Murthy KJR.

Study on lung function tests and prediction equations in Indian male

children. Indian Pediatr 2003;40:705–711.

11. Hsu KHK, Jenkins DE, Hsi BP, Bourhofer E, Thompson V,

Tanakawa N, Hsieh GSJ. Ventilatory functions of normal children and

young adults: Mexican-American, white and black. I. Spirometry. J

Pediatr 1979;95:14–23.

12. Hsi BP, Hsu KHK, Jenkins DE. Ventilatory functions of normal

children and young adults: Mexican-American, white and black. III.

Sitting height as a predictor. J Pediatr 1983;102:860– 865.

13. Cotes JE, Dabbs JM, Hall AM, Heywood C, Laurence KM. Sitting

height, fat free mass and body fat as reference variables for lung

function in healthy British children: comparison with stature. Ann

Hum Biol 1979;6:307–314.

14. Patrick JM, Patel A. Ethnic differences in the growth of lung

functions in children: a cross sectional study in inner city Nottingham.

Ann Hum Biol 1986;13:307–315.

15. Thomson AM. Diet in pregnancy. 3. Diet in relation to the course

and outcome of pregnancy. Br J Nutr 1959;13:509–525.

16. Krammer MS. Determinants of low birth weight: methodol-ogical

assessment and meta-analysis. Bull WHO 1987;65:663– 737.

17. Marmot M, Ryff CD, Bumpass LL, Shipley M, Marks NF. Social

inequalities in health: next questions and converging evidence. Soc Sci

Med 1997;44:901–910.

Socioeconomic Status and Lung Function in Indiar=~i 9

18. Prescott E, Vestbo J. Socioeconomic status and chronic obstructive

pulmonary disease. Thorax 1999;54:737-741.

19. Lynch J, Smith GD, Harper S, Hillemeier M. Is income inequality a

determinant of population health? Part 2. U.S. national and regional

trends in income inequality and age- and cause-specific mortality.

Milbank Q 2004;82:355-400.

20. Rona RJ, Mahabir D, Rocke B, Chinn S, Gulliford MC. Social

inequalities and children’s height in Trinidad and Tobago. Eur J Clin

Nutr 2003;57:143-150.

21. Wright CM, Parker L. Forty years on: the effect of deprivation on

growth in two Newcastle birth cohorts. Int J Epidemiol 2004;

33:152-153.

22. Chan KN, Noble-Jamieson CM, Elliman A, Bryan EM, Silver-man

M. Respiratory symptoms in children of low birth weight. Arch Dis

Child 1989;64:1284-1293.

23. Barker DJ, Godfrey KM, Fall C, Osmond C, Winter PD, Shakeen

SO. Relation of birth weight and childhood respiratory infection to

adult lung function and death from chronic airways disease. Br Med

J [Clin Res] 1991;303:671-675.

24. Stebbings JHJ. Chronic respiratory disease among non-smokers

in Hagerstown, Maryland. III. Social class and chronic respiratory

disease. Environ Res 1971;4:213-232. 25. Demissie K, Ernst P, Hanley JA, Locher U, Menzies D, Becklake

MR. Socioeconomic status and lung function among primary

school children in Canada. Am J Respir Crit Care Med 1996;156:

719-723. 26. Mishra D, Singh HP. Kuppuswamy’s socioeconomic status scale—a

revision. Indian J Pediatr 2003;70:273-274.

27. Slaughter MH, Lohman TG, Boileau RA, Horswill CA, Stillman RJ,

Van Loan MD, Bemben DA. Skin fold equation for estimation of

body fatness in children and youth. Hum Biol 1988;60:709-723.

28. Du-Bois D, Du-Bois EF Clinical calorimetry. Fifth paper. The

measurement of the surface area. Arch Intern Med 1915;15:868-876.

29. American Thoracic Society. Standardization of spirometry. Am J

Respir Crit Care Med 1995;152:1107-1136.

30. Mackenbach JP, Kunst AE, Cavelaars AEJM, Groenhof F, Geurts

JJM. Socioeconomic inequalities in morbidity and mortality in

Western Europe. Lancet 1997;349:1655-1659.

31. Burr ML, Holliday RM. Why is chest disease so common in South

Wales? Smoking, social class, and lung function: a survey of elderly

men in two areas. J Epidemiol Community Health 1987;41:140-144.

32. Kerstjens HA, Rijcken B, Schouten JP, Postma DS. Decline of

FEV1 by age and smoking status: facts, figures and fallacies.

Thorax 1997;52:820-827. 33. Lunn JE, Knowelden J, Handyside AJ. Patterns of respiratory

illness in Sheffield infant school children. Br J Soc Prev Med

1976 7-16. ~pl 34. Chen Y, Li WX. The effect of passive smoking on children s

pulmonary function in Shanghai. Am J Public Health 1986;76:

515-518.

35. Azizi BHO, Henry RL. Effects of indoor air pollution on lung

function of primary school children in Kaulalampur. Pediatr

Pulmonol 1990;9:24-29.