pulmonary physiologic test of the month
Interpreting Spirometric Data*
Impact of Substitution of Arm Span for Standing
Height in Adults From North India
Ashutosh N. Aggarwal, MD, DM; Dheeraj Gupta, MD, DM, FCCP; and
Surinder K. Jindal, MD, FCCP
Study objective: To evaluate if direct substitution of arm span for height during interpretation of
spirometry data leads to any significant statistical or clinical differences in Indian adults, and to
compare this method with the use of height estimated indirectly from arm span.
Design: Cross-sectional.
Setting: Respiratory laboratory of a tertiary referral hospital in North India.
Participants: Two hundred twenty-eight subjects referred for spirometry.
Measurements and results: Standing height and arm span were measured for all subjects.
Spirometry measurements included FVC, FEV1, FEV1/FVC, peak expiratory flow, and maximal
midexpiratory flow. Predicted values for each parameter were calculated separately for height,
arm span, and height estimated from fixed height:arm span ratio. Results were classified into
normal, obstructive, and restrictive defects for each height, arm span, and estimated height
measurement, and any abnormality was categorized as mild, moderate, or severe. Arm span
exceeded height in 182 (79.82%) subjects. Thirty-seven (16.2%) and 32 (14.0%) results were
classified or categorized incorrectly when arm span and estimated height were substituted
respectively, for actual height, with a kappa estimate of agreement 0.779 and 0.808, respectively;
17.4% and 11.0% normal results were classified, respectively, as restrictive defects using arm
span and estimated height. Limits of agreement, which were almost equally wide for both sets of
data, were more than the permissible intraindividual variability for FVC and FEV1.
Conclusions: The substitution of arm span for height introduces statistically significant changes in
spirometry results. Use of height estimated from arm span using fixed ratio also leads to
misclassification of data, though less than that caused by use of arm span alone. Height estimated
from arm span can be substituted for actual height in patients in whom height cannot be
measured reliably. Where racial/ethnic norms for height and arm span correlation are not
available, arm span is a reasonable surrogate for standing height.
(CHEST 1999; 115:557–562)
Key words: arm span; height; spirometry
Abbreviations: FEF25–75% 5 maximal midexpiratory flow; PEF 5 peak expiratory flow
all the physical measurements of the human
O fbody,
lung function best correlates with standing height. Almost all equations for prediction of
*From the Department of Pulmonary Medicine, Postgraduate
Institute of Medical Education and Research, Chandigarh,
India.
Manuscript received March 4, 1998; revision accepted September 3, 1998.
Correspondence to: Surinder K. Jindal, MD, FCCP, Head, Department of Pulmonary Medicine, Postgraduate Institute of Medical Education and Research, Chandigarh 160012, India
lung function in various populations include standing
height, age, and sex as the only variables.1 However,
several patients referred for pulmonary function
testing are unable to stand as a result of extreme
debility, structural defects, or neuromuscular weakness. Others have deformities of the axial skeleton
that make measurement of height both difficult and
inaccurate. Under such circumstances, arm span has
been proposed as a surrogate measurement for
height.2– 6 Height may be estimated from arm span
CHEST / 115 / 2 / FEBRUARY, 1999
557
either by application of a fixed correction factor or by
using regression equations. Although not absolutely
accurate, height obtained by such calculations closely
approximates actual height.2– 6
Previous studies have indicated that normal individuals have only a small difference between height
and arm span measurements.7,8 We hypothesized
that direct substitution of arm span for height is
likely to introduce only a minuscule error in the
interpretation of pulmonary function results, which
may not be of any statistical or clinical significance.
The present study was carried out to test this
hypothesis.
Materials and Methods
The study was conducted on a sample population of adult
subjects of either sex referred to the respiratory laboratory for
spirometry. All adult subjects seen consecutively over a 2-month
period were enrolled prospectively into the study. Subjects in
whom height could not be correctly measured due to debility,
structural, or neuromuscular defects were excluded. Similarly,
subjects with chest or upper limb deformities that made arm span
measurements inaccurate were also excluded. We perform spirometry on subjects with a variety of medical and surgical
problems, many of whom are sick, bedridden, or have skeletal
deformities. Accurate measurement of both height and arm span
in the same subject was therefore not possible in 204 of the 474
subjects on whom spirometry was performed over the period of
study. Another 42 subjects refused to give consent and were
excluded; 228 subjects were thus finally evaluated.
Standing height was measured on a barefooted subject using a
stadiometer. Arm span was measured from the tips of middle
fingers of maximally outstretched hands with the subjects standing and facing the wall. Both measurements were taken to the
nearest centimeter. Arm span:height ratio was calculated separately for both male and female subjects, and used to estimate
height from arm span measurements.
All subjects underwent evaluation using a rolling seal spirometer (Spiroflow; P. K. Morgan Ltd; Kent, UK). FVC, FEV1,
FEV1/FVC ratio, peak expiratory flow (PEF), and maximal
midexpiratory flow (FEF25–75%) were measured for all subjects
using standard guidelines,9 and they were expressed at body
temperature and pressure saturated with water vapor. The
predicted value for each of the measured parameters was calculated using regression equations for healthy north Indian adults
of either sex, previously derived by us (Table 1).10 Three sets of
values based on height, arm span, and height estimated from arm
span measurements were generated for each subject. The lower
limits of normal were calculated as the difference between the
predicted value and 1.645 times the standard error of estimate.1
FEV1, FVC, and FEV1/FVC ratio were used as basic parameters
to interpret spirometry data.1 A FEV1/FVC ratio less than the
lower limit of normal for that subject was taken to indicate an
obstructive defect. A FVC value less than the lower limit of
normal, associated with a normal FEV1/FVC ratio, was taken to
indicate a restrictive defect. Severity of the obstructive or
restrictive defect was calculated by using FEV1 or FVC values
expressed as a percentage of the predicted normal. In the
absence of any clear guidelines,1 arbitrary cutoff limits, which
have been in use at our respiratory laboratory for the past several
years, were used to categorize abnormal results. Mild obstruction
(or restriction) was defined as FEV1 (or FVC) value . 60% of
predicted but less than the lower limit of normal. Moderate
obstruction (or restriction) was defined as FEV1 (or FVC) value
between 40% and 60% of predicted, and severe obstruction (or
restriction) as FEV1 (or FVC) value , 40% of predicted.
A statistical software program (SPSS [6.0] for Windows; SPSS,
Inc; Chicago, IL) was used for data analysis. Results for the
various variables studied were expressed as mean 6 SD, and
SEM calculated where needed. Comparisons between two
groups were carried out using x2 statistics or paired t test as
required. Agreement between various sets of measurements was
evaluated by calculating the kappa measure11 (for nominal variables) and limits of agreement12 (for continuous variables).
Results
There were 228 subjects (118 male and 110
female) with an age range of 13 to 77 years (Fig 1).
Both height and arm span were significantly greater
in male as compared with female subjects (Table 2).
However, there was no significant difference in the
absolute difference between arm span and height
measurements between the two sexes. Arm span
exceeded height by a mean of 4.0 (64.4) cm; the
mean of difference between arm span and height
was only 2.43% of height. Arm span measurements
were larger than height in 182 (79.82%), less than
height in 37 (16.22%), and equal to height in 9
(3.95%) subjects. The arm span to height ratios were
similar in both groups and were used to estimate
height from arm span for either sex (Table 2). Height
thus estimated was larger than actual height in 101
Table 1—Regression Equations for Prediction of Normal Lung Function in North Indian Adults*
Parameter
FVC, L
FEV1, L
PEF, L/min
FEF25–75%, L/min
Sex
Regression Equation
SEE
Male
Female
Male
Female
Male
Female
Male
Female
23.44 2 0.013A 2 0.00005A 1 0.048H
22.05 2 0.014A 2 0.00004A2 1 0.035H
21.90 2 0.025A 1 0.00006A2 1 0.036H
21.07 2 0.030A 1 0.00013A2 1 0.027H
42.3 1 5.0A 2 0.08A2 1 2.4H
52.0 1 1.5A 2 0.04A2 1 2.1H
59.0 2 2.6A 1 0.007A2 1 1.5H
23.0 2 2.6A 1 0.01A2 1 1.5H
0.497
0.447
0.417
0.323
55
51
62.3
46.5
2
*A 5 age; H 5 height; SEE 5 standard error of estimate.
558
Pulmonary Physiologic Test of the Month
Figure 1. Age distribution in the study population.
(44.30%), less than actual height in 102 (44.74%),
and equal to height in 25 (10.96%) subjects. All
the spirometric values (FVC, FEV1, PEF, and
FEF25–75%) were significantly greater in male subjects as compared with female subjects. Only the
calculated FEV1/FVC ratios were similar in both
groups (Table 2).
One hundred nine subjects were classified as
having normal spirometry using standing height.
When arm span measurements were used, 20 subjects were incorrectly classified (19 as having restrictive defect and 1 as having obstructive defect). When
height estimated from arm span was used, 12 subjects were incorrectly classified as having restrictive
defect (Table 3).
Sixty-eight subjects were classified as having ob-
structive defect using actual height. When arm span
measurements were used, two of them were incorrectly classified (one each as having normal spirometry and restrictive defect). Of the remaining 66
subjects correctly diagnosed by both methods, 9
were placed in a worse category using arm span
measurements (from mild-to-moderate obstruction)
and 1 was placed in a better category (from moderate-to-mild obstruction). When estimated height was
used, three subjects were incorrectly classified as
having normal spirometry (Table 3). Of the other 65
subjects, 8 were placed in a worse category (from
mild-to-moderate obstruction) and 1 was placed in a
better category (from moderate-to-mild obstruction).
Fifty-one subjects were classified as having restric-
Table 2—Body Measurements and Spirometry Data*
Subjects
Age, yr†
Height, cm†
Arm span, cm†
Arm span: height
Arm span minus height, cm
Estimated height, cm†
FVC, L†
FEV1, L†
FEV1/FVC, %
PEF, L/min†
FEF25–75%, L/min†
Male (n 5 118)
Female (n 5 110)
Total (n 5 228)
45.7 (16.2)
169.9 (6.3)
174.3 (8.2)
1.026 (0.026)
4.4 (4.4)
169.9 (7.4)
3.21 (0.87)
2.53 (0.84)
77.87 (13.16)
238.55 (86.15)
136.58 (73.42)
39.4 (13.2)
156.8 (6.6)
160.4 (7.3)
1.023 (0.028)
3.6 (4.3)
156.8 (7.1)
2.27 (0.62)
1.81 (0.64)
78.42 (14.90)
188.93 (76.61)
94.53 (53.22)
42.6 (15.2)
163.6 (9.2)
167.6 (10.4)
1.024 (0.027)
4.0 (4.4)
163.6 (10.0)
2.76 (0.89)
2.18 (0.84)
78.14 (14.0)
214.73 (85.23)
116.30 (67.69)
*Values are mean (SD).
†p , 0.01.
CHEST / 115 / 2 / FEBRUARY, 1999
559
Table 3—Results of Spirometry Based on Height, Arm Span, and Estimated Height Measurements*
Based on Actual Height
Based on arm span
Normal
Obstructive
Restrictive
Total
Based on estimated height
Normal
Obstructive
Restrictive
Total
Normal
Obstructive
Restrictive
Total
89 (81.7%)
1 (0.9%)
19 (17.4%)
109
1 (1.5%)
66 (97.1%)
1 (1.5%)
68
1 (2.0%)
0
50 (98.0%)
51
91
67
70
228
97 (89.0%)
0
12 (11.0%)
109
3 (4.4%)
65 (95.6%)
0
68
6 (13.3%)
0
45 (86.7%)
51
106
65
57
228
*Figures in parentheses indicate percent agreement.
tive defects using actual height. When arm span was
used, only one subject was incorrectly classified as
having normal spirometry. Among the other 50
subjects, 1 was placed in a worse category (from
moderate to severe restriction) and 3 were placed in
a better category (2 from moderate to mild obstruction and 1 from severe to moderate obstruction).
When estimated height was used, six subjects were
incorrectly classified as having normal spirometry
(Table 3). Of the 45 subjects correctly classified, 2
were placed in a better category (one each from
moderate to mild and severe to moderate obstruction).
Overall, 37 (16.22%) and 32 (14.04%) subjects
were wrongly classified or categorized when actual
height measurements were replaced by arm span
and estimated height measurements, respectively.
These differences in misclassification rates by the
two methods were not statistically significant. Kappa
measure was calculated for agreement in classification and categorization, and a kappa value of 0.779
and 0.808 was obtained for methods using arm span
and estimated height measurements, respectively.
Limits of agreement were also calculated for differences in various spirometric indexes using height and
arm span measurements as well as height and esti-
mated height measurements. Even though the absolute numerical values were different, the limits were
equally wide for FEV1 and FEV1/FVC ratio for the
two groups, and marginally narrower for the other
variables (Table 4).
The absolute differences in the various predicted
values using height and arm span measurements
were small (Table 4). However, when paired t test
was applied to these data, p value , 0.001 was
obtained for all the variables, indicating significant
differences between the two sets of results. The
differences in predicted values using height and
estimated height were negligible and statistically
insignificant (Table 4).
Discussion
Arm span and height correlation have been shown
to be different in different racial and ethnic
groups,6,13,14 but there is a paucity of information on
this relationship in the Indian population. The arm
span to height ratios obtained in this study are in
close agreement with the previously recorded figures
for the adult white population.2– 4,6 In the vast majority of our subjects, arm span exceeded height.7,8,15
Table 4 —Absolute Difference and Limits of Agreement for Predicted Values Based on Actual Height and Arm Span
and on Actual Height and Height Estimated From Arm Span
Absolute Difference*
FVC, L
FEV1, L
PEF, L/min
FEV1/FVC, %
FEF25–75%, L/min
Arm Span†
Estimated Height
0.17 (0.01)
0.13 (0.01)
9.04 (0.66)
20.33 (0.02)
5.97 (0.44)
0 (0.01)
0 (0.01)
20.1 (0.64)
0 (0.02)
20.06 (0.64)
Limits of Agreement
Arm Span
20.20
20.14
210.52
21.06
26.91
to
to
to
to
to
0.54
0.40
28.60
0.40
18.85
Estimated Height
20.35
20.27
218.97
20.73
212.58
to
to
to
to
to
0.35
0.27
18.77
0.73
12.46
*Values expressed as mean (SEM).
†p , 0.001 (paired t test) for all variables.
560
Pulmonary Physiologic Test of the Month
Arm span has been proposed as a surrogate for
standing height in the prediction of lung volumes in
subjects who are unable to stand or who have skeletal
deformities. Considering the fact that the absolute
difference between height and arm span in any
individual is usually small (mean of 4.0 cm in the
present study), and to avoid an additional calculation
in estimating height from arm span, we proposed
that arm span may be directly substituted for height
in prediction equations, as also suggested by few
previous studies.2,5,16,17 This is likely to introduce a
small error in the final results, the clinical relevance
of which has not been studied so far (to our knowledge). Although Hepper and colleagues2 had found
that predicted vital capacity based on height and arm
span measurements were almost equal, no further
analysis was provided. Allen17 had also showed that
standardized FEV1 values using height and arm span
were not statistically different in elderly women.
Each subject in our study had three sets of
predicted values based on calculations from height,
arm span, and height estimated from arm span using
a fixed ratio. The regression equations for prediction
of these normal values in either sex use only height
and age as variables (Table 1),10 and any change in
the value of one variable will result in a corresponding change in the final calculated result. The magnitude of this change will depend on the magnitude of
change in the concerned variable, and direction of
resulting change will depend on the actual regression
equation. For example, the results of the regression
equation for FVC used by us are positively correlated
with height, and any addition (or subtraction) in
height will consistently increase (or decrease) the
predicted FVC. The consistency in the direction of
change in these values is responsible for the statistical significance of results, when arm span is substituted for height (as 79.82% subjects had arm span
greater than height), even though the absolute differences between predicted values based on height
and arm span measurements are small (Table 4).
Of the tests in the study, 83.78% and 85.96% were
classified and categorized correctly when arm span
and estimated height, respectively, were substituted
for actual height. The kappa measure of agreement
takes values between zero and unity depending on
the level of agreement between two such sets of data.
A value . 0.75 is indicative of excellent overall
agreement.11 The kappa estimates for the two sets of
readings in this study were 0.779 and 0.808, which
suggest that both arm span and height estimated
from arm span can be used in place of actual height
during classification and categorization of spirometric data, with good results. Results may be better,
however, when estimated height values are used.
Agreement can also be estimated from the mean
and SD of the differences between two sets of data
by calculating limits of agreement, and evaluating if
differences within this range are clinically important.12 We have calculated limits of agreement for
various spirometric indexes using height and arm
span as well as height and height estimated from arm
span. The limits are almost equally wide in both
instances (Table 4), and much wider than the 0.15-L
normal variability permitted for both FEV1 and FVC
measurements.9 Thus, both these methods are probably equally unacceptable (or acceptable) for clinical
purposes. The use of arm span alone instead of
height estimated from arm span may therefore be
equally appropriate in a given clinical situation.
A significant finding of this study is that a sizable
proportion of normal spirometric data may be misinterpreted as restrictive when arm span is substituted for height. Similar misinterpretation, though
less, also occurs when height estimated from arm
span is used. Both methods also wrongly classify and
categorize obstructive and restrictive defects. However, these differences in misclassification rates using the two methods are statistically insignificant. It
would appear that the use of height estimated from
arm span is only a marginally better alternative.
However, height and arm span correlation are not
available for several racial/ethnic groups, and under
such circumstances, arm span can also be directly
used.
Conclusions
The substitution of arm span for height in prediction equations for lung function introduces a small
error in the calculation of predicted values, which is
statistically significant. The use of both arm span as
well as height estimated from arm span is associated
with misclassification of spirometric data. Notably,
several normal spirometric results may be misinterpreted as restrictive. Although the use of height
estimated from arm span may be preferred in subjects in whom height cannot be measured reliably,
arm span is a reasonable surrogate for height in
populations in whom established norms for correlation between height and arm span are not available.
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