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Pediatric Pulmonology 43:11931197 (2008)
Transient Reference Values for Impulse Oscillometryfor Children Aged 318 Years
Bozena Nowowiejska, MD,1 Waldemar Tomalak, PhD,2* Jakub Radlinski, PhD,2
Grzegorz Siergiejko, MD,1 Wojciech Latawiec, PhD,2 and Maciej Kaczmarski, MD, PhD1
Summary. Impulse oscillometry (IOS) is a technique of assessing mechanical properties of
respiratory systemby means of measuring resistancesand reactances in a number of frequencies
during tidal breathing.It is especiallyuseful in preschool children, however hasalso beenvalidated
in older children and adults. The aim of the present study was to construct equations describing
normal values of oscillatory parameters in pediatric population of healthy polish children. Six
hundred twenty-six healthy children aged 3.1 18.9 years (278 boys and 348 girls) completed the
study. Analysis revealed that bodyheightwasthe bestpredictor andresistances arebest described
with exponentialmodel while reactances with linear one, with correlation coefficient r reaching the
value of 0.9. Oscillometric resistances decrease with height, while reactances increase.
Reference values for children and adolescents will allow not only the interpretation of the
measurement, but alsowill make possibleto study changes of oscillometric indices during growth.
Pediatr Pulmonol. 2008; 43:11931197. 2008 Wiley-Liss, Inc.
Key words: children; adolescents; impulse oscillometry; reference values.
INTRODUCTION
Impulse oscillometry (IOS) introduced in early 1990s1
is an alternative technique of studying respiratory system
properties especially in children. As the measurements are
made during tidal breathing and require less cooperation
than spirometry, the IOS is used with success in children
from 2 years of life. IOS measurements have been shownespecially useful in preschool children2in assessing
bronchomotor response to different stimuli, however, the
usefulness in older children is also documented.3 IOS
derived resistances have been shown to correlate strongly
with plethysmographic airway resistance3,4 and spiromet-
ric FEV1, while reactances seems to be useful in
evaluating bronchomotor response.5 Recent joint ERS/
ATS statement6 on pulmonary function testing in pre-
school children, which summarizes the application of
different techniques in children have stressed the impor-
tance of the forced oscillation technique (including IOS)
in children. The usefulness of the technique is obvious notonly in preschool children, but also in older ones, as IOSis
able to identify airway obstruction and the response to
bronchodilatators and bronchoconstrictors. It may be fully
performed in settings ranging from field studies to the
emergency room.
In the last few years several papers concerning
reference values have been published7,8 but they were
concentrated rather on theyoungest groups of children. As
IOS offers the unique chance to study respiratory system
properties starting at the age of 27,9 through childhood and
adolescency, we have attempted to create equations for
normal values for oscillometric parametersin children and
adolescents aged 3 19 years.
MATERIALS AND METHODS
The study was performed in kindergartens, primary
and secondary schools as well as in lycees in Bialystok
area in northeast Poland. School authorities have beencontacted and childrens parents gave informed consent.
The study has been approved by an Ethic Committee of
Bialystok Medical Academy.
Prior to the measurements a short questionnaire
oriented to past respiratory diseases has been distributed
to the parents. Exclusion criteria for the study, according
to the recommendations of the GAP Conference were as
1IIIrd Department of Pediatrics, Medical Academy, Biaystok, Poland.
2Department of Physiopathology of Respiratory System, National Research
Institute for Tuberculosis and Lung Diseases, Rabka Branch, Poland.
*Correspondence to: Waldemar Tomalak, PhD, Department of Physiopa-
thology of Respiratory System, National Research Institute for Tuber-
culosis and Lung Diseases, Rabka Branch, 34-700 Rabka, J. Rudnik str. 3b,
Poland. E-mail: [email protected]
Received 20 March 2008; Revised 9 July 2008; Accepted 16 July 2008.
DOI 10.1002/ppul.20926
Published online 5 November 2008 in Wiley InterScience
(www.interscience.wiley.com).
Grant sponsor: Ministry of Science and Higher Education; Grant number:
2PO5E 09027.
2008 Wiley-Liss, Inc.
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follows:10 familial asthma, diagnosed chronic respiratory
illness, obesity, premature birth, smoking (active or
passive). Included children taking part in the study were
examined by a physician in the day of measurements.
Children with respiratory tract infection in preceding
4 weeks were also excluded.
Among the children considered healthythree 3-yearold and thee 4-year old refused to perform measurements.
Twenty children 3-year old, five 4-yearold, and two 5-year
old were not able to complete the protocol. In the oldest
group of children (1519) seven refused to take part
despite the parents agreement. In total626 (all of
Caucasian descent) children were successfully examined.
The overall success rate was 96%.
The biometric characteristics of the group is given in
Table 1. Figure 1 shows the age distribution for the boys
and girls.
The measurements were made in the sitting position
with noseclip on, using IOS setup by Jaeger. Thepneumotachograph has been calibrated each day prior
to the measurements with a 3-L syringe, and the
validity of IOS calibration was tested every time against
reference impedance of 0.2 kPa/L/sec supplied by
manufacturer.
During the measurements the cheeks were supported by
hands of investigators (for younger children), or by the
children themselves. The measurements lasted for 45 sec,
during which the children were asked to breathe tidally.
Then, the procedurewas repeated to obtain two sets of data
which did not differ more than 10% between each other. In
a majority of children two measurements were needed (a
maximum of four measurements were necessary in fourchildren). For analysis mean values from the measure-
ments were taken.
IOS measurements bring resistances (R) and reactances
(X) at 5, 10, 15, 20, 25, and 35 Hz and also the so-called
resonant frequency (F)at which reactance X 0. Data
sets were analyzed for boys and girls separately and for
both sexes together. First, a multiple linear analysis using
age, weight, body height and their combinations was
performed to find out the best predictor for IOS derived
parameters. Then according to the results of multiple
Boys
Age [yrs]
Frequency
15 10 5
Age [yrs]
15 10 5
60
50
40
30
20
10
0
Frequency
60
50
40
30
20
10
0
Girls
Fig. 1. Histogram showing the distribution of the children with respect to age.
TABLE 1 Age, Height, and Weight of the ChildrenParticipating in the Study
Boys Girls
Number 278 348
Age (years)
Range 3.218.9 3.118.9
MeanSD 10.64.4 10.94.5
Height (cm)
Range 98193 95185
MeanSD 144.825.0 141.921.6
Weight (kg)
Range 1493 1486
MeanSD 41.6 19.8 38.516.0
Pediatric Pulmonology
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linear regression analysisfour models using height as
independent variable have been analyzed: linear, expo-
nential, logarithmic and multiplicative (for reactances:
linear and logarithmic). The equations were constructed
basing on the best correlationthat is, the model waschosen according to the highest correlation coefficient
between independent and dependent variables.
The analyses have been made using R (TM) statistical
package and Microsoft EXCEL.
RESULTS
Figure 2 presents frequency course of resistances and
reactances in boys andgirls in three different height ranges
(150 cm). The resistancesdecrease slightly with frequency, while reactances
increase with increasing frequency.
Theanalysis showed, that for all variables except X25 in
boys and girls height was the best predictor. Further
0.0
0.4
0.8
1.2
1.6
Boys
F [Hz]
R
[kPa/l/s]
5 10 15 20 25 35
150 cm
0.5 0.1 0.1 0.3 0.5
F [Hz]
X [kPa/l/s]
5 10 15 20 25 35
150 cm
0.0
0.4
0.8
1.2
1.6
Girls
F [Hz]
R[
kPa/l/s]
5 10 15 20 25 35
150 cm
0.5 0.1 0.1 0.3 0.5
F [Hz]
X [kPa/l/s]
5 10 15 20 25 35
150 cm
Fig. 2. Resistances and reactances at different frequencies in three different height ranges for
boys and girls.
TABLE 2 Coefficients of the Regression Equations for Boys and Girls
Parameter
Boys Girls Both sexes combined
a b r RSD a b r RSD a b r RSD
R5 0.0171 1.855 0.881 0.2305 0.0167 1.784 0.866 0.2085 0.0169 1.818 0.873 0.2185
R10 0.0177 1.765 0.89 0.2260 0.0172 1.694 0.874 0.2070 0.0174 1.729 0.883 0.2155
R15 0.0162 1.475 0.878 0.2208 0.0160 1.480 0.866 0.2006 0.0161 1.483 0.872 0.2010R20 0.0149 1.209 0.854 0.2272 0.0145 1.201 0.830 0.2114 0.0148 1.217 0.842 0.2196
R25 0.0138 1.023 0.846 0.2173 0.0136 1.025 0.815 0.2088 0.0138 1.032 0.832 0.2130
R35 0.0134 1.059 0.855 0.2034 0.0121 0.899 0.813 0.1883 0.0128 0.987 0.836 0.1960
X5 0.0035 0.699 0.850 0.0540 0.0040 0.762 0.845 0.0543 0.0037 0.728 0.845 0.0545
X10 0.0021 0.377 0.706 0.0531 0.0023 0.383 0.676 0.0532 0.0022 0.376 0.684 0.0536
X15 0.0020 0.317 0.696 0.0522 0.0022 0.330 0.677 0.0524 0.0021 0.319 0.677 0.0529
X20 0.0014 0.161 0.605 0.0457 0.0017 0.199 0.610 0.0476 0.0015 0.178 0.603 0.0469
X25 0.0039 0.063 0.223 0.0422 0.0008 0.001 0.374 0.0434 0.0006 0.030 0.305 0.0432
X35 0.0016 0.482 0.680 0.0436 0.0015 0.461 0.599 0.0429 0.0015 0.471 0.640 0.0432
Fn 0.0101 4.164 0.739 0.2299 0.0109 4.240 0.718 0.2292 0.0101 4.164 0.739 0.2299
R5, R10 . . . X35, kPa/L/sec; Fn, Hz. Models: E, exponential (X eaHb); L, linear (X a bH); a,b, model coefficients; r, correlation
coefficient; RSD, residual standard deviation.
Pediatric Pulmonology
Reference Values for IOS for Children and Adolescents 1195
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analysis was performed using body height as an
independent variable.
Table 2 presents equations for resistances, reactancesand resonant frequency in boys and girls and for both
genders together.
As expected, resistances at all frequencies show
negative correlation to height, while reactances (except
X35) increase with increasing height. Resonant frequency
F decrease with height both in boys and girls. Figure 3
presents examples of the fit of exponential model for
resistance at 5 Hz, linear model for X5 and exponential
model for F.
DISCUSSION
Our study performed on a large group of healthychildren shows well known features: height is a main
predictor of respiratory function measured with IOS as in
the other studies.7 9 Resistances and resonant frequency
decrease with increasing heights, while reactances
increase. Table 2 presents coefficients of equations for
boys, girls and the whole group, because some authors
published reference equations without gender dif-
ferentiation.8 As ours cover the age range from 3 to
19 years, separate sets of equations are also calculated
100 120 140 160 180 200
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
height [cm]
R5[kPa*l/s]
100 120 140 160 180 200
0.7
0.6
0.5
0.3
0.2
0.4
0.1
0
.0
height [cm]
X5 [kPa*l/s ]
100 120 140 160 180 200
10
15
20
25
height [cm]
Fn[Hz]
Fig. 3. An example of model fit to individual points in girls for R5, X5, and F.
100 120 140 160 180 200
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
R5 boys
height [cm]
R5[kPa*l/s]
Present studyMalmberg 2002(6)Frei 2004(7)
100 120 140 160 180 200
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
R5 girls
height [cm]
R5 [kPa*l/s]
Present studyMalmberg 2002(6)
Frei 2004(7)
Fig. 4. A comparison of the relationship of R5 and height in the present study (solid line) to the
values of Malmberg (6, dashed line) and Frei (7, dotted line).
Pediatric Pulmonology
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for boys and girls as in case of spirometry or body
plethysmography.
Table 2 contains also residual standard deviations
(RSDs) values which are necessary for calculating the so
called z-scores. z-score combines the percent predicted
and the variability into a single number (z (measured
value predicted value)/RSD) and expresses measuredvalues in terms of RSD. The presentation of a result in
terms of z scores is recommended and facilitates the
interpretation of the results, that is, determination whether
the result falls outside the defined lower or upper limit of
normal.11
A comparison of our values of calculated R5 for boys
and girls with those of Malmberg and Frei is shown on
Figure 4. Our values arevery close to previously published
ones, however their main advantage is that they cover ages
from 3 to 19 and heights from 95 to 193 cm.
IOS seems to be the only technique allowing measure-
ments of respiratory mechanics with equal ease inpreschool children as well as in schoolchildren, adoles-
cents and adults. This makes possible to compare different
populations, or, what is even more potentially interest-
ingto study the progression of lung function changes in
health and disease starting from the age of 2. This feature
is clearly seen on Figure 1 on reactance dependency on
frequency. For younger (shorter) children (