transient reference values for impulse

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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

1194 Nowowiejska et al.


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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.


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).


1196 Nowowiejska et al.


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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 (

transient reference values for impulse

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