Discussion
In the principle of forced oscillation, rectangular electric pulse is
generated by pulse generator and superimposed on the resting breath of
the subject. Through Fourier transform and spectrum analysis, different
respiratory impedance values (viscous resistance, elastic resistance,
and inertial resistance) at different frequencies can be calculated. The
impulse oscillation method (IOS) can detect airway resistance and
calculate compliance by using sound waves with frequencies from 5 to 35
Hz. Compared with conventional ventilation, IOS is a simple, no special
cooperation lung function test method, easy to use, more suitable for
the elderly, critically ill patients and children who are not easy to
cooperate with the crowd, especially 3-5 young children[5-7]. IOS can measure the resistance and
reactance at different frequencies, so it can provide important
information of different areas of the lung. According to the frequency
dependence and reactance of resistance, it can determine the location
and severity of airway obstruction, and can be used to monitor the
pathophysiological changes of the respiratory system and patients with
asthma and chronic obstructive pulmonary disease, it can replace the
conventional ventilation to assist the diagnosis and follow-up of asthma[8-10].
Reference values are essential for interpreting IOS. However, there are
few studies to determine the prediction equation of IOS parameters in
the world. Most of the existing prediction equations are based on the
data of white children of European origin. The results of lung function
are the same as other methods, because of the differences of race,
region, geographical location and environment, the parameters of lung
function are also different. For example, the relevant research reports
in Beijing, Guangzhou, Chengdu, and other regions in China found that
some parameters were significantly different from the foreign parameters
provided by the instrument, and there were also differences in different
regions in China [11-12]. Therefore, it is urgent
to establish the reference values of children’s pulse lung function in
China, to provide the basis for the rational application of IOS.
In this study, 6270 healthy children aged 4-17 years old and 100-180cm
in height from 20 Regions and 24 research centers in China were selected
as subjects. The results showed that gender had no significant influence
on the measurement of IOS, and age, weight and height were closely
related to IOS values, among which height was the most important. The
second is age, and weight has the weakest effect. With the increase of
age and height, the total respiratory impedance and airway resistance
gradually decreased, while the negative value of elastic resistance
decreased (increased). During the growth and development of children,
with the growth of height and age, vital capacity increases and airway
diameter widens. The airway resistance was inversely proportional to the
fourth order of airway radius. The airway resistance of older children
was significantly lower than that of the younger children, especially
the decrease of peripheral resistance. With the increase of vital
capacity, the elastic retraction force of lung increases, and
X5 increases with age. Fres is more sensitive to assess
lung function, and its fluctuation range is also large. It reaches as
high as 24Hz at the age of 4 years, and decreases to 14Hz at the age of
17 years, which tends to be about 10Hz in adults. It indicates that Fres
decreases dynamically with age,
and this result was similar to the
result of Zheng Jinping [11,12].
The European lechtenboerger prediction is widely used in China, but it
is found that the correlation between the respiratory function
parameters and ethnic differences is obvious, so the equation is not
suitable for the evaluation of healthy people in China, especially
children. The results of this study suggest that height is the most
important factor for IOS parameters, followed by age and weight. With
the increase of age, height and body mass, airway resistance (Rrs)
gradually decreases, Fres, which represents lung compliance, and
electrical resistance (Xrs) increases gradually.
There were some limitations in the study. This study is a multi-center
study and the results of each center are different. Considering of the
difficulty for recruiting the healthy non-smokers aged<3 years, the
subjects within such age range were excluded. However, the reference
values for Chinese aged 4 to 17 years met the most demands of clinical
practice. In addition, IOS measurements did not include area of
reactance (AX), which is considered as a useful parameter in the
evaluation of children with asthma [13,14].
Therefore, these issues will be concerned in future studies.