Lung function measurements in children - copsac
Lung function measurements in children - copsac
Lung function measurements in children - copsac
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<strong>in</strong> the previous report on normative data by Klug and Bisgaard (12). A comparison was<br />
made to ensure that time (10 years between the two studies) did not have an effect on<br />
sRaw <strong>measurements</strong> before we pooled the data. Result from center 3 was mean sRaw<br />
(SD) 1.26 (0.31). We compared the two data sets with a two sample t-test for means<br />
us<strong>in</strong>g logtransformed sRaw values. There was no significant difference between the<br />
previous data and the current normative data; p-value was 0.20 us<strong>in</strong>g the very same<br />
equipment. With no time and center effect we therefore pooled the previous data (121<br />
<strong>children</strong>) and the current normative data (105 <strong>children</strong>) show<strong>in</strong>g the normal sRaw <strong>in</strong><br />
young <strong>children</strong> to be 1.27 kPa*s (0.25) <strong>in</strong>dependent of age, height and gender (Figure<br />
5).<br />
Parameters of specific airway resistance<br />
Different estimates of sRaw can be calculated from the resistance loop: sRaw TOT<br />
(<strong>in</strong>cl<strong>in</strong>ation of the l<strong>in</strong>e between po<strong>in</strong>ts of maximum pressure (volume) dur<strong>in</strong>g<br />
<strong>in</strong>spiration and expiration), sRaw V´max (flow po<strong>in</strong>t at the maximum flow dur<strong>in</strong>g <strong>in</strong>- and<br />
expiration), sRaw 50% (flow po<strong>in</strong>t at 50% of the maximum dur<strong>in</strong>g <strong>in</strong>spiration and<br />
expiration), sRaw 0.5 or sRaw 0.2 (flow po<strong>in</strong>ts at which flow is 0.5 L/s or 0.2 L/s) and sR eff<br />
(the slope result<strong>in</strong>g from calculation of area ratio by regression technique). sRaw TOT is<br />
sensitive to partial obstruction of peripheral airways, sRaw 0.5 reflects primarily the<br />
behavior of larger, more proximal airways and less sensitivity to peripheral airway<br />
abnormalities and sR eff reflects larger central airways (67). Bronchial asthma may not<br />
only <strong>in</strong>volve the large and the medium-sized airways, but the entire airway tree (68).<br />
sRaw TOT seems to be more sensitive or as sensitive as other methods (<strong>in</strong>terrupter and<br />
impulse oscillation technique) of estimat<strong>in</strong>g the total resistance (10, 38) <strong>in</strong> asthmatic<br />
<strong>children</strong>, although this estimate may have a higher variability compared with sRaw 50%<br />
and sRaw 0.2 (13). This must be a consequence of us<strong>in</strong>g only two po<strong>in</strong>ts at the extremes<br />
of <strong>in</strong>spiratory and expiratory shift volume.<br />
The previous study on normative data by Klug and Bisgaard (12) could only estimate<br />
sRaw 0.5 <strong>in</strong> a third of the <strong>children</strong> due to flows lower than 0.5 L/s <strong>in</strong> the youngest<br />
<strong>children</strong>. We chose to report the normative data as sRaw TOT <strong>in</strong> this study for comparison<br />
and pool<strong>in</strong>g with the previous data.<br />
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