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Airway Resistance, Airway Conductance, Specific Airway Resistance, and Specific Airway Conductance in Children

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Airway Resistance, Airway Conductance, Specific Airway Resistance, and Specific Airway Conductance in Children Pediatr. Res. 17: 508-5 13 (1983) Airway Resistance, Airway Conductance, Specific Airway Resistance, and Specific Airway Conductance in Children M. LEBEN'~" AND H. VON DER HARDT Children's Hospital of the Medical School of Hannover, Division of Pediatric Pneumology [H. von der Hardt], 0-3000 Hannover, Federal Republic of Germany Summary who measure Rawat fmed flow rates during panting and those who measure Rawat maximum flow during quiet breathing. In 82 healthy children and in asthmatic children before and It is the aim of the present study to compare the f~edflow and during positive allergen provocation test, airway resistance (Raw), the "terminal" Rawinterpretation applied to the same measure- airway conductance (G,), specific airway resistance (SR,), and ments during quiet breathing in healthy and in asthmatic children. specific airway conductance (SG,) were measured by body pleth- ysmography during quiet breathing. Raw over total flow range (Raw t) and Raw at a flow rate of 0.5 liter/sec (Raw 0.5) are MATERIALS AND METHODS compared: Raw0.5 is 10.3% smaller and shows a smaller coefficient of variation in healthy children. This is interpreted as a less Measurements of FRCb,, and of Rawwere performed in an air important influence of variations of glottis opening. SRaw mean conditioned pressure-corrected volume displacement whole-body plethysmograph (29). The technical details have been described value is 7.08 hPa. sec; SGaw mean value is 0.141 hPa-' sec-'. In asthmatic children, Raw0.5 proves to be a more sensitive parameter previously (15). The electronic signals for volume displacement (integrated and pressure-cofrected flow signal) of the body ple- for the evaluation of inhalation provocation tests than Rawt. The most sensitive indices of obstruction in the central and more thysmograph (AVt,), APM, V, and its integral, AVM, were stored simultaneously on a magnetic tape and played back at a lower peripheral bronchi are SRaw0.5 and SG,, 0.5. speed on an X/Y recorder (30). The breathing air was kept at body temperature and water vapour saturated in a 60 1-Douglas Abbreviations bag. For inhalation challenges, the additional equipment de- BTPS, body temperature and ambient pressure saturated with scribed by von der Hardt and co-workers (15) was used. water vapor The investigation was performed in 82 school children (47 boys FRCb,,, functional residual capacity measured by body plethys- and 35 girls with comparable distribution of standing height), age mography 6-15 years, with the consent of their parents. Medical history and Gaw, airway conductance physical examination did not reveal any respiratory disease. In hPa, hecto Pascal addition, inhalation provocation tests taken for clinical purpose APM,pressure at the mouth from six asthmatic children (four boys and two girls, age 9-14 Raw, airway resistance years, standing height 136-162 cm) were analysed. Measurements R, ,, terminal airway resistance were taken in the sitting position, the nose closed by a nose clip. SG,,, specific airway resistance The following measurements and calculations were performed. SRawt, specific airway resistance over total flow range (1) In 76 of the 82 children (43 boys and 33 girls) FRCI,,, was $a, AVB/APM calculated from tga of the AVb/APM diagram obtained by the V, airflow Pfliiger maneuver (20). Final values were corrected for the dead- AVb, volume displacement space volume of the mouthpiece and the shutter (0.11 1) and for AVM, tidal volume deviation from the end-expiratory level detected by the spirogram recorded simultaneously. In the remaining six children, the latter correction was not exactly possible because the spirogram did not The development of body plethysmography has furnished a show a sufficient number of respiratory cycles preceeding the close noninvasive method of assessing Raw.Raw is defied as the ratio of the shutter. tga was used only to calculate Rawif the shutter of alveolar pressure to air flow. Usually, the pressure or volume was closed within the lower third of the tidal vqlume. changes of the plethysmograph corresponding to alveolar pressure (2) In 82 children, resistance curves (AVb/V diagrams) were are plotted versus air flow. Rawis then calculated from the slope recorded during quiet breathing. BTPS conditions were checked of the resulting S-shaped curve. DuBois and co-workers (8) meas- by the AVb/AVM loops (20). Rawwas calculated in two different ured Raw at a certain flow rate on the linear part of the curve ways. (A) In all children, Raw was calculated from the slope of during panting. After the problem of maintaining BTPS condi- the line connecting the points of maximum inspiratory and expir- tions in the breathing air was solved, many investigators turned to atory flow in the AVh/V diagram (Fig. 1). (B) In 46 of the 82 measuring Rawduring quiet breathing instead of panting. It was children (28 boys and 18 girls), Rawwas also calculated from the then proposed to measure Rawover the total range of alveolar slope of the line connecting the points at an inspiratory and pressure ("total Raw3',26) or over the points of maximum inspir- expiratory flow of 0.5 liter/sec (Rawo.s). If there was a difference atory and expiratory air flow (23, 20). For the latter way of in AVb at the level of 0.5 liter/sec, the bisecting points of the AVb interpretation, Haluszka (13) suggested the term "terminal Raw" difference at this level were used (Fig. 1). (Raw t) because the terminal points of the curve are used. At Rawwas determined as the mean of three to five successive and present, there seem to be mainly two groups of investigators: those nonselected respiratory cycles according to the formula by Mat- 5 10 LEBEN AND HARDT Table I. Regression equationsfor FRC*, Raw t, Raw 0.5 Gaw t, and Gaw o.s versus standing height1 Mean values Regression equation2 n Igs r 120 cm 160 cm (unit) FRCI,,, (boys) = 2.4579 1gH - 5.1309 Ig 43 0.0914 0.79 0.955 1.936 FRCh,, (boys) = 7.4. lo-" lg FRCh,, = 2.5655 1gH - 5.4014 . 33 0.0837 0.74 0.859 1.797 (1) FRCh,, (girls) = 3.97. 10-" H2566 lg Raw t = -1.9789 IgH + 4.9735 82 0.1225 -0.57 7.23 4.09 (hPa/liter/sec) Raw t = 9.41 . lo4. H-1.979 lg Raw 0.5 = -2.2492.1gH 5.51 17 + 6.85 Raw 0.5 = 3.25. lo5. H-~.~~~ 46 0.1097 -0.65 - I Abbreviation: n, number of children investigated; s, residual standard deviation; r, coefficient of correlation; and H, standing height in cm. Except for FRCb,,, regression equations are for boys and girls together. Table 2. Coefficients of variation (mean intra-individual standard Table 3. Mean change of dfferent parameters in 22positive deviation of three to five successive and non-selected respiratory provocation tests1 cycles) of Raw and Raw0.5 in healthy and in asthmatic children (%) SD VC (%) range (%) t test2 before provocation and during provoked bronchial obstruction FRCh,, +17 +12 7 1 - 13 to +39 Coefficient of variation Raw t +I13 f73 64 +28 to +332 < O.OO1 Raw0.5 +I54 f95 62 +I8 to +414 I Raw t Raw 0.5 Gaw t -49 t13 25 -22 -77 1 P < 0.01 Healthy children 13.6 f 8.6% 9.3 f 6.1% Gaw 0.6 -56 f 14 26 -16 to -81 (2.4-42.7%) (0.1-20.8%) SR., +I49 +82 55 +46 to + 280 < 0,001 Asthmatic children before provocation 5.3 + 2.8% 11.5 f 7.3% SR,, 0.5 +I93 flll 58 +52 to +3 12 1 (2.0-13.9%) (4.3-32.7%) SG,, t -56 +12 21 -)I t0-80i P<O.Ol Asthmatic children during provoked 3.4 f 1.9% 6.6 f 3.1% SG,, 0.5 -62 f 13 21 -34 to -85 bronchial obstruction (1.4-8.3%) (1.8-12.2%) ' A, mean change in % of initial value; S.D., standard deviation; and CV, coefficient of variation (S.D. in % of A). positive reaction (23.1 7.4%). The mean rise of Raw is 113%, for Paired t test shows significantly higher changes for Raw0.5 and its + derivates. Raw0.5 it is 154%, the % being only in 4 tests slightly higher in Raw,than in RawO_s. The mean changes of the different parameters in % of the initial value are summarized in Table 3. Standard and during quiet breathing is very complex (2). Rawduring panting deviations in % of the mean changes (coefficients of variation) do may be smaller or higher than Raw during quiet breathing de- not differ for the terminal and the fied-flow type of interpretation. pending on frequency, flow rate, and normal or abnormal status Individual changes in SR,, are shown in Figure 3. of the lungs. Therefore, if the equipment of the plethysmograph The mean intra-individual standard deviation of Raw , and allows, Rawshould be measured during quiet breathing. Raw0.5 (coefficient of variation) of three to five successive and Rawat fied flow rates is definitely smaller than Rawover total nonselected respiratory cycles in this group of asthmatic children flow range, in the present results at a mean of 10.3%. If only the before and during positive provocation is given in Table 2. inspiratory resistance is measured, the difference is even more pronounced (9, 22). DISCUSSION Differences due to different opinions on correction for dead- space volume and resistance of the apparatus are especially im- (1) Comparison to literature. There are some publications com- portant in smaller children because of higher Rawvalues and piling predicted values of plethysmographic data including larger dead-space volume in relation to lung volumes.
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