SummaryIn 82 healthy children and in asthmatic children before and during positive allergen provocation test, airway resistance (Raw), airway conductance (G,), specific airway resistance (SR,), and specific airway conductance (SG,) were measured by body plethysmography 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 compared: Raw 0.5 is 10.3% smaller and shows a smaller coefficient of variation in healthy children. This is interpreted as a less important influence of variations of glottis opening. SRaw mean value is 7.08 hPa. sec; SGaw mean value is 0.141 hPa-' sec-'. In asthmatic children, Raw 0.5 proves to be a more sensitive parameter for the evaluation of inhalation provocation tests than Raw t. The most sensitive indices of obstruction in the central and more peripheral bronchi are SRaw 0. 5 and SG,, 0.5. Abbreviations BTPS, body temperature and ambient pressure saturated with water vapor FRCb,,, functional residual capacity measured by body plethysmography Gaw, airway conductance hPa, hecto Pascal APM, pressure at the mouth Raw, airway resistance R, ,, terminal airway resistance SG,,, specific airway resistance SRaw t, specific airway resistance over total flow range $a, AVB/APM V, airflow AVb, volume displacement AVM, tidal volume The development of body plethysmography has furnished a noninvasive method of assessing Raw. Raw is defied as the ratio of alveolar pressure to air flow. Usually, the pressure or volume changes of the plethysmograph corresponding to alveolar pressure are plotted versus air flow. Raw is then calculated from the slope of the resulting S-shaped curve. DuBois and co-workers (8) measured Raw at a certain flow rate on the linear part of the curve during panting. After the problem of maintaining BTPS conditions in the breathing air was solved, many investigators turned to measuring Raw during quiet breathing instead of panting. It was then proposed to measure Raw over the total range of alveolar pressure ("total Raw3', 26) or over the points of maximum inspiratory and expiratory air flow (23,20). For the latter way of interpretation, Haluszka (13) suggested the term "terminal Raw" (Raw t) because the terminal points of the curve are used. At present, there seem to be mainly two groups of investigators: those who measure Raw at fmed flow rates during panting and those who measure Raw at maximum flow during quiet breathing.It is the aim of the present study to compare the f~e d flow and the "terminal" Raw interpretation applied to the same measurements during quiet breathing in healthy and in asthmatic children. MATERIALS AND METHODSMeasurements of FRCb,, and of Raw were performed in an air conditioned pressure-corrected volume displacement whole-body plethysmograph (29). The technical details have been described previously (15). The electronic signals for volume displacement (integrated and pressure-cofrected flow signal) of the body plethysmograph (AVt,), APM, V, and its integral, AVM, were stored simultaneously on a magn...

In 94 healthy children, 6-15 years of age, the intrathoracic gas volume at resting expiratory level (TVG) was measured by means of a pressure corrected flow body plethysmograph and compared to functional residual capacity (FRC), measured simultaneously to TGV by means of the Helium dilution technique. TGV is 1.9% (+/- 11.7% SD) smaller than FRC, this difference being not significant (P greater than 0.05). A predicted equation for TGV (in ml) in correlation to standing height (in cm) is published in boys and girls. In 82 healthy children, 6-15 years of age, airway resistance (Raw) was measured plethysmographically. Raw(in cmH2O/1/s) is smaller, the larger is the child (r = -0.57; P less than 0.01), the residual standard deviation around the regression line is considerable (29%) and corresponding to the value, published previously for total pulmonary flow resistance. Difficulties in the evaluation of recorded resistance curves as well as calculation and lung volume correction of the Raw-value are discussed.