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

Abstract

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...

Specific airway resistance, interrupter resistance, and respiratory impedance in healthy children aged 2–7 years

“…We have found that this method greatly improves the acceptability of the plethysmographic procedure in young children without introducing bias to the estimate of sRaw or loss of reproducibility. 9 The mean sRaw VЈmax (1.1 kPa и s) observed in the present study is higher than in other studies, which have reported values ranging from 0.45 to 1.0 kPa и s. 8,13,14,20 This discrepancy can probably be ascribed to the fact that we, in contrast to most previous workers, used a plethysmograph with electronic BTPS compensation, which has introduced a positive frequency dependence and has resulted in significantly higher estimates of sRaw in comparison with measurements obtained with a heated rebreathing system to ensure BTPS conditions. 9 One of the advantages of sRaw ⌬Vmax and sRaw VЈmax is that these two measures can be estimated irrespective of the magnitude of the flow, and they are therefore applicable to subjects of all ages.…”

“…In keeping with other investigators, we found no significant correlation between sRaw and either age, weight, or height. 8,13,14 We measured sRaw by a single-step procedure from the relation between variations of respiratory flow and variations of plethysmographic volume during normal breathing. The single-step procedure obviates the need for measuring breathing efforts against a closed shutter.…”

Diagnosis and Management of Asthma in Older Adults

“…It does not rely on maximal expiratory effort and may thus be particularly suitable for older patients. Its value in the assessment of asthma in children has long been established, 53 but no studies examining the feasibility of this technique in older patients have been performed, so it is not routinely encountered in clinical practice. This represents an area for future studies to address validity and practicality of these techniques to assess airway obstruction in older patients.…”

Measurement of the specific airway resistance by plethysmography in young children accompanied by an adult

“…From these observations it would seem that in airway obstruction, the diagnostic yield from the single-step procedure is comparable to that of the combined measurement of Raw and TGV. Yet another advantage of measuring sRaw is that beyond infancy sRaw is largely independent of body size [22][23][24], facilitating the interpretation of measurements carried out longitudinally in individual children.…”