The aim of this study was to compare the feasibility of three techniques for measuring the response to bronchial challenge in young children: a direct airway measurement, the forced oscillation technique (FOT) for determining respiratory system resistance at 6 and 8 Hz (Rrs6 and Rrs8), and two indirect methods, the change in transcutaneous oxygen tension (PtcO 2 ) and the detection of wheeze on auscultation of the chest. Thirty children aged 5 yrs, with a history of wheeze, and six asymptomatic controls, took part in a bronchial challenge test using methacholine administered by Wright nebulizer by the tidal-breathing method. The provocative concentration which produced a 35% increase in Rrs6 (PC35Rrs6) and a 15% decreases in PtcO 2 (PC15PtcO 2 ) were determined by interpolation, and the chest was auscultated after each dose of methacholine.The FOT was found to be unreliable in this age group: in seven children, the data were technically unsatisfactory in the presence of induced bronchoconstriction, whilst in three children, changes in Rrs were inconsistent after challenge. The use of Rrs8 did not improve the detection of positive responses. PC15PtcO 2 was measurable in 29 of 30 children, and in 18 of these PC35Rrs6 was also measurable. In no subject did a significant, sustained increase in Rrs occur during challenge in the absence of a significant change in PtcO 2 . Wheeze was audible in only 4 of 25 (16%) of the positive and in no negative challenges.With this protocol, we found the FOT to be unreliable and the auscultation method valueless and potentially dangerous, since marked falls in PtcO 2 of up to 33% sometimes occurred in the absence of wheeze. The PtcO 2 method seems to be the most technically reliable technique for measuring the response to bronchial challenge in 5 year old children. The underlying pathophysiology and diagnostic value of PC15PtcO 2 values in young children remain to be established.

No abstract

The interrupter technique is a noninvasive method for measuring airway resistance during quiet breathing which requires minimal subject cooperation. It, therefore, has enormous potential for use in young children unable to cooperate with conventional lung function tests. We evaluated the interrupter technique during bronchial challenge with methacholine administered by the tidal breathing method in 10 5-year-old asthmatic children. The mouth pressure/time [P mo(t)] curve obtained following brief airflow interruption during the expiratory phase of quiet breathing was analyzed to determine the interrupter resistance (Rint) using four different methods: RintC, a smooth curve fit with back-extrapolation; RintEO, calculated from the pressure change after the postinterruption oscillations had decayed (end-oscillation); RintL, two-point linear fit with back-extrapolation; and RintEI, calculated from the pressure change at the end of the period of interruption. The four Rint methods were compared for repeatability and sensitivity with the direct measurement of resistance by the forced oscillation technique (Rrs), and with an independent method of measuring the response to challenge, utilizing the change in transcutaneous oxygen tension (PtcO2). The sensitivity of the methods was defined by a sensitivity index (SI), the change after challenge expressed in multiples of the baseline standard deviation. The PtcO2 method had the lowest variability and was by far the most sensitive method (geometric mean SI 18.9), at least 1 doubling concentration more sensitive than the other techniques in every subject (P < 0.05). RintL was more sensitive than the other interrupter methods (geometric mean SI: RintL 4.2; RintC 1.0; RintEO 2.7; RintEI 3.1; P < 0.05) and similar in sensitivity to Rrs (geometric mean SI 4.6) in 7 out of 10 children in which this could be measured. We conclude that the interrupter method provides a simpler method than the oscillation technique for assessing airway obstruction in this age group.

Respiratory resistance (Rrs6), transcutaneous oxygen tension (Ptco2), and oxygen saturation (Sao2) were measured during methacholine challenge in 15 asthmatic children and six normal adults. During bronchoconstriction, induced by a wide range of inhaled methacholine concentrations (0 5-256 could examine the relation between bronchoconstriction and hypoxaemia over a wide range of inhaled methacholine concentrations, we studied normal adults and asthmatic children. Method SUBJECTSNineteen asthmatic children (age range 4-11 years) were selected from the children's asthma clinic. All were in a stable condition but represented a wide range of clinical severity. All bronchodilator and cromoglycate treatment was stopped at least 12 hours before the study. Six normal adult volunteers aged 23-46 years were recruited (table).The study had approval from the hospital ethics committee and informed consent was obtained from all subjects and where applicable their parents. CHALLENGE PROCEDUREAfter the subject had inhaled normal saline doubling concentrations of methacholine chloride were administered for one minute each, by Wright nebuliser, with 8 1/min of air as the driving gas. The initial concentration was 0-5 g/l for asthmatic subjects and 4-16 g/l for normal subjects. The subject breathed quietly through a mouthpiece with a nose clip in place. The inhalations were repeated at five minute intervals until a 40% increase in -respiratory resistance had occurred or the maximum concentration of methacholine (32 g/l for asthmatic children and 256 g/l for normal adults) had been delivered. The same nebuliser was used throughout the study. LUNG FUNCTIONRespiratory resistance was measured by the forced oscillation technique with the apparatus designed and built by Landser.6 The subject sat resting on his elbows with a nose clip in place and cheeks supported while breathing normally into the apparatus through a mouthpiece. Rrs was determined over the frequency spectrum 2-26 Hz. The average Rrs over the whole frequency range and Rrs at each oscillation frequency were recorded. Only values with a coherence of at least 0-95 (signal to noise ratio) were accepted. As 6 Hz was the lowest single frequency that consistently produced a value of Rrs with an acceptable coherence in all subjects, this value of Rrs (Rrs6) was used to assess the response to methacholine inhalation. The Rrs6 values were compared with predicted values.7 433 on 11 May 2018 by guest. Protected by copyright.

Unlike conventional methods, the interrupter method for measuring airway resistance is non-invasive and requires minimal patient co-operation. It can therefore be applied in critically ill patients, acute asthmatics, neonates, pre-school children, geriatric patients and unconscious patients. The method is based on transient interruption of airflow at the mouth for a brief period during which alveolar pressure equilibrates with mouth pressure. Measurement of mouth pressure is used to estimate alveolar pressure prior to interruption and the ratio of this to flow prior to interruption gives airway resistance. Using the interrupter method we have developed a portable device for measuring airway resistance which is simple to use and gives a direct instantaneous reading. Measurements of airway resistance obtained using the new device were compared with those obtained using conventional body plethysmograph methods in 43 adult patients. A close correlation was seen (r = 0.86). The two methods appear equally sensitive in detecting changes in airway resistance following bronchodilator therapy. The device has been used successfully in pre-school children unable to co-operate with conventional methods.