Use of transcutaneous oxygen tension, arterial oxygen saturation, and respiratory resistance to assess the response to inhaled methacholine in asthmatic children and normal adults.

Abstract

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.

Lung function measurement in awake young children

“…Although Ptc,O 2 may not be an accurate measure of arterial oxygen tension (Pa,O 2 ), Ptc,O 2 and Pa,O 2 covariate during acute asthma in young and in older children and even after inhalation of the potent vasodilator, the b 2 -agonist [20,21,43]. Ptc,O 2 has previously been found to correlate to the clinical state [44], to respiratory impedance measurements [41,45], and to spirometry [46], with a precision that compared favourably with the latter [47]. In this study, Ptc,O 2 exhibited a covariation with the "gold standard" measurements of sRaw and FEV1.…”

Distinguishing phenotypes of childhood wheeze and cough using latent class analysis

“…Physiological measurements included in the present analysis were age-and height-standardised z-scores [20] of the prebronchodilator forced expiratory volume in 0.5 s (FEV0.5), bronchial responsiveness (provocative concentration of methacholine causing a 20% decrease in transcutaneous oxygen tension (PC20-Ptc,O 2 )) [21], and atopy assessed by skin-prick testing. Subjects responding to one or more of four aeroallergens (cat hair, dog danders, Dermatophagoides pteronyssinus and mixed grass pollen) were designated atopic (for further details see supplementary data).…”

Factors relating to the severity of symptoms at 5 yrs in children with severe wheeze in the first 2 yrs of life

“…The inhalations continued until the Ptc,O 2 had fallen by at least 15%, the child was dyspnoeic or the maximum concentration had been inhaled, whichever was the soonest. The response to challenge was assessed 3 min after each inhalation both by Ptc,O 2 and Rrs6, as described previously [10]. Since Rrs6 was found to be unreliable during induced bronchoconstriction, only the Ptc,O 2 was used [11].…”