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The aims of this study were to investigate lung function in 2-5-yr-old stable asthmatic children consecutively referred from general practitioners and to analyse the outcome on the basis of their requirement for antiasthmatic treatment and symptoms after 1.6-4.5 yrs. Lung function was measured in 110 children with a mean+/-SD age of 3.8+/-1.0 yrs using the interruptor technique (resistance assessed using the interruptor technique (Rint)), whole body plethysmography (specific airway resistance (sRaw) and respiratory resistance (Rrs,5)and reactance at 5 Hz (Xrs,5) using the impulse oscillation technique. Rint, sRaw, Xrs,5 and Rrs,5 were suggestive of impaired lung function in 44%, 14%, 11% and 7.5% of the children, respectively, with a predominance of children aged 2-3 yrs. Sixty-five per cent were treated with inhaled steroids, and 35% were treated only with beta2-agonists as needed; lung function was not significantly different between these two groups. Outcome after 2.9+/-0.7 yrs was not significantly different between children with Rint measurements above and those children with Rint measurements within the reference range at enrolment. Of these children, 58 and 59% were currently on antiasthmatic treatment, and 40% and 49% had current symptoms, respectively. Impairment of lung function may be a common finding in stable young asthmatic children, but apparently this is not a risk factor for persistence of asthmatic symptoms.

The study aimed to investigate dose consistency and particle distribution from the dry powder inhalers Diskus and Turbuhaler. Full profiles of inhalation pressure versus time were recorded in 18 4 yr old and 18 8 yr old asthmatic children through Diskus and Turbuhaler inhalers. These data were used in an inhalation profile simulator to assess drug delivery from both a Diskus inhaler and a Turbuhaler inhaler, and in particular to assess the proportion of drug emitted in the coarse (>4.7 microm) and fine (<4.7 microm) particle size range from each type of inhaler. The inhalation profile more accurately represents the changes in flow rate over time through the device than the constant flow rate usually applied with an impactor alone. The aerosol cloud was released before the peak inspiratory effort had been achieved and accordingly the early part and not the peak of the inspiratory performance is a determinant of the quality of the aerosol. The mean (SD) amount of drug in large particles (>4.7 microm), fine particles (<4.7 microm) and very fine particles (<2.1 microm) in percentage of label claim from the Fluticasone Diskus was 72 (5), 15 (2) and 2 (1) from the 4 yr old children and 71 (3), 18 (2) and 2 (1) from the 8 yr old children, respectively. Similar particle fractions from the Budesonide Turbuhaler were 35 (9), 21 (10) and 7 (5) from 4 yr old children and 30 (7), 32 (9) and 12 (6) from 8 yr old children. In conclusion, the Diskus inhaler provides an improved dose consistency through the varying age groups and inspiratory flow performances when compared to the Turbuhaler in terms of the proportion of the dose emitted at each particle size. This improvement is at the expense of a low fine particle mass and a high proportion of coarse particles from the Diskus as compared with the Turbuhaler.

The purpose of this study was to evaluate a procedure for measurement of specific airway resistance (sRaw) by whole body plethysmography in young awake children accompanied by an adult. sRaw was measured by a single-step procedure, omitting the measurement of the thoracic gas volume. The frequency dependency of sRaw was investigated and the accuracy of simulating body temperature, atmospheric pressure and saturation with water vapour (BTPS) conditions by electronic compensation was assessed. One hundred and thirty one children with asthma were studied. In 57 children (mean (SD) age 5.6 (1.8) yrs) who performed measurements with and without an accompanying adult, the mean value of sRaw was 1.45 (0.36) and 1.44 (0.38) kPa x s, respectively, with a mean difference of 0.008 (0.152) kPa x s, and mean within-subject coefficients of variations (CV) of 8% and 10%, respectively. In 52 children (mean age 3.3 (0.8) yrs), for whom measurements made only in the presence of an accompanying adult, the CV was 8.5%. No measurements could be obtained in 22 children (17%) (mean age 2.8 (0.5) yrs). Measurements exhibited a significant frequency dependency, and electronic BTPS compensation substantially overestimated SRaw. In conclusion, the use of electronic compensation for simulating body temperature, atmospheric pressure and saturation with water vapour introduces a bias that affects the accuracy of the estimate of specific airway resistance. Nevertheless, plethysmographic measurements with and without an accompanying adult yielded comparable and equally repeatable estimates of specific airway resistance. The single-step plethysmographic procedure with an accompanying adult is a clinically useful method for evaluating airway function in children too young to perform plethysmographic measurements alone.

To determine the repeatability of bronchial responsiveness in awake young children, two methacholine challenge tests were performed on separate days in 16 children with stable asthma (mean age, 3 3/4 years). Methacholine was administered using a new method for quantitative delivery of aerosol that eliminates the effect of dilution of the aerosol by entrainment of air and enables quantitative delivery of aerosol according to body weight. Respiratory function was monitored by measurement of respiratory resistance by the interrupter technique (Rint), respiratory resistance and reactance at 5 Hz (Rrs5, Xrs5) by the impulse oscillation technique, transcutaneous measurements of oxygen (PtcO2), and specific airway resistance (sRaw). Repeatability was evaluated by determining the provocative dose that caused a defined percentage of change relative to baseline (PD%: Rint PD30, Rrs5 PD30, Xrs5 PD80, PtcO2 PD10, and sRaw PD80. Repeatability was estimated from the difference between the PD% obtained at the time of the two tests. Using the numeric value of these differences, the repeatability of Xrs5 PD60, PtcO2 PD10, and sRaw PD50 was [mean (SD)]: [0.8 (0.5)] [0.5 (0.4)] and [0.7 (0.6)] doubling doses, respectively. Rint PD30 and Rrs5 PD30 proved to be less reproducible: [1.2 (1)] and [1.6 (0.9)] doubling doses, respectively. The new method of aerosol delivery offers a means of standardizing the bronchoconstrictor stimulus, and the results show that estimates of bronchial responsiveness in young children can be obtained reproducibly within one doubling dose of methacholine.

This study evaluated three techniques for testing of lung function in young awake children. We compared measurements by the forced or impulse oscillation technique (IOS), the interrupter technique (IT), and transcutaneous measurements of oxygen (tcPo2) with concomitant measurements of specific airway resistance (sRaw) during methacholine challenge in 20 stable asthmatic children, 2-4 years old. Measurements were performed with all techniques after each dose of methacholine and after inhalation of a bronchodilator. Measurements were carried out during tidal breathing using a face-mask with a built-in mouthpiece. The ranking of sensitivity was as follows: sRaw > IOS, respiratory reactance at 5 Hz (Xrs5) > tcPo2 > interrupter resistance (Rint) > IOS, respiratory resistance at 5 Hz (Rrs5). The sensitivity of sRaw and Xrs5 was not significantly different, but both were significantly more sensitive than Rint and Rrs5; the sensitivity of tcPo2, Rint, and Rrs5 was not significantly different. Measurements in eight of the subjects performed during an episode of acute asthma yielded comparable results in regard to the sensitivity of the techniques. Measurements improved significantly after bronchodilator administration; however, the response to bronchodilator tended to be less during acute asthma and was best demonstrated by a deterioration of tcPo2. All the evaluated techniques reliably reflect short-term changes in respiratory function and can provide clinically useful estimates of airway function. The techniques are non-invasive, are not dependent on the active co-operation or sedation of the subjects, and therefore are well suited for routine use in young children.