Reference ranges for interrupter resistance technique: the Asthma UK Initiative.

Measuring interrupter resistance (R(int)) is an increasingly popular lung function technique and especially suitable for preschool children because it is simple, quick and requires only passive cooperation. A European Respiratory Society (ERS)/American Thoracic Society (ATS) Task Force recently published empirical recommendations related to procedures, limitations and interpretation of the technique. However, for valid interpretation, high-quality reference equations are required and these have been lacking. The aim of the present study was to collate R(int) data from healthy children in order to produce more robust reference equations. A further aim was to examine the influence of methodological differences on predicted R(int) values. R(int) data from healthy children were collected from published and unpublished sources. Reference equations for expiratory and inspiratory R(int) were developed using the LMS (lambda, mu, sigma) method. Data from 1,090 children (51% males) aged 3-13 yrs were collated to construct sex-specific reference equations for expiratory R(int) and data from 629 children (51% males) were collated for inspiratory R(int). Height was the best independent predictor of both expiratory and inspiratory R(int). Differences between centres were clinically irrelevant, and differences between ethnic groups could not be examined. The availability of a large and generalisable sample and the use of modern statistical techniques enabled the development of more appropriate reference equations for R(int) in young children.

Methacholine challenge in pre-school children--which outcome measure?

The aim of our study was to evaluate the utility of interrupter resistance (R(int)), transcutaneous oximetry and auscultation as outcome measures for a recently suggested tripling-dose methacholine (Mch) challenge in pre-school children. We studied 57 children aged 3-6 years. R(int) was measured at baseline and after each Mch dose. Oxygen saturation (SaO(2)) and transcutaneous oxygen pressure (tcpO(2)) were monitored during the challenge. Mch concentrations of 0.22, 0.66, 2.0, 6.0 and 18.0 mg/ml were nebulised during tidal breathing. The challenge was terminated if there was wheeze, SaO(2) below 91% or persistent cough; this final Mch dose was considered as PCW. Nine healthy children, 17 with cough and 25 with wheeze performed the study up to the point of PCW or all five Mch inhalations. If a change of 20% of predicted R(int) or termination by wheeze, desaturation or cough is taken as a completed test, then 39 out of 51 children (78%) had adequate R(int) measurements on each occasions from start to completion. The success rate for tcpO(2) measurements was similar: 38 out of 51 (76%) had complete tcpO(2) data until a 15% fall of tcpO(2) or clinical endpoint was reached. Using the above-mentioned cut-off levels significant change in R(int) or tcpO(2) preceded PCW in most of the cases. Both R(int) and tcpO(2) measurements may allow detection of bronchial hyper-responsiveness at lower Mch doses and also provide a less subjective measure, but will not be feasible in all children.

Feasibility of shortened methacholine challenge in preschool children.

The aim of our study was to assess the feasibility and safety of a recently suggested tripling-dose methacholine (Mch) challenge in preschool children. Fifty-seven children aged 3-6 years were studied. Mch challenge was carried out using a tidal breathing method, with concentrations of 0.22, 0.66, 2.0, 6.0, and 18.0 mg/ml, at 5-min intervals, given by a Pari Turbo Boy compressor and Pari LC Plus nebulizer, for 1 min only. Oxygen saturation (SaO(2)) was monitored during the challenge. The challenge was terminated if there was wheeze, SaO(2) below 91%, or persistent cough. This final Mch dose was considered the provocative concentration inducing audible wheeze (PCW). Nine healthy children, 17 with cough and 25 with wheeze, completed the study. Mean output from nebulizers (SD) in these 51 children was 0.30 (0.05) ml/min. Geometric means for PCW in these groups were 2.88, 2.58, and 1.28 mg/ml Mch, respectively. The wheezing children were significantly more hyperresponsive than the coughing children (P < 0.05). A tripling-dose Mch protocol is safe and practicable in children over 3 years of age. A further reduction in nebulized dose may be needed for a more discriminatory test.

Simultaneous application of differential servo-oscillometry and volume-clamp plethysmography for continuous non-invasive recording of the finger blood pressure response to a hand postural change.

Continuous blood pressure recordings obtained by the volume-clamp method (Finapres 2300 BP monitor, Ohmeda, USA) were compared with measurements made by using the modified oscillometric method (UT9201 beat-to-beat monitor, University of Tartu, Estonia) in normal subjects during a hand postural change. Changes in the local blood pressure were induced in 11 healthy volunteers by passive elevation of the hand by 40 cm and lowering it again after one minute. We did not reveal a statistically significant difference between the group-averaged responses of the oscillometric finger mean blood pressure measurement device and those of Finapres during this test. The difference UT9201 minus Finapres equalled -1.3 +/- 3.1 mm Hg (p = 0.15). Blood pressure responses were similarly tracked by both beat-to-beat finger blood pressure monitors despite the considerable variability in the shape of the subjects' individual responses.

Comparison of oscillometric pulse amplitude envelopes recorded from the locally compressed radial arteries.

Simultaneously recorded oscillometric envelopes, obtained pneumo- and photoplethysmographically from a small local pad-type pneumatic cuff on the left and from a larger cuff on the right radial artery, were compared in 17 healthy subjects. For oscillometric estimation, specific fixed ratios based on evidence in the literature were used. The obtained envelopes for each person were shifted and aligned at the point of upper arm mean arterial pressure for this person, thus eliminating the brachial-to-radial mean blood pressure gradient and possible left-right difference. In this way, the shape of differently recorded envelopes as a determinant of the accuracy of oscillometric estimation was studied. Results showed an advantage of photoplethysmographically compared to pneumoplethysmographically recorded envelopes. For a smaller cuff (diameter 40mm), the mean difference in mmHg 'oscillometric estimate minus auscultatory reference' and standard deviation were in the case of photo recording for systolic and diastolic pressures -0.6 (6.3) and 1.2 (3.4), respectively. In the case of pneumo recording, these parameters were considerably larger, being 12.1 (11.9) and -6.2 (10.9), respectively. For a larger cuff the same tendency was revealed. Photo recording was found to be less sensitive to alterations in the cuff size and characteristic ratios.

Interrupter technique and pressure oscillation analysis during bronchoconstriction in children.

The use of interrupter resistance (R(int)) is a feasible method of measuring bronchodilator responsiveness and bronchial hyperresponsiveness in preschool children. It has been suggested that analysis of recorded oscillations of the mouth pressure may provide additional indices of changes in airway mechanics. The aim of our study was to determine whether amplitude or damping properties of oscillations were more sensitive than R(int) in describing changes during bronchoconstriction. Data from 44 children (24 boys) who completed tripling dose methacholine (Mch) challenge were analysed. The median (range) age of children was 4.9 (3.1-6.1 years). In addition to baseline and maximal R(int) after Mch [mean (SD) were 0.92 (0.19) and 1.44 (0.35) kPa l(-1) s, respectively], obtained from a commercial device we analysed the following parameters: difference between the first maximum and minimum (A(MxMn)), maximum instantaneous amplitude (A(inst)), amplitudes of fitted mathematical model and the dominant frequency, sum of frequency component amplitudes, two damping factors and frequency. All amplitude parameters changed significantly after Mch. For comparison of the decrease in amplitudes and increase in R(int) we additionally used reciprocals of amplitudes. Using the sensitivity index (SI) i.e. the change after intervention divided by the baseline SD, 1/A(inst) and 1/A(MxMn) were the most sensitive indices to describe the change (with median SI of 6.29 and 6.28, respectively). R(int) had a median SI of 5.13. Frequency and damping factors were less sensitive, with median SI values <1. These findings suggest that oscillation amplitude analysis implemented in the software of commercial devices could have further applications in assessing respiratory mechanics.

Lung function in Estonian children: effect of sitting height.

The present analysis formed part of the population study of Estonian school-children and was undertaken in order to examine the relationships between lung function variables, standing and sitting height. We measured forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), peak expiratory flow and forced expiratory flows when 50 and 75% of FVC had been exhaled, and anthropometric indices in 645 healthy schoolchildren, aged 6-18 years. The growth spurt in standing and sitting height occurred between the ages of 11 and 13 years in girls, and 13 and 15 years in boys. Growth spurts of lung parameters occurred during the same periods. FVC and FEV1 showed close correlations (r = 0.89-0.94) with all anthropometric parameters and age, whereas correlation coefficients for the flows were less close (r = 0.65-0.88). In boys, correlations between sitting height and lung function variables were greater than those with standing height. Using stepwise regression analysis, in boys sitting height was selected in all lung function parameters, and in girls sitting height was never selected. We conclude that there is a very close correlation between sitting height and lung function variables. The use of sitting height in parallel with standing height in predicted values for Estonian schoolchildren would make the values more exact.

Differences in lung function and chest dimensions in school-age girls and boys.

The present analysis was undertaken to find out whether differences in the performance of the lungs of boys and girls of the same height are explicable by differences in thoracic size. We measured forced vital capacity (FVC), peak expiratory flow (PEF) and forced expiratory flows (FEFs), when 50% and 75% of FVC had been exhaled (FEF50, FEF75), and standing height, chest width and depth and biacromial diameter in 1187 schoolchildren aged 6-18 years. Thoracic dimensions were usually greater in boys than in girls of the same height, except for the height range of 150.0-164.9 cm. For this height range, the pulmonary function variables (PEF, FEF50, FEF75 and PEF/FVC) were significantly higher in girls, and for FVC almost as high as the male values. For FEF50/FVC and FEF75/FVC, the female values were larger over the whole height range (115.0-184.9 cm), but even for these parameters the differences were greatest for the height range 150.0-164.9 cm. In conclusion, very similar growth patterns of lung function and thoracic parameters can suggest that differences in the lung function parameters of boys and girls of the same height may be explained by differences in the thorax size.

Spirometric reference values in Estonian schoolchildren.

This study was conducted to describe the relationship between anthropometric parameters and lung function in Estonian children, to determine the reference values for spirometry, and to compare these results with other data sets. The results are based on 1170 healthy non-smoking children (643 girls and 527 boys), aged 6-18 years. The spiroanalyser Pneumoscreen II (Jaeger) was used to register dynamic lung parameters. Natural logarithmic values of lung volumes, standing or sitting height and age were used in the final regression model. Prediction equations for forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), peak expiratory flow, forced expiratory flows when 50 and 75% of FVC has been exhaled, and mean forced expiratory flow over the middle 50% of the FVC for both sexes are presented. In comparison with recent data from European children the reference values were close for FVC, the differences were bigger for FEV1 and forced expiratory flows, especially in taller children.