Reference equations for specific airway resistance in children: the Asthma UK initiative.

Plethysmographic specific airway resistance (sR(aw)) is a useful research method for discriminating lung disease in young children. Its use in clinical management has, however, been limited by lack of consensus regarding equipment, methodology and reference data. The aim of our study was to collate reference data from healthy children (3-10 yrs), document methodological differences, explore the impact of these differences and construct reference equations from the collated dataset. Centres were approached to contribute sR(aw) data as part of the Asthma UK initiative. A random selection of pressure-flow plots were assessed for quality and site visits elucidated data collection and analysis protocols. Five centres contributed 2,872 measurements. Marked variation in methodology and analysis excluded two centres. sR(aw) over-read sheets were developed for quality control. Reference equations and recommendations for recording and reporting both specific effective and total airway resistance (sR(eff) and sR(tot), respectively) were developed for White European children from 1,908 measurements made under similar conditions. Reference sR(aw) data collected from a single centre may be misleading, as methodological differences exist between centres. These preliminary reference equations can only be applied under similar measurement conditions. Given the potential clinical usefulness of sR(aw), particularly with respect to sR(eff), methodological guidelines need to be established and used in prospective data collection.

Spirometric parameters in malnourished girls with anorexia nervosa.

Repercussions of obesity on the lung function have been widely studied. The effect of serious malnutrition is less well known. The aim of study was to determine spirometric parameters in 102 malnourished girls with anorexia nervosa. Among these patients, only 71 aged 12-18 years (mean 15.6), mean BMI 15.8 kg/m(2), met the ATS/ERS forced expiratory maneuver criteria for spirometry. The most frequently observed abnormalities were: decreased IC seen in 33 (46%) girls and decreased PEF in 45 (63%) patients. Maximum voluntary ventilation was within the normal range in all but 2 subjects. Diminished values of FEV(1), FVC, FEV(1)/FVC, MEF(50) were observed in 10 (14%), 13 (18%), 3 (4%), and 3 (4%) patients, respectively. We found strong positive correlations between weight and absolute values of the examined parameters. We assume that spirometric abnormalities in anorexia are probably a result of respiratory muscle weakness and body mass loss.

Diurnal variations of respiratory system resistance and compliance derived from input impedance in asthmatic children.

The forced oscillation technique is more and more often used in the evaluation of the results of bronchomotor tests and in assessing respiratory mechanics in children. There is little information available concerning diurnal variability of indices of respiratory mechanics derived from input impedance (Z(rsin)). In 29 asthmatic children, aged 8-13 years we have studied diurnal changes of respiratory system resistance (R(rs)) and compliance (C(rs)) by measuring input impedance with the head generator every hour from 08:00 to 21:00 h. Diurnal coefficient of variation for zero frequency resistance (R(0)), mean resistance in the range 4-32 Hz (R(avg)) and C(rs) were 10.6+/-4.9, 11.2+/-4.5 and 8.9+/-3.3%, respectively. Significant circadian rhythm on R(0) was detected in 11 children, on R(avg) in nine children and on C(rs) in seven children. Only three children had all the three rhythms significant. We conclude, that diurnal variability of input impedance derived indices of respiratory mechanics is rather small, and circadian variability is present in about one third of the examined children. Diurnal variations of respiratory mechanics in children with significant circadian rhythm do not exceed 20%.

Input respiratory impedance measured by head generator in preschool children.

The upper airway wall motion represents a serious problem when measuring the input impedance of the respiratory system (Zrs) by the forced oscillation technique, particularly in young children. To minimize this error, it has been proposed to vary transrespiratory pressure around the head rather than directly at the mouth, using the head generator technique (HGT). The aim of this study was to collect normative data in preschool children in whom the technique may prove most useful. Zrs was measured using HGT and 4-32-Hz pseudorandom noise input in 127 healthy children. Age ranged from 2. 8 to 7.4 years and height (H) from 0.89 to 1.29 m. The fast Fourier transforms of pressure and flow allowed us to calculate respiratory system resistance (Rrs(f)) and reactance (Xrs(f)) at each frequency (f). Resonant frequency (fn), respiratory system inertance (Irs), and compliance (Crs) were derived from the Xrs(f) data. The technique was accepted by more than 95% of the children. A coherence function

Variations in airways impedance during respiratory cycle derived from combined measurements of input and transfer impedances.

Simultaneous measurement of input (Zin) and transfer impedances (Ztr) allows separation of airway and tissue properties at a single frequency, without making assumptions concerning the structure of the two compartments. This approach offers the possibility of studying the variation in airway impedance (Zaw) during the respiratory cycle. Zin and Ztr were measured at frequencies of 10, 20, 30 and 40 Hz in eight healthy subjects to study the variations in Zaw according to a modification of the Rohrer's equation: X=K1+K2(V'ao)-K3V, where V is volume and V'ao the flow at the airway opening. The results showed that Zaw could be modelled as a simple resistance-inertance pathway. Variations in airway resistance (Raw) with flow were greater during expiration than during inspiration with K2 values varying from 0.76-0.90 hPa x s2 x L(-2) during inspiration and 0.84-1.47 hPa x s2 x L(-2) during expiration, independently of frequency. Raw was negative volume dependent; it decreased more with increasing volume during inspiration than during expiration. Airways inertance calculated from the imaginary part of Zaw also underwent systematic variations during the respiratory cycle, but, in contrast to Raw, flow dependence was negative during both phases. In conclusion, the approach used in this study allows flow and volume dependencies of airways mechanical properties to be studied and can also provide indices of airway patency independently of flow, which is of great potential interest for studying variations in airway resistance during bronchomotor tests.

Influence of external loading and assisted ventilation on chest wall mechanical properties.

Instantaneous respiratory effective elastance (Eteff) and tissue resistance (Rt) may be measured by studying the relationship between flow at the airway opening and at the chest during forced oscillations; using that method it has been shown that Rt varies little during breathing while Eteff presents much larger phasic variations than can be explained by the curvature of the static pressure-volume curve (Tomalak et a1., 1997). The aim of this study was to test the hypothesis that the large variations of Eteff were related to the activity of respiratory muscles. For this, we studied in six healthy subjects the changes in Eteff and Rt induced by inspiratory and expiratory elastic loading (IEL and EEL, respectively), resistive loading (REL) and assisted ventilation (ASV) while keeping lung volume, ventilation and breathing pattern as constant as possible. IEL and EEL predominantly increased Eteff during the inspiratory and expiratory phases, respectively; in contrast, ASV decreased Eteff during inspiration and almost completely abolished its positive volume dependence. The changes of Rt usually paralleled those of Eteff. We conclude that respiratory muscle activity is responsible for most of the variations of Eteff during spontaneous breathing.

Respiratory tissue properties derived from flow transfer function in healthy humans.

Assuming homogeneity of alveolar pressure, the relationship between airway flow and flow at the chest during forced oscillation at the airway opening [flow transfer function (FTF)] is related to lung and chest wall tissue impedance (Zti): FTF = 1 + Zti/Zg, where Zg is alveolar gas impedance, which is inversely proportional to thoracic gas volume. By using a flow-type body plethysmograph to obtain flow rate at body surface, FTF has been measured at oscillation frequencies (f(os)) of 10, 20, 30 and 40 Hz in eight healthy subjects during both quiet and deep breathing. The data were corrected for the flow shunted through upper airway walls and analyzed in terms of tissue resistance (Rti) and effective elastance (Eti,eff) by using plethysmographically measured thoracic gas volume values. In most subjects, Rti was seen to decrease with increasing f(os) and Eti,eff to vary curvilinearly with f(os)2, which is suggestive of mechanical inhomogeneity. Rti presented a weak volume dependence during breathing, variable in sign according to f(os) and among subjects. In contrast, Eti,eff usually exhibited a U-shaped pattern with a minimum located a little above or below functional residual capacity and a steep increase with decreasing or increasing volume (30-80 hPa/l2) on either side. These variations are in excess of those expected from the sigmoid shape of the static pressure-volume curve and may reflect the effect of respiratory muscle activity. We conclude that FTF measurement is an interesting tool to study Rti and Eti,eff and that these parameters have probably different physiological determinants.

[Acute-phase proteins in children from industrially polluted regions: influence of treatment]. / Zachowanie sie wybranych bialek ostrej fazy u dzieci z rejonów skazen przemyslowych: wplyw zastosowanego leczenia.

We present the results of observation and treatment of 440 children aged 8-10 years coming from a region of heavy industrial pollution around Legnica. The majority of children from the investigated group presented signs of chronic inflammation of the upper airways (at the beginning of their stay in Rabka the entire group had an average 16.6 +/- 15.7 mm/1h ESR-Erythrocyte sedimentation rate and their whole-blood lead level ranged from 5 to 15 micrograms%, averaging was 9.1 +/- 2.7 micrograms%). At the beginning of their stay in Rabka, acute-phase proteins levels of the Legnica children were compared to those of children from health-resort region of Rabka and were found to differ significantly in respect to ferritin (p < 0.001) and transferrin (p < 0.01) serum levels. Treatment with propolis significantly modified the climatic effects on ESR, on some electrophoretical fractions of serum proteins and on some A-PhP involved in iron metabolism. There was no individual correlation between the whole blood lead level and acute-phase proteins levels and the intensity of their changes after treatment.

[The usefulness of the conduction sweat test in diagnosis of cystic fibrosis]. / Przydatnosc konduktometrycznego testu potowego w diagnostyce mukowiscydozy.

In this paper we present a new test for evaluating the conductivity of sweat--an alternative to the classic Gibson-Cooke test used in diagnosis cystic fibrosis. Comparison of the results of 45 subjects (26 with cystic fibrosis and 19 with other diseases) showed a significant correlation between the two tests (r = 0.923, p < 0.001). The conductometric Wescor test should be included in diagnostic procedures for cystic fibrosis.

[Forced oscillation technique in respiratory system studies. I. Theoretical basis, interpretation of results. Equipment]. / Technika oscylacji wymuszonych (FOT) w badaniu ukladu oddechowego. I. Podstawy teoretyczne. Interpretacja wyników pomiaru. Sprzet.

The paper presents short description of the forced oscillation technique--a noninvasive technique used to examine respiratory mechanics. The setup, interpretation of the results and also advantages and disadvantages of that technique in measurement and interpretation of human respiratory input impedance are described.

[Forced oscillation technique in respiratory system studies. II. Clinical interpretation of results in respiratory system diseases]. / Technika oscylacji wymuszonych (FOT) w badaniu ukladu oddechowego. II. Kliniczna interpretacja wyników badania ukladu oddechowego.

The paper presents short description of changes in FOT parameters in different respiratory system disease. Clinical interpretation of results and usefulness of FOT are described.

[Forced oscillation technique in respiratory system studies. III. Compliance and airway resistance in children with lung fibrosis]. / Technika oscylacji wymuszonych (FOT) w badaniu ukladu oddechowego. III. Podatnosc i opór ukladu oddechowego u dzieci ze zwlóknieniem pluc.

In patient with lung fibrosis we need to monitor lung compliance to evaluate the progress of the illness or efficacy of the treatment. This examination is not well tolerated and difficult to perform, especially in children. We compared classic measurements of static compliance of the lung and airway resistance with parameters derived from forced oscillations measurements--compliance and resistance of respiratory system. Correlation coefficients were respectively 0.85 for compliance and 0.70 for resistance. We conclude that it is possible to supplement classic measurements, especially in evaluating the dynamics of illness.

Optimal frequency range to analyze respiratory transfer impedance with six-element model.

The aim of this investigation was to assess the optimal frequency range for analyzing respiratory transfer impedance (Ztr) in terms of tissue and airway mechanical properties using the six-element model of DuBois et al. (J. Appl. Physiol. 8:587-594, 1956). Ztr was measured in nine healthy subjects from 2 to 64 Hz by studying the relationship between airway flow and pseudorandom pressure oscillations applied around the chest. The measurements were performed with and without two mechanical loads placed at the mouth: an added inertance of 1.4 Pa.s2.l-1 and an added resistance of 1.65 hPa.s.l-1. The data were corrected for the shunt effect of upper airway walls. The changes in Ztr induced by the loads were very consistent up to 56 Hz with the T-network topology assumed in DuBois's model; the agreement deteriorated at higher frequencies, presumably due to the difficulty of obtaining a homogeneous pressure field around the chest. The fit of the model to the data also worsened sharply at above 56 Hz. In the 2- to 56-Hz frequency range, similar values of the tissue and airway coefficients were obtained with and without the loads. In that frequency range the confidence intervals of the coefficients were better than 10%. We conclude that DuBois's model is valid from 2 to 56 Hz in healthy subjects and allows accurate partitioning of airways and tissue properties. In addition, we present evidence that the upper airway shunt negligibly influences Ztr data and the derived coefficients provided airway flow is measured with a low-impedance pneumotachograph.

[Computer-assisted calibration of inductive plethysmography]. / Komputerowo wspomagana kalibracja pletyzmografu indukcyjnego.

A software program was written assisting calibration and measurement of the inductive plethysmography RESPITRACE. In 6 subjects calibration was carried out using both methods and a confirmation was found in the 20% area of dispersion. The use of only one measuring tape enables a very precise measurement of ventilation.