Air pollution and respiratory symptoms in preschool children.

A diary study on a random sample of 625 Swiss children aged 0 to 5 yr was conducted in two cities in Switzerland to investigate the association between air pollution and respiratory symptoms. Total suspended particulates (TSP), SO2 and NO2 were measured by city monitor. In addition, passive samplers inside and outside the home measured NO2 concentration during the 6 wk each child was on the diary. Diaries were filled out by parents, and 20% were validated with the attending pediatrician's case notes. Incidence and duration of symptom episodes were examined separately. The study included any episode, episodes of coughing without runny nose, upper respiratory episodes, and episodes of breathing difficulty. In regressions using 6-wk average pollution that controlled for medical history, NO2 measured outdoors but not indoors was associated with the duration of any symptom. Total suspended particulates were a more significant predictor of duration of any symptom than NO2. The 6-wk average TSP was significantly associated with incidence of coughing episodes and marginally significant as a predictor of upper respiratory episodes. Previous day's TSP was a significant predictor of incidence of upper respiratory symptoms. Annual average of NO2 was associated with the duration of any episode and of upper respiratory episodes. We conclude that the incidence and duration of respiratory symptom episodes are likely associated with particulate concentrations and duration may be associated with NO2.     

Airway resistance and atopy in preschool children with wheeze and cough.

The extent to which the measurement of airways resistance by the interrupter technique (Rint) distinguishes preschool children with previous wheeze from those with no respiratory symptoms and helps to classify subjects with persistent cough, was investigated. Rint was measured before and after salbutamol treatment in 82 children with recurrent wheeze, 58 with isolated cough and 48 with no symptoms (control subjects). Their mean age (range) was 3.7 yrs (2-<5 yrs). Median baseline Rint was higher (p<0.0001) in wheezers than in either coughers or control subjects (1.16, 0.94 and 0.88 kPa x L(-1) x s(-1) respectively); coughers did not differ significantly from control subjects (p=0.14). The median ratios of baseline to post-salbutamol measurements (bronchodilator response (BDR)) in the groups differed significantly (1.40, 1.27 and 1.07, p< or =0.01 for all), suggesting that coughers occupy an intermediate position. A BDR ratio of >1.22 had a specificity and sensitivity for wheeze of 80% and 76% respectively. Twenty-eight coughers had a BDR ratio >1.22. Wheezers' immunoglobulin E was inversely related to baseline Rint. It is concluded that measurements of airway resistance by the interrupter technique are useful for classifying preschool children with respiratory symptoms and could be used to monitor the effect of interventions. The relation between atopy and airways resistance suggests that they have separate roles in preschool wheezing. Coughers with a high bronchodilator response could represent "cough-variant" asthma in children who have baseline airway resistance by the interrupter technique measurements similar to control subjects. Whether these children develop classical asthma will only be known at follow-up later in childhood.     

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 相似文献   

Interrupter resistance short-term repeatability and bronchodilator response in preschool children

Interrupter resistance (Rint) technique can be easily and successfully performed in preschool children. The establishment of Rint short-term repeatability is essential to interpret any Rint change after a pharmacological intervention. AIMS OF THE STUDY: In preschool children with asthma or chronic cough: (1) to assess two indices of short-term repeatability: (a) intra-measurement and (b) within-occasion between-test repeatability; (2) to study the relationship between short-term repeatability and bronchodilator response (BDR). RESULTS: Rint intra-measurement repeatability assessed by the coefficient of variation was similar at baseline and after bronchodilator in asthmatics and in coughers (median 10% and 12%, respectively). There was no significant difference between asthmatics and coughers for both coefficient of repeatability (CR) (0.25 kPa L(-1)s and 32% of predicted vs 0.16 kPa L(-1) s and 21% of predicted, respectively) and BDR (median -14.7% vs -21.1% of predicted, respectively). However, in 20% of the study children, baseline variability of Rint modified the significance of the BDR. CONCLUSION: In the present study, Rint short-term repeatability was similar to that of previous studies. Similar Rint repeatability in coughers and in asthmatic children favored the use of asthmatic CR for both populations, and a -35% cut-off as a positive BDR. In 20% of study children, baseline Rint variability could influence the significance of the BDR. In order to improve assessment of BDR using Rint, further studies are needed (1) to compare the variability of Rint to other resistance measurement techniques and (2) to define the best method for Rint calculation and for expression of BDR.     

Snoring in French preschool children.

The prevalence of habitual snoring and its associations with respiratory symptoms, personal and familial risk factors, ear, nose, and throat (ENT) abnormalities, and its influence on ventilatory function were studied in a sample of 190 children aged 5 to 6 years from nine kindergartens in Nancy (northeastern France). Nineteen (10%; 95% CI 5.7-14.3%) of the children were habitual snorers; the prevalence was the same in boys and girls. In univariate analysis habitual snoring was significantly associated with a personal history of exercise-induced bronchospasm [relative risk (RR) 4.50]; a history of adenotonsillectomy (RR, 2.56); a personal history of allergy (RR, 2.83); a sibling history of atopy (RR, 2.39); and doctor-assessed tonsillar hypertrophy (RR, 2.51). These factors were entered into a logistic regression model that retained as independent determinants exercise-induced asthma, personal history of allergy, sibling history of allergy, and tonsillar hypertrophy. The height-adjusted peak expiratory flow rate was slightly, non-significantly lower in habitual snorers as compared to non-snorers (2.01 +/- 0.32 vs 2.10 +/- 0.38 L/s/m2). Due to the limited numbers in the sample, the increased risk for paternal (RR, 1.8) and maternal (RR, 1.6) smoking at home remained nonsignificant.     

Personally measured weekly exposure to NO2 and respiratory health among preschool children.

Nitrogen dioxide is known as a deep lung irritant. The aim of this study was to find out whether the relatively low ambient air NO2 concentrations in the northern city of Helsinki had an impact on the respiratory health of children. The association between personal exposure to ambient air NO2 and respiratory health was investigated in a 13-week follow-up study among 163 preschool children aged 3-6 yrs. Personal weekly average exposure to NO2 was measured by passive diffusion samplers attached to the outer garments. Symptoms were recorded daily in a diary by the parents. Among 53 children, peak expiratory flow (PEF) was measured at home in the mornings and evenings. The association between NO2 exposure and respiratory symptoms was examined with Poisson regression. The median personal NO2 exposure was 21.1 microg x m(-3) (range 4-99 microg x m(-3)). An increased risk of cough was associated with increasing NO2 exposure (risk ratio = 1.52; 95% confidence interval 1.00-2.31). There was no such association between personal weekly NO2 exposure and nasal symptoms, but a nonsignificant negative association was found between the exposure and the weekly average deviation in PEF. In conclusion, even low ambient air NO2 concentrations can increase the risk of respiratory symptoms among preschool children.     

Impulse oscillometry vs. body plethysmography in assessing respiratory resistance in children

In 334 children aged 5-18 years, we compared the results of plethysmographic measurements of airway resistance (Raw) with oscillometric (impulse oscillometry; IOS) assessment of respiratory properties of the respiratory system (resistance (R) at 5, 20, and 35 Hz). All three resistances correlated significantly with plethysmographic Raw, and the strongest correlation was seen for R5 (r = 0.64). R5, R20, and R35 were significantly greater than Raw in the whole group. In the group of children with obstruction (FEV(1)%FVC below lower limit of normal), R5 was still greater than Raw, while R20 and R35 were not. The Bland-Altman analysis comparing plethysmographic measurements with oscillometric R5 revealed a significant difference between Raw and R5 in the whole group, which disappeared in the group of obstructed patients. Oscillometric assessment of resistive properties of the respiratory system of the lung requires less patient cooperation than does plethysmography. As the results of measurements using oscillometric R5 are similar to those obtained by plethysmography, IOS may be useful in diagnosing children with obstructive respiratory diseases.     

Significant association between outdoor NO2 and respiratory symptoms in preschool children

A study on 1225 preschool children was conducted in four regions of Switzerland with different levels of air pollution to investigate the relationship between air pollution and respiratory symptoms. Daily symptoms were recorded by parents on a diary form and air pollution exposure assessed by personal NO₂ samplers. Each family participated for 6 weeks and personal samplers were changed every week. The frequency of respiratory symptoms per child and day was found to increase with increasing levels of NO₂ measured outdoors. This relationship remained significant in a multiple regression model in which the factors smoking, origin, indoor air pollution, age and sex, season, and parents appreciation of air pollution at the living site were taken into account.     

Measurement of airway resistance using the interrupter technique in preschool children in the ambulatory setting.

This study describes the feasibility, repeatability, and interrater reliability of the measurement of airway resistance by the interrupter technique (Rint) in children 2-5 yrs of age, and examines whether reversibility to bronchodilator can be demonstrated in wheezy children. The mean of six Rint values was taken as a measurement. If subjects could complete one measurement and then a second 15 min after bronchodilator, baseline testing and reversibility testing were considered feasible. To measure repeatability, two measurements 30 s apart and measurements before and 15 min after placebo bronchodilator were compared. Measurements by two testers were compared for interrater reliability. Change in Rint in wheezy children was measured after bronchodilator. Fifty-six per cent of 2-3-yr-olds (n=79), 81% of 3-4-yr-olds (n=104) and 95% of 4-5-yr-olds (n=88) completed baseline testing, and 53%, 71% and 91% completed reversibility testing. Baseline measurements were 0.47-2.56 kPa x L(-1) x s. Repeatabilities (2 SD of the mean differences between measurements) at 30 s in the three age bands were 0.21, 0.17 and 0.15 kPa x L(-1) x s and 0.19 kPa x L(-1) x s after placebo. Using 0.21 kPa x L(-1) x s as the threshold for reversibility, reversibility was demonstrated in most wheezy children. Interrater reliability was 0.15 kPa x L(-1) x s. Preschool children can undertake measurements of airway resistance by the interrupter technique in ambulatory settings and reversibility to bronchodilator in wheezy children can be demonstrated. This technique promises to be a useful clinical and research tool.     

Interrupter resistance in preschool children: measurement characteristics and reference values

There is a need for quick, reliable, and noninvasive lung function tests to assess airway obstruction in preschool children both for pediatric pulmonary care as well as for research purposes. We studied feasibility, reproducibility, and validity of measurements of the respiratory system using the interrupter technique (interrupter resistance [Rint]) and obtained reference values in children from a general population, 2 to 7 yr of age. Accuracy was studied by comparisons of Rint with plethysmographic airway resistance (Raw) in 20 patients (7 to 14 yr) with mild to severe chronic airways obstruction and was satisfactory in patients with FEV(1) > 60% predicted. The technique proved sensitive enough to detect changes in airway caliber within a small group of 12 children who developed mild respiratory tract infections. Among children from a general population, subgroups with mild respiratory symptoms or mild respiratory disease had higher mean Rint values. Airway obstruction was better detected using expiratory rather than inspiratory interruptions, both programmed at peak tidal ventilatory flow. Reproducibility within subjects was satisfactory (intraclass correlation 0.82 and 0.79). The same applied to interobserver agreement (intraclass correlation 0.98). The interrupter technique proves to be a reliable and practical test of airway function, suitable for clinical and epidemiologic studies in preschool children.     

Density dependence of the maximal expiratory flow volume curves in normal and asthmatic children.

We have studied the maximal expiratory flow volume curves with air and with an 80% helium-oxygen mixture, using 12 normal and 33 asthmatic children chosen according to clinical, functional and immunological criteria. In the normal children, the average delta Vmax (difference between the maximal flow in HeO2 and in air at corresponding lung volumes) was 49% and was similar from 60% to 20% of vital capacity. The iso flow volume (lung volume level at which the HeO2 and air flow volume curves intersect) was 3% of vital capacity. Eleven of the asthmatics were non-responders to the helium mixture (no significant differences in flow between HeO2 and air curves), five at 50% and 25% VC and six at only 25% VC. The other 22 asthmatics were responders, but nine of them showed a rise of the iso flow volume. Eight subjects showed no obstruction according to the flow volume curves in air; three of these had an abnormal response to the helium mixture. All the non-responders at 50% VC and half of the non-responders at 25% VC had a clinical history of recurrent infections. These results suggest, firstly, that when there is no history of recurrent infections, the site of obstruction in asthmatic children is mainly central. This does not exclude a coexisting peripheral obstruction which could persist after recovery of the central component. Secondly, by studying the HeO2 response at 25% VC, we can get more information than by measuring only the delta Vmax50 or iso flow volumes.     

The low-frequency dependence of respiratory system resistance and elastance in normal dogs

The resistance (R) and elastance (E) of the respiratory system were determined by fitting the equation: pressure = R x flow + E x volume to data obtained from normal anesthetized/paralyzed dogs during mechanical ventilation at different frequencies (5 to 50 breaths per min) and tidal volumes. R exhibited a 50% decrease with increasing frequency while E showed a less marked but still distinct increase with frequency. Volume-time profiles were also recorded in the same animals during passive expiration, and the frequency dependence of resistance and elastance from 0 to 1 Hz predicted from the bi-exponential curves fitted to the profiles. The way in which resistance and elastance were predicted to vary with frequency was similar to the variations determined from regular ventilation data. There were, however, some systematic differences between the actual values of resistance and elastance obtained by the two methods which may reflect certain nonlinear characteristics of the respiratory system such as static hysteresis. Nonlinearities were also evident in that both the resistances and the elastances at all frequencies showed a slight decrease with increasing tidal volume. We conclude that a large part of the mechanical behaviour of the normal canine respiratory system at low frequencies can be accounted for in terms of a two-compartment model describing a homogeneous alveolar region surrounded by viscoelastic tissue.     

A portable device based on the interrupter technique for measuring airway resistance in preschool children.

The interrupter technique for measuring airway resistance is a noninvasive method reported to require minimal subject cooperation. Therefore it has a good potential for use in young children who are not able to cooperate with conventional lung function tests. The interrupter method is based on transient interruption of airflow at the mouth for a brief period during which alveolar pressure equilibrates with mouth pressure. In order to investigate the compliance rate with the interrupter technique in preschool children and to look for associated baseline measures of RINT we performed a study in 214 children of ages from 3 months to 5 years. There was a significant inverse correlation between baserint and age (r = -0.672, p<0.001), and standing height (r = -0.692, p<0.001) in children with recurrent wheezing. However, this was not seen in healthy children. We concluded that the portable interrupter device is very useful in preschool children. The measurements showed that the age and standing height are inversely proportional to the baseline RINT values measured. We reported that these differences would be more apparent in children with a history of recurrent wheezing.     

Normal values for forced oscillatory respiratory resistance in children

Forced oscillatory respiratory resistance was measured in 138 healthy children aged 2- to 16-years-old using a commercial unit. Regression analysis was performed using the resistance measurements obtained at frequencies of 6 Hz and 26 Hz and averages of measurements obtained at frequencies of from 6-26 Hz, 6-10 Hz, and 22-26 Hz. The analysis suggested that regression curves and 95% confidence intervals obtained using a quadratic model with height as the independent variable provided the best prediction of normal values and their ranges. Three independent sets of resistance measurements, which were obtained for all 138 subjects, were used to calculate the average individual coefficients of variation (CV) for the five resistance parameters noted above; these ranged from 9 to 13%. This analysis suggested that the expected CV of repeated measurements would be about 10%. Finally, values from 13 children who had asthma with mild bronchial obstruction (FEV1 less than 80% of predicted) were compared with the normal values derived from the regression curves. Values from all but two of the children fell within the reference intervals, suggesting that FEV1 may be a more sensitive measure of obstruction than forced oscillatory resistance. The main applications of this new approach may be in the evaluation of young children, in following individual patients, and in bronchodilation and bronchial challenge tests.     

Effect of tidal volume on respiratory system elastance and resistance during anesthesia and paralysis.

Recent studies have shown that the mechanical properties of the respiratory system at normal breathing frequency in awake humans depend on tidal volume. Few measurements of respiratory system properties during anesthesia have accounted for this dependence. From measurements of airway pressure, flow and esophageal pressure, we calculated elastances and resistances of the total respiratory system (Ers and Rrs), chest wall (Ecw and Rcw), and lungs (El and Rl) in supine human volunteers during quasisinusoidal volume forcing in a normal range of breathing (250 to 800 ml) at normal breathing frequency (0.2 Hz). Measurements were made (1) with subjects awake and voluntarily relaxed; (2) after isoflurane-N2O anesthesia (end-tidal isoflurane concentration 0.3 to 0.5%); and (3) after complete muscle paralysis with vecuronium. In all conditions, Ers, Ecw, El, Rrs, and Rcw decreased at 800 ml tidal volume compared with 250 ml; Rl showed a similar decrease in awake measurements only. Compared with awake measurements, each elastance tended to increase after anesthesia, but only the increase in Ers was significant. Compared with anesthesia, there was no effect of paralysis on any measurement. We conclude that (1) tidal volume dependence of respiratory system properties in the normal range of breathing occurs in the absence of muscle activity; (2) anesthesia increases Ers and (3) respiratory muscle activity appears to be inhibited by isoflurane-N2O anesthesia at end-tidal isoflurane concentration of 0.3 to 0.5% during normocapnia.