Search

Background and objective Selecting ‘healthy’ preschool-aged children for reference ranges may not be straightforward. Relaxing inclusion criteria for normative data does not affect spirometry z-scores. We therefore investigated the effect of similarly relaxing inclusion criteria in preschoolers on reference ranges for respiratory impedance (Zrs) using a modified forced oscillation technique (FOT). Methods The International Study of Asthma and Allergies in Childhood questionnaire classified 585 children into a healthy and five mutually exclusive groups. Zrs was measured between 4 and 26 Hz and resistance (R) and compliance (C) obtained by model fitting. Prediction models were determined using mixed effect models and z-scores compared between healthy children and the five groups. Results Zrs data were obtained for 494 participants (4.30 ± 0.7 years) on 587 occasions. Comparison of the Zrs z-scores between the healthy children and the health groups found significant differences in children with asthma, current wheeze and respiratory symptoms, but not in children born preterm or with early-life wheeze. Adding these two groups to the healthy dataset had no significant effect on the distribution of z-scores and increased the size of the dataset by 22.3%. Conclusion Our data suggest that preschool-aged children born preterm or with early-life wheeze can be included in FOT reference equations, while those with asthma, current wheeze and respiratory symptoms within 4 weeks of testing should be excluded. This more inclusive approach results in more robust FOT reference ranges.

Background Low lung function in early life is associated with later respiratory illness. There is limited data on lung function in African infants despite a high prevalence of respiratory disease. Aim To assess the determinants of early lung function in African infants. Method Infants enrolled in a South African birth cohort, the Drakenstein child health study, had lung function measured at 6–10 weeks of age. Measurements, made with the infant breathing via a facemask during natural sleep, included tidal breathing, sulfur hexafluoride multiple breath washout and the forced oscillation technique. Information on antenatal and early postnatal exposures was collected using questionnaires and urine cotinine. Household benzene exposure was measured antenatally. Results Successful tests were obtained in 645/675 (95%) infants, median (IQR) age of 51 (46–58) days. Infant size, age and male gender were associated with larger tidal volume. Infants whose mothers smoked had lower tidal volumes (−1.6 mL (95% CI −3.0 to −0.1), p=0.04) and higher lung clearance index (0.1 turnovers (95% CI 0.01 to 0.3), p=0.03) compared with infants unexposed to tobacco smoke. Infants exposed to alcohol in utero or household benzene had lower time to peak tidal expiratory flow over total expiratory time ratios, 10% (95% CI −15.4% to −3.7%), p=0.002) and 3.0% (95% CI −5.2% to −0.7%, p=0.01) lower respectively compared with unexposed infants. HIV-exposed infants had higher tidal volumes (1.7 mL (95% CI 0.06 to 3.3) p=0.04) compared with infants whose mothers were HIV negative. Conclusion We identified several factors including infant size, sex, maternal smoking, maternal alcohol, maternal HIV and household benzene associated with altered early lung function, many of which are factors amenable to public health interventions. Long-term study of lung function and respiratory disease in these children is a priority to develop strategies to strengthen child health.

Lung function testing in early life can provide information on lung growth and development and can help clinicians in the decision making process. However, the techniques available in infants and preschool-age children are usually not adequately validated for these age groups. Understanding the impact of measurement conditions on the data is essential to achieving valid results. Infant lung function tests are still limited to research settings in highly specialized lung function laboratories and are not suited for the everyday clinical use. In contrast, tests in preschoolers are easy to perform; most of the tests only require minimal subject cooperation and can be undertaken as early as 3 years of age with high feasibility. The main limitations of these techniques are that they are more useful at detecting differences between groups of healthy children and children with lung disease, but they are not specific and sensitive enough to be utilized in individuals in the clinical practice. Interpretation of the results also requires comprehensive understanding of respiratory physiology. There are promising techniques in the focus of pediatric respiratory research in recent years that are likely to improve the clinical utility of lung function measurements during these critical years of lung development.

Background and objective: Non-invasive techniques for measuring lung mechanics in infants are needed for a better understanding of lung growth and function and to study the effects of prenatal factors on subsequent lung growth in healthy infants. The forced oscillation technique requires minimal cooperation from the individual but has rarely been used in infants. The study aims to assess the use of the forced oscillation technique to measure the influence of antenatal exposures on respiratory mechanics in unsedated infants enrolled in a birth cohort study in Cape Town South Africa. Methods: Healthy term infants were studied at 6-10 weeks of age using the forced oscillation technique. Respiratory impedance was measured in the frequency range 8-48 Hz via a face mask during natural sleep. Respiratory system resistance compliance and inertance were calculated from the impedance spectra. Results: Of 177 infants tested successful measurements were obtained in 164 (93%). Median (25-75%) values for resistance compliance and inertance were 50.2 (39.5-60.6) cmH2O.s.L-1 0.78 (0.61-0.99) mL.cmH2O-1 and 0.062 (0.050-0.086) cmH2O.s2.L-1 respectively. As a group male infants had 16% higher resistance (P = 0.006) and 18% lower compliance (P = 0.02) than females. Infants whose mothers smoked during pregnancy had a 19% lower compliance than infants not exposed to tobacco smoke during pregnancy (P = 0.005). Neither maternal HIV infection nor ethnicity had a significant effect on respiratory mechanics. Conclusions: The forced oscillation technique is sensitive enough to demonstrate the effects of tobacco smoke exposure and sex in respiratory mechanics in healthy infants. This technique will facilitate assessing perinatal influences of lung function in infancy. © 2015 Asian Pacific Society of Respirology.

The use of the forced oscillation technique (FOT) to assess within-breath respiratory mechanics has lead to new insights into airway obstruction (Czovek et al., Thorax, 2016), flow limitation and lung inhomogeneity (Lorx et al., ERJ2017) in adults and older children. Aim: To test within-breath respiratory mechanics in a South African birth cohort (Drakenstein study) for predicting lower respiratory tract illness (LRTI) during the first 6 months of life. Methods: The within-breath changes of respiratory resistance (R) and reactance (X) were measured at 16 Hz with a modified FOT during natural sleep in healthy infants at 6-10 weeks. The mean total R and X values, and the changes between end-expiration and end-inspiration (ΔR and ΔX) were calculated. LRTI surveillance was performed and any episode was confirmed by study staff. Results: Acceptable assessments of respiratory mechanics were available in 666 infants (50.1% male, median[IQR] gestational age: 39[37;40] w, length z-score: -0.76[-1.67;0.11]) of which 113 infants had 177 LRTI episodes in the first 6 months of life. From the impedance variables, ΔX and ΔR were significantly different between the two groups (p Conclusion: This study is the first to show that within-breath measures of respiratory mechanics in infants may predict susceptibility to LRTI. The altered ΔX in healthy infants suggests that lung inhomogeneity may be a predisposing factor for lung disease in early life. Wellcome Trust;Gates Foundation;HRF

Selecting 'healthy' preschool-aged children for reference ranges may not be straightforward. Relaxing inclusion criteria for normative data does not affect spirometry z-scores. We therefore investigated the effect of similarly relaxing inclusion criteria in preschoolers on reference ranges for respiratory impedance (Zrs) using a modified forced oscillation technique (FOT).The International Study of Asthma and Allergies in Childhood questionnaire classified 585 children into a healthy and five mutually exclusive groups. Zrs was measured between 4 and 26 Hz and resistance (R) and compliance (C) obtained by model fitting. Prediction models were determined using mixed effect models and z-scores compared between healthy children and the five groups.Zrs data were obtained for 494 participants (4.30 ± 0.7 years) on 587 occasions. Comparison of the Zrs z-scores between the healthy children and the health groups found significant differences in children with asthma, current wheeze and respiratory symptoms, but not in children born preterm or with early-life wheeze. Adding these two groups to the healthy dataset had no significant effect on the distribution of z-scores and increased the size of the dataset by 22.3%.Our data suggest that preschool-aged children born preterm or with early-life wheeze can be included in FOT reference equations, while those with asthma, current wheeze and respiratory symptoms within 4 weeks of testing should be excluded. This more inclusive approach results in more robust FOT reference ranges.

SUMMARY. Background:Lungfunctiondatainhealthynewborninfantsarescarcelargelydueto lack of suitable techniques, although data for developmental and prenatal exposure studies are much needed. We have modified the forced oscillation technique (FOT) for the measurement of respiratory mechanical impedance (Zrs) in unsedated sleeping infants in the first 3 days of life. Methods: Zrs was measured during 30-s epochs of quiet sleep in term neonates born via spontaneous vaginal delivery with a non-invasive FOT between 8 and 48Hz. Total respiratory resistance (R), compliance (C) and inertance (I) were obtained by fitting Zrs spectra. Cluster analysis was used to determine a set of minimal Zrs spectra representing optimal respiratory mechanics for each infant. Results: Successful measurements were obtained in each of the first 3 days in 30/38 (78.9%) neonates. Group mean (� SD) values of R, C, I, and resonant frequency pooled for the 3 days were 45.9 � 16.6hPasL � 1 , 0.97 � 0.21mlhPa � 1 , 0.082 � 0.031hPas 2 L � 1 and 19.2 � 3.2Hz, respectively. Within-session variability represented by coefficient of variation was 5.34 � 3.18% for R and 13.80 � 8.57% for C. Greater between-session variability was observed for the individual infants; however, the only statistically significant change over time was a 13% increase in R from day 1 to day 2. Parameter interdependence was significant (r 2 ¼0.63) between R and I reflecting thelarge contribution of theupper airways to the total Zrs. Conclusions: Noninvasive measurement of Zrs can be made in neonates during natural sleep with a high success rate, even in the first hours of life. Pediatr Pulmonol. 2014 Wiley Periodicals, Inc.

Tracking of the within-breath changes of respiratory mechanics using the forced oscillation technique may provide outcomes that characterise the dynamic behaviour of the airways during normal breathing.We measured respiratory resistance (Rrs) and reactance (Xrs) at 8 Hz in 55 chronic obstructive pulmonary disease (COPD) patients and 20 healthy controls, and evaluatedRrsandXrsas functions of gas flow (V′) and volume (V) during normal breathing cycles. In 12 COPD patients, additional measurements were made at continuous positive airway pressure (CPAP) levels of 4, 8, 14 and 20 hPa.TheRrsandXrsversus V′ andVrelationships displayed a variety of loop patterns, allowing characterisation of physiological and pathological processes. The main outcomes emerging from the within-breath analysis were theXrsversus Vloop area (AXV) quantifying expiratory flow limitation, and the tidal change inXrsduring inspiration (ΔXI) reflecting alteration in lung inhomogeneity in COPD. With increasing CPAP, AXV and ΔXIapproached the normal ranges, although with a large variability between individuals, whereas meanRrsremained unchanged.Within-breath tracking ofRrsandXrsallows an improved assessment of expiratory flow limitation and functional inhomogeneity in COPD; thereby it may help identify the physiological phenotypes of COPD and determine the optimal level of respiratory support.

The environmental disaster following flooding by red sludge in the Ajka region in Hungary poses a serious public health threat with particular concern regarding the potentially adverse respiratory effects of the inhalation of red sludge dust (RSD). The respiratory consequences of the inhalation of RSD obtained from field samples were investigated in rats. Rats were either exposed to RSD at a high concentration (2 weeks, 8h/day), or kept in room air. After the exposures, the airway resistance (R(aw)) and the respiratory tissues mechanics were measured under baseline condition, and following methacholine (MCh) challenges with the aim of establishing airway hyper-responsiveness (AH). Histopathology was performed to assess lung morphologic alterations. The physical properties and the chemical composition of the RSD were also characterized. The size distribution, chemical composition and topology of the RSD particles applied in our experiments were similar to those observed at the site of the disaster. The inhalation of RSD did not alter the basal respiratory mechanics, whereas it led to greater MCh-induced responses in R(aw), demonstrating the progression of mild AH. Histopathological investigations revealed fine, granular particles in the alveolar macrophages, as evidence that RSD had reached the lower respiratory tract and induced mild inflammation around the alveoli and the pulmonary vasculature. The mild respiratory symptoms that developed following short-term exposure of healthy individuals to high concentrations of airborne RSD do not appear to pose a greater respiratory hazard than the inhalation of urban dust at a comparable concentration.

Lower respiratory tract illness (LRTI) is a leading cause of mortality and morbidity in children. Sensitive and noninvasive infant lung function techniques are needed to measure risk for and impact of LRTI on lung health. The objective of this study was to investigate whether lung function derived from the intra-breath forced oscillation technique (FOT) was able to identify healthy infants at risk of LRTI in the first year of life. Lung function was measured with the novel intra-breath FOT, in 6-week-old infants in a South African birth cohort (Drakenstein Child Health Study). LRTI during the first year was confirmed by study staff. The association between baseline lung function and LRTI was assessed with logistic regression and odds ratios determined using optimal cut-off values. Of the 627 healthy infants with successful lung function testing, 161 (24%) had 238 LRTI episodes subsequently during the first year. Volume dependence of respiratory resistance (ΔR) and reactance (ΔX) was associated with LRTI. The predictive value was stronger if LRTI was recurrent (n=50 (31%): OR 2.5, ΔX), required hospitalisation (n=38 (16%): OR 5.4, ΔR) or was associated with wheeze (n=87 (37%): OR 3.9, ΔX). Intra-breath FOT can identify healthy infants at risk of developing LRTI, wheezing or severe illness in the first year of life., Novel measurements of respiratory mechanics are feasible in infants in a community setting and able to detect changes in lung function in healthy infants associated with increased risk of subsequent LRTI in infancy http://ow.ly/IUKk30mCfi3

Rationale Individual assessment of airway obstruction in preschool-age children requires sensitive and specific lung function methods with low demand of cooperation. Although the forced oscillation technique (FOT) is feasible in young children, conventional measurements of respiratory impedance (Zrs) have limited diagnostic power in individuals. Objective To find descriptors of within-breath Zrs that are sensitive indicators of airway obstruction during tidal breathing in children. Methods Zrs was measured with (i) a standard multifrequency FOT (4–26 Hz) to assess the mean values of resistance and reactance for whole breaths and (ii) a 10 Hz signal to track the within-breath changes. Various Zrs measures obtained in healthy children (n=75) and those with acute wheeze (n=31) were investigated with receiver operator characteristic (ROC) analysis. The cut-off values obtained for airway obstruction were then tested in children with recurrent wheeze (n=20) before and after administration of salbutamol. Results The largest area under the ROC curve (0.95) was observed for the tidal changes of resistance between the zero-flow values (ΔR). The ΔR cut-off value of 1.42 hPa s/L detected airway obstruction with sensitivity of 92% and specificity of 89% in children with acute wheeze and distinguished children with recurrent wheeze (16/20 above the cut-off value) from healthy children (22/23 below the cut-off value). Furthermore, ΔR significantly decreased after salbutamol in wheezy children but remained unchanged in healthy children. Conclusions New lung function measure ΔR is able to detect airway obstruction with high sensitivity and specificity and is suitable for use in lung function testing in young children.

The diagnostic value of FEV1 for assessing functional impairment in asthma has been debated, primarily because forced expiratory manoeuvres may alter bronchial tone. The forced oscillation technique (FOT) does not affect the baseline tone, thus may be a more appropriate tool to evaluate the bronchodilator response (BDR) in children. FOT and spirometry were performed before and after administration of 400 ug salbutamol in school-aged children with stable asthma. Mean R at 6 Hz (R6) was calculated for several breaths and the end-expiratory (ReE) and end-inspiratory (ReI) values at 10 Hz were also determined. Positive BDR was defined according to the guidelines. Four children had positive BDR with both the FOT and spirometry (Group 1, Table 1), 6 had positive BDR with FOT but not with FEV1 (Group 2) and 15 did not have a BDR with either technique (Group 3). Baseline ReE was elevated in Groups 1 and 2 as compared to Group 3 (p

Background: Even though laryngeal mask airways (LMAs) are the most commonly used airway in paediatric anaesthesia, little is known about the assessment of respiratory mechanics in this setting. Methods: We measured respiratory resistance (R) and reactance (X) with forced oscillations at 16 Hz superimposed on spontaneous breathing following induction of anaesthesia. Children between 1.3 and 5.6 years of age (n=20) with healthy respiratory status were studied. R and X were corrected for the impedance of the LMA and other equipment parts. Results: R exhibited large flow related fluctuations ([Fig. 1][1]) amounting on average to 169% and 180% in expiration and inspiration, while the changes in X were milder. Minimum R was attained at end expiration (10.2±3.6 hPa.s/L), much lower than the mean values for whole breaths (18.1±5.1 hPa.s/L). Fast flow transitions at end inspiration resulted in high R values (16.4±5.9 hPa.s/L). All R indices were significantly (r=-0.49 … -0.75) related to height. ![Figure][2] Conclusions: LMA introduces marked flow-related nonlinearities in R, making the conventional assessment of the lower respiratory tract difficult. However, within-breath tracking identifies the flow-independent values of R and can be instructive for the proper placement of LMA. Grant Support: HSRF (105403), NHMRC (APP1050427), ANZCA (AEG13/003) and Princess Margaret Hospital Foundation (9622). [1]: #F1 [2]: pending:yes

Background and objective Population-appropriate lung function reference data are essential to accurately identify respiratory disease and measure response to interventions. There are currently no reference data in African infants. The aim was to describe normal lung function in healthy African infants. Methods Lung function was performed on healthy South African infants enrolled in a birth cohort study, the Drakenstein child health study. Infants were excluded if they were born preterm or had a history of neonatal respiratory distress or prior respiratory tract infection. Measurements, made during natural sleep, included the forced oscillation technique, tidal breathing, exhaled nitric oxide and multiple breath washout measures. Results Three hundred sixty-three infants were tested. Acceptable and repeatable measurements were obtained in 356 (98%) and 352 (97%) infants for tidal breathing analysis and exhaled nitric oxide outcomes, 345 (95%) infants for multiple breath washout and 293 of the 333 (88%) infants for the forced oscillation technique. Age, sex and weight-for-age z score were significantly associated with lung function measures. Conclusions This study provides reference data for unsedated infant lung function in African infants and highlights the importance of using population-specific data.

Background Provocation tests are routinely used to detect airway hyperreactivity (AH) in the diagnosis of asthma. We compared the sensitivities of the forced oscillation technique (FOT) and spirometry in the detection of AH in asthmatic children. Methods FOT and spirometry were performed in 20 asthmatic children (aged 5–18 years) following aerosolized histamine and methacholine at an interval of 2 weeks. The respiratory system input impedance was measured by FOT; the resistance at 6 Hz (R6), the average resistance between 4 and 24 Hz, the area under the reactance curve (AX) and the resonant frequency were extracted from these recordings. Spirometry was used to obtain forced expiratory volumes and flow parameters. Results Following provocation with the two agonists, the FOT detected the airway response as early as spirometry. When the greater variability of the impedance parameters was taken into account, the two methods were observed to have similar sensitivities. Among the lung function parameters studied, AX and R6 were the most sensitive for the demonstration of AH. Conclusions Our findings demonstrate that FOT is as suitable as spirometry for the measurement of bronchoconstriction and thus it may be considered for the detection of AH in asthmatic children. Since its application requires minimal cooperation, this approach imposes less stress and may be particularly favorable in the diagnosis of asthma at a young age. Pediatr Pulmonol. 2012. 47:956–965. © 2012 Wiley Periodicals, Inc.

Introduction The slope of phase III of the capnogram (SIII) relates to progressive emptying of the alveoli, a ventilation/perfusion mismatch, and ventilation inhomogeneity. SIII depends not only on the airway geometry, but also on the dynamic respiratory compliance (Crs); this latter effect has not been evaluated. Accordingly, we established the value of SIII for monitoring airway resistance during mechanical ventilation. Methods Sidestream capnography was performed during mechanical ventilation in patients undergoing elective cardiac surgery (n = 144). The airway resistance (Raw), total respiratory resistance and Crs displayed by the ventilator, the partial pressure of arterial oxygen (PaO2) and SIII were measured in time domain (ST-III) and in a smaller cohort (n = 68) by volumetry (SV-III) with and without normalization to the average CO2 phase III concentration. Measurements were performed at positive end-expiratory pressure (PEEP) levels of 3, 6 and 9 cmH2O in patients with healthy lungs (Group HL), and in patients with respiratory symptoms involving low (Group LC), medium (Group MC) or high Crs (Group HC). Results ST-III and SV-III exhibited similar PEEP dependencies and distribution between the protocol groups formed on the basis of Crs. A wide interindividual scatter was observed in the overall Raw-ST-III relationship, which was primarily affected by Crs. Decreases in Raw with increasing PEEP were reflected in sharp falls in SIII in Group HC, and in moderate decreases in SIII in Group MC, whereas ST-III was insensitive to changes in airway caliber in Groups LC and HL. Conclusions SIII assessed in the time domain and by volumetry provide meaningful information about alterations in airway caliber, but only within an individual patient. Although ST-III may be of value for bedside monitoring of the airway properties, its sensitivity depends on Crs. Thus, assessment of the capnogram shape should always be coupled with Crs when the airway resistance or oxygenation are evaluated.