Use of specific airway resistance to assess bronchodilator response in children

Longitudinal assessment of loss and gain of lung function in childhood asthma

OBJECTIVE

The Childhood Asthma Management Program revealed that 25.7% of children with mild to moderate asthma exhibit loss of lung function. The objective was to assess the trajectories of function by means of serial FEV₁ in asthmatic children participating in out-of-hospital follow-up.

METHODS

A total of 295 children (199 boys) who had undergone at least 10 spirometry tests from the age of 8 were selected from a single-center open cohort. The annualized rate of change (slope) for prebronchodilator FEV₁ (percent predicted) was estimated for each participant and three patterns were defined: significantly positive slope, significantly negative slope, and null slope (non-significant P-value; Pearson test). The standard deviation (SD) of each individual slope was recorded as a variability criterion of FEV₁.

RESULTS

The median (25^th; 75^th percentile) age at inclusion and the last visit was 8.5 (8.2; 9.3) and 15.4 (14.8, 16.0) years, respectively. Tracking of function (null slope) was observed in 68.8% of the children, while 27.8% showed a loss of function or reduced growth (negative slope) and 3.4% showed a gain in function (positive slope). The children characterized by loss of function depicted a better initial function and a lower FEV₁ variability during their follow-up than children with tracking or gain of lung function. At the last visit, these children were characterized by a lower lung function than children with tracking or gain of lung function.

CONCLUSION

Better initial FEV₁ value and less FEV₁ variability are associated with loss of lung function or reduced lung growth in asthmatic children.

Relationship between baseline and post-bronchodilator interrupter resistance and specific airway resistance in preschool children

BACKGROUND

The assessment of airway function in preschool children can be done using simple measurement techniques such as interrupter resistance (Rint) or specific airway resistance (sRaw).

OBJECTIVE

The aim of the study was to assess the relationship and the agreement between Rint and sRaw baseline measurements expressed in z-score and bronchodilator response (BDR) in accordance with the latest reference equations and recommended procedures.

METHODS

One hundred thirty children aged 3 to 6 years old, referred to our pediatric pulmonary function test unit for assessment of airway function were consecutively included. Children performed baseline and post-bronchodilator measurements of Rint and sRaw.

RESULTS

One hundred twenty baseline measurements were obtained (98.7%) with both techniques. At baseline there was a strong correlation between Rint and sRaw z-score (r = 0.5, P < .01) despite the poor agreement (Cohen Kappa coefficient 0.09 [-0.08; 0.26]). The agreement for BDR was fair, with Cohen Kappa coefficient (95% IC) = 0.33 (0.13; 0.54). Children with poorly or partially controlled asthma had both higher baseline Rint and sRaw (P < .01), and higher post-bronchodilator mean change (P < .01), than children with well-controlled asthma.

CONCLUSION

The poor agreement between the Rint and sRaw reference measurements demonstrates the lack of reliability of sole Rint or sRaw technique for airway obstruction diagnosis and the need to perform each technique concomitantly with BDR test. Other longitudinal and larger sample studies are needed to confirm the threshold value for a positive BDR, especially for sRaw.

Flow dependence of specific airway resistance and diagnostic of asthma in children

Panting majors turbulent flow and contribution of larger airways to the measurement of specific airway resistance (sRaw). The hypothesis was tested that the difference between asthmatic and healthy children is enhanced by narrowing the flow interval to compute sRaw. sRaw was measured during panting in 40 asthmatic and 25 healthy children and computed using all data points (full scale flow) and limited to the flow intervals ± 1L/sec and ± 0.5 L/sec. sRaw was not different between asthmatics (0.87 ± 0.20 kPa.s) and controls (0.80 ± 0.25 kPa.s) when computed full scale, while it was significantly larger in asthmatics than controls within ± 1L/sec (0.77 ± 0.16 kPa.s vs 0.65 ± 0.15 kPa.s, P < 0.004) or ± 0.5 L/sec (0.77 ± 0.21 kPa.s vs 0.61 ± 0.17 kPa.s, P < 0.002). On the other hand, the within subject coefficient of variation was significantly larger when sRaw was computed within ± 1L/sec (13.7 ± 7.2%) or ± 0.5 L/sec (28.3 ± 18.1%) than full scale (11.0 ± 6.7%), respectively P < 0.002 and P < 0.0001. It is concluded that narrowing the flow interval to compute sRaw is associated with better discrimination between asthma and health in children, although the short term variability of sRaw is increased.

Total specific airway resistance vs spirometry in asthma evaluation in children in a large real-life population

BACKGROUND

Total specific airway resistance (sRtot) has been introduced as an alternative technique to assess lung function with a particular application to younger children with asthma.

OBJECTIVE

To establish a diagnostic value of the body plethysmographic parameter (sRtot) in asthma diagnosis in young children.

METHODS

This was a prospective, noninterventional study. Children 4 to 18 year old with symptoms suggestive of asthma were included (n = 885). Subjects underwent body plethysmography and spirometry (when capable) with reversibility tests. Of 788 subjects who could perform spirometry in addition to body plethysmography, 578 were diagnosed with asthma. Subjects with asthma were treated for minimum of 6 months and then their asthma was confirmed or refuted.

RESULTS

In 471 patients, asthma diagnosis was confirmed after 6 months of antiasthmatic treatment; 142 patients were 4 to 6 years old and 329 were 7 to 18 years old. Change in response to bronchodilator in children with asthma was significant for sRtot (P = .02) but not for forced expiration volume in 1 second (P = .21); sRtot was more sensitive and specific in identifying children with reversible obstruction than spirometry. There was a significant association between sRtot and asthma diagnosis in patients 4 to 6 years old (odds ratio 1.02, 95% confidence interval 1.01-1.03, P = .001); to differentiate subjects with asthma from those without asthma, the optimal cutoff point for sRtot was 174.5%. A sRtot value higher than 174.5% was associated with a positive prediction of an asthma diagnosis in patients 4 to 6 years old. A ratio of forced expiration volume in 1 second to forced vital capacity below 80% was not significantly associated with asthma.

CONCLUSION

These data support the recommendation of performing sRtot rather than spirometry in young children as a fairly sensitive marker of asthma.

TRIAL REGISTRATION

www.ClinicalTrials.gov (NCT01805635).

Airways resistance and specific conductance for the diagnosis of obstructive airways diseases

BACKGROUND

Airway resistance (RAW) and specific airway conductance (sGAW) are measures that reflect the patency of airways. Little is known of the variability of these measures between different lung diseases. This study investigated the contribution of RAW and sGAW to a diagnosis of obstructive airways disease and their role in differentiating asthma from COPD.

METHODS

976 subjects admitted for the first time to a pulmonary practice in Belgium were included. Clinical diagnoses were based on complete pulmonary function tests and supported by investigations of physicians' discretion. 651 subjects had a final diagnosis of obstructive diseases, 168 had another respiratory disease and 157 subjects had no respiratory disease (healthy controls).

RESULTS

RAW and sGAW were significantly different (p < 0.0001) between obstructive and other groups. Abnormal RAW and sGAW were found in 39 % and 18 % of the population, respectively, in which 81 % and 90 % had diagnosed airway obstruction. Multiple regression revealed sGAW to be a significant and independent predictor of an obstructive disorder. To differentiate asthma from COPD, RAW was found to be more relevant and statistically significant. In asthma patients with normal FEV1/FVC ratio, both RAW and sGAW were more specific than sensitive diagnostic tests in differentiating asthma from healthy subjects.

CONCLUSIONS

RAW and sGAW are significant factors that contribute to the diagnosis and differentiation of obstructive airways diseases.

[Body plethysmography (I): Standardisation and quality criteria]

Whole body plethysmography is used to measure lung volumes, capacities and resistances. It is a well standardised technique, and although it is widely used in paediatric chest diseases units, it requires specific equipment, specialist staff, and some cooperation by the patient. Plethysmography uses Boyle's law in order to measure the intrathoracic gas volume or functional residual capacity, and once this is determined, the residual volume and total lung capacity is extrapolated. The measurement of total lung capacity is necessary for the diagnosis of restrictive diseases. Airway resistance is a measurement of obstruction, with the total resistance being able to be measured, which includes chest wall, lung tissue and airway resistance, as well as the specific airway resistance, which is a more stable parameter that is determined by multiplying the measured values of airway resistance and functional residual capacity. The complexity of this technique, the reference equations, the differences in the equipment and their variability, and the conditions in which it is performed, has led to the need for its standardisation. Throughout this article, the practical aspects of plethysmography are analysed, specifying recommendations for performing it, its systematic calibration and the calculations that must be made, as well as the interpretation of the results obtained. The aim of this article is to provide a better understanding of the principles of whole body plethysmography with the aim of optimising the interpretation of the results, leading to improved management of the patient, as well as a consensus among the speciality.

Alternative functional criteria to assess airflow-limitation reversibility in asthma

INTRODUCTION

International guidelines define significant bronchodilator response as absolute and percentage change from baseline in forced expiratory volume (FEV1) in the first second and/or forced vital capacity (FVC) ≥12% and 200 mL. However, bronchodilator effects on other lung function parameters have also been correlated to some degree of reversible airflow limitation.

OBJECTIVES

To determine whether changes in other lung function parameters apart from FEV1 and FVC detect functional responses to bronchodilator in asthmatic patients.

MATERIALS AND METHODS

Spirometry and body plethysmography were performed at baseline conditions and after administration of 400 μg of salbutamol by metered-dose inhaler through a space chamber device in asthmatic patients. Paired t-tests were used to compare lung function parameters between those with and without criteria for reversibility of airway obstruction according to ATS/ERS criteria. Cut-off values were obtained from the corresponding ROC curves. Measurements evaluated were FEV1, FVC, maximum mid-forced expiratory flow (FEF25-75%), residual volume (RV), inspiratory capacity (IC), airway resistance (Raw) and specific airway conductance (sGaw).

RESULTS

From a total of 100 consecutive asthmatics patients (46% of them men; average age 58.7±14.1 years; 76% with mild to moderate obstruction), 50 patients had a significant bronchodilator response. All of these had noteworthy variations (p<0.004) in PEF, FEF25-75%, RV, Raw and sGaw. The most accurate in predicting a significant bronchodilator response were the absolute and percentage improvements in PEF (≥0.4 L/s and 8%), FEF25-75% (≥0.087 L/s and 27%) and the percentage of sGaw compared with that at baseline (≥25%). Based on these cut-off values, a sizeable number of the patients defined as non-responders had important changes in airway caliber. 17 patients had significant increments in the percentage of PEF and 10 had changes in absolute volume; 6 patients had increments in percentage and 16 in absolute change of FEF25-75%; 22 patients had increments in the percentage change of sGaw.

CONCLUSIONS

Changes of FEV1 and/or FVC may underestimate significant functional response to bronchodilators in asthmatic patients with airway obstruction when considering the change in other lung function parameters.

WITHDRAWN: Alternative functional criteria to assess airflow-limitation reversibility in asthma

This article has been withdrawn for editorial reasons because the journal will be published only in English. In order to avoid duplicated records, this article can be found at http://dx.doi.org/10.1016/j.rppnen.2014.08.002. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Forced expiratory flows' contribution to lung function interpretation in schoolchildren

Forced expiratory flow (FEF) at low lung volumes are supposed to be better at detecting lung-function impairment in asthmatic children than a forced volume. The aim of this study was to examine whether FEF results could modify the interpretation of baseline and post-bronchodilator spirometry in asthmatic schoolchildren in whom forced expiratory volumes are within the normal range. Spirometry, with post-bronchodilator vital capacity within 10% of that of baseline in healthy and asthmatic children, was recorded prospectively. We defined abnormal baseline values expressed as z-scores <-1.645, forced expiratory volume in 1 s (FEV1) reversibility as a baseline increase >12%, FEF reversibility as an increase larger than the 2.5th percentile of post-bronchodilator changes in healthy children. Among 66 healthy and 50 asthmatic schoolchildren, only two (1.7%) children with normal vital capacity and no airways obstruction had abnormal baseline forced expiratory flow at 25-75% of forced vital capacity (FEF25-75%). After bronchodilation, among the 45 asthmatic children without FEV1 reversibility, 5 (11.1%) had an FEF25-75% increase that exceeded the reference interval. Isolated abnormal baseline values or significant post-bronchodilator changes in FEF are rare situations in asthmatic schoolchildren with good spirometry quality.

Diagnostic value of lung function parameters and FeNO for asthma in schoolchildren in large, real-life population

BACKGROUND AND OBJECTIVE

To establish a diagnostic value of fractional exhaled nitric oxide (FeNO), interrupter resistance measurement (Rint), specific resistance of the airways (sRaw), spirometric parameters in asthma diagnosis in schoolchildren.

METHODS

It was a retrospective, cross-sectional study. We evaluated data from medical documentation of 6,439 children (aged 6-18) with symptoms suggestive of asthma, who attended our Pediatric Allergic Outpatient Clinic. Medical documentation of the patients was analyzed with special attention to the first ever obtained results (before the introduction of controller medication) of: FeNO, Rint, sRaw, spirometry, diagnoses of allergic diseases, and allergen sensitization (specific IgE results).

RESULTS

We included 3,612 children in the analysis. Older age, male gender, the presence of allergic rhinitis, sensitization to perennial and seasonal allergens, higher FeNO and Rint, and FEV1 /FVC <80% were significantly associated with asthma. We observed a significant association between FeNO and Rint in the prediction of asthma diagnosis. Optimal cutoff points to differentiate asthmatics from non-asthmatics were established. Thus, Rint >175.4% was defined as asthma-predicting Rint, and FeNO >15.8 ppb was defined as asthma-predicting FeNO. In all study subgroups, sensitivity for asthma-predicting Rint was significantly higher than for asthma-predicting FeNO with an inverse trend in specificity value.

CONCLUSION

Our results suggest that asthma-predicting Rint and, to a lesser extent, asthma-predicting FeNO, defined in the present study, could serve as a reliable tool to exclude asthma in schoolchildren. However, our results also indicate a clinically important fact that all lung function parameters or FeNO should be interpreted in the context of age, gender, allergy profile, and the presence of co-morbidities in schoolchildren. Pediatr Pulmonol. 2014; 49:632-640. © 2013 Wiley Periodicals, Inc.

Inspiratory high frequency airway oscillation attenuates resistive loaded dyspnea and modulates respiratory function in young healthy individuals

Direct chest-wall percussion can reduce breathlessness in Chronic Obstructive Pulmonary Disease and respiratory function may be improved, in health and disease, by respiratory muscle training (RMT). We tested whether high-frequency airway oscillation (HFAO), a novel form of airflow oscillation generation can modulate induced dyspnoea and respiratory strength and/or patterns following 5 weeks of HFAO training (n = 20) compared to a SHAM-RMT (conventional flow-resistive RMT) device (n = 15) in healthy volunteers (13 males; aged 20–36 yrs). HFAO causes oscillations with peak-to-peak amplitude of 1 cm H₂O, whereas the SHAM-RMT device was identical but created no pressure oscillation. Respiratory function, dyspnoea and ventilation during 3 minutes of spontaneous resting ventilation, 1 minute of maximal voluntary hyperventilation and 1 minute breathing against a moderate inspiratory resistance, were compared PRE and POST 5-weeks of training (2×30 breaths at 70% peak flow, 5 days a week). Training significantly reduced NRS dyspnoea scores during resistive loaded ventilation, both in the HFAO (p = 0.003) and SHAM-RMT (p = 0.005) groups. Maximum inspiratory static pressure (cm H₂O) was significantly increased by HFAO training (vs. PRE; p<0.001). Maximum inspiratory dynamic pressure was increased by training in both the HFAO (vs. PRE; p<0.001) and SHAM-RMT (vs. PRE; p = 0.021) groups. Peak inspiratory flow rate (L.s⁻¹) achieved during the maximum inspiratory dynamic pressure manoeuvre increased significantly POST (vs. PRE; p = 0.001) in the HFAO group only. HFAO reduced inspiratory resistive loading–induced dyspnoea and augments static and dynamic maximal respiratory manoeuvre performance in excess of flow-resistive IMT (SHAM-RMT) in healthy individuals without the respiratory discomfort associated with RMT.

Specific airway resistance in children: panting or tidal breathing?

BACKGROUND

The measurement of specific airway resistance during tidal breathing (sRaw(tb)) has gained popularity in children, but methodological concerns have been raised regarding the electronic compensation for the thermal artifact. The panting method (sRaw(p)) is efficient in minimizing the latter, but may be associated with a change in end expiratory lung volume if the effort is not properly balanced. The aim of the study was to compare sRaw(tb) with sRaw(p) in children.

METHODS

Fifty-five children aged 6.5-11.5 years were studied. sRaw(tb) was measured in a commercial plethysmograph. sRaw(p) was measured with a home made equipment that allowed breath by breath analysis (sRaw(p1)) as well as with the commercial body box (sRaw(p2)).

RESULTS

sRaw(tb) was significantly larger than either sRaw(p1) or sRaw(p2) (P < 0.0001). The mean (95% CI) difference sRaw(p1)  - sRaw(tb) was -0.374 (-0.835 to 0.088) kPa s. The difference between sRaw(p1) and sRaw(p2) was significant (P < 0.005) but not clinically relevant, and mean (95% CI) difference sRaw(p1) - sRaw(p2) was 0.115 (-0.094 to 0.324) kPa s. The breath by breath analysis showed small but significant increase in sRaw(p1) throughout the maneuver (P < 0.001), whatever the pattern of end expiratory level.

CONCLUSION

Tidal breathing is associated with an overestimation of sRaw compared with panting in children. Although the latter results in small increase throughout the panting maneuver, sRaw(p) is probably more trustful than sRaw(tb).

[Physiological characteristics associated with previous control in asthmatic children]

OBJECTIVE

To analyze MEF(50%) (central airways), RV/TLC (distal airways), reversibility of FEV(1) (bronchial tone, REV(FEV1)) and FE(NO) (inflammation) in relation to clinical events in asthmatic children on the assumption that mild symptoms and severe exacerbations in the previous 3 months could be associated with distinct functional characteristics.

PATIENTS AND METHODS

A retrospective, single center, out-patient hospital study including all asthmatic children who had complete lung function testing (without and with bronchodilation) during a period of clinical stability, without treatment on the day of the test.

RESULTS

Two hundred and forty-five children (11.4±2.4 years) were included: 114 (46%) were asymptomatic, 87 (36%) had minor symptoms and 44 (18%) had had a severe exacerbation in the past 3 months. FEV(1), FEV(1)/FVC and MEF(50%) were not different in these three groups. REV(FEV1) was higher in the symptomatic than in the asymptomatic group (P=0.019), RV/TLC was greater in the exacerbation group than in the asymptomatic group (P=0.019), and FE(NO) was higher in the symptomatic group than in the asymptomatic and exacerbation groups (P=0.006).

CONCLUSIONS

In asthmatic children, minor symptoms and severe exacerbation in the previous 3 months are associated with distinct functional characteristics that are not detected by single baseline spirometry without treatment on the day of testing.

Exhaled nitric oxide and clinical phenotypes of childhood asthma

Whether exhaled NO helps to identify a specific phenotype of asthmatic patients remains debated. Our aims were to evaluate whether exhaled NO (FENO(0.05)) is independently associated (1) with underlying pathophysiological characteristics of asthma such as airway tone (bronchodilator response) and airway inflammation (inhaled corticosteroid [ICS]-dependant inflammation), and (2) with clinical phenotypes of asthma.We performed multivariate (exhaled NO as dependent variable) and k-means cluster analyses in a population of 169 asthmatic children (age ± SD: 10.5 ± 2.6 years) recruited in a monocenter cohort that was characterized in a cross-sectional design using 28 parameters describing potentially different asthma domains: atopy, environment (tobacco), control, exacerbations, treatment (inhaled corticosteroid and long-acting bronchodilator agonist), and lung function (airway architecture and tone). Two subject-related characteristics (height and atopy) and two disease-related characteristics (bronchodilator response and ICS dose > 200 μg/d) explained 36% of exhaled NO variance. Nine domains were isolated using principal component analysis. Four clusters were further identified: cluster 1 (47%): boys, unexposed to tobacco, with well-controlled asthma; cluster 2 (26%): girls, unexposed to tobacco, with well-controlled asthma; cluster 3 (6%): girls or boys, unexposed to tobacco, with uncontrolled asthma associated with increased airway tone, and cluster 4 (21%): girls or boys, exposed to parental smoking, with small airway to lung size ratio and uncontrolled asthma. FENO(0.05) was not different in these four clusters.In conclusion, FENO(0.05) is independently linked to two pathophysiological characteristics of asthma (ICS-dependant inflammation and bronchomotor tone) but does not help to identify a clinically relevant phenotype of asthmatic children.