Breathing-related changes of respiratory resistance in vocal cord dysfunction.

Vocal cord dysfunction induced by exercise in children with uncontrolled asthma was identified by laryngoscopy. The paradoxical adduction of the vocal cords was also indicated by the breathing-related changes of the forced oscillation respiratory resistance showing prominent increase during inspiration and a large positive difference between inspiration and expiration. The breathing-related changes of respiratory resistance offer thus a useful first-line technique to diagnose vocal cord dysfunction.

Exercise-induced bronchoconstriction in school-age children born extremely preterm.

BACKGROUND: School children born preterm often show airway hyperresponsiveness to methacholine or histamine. Less attention has been paid to their airway response to exercise, an important point because of the role of exercise in the child's daily life. The aim of this study was to describe the characteristics of, and potential determinants to, the airway response to exercise in children born extremely preterm. METHODS: Forty-two nonasthmatic nonatopic children born before 32 wk gestation were compared with 27 healthy nonasthmatic nonatopic term children at age 7. Spirometry and respiratory impedance were measured at baseline and repeated after a single-step 6-min treadmill exercise in a climate-controlled room. RESULTS: The preterm group showed significant broncho-constriction induced by exercise. Prematurity, but not low baseline lung function, neonatal oxygen supplementation, mechanical ventilation, chronic lung disease, or maternal smoking, was a determinant of exercise-induced bronchoconstriction. CONCLUSION: Children born extremely preterm present significant exercise-induced airway obstruction at age 7. The response has different characteristics from that occurring in asthmatics and is likely to express airway noneosinophilic inflammation.

Unattended home sleep studies for the diagnosis of obstructive sleep apnea in a population of French children.

BACKGROUND: Ambulatory exams were preferred in children during the COVID-19 pandemic. Polysomnography (PSG), the gold standard for obstructive sleep apnea (OSA) diagnosis, requires several leads and sensors to be attached to the child's body. Children are more comfortable with respiratory polygraphic (RP) recording, which needs fewer sensors. OBJECTIVE: To compare respiratory parameters obtained by home RP with those obtained by home PSG with the device installed at the child's home by a trained sleep nurse from a national health care provider. METHODS: Data from home PSGs performed in children aged 2-19 years were retrospectively included. The obstructive apnea-hypopnea index (OAHI) was computed in PSG and then in RP after removing the sleep signals. The two indexes were compared using non-parametric paired Wilcoxon rank test, Bland-Altman analysis and sensitivity-specificity analysis. RESULTS: 44 PSGs of 44 children were included with only 34 (77%) PSGs interpretable. Median (min-max) OAHI was significantly underestimated in RP than in PSG (2.2 (0-25) vs 4.0 (0.4-28), p < 0.0001), confirmed also by the Bland-Altman diagram, the magnitude of the difference being mean ± standard deviation -1.7 ± 1.7. The sensitivity and specificity of OAHI in RP to identify an OAHI ≥2/h in PSG was 0.91 for both. CONCLUSION: Unattended ambulatory RP performed at child's house and installed under carefully controlled conditions is a useful exam for diagnosing OSA in children with or without comorbidities. However, RP must be installed in a supervised environment and interpreted with caution as it tends to underestimate OSA severity.

Outcomes at 7 Years of Age of Former Very Preterm Neonates with Repeated Surfactant Treatment for Prolonged Respiratory Distress in the Neonatal Period.

This study aimed at evaluating the 7-year outcomes of 118 very preterm newborns (VPNs, gestational age = 26 ± 1.4 w) involved in a randomized controlled trial. They presented neonatal respiratory distress (RDS), requiring ventilation for 14 ± 2 days post-natal age (PNA). A repeated instillation of 200 mg/kg poractant alfa (SURF) did not improve early bronchopulmonary dysplasia, but the SURF infants needed less re-hospitalization than the controls for respiratory problems at 1- and 2-year PNA. There was no growth difference at 7.1 ± 0.3 years between 41 SURF infants and 36 controls (80% of the eligible children), and 7.9% SURF infants vs. 28.6% controls presented asthma (p = 0.021). The children underwent cognitive assessment (WISC IV) and pulmonary function testing (PFT), measuring their spirometry, lung volume, and airway resistance. The spirometry measures showed differences (p < 0.05) between the SURF infants and the controls (mean ± standard deviation (median z-score)) for FEV1 (L/s) (1.188 ± 0.690(-0.803) vs. 1.080 ± 0.243 (-1.446)); FEV1 after betamimetics (1.244 ± 0.183(-0.525) vs. 1.091 ± 0.20(-1.342)); FVC (L) (1.402 ± 0.217 (-0.406) vs. 1.265 ± 0.267 (-1.141)), and FVC after betamimetics (1.452 ± 0.237 (-0.241) vs. 1.279 ± 0.264 (-1.020)). PFT showed no differences in the volumes or airway resistance. The global IQ median (interquartile range) was 89 (82:99) vs. 89 (76:98), with 61% of the children >85 in both groups. Repeated surfactant treatment in VPNs presenting severe RDS led to the attenuation of early lung injuries, with an impact on long-term pulmonary sequelae, without differences in neurodevelopmental outcomes.

Assessment of bronchial obstruction and its reversibility by shape indexes of the flow-volume loop in asthmatic children.

Asthma assessment by spirometry is challenging in children as forced expiratory volume in 1 s (FEV1) is frequently normal at baseline. Bronchodilator (BD) reversibility testing may reinforce asthma diagnosis but FEV1 sensitivity in children is controversial. Ventilation inhomogeneity, an early sign of airway obstruction, is described by the upward concavity of the descending limb of the forced expiratory flow-volume loop (FVL), not detected by FEV1. The aim was to test the sensitivity and specificity of FVL shape indexes as ß-angle and forced expiratory flow at 50% of the forced vital capacity (FEF50)/peak expiratory flow (PEF) ratio, to identify asthmatics from healthy children in comparison to "usual" spirometric parameters. Seventy-two school-aged asthmatic children and 29 controls were prospectively included. Children performed forced spirometry at baseline and after BD inhalation. Parameters were expressed at baseline as z-scores and BD reversibility as percentage of change reported to baseline value (Δ%). Receiver operating characteristic curves were generated and sensitivity and specificity at respective thresholds reported. Asthmatics presented significantly smaller zß-angle, zFEF50/PEF and zFEV1 (p ≤ .04) and higher BD reversibility, significant for Δ%FEF50/PEF (p = .02) with no difference for Δ%FEV1. zß-angle and zFEF50/PEF exhibited better sensitivity (0.58, respectively 0.60) than zFEV1 (0.50), and similar specificity (0.72). Δ%ß-angle showed higher sensitivity compared to Δ%FEV1 (0.72 vs. 0.42), but low specificity (0.52 vs. 0.86). Quantitative and qualitative assessment of FVL by adding shape indexes to spirometry interpretation may improve the ability to detect an airway obstruction, FEV1 reflecting more proximal while shape indexes peripheral bronchial obstruction.

A Calibration Device to Compare Body Plethysmographs Among Pediatric Lung Function Laboratories.

Multi-center studies in specific airway resistance have shown significant inter laboratory variability. Comparison of plethysmographic equipment using a lung model easily transportable from one site to another should be of help to international normative studies. A resistor made of parallel capillary tubes - insuring adequate linearity within 1 L/sec - was connected to a glass bottle. Thermal time constants were measured while the bottle was empty and while stuffed with steel wool. In the latter, isothermal condition was estimated to occur only at very low frequency (around 0.01 Hz) and gas compression was polytropic up to 0.6 Hz. With the empty analog, adiabatic gas compression was estimated to occur at frequencies ≥0.2 Hz, and more accurate volume estimation was obtained. The empty analog volume and specific resistance measured in a body plethysmograph on different days indicated within 5% accuracy as well as intersession repeatability. It is concluded that a physical analog built out of simple material provides accurate measurements of specific resistance. The apparatus should be of help to compare plethysmographic equipments from different laboratories.

Expiratory Flow - Vital Capacity: Airway - Lung Dysanapsis in 7 Year Olds Born Very Preterm?

An index normalizing airway dimension for lung size derived from spirometry was found inversely correlated to lung size in school children born very preterm, indicating larger alveolar volumes draining into comparatively smaller airways. In contrast in children born full term the index was independent of lung size.

Maturation of Airway Defensive Reflexes Is Related to Development of Feeding Behavior during Growth in Rabbits.

Introduction: Cough and expiration reflex are major lower airway defense mechanisms that have not been studied throughout development in relation with the feeding behavior. Aim: To describe airway defense reflexes evoked by mechanical stimulation of the trachea in developing rabbit pups. Material and Methods: Sixty one pups were allocated to 3 groups according to their feeding behavior: suckling (n = 22), weanling (n = 21) and weaning (n = 18) group. The incidence and sensitivity of defense reflexes triggered by mechanical tracheal stimulation were studied in anesthetized and tracheotomized animals. Data are expressed as median (25th to 75th percentile). Results: The overall incidence of defensive responses (cough and/or expiration reflex) was found to be significantly higher in suckling [100% (50-100%); p = 0.01] and weanling [75% (40-100%); p = 0.05] animals when compared to weaning ones [37.5% (0-75%)]. However, cough motor pattern accounted for only 29% (0-62%) of all defensive responses in suckling rabbits and its frequency was significantly lower in this group when compared with weanling [100%(50-100%); p = 0.006] or weaning group [62%(50-100%), p = 0.05]. In other word the expiration reflex was the dominant response in suckling animals. Conclusion: Incidence and motor pattern of defensive responses were found to be linked to the pup feeding behavior and the expiration reflex was the major response triggered in suckling pups. The results suggest that this reflex is especially fitted to occur during the coordinated swallowing - breathing fast activities of sucking.

More Relaxation by Deep Breath on Methacholine- Than on Exercise-Induced bronchoconstriction during the Routine Testing of Asthmatic Children.

Deep inspiration (DI) dilates normal airway precontracted with methacholine. The fact that this effect is diminished or absent in asthma could be explained by the presence of bronchial inflammation. The hypothesis was tested that DI induces more relaxation in methacholine induced bronchoconstriction-solely determined by the smooth muscle contraction-than in exercise induced bronchoconstriction, which is contributed to by both smooth muscle contraction and airway wall inflammation. The respiratory conductance (Grs) response to DI was monitored in asthmatic children presenting a moderately positive airway response to challenge by methacholine (n = 36) or exercise (n = 37), and expressed as the post- to pre-DI Grs ratio (GrsDI). Both groups showed similar change in FEV1 after challenge and performed a DI of similar amplitude. GrsDI however was significantly larger in methacholine than in exercise induced bronchoconstriction (p < 0.02). The bronchodilatory effect of DI is thus less during exercise- than methacholine-induced bronchoconstriction. The observation is consistent with airway wall inflammation-that characterizes exercise induced bronchoconstriction-rendering the airways less responsive to DI. More generally, it is surmised that less relief of bronchoconstriction by DI is to be expected during indirect than direct airway challenge. The current suggestion that airway smooth muscle constriction and airway wall inflammation may result in opposing effects on the bronchomotor action of DI opens important perspective to the routine testing of asthmatic children. New crossover research protocols comparing the mechanical consequences of the DI maneuver are warranted during direct and indirect bronchial challenges.

Bronchial or Laryngeal Obstruction Induced by Exercise?

A child suspected of exercise-induced laryngeal obstruction and asthma is examined by laryngoscopy and respiratory resistance (Rrs) after exercise challenge. Immediately at exercise cessation, the visualized adduction of the larynx in inspiration is reflected in a paroxystic increase in Rrs. While normal breathing has apparently resumed later on during recovery from exercise, the pattern of Rrs in inspiration is observed to reoccur following a deep breath or swallowing. The procedure may thus help diagnosing the site of exercise-induced obstruction when laryngoscopy is not available and identify re-inducers of laryngeal dysfunction.

Down-Regulation of Cough during Exercise Is Less Frequent in Healthy Children than Adults. Role of the Development and/or Atopy?

Cough is typically associated with physical activity in children with asthma, but the characteristics of the relationship between cough and exercise has not been established under physiological conditions. The aim of the study was to describe the effect of exercise on the reflex cough response elicited by a single breath of capsaicin in non-asthmatic children. A group of non-asthmatic adults was studied as reference. Thirty children and 29 adults were recruited. The cough reflex sensitivity to capsaicin was first determined to establish the dose that provokes 5 cough efforts (C5). The number of coughs elicited by C5 (NC5) was then compared at baseline and during a standardized submaximal treadmill exercise. Data are expressed as median (interquartile range). Children and adults showed a significant decrease in NC5 (respectively from 5.0 (4.0-6.0) to 2.5 (2.0-4.0), p < 0.0005 and from 6.0 (5.0-7.0) to 2.0 (0.0-3.0, p < 0.0005). During exercise, NC5 was observed to decrease in all adult subjects, but in only 24/30 children (80%, p = 0.02). A trend for a higher incidence of personal and familial atopy was observed in children that lacked cough down-regulation during exercise compared with other children. It is concluded that the cough reflex response to capsaicin is down regulated by exercise in both children and adults. The effect however is less consistently observed in the former. The difference may reflect maturation of descending inhibitory pathways of the cough reflex, but may also be associated to atopy. The data stress the importance of assessing the time relationship of cough and exercise in questionnaire studies of asthma.

Airway obstruction, upper airway artifact and response to bronchodilator in asthmatic and healthy children.

BACKGROUND: The forced oscillation technique (FOT) may be affected by the upper airway artifact in children with airway obstruction. The aim was to test the impact of the artifact on FOT ability to diagnose asthma in children as recommended by current guidelines. METHODS: The FOT was performed in 58 asthmatics and 27 controls before and after salbutamol. Respiratory resistance (Rrs) was measured at 8 Hz with a standard generator (SG), and a head generator (HG) that minimizes the upper airway artifact. The response to salbutamol was computed as change in respiratory resistance (Δ%Rrs) and admittance (Δ%Ars) that almost cancels the effect of the upper airway artifact. RESULTS: Rrs and Δ%Rrs were significantly larger in patients than controls by HG (respectively P < 0.001 and P = 0.002) but not SG, while Δ%Ars was larger in asthma than control by both (P < 0.04). Best discriminators between patients and controls were Rrs or Δ%Rrs by HG and Δ%Ars by SG. CONCLUSION: In asthmatic children, the upper airway artifact significantly impacts FOT measurements. The diagnostic value may be improved by minimization of the shunt, such as the computation of Δ%Ars.

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.

Specific airway resistance in healthy young Vietnamese and Caucasian adults.

In healthy Vietnamese children the respiratory resistance has been suggested to be similar at 110 cm height but larger at 130 cm when compared with data in Caucasians from the literature, suggesting smaller airways in older Vietnamese children (Vu et al., 2008). The hypothesis tested here is whether the difference in airway resistance remains consistent throughout growth, and if it is larger in adult Vietnamese than in Caucasians. Airway resistance and Functional Residual Capacity were measured in healthy young Caucasian and Vietnamese adults in their respective native country using identical equipment and protocols. Ninety five subjects in Vietnam (60 males) and 101 in France (41 males) were recruited. Airway resistance was significantly larger in Vietnamese than in Caucasians and in females than in males, consistent with difference in body dimensions. Specific airway resistance however was not different by ethnicity or gender. The findings do not support the hypothesis that airway size at adult age - once normalized for lung volume - differs between Vietnamese and Caucasians.

Neonatal hyperoxia up regulates cough reflex in young rabbits.

A link between cough in childhood and neonatal exposure to hyperoxia following preterm birth has been suggested. The hypothesis is tested that neonatal exposure to hyperoxia is associated with long term up regulation of cough. Airway hyperresponsiveness is also investigated because it is a frequent finding in children born preterm and may be linked to cough. Thirty nine young rabbits survived a 48 h neonatal exposure to 93% oxygen (H, n=26) or continued room air (A, n=13). Cough response to mechanical tracheal stimulation and airway responses to a mock exercise and to methacholine were studied under anaesthesia. Larger incidence of coughs and increased sensitivity to tracheal stimulation occurred in H vs A (p<0.01), while bronchial responses to exercise or methacholine were similar in both groups. Neonatal hyperoxia is associated with up regulation of cough in young rabbits. The lack of a parallel increase in airway responsiveness suggests up regulation may be of central origin.

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).