Discussion
In this study, we evaluated the Infant Pulmonary Function Tests in 53 children with airway anomalies and co-related with bronchoscopy findings. The isolated laryngomalacia (28, 52.8%) was the most common airway anomaly, followed by laryngo-tracheomalacia (7, 13.2%), laryngo-tracheo-bronchomalacia (6, 11.3%), and laryngomalacia with subglottic stenosis (4, 7.5%). Among isolated laryngomalacia, pattern 3 (fluttering of inspiratory limb) was most common in TBFVL, followed by pattern 4 (fluttering of inspiratory limb and flattening of expiratory limb) in 13 (46.4) and 8 (28.6%) cases, respectively.
In our study, isolated laryngomalacia was found in 28 (52.8%), and laryngomalacia was associated with other airway anomalies in 24 (45.3%) children, which is comparable with other studies (7)(8). Filippone et al. used TBFVL as the first test to evaluate 113 children to predict the possible airway anomaly based on TBFVL patterns (5). They reported that pattern 3 (fluttering of inspiratory limb) was always associated with laryngomalacia (100% sensitive). In our study, 21 (75%) children with isolated laryngomalacia had pattern 3; the fluttered inspiratory limb (13 had an only inspiratory flutter, and eight had associated expiratory flattening). Out of 24 cases of laryngomalacia had associated with other airway anomalies, 12 (50%) had inspiratory fluttering, 5 had only inspiratory fluttering (pattern 3), and 7 had inspiratory fluttering with expiratory flattening. The slight discrepancy in pattern 3 (fluttered inspiratory limb) for isolated laryngomalacia in our study may be explained by the that we performed TBFVL in a few children after bronchoscopy on the same day. In our study, 18 children had obstruction between glottis and bifurcation of the trachea (7 had laryngotracheomalacia, 6 had laryngo-tracheo-bronchomalacia, 4 had laryngomalacia with subglottic stenosis, and 1 had laryngomalacia with tracheal diverticulum). Of these 18 children, nine (50%) had expiratory flattening (4 had isolated expiratory flattening, and 5 had expiratory flattening and inspiratory fluttering). In our study, the Ti/Te ratio was significantly higher in children with isolated laryngomalacia compared to controls. The possible explanation for these findings may be prolonged inspiratory time in cases of isolated laryngomalacia. In contrast, in a study by Filippone et al., we found significantly high PTEF/tE in laryngomalacia plus sub-glottic stenosis compared to controls. The possible explanation may be that they had a variety of diagnoses in pattern 2, and only four cases had associated laryngomalacia out of 46. In contrast, all four patients in this category had laryngomalacia plus subglottic stenosis.
Filippone et al. performed follow-up TBFVL in 12 cases of airway obstruction between glottis and carina after surgical or medical intervention (five had sub-glottic hemangioma, one had postintubation tracheal stenosis, five had secondary tracheomalacia) and found improvement in the expiratory limb from pattern 2 (flattened expiratory limb) to pattern 1 (normal pattern) and increase in expiratory flow rates (9). We had 14 children (mostly laryngomalacia) follow-up without any specific intervention. We found significant improvement in the pattern of TBFVL towards normal pattern, though we could not find a difference in TBFVL parameters, likely due to a small number of follow-up cases. Moore et al. evaluated 21 children at a median (range) age of 9.4 (7.6-14.3) who were diagnosed with tracheobronchomalacia during infancy. They found that symptoms and abnormal function tests persisted for a long time, and there was no evidence of reactive airway disease (10).
Based on our study and reviewing the literature, it may be said that graphic patterns in TBFVL may be suggestive of airway obstruction at a particular site (larynx or below the larynx) and may also suggest an associated component of reactive airway disease. Similarly, this non-invasive TBFVL pattern may indicate improvement in the follow-up spontaneously and after an intervention. Therefore, if the facility of TBFVL is available, it may be used as a screening test for airway anomalies, and invasive bronchoscopy procedures may be avoided in many infants with airway anomalies. But, it should be remembered that the TBFVL pattern will usually suggest a site of obstruction, not a specific diagnosis. For example, pattern 2 (flattening of expiratory limb) suggests an obstruction between glottis and carina. The specific lesion may be sub-glottic stenosis (a haemangioma or post-extubation) or primary/secondary tracheomalacia. Similarly, pattern 3 (fluttering of inspiratory limb) may suggest obstruction at the glottic level like laryngomalacia or laryngeal papilloma. Finally, the airway anomaly frequently occurs in combination, and TBFVL patterns may be combined. As seen in our study, they may be challenging to interpret, where about 50 % of cases had combined airway anomalies. Thus, findings of TBFVL must be interpreted in context and history and physical examination findings. If TBFVL had pattern 3 (fluttering of inspiratory limb) and history and examination are compatible with laryngomalacia, the bronchoscopy can be avoided. Suppose TBFVL had pattern 2 (flattening of expiratory limb). In that case, bronchoscopy should be considered as it suggests an obstruction between glottis and carina, and various airway anomalies may cause this pattern, as mentioned above. Further, TBFVL may help to identify airway anomalies in children with recurrent wheezing who respond poorly to asthma therapy.