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.