Increased Work of Breathing due to Tracheomalacia in Neonates

Abstract

Rationale: Dynamic collapse of the tracheal lumen (tracheomalacia) occurs frequently in premature neonates, particularly in those with common comorbidities such as bronchopulmonary dysplasia. The tracheal collapse increases the effort necessary to breathe (work of breathing [WOB]). However, quantifying the increased WOB related to tracheomalacia has previously not been possible. Therefore, it is also not currently possible to separate the impact of tracheomalacia on patient symptoms from parenchymal abnormalities.Objectives: To measure the increase in WOB due to airway motion in individual subjects with and without tracheomalacia and with different types of respiratory support.Methods: Fourteen neonatal intensive care unit subjects not using invasive mechanical ventilation were recruited. In eight, tracheomalacia was diagnosed via clinical bronchoscopy, and six did not have tracheomalacia. Self-gated three-dimensional ultrashortecho-time magnetic resonance imaging (MRI) was performed on each subject with clinically indicated respiratory support to obtain cine images of tracheal anatomy and motion during the respiratory cycle. The component of WOB due to resistance within the trachea was then calculated via computational fluid dynamics (CFD) simulations of airflow on the basis of the subject's anatomy, motion, and respiratory airflow rates. A second CFD simulation was performed for each subject with the airway held static at its largest (i.e., most open) position to determine the increase in WOB due to airway motion and collapse.Results: The tracheal-resistive component of WOB was increased because of airway motion by an average of 337% 6 295% in subjects with tracheomalacia and 24% 6 14% in subjects without tracheomalacia (P , 0.02). In the tracheomalacia group, subjects who were treated with continuous positive airway pressure (CPAP) using a RAM cannula expended less energy for breathing compared with the subjects who were breathing room air or on a high-flow nasal cannula.Conclusions: Neonatal subjects with tracheomalacia have increased energy expenditure compared with neonates with normal airways, and CPAP may be able to attenuate the increase in respiratory work. Subjects with tracheomalacia expend more energy on the tracheal-resistive component of WOB alone than nontracheomalacia patients expend on the resistive WOB for the entire respiratory system, according to previously reported values. CFD may be able to provide an objective measure of treatment response for children with tracheomalacia.

Subglottic Stenosis Position Affects Work of Breathing

“…is small in healthy subjects but can rise dramatically in subjects with airway disease. 28 The energy flux, E ϕ , through any crosssectional plane in the airway is calculated…”

Quantitative Evaluation of Subglottic Stenosis Using Ultrashort Echo Time MRI in a Rabbit Model

“…Previously published literature has demonstrated the ability of UTE-MRI to detect tracheomalacia in neonates with respiratory conditions such as bronchopulmonary dysplasia. 24,33 Therefore, the absence of increased airway dynamics in rabbits with SGS in this study is a true observation and not a limitation of UTE-MRI. Furthermore, although there was no dynamic airway collapse, there was a significant increase in eccentricity of the airway from glottis to the mid-point of the trachea post balloon dilation at end-inspiration and end-expiration.…”

Central Airway Issues in BPD

“…(14) This collapsed airway results in marked increased tracheal work of breathing in neonates. (15) Failure of the natural developmental progression of the premature trachea and frequent need for positive pressure ventilation predisposes neonates with BPD to central airway pathologies. Central airway disease can be divided into two main categories: 1) dynamic airway obstruction and 2) fixed airway obstruction.…”

“…CPAP serves as a pneumatic stent which decreases airway resistance, reduces respiratory work, and raises lung volumes in infant with TBM. (15,36,37) Positive airway pressure can also be provided invasively via an endotracheal tube or tracheostomy tube, and the artificial airway can bypass the collapsible segment of airway.…”