Predicting tracheal work of breathing in neonates based on radiological and pulmonary measurements

Abstract

Tracheomalacia is an airway condition in which the trachea excessively collapses during breathing. Neonates diagnosed with tracheomalacia require more energy to breathe, and the effect of tracheomalacia can be quantified by assessing flow-resistive work of breathing (WOB) in the trachea using computational fluid dynamics (CFD) modeling of the airway. However, CFD simulations are computationally expensive; the ability to instead predict WOB based on more straightforward measures would provide a clinically useful estimate of tracheal disease severity. The objective of this study is to quantify the WOB in the trachea using CFD and identify simple airway and/or clinical parameters that directly relate to WOB. This study included 30 neonatal intensive care unit subjects (15 with tracheomalacia and 15 without tracheomalacia). All subjects were imaged using ultrashort echo time (UTE) MRI. CFD simulations were performed using patient-specific data obtained from MRI (airway anatomy, dynamic motion, and airflow rates) to calculate the WOB in the trachea. Several airway and clinical measurements were obtained and compared with the tracheal resistive WOB. The maximum percent change in the tracheal cross-sectional area (ρ = 0.560, P = 0.001), average glottis cross-sectional area (ρ = -0.488, P = 0.006), minute ventilation (ρ = 0.613, P < 0.001), and lung tidal volume (ρ = 0.599, P < 0.001) had significant correlations with WOB. A multivariable regression model with three independent variables (minute ventilation, average glottis cross-sectional area, and minimum of the eccentricity index of the trachea) can be used to estimate WOB more accurately (R² = 0.726). This statistical model may allow clinicians to estimate tracheal resistive WOB based on airway images and clinical data.NEW & NOTEWORTHY The work of breathing due to resistance in the trachea is an important metric for quantifying the effect of tracheal abnormalities such as tracheomalacia, but currently requires complex dynamic imaging and computational fluid dynamics simulation to calculate it. This study produces a method to predict the tracheal work of breathing based on readily available imaging and clinical metrics.

Keywords: computational fluid dynamics; neonates; tracheomalacia; ultrashort echo time magnetic resonance imaging; work of breathing.

Graphical abstract

Figure 1.

The airway obtained from end-expiration image in an example subject without tracheomalacia (left) and a subject with tracheomalacia (right; A). Cross-sectional area change along the airway of an example subject with tracheomalacia between end-expiration (green) and end-inspiration (black) time points (B). Airflow velocity distribution at peak expiration in an example subject without tracheomalacia (left) and a subject with tracheomalacia (right; C). A: the cross-sectional planes were created orthogonal to the centerline in each airway. The tracheal cross section in the subject without tracheomalacia was more circular compared with the subject with tracheomalacia. B: the maximum percent change in the cross-sectional area compared with the end-inspiration cross-sectional area in the trachea was 65% (red arrow). C: the daily tracheal resistive work of breathing was 24 and 317 J in the subject without tracheomalacia and with tracheomalacia, respectively. In the subject with tracheomalacia, the high-velocity jet in the lower region of the trachea elevated the breathing effort.

Figure 2.

The daily tracheal resistive work of breathing vs. maximum percent change in the tracheal cross-sectional area (A), average glottis cross-sectional area (B), tracheal volume at end expiration time point (C), and minimum of the eccentricity index of the trachea (D). Black and blue dots represent neonates without tracheomalacia and with tracheomalacia, respectively. ρ, P are Spearman’s coefficients. TM, tracheomalacia.

Figure 3.

Plots showing the daily tracheal resistive work of breathing vs. minute ventilation (A), lung tidal volume (B), respiratory rate (C), and body mass (D). Black and blue dots represent neonates without tracheomalacia and with tracheomalacia, respectively. ρ, P are Spearman’s coefficients. TM, tracheomalacia.