Development of an experimental evaluation of work of breathing in patients with excessive dynamic airway collapse (EDAC)

Abstract

EDAC is defined by an abnormal expiratory reduction of the tracheal lumen leading to an elevation of airflow resistance. No data supports the clinical threshold of 50% closure. The aim of our study was to develop an experimental model of EDAC in order to assess the consequences of airway collapse on the work of breathing (WOB) and evaluate the impact of CPAP.

We have modelled and manufactured a realistic 3D silicon trachea and a static compression system to simulate tracheal collapse. The trachea was linked to a dummy head with realistic upper airways and to an artificial lung (ASL 5000, IngMar Medical) which simulated tidal breathing (TB) from three lung models (normal, COPD and restrictive). We simulated tracheal compressions (length 4 or 8 centimeters, closure of 0,31,49,63 and 87%) at rest and on exercise, without and with CPAP (PEP 5, 10, 15 and 20cmH₂O). We measured pressure on both sides of collapse and computed expiratory resistance R_exp, flow Q_exp and pressure time product (PTP_exp which reflects WOB).

There was a significant impact of the degree of collapse on R_exp, Q_exp and PTP_exp for a closure ≥49%. During TB, median R_exp was 8,05 [6,60;9,90]cmH₂O.s/L at 87% collapse versus 0,12 [0,11;0,14]cmH₂O.s/L without collapse (p<0,001). R_exp and PTP_exp were also correlated with the length of stenosis (respectively rho=0,38, p=0,004 and rho=0,34, p=0,012). All indicators were different between rest and exercise (p=0,001). At 87% collapse, the average PTP_exp was 80,2±35,8 cmH₂O.s during TB versus 0,8±0,6 cmH₂O.s if the collapse was corrected by a 5 cmH₂O PEP.

Our experimental model supports the 49% closure threshold associated with significant consequences on WOB.