Airway bypass improves the mechanical properties of explanted emphysematous lungs

Abstract

Rationale: By creating artificial communications through bronchial walls into the parenchyma of explanted lungs (airway bypass), we expect to decrease the amount of gas trapped and to increase the rate and volume of air expelled during forced expirations.

Objectives: To describe the mechanism by which airway bypass improves the mechanical properties of the emphysematous lung.

Methods: Lung compartments and mechanics were measured before and after airway bypass, which was created by placement of three or four stent-supported fenestrations in 10 emphysematous lungs removed at transplantation surgery.

Measurements and main results: Minimal volume after passive deflation decreased by a mean of 1.54 L (range, 0.7-2.5 L) or 60% (range, 37-86%). Explanted VC increased by 1.30 L or 132% (range, 78-318%). Maximal expiratory flows and volumes increased. Flow resistance decreased.

Conclusions: Because these data show that airway bypass improves the mechanics of breathing in severely emphysematous lungs in vitro, there is now strong empirical support that this procedure can improve ventilatory function in patients by reducing gas trapping and flow resistance.

Figure 1.

Two photographs of the same emphysematous lung after inflation to total lung capacity and passive emptying with the bronchus open to room air for 5 minutes. The left panel shows the lung before airway bypass. The right panel shows the lung after placement of three transbronchial stents. The minimal lung volume (explanted residual volume) decreased markedly after airway bypass.

Figure 2.

Bar graph illustrating the change in lung compartments after airway bypass with three or four transbronchial stents. For each lung number on the abscissa, the vertical bar directly above the numeral depicts explanted residual volume (ERV) and explanted vital capacity (EVC) before bypass, and the bar on the right shows the same parameters in each lung after bypass. The reduction in ERV was uniformly accompanied by an increase in EVC.

Figure 3.

Isotime identity plot of volume–time curves before and after airway bypass for each of the 10 lungs studied. Pre-bypass volumes are plotted on the ordinate at four points in time, and post-bypass data at these same time points are plotted on the abscissa. The diagonal line marks the line of identity. Additional considerations are presented in the text, and the data are presented in Table E3.

Figure 4.

Individual but representative explanted maximal expiratory flow volume curves from lung 2, plotted together with the explanted residual volume measurements determined by liquid volume displacement and depicted by the shaded panels before (the smaller curve) and after airway bypass (the larger curve). Peak flow occurs roughly 0.2 seconds after the onset of each curve. The thick solid lines (before bypass) and dashed lines (after bypass) depict recorded data. The light lines connect these to the previously measured explanted residual volume values. After airway bypass, the rate and volume of flow increased significantly. Additional details are presented and discussed in the text and the data are presented in Table E3.

Figure 5.

Individual but representative static pressure volume diagrams from lung 2, plotted with explanted residual volume determined from liquid displacement and depicted by the shaded bars before and after airway bypass. The solid lines (before bypass) and dashed lines (after bypass) depict recorded data. Additional details are discussed in the text, and the data are presented in Table E4.