Transpleural ventilation of explanted human lungs

Hyperinflation and gas trapping are devastating consequences of severe emphysema. The increase in total lung capacity (TLC) compromises chest wall mechanics as the thorax approaches the limit of expansion. Gas trapping increases the residual volume (RV) to TLC ratio and reduces both the slow and forced vital capacity (VC and FVC, respectively). This in turn is a major cause of reduction in forced expiratory volume in 1 s (FEV₁ ). The progressively narrowing gap between RV and TLC increases the work of breathing and continues to decrease ventilatory capacity until the patient becomes flow-limited even while breathing at rest. Thus, a major objective of treatment must be to decrease the amount of trapped gas.

Collateral ventilation in emphysema greatly exceeds that in normal lungs, as demonstrated in lungs removed at necropsy by Hogg et al in 1969, ¹ confirmed using a different technique in patients by Terry et al in 1978 ² and reconfirmed more recently by Morrell et al . ³ Macklem, in an editorial comment, stated: "... if collateral flow resistance is less than airway resistance ... ventilation ... through openings directly through the chest wall into the parenchyma should bypass the obstruction, decrease work of breathing, increase alveolar ventilation and improve dyspnea. Insects breathe through openings on their body surface ... called spiracles." ⁴

Lausberg et al recently reported that the creation of fistulas between segmental bronchi and adjacent lung parenchyma increased FEV₁ and FVC in explanted emphysematous human lungs. ⁵ The present study was designed to test the hypothesis that ventilation of low resistance collateral pathways in emphysema via spiracles through the pleura will allow trapped gas to escape and increase passive flow and volume on deflation. Openings were made directly into the parenchyma through tubes glued to the pleural surface (spiracles) in order to measure flow and volume that traversed the spiracles. Emphysematous lungs explanted from lung transplant recipients were compared with nearly normal lungs obtained from donors but rejected for transplantation because of minor abnormalities.

METHODS

Preliminary studies on four emphysematous lungs showed the feasibility of studying ventilation through transpleural communications. This allowed us to develop a protocol by which we measured: (1) volume-flow-time relationships during passive deflation through either the bronchial tree or the spiracles from...