Stress Relaxation, another cause of “Pseudo Auto-Peep”?

Abstract In critically ill patients receiving mechanical ventilation, a positive end-expiratory pressure greater than the applied externally (auto-PEEP) reflects dynamic hyperinflation of the lungs. The term “Pseudo Auto-Peep” (Bilen & Cohen, 1993) 1 was coined to describe a progressive increase in expiratory plateau pressure in prolonged occlusion, attributed to a retrograde flow of extraluminal gas into the airways. However, the mechanism has not been studied closely. We intend to describe another mechanism for this phenomenon, explained by stress relaxation due to inequalities in expiratory time constant (τE), manifested in inspiration and expiration.