Flow Controlled Expiration is perceived as less uncomfortable than positive end expiratory pressure

• Flow Controlled Expiration (FLEX) is a new option for mechanical ventilation.
• FLEX delays expiratory lung volume decrease without prolonging expiration duration.
• FLEX increases breathing discomfort in healthy subjects to a lesser extent than PEEP.
• FLEX might support ventilation therapy in spontaneously breathing patients.

Recently, we presented Flow Controlled Expiration (FLEX) as a new option for lung-protective ventilation. FLEX delays the expiratory volume decrease in the lungs without prolonging the duration of expiration. Most ventilated patients nowadays receive spontaneous breathing support. We investigated whether FLEX is tolerated by awake subjects.In 24 healthy subjects restrictive lung disease was simulated by bandaging the thorax. The subjects were asked to indicate the perceived discomfort of breathing at various levels of positive end expiratory pressure (PEEP = 0, 3, 6 or 9 cmH2O) with and without FLEX. Breathing discomfort was not affected by FLEX (p = 0.269), but higher PEEP increased breathing discomfort (p < 0.001). Only in forced choice comparison a stronger FLEX condition was perceived as less comfortable (p < 0.01) than a weaker one.We conclude that FLEX decreases the breathing comfort in healthy subjects to a lesser extent than PEEP. Therefore, FLEX might be used to support ventilation therapy in spontaneously breathing patients.