Control of the expiratory flow in a lung model and in healthy volunteers with an adjustable flow regulator: a...

Pursed-lips breathing (PLB) is a technique to attenuate small airway collapse by regulating the expiratory flow. During mandatory ventilation, flow-controlled expiration (FLEX), which mimics the expiratory flow course of PLB utilizing a digital system for measurement and control, was shown to exert lung protective effects. However, PLB requires a patient's participation and coordinated muscular effort and FLEX requires a complex technical setup. Here, we present an adjustable flow regulator to mimic PLB and FLEX, respectively, without the need of a patient's participation, or a complex technical device.

Our study consisted of two parts: First, in a lung model which was ventilated with standard settings (tidal volume 500 ml, respiratory rate 12 min^-1, positive end-expiratory pressure (PEEP) 5 cmH₂O), the possible reduction of the maximal expiratory flow by utilizing the flow regulator was assessed. Second, with spontaneously breathing healthy volunteers, the short-term effects of medium and strong expiratory flow reduction on airway pressure, the change of end-expiratory lung volume (EELV), and breathing discomfort was investigated.

In the lung model experiments, expiratory flow could be reduced from - 899 ± 9 ml·s^-1 down to - 328 ± 25 ml·s^-1. Thereby, inspiratory variables and PEEP were unaffected. In the volunteers, the maximal expiratory flow of - 574 ± 131 ml·s^-1 under baseline conditions was reduced to - 395 ± 71 ml·s^-1 for medium flow regulation and to - 266 ± 58 ml·s^-1 for strong flow regulation, respectively (p < 0.001). Accordingly, mean airway pressure increased from 0.6 ± 0.1 cmH₂O to 2.9 ± 0.4 cmH₂O with medium flow regulation and to 5.4 ± 2.4 cmH₂O with strong flow regulation, respectively (p < 0.001). The EELV increased from baseline by 31 ± 458 ml for medium flow regulation and 320 ± 681 ml for strong flow regulation (p = 0.033). The participants rated breathing with the flow regulator as moderately uncomfortable, but none rated breathing with the flow regulator as intolerable.

The flow regulator represents an adjustable device for application of a self-regulated expiratory resistive load, representing an alternative for PLB and FLEX. Future applications in spontaneously breathing patients and patients with mandatory ventilation alike may reveal potential benefits.

DRKS00015296, registered on 20th August, 2018; URL: https://www.drks.de/drks_web/setLocale_EN.do .