Flow controlled expiration does not impair pedal power during physical exercise on a bicycle ergometer

Control of the expiratory flow in a lung model and in healthy volunteers with an adjustable flow regulator: a combined bench and randomized crossover study

Background

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.

Methods

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.

Results

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.

Conclusions

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.

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

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01886-7.

Flow-controlled expiration (FLEX) homogenizes pressure distribution in a four compartment physical model of the respiratory system with chest wall compliance

Objective.Flow-controlled expiration (FLEX) has been shown to attenuate ventilator-induced lung injury in animal models. It has also shown to homogenize compartmental pressure distribution in a physical model of the inhomogeneous respiratory system having independent compartments. We hypothesized that the homogenizing effects of FLEX are also effective in this regard when the independence of compartments is suspended by simulated chest wall compliance.Approach.A four compartment physical model of the respiratory system having chest wall compliance (137 ml/cmH₂O) was developed. Two of the four compartments had high compliance (18 ml/cmH₂O) and two had low compliance (10 ml/cmH₂O). These compartments were each combined with either high (6.8 cmH₂O·s/l) or low resistance (3.5 cmH₂O·s/l). The model was ventilated in the volume-controlled ventilation mode with either passive expiration or with FLEX. The maximal pressure differences (ΔP_max) and the maximal differences of mean pressure (ΔP_mean) between the compartments during expiration were determined.Main results.With passive expiration ΔP_maxreached up to 3.4 ± 0.03 cmH₂O but only 0.9 ± 0.01 cmH₂O with FLEX (p < 0.001). Maximal differences of ΔP_meanwere significantly lower with FLEX as compared to passive expiration (extending up to 0.4 ± 0.04 cmH₂O versus 2.0 ± 0.15 cmH₂O,p < 0.001).Significance.The homogenizing effects of FLEX on compartmental pressure distribution could be reproduced in a more complex physical model of the inhomogeneous respiratory system having chest wall compliance and might be a mechanism underlying the lung protective effects of ventilation with FLEX.