Bench experiments comparing simulated inspiratory effort when breathing helium-oxygen mixtures to that during positive pressure support with air

Abstract

BackgroundInhalation of helium-oxygen (He/O2) mixtures has been explored as a means to lower the work of breathing of patients with obstructive lung disease. Non-invasive ventilation (NIV) with positive pressure support is also used for this purpose. The bench experiments presented herein were conducted in order to compare simulated patient inspiratory effort breathing He/O2 with that breathing medical air, with or without pressure support, across a range of adult, obstructive disease patterns.MethodsPatient breathing was simulated using a dual-chamber mechanical test lung, with the breathing compartment connected to an ICU ventilator operated in NIV mode with medical air or He/O2 (78/22 or 65/35%). Parabolic or linear resistances were inserted at the inlet to the breathing chamber. Breathing chamber compliance was also varied. The inspiratory effort was assessed for the different gas mixtures, for three breathing patterns, with zero pressure support (simulating unassisted spontaneous breathing), and with varying levels of pressure support.ResultsInspiratory effort increased with increasing resistance and decreasing compliance. At a fixed resistance and compliance, inspiratory effort increased with increasing minute ventilation, and decreased with increasing pressure support. For parabolic resistors, inspiratory effort was lower for He/O2 mixtures than for air, whereas little difference was measured for nominally linear resistance. Relatively small differences in inspiratory effort were measured between the two He/O2 mixtures. Used in combination, reductions in inspiratory effort provided by He/O2 and pressure support were additive.ConclusionsThe reduction in inspiratory effort afforded by breathing He/O2 is strongly dependent on the severity and type of airway obstruction. Varying helium concentration between 78% and 65% has small impact on inspiratory effort, while combining He/O2 with pressure support provides an additive reduction in inspiratory effort. In addition, breathing He/O2 alone may provide an alternative to pressure support in circumstances where NIV is not available or poorly tolerated.

Mechanical ventilation with heliox in an animal model of acute respiratory distress syndrome

“…Whereas airway obstruction is present in our model of acute lung injury, the severity of airway obstruction is far less compared to asthma, respiratory syncytial virus, or other disease states in which hyper-reactivity of bronchi plays an important role [ 27 – 29 ]. In line with this, in a test lung, the effect of heliox on reducing the inspiratory effort was shown to be dependent on the kind of obstruction and severity [ 30 ]. Our model may also have been a too mild model of lung injury, in which beneficial effects may be hard to tease out.…”

Extremely low flow tracheal gas insufflation of helium-oxygen mixture improves gas exchange in a rabbit model of piston-type high-frequency oscillatory ventilation

“…The low density of helium does not always reduce resistance [18]. Different types and phenotypes of obstructive airway disease manifest in different regions of the lung.…”

Patient–Ventilator Interaction Testing Using the Electromechanical Lung Simulator xPULM™ during V/A-C and PSV Ventilation Mode

“…Examples for the passive test systems are the IMT test lung (imtmedical, Buchs, Switzerland) ), representing a single compartment solution as well as the TTL lung simulator (Michigan Instruments, Kentwood, USA) , allowing a two compartment simulation. The ASL500 breathing simulator (IngMar Medical, Pittsburgh, USA) is an example of a more sophisticated test system, targeting also the comparison of ventilation modes, which has been shown in several studies [39][40][41][42]. The fundamental disadvantage of such methods are the unchangeable maximum volume of the test lung, restricted possibility of simulating lung behavior and limited simulation of expiratory efforts [41].…”