Bench and mathematical modeling of the effects of breathing a helium/oxygen mixture on expiratory time constants in the presence of heterogeneous airway obstructions

Katz, Ira; Terzibachi, Karine; Gouinaud, Laure; Caillibotte, Georges; Texereau, J.

doi:10.1186/1475-925x-11-27

Cited by 10 publications

(5 citation statements)

References 22 publications

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“…However, single‐compartment models of τ E will disproportionately reflect lung units with small time constants (Martin et al . ). Lung units with large τ E will be represented by a later portion of the expiratory

\overset{V}{true}

– V curve than those with small τ E .…”

Section: Discussionmentioning

confidence: 97%

Gas density alters expiratory time constants before and after experimental lung injury

Henderson

Molgat‐Seon

Dominelli

et al. 2015

Experimental Physiology

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New Findings r What is the central question of this study?Does the induction of a model of lung injury affect the expiratory time constant (τ E ) in terms of either total duration or morphology? Does ventilation with gases of different densities alter the duration or morphology of τ E either before or after injury? r What is the main finding and its importance?The use of sulfur hexafluoride in ventilating gas mixtures lengthens total expiratory time constants before and after lung injury compared with both nitrogen and helium mixtures. Sulfur hexafluoride mixtures also decrease the difference and variability of τ E between fastand slow-emptying compartments before and after injury when compared with nitrogen and helium mixtures.Acute lung injury is characterized by regional heterogeneity of lung resistance and elastance that may lead to regional heterogeneity of expiratory time constants (τ E ). We hypothesized that increasing airflow resistance by using inhaled sulfur hexafluoride (SF 6 ) would lengthen time constants and decrease their heterogeneity in an experimental model of lung injury when compared with nitrogen or helium mixtures. To overcome the limitations of a single-compartment model, we employed a multisegment model of expiratory gas flow. An experimental model of lung injury was created using intratracheal injection of sodium polyacrylate in anaesthetized and mechanically ventilated female Yorkshire-cross pigs (n = 7). The animals were ventilated with 50% O 2 and the remaining 50% as nitrogen (N 2 ), helium (He) or sulfur hexafluoride (SF 6 ). Values for τ E decreased with injury and were more variable after injury than before (P < 0.001). Values for τ E increased throughout expiration both before and after injury, and the rate of increase in τ E was lessened by SF 6 (P < 0.001 when compared with N 2 both before and after injury). Altering the inhaled gas density did not affect indices of oxygenation, dead space or shunt. The use of SF 6 in ventilating gas mixtures lengthens total expiratory time constants before and after lung injury compared with both N 2 and He mixtures.

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\overset{V}{true}

– V curve than those with small τ E .…”

Section: Discussionmentioning

confidence: 97%

Gas density alters expiratory time constants before and after experimental lung injury

Henderson

Molgat‐Seon

Dominelli

et al. 2015

Experimental Physiology

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“…For these patients, the elastic work of breathing is elevated because lung compliance decreases as lung volume increases towards total lung capacity (TLC) [25]. He/O 2 can improve expiratory flow by lowering airway resistance [26-28], so as to reduce end-expiratory lung volumes and improve compliance, which in turn will decrease the elastic work of breathing upon inhalation. In the present experiments, replacing air with He/O 2 allowed the breathing chamber to empty faster (Figure 4); however, this did not translate to reduced elastic work because the volume to which the test lung chamber was inflated had little influence on its compliance.…”

Section: Discussionmentioning

confidence: 99%

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

et al. 2012

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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.

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“… 32 An obstruction model in the ETT was based on a numerical representation of the Rp50 resistor which is the smallest resistance value provided for use with an infant test lung (Michigan Instruments, Kentwood, MI, USA). 33 The Rp resistors are simple orifice plates, a metal disc with a concentric hole in it that creates a purely inertial loss, such that the loss is a parabolic function of the flow rate.…”

Section: Aterials and M Ethodsmentioning

confidence: 99%

Numerical analysis of mechanical ventilation using high concentration medical gas mixtures in newborns

Katz¹,

Milet²,

Chalopin³

et al. 2019

Med Gas Res

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Bench and mathematical modeling of the effects of breathing a helium/oxygen mixture on expiratory time constants in the presence of heterogeneous airway obstructions

Cited by 10 publications

References 22 publications

Gas density alters expiratory time constants before and after experimental lung injury

Gas density alters expiratory time constants before and after experimental lung injury

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

Numerical analysis of mechanical ventilation using high concentration medical gas mixtures in newborns

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