Impact of Airway Gas Exchange on the Multiple Inert Gas Elimination Technique: Theory

Abstract

The multiple inert gas elimination technique (MIGET) provides a method for estimating alveolar gas exchange efficiency. Six soluble inert gases are infused into a peripheral vein. Measurements of these gases in breath, arterial blood, and venous blood are interpreted using a mathematical model of alveolar gas exchange (MIGET model) that neglects airway gas exchange. A mathematical model describing airway and alveolar gas exchange predicts that two of these gases, ether and acetone, exchange primarily within the airways. To determine the effect of airway gas exchange on the MIGET, we selected two additional gases, toluene and m-dichlorobenzene, that have the same blood solubility as ether and acetone and minimize airway gas exchange via their low water solubility. The airway-alveolar gas exchange model simulated the exchange of toluene, m-dichlorobenzene, and the six MIGET gases under multiple conditions of alveolar ventilation-to-perfusion, V̇A/Q̇, heterogeneity. We increased the importance of airway gas exchange by changing bronchial blood flow, Q̇br. From these simulations, we calculated the excretion and retention of the eight inert gases and divided the results into two groups: 1) the standard MIGET gases which included acetone and ether and 2) the modified MIGET gases which included toluene and m-dichlorobenzene. The MIGET mathematical model predicted distributions of ventilation and perfusion for each grouping of gases and multiple perturbations of V̇A/Q̇ and Q̇br. Using the modified MIGET gases, MIGET predicted a smaller dead space fraction, greater mean V̇A, greater log(SDVA), and more closely matched the imposed V̇A distribution than that using the standard MIGET gases. Perfusion distributions were relatively unaffected.

FEV manoeuvre induced changes in breath VOC compositions: an unconventional view on lung function tests

“…However, in contrast to pCO 2 , there was a small (~4.5%) but significant (P < 0.001) increase in alveolar acetone concentrations at forced expiration. A possible explanation could be, that under the special conditions of forced expiration exchange phenomena from bronchial epithelium contributed to the exhaled concentrations of acetone3536. Recent studies have also suggested partial exchange of VOCs with good water solubility and relatively higher blood:air partition coefficient within the bronchial tree in certain conditions such as increased bronchial perfusion or elevated exhalation flow363738.…”

A modeling-based evaluation of isothermal rebreathing for breath gas analyses of highly soluble volatile organic compounds

“…This "common knowledge" has first been put into question in the field of breath alcohol testing, revealing observable blood-breath concentration ratios of ethanol during tidal breathing that are unexpectedly high compared to the partition coefficient derived in vitro [13]. Similarly, excretion data (i.e., the ratios between steady state partial pressures in expired air and mixed venous blood) of highly water soluble compounds (including the MIGET test gas acetone) have been shown to underestimate the values anticipated by treating the airways as an inert tube [19,20].…”

Transport of Gases between the Environment and Alveoli—Theoretical Foundations

“…Conservation of mass in this reduced coordinate system becomes ∂ A ρ̅ / ∂ t = −∂ J / ∂ x − α, where α represents the mass loss rate; it is typically taken to be negligible in the conducting airways for O 2 and CO 2 transport. For other gases, this may not be valid; airway gas exchange has recently been investigated with respect to gas exchange measurements probed with MIGET (Anderson and Hlastala, 2010; see also Hlastala 2003). They found significant effects of airway exchange (especially ether and acetone) on estimated ventilatory distributions, while perfusion distributions were relatively unaffected.…”