Please use this identifier to cite or link to this item: https://ahro.austin.org.au/austinjspui/handle/1/28725
Title: Ideal alveolar gas defined by modal gas exchange in ventilation-perfusion distributions.
Austin Authors: Peyton, Philip J 
Affiliation: Institute for Breathing and Sleep..
Department of Critical Care, Melbourne Medical School, Faculty of Medicine Dentistry and Health Sciences, University of Melbourne, Melbourne, Victoria, Australia..
Department of Anaesthesia, Austin Health, Heidelberg, Victoria, Australia..
Issue Date: 2021
Date: 2021
Publication information: Journal of applied physiology 2021; 131(6): 1831-1838
Abstract: Under the three-compartment model of ventilation-perfusion ([Formula: see text]) scatter, Bohr-Enghoff calculation of alveolar deadspace fraction (VDA/VA) uses arterial CO2 partial pressure measurement as an approximation of "ideal" alveolar CO2 (ideal [Formula: see text]). However, this simplistic model suffers from several inconsistencies. Modeling of realistic physiological distributions of [Formula: see text] and [Formula: see text] instead suggests an alternative concept of "ideal" alveolar gas at the [Formula: see text] ratio where uptake or elimination rate of a gas is maximal. For alveolar-capillary partial pressure, this "modal" point equals the mean of expired alveolar and arterial partial pressures, regardless of [Formula: see text] scatter severity or overall [Formula: see text]. For example, modal ideal [Formula: see text] can be estimated from the following equation: [Formula: see text]Using a multicompartment computer model of log-normal distributions of [Formula: see text] and [Formula: see text], agreement of this estimate with the modal ideal [Formula: see text] located at the [Formula: see text] ratio of maximal compartmental [Formula: see text] was assessed across a wide range of severity of [Formula: see text] scatter and overall [Formula: see text] ratio. Agreement of VDA/VA for CO2 from the Bohr equation using modal ideal PCO2, with that using the estimated value was also assessed. Estimated modal ideal [Formula: see text] agreed closely with modal ideal [Formula: see text], intraclass correlation (ICC) > 99.9%. There was no significant difference between VDA/VA using either value for ideal [Formula: see text]. Modal ideal [Formula: see text] reflects a physiologically realistic concept of ideal alveolar gas where there is maximal gas exchange effectiveness in a physiological distribution of [Formula: see text], which is generalizable to any inert gas and is practical to estimate from arterial and end-expired CO2 partial pressures.NEW & NOTEWORTHY The three-compartment model of lung ventilation-perfusion mismatch postulates definitive alveolar deadspace and "ideal gas" lung compartments, but these are, in fact, widely different for gases of different blood solubility. Physiologically realistic distributions of ventilation, perfusion, and gas exchange instead suggest an individual "ideal" ventilation-perfusion ratio for every gas, where its alveolar-capillary uptake or elimination rate is maximal (modal). For carbon dioxide, this "ideal" partial pressure is the mean of the arterial and end-tidal partial pressures.
URI: https://ahro.austin.org.au/austinjspui/handle/1/28725
DOI: 10.1152/japplphysiol.00597.2021
ORCID: 0000-0003-1185-2869
Journal: Journal of applied physiology (Bethesda, Md. : 1985)
PubMed URL: 34672764
PubMed URL: https://pubmed.ncbi.nlm.nih.gov/34672764/
Type: Journal Article
Subjects: alveolar gas exchange
carbon dioxide
dead space
ventilation-perfusion distribution
ventilation-perfusion mismatch
Appears in Collections:Journal articles

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