AUTHOR=Miserocchi Giuseppe , Beretta Egidio , Rivolta Ilaria , Bartesaghi Manuela 

TITLE=Role of the Air-Blood Barrier Phenotype in Lung Oxygen Uptake and Control of Extravascular Water

JOURNAL=Frontiers in Physiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2022.811129

DOI=10.3389/fphys.2022.811129

ISSN=1664-042X

ABSTRACT=<p>The air blood barrier phenotype can be reasonably described by the ratio of lung capillary blood volume to the diffusion capacity of the alveolar membrane (<italic>Vc/Dm</italic>), which can be determined at rest in normoxia. The distribution of the <italic>Vc/Dm</italic> ratio in the population is normal; <italic>Vc/Dm</italic> shifts from ∼1, reflecting a higher number of alveoli of smaller radius, providing a high alveolar surface and a limited extension of the capillary network, to just opposite features on increasing <italic>Vc/Dm</italic> up to ∼6. We studied the kinetics of alveolar-capillary equilibration on exposure to edemagenic conditions (work at ∼60% maximum aerobic power) in hypoxia (HA) (P<sub>I</sub>O<sub>2</sub> 90 mmHg), based on an estimate of time constant of equilibration (τ) and blood capillary transit time (<italic>Tt</italic>). A shunt-like effect was described for subjects having a high <italic>Vc/Dm</italic> ratio, reflecting a longer τ (&gt;0.5 s) and a shorter <italic>Tt</italic> (&lt;0.8 s) due to pulmonary vasoconstriction and a larger increase in cardiac output (&gt;3-fold). The tendency to develop lung edema in edemagenic conditions (work in HA) was found to be directly proportional to the value of <italic>Vc/Dm</italic> as suggested by an estimate of the mechanical properties of the respiratory system with the forced frequency oscillation technique.</p>