Differences in alveolo-capillary equilibration in healthy subjects on facing O2 demand

Abstract

Oxygen diffusion across the air-blood barrier in the lung is commensurate with metabolic needs and ideally allows full equilibration between alveolar and blood partial oxygen pressures. We estimated the alveolo-capillary O2 equilibration in 18 healthy subjects at sea level at rest and after exposure to increased O2 demand, including work at sea level and on hypobaric hypoxia exposure at 3840 m (PA ~ 50 mmHg). For each subject we estimated O2 diffusion capacity (DO2), pulmonary capillary blood volume (Vc) and cardiac output (). We derived blood capillary transit time and the time constant of the equilibration process (, β being the slope of the hemoglobin dissociation curve). O2 equilibration at the arterial end of the pulmonary capillary was defined as . Leq greately differed among subjects in the most demanding O2 condition (work in hypoxia): lack of full equilibration was found to range from 5 to 42% of the alveolo-capillary PO2 gradient at the venous end. The present analysis proves to be sensible enough to highlight inter-individual differences in alveolo-capillary equilibration among healthy subjects.

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

“…Based on Equation 4, the equilibrium at the exit from the capillary may be written as ( Beretta et al, 2019 ):…”

“… Time course of 1- Leq (an index of alveolar-capillary equilibration) in normoxia at rest (a continuous line) and on exposure to severe hypoxia (3,840 m, P I O 2 90 mmHg, a dashed line) in two representative subjects having a high (A) or a low (B) Vc/Dm ratio at the sea level (SL) in resting condition (data from Beretta et al, 2019 ). …”

“…(B) A plot of Leq vs. 1/Tt (an index of blood velocity). Red and blue dots refer to the two subjects shown in Figures 5A,B , respectively (data from Beretta et al, 2019 ).…”

“… Correlation between Leq and a cardiac output ( ) in the condition indicated. Red and blue dots refer to the two subjects shown in Figures 5A,B , respectively (from Beretta et al, 2019 ). …”

“… Distribution of Leq values in all subjects at the end of exercise in severe hypoxia (HA) (3,840 m, P I O 2 90 mmHg). Red and blue dots refer to the two subjects shown in Figures 5A,B , respectively (data from Beretta et al, 2019 ). …”