Mechanisms behind inter-individual differences in lung diffusing capacity

Abstract

We measured diffusing capacity (DLCO), alveolar membrane properties (D (m)), capillary lung volume (V (c)), and alveolar volume (V (A) ) in 20 healthy subjects (12 males; age 32.4 +/- 13 (SD); BMI 21.7 +/- 3; non smokers) at total lung capacity (TLC) and at approximately 80, 60, and 40% TLC. In all subjects, D (m) increased with lung volume, the increase being significantly greater for higher values of D (m)(TLC): the inter-individual differences can be interpreted by a greater number of alveolar units coupled to a lower thickness of the air-blood barrier (thus a higher alveolar surface to thickness ratio S (A)/tau). On the average, the volume-dependent increase of D (m) from approximately 40 to 100% TLC is less than expected based on geometrical increase of S (A) /tau. In fact, up to approximately 80% TLC, the increase in D (m) closely reflects only the increase of S (A), suggesting "unfolding" of the septa with no appreciable decrease in tau. Conversely, above 80% TLC, the decrease in tau due to parenchymal stretching becomes the main factor affecting D (m). In all subjects, V (c) decreased with increasing lung volume, in line with an increase in parenchymal stretching; the decrease was significantly larger for higher values of V (c) (40% TLC). Possibly reflecting differences in alveolar capillary density. No correlation was found between D (m)(TLC) and V (c)(40%TLC). The individual specificity in the lung volume dependence of V (c) and D (m) can be reasonably described by evaluating the V (c)/D (m) ratio at TLC and at approximately 40%TLC.

Sex differences in respiratory and circulatory cost during hypoxic walking: potential impact on oxygen saturation

“…Instead, anatomical interpretations of the present results are based on previous studies 4–8 and should be treated with caution. Similarly, although a reduction in SpO 2 has been thought to be related pulmonary O 2 diffusion capacity 1,2 , a previous study found greater inter-individual differences in the alveolar-capillary membrane diffusing capacity and the pulmonary capillary blood volume, which are subcomponents of total lung diffusion capacity with an inspiration of different concentration of O 2 (20-40-60% O 2 ) 35 . Similar results (i.e., greater inter-indvidual differences in lung diffusion capacity) were found under hypobaric hypoxia at rest 36 and during sub-maximal exercise 37 .…”

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

“…The importance of this point becomes relevant when balanced against an increase in cells metabolic requirement, namely the increased oxygen demand, as in exercise, as well as in conditions causing a limitation to oxygen delivery (environmental hypoxia and cardio-pulmonary disorders). Recent work from our group revealed considerable inter-individual differences in the adaptive response of the air-blood barrier to work in normoxia and hypoxia 1–3 and further the adaptations correlated with the morpho-functional phenotype of the air-blood barrier 4 .…”

The effect of exogenous surfactant on alveolar interdependence

“…After surfactant instillation, in preterm, alveolar compliance increased dramatically in line with an increase in average alveolar size and a decrease in alveolar size distribution (Cattarossi et al, 2010). A greater alveolar perfusion was demonstrated in humans at low lung distending pressure (Miserocchi et al, 2008) and, in particular, for P d < 2 cmH 2 O in experimental animal (Godbey et al, 1995). Thus, the decrease in P d can justify the reported improvement in oxygenation index following surfactant replacement therapy by a parallel increase in diffusive and convective conductance for oxygen (Piiper and Scheid, 1981).…”