Gravity outweighs the contribution of structure to passive ventilation-perfusion matching in the supine adult human lung

Gravity and matched airway/vascular tree geometries are both hypothesized to be key contributors to ventilation-perfusion (V/Q) matching in the lung, but their relative contributions are challenging to quantify experimentally. We used a structure-based model to conduct an analysis of the relative contributions of tissue deformation (the 'Slinky' effect), other gravitational mechanisms (weight of blood and gravitational gradient in tissue elastic recoil), and matched airway and arterial tree geometry to V/Q matching and therefore to total lung oxygen exchange. Our results showed that the heterogeneity in V and Q were lowest and the correlation between V and Q was highest when the only mechanism for V/Q matching was either tissue deformation or matched geometry. Heterogeneity in V and Q was highest and their correlation was poorest when all mechanisms were active (that is, at baseline). Eliminating the contribution of matched geometry did not change the correlation between V and Q at baseline. Despite the much larger heterogeneities in V and Q at baseline, the contribution of in-common (to V and Q) gravitational mechanisms provided sufficient compensatory V/Q matching to minimize the impact on oxygen transfer. In summary, this model predicts that during supine normal breathing under gravitational loading, passive V/Q matching is predominantly determined by shared gravitationally-induced tissue deformation, compliance distribution, and the effect of the hydrostatic pressure gradient on vessel and capillary size and blood pressures. Contribution from the matching airway and arterial tree geometries in this model is minor under normal gravity in the supine adult human lung.

from Physiology via xlomafota13 on Inoreader http://ift.tt/2yB1c5E
via IFTTT