Results of the oxygen Fick method in a closed blood circulation model including “total arteriovenous diffusive shunt of oxygen”

Abstract

It is considered that arteriovenous diffusive shunts of oxygen may cause inaccuracy of the oxygen Fick method as$Up\dot VO_2 > \dot Q(CaO_2 - CvO_2 )$ where$Up\dot VO_2$ is the pulmonary oxygen uptake,$\dot Q$ is the cardiac output, and CaO₂ and CvO₂ are the arterial and venous oxygen contents, respectively.

A simple circulation model, including the whole circulation with nine well-mixed compartments (C1, ... C9), is constructed: the$\dot Q$ is assigned as constant as 6000 ml min⁻¹; the blood portions of 60 ml move at an interval of 600 ms. C1 and C2 compartments, each having 60 ml volume, represent the blood of pulmonary microcirculation, C3 represents the arterial blood with a volume of 1500 ml, C4, ..., C8, each also having a volume of 60 ml, represent the blood of peripheral microcirculation, whereas C9 represents the venous blood with a volume of 3000 ml. The pulmonary oxygen uptake$(Up\dot VO_2 )$, related to C1 and C2, the oxygen release$(rel\dot VO_2 )$, related to C4,...,C8, as well as a “total arteriovenous diffusive shunt of oxygen”$(av\dot VO_2 )$, from the arterial blood (C3) to the venous blood (C9), are calculated simultaneously. The alveolar gas has a constant oxygen partial pressure, and the pulmonary diffusion capacity is also constant; similar to modeling the pulmonry, oxygen diffusion, constant partial oxygen pressures for all peripheral tissues as well as constant diffusion capacities for all peripheral oxygen diffusion are also assigned. The diffusion capacities for the$av\dot VO_2$ (between C3 and C9) are arbitrarily assigned.

The Fick method gives incorrect results depending on the total arteriovenous diffusive shunt of oxygen$(av\dot VO_2 )$. But the mechanism determining the magnitude of$av\dot VO_2$ remains unclear.