Oxygenation performance assessment of an artificial lung in different central anatomic configurations

Objectives: Aim of this work was to characterize possible central anatomical configurations in which a future artificial lung (AL) could be connected, in terms of oxygenation performance. Methods: Pulmonary and systemic circulations were simulated using a numerical and an in vitro approach. The in vitro simulation was carried out in a mock loop in three phases: (1) normal lung, (2) pulmonary shunt (50% and 100%), and (3) oxygenator support in three anatomical configurations: right atrium-pulmonary artery (RA-PA), pulmonary artery-left atrium (PA-LA), and aorta-left atrium (Ao-LA). The numerical simulation was performed for the oxygenator support phase. The oxygen saturation (SO2) of the arterial blood was plotted over time for two percentages of pulmonary shunt and three blood flow rates through the oxygenator. Results: During the pulmonary shunt phase, SO2 reached a steady state value (of 68% for a 50% shunt and of nearly 0% for a 100% shunt) 20 min after the shunt was set. During the oxygenator support phase, physiological values of SO2 were reached for RA-PA and PA-LA, in case of a 50% pulmonary shunt. For the same conditions, Ao-LA could reach a maximum SO2 of nearly 60%. Numerical results were congruous to the in vitro simulation ones. Conclusions: Both in vitro and numerical simulations were able to properly characterize oxygenation properties of a future AL depending on its placement. Different anatomical configurations perform differently in terms of oxygenation. Right to right and right to left connections perform better than left to left ones.

Arterial saturation was calculated in 1 min intervals (each cycle) based on the venous saturation and the oxygen transfer rate of the lungs. The arterial and venous saturation were calculated in total for 25 cycles.
A commercially available oxygenator was tested in vitro, and the inlet/outlet blood-gas data were used to model the performance of a generic oxygenator. The contribution of the oxygenator was added according to the chosen configuration.

PA-LA
The blood from the PA flows through three ramifications: lung, bypass and oxygenator.
Where is the total blood flow in the system and , , and are the blood flows through the lungs, the bypass and the oxygenator respectively.
From the definition of the shunt: where is the percentage of the pulmonary shunt considered.
The oxygen transfer rate (OTRlung) of the lungs was calculated as follows: = ( * * ∆ 2 + 0.00314 * 2( ) ) * where H=1,34 is a constant, Hb is the blood hemoglobin, ∆ 2 is the difference between oxygen saturation of the arterial and venous blood, 2( ) is the oxygen partial pressure, and is the blood flow rate through the lungs. Since the 2( ) cannot exceed 100 mmHg, the term 0.00314 * 2( ) is very small and can be neglected.
We defined as normal transfer rate (OTRnormal) the oxygen transfer rate that by a total blood flow could increase the saturation from a venous value ( 2 =70%) to an arterial value From equation (3) and (4):
We assumed that the oxygenator can bring the oxygen saturation of the blood to 100%.
Once calculating the oxygen content in LA, we can calculate the saturation as well: 2( ) = 100 * 2( ) * Once the blood flows through the body periphery, oxygen will be transferred to the body periphery and the oxygen saturation of the blood will change. As mentioned before, in a normal functioning lung, the saturation will change from 100% to approx. 70% (∆ 2 =0,3).
We consider for the simulation, a constant need of the body in terms of oxygen, so a constant OTR, and since OTR is directly proportional to the ∆ 2 , a constant ∆ 2 of 0,3 too.