Blood oxygen transfer rate

Matsuda N, Nakamura M, Sakai K, Kuwana K, and Tahara K. Theoretical and experimental evaluation for blood pressure drop and oxygen transfer rate in outside blood flow membrane oxygenator. J. Chem. Eng. Jpn. 1999 32(6) 752-759. 

Evaluating this unit in vitro, Clark and Mills found the maximal oxygen transfer rate to be 34 ml/min at a gas-to-blood flow ratio of 8 1 and at 1500 ml/min blood flow (Figure 5). 

Figure 5. Oxygen transfer rate vs. blood flow at various gas-to-blood flow...

We can think of the oxygen transfer from the lung to the blood as a simple chemical reaction molecules of gas strike the alveoli. By analogy with simple solution-phase reactions, the rate equation describing the rate at which oxygen enters the blood is formulated according to... 

Some of these stability issues can be addressed by the use of protective barrier membranes, at the risk of aggravating another fundamental challenge reactant mass transfer. Typical reactants present in vivo are available only at low concentrations (glucose, 5 mM oxygen, 0.1 mM lactate, 1 mM). Maximum current density is therefore limited by the ability of such reactants to diffuse to and within bioelectrodes. In the case of glucose, flux to cylindrical electrodes embedded in the walls of blood vessels, where mass transfer is enhanced by blood flow of 1—10 cm/s, is expected to be 1—2 mA/cm. ° Mass-transfer rates are even lower in tissues, where such convection is absent. However, microscale electrodes with fiber or microdot geometries benefit from cylindrical or spherical diffusion fields and can achieve current densities up to 1 mA/cm at the expense of decreased electrode area. ... 

Carbon Dioxide Transfer Rates in Blood Oxygenators... 

The second generation of nonporous membranes was silicon based which displayed increased CO2 permeabilities. In 1965, Bramson et al. commercialized the first nonporous membrane BO [18]. Since the diffusion coefficient of oxygen and carbon dioxide in air is about four orders of magnitude higher than in blood, the gas side mass-transfer resistance was negligible. The major resistance to respiratory gas transfer was due to the membrane and the liquid side concentration boundary layer [19]. Though nonporous membrane BOs reduced blood damage, up to 5.5 m membrane surface area was often required to ensure adequate gas transfer rates. 

The rate of oxygen transfer per unit area of liquid membrane was estimated. The rate of oxygen uptake was measured from the initial slope of the curve for liquid membranes in Figure 2 and the measured 13 gm/100 ml hemoglobin content of the blood. The volume formation... 

Liquid membrane of fluorocarbons can be formed encapsulating oxygen bubbles in blood. The transfer of oxygen and carbon dioxide through the liquid membrane to and from the blood, respectively, have been shown. Very similar transfer rates with and without liquid membranes indicate that the resistance of the liquid membranes is small. 

The specific rate of oxygen transfer per unit of liquid membrane area seems to be quite reasonable. However, methods to form and utilize effectively much smaller diameter liquid membranes, perhaps similar to those used in other liquid membrane applications, would be required to obtain enough membrane area per unit blood volume for a practical blood oxygenator. The stability of the liquid membranes does not seem to be a major problem however, more definitive liquid membrane stability information would be required before the blood oxygenator application. 

In the placenta a volume of oxygen sufficient for fetal needs must diffuse across the membranes from maternal to fetal blood during the short time the two circulations are in close contact. This oxygen transfer is a function of several factors which include uterine and umbilical arterial 02 partial pressures, maternal and fetal placental blood flow rates, the 02 capacity and 02 affinity of maternal and fetal hemoglobin, the diffusing capacity of the placenta, the amount of C02 exchanged, and the vascular arrangement of maternal to fetal vessels. 

Calculations show that if the maternal blood flow rate is allowed to increase indefinitely while fetal blood flow rate is maintained constant, the quantity of oxygen transferred increases asymptotically toward a value above the normal. Reductions in maternal blood flow rate in the normal region (Fm/Ff = 2.1) result in only small decreases in the amount of oxygen transferred. 

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