Masaji Mochizuki

Estimation of contact time and diffusing capacity for oxygen in the chorioallantoic vascular plexus

The contact time of erythrocyte in the chorioallantioc capillaries of chicken embryos was estimated by referring to the oxygenation rate measured with a microphotometer. The chorioallantioc membrane was excised from an incubated egg and the SO2 of blood in its capillary was changed by varying the gas composition around the membrane from the venous blood PO2 level to the air space gas. The oxygenation time (te) required to attain the level of arterialized blood SO2 was measured as the contact time (tc) in the capillaries, which resulted in 0.87, 0.74, 0.57, 0.49 and 0.36 sec for 10, 12, 14, 16 and 18 days of incubation, respectively. The obtained te value coincided with the contact time calculated from the CO diffusing capacity referring to the reaction rate of CO with oxygenated erythrocyte. Using the te value, the diffusing capacity for O2 in the chorioallantoic capillary was calculated; 1.1, 2.2, 4.4, 6.0 and 6.6 x 10(-3) ml-min-1 - mm Hg-1 for the same incubation days as above. The capillary blood volume (Vc) was also estimated, which increased from about 16 to 35 mul during development from 10 to 18 days. The values of DO2 and Vc converted per kg weight of embryo at the days near hatching were similar to those per kg body weight estimated in human lung.

Oxygen transport to tissue X

Hyperthermia is a developing modelity for the treatment of cancer. This therapy is occasionally used by itself, however, usually it is used as an adjuvate with chemo or radiation therapy. The mechanism for this treatment is based on, the fact that cancer cells are heated preferentially by heat application due to lower vascularity in the tumor tissue as compared with the surrounding normal tissue and that, when used with radiation therapy or chemo therapy, higher oxygen partial pressure in the tumor results in increased tumor cell damage. Appropriate mathematical models and their real time prediction of oxygen and temperature profiles could be very helpful in achieving optimal results via hyperthermia and to avoid possible danger which might occur during the treatment. Because of the complexity and the heterogeneous nature of physiological system, it is necessary to include heterogeneous properties in the mathematical models for them to be useful for biomedicai calculations. Of course, it is much more difficult to sorve mathematically the heterogeneous system than the homogeneous one. In this paper, the importance of the implementation of heterogeneities in the heat and mass transport for biological system mathematical modelling is discussed. Results of a three dimensional computer simulation of mass and heat transfer in tumor tissue with different capillary geometries during hyperthermia are demonstrated. The method used for the computer simulation is a deterministic/ probabilistic technique, Williford-Bruley calculational strategy.

Determination of the PCO2-Dependent Component of the H+ Concentration in Venous and Arterial Blood Plasma

In normal venous blood plasma, the regression line of [H+] plotted against the PCO2 was linear against the square root of PCO2. Sequential measurements in venous and arterial blood of PCO2 and [H+] showed that the venous-arterial (V-A) difference in [H+] was linearly related to the V-A difference in the square root of PCO2, the regression line having the same slope as that of the venous [H+] plotted against the square root of PCO2. These findings suggested that the venous [H+] on the regression line represents the PCO2-dependent component, of [H+], [H+]*. The PCO2-independent component, delta [H+], can then be given by subtracting [H+]* from the measured [H+]. The delta [H+] in venous blood agreed well with that in arterial blood with a correlation coefficient of 0.99, supporting the validity of the value of [H+]*.

Blood-Gas Transfer of O2 and CO2 in the Lungs: New Models Measurements and Conclusions

Three simultaneous differential equations for O2, CO2 and HCO 3 - diffusion in the red blood cell (RBC) were solved numerically, taking the Bohr and Haldane effects into account (Mochizuki and Kagawa, 1986). Then, from the numerical solution the relationship of the gas exchange ratio (R) to alveolar PCO2 (PACO2) during rebreathing was derived (Kagawa and Mochizuki, 1987). R in rebreathing air is linearly related to PACO2. Since CO2 diffusion in the RBC accompanies HCO 3 - shift and partly results from the Haldane effect, the CO2 reactions are generally slower than the O2 reactions. Therefore, the slope of R-CO2 line (θ) depends not only on the true venous PCO2 (trPvCO2) and arterial-venous O2 content difference (C(a-v)O2), but also on the contact time (tc). Using the theoretical equation for the R-PCO2 line as a gas exchange model, the relationship between tc and C(a-v)O2 is obtained from the experimental data of rebreathing in normal subject (Shibuya et al, 1987).

Relationship between Alveolar-Arterial Po2 and Pco2 Differences and the Contact Time in the Lung Capillary

From the numerical solutions of simultaneous O2 and CO2 diffusions in the RBC, we calculated the P(A-a)CO2 by varying the tc at various PvO2 and PvCO2 levels, whereas the PAO2 and PACO2 were kept constant at 90 and 40 Torr, respectively. From the results we could clarify the relationship between the P(A-a)CO2 and the tc and its dependency on PvO2 and PvCO2. Furthermore, the influence of the tc on the C(a-v)O2, C(v-a)CO2 and R was clarified quantitatively.

Relation between the contact time and venous and alveolar PCO2 at rest.

The simultaneous partial differential equations for diffusions of O2, CO2, and HCO 3 − ions in the red blood cell (RBC) were solved numerically, taking chemical reactions of Bohr- and Haldane-effects into account. The diffusion equations and the chemical reactions were computed alternatively in an increment time of 2 msec. After solving each of the three diffusion equations, the Po2, O2 saturation (S), Pco2, pH and HCO 3 − content were corrected by using the equations of Bohr- and Haldane-effects, and a modified Henderson-Hasselbalch equation (Kagawa and Mochizuki, 1984). The Bohr-shift was calculated from Hill’s equation by assuming its K value to be a function of the intracellular pH. The change in intracellular Pco2 due to the Haldane effect was also evaluated by means of the modified Henderson-Hasselbalch equation, in which the buffer value was taken as 44 mmol · 1(RBC)−1 · pH c −1 . The computed Pco2 profiles during the Haldane effect in a closed vessel was compatible wit the experimental data of Klocke (1973). The extracellular Po2 profile computed during the Bohr-off-shift in a closed system coincided well with the experimental data of Nakamura and Staub (1964) and Forster and Steen (1968).

EFFECT OF DIFFUSION HETEROGENEITY ON OXYGEN TENSION IN TISSUE

Publisher Summary This chapter discusses the effect of diffusion heterogeneity on oxygen tension in tissue. It describes a theoretical study on the diffusion heterogeneity that was performed to elucidate the extent to which the diffusion rate and the PO 2 profile were influenced by the facilitated diffusion because of such an enzyme as cytochrome P-450. In the study, a simulation was made in a three-dimensional tissue model, assuming that a flat diffusion layer with an appropriate thickness was lying side by side at a constant distance. The PO 2 profile was calculated from the differential equation of the diffusion with a zero-order O 2 consumption rate in the steady state by using a point iterative method. The influence of the heterogeneity was apparently observed in a large cell of about 20 μm, suggesting a possibility to estimate the diffusivity of the facilitated diffusion layer quantitatively through the simulation technique. The PO 2 pattern in the semi-infinite tissue model was first calculated by changing the density of the facilitated diffusion layer, its thickness, and the PO 2 at the boundary. The diffusion quantity across the unit surface area increased with the PO 2 in the medium. The former was proportional to the square root of the latter; however, the ratio of the increase in diffusion quantity through the facilitated layer to the total diffusion quantity was almost independent of the PO 2 in the outer medium.

Analysis of Oxygen Transport in Bullfrogs

The O2 transport system in frogs is different from other higher vertebrates, because of the structure of their heart consisting of the two atria and one ventricle, and rather similar to the mammalian fetuses (Dawes et al., 1954) and avian embryos (Tazawa and Mochizuki, 1977). Both the arterialized blood from the lung and the venous blood from the systemic tissues become confluent in the univentricle, and the confluent flow goes on into the systemic and pulmocutaneous circulations simultaneously. The O2 quantity in the systemic arterial blood was reported to be larger than in the pulmocutaneous artery, indicating a selective streaming in frog’s heart (DeLong, 1962; Johansen and Ditadi, 1966; Emilio and Shelton, 1974). In the present report, we attempted to obtain the basic data on the O2 transport in bullfrogs and present an analytical method for showing the O2 distribution in the pulmocutaneous and systemic circulations.

Measurement of Oxygenation and Deoxygenation of a Single Red Cell of Chicken Embryo by Means of a Microphotometer

In order to overcome difficulties inherent in the flow reaction apparatus so far used for kinetic studies of red cells, we have developed a technique of microphotometry. Since in a microphotometer a small light beam of about 10 u is transmitted through a single red cell, the reactions with O2 and CO can be measured by flushing a reacting gas onto the red cells. In the previous studies (1,2), the method of reaction measurement was elaborated and the CO reaction was determined in the red cells existing in the chorioallantoic capillary of chicken embryo. Since then, by using the same method and material, we have measured the oxygenation and deoxygenation rates and examined the velocity of combination and dissociation of O2 due to the Bohr effect.

A Proposal for Analysing the Acid-Base Balance at Steady State in Vivo

[H+] in plasma in vivo is composed of a PCO2-dependent component [H+]* and a PCO2-independent component delta [H+]. The correct equation for the calculation of [H+]* was found by referring to the slope of the regression line between the venous-arterial difference of delta [H+] and that of PCO2. Using [H+]*, the buffer value in vivo and the base excess were calculated. Since the base excess was hyperbolic against delta [H+] and dependent on PCO2, we concluded that it was better to use delta [H+] rather than the base excess to evaluate the metabolic change of [H+] in plasma.