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Biomedical subjects

H Tazawa

Publications and source records attributed to H Tazawa.

At least 127 records · Page 7Linked to original sources
PubMed1981

Effect of O2 and CO2 in N2, He, and SF6 on chick embryo blood pressure and heart rate.

Arterial pressure of chick embryos was measured electromanometrically to investigate the effect of altered gaseous environments on blood pressure (BP) and heart rate (HR). The experiments were made in eggs incubated for 14-16 days at 38 degrees C without impeding the diffusive respiratory gas exchange through the shell and chorioallantois. In air, the HR was counted 260-270 beats/min and the BP increased from 14/7 Torr at day 14 to 21/12 Torr at day 16. Both the BP and HR decreased with hypoxia, whereas hyperoxia affected a slight increase in BP and little change in HR. Hypercapnia decreased the HR and tended to enhance a systolic maximum pressure. The effect of hypoxia was augmented markedly in the presence of hypercapnia and vice versa. When N2 was replaced with helium (He), the effect of hypoxia was mitigated significantly. On the contrary, replacement of N2 with sulfur hexafluoride (SF6) augmented the effect of hypoxia. Because the respiratory gas exchange of the egg takes place by diffusion through the shell and chorioallantoic capillaries, the effect of He and SF6 atmospheres on BP and HR is attributed to an altered diffusivity of O2 and CO2 in these inert gases.

Animals↗
PubMed1981

Measurement of blood pressure of chick embryo with an implanted needle catheter.

A catheter, consisting of a hypodermic needle and polyethylene tube, was implanted in the allantoic artery and/or vein of chick embryos ranging in incubation ages from 13 to 17 days. The procedure was performed through a small hole opened in the shell (less than 1 cm2). The hole was covered after implantation of the catheter, ensuring the adequate gas exchange by the chorioallantois and physiological values of blood gases. Blood pressure was measured with an electromanometric transducer. The arterial pressure lacked a dicrotic elevation. Both the systolic and diastolic pressures increased markedly with days of incubation, but the heart rate showed no significant change. The venous pressure was pulsatile in some eggs, and the pulsations became prominent after administration of epinephrine.

Allantois↗
PubMed1981

Relationship between venoarterial CO2 content difference and venoalveolar PCO2 difference in acute hypercapnia in dogs.

When mixed venous blood is oxygenated in alveolar air with higher PCO2, the PCO2 within the red cell is though to exceed the alveolar PCO2 due to the Haldane effect and to block the inward CO2 diffusion. If the direction of the CO2 diffusion is not reversed during the contact time, the HCO2-gain in the plasma will not exceed the amount estimated from venoalveolar PCO2 difference by using a CO2 dissociation curve of separated plasma. In order to clarify the validity of the above thought, the venoarterial CO2 content difference was measured by using a van Slyke apparatus and a PCO2 electrode at various alveolar PCO2 levels in rebreathing dogs. The HCO3-rise in the whole blood was obviously reduced when acute hypercapnia was administered in both normoxia and hyperoxia. Quantitatively, the decrease of CO2 content under hypercapnia corresponded to the difference in CO2 content between the true and separated plasma. The reduction, however, was slightly stronger in normoxia than in hyperoxia with alveolar PO2 of 300 to 420 mmHg. These data seem to support the following explanation: When venous blood was oxygenated in normoxic air with PCO2 higher than true venous, the inward CO2 diffusion was inhibited by the Haldane effect and the reversed diffusion after the oxygenation could also be disregarded during the contact time. Because the oxygenation was accelerated in hyperoxia and the direction of the CO2 diffusion was reversed earlier than in normoxia, the plasma CO2 content became higher in hyperoxia than in normoxia.

Animals↗
PubMed1980

Adverse effect of failure to turn the avian egg on the embryo oxygen exchange.

Fertile chicken eggs belonging to the same flock of hens were divided into two groups and incubated for 16 days. During incubation, group 1 eggs were turned twice a day and group 2 eggs were left unturned. Blood sampled from the allantoic vein or artery was analyzed for gas tensions (PO2 and PCO2), pH and Hct. These values were compared by unmpaired t-test for significance differences between the two groups. While the differences of PCO2 and pH were found insignificant, failure to turn the eggs caused a pronounced fall in the arterialized PO2 which was accompanied with an increase in Hct. In addition, the embryo weight was reduced in unturned eggs. Lack of turning retarded the absorption of albumen. The unabsorbed albumen interposed between the chorioallantoic membrane and inner shell membrane, impeding the blood oxygenation through the chorioallantois. Little change in PCO2 might be attributed to a large diffusive conductance of the chorioallantois for CO2. The present results suggest that the eggs must be turned periodically during incubation to prevent the distortion of normal oxygen exchange especially for the study of egg respiration.

Animals↗
PubMed1980

Analysis of chorioallantoic gas exchange in the chick embryo.

To analyze the gas exchange mechanisms in the chorioallantois, PO2 and PCO2 were measured in air cell gas, in the allantoic artery and in the allantoic vein in chicken embryos on the 16th day of incubation. In addition, the O2 dissociation curve of blood, and O2 uptake and CO2 output of the embryo were determined. From O2 measurements performed in hypoxia (FIO2=0.14), normoxia and hyperoxia (FIO2=0.67), it was concluded that there was a sizable functional arterio-venous shunt amounting to 10-15% of the total chorioallantoic blood flow and that the diffusing capacity of the air cell-blood barrier for O2 was about 7 microliter . min-1. Torr-1. The CO2 measurements are in agreement with the model. In hypoxia, the air cell-blood transfer of O2 was markedly diffusion limited. The diffusion limitation effect was slight in normoxia, and not detectable in hyperoxia. At all oxygenation levels the effect of the shunt on blood arterialization was marked, particularly so in hyperoxia where the air cell-arterialized blood PO2 difference averaged 180 Torr.

Allantois↗
PubMed1979

Respiratory gas transport by the incompletely separated double circulation in the bullfrog, Rana catesbeiana.

To investigate respiratory gas transport in the bullfrog, Rana catesbeiana (mean body weight 249 g. ambient temperature 25 degrees C), O2 uptake and CO2 output were determined, and blood gas parameters (PO2, PCO2, pH, O2 content, O2 capacity and hematocrit) were measured in blood samples taken from various heart cavities and blood vessels. Analysis of the data on the basis of a simplified circulatory gas transport model allowed to estimate the cardiac output and its distribution, and to describe the O2 and CO2 exchange in lungs, skin and tissues. The total cardiac output (average 20.5 ml/min) was estimated to be distributed about equally to the pulmocutaneous (56%) and systemic arterial vessels (44%), whereas the systemic venous return (62%) was larger than the pulmonary venous return (38%). The marked difference in oxygenation between aortic and pulmocutaneous arterial blood (average O2 saturation 85% and 47%, respectively) showed a highly effective separation of systemic venous and pulmonary venous blood in the ventricle and conus arteriosus. After enlargement of the ventricle produced by incision of the pericardium, the separation of arterialized and venous blood was markedly reduced, but not abolished.

Animals↗
PubMed1978

Oxygen transport in chicken embryos under hypothermal exposure.

Fertile hens' eggs incubated for 16 days at 38 degrees C were abruptly exposed to a temperature of 30 degrees C for 2 h and then determinations of blood gas parameters and the O2 dissociation curve were performed. In addition, O2 uptake was measured. Under hypothermal exposure the O2 dissociation curve showed a marked leftward shift in accordance with the increase in pH. The O2 saturation in arterialized blood of the allantoic vein reached almost 100%, and the blood S(O2) of the allantoic artery also increased up to about 50% in contrast with about 20% in normothermal controls. The blood flow rate through the chorioallantoic capillary plexus seemed to be almost identical with that of normothermal embryos. Because of the increased O2 affinity and the decreased O2 consumption, the systemic venous O2 reserve should be raised by hypothermal exposure. In connection with this conjecture, the redistribution of blood flow and O2 quantity by hypothermal exposure were calculated using the same circulation model as used in normothermal embryos. The result came closer to fetal lambs than to normothermal embryos.

Animals↗
PubMed1977

Oxygen analyses of chicken embryo blood.

According to data obtained previously on the blood gas tensions and the oxygen dissociation curve of chicken embryos, the arteriovenous oxygen saturation difference in the allantoic circulation has been conjectured fairly large. In order to confirm this conjecture as well as to check the validity of the in vitro dissociation curve, both the blood oxygen capacity and content in allantoic artery and vein were measured. The in vivo O2 saturation measured here resulted in a similar value to that estimated from the dissociation curve. The O2 content in allantoic vein ranges from about 7 to 11.5 vol% during the 10th to the 18th days of incubation and that in artery is pronouncedly low in a range of 1 to 2.5 vol%, suggesting that the blood flow rate through the body tissues is fairly larger than that through the gas exchange capillary plexus. Then, the distribution of blood flow was estimated from the analyzed data based on a model of blood circulation and some assumptions. In connection with this estimation, the diffusing capacity for deoxygenation in the tissues was speculated to be much larger than that for oxygenation in the chorioallantoic capillaries.

Allantois↗
PubMed1976

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 it's 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.

Allantois↗
PubMed1976

Oxygen dissociation curve for chorioallantoic capillary blood of chicken embryo.

Oxygen dissociation curves for blood in the chorioallantoic capillary of chicken embryos were determined using a microphotometric apparatus made for measuring the reaction velocity of a red blood cell with oxygen and carbon monoxide. The modified Hill's equations expressing the dissociation curve during development were calculated by two methods. P50's at pH of 7.4 were found to be 60.0, 54.4, 46.2, 33.1, and 28.6 mmHg for 10, 12, 14, 16 and 18 days of incubation, respectively. Although the Bohr factor did not show a clear relation to age, the oxygen affinity and the oxygen capacity tended to increase with the lapse of days, and the power of heme-to-heme interaction, to decrease with age. The findings imply that there is a respiratory adaptation of embryos during development.

Allantois↗
PubMed1976

Oxygenation and deoxygenation velocity factors of chorioallantoic capillary blood.

The oxygenation and deoxygenation rates of capillary blood of chicken embryo were measured precisely with a microphotometric reaction apparatus. The velocity factors expressed as Fcox and Fcdeox in ml O2-ml RBC-1-S-1-mmHg-1 were calculated as functions of oxygen saturation. They were similar to results previously obtained in human blood using the rapid flow apparatus. The continuous registration of the reaction with oxygen enables us to estimate the equilibrium time of blood when passing through the chorioallantoic capillary. The value obtained was almost identical to the contact time indirectly assessed from the CO reaction. The diffusing capacity of the chorioallantoic capillary plexus of the 16-day-old embryos was estimated as 7.3 x 10(-3) ml-min-1mmHg-1 by using the values of the Fcox and the equilibrium time determined here together with the values of the blood flow and hematocrit which had been obtained in the previous experiments.

Allantois↗
PubMed1975

Microphotometric method for measuring the oxygenation and deoxygenation rate in a single red blood cell.

A new reaction apparatus combining a microscope and a photometric device was developed for kinetic studies of a single red cell. A monolayer of red cells was placed in a closed reaction cuvette set on a microscope stage, a light beam of 5 to 10 mum in diameter was directed into one of the red cells, and the light transmission change in the cell was analyzed. The light beam with a wavelength range shorter than 460 nm was made by placing a narrow iris diaphragm in the light path. The space in the cuvette prevented the red cells from drying thereby providing favorable physiological conditions during measurements. The cuvette was filled with reagent gas mixtures of O2, CO2, and N2 which came in contact with the red cells. Transmission change due to the reaction was detected separately at two wavelengths of 418 and 402 nm by means of two photomultipliers mounted on the microscope. The linearity was tested by comparison between SO2 measured with a Van-Slyke apparatus and the microphotometer. Both SO2 measurements agreed well with each other, but the latter was about 3% greater than the former at around 50% SO2. Using this apparatus the oxygenation and deoxygenation velocities were measured over an entire O2-saturation range. The velocity factors showed good agreement with those obtained by using conventional flow methods.

Carbon Dioxide↗