Effects of pH and SO2 on solubility coefficients of inert gases in human whole blood

We systematically investigated the quantitative importance of pH and O2 saturation (SO2) of hemoglobin on the solubility coefficients (alpha) for six inert gases: sulfur hexafluoride, N2, ethane, cyclopropane, halothane, and diethyl ether. Measurements of alpha were made at 37 degrees C with SO2 of 0-1.0 and pH of 7.2-7.7 by use of whole blood obtained from three healthy subjects. No significant dependence of alpha on pH was demonstrated for sulfur hexafluoride, N2, halothane, or diethyl ether, but an appreciable augmentation of alpha with increasing pH was found for ethane and cyclopropane. No alpha value obtained for oxygenated blood differed statistically from that for deoxygenated blood. In addition to the basic findings on the effects of pH on alpha values of ethane and cyclopropane with the multiple inert gas elimination technique (data obtained from 22 patients with either interstitial pneumonia or chronic obstructive pulmonary disease), we also found that dependence of alpha on blood pH exerted no significant influence on the recovery of ventilation-perfusion distribution in the lung. We concluded that: 1) pH plays an appreciable role in determining gas solubilities in blood, 2) SO2 is not a decisive factor for gas solubilities in blood, and 3) the influence of various pH values in pulmonary capillaries on inert gas exchange is negligible.

[Alteration of oxygen extraction and blood flow in various organs under acute hypoxia]

To assess the compensatory mechanisms involved in maintaining aerobic metabolism in various organs during exposure to acute hypoxia, five anesthetized and paralyzed dogs were ventilated with either normoxic (FIO2: 0.21) or hypoxic gas mixture (FIO2: 0.13). Under both conditions, we examined systemic and pulmonary hemodynamic parameters, and took samples of arterial and mixed venous blood as well as venous blood from various organs including the heart, brain splanchic organs (hepatic vein) and kidney. Based on PO2, PCO2 and pH values as measured with electrodes, we calculated O2 and CO2 contents in each blood sample. The values thus obtained were then used to estimate the O2 extraction ratio (ER), gas exchange ratio (R) and difference of base excess between arterial and venous blood (avBE) in the whole body as well as in each organ. In addition, both O2 delivery (DO2) and O2 consumption (VO2) in the whole body were calculated. Although the whole body showed a decrease in DO2 and an increase in ER during hypoxic gas breathing, other parameters including R, avBE and VO2 did not change significantly. Higher ER values were found in the heart and brain than those in the splanchic organs and kidney, the qualitative trend being the same irrespective of FIO2. On the other hand, increase in ER during hypoxic gas breathing was considerably larger in the splanchic organs and kidney than that in the heart and brain. There was no significant difference in R and avBE in any of the organs between normoxic and hypoxic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

[A case of pulmonary eosinophilic granuloma with three-day fever]

A 45-year-old man was admitted to our hospital with chief complaint of fever. The chest X-ray examination showed 2-3 mm fine nodular shadows throughout the entire lung fields. Eosinophilia was present in the peripheral blood. Spike-like high fever (39 degrees C) appeared every 48 hours. All bacteriologic cultures from blood, bone marrow aspirate, sputum, gastric juice, and bronchoalveolar lavage fluid were negative. Furthermore, the antibody titer of malaria was negative. No antibiotics were effective in this case. Histological examination of the transbronchial lung biopsy showed non-specific inflammation, but the open lung biopsy specimen showed scattering of tiny granulomatous lesions. These granulomas were composed of histiocytes with indented nuclei, fibroblasts, varying amounts of collagen fibers, and eosinophils. The histiocytes were positive for S-100 protein staining and identified as Langerhans' cells. Therefore, this patient was diagnosed as having pulmonary eosinophilic granuloma. Two months later, the abnormal shadows on the chest X-ray and high fever spontaneously resolved without steroid therapy. This case was considered to be unique with respect to the peripheral blood eosinophilia, the three-day fever, and spontaneous improvement, compared with the former reported case.

Distribution of ventilation and of diffusing capacity to perfusion in the lung

We developed a method for estimating the distribution of ventilation (VA) and of diffusing capacity (G) to perfusion (Q) in the lungs. We used O2, CO2 and CO together with six inert gases of widely differing solubility and assumed that mass transfer efficiency of each gas in a gas exchange unit is limited by both VA/Q and G/Q ratios. The underlying lung model comprised 20 units along both the VA/Q and G/Q axes. Using numerical analysis, we transformed the data into a virtually continuous distribution of Q in the VA/Q-G/Q field. We tested the precision of the numerical procedure by examining the recovery of various artificial distributions, and found that distributions with up to two modes could be recovered with reasonable accuracy. Analytical results from 15 patients with interstitial pneumonia of unknown etiology (IPF) revealed the following features. (1) In an early disease stage, most of the lung was operating in the range of normal VA/Q, without a significant contribution of diffusion limitation. (2) An advanced stage of the disease exhibited a widening of VA/Q distribution and either broad unimodal or bimodal distribution of G/Q, extending to G/Q below 10(-3) ml (STPD)/(ml.Torr) with diffusion-limited O2 exchange. (3) Severe diffusion limitation causing disequilibrium of inert gas across the blood-gas barrier was observed in three (far advanced fibrosis; active interstitial inflammation) out of 15 patients. These findings suggest that inhomogeneity of G/Q does exist and may play an appreciable role in causing impairment of gas exchange in patients with interstitial pneumonia.

[A case of congenital antithrombin II deficiency with pulmonary infarction]

A 48-year-old woman was admitted because of increased bloody sputum. Since she had had a history of repeated thrombotic episodes including venous thrombosis in the lower limbs (21 year old) and pulmonary emboli developing into pulmonary infarction (41 years old), the patient was treated with anti-coagulant therapy using Warfarin for 7 years. Warfarin was discontinued after admission and heparin was administered instead at a relatively low dose of 5,000 units daily, resulting in a considerable diminution of hemoptysis. Unfortunately however, it caused a relapse of active thrombosis associated not only with a significant increase of the product of fibrinolysis (FDP), LDH and GOT but with a concomitant decrease of the platelet count. Hematological examinations concerning coagulation and fibrinolysis remained within a normal range except for the serum concentration of antithrombin III (AT III) and its functional property with regard to the heparin cofactor, which were 8.8 mg/dl and 48%, respectively. Since the findings were consistent with congenital deficiency of AT III, some members of her family were also examined. The concentration of AT III and its activity in the patient's son and her daughter deteriorated in a similar manner, indicating that this was a definite case of congenital deficiency of AT III. The clinical manifestations of 87 cases with congenital AT III deficiency, belonging to 24 families reported in Japan were reviewed.

[Impairment of gas exchange in acute lung injury]

To demonstrate the characteristics of impaired gas exchange in acute respiratory distress syndrome (ARDS), an experimental model of lung injury was produced in 24 mongrel dogs by intravenously injecting 0.07 ml/kg of oleic acid. While allowing the animal to breathe a mixture of 0.1% CO in air, normal saline, which contained appropriate amounts of six inert gases such as SF6, ethane, cyclopropane, halothane, ether and acetone, was infused at a constant rate through a peripheral vein. After a steady state was established, the expired gas was collected and the samples of both arterial and mixed venous blood were taken simultaneously. The concentrations of the nine indicator gases (O2, CO2, CO and six inert gases) in the samples were measured in terms of a gas chromatograph, permitting analysis of the distribution of ventilation to perfusion (VA/Q) as well as the diffusing capacity to perfusion (G/Q) in injured lungs. To determine the role of hypoxic pulmonary vasoconstriction (HPV) in maintaining gas exchange in ARDS, hemodynamic and gas-exchange parameters were investigated at inspired O2 concentrations (FIO2) of either 21 or 60%. The impairment of gas exchange was examined by measuring the fractional retention (R) of the inert gases in arterial blood. Furthermore, to assess the possible contribution of vasoactive prostanoids in regulating vascular reactivity in ARDS, observations at FIO2 of 60% were repeated after administered indomethacin at a dose of 5 mg/kg. Analytical results revealed that shunt flow in experimental dogs with lung damage caused by oleic acid averaged 17%. Furthermore, widening of VA/Q distribution was found accompanied with significant contribution of extremely low VA/Q areas. In addition, most of the lung was operating in G/Q units with values ranging from 10(-3) to 10(-2) but 9.8% of total Q(QT) was received by the area with G/Q less than 10(-3), which might limit O2 exchange between the alveolar gas phase and capillary blood. Although pulmonary vascular resistance (PVR) in injured lungs observed at FIO2 of 60% was significantly smaller than the value obtained at FIO2 of 21%, QT as well as extravascular lung water did not differ in the two conditions. The R value for the indicator gas was consistently lower at FIO2 of irrespective of gas species. Administration of indomethacin caused a considerable diminution of the R value for inert gas but a rise in PVR without an appreciable change of either QT or extravascular lung water. This was followed by a significant rise in arterial PO2 from 84 to 99 Torr.(ABSTRACT TRUNCATED AT 400 WORDS)

[Characteristics of impaired gas exchange in patients with chronic obstructive pulmonary disease]

Eleven patients with chronic obstructive pulmonary disease (COPD), placed in a supine position, were given a mixture of 0.1% CO and 21% O2 in N2 as inspired gas and normal saline containing the six inert gases including SF6, ethane, cyclopropane, halothane, diethyl ether and acetone via the antecubital vein. After the steady state was established, the expired gas was collected and both arterial and mixed venous blood were simultaneously sampled through the catheter inserted either into the femoral or pulmonary artery. Assuming that mass transfer efficiency of a given indicator gas at each gas exchange unit would be limited by the ratio of ventilation to perfusion (VA/Q) and by that of diffusive conductance to perfusion (G/Q), the data were analyzed by means of a lung model with 20 units along the VA/Q and G/Q axes, respectively. By application of the method of weighted least-squares combined with the idea of constrained optimization, the data were transformed into a virtually continuous distribution of Q against VA/Q and G/Q axes. Analytical results revealed that: 1) patients with advanced COPD show widening of VA/Q distribution accompanied with a significant contribution of either high VA/Q (emphysematous change) or low VA/Q area (peripheral airway involvement). and 2) their Q distributions along the G/Q axis are unimodal but have an area with a relatively low G/Q, indicating a small but appreciable contribution of diffusion limitation to their hypoxemia. In conclusion, the findings consistently suggest that inhomogeneity of G/Q may partly be responsible for the impaired gas exchange in the cases of COPD.

[Simultaneous analysis of the distribution of ventilation and diffusive conductance to perfusion in the lungs]

Theoretical analysis and experimental observations were performed to establish an essential method allowing demonstration of the characteristics of distribution of ventilation (VA) as well as of diffusive conductance (G) to perfusion (Q) in the lungs. O2, CO2 and CO binding to hemoglobin molecules within erythrocytes, together with six inert gases including SF6, ethane, cyclopropane, halothane, diethyl ether and acetone, possessing various degrees of solubility in blood and different degrees of diffusibility in lung tissue were used as indicator gases. Fifteen patients with interstitial pneumonia of unknown etiology, placed in a supine position, were given a mixture of 21% O2 and 0.1% CO in N2 as the inspired gas and normal saline containing appropriate amounts of the six inert gases via the antecubital vein. After a steady state was established, the expired gas was collected and both arterial and mixed venous blood were simultaneously sampled through the catheter inserted either into the femoral or pulmonary artery. The concentrations of the indicator gases in the samples were measured by gas chromatography, with electrodes or with Scholander gas analyzer. Assuming that the mass transfer efficiency of a given indicator gas at each gas exchange unit would be limited by the ratio of VA to Q (VA/Q) and by that of G/Q, the data obtained from the human subjects were analyzed in terms of a lung model having 20 units along the VA/Q and G/Q axes, respectively. The numerical analysis including the procedure of a simultaneous Bohr integration for O2, CO2 and CO in a pulmonary capillary and the method of weighted least-squares combined with the idea of constrained optimization permitted the data to be transformed into a virtually continuous distribution of Q against VA/Q and G/Q axes. The numerical procedure was strictly tested based on many artificial distributions of VA/Q and G/Q ratios, showing that it could characterize distributions containing up to at least two modes in the VA/Q-G/Q field with a substantial accuracy. Analytical results estimated from the patients with interstitial lung disease revealed: 1) most of the lung is operating in the range of normal VA/Q in an early stage of their illness, while widening of VA/Q distribution accompanied with a significant contribution of both high and low VA/Q areas is observed in an advanced stage of the disease.(ABSTRACT TRUNCATED AT 400 WORDS)

[Diagnosis of peripheral-type lung cancer using a new type of endoscope]

A new device, the BF-2.2T, has been designed to go through the 2.6 mm channel of the conventional fiberoptic bronchoscope (Olympus BF-1T20). It measures 2.2 mm in outer diameter; it has a visual angle of 75 degrees, a focal depth of 3 to 50 mm, a working length of 1150 mm, and a total length of 1400 mm. It bends 120 degrees in an upward direction and 120 degrees in a downward direction. The tip, 2.2 mm phi, of the BF-2.2 T angulates like a conventional bronchofiberscope, and this is the main characteristic of this instrument. The BF-2.2 T yields clinically satisfactory observation and photography, as a method for determining morphological changes in peripheral type lung cancer.

Oxygen transfer kinetics of red blood cells of the turtle Pseudemys scripta elegans

The kinetics of O2 uptake into, and release from, the red blood cells (RBC) of the turtle Pseudemys scripta elegans were determined with a stopped-flow technique at varied temperature (10-30 degrees C) and pH (7.5-7.9). The results were compared to those obtained for RBC of other vertebrates and related to morphometric and physiological data on gas/blood diffusion in turtle lungs. The O2 transfer conductance of RBC, G, for O2 release into high concentrations of dithionite, considered to represent the best estimate of true RBC transfer conductance for O2 uptake and release, averaged 0.17 +/- 0.01 at 30 degrees C, 0.13 +/- 0.01 at 20 degrees C, 0.09 +/- 0.01 at 10 degrees C (mean +/- SD, in mmol.min-1.Torr-1.(mlRBC)-1). These values are about one half the corresponding value for human RBC, and this difference may be due to the larger size of turtle RBC (volume, 327 microns 3) compared to human RBC (90 microns 3). The temperature dependence of G, Q10 = 1.3 indicates that, as in human RBC, diffusion through aqueous media is the main limiting factor for O2 exchange. Morphometric data on the lungs of Pseudemys scripta suggest that the resistance to O2 transfer by RBC is lower than that offered by the gas-blood barrier. The total apparent transfer resistance to CO, obtained from previous measurements of pulmonary diffusing capacity for CO in the same species, is much higher than that predicted from the combination of RBC O2 kinetics and morphometric data on gas-blood barrier.

Oxygen transfer of red blood cells: experimental data and model analysis

Kinetics of O2 uptake and release by human red blood cells (RBC) as measured by stopped-flow techniques were simulated using an RBC model shaped as a spheric shell. The O2 transfer mechanisms in this model include diffusion and reaction within the RBC and diffusion and convection in the medium surrounding the RBC. Unknown model parameters were determined by comparing simulations with experimental data. The following conclusions were drawn. (1) Both diffusion and convection contribute to O2 transport in the medium surrounding the RBC, and this transport importantly limits the overall O2 transfer kinetics in stopped-flow experiments. (2) Intraerythrocyte transport mechanisms become predominant in limiting O2 transfer, and can thus be investigated by stopped-flow techniques, only when the perierythrocyte O2 transport resistance is minimized, e.g. by high levels of dithionite in measurements of O2 release from RBC. (3) Intraerythrocyte O2 transfer is shown to be mainly limited by diffusion of O2 and, to a lesser extent, by diffusion of oxyhemoglobin ('facilitated O2 diffusion') and by O2/hemoglobin reaction. The results suggest that diffusion is the main process limiting O2 uptake and release by RBC, the finite reaction kinetics of O2 with hemoglobin exerting a smaller limiting effect.

Endoscopic observation of peripheral airway lesions

Peripheral airways of 2 mm or less in diameter were observed in 142 patients by means of an ultrathin bronchofiberscope measuring 1.8 mm in outside diameter. On the basis of the observed and photographed endoscopic findings, an endoscopic classification of peripheral airway lesions was proposed. The endoscopic findings showed changes in the bronchial wall consisting of reddening, pallor, absence of mucosal luster, edema, engorgement of blood vessels, irregular mucosal surface, and elevated mucosa. In the lumen, stenosis, obstruction, ectasis, and deformation due to pressure were recognized, in addition to excessive secretion and pigmentation as morphologic abnormalities or abnormal findings at bifurcation.

Influences of carbon monoxide on the binding of oxygen, carbon dioxide, proton and 2,3-diphosphoglycerate to human hemoglobin

In an attempt to estimate the influences of CO on the CO2 Bohr effect and the 2,3-diphosphoglycerate (DPG) effect linked to the reversible binding of O2 to the hemoglobin molecule (Hb), O2 dissociation curves of human blood in the presence of CO were investigated at 37 degrees C over a DPG concentration ranging from 2.2 to 4.3 mmol/(1RBC) and a pH range of 7.2 to 7.6. The sample with a low DPG concentration was made by incubating whole blood for 6 hrs, whereas the saturation of Hb with CO, SCO in the sample was adjusted by anaerobically mixing completely carboxygenated blood with that free of O2 and CO so as to give the final SCO at either 0, 10, 15, 20, 40 or 50%. The blood samples thus prepared were diluted at 1:100 in isotonic buffer solution and were equilibrated with gas mixtures containing O2 ranging from 1 to 9% and CO2 from 4 to 9%. The SO2 and SCO values of diluted red cell suspensions were examined by means of a dual-wavelength spectrophotometric method based on the isosbestic points for reduced Hb, HbO2 and HbCO. The extinction difference at 562.7 and 578.0 nm was monitored as a measure of SO2, while that at 570.1 and 584.6 nm was recorded for determining SCO. Fitting the experimental results by the Hill equation, the coefficients describing allosteric interaction induced by CO2 hydration and by DPG in the presence of both O2 and CO were calculated for the total saturation, ST defined as the sum of SO2 and SCO, ranging from 20 to 90%.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen binding properties, capillary densities and heart weights in high altitude camelids

The oxygen binding properties of the blood of the camelid species vicuna, llama, alpaca and dromedary camel were measured and evaluated with respect to interspecific differences. The highest blood oxygen affinity, not only among camelids but of all mammals investigated so far, was found in the vicuna (P50 = 17.6 Torr compared to 20.3-21.6 Torr in the other species). Low hematocrits (23-34%) and small red blood cells (21-30 microns 3) are common features of all camelids, but the lowest values are found in the Lama species. Capillary densities were determined in heart and soleus muscle of vicuna and llama. Again, the vicuna shows exceptional values (3720 cap/mm2 on average in the heart) for a mammal of this body size. Finally, heart weight as percent of body weight is higher in the vicuna (0.7-0.9%) than in the other camelids studied (0.5-0.7%). The possibility that these parameters, measured in New World tylopodes at sea level, are not likely to change considerably with transfer to high altitude, is discussed. In the vicuna, a unique combination of the following features seems to be responsible for an outstanding physical capability at high altitude: saturation of blood with oxygen in the lung is favored by a high blood oxygen affinity, oxygen supply being facilitated by low diffusion distances in the muscle tissue. Loading, as well as unloading, of oxygen is improved by a relatively high oxygen transfer conductance of the red blood cells, which is due to their small size and which compensates the negative effect of a low hematocrit on the oxygen conductance of blood.(ABSTRACT TRUNCATED AT 250 WORDS)

Dependence of O2 transfer conductance of red blood cells on cellular dimensions

To estimate the significance of the dimensions of RBC on O2 transfer, the kinetics of O2 release from RBC into medium containing dithionite (40 mmol/l) was measured, by a stopped-flow technique, for nine different species with varying RBC size (man, llama, vicuna, alpaca, dromedary camel, pygmy goat, domestic hen, muscovy duck and turtle). The observed O2 transfer kinetics were found to be size-dependent, i.e. the O2 transfer conductance of the single RBC, gst, was lower, whereas the specific O2 transfer conductance of packed RBC, Gst, or of whole blood, theta st, was higher for smaller RBC. The ratio of surface area to effective diffusion path length which was found to be about one fourth of the mean cell thickness irrespective of cell size and cell shape, may be considered as the essential morphological factor determining O2 transfer efficiency of the single RBC.

Oxygen transfer conductance of human red blood cells at varied pH and temperature

The influence of temperature (varied from 37 to 7 degrees C) and of medium pH (varied from 7.7 to 7.1) on the kinetics of O2 uptake and release by human red blood cells (RBC) under stopped-flow conditions was investigated by double-beam spectrophotometry. From the rate of O2 saturation change and the mean effective PO2 difference between the medium and the Hb of RBC, the specific transfer conductance for O2, G, was calculated. The temperature coefficient, Q10, of G for O2 uptake averaged 1.17, activation energy, Ea, 2.6 kcal/mol O2; the average values for O2 release were: Q10 = 1.32, Ea = 4.8 kcal/mol O2. The G value for release of O2 from oxyhemoglobin solution, Gsol, yielded Q10 = 2.25, Ea = 13.5 kcal/mol O2. Comparison of these Q10 and Ea values with those for diffusion of O2 and hemoglobin in aqueous media leads to the conclusion that in the stopped-flow condition the conductance for O2 transfer was mainly limited by diffusion of O2 and hemoglobin in the red cell interior and by diffusion of O2 in the medium, and to a lesser degree by chemical reaction kinetics. This was further supported by the lack of dependence of O2 transfer conductance values on pH.

Effects of temperature on oxygen transfer conductance of human red blood cells

The influence of temperature (varied from 37 to 7 degrees C; average pH = 7.4) on the kinetics of O2 uptake and release by human red blood cells under stopped-flow conditions was investigated by double-beam spectrophotometry. The kinetics were characterized by the specific transfer conductance for O2, G. The temperature coefficient of G, Q10(G), for O2 uptake averaged 1.17, and activation energy, Ea(G) = 2.9 kcal/mol O2. The average values for O2 release were: Q10(G) = 1.30, and Ea(G) = 4.8 kcal/mol O2. The G values for release of O2 from oxyhaemoglobin solution, Gsol, yielded Q10(Gsol) = 2.06, Ea(Gsol) = 13.4 kcal/mol O2. Comparison of these Q10 and Ea values with those for diffusion of O2 and haemoglobin in aqueous media leads to the conclusion that the kinetics of O2 uptake and release by red blood cells in the stopped-flow condition is mainly limited by diffusion of O2 and haemoglobin in the red cell interior and by diffusion of O2 in the medium, and to a lesser degree by chemical reaction kinetics.

Oxygen transfer properties and dimensions of red blood cells in high-altitude camelids, dromedary camel and goat

To estimate the advantage of the small red blood cells (RBC) of high-altitude camelids for O2 transfer, the kinetics of O2 uptake into and release from the RBC obtained from llama, vicuña and alpaca were investigated at 37 degrees C with a stopped-flow technique. O2 transfer conductance of RBC (G) was estimated from the rate of O2 saturation change and the corresponding O2 pressure difference between medium and hemoglobin. For comparison, O2 kinetics for the RBC of a low-altitude camelid (dromedary camel) and the pygmy goat were determined and previously measured values for human RBC were used. O2 transfer of RBC was found to be strongly influenced by extracellular diffusion, except with O2 release into dithionite solutions of sufficiently high concentration (greater than 30 mM). The G values measured in these 'standard' conditions, Gst (in mmol X min-1 X Torr-1 X (ml RBC)-1) were: high-altitude camelids, 0.58 (averaged for llama, alpaca and vicuña since there were no significant interspecific differences); camel 0.42; goat, 0.42; man, 0.39. The differences can in part be attributed to expected effects of the size and shape of the RBC (volume, surface area, mean thickness), as well as to the intracellular O2 diffusivity which depends on the concentration of cellular hemoglobin. The high Gst of RBC of high-altitude camelids may be considered to enhance O2 transfer in lungs and tissues. But the O2 transfer conductance of blood, theta, equal to Gst multiplied by hematocrit (in mmol X min-1 X Torr-1 X (ml blood)-1), was only slightly higher as compared to other species: 0.20 (llama, alpaca, vicuña), 0.14 (camel), 0.18 (goat), 0.17 (man).

Kinetics of oxygen uptake and release by red blood cells of chicken and duck

The specific conductance (G) for O2 transfer by red blood cells (RBCs) of chicken and muscovy duck was measured using the experimental (stopped-flow) and analytical techniques (RBC model) previously applied to human RBC (Yamaguchi, Nguyen Phu, Scheid & Piiper, 1985). Avian RBCs behaved similarly to human RBCs: G values were of similar magnitude; G for O2 uptake decreased with time and increasing O2 saturation; G for O2 release at high levels of dithionite decreased slightly with decreasing O2 saturation; G for O2 release was higher than G for O2 uptake. The deoxygenation kinetics of oxyhaemoglobin in solution was similar for both avian species. The G measured for O2 release at high dithionite concentration, considered to represent a good approximation to intra-erythrocyte O2 diffusion conductance, averaged (in mmol min-1 Torr-1 ml-1 RBC) 0.33 for chicken and 0.25 for duck (at 41 degrees C, pH of the suspension = 7.5, O2 saturation range 0.4-0.8). These species differences can be explained by differences in cell size, the RBC volume averaging 104 micron3 in the chicken and 155 micron3 in the duck. Compared with human RBCs, the G estimates for avian RBCs are somewhat smaller than would be predicted from size differences, which can be explained by the discoid shape of mammalian RBCs which constitutes an advantage compared with the ovoid avian RBC.

Kinetics of O2 uptake and release by human erythrocytes studied by a stopped-flow technique

The kinetics of O2 uptake into and release from human erythrocytes was investigated at 37 degrees C by a stopped-flow technique. From the time course of O2 saturation (SO2) change a specific transfer conductance of erythrocytes for O2 (GO2) was calculated. The following results were obtained: 1) GO2 decreased in the course of O2 uptake, but initial GO2 was nearly independent of SO2 at which uptake started; 2) addition of albumin to the medium reduced GO2; 3) increasing dithionite concentration in the medium in O2-release experiments progressively enhanced GO2, which became virtually constant for nearly the entire course of release; and 4) O2 uptake and O2 release (without dithoite) in the same SO2 range yielded very similar GO2. These results suggested that O2 uptake and release were importantly limited by diffusion through the external medium and that in the SO2 range between 0.3 and 0.8, chemical reaction exerted little limiting effect. Since O2 release at the highest dithionite concentration (40 mmol/l) appeared to be virtually unlimited by external diffusion, GO2 measured under these conditions, averaging 8.7 ml X min-1 X Torr-1 X ml erythrocytes-1, was considered to mainly reflect intracellular diffusion limitation. The corresponding specific transfer conductance for O2 transfer in whole blood (hematocrit, 0.45) is 3.9 ml X min-1 X Torr-1 X ml blood-1.