An oxyhemoglobin dissociation analyzer

Effects of Carbon Dioxide and Temperature on the Oxygen-Hemoglobin Dissociation Curve of Human Blood: Implications for Avalanche Victims

Completely avalanche-buried patients are frequently exposed to a combination of hypoxia and hypercapnia with a risk of normothermic cardiac arrest. Patients with a long burial time and an air pocket are exposed to a combination of hypoxia, hypercapnia, and hypothermia which may lead to the development of the “triple H syndrome”. This specific combination has several pathophysiological implications, particularly on the cardiovascular system and oxygen transport (oxygen supply and oxygen consumption). To examine the effects on hemoglobin oxygen affinity, we investigated venous blood samples from 15 female and 15 male healthy subjects. In a factorial design of four different carbon dioxide partial pressure (PCO2) levels (20, 40, 60, and 80 mmHg) and five different temperature levels (13.7°C, 23°C, 30°C, 37°C, and 42°C), 30 unbuffered whole blood samples were analyzed in a newly developed in vitro method for high-throughput oxygen dissociation curve (ODC) measurements. P50s, Hill coefficients, CO2-Bohr coefficients, and temperature coefficients were analyzed using a linear mixed model (LMM). Mean P50 at baseline (37°C, 40 mmHg PCO2) was 27.1 ± 2.6 mmHg. Both CO2-Bohr (p < 0.001) and temperature coefficients (p < 0.001) had a significant effect on P50. The absolute CO2 effect was still pronounced at normothermic and febrile temperatures, whereas at low temperatures, the relative CO2 effect (expressed by CO2-Bohr coefficient; p < 0.001, interaction) was increased. The larger impact of PCO2 on oxygen affinity at low temperature may be caused by the competition of 2,3-BPG with PCO2 and the exothermic binding characteristic of 2,3-BPG. In a model of an avalanche burial, based on published data of CO2 levels and cooling rates, we calculated the resulting P50 for this specific condition based on the here-reported PCO2 and temperature effect on ODC. Depending on the degree of hypercapnia and hypothermia, a potentially beneficial increase in hemoglobin oxygen affinity in the hypoxic condition might ensue.

High-throughput determination of oxygen dissociation curves in a microplate reader-A novel, quantitative approach

In vitro determination of the hemoglobin oxygen dissociation curve (ODC) requires highly elaborate, specialized, and costly technical equipment. In addition, there is a lack of methods that combine reliable ODC recordings with high throughput in small blood samples for routine analysis. We here introduce a modified, commercial 96-well plate with an integrated unidirectional gas flow system specifically adapted for use in fluorescence microplate readers. Up to 92 samples of whole or hemolyzed, buffered or unbuffered blood, including appropriate controls or internal standard hemoglobin solutions, can be analyzed within ~25 min. Oxygen saturation is measured in each well with dual wavelength spectroscopy, and oxygen partial pressure using fluorescence lifetime of commercial oxygen sensors at the in- and outlet ports of the gas-flow system. Precision and accuracy of this method have been determined and were compared with those of a standard method. We further present two applications that exemplarily highlight the usefulness and impact of this novel approach for clinical diagnostics or basic research.

The in-vivo oxyhaemoglobin dissociation curve at sea level and high altitude

Animals native to hypoxic environments have adapted by increasing their haemoglobin oxygen affinity, but in-vitro studies of the oxyhaemoglobin dissociation curve (ODC) in humans show no changes in affinity under physiological conditions at altitudes up to 4000m. We conducted the first in-vivo measurement of the ODC; inducing progressive isocapnic hypoxia in lowlanders at sea level, acutely acclimatized lowlanders at 3600m, and native Andeans at that altitude. ODC curves were determined by administering isocapnic steps of increasing hypoxia, and measuring blood oxygen partial pressure and saturation. The ODC data were fitted using the Hill equation and extrapolated to predict the oxygen partial pressure at which haemoglobin was 50% saturated (P50). In contrast to findings from in-vitro studies, we found a pH-related reduction in P50 in subjects at altitude, compared to sea-level subjects. We conclude that a pH-mediated increase in haemoglobin oxygen affinity in-vivo may be part of the acclimatization process in humans at altitude.

Red blood cell 2,3-diphosphoglycerate concentration and in vivo P50 during early critical illness

OBJECTIVE

To measure red blood cell 2,3-diphosphoglycerate (RBC 2,3-DPG) concentrations in early critical illness; to investigate factors associated with high or low RBC 2,3-DPG levels; to calculate in vivo P50 in patients with early critical illness; and to explore the relationship between RBC 2,3-DPG and intensive care mortality.

DESIGN

Prospective cohort study.

SETTING

General medical-surgical intensive care unit (ICU) of a major Scottish teaching hospital.

PATIENTS

One-hundred eleven critically ill patients during the first 24 hrs in the ICU with no history of chronic hematologic disorders or RBC transfusion within 24 hrs and 34 age- and sex-matched healthy reference subjects.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We measured RBC 2,3-DPG concentration, plasma biochemistry values, and arterial blood gas parameters. On average, RBC 2,3-DPG was lower among critically ill patients than controls (mean [sd], 14.1 [6.3] vs. 16.7 [3.7] mumol/g hemoglobin; p = .004) and had a wider range of values (patients, 3.2-32.5 mumol/g hemoglobin; reference group, 9.1-24.3). Regression analysis indicated a strong independent association between plasma pH and RBC 2,3-DPG (B, 32.15 [95% confidence interval, 19.07-46.22], p < .001) and a weak association with plasma chloride (B, -0.196 [95% confidence interval, -0.39 to -0.01], p = .044) but not with hemoglobin or other measured biochemical parameters. The mean calculated in vivo P50 level was normal (3.8 kPa) but varied widely among patients (range, 2.0-5.5 kPa). RBC 2,3-DPG concentration was similar for ICU survivors and nonsurvivors.

CONCLUSIONS

RBC 2,3-DPG concentrations vary widely among critically ill patients. Acidosis is associated with lower RBC 2,3-DPG concentrations, but anemia is not associated with a compensatory increase in RBC 2,3-DPG early in critical illness. Lower RBC 2,3-DPG concentrations during the first 24 hrs of intensive care are not associated with higher ICU mortality.

Haemoglobin J-Biskra: a new mildly unstable alpha1 gene variant with a deletion of eight residues (alpha50-57, alpha51-58 or alpha52-59) including the distal histidine

Single point mutation, which accounts for 92% of the 700 known variants, is the most frequent genetic defect responsible for abnormal haemoglobins. Small deletions (or insertions) involving from one to five residues are also observed, but in only approximately 5% of cases. The remaining variants produce fusion or extended haemoglobins. A deletion of eight residues, which included the distal histidine and its neighbours (alpha50-57, alpha51-58 or alpha52-59), was found in Hb J-Biskra. This new alpha-chain variant was mildly unstable in vitro only and there was no haematological or biochemical evidence of haemolysis in the affected family members. 24 nucleotides were missing in a region of the alpha1 gene showing an identical sequence of eight nucleotides at both ends. Several starting points could therefore lead to the same nucleotide and aminoacid remaining sequence. This deletion is the largest up to now reported in a haemoglobin molecule which is expressed at an almost normal level in the red blood cell. Comparison of the DNA sequences near to the deleted (or inserted) regions in the various haemoglobins carrying this type of abnormality almost always revealed the presence of a sequence that was hypothesized to slow down progression of the replication fork, and of repeats that may lead to possible secondary structures favouring slipped mispairing.

Two families with hemoglobin Sogn, beta(A11)14 Leu----Arg, in Minnesota and Indiana: hematologic, functional, and biosynthetic features

Sogn hemoglobinopathy was identified in a young American woman and in a young American man of apparently unrelated families of Norwegian ancestry. Both persons were asymptomatic and without clinical or hematologic manifestations. Hemoglobin Sogn, beta(A11)14 Leu----Arg, is an unstable hemoglobin that may easily be mistaken for hemoglobin S, G, or D by alkaline hemoglobin electrophoresis. These are the first known instances of hemoglobin Sogn outside of Norway. Oxygen affinity is normal. Sogn hemoglobinopathy is an incidental finding that has no adverse implication for the health of heterozygotes.

Application of new calculation algorithms to oxygenation parameters of cirrhotic patients. A comparison between calculated and measured data

Oxygen status from both arterial and mixed venous blood was analyzed by reliable methods in 39 cirrhotic patients. These measured data were checked with computed oxygen parameters by new calculation algorithms. Calculated oxygen contents were higher than directly measured values but there was a highly significant correlation between them. Calculated and measured 2,3-DPG mean values were not significantly different but there was no correlation between them. A large difference was observed between measured and computed evaluation of oxygen-hemoglobin affinity without correlation between P50. In hyperkinetic patients, no correlation was observed between 'compensation factor' and the increase of cardiac index. So, in these patients the new iterative equations were not valid to determine traditional oxygen parameters from only Po2 and So2 arterial measurements. Moreover the new oxygenation parameters appeared frankly inadequate.

Pyridoxylated polymerized hemoglobin solution processing. Interest of a membrane molecular fractionation step

Glutaraldehyde hemoglobin polymerization gives too many high polymers, resulting in a too viscous solution. We describe here an alternate method leading to superior results, as compared to the classical one. This method includes a molecular fractionation step using a tangential flow ultrafiltration that secondarily lowers the unpolymerized tetramer's content of a mildly polymerized, pyridoxylated hemoglobin solution (Pyr-Poly Hb). This leads to an adequately polymerized product with a lesser high polymer content, implying a lower viscosity. We thus obtain a pyridoxylated, polymerized molecular fractionated solution presenting suitable features as a blood substitute: A 7.5 g% hemoglobin 2 g% albumin solution had a 16% unpolymerized tetramer's ratio, a 1.8 mPas viscosity, a P50 of 2.8 kPa, a Hill coefficient of 2.1, a binding coefficient of 1.3 mL/g, a colloid osmotic pressure of 2.4 kPa, and a methemoglobin concentration of 3% Male-Sprague-Dawley rats undergoing an isovolumic blood exchange with this Pyr-Poly Hb solution, down to a 2% hematocrit, present a mean survival time of 20 h.

History of blood gas analysis. VI. Oximetry

Oximetry, the measurement of hemoglobin oxygen saturation in either blood or tissue, depends on the Lambert-Beer relationship between light transmission and optical density. Shortly after Bunsen and Kirchhoff invented the spectrometer in 1860, the oxygen transport function of hemoglobin was demonstrated by Stokes and Hoppe-Seyler, who showed color changes produced by aeration of hemoglobin solutions. In 1932 in Göttingen, Germany, Nicolai optically recorded the in vivo oxygen consumption of a hand after circulatory occlusion. Kramer showed that the Lambert-Beer law applied to hemoglobin solutions and approximately to whole blood, and measured saturation by the transmission of red light through unopened arteries. Matthes in Leipzig, Germany, built the first apparatus to measure ear oxygen saturation and introduced a second wavelength (green or infrared) insensitive to saturation to compensate for blood volume and tissue pigments. Millikan built a light-weight ear "oximeter" during World War II to train pilots for military aviation. Wood added a pneumatic cuff to obtain a bloodless zero. Brinkman and Zijlstra in Groningen, The Netherlands, showed that red light reflected from the forehead could be used to measure oxygen saturation. Zijlstra initiated cuvette and catheter reflection oximetry. Instrumentation Laboratory used multiple wavelengths to measure blood carboxyhemoglobin and methemoglobin is cuvette oximeters. Shaw devised an eight-wavelength ear oximeter. Nakajima and co-workers invented the pulse oximeter, which avoids the need for calibration with only two wavelengths by responding only to the pulsatile changes in transmitted red and infrared light. Lübbers developed catheter tip and cuvette fiberoptic sensors for oxygen tension, carbon dioxide tension, and pH.

Oxygen affinity of hemoglobin solutions modified by coupling with NFPLP and the effects on tissue oxygenation in the isolated perfused rat liver

From these liver perfusions with Hb and Hb/HbNFPLP solutions the following conclusions can be drawn: In spite of the chemical modification of the hemoglobin molecule, no rheological differences are seen. All parameters measured were sensitive to hypoxia induced by a decrease in perfusion flow rate. The NFPLP-induced decrease in oxygen affinity was reflected in a higher venous PO2. These in-vivo observations are in agreement with the in-vitro measured oxygen dissociation curves. The difference in PO2 did not result in a change in the other oxygen-sensitive parameters in this model under the chosen conditions. Possible causes for these observations are: the level of hypoxia was too low the oxygen supply in the perfusions with the modified hemoglobin solutions was lower than the oxygen supply in the perfusions with normal hemoglobin. Whether or not this observation is due to an intrinsic property of the modified hemoglobin molecule remains to be established.

Induced low P50 in anesthetized rats: blood gas, circulatory and metabolic adjustments

In anesthetized, normoxic or hypoxic rats the hemodynamic, metabolic and O2 transport characteristics following exchange transfusion with human erythrocytes containing a high O2 affinity hemoglobin (Hemoglobin Creteil, beta 89 Ser----Asp) have been studied. The in vivo oxygen partial pressure at 50% oxygen hemoglobin saturation (P50) decreased from 37.4 +/- 2.1 to 12.7 +/- 0.7 mm Hg; the arterial oxygen tension was reduced significantly from 109.9 +/- 7.7 to 87.3 +/- 12.0 mm Hg. There was a decrease in right ventricular partial pressure of oxygen (PvO2), (P less than 0.001), oxygen consumption (VO2), (P less than 0.001), arterio-venous difference, (P less than 0.001), and peripheral vascular resistance index, (P less than 0.01). Exchange transfusion with normal rat blood (P50 = 37.2 +/- 2.4 mm Hg) or with 2,3-diphosphoglycerate-enriched human red blood cells (P50 = 34.7 +/- 2.2 mm Hg), did not modify these variables in normoxic rats. In hypoxia, the reduction in P50 was associated with a further decrease in PvO2 an increase in serum lactate concentration and a VO2 decrease.

Diabetic oxygen-hemoglobin equilibrium curves evaluated by nonlinear regression of the Hill equation

The oxygen-hemoglobin equilibrium curves ( OHECs ) were measured on whole blood samples from 131 individuals (33 normal and 26 diabetic adults and 30 normal and 42 diabetic juveniles) using a Radiometer Dissociation Curve Analyzer (DCA-1). All measurements were made in the morning following an overnight fast and without exogenous insulin. The saturation versus Po2 data were fitted to the Hill equation using a previously described nonlinear regression algorithm to yield the parameters describing the position (P50) and shape (n) of each OHEC . It was found that the Hill model could be used to describe OHECs of both normal and diabetic subjects. A small (approximately 10%) but significant decrease in P50 was found for the diabetic juveniles compared to normal juveniles. There appeared to be no change in P50 with diabetes in adults. However, in these diabetic subjects, the P50 had been increased by the somewhat elevated levels of 2,3-DPG. No difference in n was found between either group of diabetics and their corresponding group of normals but n was approximately 5% lower in juveniles than in adults. The ability of blood to release oxygen to tissue may be transiently impaired in diabetic juveniles because of the left shift of their OHECs .

Effects of ortho-iodo sodium benzoate on acute myocardial ischemia, hemodynamic function, and infarct size after coronary artery occlusion in dogs

Ortho-iodo sodium benzoate (OISB) decreases the affinity of blood for oxygen, thus enhancing potential tissue oxygen delivery. To test the hypothesis that a change in oxygen affinity would ameliorate regional myocardial ischemic injury resulting from occlusion of the left anterior descending (LAD) coronary artery, experiments were carried out in 55 anesthetized dogs which received an intravenous infusion of OISB. In Protocol I studies (n = 9), preocclusion intravenous infusion of OISB (500 mg/kg) reduced epicardial S-T segment elevation 15 minutes after coronary occlusion, while a similar volume of normal saline solution did not affect this index of ischemic damage. In Protocol II experiments, 34 dogs were randomized to either an OISB or saline group, after which the LAD was ligated, the chest closed, and the animal allowed to recover from anesthesia. Myocardial infarction (MI) size was assessed after the animal died or was killed 8 to 24 hours later, and was found to be 29% smaller in dogs receiving OISB. In 6 dogs, blood P50 (the partial oxygen pressure at which hemoglobin is 50% saturated with oxygen) was increased by OISB infusion, confirming that its administration effected a rightward shift in the oxyhemoglobin dissociation curve. Protocol III studies assessed the effects of OISB on cardiac hemodynamic function and acute myocardial ischemic damage when infusion was begun 15 minutes after LAD occlusion: average epicardial S-T segment elevation was not altered by saline solution, but decreased when OISB was infused during the last 15 minutes of myocardial ischemia. Reductions in heart rate, left ventricular dP/dt, and cardiac output were observed in 7 dogs during OISB infusion, but there were no changes in these measurements during coronary occlusion in 5 dogs receiving a constant infusion of saline solution. There were no changes in regional myocardial blood flow (microsphere technique) to either ischemic or nonischemic zones in either the saline control or OISB treatment groups. Thus, both acute myocardial ischemic injury (assessed by epicardial electrocardiographic mapping) and ultimate MI size are reduced when OISB is infused before experimental coronary artery occlusion. OISB also reduces myocardial ischemic injury when its administration is begun 15 minutes after coronary occlusion, while effecting decreases in heart rate, left ventricular contractility, and cardiac output.

Characterization of oxygen-hemoglobin equilibrium curves using nonlinear regression of the Hill equation: parameter values for normal human adults

Measurements of oxygen concentration versus PO2 in blood from 33 normal adults were fitted, using a special nonlinear regression analysis, to the Hill equation to obtain the parameters describing the position (P50) and shape (n) of each oxygen-hemoglobin equilibrium curve (OHEC). Data between 20% and 97% saturation were described well by this empirical two-parameter model. The mean (+/- SD) P50 and n were found to be 26.2 (+/- 0.8) torr and 2.50 (+/- 0.07), respectively, in good agreement with previously published values. Some normal individuals, however, deviated markedly from the averages indicating that the published values cannot be applied to everyone.

Consequences of an acute increase in P50 in anaesthetized guinea pigs

In anaesthetized guinea pigs, ventilated with ambient air, the peripheral haemodynamics and oxygen transport characteristics have been studied following a blood exchange transfusion with rat erythrocytes suspended in guinea pig plasma. Since the rat haemoglobin exhibited a lower oxygen affinity than guinea pig haemoglobin, the oxygen partial pressure at 50% of oxygen haemoglobin saturation (P50) increased from 25.2 +/- 1.1 to 37.2 +/- 0.9 mm Hg (n = 10). This increase in P50 was accompanied by a significant increase in arterial oxygen partial pressure (PaO2) and in arterio-venous difference (AVDO2). Cardiac output (Q) was decreased significantly, but oxygen consumption (VO2) remained within control values. The increase in P50 was associated with a venous oxygen partial pressure (P-VO2) which remained constant but an increase in blood lactate concentration was observed. Control exchange transfusion with fresh guinea pig blood had no effect on acid-base status, on oxygen transport, or on peripheral resistance. The sudden reduction in haemoglobin oxygen affinity induced an increase in peripheral resistance with a decrease in cardiac output, the arterial systemic pressure being maintained. These results suggested that an acute decrease in haemoglobin oxygen affinity was compensated for by a simultaneous diminution of overall tissue blood flow and reduction of capillary recruitment.

Simple and rapid method for the assessment of the oxygen affinity of haemoglobin

The affinity of haemoglobin for oxygen may be expressed as the oxygen tension at 50% saturation under standard conditions (P50). A rapid technique for the determination of P50 using a micro-tonometer with pH electrode and oximeter was evaluated. Equilibration time was found to be 15 minutes with no change in PCV, although plasma haemoglobin levels were slightly elevated. Estimation of P50 in blood from 32 non-smokers gave a mean of 26.4 +/- 0.9 (SD) mm Hg (3.51 +/- 0.12 kPa) with a precision of 0.3 (SD) mm Hg (0.04 kPa). The system was found to be accurate, precise, and simple in operation, allowing up to 16 P50 determinations an hour to be performed with 85 microliters blood samples.

The effect of etidronate disodium (EHDP) on retinopathy in insulin-dependent diabetic patients

In a randomized double-blind study the effect of etidronate disodium (EHDP) on retinopathy, plasma inorganic phosphate and blood oxygen transport was assessed in 26 insulin-dependent diabetic patients. Following 6 months of EHDP administration, plasma inorganic phosphate had increased significantly (1.48 vs 1.14 mmol/l; P less than 0.01). Red cell, 2,3-diphosphoglycerate concentration (16.9 vs 15.1 mumol/g Hb; P less than 0.01) and the haemoglobin-oxygen affinity measured by pO2 at 50% oxygen saturation (P50) had also increased significantly (27.5 vs 26.3 mmHg; P less than 0.01). No changes had occurred in mean blood glucose and haemoglobin A1c concentrations, indicating a comparable degree of glucose regulation. Following 6 months of EHDP administration an association was found between improvement in retinopathy and the increase in plasma inorganic phosphate.

Changes in red blood cell oxygen transport in diabetic pregnancy

Parameters of red cell oxygen transport were studied in 23 nonsmoking, insulin-dependent diabetic women and 20 nonsmoking healthy women late during pregnancy. In the pregnant diabetic women, arterial oxygen saturation (SAT) and arterial oxygen tension were significantly decreased. SAT correlated inversely with hemoglobin Alc (Hb Alc) (diabetic women: r = -0.43, p less than 0.05; total material: r = 0.66, p less than 0.001). Red blood cell 2,3-diphosphoglycerate (2,3-DPG) was significantly increased in the pregnant diabetic women (p less than 0.01), but the 2,3-DPG-induced change in hemoglobin-oxygen affinity was impaired. P50 (oxygen affinity, i.e., Po2 at 50% oxygen saturation) at actual pH correlated inversely with Hb Alc of the diabetic women (r = -0.45, p less than 0.05). The suggestion is made that, in diabetic pregnancy, particularly in poorly regulated cases, fetal hypoxia may be an important factor of the increased risk of intrauterine fetal death.

A rapid micro method for obtaining oxygen equilibrium curves on whole blood

A method for recording complete dynamic oxygen equilibrium curves (O2EC) from microliter samples of whole blood is described. The blood sample is compressed into a thin film between two 6-micron thick Teflon membranes in order to promote rapid gas exchange with gas volume surrounding the membranes. Oxygen tension of the gas volume around the blood film is charged at a controlled rate from zero to ca. 100 Torr by a specially designated gas-exchanging cuvette. Saturation of red cell hemoglobin in the film is measured by dual-wavelength spectrophotometry using Soret wavelengths of 430-453 nm. Gas volume oxygen tension is measured with a Teflon membrane covered oxygen cathode. Full saturation is secured by introducing an oxygen mixture whose PO2 exceeds 650 Torr. A single O2EC can be run in about 4 min at 37 degrees; multiple O2EC can be recorded from the same blood film. Each curve is run isocapnically at a preselected carbon dioxide tension. Blood film pH is calculated from the CO2 partial pressure and an independently determined buffer line. Data are presented to show that normal standard curve for man as determined with this blood-film method and those determined by other methods are equivalent.

Chicken oxygen dissociation curve by dynamic tonometry

Oxygen dissociation curves were determined for blood from mature (5 male, 5 female) Single Comb White Leghorn chickens. Blood was oxygenated by bubbling with humidified 95% O2, 5% CO2, 0% N2 at 100 ml/min for 30 min, then gradually deoxygenated with 0% O2, 5% CO2, 95% N2 at 4 ml/min. During deoxygenation .5 ml samples were drawn at 7 in intervals. The PO2, PCO2, and pH were measured polarographically and the content of O2 was measured by gas chromatography. The PO2 was corrected to T = 42 C, pH = 7.5, and PCO2 = 40 Torr. The curves were determined by plotting: 1) PO2 vs. % Saicont based on O2 content of each serial sample as compared to the fully oxygenated blood O2 content, and 2) PO2 vs. duration of dynamic tonometry plots. The curves determined by the two methods of data analysis corresponded closely, the P50 values (x +/- SD) being 36.2 +/- 2.5, 34.3 +/- 3.1 Torr, respectively.

Temperature and oxygenation of human blood at constant total CO2 content

The influence of temperature on the oxygeneration of normal and 2,3-diphosphoglycerate-depleted human blood suspensions (final hemoglobin concentration: 0.75%) was studied under closed-system conditions (constant total CO2 content) beginning with standard values:pH 7.40, Pco2 40 torr, at 37 degrees C. The present results quantify the temperature-induced changes in Po2 occuring in association with the concomitant acid-base variations prevailing in a closed system. When the temperature was raised from 25 to 42 degrees C, P50 varied from 13.9 +/- 1.1 to 40.7 +/- 1.9 torr in the presence of 2,3-DPG and from 7.6 +/- 0.4 to 24.8 +/- 1.2 torr in the absence of the cofactor. The derived equations correlate Po2 variations with those of temperature (T: 25--42 degrees C) and oxygen saturation (So2:10--90%). The temperature coefficient of oxygenation and the DPG-induced decrease in the heat of hemoglobin oxygenation were shown to be saturation dependent. DPG lowered dlog Po2/dT from 0.0299 to 0.0275 and delta H from --12.9 to --11.8 kcal/mole O2 bound at 50% So2 but had no significant influence on these parameters for So2 less than or equal to 20%. The results suggest that the release of carbamate at the beginning of oxygenation is virtually unaffected by presence of 2,3-DPG in the 25--42 degree C temperature range.

Homozygous hemoglobin E mimics beta-thalassemia minor without anemia or hemolysis: hematologic, functional, and biosynthetic studies of first North American cases

A young American woman of Thai ancestry living in Ohio and a man of Vietnamese origin living in Iowa are believed to be the first recognized hemoglobin E homozygotes residing in the western hemisphere. Both were clinically well and exhibited neither pallor nor icterus nor splenomegaly. Their blood exhibited marked microcytosis and mild erythrocytosis. Hemoglobin was 99% E and 1% F, 97% E and 3% F, respectively. These features were similar to those previously reported from Southeast Asia and Madagascar in the few well-documented reports of homozygous hemoglobin E. A 51Cr erythrocyte survival study indicated a normal t1/2 of 28 days. Also demonstrated were minimal decrease in whole blood O2 affinity and increased ratio of alpha/non-alpha globin chain synthesis. Mild hemolytic anemia is not, as usually stated, a feature of this condition, which closely mimics a very mild thalassemia minor. Anemia, when found with high proportions of hemoglobin E, should not be attributed to the homozygous hemoglobinopathy. Persons with homozygous hemoglobin E should be reassured as to its benign implications.

Further studies on the functional properties of hemoglobin M Hyde Park

The oxygen binding properties of Hb M Hyde Park (92 beta, histidine leads to tyrosine) were reinvestigated directing special care to testing the wave length-dependence of the oxygen equilibrium curve and to stabilizing hemoglobin samples using a methemoglobin reductase system. There was no indication that the Hb M Hyde Park fraction separated on a DEAE Sephadex column contained an unknown hemoglobin derivative which appeared in earlier studies. Contrary to earlier observations, there was no significant wave length-dependence of the equilibrium curve of Hb M Hyde Park, verifying the spectrophotometric determination of oxygen saturation. The reductase system satisfactorily reduced the normal alpha chain met hemes without reducing the abnormal beta chain met hemes. The oxygen binding property of Hb M Hyde Park is characterized by 3 to 4 times higher oxygen affinity than that for normal hemoglobin, complete loss of cooperativity, and substantially preserved Bohr effect. These results are consistent in part but not entirely with those observed by earlier investigators. The oxygen affinity of Hb M Hyde Park is between the affinity of the oxy structure and the deoxy structure of normal hemoglobin. Oxygen equilibrium curve of red cell suspension and whole hemolysate containing Hb M Hyde Park were biphasic, indicating that Hb M Hyde Park also exhibited the high oxygen affinity in those samples.

Distribution of erythrocyte nucleotides in pyrimidine 5'-nucleotidase deficiency

In pyrimidine 5'-nucleotidase deficiency, erythrocytes contain elevated levels of pyrimidine nucleotides. The composition of this nucleotide pool was examined by ion exchange chromatography on Dowex formate columns using a linear ammonium formate elution gradient. In contradistinction to normal erythrocytes, adenine nucleotides accounted for only 32% of the nucleotide pool. The remainder consisted of 50% cytidine and 16% uridine nucleotides. The remaining 2% was not identified. The most abundant compound appeared to be UDP glucose whilst high levels of CTP, CMP and an unidentified cytidine compound less polar than CMP accounted for most of the cytidine nucleotide pool. The possibility that the abnormal nucleotides were due to an elevated reticulocyte count was excluded and it was also shown that erythrocytes from subjects heterozygous for pyrimidine 5'-nucleotidase deficiency did not have detectable levels of the abnormal nucleotides.

Effect of an increase in HbO2 affinity on the calculated capillary recruitment of an isolated rat heart

The effect of an increase in hemoglobin O2 affinity on myocardial O2 delivery was studied in a blood perfused working rat heart preparation. In a first series of experiments P50 (PO2 for which saturation is 50%) was lowered by use of carbon monoxide. The heart was alternatively perfused with the blood sample of P50 = 32 mm Hg and the blood sample of P50 = 17 mm Hg. O2 capacity of both samples was kept the same by appropriate hemodilution. In a second serie of experiments change of P50 was obtained by the use of adult human erythrocytes containing hemoglobin creteil with a P50 of 13.6 mm Hg. As P50 decreased from 25 to 10 mm Hg, coronary sinus PO2 (PcsO2) diminished from 26 +/- 2 to 18 +/- 2 mm Hg (-29 +/- 2%), coronary sinus O2 content (CcsO2) increased by 15 +/- 3%, myocardial oxygen consumption did not change significantly. The percentage of increase of coronary flow was 23 +/- 4%. Analysis of these results with a simple mathematical model of O2 delivery suggest that increase in HbO2 affinity is corrected by a simultaneous increase in coronary flow and capillary recruitment.

Hemoglobin AIc and red cell oxygen release capacity in relation to early retinal changes in newly discovered overt and chemical diabetics

The average Hb A1c concentration in consecutive cases of newly discovered nonacidotic diabetics was 11.4% prior to diet and insulin, as compared to 5.5% following prolonged optimal control (p less than 0.001). Hemoglobin A1c was significantly correlated with fasting blood sugar. In a controlled study the average Hb A1c in 30 subjects with chemical diabetes was 5.8% as opposed to 5.3% in controls with normal OGTT (p less than 0.05). Thirty-seven percent of the chemical diabetics had Hb A1c values greater than or equal to 6.5%, while none in the control group showed such high values. Hb A1c in whole blood has increased oxygen affinity. A decrease in red-cell oxygen release was noted in some untreated nonacidotic diabetics, and an adverse effect of insulin on the oxygen release capacity was demonstrated in both newly diagnosed ketoacidotic and nonacidotic diabetics. The importance of this defect in red-cell oxygen-releasing capacity on the function of the microcirculation is discussed. Signs of an early breakdown of the blood-retinal barrier was demonstrated in 20% of the chemical diabetics by fluorescein angiography.

Comparative effects of CO2 on the affinity for O2 of fetal and adult erythrocytes

1. Oxygen-linked carbamino formation in fetal erythrocytes was compared to that measured in adult erythrocytes. 2. Whole oxygen binding curves were recorded on washed intact erythrocytes either fresh or D-glycerate-2,3-P depleted with a continuous recording technique. Erythrocytes were resuspended in buffer media of different pH and PCO2 varying from 0-10.7 kPa (80 torr) at physiological ionic strength. Oxygen linked carbamates were estimated as deltalog PO2/delta log PCO2 at constant pH and constant saturation levels from 10-90% oxygen saturation. 3. The overall CO2 effect (deltalog P50/deltalog PCO2) was consistently lower in fetal erythrocytes than in the adult. The deltalog PO2/deltalog PCO2 ratio was markedly dependent on oxygen saturation in both types of erythrocytes and highest at the early part of the oxygen binding curve. This was more so in fetal erythrocytes. 4. Carbamino formation was lower in fetal erythrocytes than in adult erythrocytes at any pH value, indicating a higher apparent pK of the alpha amino groups involved in CO2 binding in fetal erythrocytes. This may be related to the different primary structures of the non alpha chains of HbFII and HbAI. 5. The large effect of low PCO2 on both fetal and adult erythrocytes was related to the higher affinity for CO2 of deoxyhemoglobin compared to oxyhemoglobin and a model for CO2 binding analogous to that described by de Bruin et al. [6] for anion binding is proposed. 6. It is concluded that the lower CO2 binding to fetal erythrocytes is in keeping with the lower allosteric effect of other major effectors of hemoglobin within the cells. This leads to a higher affinity for O2 of fetal erythrocytes well suited for O2 transport in utero.

Application of an automatic oxygenation technique to analysis of oxygen equilibrium curves for hemoglobinopathic red cells and functional screening of clinically important hemoglobinopathies

The automatic oxygenation technique of Imai et al (Biochimica Biophysica Acta, 200:189--196, 1970) was slightly modified and applied to the study of oxygen equilibrium curves of dilute, red-cell suspensions from normal subjects and individuals with hemoglobinopathies, enzymopathies, and other hematologic disorders. The p50 values of non-smoking, normal adults were 25.9 +/- 0.6 mm Hg at pH 7.4 and 37 degrees C, and corresponded to the values for whole blood reported in the literature. The oxygen equilibrium curves of suspensions from subjects with enzymopathies revealed shifts in position which are thought to be due to alterations in the concentration of 2,3-DPG of the red cells. Abnormalities in shape of the equilibrium curves were observed only for the hemoglobinopathic red cells, and could best be illustrated by the abnormally low Hill's exponent (n*). Analyses of the n* values of 34 patients with various red-cell disorders of unknown causes led to the identification of ten cases showing low values. In five of the ten patients, the presence of an abnormal hemoglobin was confirmed using column chromatography on Amberlite CG--50. These results point to the usefulness of the Hill Plot analysis of red-cell oxygen dissociation curves in functional screening for clinically important hemoglobinopathies.

An adverse effect of insulin on the oxygen-release capacity of red blood cells in nonacidotic diabetics

Oxyhemoglobin dissociation curves (ODC) were performed on blood from newly diagnosed, nonketotic diabetics prior to and following initial insulin treatment and from ambulatory juvenile diabetics before and after their usual morning insulin. In 10 newly discovered diabetics the average P50 at in vivo pH was normal prior to insulin (26.2 mm Hg), decreased to 24.5 mm Hg (p less than 0.005) on the day following the initial insulin administration, and was within normal limits (26.9 mm Hg) when the diabetes was finally well controlled and red cell 2,3-diphosphoglycerate (2,3-DPG) had risen to elevated levels. Oxygen affinity of hemoglobin was closely correlated with the content of red cell 2,3-DPG (r = 0.61, p less than 0.001) but was unrelated to the level of hemoglobin Alc. In 40 juvenile patients the average P50 was also normal prior to insulin administration but was significantly lower 3-4 hr after they had received their usual insulin dose (p less than 0.001). The study indicates that insulin administration to diabetics with high blood glucose levels may lead to transient decreases in red cell 2,3-DPG and in oxygen-releasing capacity of the red blood cells.

Hemoglobin-ligand interaction in fetal and maternal sheep blood

Hemoglobin-ligand interaction was studied in maternal and fetal sheep blood as a function of oxygen saturation. pH was changed by varying CO2 concentration (CO2 Bohr effect) or by addition of NaOH or HCl at constant PCO2 (fixed acid Bohr effect). For maternal blood, CO2 Bohr factor was -0.41 at 50% oxygen saturation, increasing in magnitude at lower saturation and decreasing in magnitude at higher saturation. For fetal blood, CO2 Bohr factor was -0.45 at 50% oxygen saturation, unchanging at lower saturation and decreasing in magnitude at higher saturation. Fixed acid Bohr factor was relatively saturation independent with a value of -0.36 for fetal blood and -0.27 for maternal blood. The pH-independent effect of molecular CO2 on oxygen affinity was markedly saturation dependent being greatest at low oxygen saturation. The CO2 effect was greater in maternal blood than fetal blood. However, the magnitude of the saturation dependency of Bohr factor is not great enough to have major physiological significance in oxygen transfer across the sheep placenta.

Oxygen affinity of avian blood

Oxygen dissociation curves plotted directly on whole blood during oxygenation using a Radiometer DCA 1 gave P50 values of 39.2 +/- 2.2 mm Hg and 51.3 +/- 6.2 mm Hg for pigeon and chicken blood, respectively, at 41 degrees C, pH 7.5 and PCO2 29 mm Hg. These values agree well with earlier results obtained by a variety of methods; however, they do conflict with recent findings of a much higher oxygen affinity in avian blood which were obtained using a different plotting method. It was shown that with the method used in this paper the high metabolic rate of avian blood has little effect on the plotted curve at saturations below 50%. At higher saturations O2 consumption of red cells affects a progressive shift of the curve to the left so that to obtain accurate curves at high saturation it is necessary to correct the plotted curves for the oxygen utilization.

Properties of blood oxygen transport in the turtle Pseudemys scripta and the tortoise Testudo graeca: effects of temperature, CO2 and pH

Properties of oxygen-haemoglobin binding have been investigated in the aquatic turtle Psuedemys scripta and the terrestrial tortoise Testudo graeca. Haematocrit (30-35%) and haemoglobin concentration (12-14 g/100 ml blood) were similar in both species. P50 at physiological levels of PCO2 (20-25 mm Hg) was 21 mm Hg in Pseudemys, compared with 23 mm Hg in Testudo. The Bohr shift of the blood of both the turtle and the tortoise was almost identical at -0.28. The heat of oxygenation, deltaH, reflecting the temperature sensitivity of O2-Hb affinity, was -10.55 in Pseudemys and -8.12 kcal/mol in Testudo. These data on whole blood do not support previous generalizations in the literature suggesting marked differences in oxygen-haemoglobin binding between aquatic and terrestrial chelonian reptiles.

Increased hemoglobin-oxygen affinity in patients with pancreatitis associated with type I and V hyperlipoproteinemia

Oxyhemoglobin dissociation curves were performed from blood of subjects with pancreatitis associated with Type V and Type I hyperlipoproteinemia. The hemoglobin-oxygen affininty was markedly increased with P50 varying from 22.3 to 17.7 mmHg. As the hyperlipoproteinemia subsided the clinical and laboratory signs of pancreatic affection disappeared. The increased hemoglobin-oxygen affinity and decreased flow of red cells due to hyperchylomicronemia in the microcirculation may lead to tissue hypoxia, which may act as a precipitating injurious factor leading to pancreatitis during severe hyperlipemia.

Sickle hemoglobin aggregation: a new class of inhibitors

A number of tri- and tetrapeptides have been found to inhibit aggregation and gelation of deoxygenated sickle cell hemoglobin. These inhibitors have hydrophobic phenylalanine residues at one end and hydrogen bonding lysine or arginine side chains at the other end. The backbone is not very specific. The inhibitors do not modify the oxygen carrying properties of hemoglobin. When the inhibitor and sickle hemoglobin are put inside reconstituted cells, the erythrocytes do not sickle upon deoxygenation. Compounds of this type may develop useful agents in the therapy of sickle cell anemia.