Myeloproliferative Disorders
Harold R. Schumacher, William A. Rock, Sanford A. Stass in Handbook of Hematologic Pathology, 2019
Oxygen Dissociation Curve. Proper tissue oxygenation depends on amount of environmental or available oxygen, Hb concentration, and affinity of oxygen for Hb [pO2 (0.5)]. The point of reference for affinity of oxygen for Hb has been designated as that partial pressure of oxygen at which the Hb is one-half saturated, i.e., the P50. Under standard conditions of temperature (37°C) and pH (7.4), the P50 of normal Hb A is 26.6 mm Hg (Fig. 2). If the value is lower, the P50 has shifted to the left; this indicates an increased affinity of Hb for oxygen. Conversely, if the P50 value is >26.6 mm Hg, the oxygen affinity of Hb has decreased and the P50 has shifted to the right. Those abnormal Hbs with amino acid substitutions resulting in increased oxygen affinity retain oxygen. This retention results in tissue hypoxia, increased Epo formation, and an erythrocytosis. Some examples are Hemoglobins Chesapeake, Vanderbilt, Little Rock, Syracuse.
Single Best Answer Questions
Vivian A. Elwell, Jonathan M. Fishman, Rajat Chowdhury in SBAs for the MRCS Part A, 2018
Which one of the following is true of the haemoglobin oxygen/dissociation curve?It is a rectangular hyperbolaIt is shifted to the left by an increase in pCO2Foetal haemoglobin shifts the curve to the rightThe Haldane effect describes the changes in affinity of the haemoglobin chain for oxygen following variations in pCO2The shape of the curve is explained by the physico-chemical properties of haemoglobin
Cardiovascular system during a progressive work test
Robert B. Schoene, H. Thomas Robertson in Making Sense of Exercise Testing, 2018
The oxygen dissociation curve is not fixed but rather can be shifted to the right by three different influences: increases in temperature, hydrogen ion, and CO2. A right shift of the curve means that, at any given cellular PO2, more oxygen is released. All three of these influences arise in exercising muscle, although the elevation of muscle temperature is the most important effect causing the right shift of the curve. Hence, arterial blood entering exercising muscle readily releases its oxygen at a relatively higher muscle PO2 because of these influences. The movement of oxygen from muscle capillary to muscle mitochondria is facilitated by myoglobin within the muscle cells. While myoglobin binds more firmly to oxygen than hemoglobin at any given PO2, the mitochondrial utilization of oxygen remains fully functional even at partial pressures of oxygen as low as 2–3 mmHg.
Hb Santa Juana (β 108(G10) Asn > Ser): a low oxygen affinity hemoglobin variant in a family of Bosnian background
Published in Hematology, 2023
N. P. Wildenberg, C. Rossi, A. E. Kulozik, J. B. Kunz
Hemoglobin is a heterotetramer composed of two α- and two β-globin chains, with a total of four heme groups as oxygen binding sites. According to the allosteric two-state-model [2], the heterotetramer can exist in a relaxed R state with high oxygen affinity and a strained T state with low oxygen affinity. Binding of an oxygen molecule to one heme group increases the oxygen affinity of the other subunits. This effect explains the sigmoidal shape of the oxygen binding curve. Hemoglobin variants with decreased oxygen affinity stabilize the T-state and result in increased oxygen delivery to the tissues, while oxygen uptake in the lungs is decreased. The oxygen dissociation curve is right-shifted and characterized by a higher oxygen tension required to reach 50% saturation (p50). However, additional factors contribute to oxygen release into the tissue, such as the concentration of 2,3-bisphosphoglycerate, pH, and CO2 tension. Weak oxygen binding to hemoglobin favors oxygen release into the tissue, suppressing erythropoietin secretion and causing normocytic anemia. Although some patients expressing hemoglobin variants with decreased oxygen affinity present with cyanosis, most are asymptomatic. A low oxygen affinity hemoglobin variant may be suggested by otherwise unexplained reduced pulse oximetry measurements and normocytic anemia.
Compound Danshen Dripping Pill inhibits high altitude-induced hypoxic damage by suppressing oxidative stress and inflammatory responses
Published in Pharmaceutical Biology, 2021
Yunhui Hu, Jia Sun, Tongxing Wang, Hairong Wang, Chunlai Zhao, Wenjia Wang, Kaijing Yan, Xijun Yan, He Sun
Rat arterial blood (1 mL) was used for blood-gas analyses. The partial pressure of oxygen (PO2), SO2, and pH were detected at 37 °C by microelectrodes in a blood gas analyzer (iSTAT-300; Abbott Laboratories, Chicago, IL, USA). The oxygen-dissociation curve and the pressure of oxygen when SO2 level reaches 50% (P50) was calculated according to the Hill equation (Balaban et al. 2013): Equation (a), K is the oxygen dissociation constant, and n is the Hill coefficient. We converted Equation (a) into Equation (b) mathematically. After taking the logarithm on both sides of Equation (b), we obtained Equation (c) for a linear equation in the form of Y = aX + b. When we made Y = log10 SO2/(100 – SO2) and Y = log10 PO2, the slope ‘a’ became the ‘n’ value of the Hill equation, and b the logarithmic value of k. We calculated n and K values using the data for PO2 and SO2 of each group. After the regression, and making PO2 range from 0 to 100, the oxygen-dissociation curve was fitted and P50 was calculated.
Phenotypic variation in sickle cell disease: the role of beta globin haplotype, alpha thalassemia, and fetal hemoglobin in HbSS
Published in Expert Review of Hematology, 2022
HbS within the red blood cell behaves with a low oxygen affinity so that molecules may become fully oxygenated in the lungs but in the periphery, release oxygen more readily than HbA. This shift in the oxygen dissociation curve means that most patients at their steady state hemoglobin levels of 6–9 g/dl may be well adjusted in terms of oxygen delivery. Red cell survival in African HbSS has been measured as a mean of 12.6 days (range 4.2–25.0) [17] and with such short survival, the 6–8 days aplasia caused by parvovirus B19 [18] may cause death in the aplastic crisis. Increased bilirubin formation consequent on the rapid hemolysis engenders gallstones, and annual ultrasound examinations in the Cohort showed these in 7% by the age of 5 years, increasing steadily to 50% by the age of 25 years [19]. The bone marrow, expanded to compensate for the greater hemolysis, has increased metabolic requirements, and folate deficiency may result in megaloblastic change and a falling hemoglobin level [20]. Particularly common in West Africa [21] where dietary folate levels were low, folate supplementation has become routine in the management of HbSS elsewhere. Although folate requirements are increased in HbSS, the crucial question is whether these are met by dietary availability which may vary with local and other environmental conditions [22].
Related Knowledge Centers
- Carbon Dioxide
- Heme
- Molecule
- Oxygen
- Prosthetic Group
- Oxygen Saturation
- Partial Pressure
- Blood
- Hemoglobin
- Blood Gas Tension