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Pulmonary gas exchange
Published in Andrew M. Luks, Philip N. Ainslie, Justin S. Lawley, Robert C. Roach, Tatum S. Simonson, Ward, Milledge and West's High Altitude Medicine and Physiology, 2021
Andrew M. Luks, Philip N. Ainslie, Justin S. Lawley, Robert C. Roach, Tatum S. Simonson
By using Fick's law of diffusion and data on reaction rates of oxygen with hemoglobin, it is possible to calculate the time course of PO2 along the pulmonary capillary as the oxygen is loaded by the blood. The application of Fick's law to this situation is not trivial because of the chemical bond which forms between oxygen and hemoglobin. This means that the relationship between PO2 and oxygen concentration in the blood is nonlinear, as shown by the hemoglobin-oxygen dissociation curve. This problem was first solved by Bohr (1909) and the numerical integration procedure which he developed is known as the Bohr integration. A further complication occurs because, as oxygen is being taken up, carbon dioxide is given off, and this alters hemoglobin's affinity for oxygen and, as a result, the position of the oxygen dissociation curve. A full treatment of this latter process should take into account not only the rate of diffusion of carbon dioxide through the blood-gas barrier, but also the rates of reaction of carbon dioxide in blood. Since not all the rate constants are known under all the required conditions, some assumptions and simplifications are necessary.
Diagnosis and Treatment of Inhalation Injury in Burn Patients
Published in Jacob Loke, Pathophysiology and Treatment of Inhalation Injuries, 2020
Khan Z. Shirani, Joseph A. Moylan, Basil A. Pruitt
The most abundant gas generated in fires, carbon monoxide, on the other hand, has no direct cytotoxic properties but causes injury through the production of systemic hypoxemia. Carbon monoxide causes a leftward shift in the oxygen dissociation curve, which accentuates tissue hypoxia and leads to cell injury. Both hypoxia and hypothermia cause a suppression of membrane-based adenosine triphosphate synthesis rate that is unmatched by a reciprocal reduction in the intracellular metabolic processes. Such imbalance in the supply and demand of energy results in uncoupling of the metabolic and membrane cell functions, increased membrane permeability, and irreversible cell damage (Hochachka, 1986).
Haematology and oncology
Published in Jagdish M. Gupta, John Beveridge, MCQs in Paediatrics, 2020
Jagdish M. Gupta, John Beveridge
Fetal haemoglobin has the same iron content as adult haemoglobin but has greater affinity for oxygen, which shifts the oxygen dissociation curve to the left. Although it is the major form of haemoglobin in fetal life (90% at 28 weeks, 70% at term), the proportion of adult haemoglobin progressively increases as gestation progresses and very small amounts (less than 2%) of haemoglobin F are present in late infancy. It is resistant to alkali denaturation.
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.
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].
Gavage approach to oxygen supplementation with oxygen therapeutic Ox66™ in a hypoventilation rodent model of respiratory distress
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2021
William H. Nugent, Danuel A. Carr, Rosa MacBryde, Erica D. Bruce, Bjorn K. Song
In the clinic, ARDS is quantified and stratified by the PaO2/FiO2 ratio. Values of <300 mmHg, <200 mmHg, and <100 mmHg qualify as mild, moderate, and severe, respectively. For reference, the ratios seen in this study were generally 330–350, which—without scaling between species—would suggest very mild or emergent ARDS. However, if factoring in the oxygen demand differential between rats and humans, values of 350 become more severe because oxygen consumption is fivefold higher in rats at rest [27,28], Thus, similarities in supply may not meet the same needs between species, which was supported by our findings of increased rodent mortality when the tidal restriction is increased to 50% (data not published, under review). Returning to the present study, another issue with the PaO2/FiO2 ratio may be oxyhaemoglobin. Since inspired air was fixed at 21% oxygen, the ratio is dependent on dissolved oxygen (PaO2), which is subject to the much larger mass of oxygen (70-fold higher) bound to haemoglobin. The slight rise in PaCO2 from hypoventilation could have right-shifted the oxygen dissociation curve of haemoglobin leading to inflated PaO2 values. While this effect was not quantified, it is posited as a confounder of arterial blood gas measurements in over-estimating oxygen delivery to tissues, especially in situations where more marked shifts in CO2 and pH occur.