Oxygen dissociation curve of the

In cases of metabolic acidosis due to circulatory collapse, the acidaemia confers some physiological advantage in that it causes a shift to the right of the oxygen dissociation curve of the blood (Chapter 6). This assists in the unloading of oxygen from blood to the tissues and to a slight extent counteracts the tissue hypoperfusion. 

Goodford PI, St-Louis J, Wootton R. A quantitative analysis of the effects of 2,3-diphosphoglycerate, adenosine triphosphate and inositol hexaphosphate on the oxygen dissociation curve of human haemoglobin. J Physiol 1978 283 397. 

Hyperbolic shape of the enzyme kinetics curve Most enzymes show Michaelis-Menten kinetics (see p. 58), in which the plot of initial reaction velocity, v0, against substrate concentration [S], is hyperbolic (similar in shape to that of the oxygen-dissociation curve of myoglobin, see p. 29). In contrast, allosteric enzymes frequently show a sigmoidal curve (see p. 62) that is similar in shape to the oxygen-dissociation curve of hemoglobin (see p. 29). 

Figure 7.11 shows the oxygen dissociation curve of one such hemoglobin, Hb Rainier, where it is seen that this hemoglobin is still 50% saturated with oxygen at a p02 of about 12 mm Hg compared to 27 mm Hg in normal hemoglobin. The value of n in the Hill equation is 1.5 for this hemoglobin. 

Early this century, A.V. Hill derived a useful equation that describes the oxygen dissociation curve of hemoglobin fairly accurately. It is... 

Ascorbic acid appears to be toxic to certain tumor tissues however, it may increase the biological effectiveness of red blood cells by increasing the level of 2,3-diphosphoglycerate (30,31), 2,3-Diphosphoglycerate is essential to maintaining the normal oxygen dissociation curve of hemoglobin. This increase has been shown in vitro (30) and in vivo, in human subjects (31). 

A 72-year-old woman with emphysema presents to the emergency room with fatigue and respiratory distress. Which set of arterial blood gas values below would represent her condition and reflect a shift of the hemoglobin oxygen dissociation curve to the right ... 

A general model that considers nonequilibrium oxygen tension conditions between the erythrocytes and plasma has been derived. The rate of oxygen transport between the erythrocyte and plasma is assumed to be a function of the difference between the equilibrium and dynamic oxygen dissociation curves, and the rate of oxygen transfer to the tissue is based on the oxygen tension difference between the plasma and tissue. The three-lump model can be written as follows,... 

Adair, G.S. 1925. The hemoglobin system. VI. The oxygen dissociation curve of hemoglobin. J. Biol. Chem. 63 529-45. 

G. S. Adair, The Hemoglobin System. VI. The Oxygen Dissociation Curve of Hemoglobin. J. Biol Chem., 63,529-545,1925. 

However it is necessary to compare values of pto obtained under comparable conditions. Changes in temperature and pH displace the dissociation curve. The combination of molecular oxygen with a carrier being an exothermic process, an increase in temperature will lower the affinity, and a decrease in temperature will increase it. Figure 87 illustrates the shift in the dissociation curve of the oxyhaemoglobin of the ray Rata ocellata with temperature. 

The administration of bicarbonate is to be used with cautioa The indiscriminate use of bicarbonate is particularly dangerous in resuscitation of patients with metabolic acidosis as a concomitant of hypovolaemic shock lactic acid itself is innocuous and is readily removed by the liver as soon as the perfusion of the tissues is re-established. If administration of bicarbonate causes alkalosis and shifts the oxygen dissociation curve to the left, there is interference with oxygen unloading at the cellular level in tissues which are already hypoxic. Treatment of metabolic acidosis by bicarbonate therapy is reserved for situations in which partial correction of the pH is needed to restore cardiac function, which is depressed by acidaemia as described in Chapter 4. 

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