Q. An increase in the of an oxyhaemoglobin curve would result from a decrease in
Solution:
Solution:
The oxyhaemoglobin dissociation curve describes the relation between the partial pressure of oxygen (x-axis) and the oxygen saturation (y-axis). Haemoglobins' affinity for oxygen increases as successive molecules of oxygen bind. More molecules bind as the oxygen partial pressure increases until the maximum amount that can be bound is reached. As this limit is approached, very little additional binding occurs and the curve levels out as the haemoglobin becomes saturated with oxygen. Hence, the curve has a sigmoid or S-shape.
At pressures above about 60 mmHg, the standard dissociation curve is relatively flat, which means that the oxygen content of the blood does not change significantly even with large increases in the oxygen partial pressure. To get more oxygen to the tissue would require blood transfusions to increase the haemoglobin count (and hence the oxygen-carrying capacity), or supplemental oxygen that would increase the oxygen dissolved in plasma. Although binding of oxygen to haemoglobin continues to some extent for pressures about 50 mmHg, as oxygen partial pressures decrease in this steep area of the curve, the oxygen is unloaded to peripheral tissue readily as the haemoglobins' affinity diminishes. The partial pressure of oxygen in the blood at which the haemoglobin is 50% saturated, typically about 26.6 mmHg (3.5 kPa) for a healthy person, is known as the P50. The P50 is a conventional measure of haemoglobin affinity for oxygen. In the presence of disease or other conditions that change the haemoglobin oxygen affinity and, consequently, shift the curve to the right or left, the P50 changes accordingly. An increased P50 indicates a rightward shift of the standard curve, which means that a larger partial pressure is necessary to maintain a 50% oxygen saturation. This indicates a decreased affinity. Conversely, a lower P50 indicates a leftward shift and a higher affinity.