Shift to right in Oxygen dissociation curve is seen in all except: March 2007

Ans. B: Decreased PaCO2 Haemoglobin is the primary vehicle for transpoing oxygen in the blood. The oxygen carrying capacity is determined by the amount of haemoglobin present in the blood. Oxygen is also carried dissolved in the blood's plasma, but to a much lesser degree. A hemoglobin molecule can bind up to four oxygen molecules in a reversible way. The oxygen-hemoglobin dissociation curve has a sigmoidal or S-shape. The paial pressure of oxygen in the blood at which the hemoglobin is 50% saturated, is known as the P50. The P50 is a conventional measure of hemoglobin affinity for oxygen. An increased P50 indicates a rightward shift and a decreased affinity of the standard curve, which means that a larger paial pressure is necessary to maintain a 50% oxygen saturation. Conversely, a lower P50 indicates a leftward shift and a higher affinity. Left shift of the curve is a sign of hemoglobin's increased affinity for oxygen (e.g. at the lungs). Similarly, right shift shows decreased affinity, as seen in: An increase in body temperature, An increase in hydrogen ion, An increase in 2, 3-bisphosphoglycerate An increase in carbon dioxide concentration (the Bohr effect) With fetal hemoglobin, the shift facilitates diffusion of oxygen across the placenta. The oxygen dissociation curve for myoglobin exists even fuher to the left.