oxygen dissociation curve

oxygen dissociation curve

Oxygen saturation curve Physiology A curve that describes the relationship between Hb O2 saturation and tension; defined by a sigmoid curve which reflects the interaction of the 4 Hb molecules involved in O2 uptake, transport and release; a 'right shift' of the curve indicates ↓ Hb affinity for O2, as occurs in ↓ pH–ie, acidosis, ↑ temperature, ↑ PCO2, while a 'left shift' indicates ↑ O2 affinity with ↑ pH, ↓ temperature, ↓ 2,3 DPG and ↓ PCO2 Right shifts Acidosis, hyperthermia, alveolar hypoventilation, anemia Left shifts Alkalosis, hypothermia, hyperventilation, carboxyhemoglobinemia, hypophosphatemia, ↑ fetal Hb. See 2,3 DPG.
Oxygen dissociation curveclick for a larger image
Fig. 242 Oxygen dissociation curve .The characteristic S-shaped curve of oxygen dissociation.

oxygen dissociation curve

a curve derived from plotting the percentage saturation of blood with oxygen, against the oxygen tension (the oxygen exchange).

The curve is S-shaped and shows that HAEMOGLOBIN has a high affinity for oxygen.Blood can become saturated at relatively low oxygen tensions, but a small drop in oxygen tension brings about a big fall in the saturation of the blood. If tissues use up oxygen, then haemoglobin responds by giving it up.

Where CO2 is present, haemoglobin has to be under higher oxygen tension in order to become fully saturated. However, under these circumstances it releases O2 at higher oxygen tensions. CO2 affects the efficiency of oxygen uptake by haemoglobin but increases its efficiency in releasing it. The oxygen-carrying capacity of blood is also affected by pH (see BOHR EFFECT).

References in periodicals archive ?
This oxidized ferric iron bounds to hydroxyl group of water molecule in which this complex has a shift toward the left in oxygen dissociation curve and is incapable to transport oxygen which leads to an ablated oxygenation in tissue with consequent hypoxic features.
A highaffinity hemoglobin variant will have a left-shifted oxygen dissociation curve, reflecting the aberrant molecule's ability to bind oxygen at relatively low oxygen pressure.
The effect of blood transfusion on the haemoglobin oxygen dissociation curve of very early preterm infants during the first week of life.
CO can displace oxygen and lead to the shifting of the oxygen dissociation curve to the left.
Additionally, with the increased RBC 2,3-DPG the oxygen dissociation curve shifts to the right indicating a facilitated release of oxygen to the muscles.
On this occassion I also would like to emphasize that methylenblue (1-2 mg/kg in 1% solution; in higher concentration and doses causes and or increases methemoglobinemia) should be preferred in acquired as well as hereditary enzymopenic methemoglobinemias, since it is effective within minutes with corrected oxygen dissociation curve. It was also used orally (2-5 mg/kg/day) in our enzymopenic methemoglobinemia patients successfully.
A high [P.sub.50] indicates a rightward shift in the oxygen dissociation curve, i.e., a low oxygen affinity.
The [So.sub.2], when measured by means of arterial blood-gas analysis, is calculated from the blood PH, the [Po.sub.2], and the standard Hb oxygen dissociation curve. Unfortunately, this approach to calculating the (So.sub.2) assumes a normal oxygen dissociation curve, and metHb can falsely elevate the calculated (So.sub.2).
In addition, the remaining [Fe.sup.2+] ferrous haems within the haemoglobin tetramer containing [Fe.sup.3+] ferric haems paradoxically exhibit increased oxygen affinity, causing the oxygen dissociation curve to be shifted 'to the left', which further impairs oxygen delivery to the tissues (Fig.
This is known as cooperative binding, and is the reason for the sigmoid shape of the oxygen dissociation curve. This also explains why hemoglobin is most attracted to oxygen when three of the four subunits are bound to oxygen.
However, 88% were not aware of the basic relationship between oxygen saturation and the partial pressure of oxygen in arterial blood (oxygen dissociation curve).
Owing to the sigmoid shape of the oxygen dissociation curve arterial oxygen saturation is an insensitive reflection of arterial oxygen tension.