Methemoglobin과 oxyhemoglobin dissociation curve

Methemoglobin은 heme의 ferrous (Fe⁺⁺) irons이 ferric (Fe⁺⁺⁺) state로 산화된 hemoglobin의 변화된 상태입니다. Methemoglobin의 ferric hemes은 산소와 가역적으로 결합할 수 없습니다. 게다가 hemoglobin tetramer에서 남아 있는 globins' ferrous hemes의 산소에 대한 친화도는 증가합니다. 그 결과 oxygen dissociation curve는 좌측으로 이동합니다.

Depicted here is the oxyhemoglobin dissociation curve for normal adult hemoglobin (hemoglobin A, solid line). Note that at a partial pressure of oxygen of 27 mmHg on the X axis, hemoglobin is 50 percent saturated with oxygen (the P50 is 27 mmHg), and at an arterial partial pressure of oxygen of 100 mmHg, hemoglobin is 100 percent saturated. At the typical mixed venous oxygen tension of approximately 40 mmHg, the oxygen saturation of hemoglobin is approximately 75 percent. Shifting the curve to the right (red line) can reduce oxygen saturation to 50 to 60 percent for the partial oxygen pressure of 40 mmHg, meaning that less oxygen is bound to hemoglobin and more oxygen is delivered to the tissues. The opposite occurs with left shifts (blue line). A high proportion of fetal hemoglobin, which has high oxygen affinity, shifts this curve to the left in newborns. The effect of right- or left-shifting of the curve is most pronounced at low partial pressures of oxygen.

이것의 전체 효과로서 methemoglobin이 갑작스럽게 상승한 환자는 functional anemia가 생깁니다. Functional anemia라 함은 functional hemoglobin의 양이 측정된 총 헤모글로빈보다 낮다는 뜻입니다. 순환하는 functional hemoglobin의 양은 산소를 운반할 수 없고 남아 있는 oxyhemoglobin의 산소에 대한 친화도가 증가하며 말초 조직으로의 산소를 운반하는 능력이 감소합니다. Methemoglobinemia가 만성적으로 증가하고 functional anemia가 있는 환자는 보상적으로 polycythemia/erythrocytosis가 생길 수 있습니다.

Note the chocolate brown color of methemoglobinemia. Tube 1 and tube 2 have a methemoglobin concentration of 70 percent; tube 3, a concentration of 20 percent; and tube 4, a normal concentration. Image reprinted with permission from: Medscape.com, 2011. Available at: http://emedicine.medscape.com/article/956528-overview.

REF. UpToDate 2018.07.09