Effect On Oxygen Transport

The quantity of CO absorbed by the body depends on the inspired CO concentration, alveolar ventilation, and duration of exposure4. Exposure to high concentration for a short period appears less harmful than exposure at a lower concentration but over a longer period of time.

Once inhaled, carbon monoxide crosses the alveolar membrane and dissolves in the plasma. Very little CO is metabolized in the body (less than 1 % is oxidized in CO2). It binds to hemoglobin to form carboxyhemoglobin (COHb), blocking heme binding sites for oxygen transport. Carbon monoxide has about 250 times greater affinity for hemoglobin than has oxygen5'6. Because of alterations in the structure of the carboxyhemoglobin, the dissociation curve is shifted to the left. Red cell 2,3-diphosphoglycerate reduction accentuates the effect further7.

The proportion between the partial pressure of carbon monoxide and oxygen determines the quantity of COHb formed. Carbon monoxide uptake is inversely proportional to the partial pressure of oxygen. This explains why the confinement (i.e., environmental oxygen depletion) increases the severity of CO poisoning significantly.

The binding of CO to hemoglobin leads to a non-functional form of hemoglobin. Consequently, arterial blood oxygen content decreases. But because oxygen delivery in ambient air relies on hemoglobin transported oxygen, CO poisoning induces an hypoxemic peripheral hypoxia.

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