Hypoxia can be caused by which of the following?
1. A decreased saturation of oxygen in the blood due to carbon monoxide attached to the haemoglobin.
2. Low partial pressure of oxygen in the atmosphere when flying at high altitudes without pressurisation and supplemental oxygen.
3. Malfunction of the body cells to metabolise oxygen.
4. Blood pooling in the lower extremities due to inertia (+Gz).
The four statements include aviation examples for four forms of hypoxia:
"1. A decreased saturation of oxygen in the blood due to carbon monoxide attached to the haemoglobin." CORRECT.
This statement refers to Anaemic/Hypemic hypoxia - caused by the reduced ability of the blood to carry oxygen. There are a variety of reasons for this to happen but the most common cause for hypemic hypoxia in aviation is when carbon monoxide is inhaled because of aircraft heater malfunctions, engine manifold leaks, or cockpit contamination with exhaust from other aircraft. Hemoglobin bonds with carbon monoxide 200 times more readily than it bonds with oxygen.
"2. Low partial pressure of oxygen in the atmosphere when flying at high altitudes without pressurisation and supplemental oxygen." CORRECT.
This statement refers to hypoxic hypoxia - the most common form of hypoxia encountered in aviation and occurs at the lung level. Pilots may experience hypoxic hypoxia when flying at altitude in an unpressurized aircraft. With increasing altitude, the molecules of oxygen in ambient air get farther apart and exert less pressure per square inch. The percentage of oxygen does not change as we ascend; however, the partial pressure of oxygen in ambient air decreases as we go to altitude. In other words, with increasing altitude, the partial pressure of oxygen gets lower and the lungs cannot effectively transfer oxygen from the ambient air to the blood to be carried to all tissues in the body.
"3. Malfunction of the body cells to metabolise oxygen." CORRECT.
This statement refers to histotoxic hypoxia - which happens at the cell level. This means that the cell expecting and needing the oxygen is impaired and cannot use the oxygen to support metabolism. Alcohol, narcotics, and cyanide are three primary factors that can cause histotoxic hypoxia.
"4. Blood pooling in the lower extremities due to inertia (+Gz)." CORRECT.
This statement refers to ischemic/stagnant hypoxia - Reduced brain oxygen is caused by inadequate blood flow to the brain. This can occur as a result of positive accelerations (+Gz) - lack of blood in the upper body parts because it is pulled down by gravity.
"2. Low partial pressure of oxygen in the atmosphere when flying at high altitudes without pressurisation and supplemental oxygen." CORRECT.
This statement refers to hypoxic hypoxia - the most common form of hypoxia encountered in aviation and occurs at the lung level. Pilots may experience hypoxic hypoxia when flying at altitude in an unpressurized aircraft. With increasing altitude, the molecules of oxygen in ambient air get farther apart and exert less pressure per square inch. The percentage of oxygen does not change as we ascend; however, the partial pressure of oxygen in ambient air decreases as we go to altitude. In other words, with increasing altitude, the partial pressure of oxygen gets lower and the lungs cannot effectively transfer oxygen from the ambient air to the blood to be carried to all tissues in the body.
"3. Malfunction of the body cells to metabolise oxygen." CORRECT.
This statement refers to histotoxic hypoxia - which happens at the cell level. This means that the cell expecting and needing the oxygen is impaired and cannot use the oxygen to support metabolism. Alcohol, narcotics, and cyanide are three primary factors that can cause histotoxic hypoxia.
"4. Blood pooling in the lower extremities due to inertia (+Gz)." CORRECT.
This statement refers to ischemic/stagnant hypoxia - Reduced brain oxygen is caused by inadequate blood flow to the brain. This can occur as a result of positive accelerations (+Gz) - lack of blood in the upper body parts because it is pulled down by gravity.
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