Florida natives Marsha and Charlie have arrived in Colorado for a week of hiking in the Rocky Mountains. Within an hour of their first hike (at 10,000 ft), Charlie develops a headache and soon begins to complain about dizziness. Briefly describe how these symptoms are related to changes in blood oxygen and carbon dioxide levels. Is the pH of their blood affected by the change in blood gases?
Marsha and Charlie are suffering from altitude sickness. Altitude sickness is actually a complex group of problems all resulting from hypoxia, or lack of oxygen, combined with physical exertion.
In both the lungs and the brain, lowered blood oxygen levels result in increased capillary permeability and edema in the tissues. Additionally, the low levels of blood oxygen stimulate the O2 receptors in the carotid, which causes the victim's respiratory rate to increase. This increase in breathing rate causes the victim to blow off carbon dioxide more rapidly than normal. Since CO2 in solution creates a mild acid, the lower CO2 levels mean the victim's blood begins to become more alkaline. Receptors in the brain react to the alkaline blood situation by slowing the respiratory rate. Over time, this situation will begin to resolve itself as the kidneys excrete bicarbonate ions into the urine, which brings the blood pH back down. This response can be sped up by giving the victim diuretics, which both reduce the edema and make the kidneys work more rapidly.