Alan Forsythe, a middle-aged college professor from Boston, is in the Swiss Alps studying astronomy during his sabbatical leave. He has been there for two days and plans to stay the entire year. However, he notices that he is short of breath when he walks up steps and tires easily with any physical activity. His symptoms gradually disappear, and he feels fine after less than a month. Upon returning to the United States, he has a complete physical exam and is told that his erythrocyte count is higher than normal.
a. Attempt to explain this finding.
b. Will his RBC count remain at this higher-than-normal level? Why or why not?

Verified step by step guidance

1. Step 1: Understand the physiological context. Alan was at high altitude in the Swiss Alps, where the oxygen level in the air is lower than at sea level. This causes a condition called hypoxia, meaning less oxygen is available for the body’s tissues.
2. Step 2: Explain the body's response to hypoxia. To compensate for lower oxygen availability, the kidneys release more erythropoietin (EPO), a hormone that stimulates the bone marrow to produce more red blood cells (RBCs). This increase in RBCs helps improve oxygen transport in the blood.
3. Step 3: Connect the symptoms to the physiological changes. Alan’s shortness of breath and fatigue are typical initial responses to hypoxia as his body adjusts. As his RBC count increases, oxygen delivery improves, and his symptoms resolve.
4. Step 4: Address the erythrocyte count after returning to sea level. Once Alan returns to a normal oxygen environment, the stimulus for increased EPO production decreases. Consequently, RBC production slows down, and the elevated RBC count will gradually return to normal.
5. Step 5: Summarize the overall process. The higher RBC count is a temporary adaptation to high altitude hypoxia, which reverses when the oxygen level normalizes, explaining both the initial symptoms and the later blood test findings.

Key Concepts

Altitude and Oxygen Availability

At high altitudes, such as the Swiss Alps, the atmospheric pressure is lower, resulting in reduced oxygen availability. This lower oxygen level causes the body to experience hypoxia, which triggers physiological adaptations to improve oxygen delivery to tissues.

Erythropoiesis and Red Blood Cell Production

In response to hypoxia, the kidneys release erythropoietin, a hormone that stimulates the bone marrow to produce more red blood cells (RBCs). This increase in RBCs enhances the blood's oxygen-carrying capacity, helping to alleviate symptoms like shortness of breath and fatigue.

Reversibility of Altitude-Induced Polycythemia

When returning to lower altitudes with normal oxygen levels, the stimulus for increased RBC production diminishes. Consequently, the elevated RBC count gradually returns to baseline as the body reduces erythropoietin production and removes excess red blood cells.