Hemoglobin Oxygen Saturation Simulation

The Effects of Altitude

Case Study: How Altitude Alters Hemoglobin Oxygen Saturation

Table of Contents

Table of Contents ►

How Altitude Reduces Oxygen Pressures and Hemoglobin Saturation
Altitude and Hypoxemia-Induced Physiological Effects
Physiological Adaptations to High Altitude
Case Study

Subject
Procedures
Results

Analysis and Assessment
Terms of Use
References and Attributions

How Altitude Reduces Oxygen Pressures and Hemoglobin Saturation

At higher altitudes, the partial pressure of oxygen (pO₂) in the atmosphere decreases while still comprising ~21% of the air, thus reducing the pO₂ of inhaled (alveolar) air.

The drop in alveolar pO₂ causes a corresponding drop in arterial pO₂(PaO₂). Since oxygen binding to hemoglobin is driven by the PaO₂, a decline in PaO₂ leads to lower hemoglobin oxygen saturation, which is typically determined by a pulse oximeter and reported as SpO₂ percentage (or % peripheral oxygen saturation).

A decline in SpO₂ indicates low oxygen levels in the blood, a condition known as hypoxemia. This condition reduces oxygen delivery to tissues, decreasing the synthesis of ATP by mitochondria. The loss of ATP decreases the rate of cellular reactions, which can cause cell damage if prolonged.

Altitude Effects Widget

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Altitude and Hypoxemia-Induced Physiological Effects

As altitude increases, the availability of oxygen decreases, leading to hypoxemia. This condition progressively impairs both physical performance and cognitive function.

3,000 – 8,000 feet:

Mild hypoxemia causes reduced endurance and subtle cognitive effects, such as reduced attention or memory.

8,000 – 12,000 feet:

Moderate hypoxemia may trigger Acute Mountain Sickness (AMS), which can cause headaches, nausea, sleep disturbances, impair cognition, and reduce exercise tolerance.

12,000 – 18,000 feet:

Severe hypoxemia increases the risk of High-Altitude Cerebral Edema (HACE), which can lead to confusion, ataxia, and severely impaired judgment. High-altitude pulmonary Edema (HAPE) can also cause shortness of breath, cough, and significantly decreased exercise tolerance.

Above 18,000 – 20,000 feet:

Critical hypoxemia limits the time of useful consciousness, and supplemental oxygen is required to prevent severe impairment.

Physiological Adaptations to High Altitude

Several physiological responses occur over time to compensate for decreased oxygen availability (hypoxemia).

Immediate:

Breathing becomes faster and deeper to increase ventilation.
The heartbeat rate and stroke volume increase to improve cardiac output.

Hours to Days:

The levels of 2,3-DPG (2,3-diphosphoglycerate) in red blood cells start to rise within 12 to 24 hours after the onset of hypoxemia. The binding of this molecule to hemoglobin causes the oxygen dissociation curve to shift to the right, which facilitates the release of oxygen from hemoglobin to tissue cells.

Hours to months:

The kidneys rapidly begin secreting the hormone erythropoietin (EPO) in response to hypoxemia, which stimulates red blood cell production in the bone marrow. However, it takes weeks to months for fully mature red blood cells to appear in the bloodstream.

Case Study Simulation

Subject

The subject is 30 years old and in good health.

She lives in Seattle, Washington, where she is a graduate student in exercise science. As part of her degree program, she volunteered for this study.

Before starting the exercise, the subject had her blood tested, and the results of her hemoglobin concentration, hematocrit, and total RBC count were within normal range.

Procedures

The subject will first obtain an oximeter reading in Seattle, which will serve as a baseline of comparison for readings taken at other locations.

She will then sequentially travel to the locations shown in the following activity. At each location, the subject will obtain a pulse oximeter reading upon arrival.

Due to its high altitude, the last location, Mt. Whitney, will be limited to a 15-minute flyover.

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Results

The following simulation shows the subject’s physiological responses to visiting the five selected locations. Use the “Previous” and “Next” buttons to navigate to the different locations. At each location:

Note the pulse oximeter readings:
- SpO₂ (% oxygen saturation).
- Pulse Rate (bpm).
Analyze the “pO₂ vs. Altitude” graph:
- Identify and compare the atmospheric pO₂ and arterial pO₂ (PaO₂) at each location.
- Note how these values shift with increasing altitude.
Make Connections:
- Observe how SpO₂ (hemoglobin saturation) changes with altitude.
- Consider how decreasing atmospheric and arterial pO₂ levels impact the blood’s ability to carry oxygen.

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Analysis and Assessment

1. Use the simulator above to compare the approximate atmospheric pO₂ in Seattle, WA, with that in Salt Lake City, UT.

What is the approximate percentage of oxygen in the atmosphere at both locations?
If the percentage of oxygen in the atmosphere is the same at both locations, why do the partial pressures of oxygen (pO₂) differ?

2. Why might the subject experience cognitive impairment and fatigue after initially arriving at the Aspen ski slopes from Santa Fe?

Refer to the simulation to compare the altitude, atmospheric pO₂, and SpO₂ in Santa Fe and Aspen, CO.
In your explanation, also discuss how hemoglobin oxygen saturation levels influence cellular activity.
How may the subject’s SpO₂ be affected due to prolonged exposure to low temperatures at the summit of the Aspen ski slopes?
Describe the physiological adaptations that would occur when she arrives in Aspen, and if she decides to extend her stay.

3. Explain why the subject’s visit to Mt. Whitney would be limited to 15 minutes.

Include details about the location’s altitude and atmospheric pO₂, as well as the subject’s SpO₂ readings and physiological responses.

4. Suppose the subject continues the exercise to include a brief flyover of the summit of Mt. McKinley (Denali) in Alaska, which has an altitude of approximately 20,000 feet.

Create a graph that integrates the information presented in the five “Atmospheric pO2 vs. Altitude” graphs. Based on the slope of the data points, calculate the atmospheric pO₂ at the summit of Mt. McKinley.
What is the percentage decrease in atmospheric pO₂ at the summit of Mt. McKinley compared to sea level?
Determine what might happen to her SpO₂ upon arrival.
Would supplemental O₂be immediately required? Why?

Terms of Use

Human Bio Media materials are open-source and can be adapted and shared by anyone according to the Creative Commons Attribution 4.0 License guidelines.