Colorado’s high altitude presents a physiological challenge, especially for visitors arriving from sea level. They frequently notice a difference in their ability to breathe and perform physical activity. This sensation is a normal reaction to the reduced air density found at elevations generally above 5,000 feet. The body adapts to this change through a process called acclimatization. Understanding this adjustment and how to manage it can make a trip to the mountains more enjoyable.
The Physiological Impact of High Altitude
The feeling of breathlessness at altitude is primarily caused by a drop in barometric pressure. While the air still contains about 21% oxygen at all elevations, the lower barometric pressure means the oxygen molecules are farther apart. This results in a reduced partial pressure of inspired oxygen, which drives oxygen from the lungs into the bloodstream. This reduced pressure impairs the efficiency of gas exchange across the alveolar membrane, lowering the amount of oxygen that dissolves into the blood.
At an elevation like Denver’s 5,280 feet, the effective amount of oxygen is roughly 17.3% compared to sea level, making the work of breathing noticeably harder. The body immediately detects this reduction in oxygen availability, known as hypoxia, through specialized peripheral chemoreceptors. In response, the body initiates two primary compensatory actions to maintain oxygen delivery.
The first action is an increased breathing rate, known as hyperventilation, which attempts to draw in more oxygen. Simultaneously, the sympathetic nervous system is stimulated, causing the heart rate to increase by 10 to 30%. This faster heart rate ensures that the blood, carrying less oxygen per volume, circulates more quickly throughout the body. These acute adjustments are the body’s first attempt to cope with the environmental change, but they are not sufficient for full adaptation.
Recognizing Symptoms of Acute Mountain Sickness
Mild breathlessness and a small increase in heart rate are expected at higher elevations. However, a more severe collection of symptoms signals the onset of Acute Mountain Sickness (AMS). AMS is the mildest and most common form of altitude illness, typically manifesting when a person ascends too quickly. Symptoms usually begin to appear between 6 and 12 hours after arrival, though they can take up to two days to fully develop.
The most common complaint is a persistent headache, often feeling like a pounding or throbbing sensation, which may be accompanied by nausea or loss of appetite. Other frequent symptoms include fatigue, lightheadedness, and difficulty sleeping due to altered breathing patterns. These symptoms result from the body struggling to adjust to the reduced oxygen pressure and commonly worsen with physical exertion.
For most people, mild AMS symptoms are uncomfortable but resolve within a few days as the body acclimatizes. It is important to monitor symptoms closely, as AMS can progress to more dangerous forms, such as fluid accumulation in the lungs or brain. If symptoms become severe, such as a headache unrelieved by medication, increasing weakness, or impaired coordination, it signals that the condition may be worsening. The only reliable treatment in such cases is immediate descent to a lower elevation.
Strategies for Acclimatization and Prevention
Preventing altitude illness relies on providing the body with sufficient time to adapt to the lower oxygen environment. The most effective strategy involves a controlled and gradual ascent, often summarized as “climb high, sleep low.” Travelers should avoid going directly from a low altitude to a sleeping altitude above 9,000 feet in a single day.
Once above 9,000 feet, limit the increase in sleeping elevation to no more than 1,600 feet per day, incorporating a rest day for every 3,300 feet gained. Upon arrival, postpone strenuous physical activity for the first day or two, allowing initial compensatory mechanisms to stabilize. Aggressive hydration is also effective, as the dry mountain air and increased breathing rate cause rapid fluid loss.
Consuming ample non-alcoholic fluids helps maintain blood volume and counteracts the diuretic effect of altitude. It is recommended to avoid alcohol for the first 48 hours, as it can worsen dehydration and suppress the respiratory drive, particularly during sleep. Certain prescription medications can accelerate the acclimatization process by helping correct the chemical imbalances caused by hyperventilation.
One common option is a carbonic anhydrase inhibitor, which works by acidifying the blood to stimulate increased ventilation and improve oxygen delivery. Starting this medication a day before ascent and continuing throughout the stay can lower the risk of developing AMS.
Elevation Variation Across Colorado
The risk of experiencing breathing difficulties varies dramatically across Colorado, which has a mean elevation of about 6,800 feet. Cities on the high plains, such as Denver, sit at 5,280 feet, earning the nickname “Mile High City.” While mild symptoms are possible, the risk of developing full Acute Mountain Sickness is low.
The danger increases substantially in mountain communities and ski resorts, where elevations commonly range from 8,000 to over 10,000 feet. Towns like Breckenridge (9,600 feet) or ski slopes with peaks exceeding 12,000 feet present a greater challenge for unacclimatized visitors. Medical experts suggest that altitude illness typically occurs only above 8,000 feet, making these destinations the primary concern for travelers.