Traveling above sea level increases the likelihood of experiencing negative physical effects. Altitude sickness is the general term for the various symptoms and conditions that arise when the body fails to properly adjust to a rapid gain in elevation. These reactions are primarily caused by changes in the atmosphere that directly impact the availability of oxygen for the body to use.
The Primary Biological Trigger: Reduced Oxygen Availability
The air we breathe contains a consistent 21% oxygen content, regardless of elevation. The problem at altitude is not the percentage of oxygen, but the total amount of air pressure pushing down on us, known as barometric pressure. As elevation increases, the barometric pressure drops significantly, causing the air molecules to be spread farther apart. This means that with every breath taken, fewer oxygen molecules enter the lungs.
The decrease in barometric pressure directly lowers the partial pressure of oxygen, which is the force that drives oxygen across the lung membranes into the bloodstream. This state of reduced oxygen availability to the body’s tissues and cells is termed hypoxia. In response to this sudden oxygen deficit, the body attempts to compensate by increasing both heart rate and breathing rate, known as hyperventilation.
Acute Altitude Sickness
The most common negative reaction to altitude is Acute Altitude Sickness (AAS), which typically affects individuals who ascend rapidly to elevations above 8,000 feet (about 2,400 meters). Symptoms of AAS usually begin 6 to 24 hours after arrival and are often vague, resembling a severe hangover or the flu. Symptoms include a persistent headache, which may not be relieved by common pain medications, along with general fatigue, dizziness, and lightheadedness.
AAS also affects the digestive system and sleep patterns, causing nausea, occasional vomiting, and a loss of appetite. Many people also experience difficulty sleeping, including frequent waking or periodic breathing disturbances during the night. For most individuals, these mild symptoms improve within 24 to 48 hours as the body begins acclimatization.
Managing AAS requires resting at the current elevation and avoiding further ascent until symptoms have fully resolved. If symptoms worsen or do not improve within a day, a prompt descent to a lower altitude is necessary.
High-Altitude Emergencies
While AAS is common and generally self-limiting, the most severe negative effects of altitude are two distinct and life-threatening conditions: High-Altitude Cerebral Edema (HACE) and High-Altitude Pulmonary Edema (HAPE). Both conditions represent extreme responses to hypoxia and involve fluid leakage into delicate tissues. HACE is characterized by brain swelling, where fluid leaks from the capillaries into the brain tissue, often developing after several days at high altitude.
Neurological symptoms are the hallmark of HACE, starting with confusion, severe headache, and an altered mental state. The most telling sign is ataxia, or a loss of coordination, manifesting as difficulty walking or maintaining balance.
HAPE involves the lungs filling with fluid. This occurs because low oxygen causes excessive constriction of blood vessels in the lungs, leading to leakage. Symptoms of HAPE include severe breathlessness even while resting, a persistent cough that may produce pink or frothy sputum, and chest tightness. A visible sign of severe HAPE is cyanosis, where the lips or skin take on a bluish tint due to extremely low blood oxygen levels. Both HACE and HAPE are medical emergencies demanding immediate descent and prompt medical intervention.