The respiratory sensation at high altitude

Area of Science:

• Physiology
• Altitude Medicine
• Respiratory Research

Background:

• Respiratory sensation, including dyspnea and load perception, is crucial for breathing regulation.
• Altitude exposure presents physiological challenges, including hypoxia and altered environmental conditions, which may affect respiratory function.

Purpose of the Study:

• To investigate the impact of varying altitudes on respiratory sensation, specifically dyspnea and the perception of external resistive loads.
• To compare respiratory sensation in individuals ascending to altitude with a control group at sea level under different breathing conditions.

Main Methods:

• Nine subjects were studied at four altitudes in Nepal (1377m, 2800m, 3900m, 530m) and rated external resistive loads.
• Sensory Decision Analysis was used to assess load discrimination (sensitivity).
• A control group (six subjects) was studied at sea level breathing air, hypoxic mixture (FIP2:11%), and cold air (-6°C).

Main Results:

• Dyspnea increased progressively with altitude and exertion in the nine subjects.
• Load perception was generally not altered at altitude, with some subjects showing slight improvement at rest.
• Three subjects, including those with clinical impairment, showed impaired load perception, potentially linked to chronic hypoxia effects.

Conclusions:

• Respiratory sensation, particularly load perception, is not impaired in individuals well-adapted to altitude.
• Transient hypoxia and cold environments at sea level did not alter load perception in the control group.
• Impaired load perception at altitude may be associated with secondary effects of chronic hypoxia, such as cerebral and/or pulmonary subedema.