Question

You arrive at 4200m from Kelowna and send the next 6 months at this elevation. Evaluate the magnitude of change and mechanisms that alter ventilation over this time. What are the physiological implication of these changes in ventilation? (200 words)

Answer 1

As the altitude increase, the partial pressure of oxygen in the atmosphere decreases, resulting in hypoxic conditions. When the baroreceptors and peripheral chemoreceptors are triggered by the hypoxia, the lung ventilation increases and so does the breathing rate. This is known as hyperventilation. The tidal volume increases from the normal 500mL to compensate for the hypoxia.The change in breathing rate also depends on a number of other factors like humidity, temperature, reduction in air density, pollution, etc. The hyperventilation later decreases and rate of breathing returns to normal after some time. When the person spends more time at the high altitude, he experiences acclimatization, i.e., the physiological responses of the body to adapt to the oxygen stress. The increased ventillation is coupled with increase in heart rate and as a result increased cardiac output to ensure sufficient tissue perfusion. There is also increase in the pulmonary artery pressure and endothelial permeability, which accounts for the increased incidences of edema in people living at higher altitudes. Haematological adaptations also occurs and there is increased production of the hormone, erythropoietin, by the lungs and kidneys. This increases the production of red blood cells or erythropoesis in the bone marrow. As a result there is polycythemia in such individuals. Metabolic alkalosis may result due to increased arterial carbon dioxide concentration which is a result of hyperventilation. This is a harmful side effect, which gets resolved later once the person is acclimatized.