Public defense of doctoral thesis in Health Science with Pontus Holmström
Welcome to the defense of doctoral thesis in Health Science with Pontus Holmström. He will present his doctoral thesis: "Protective Responses to Freediving Reveal High-Altitude Tolerance".
Main supervisor: Erika Schagatay, Mid Sweden University.
Co-supervisors: Dr. Angelica Lodin-Sundström och Dr. Harald Engan, Mid Sweden University.
Opponent: Prof. Ola Eiken, Royal Institute of Technology in Stockholm, Sweden.
Abstract
High-altitude mountaineers - just as freedivers - are exposed to hypoxia. During freediving, the diving response leads to reduced oxygen consumption, and splenic contraction increases the amount of circulating red blood cells, which protects against hypoxia. It is, however, unknown whether these responses relate with altitude-induced responses and what role the spleen has at high-altitude. My thesis aimed to explore whether associations exist between these apnea-induced responses and tolerance to high-altitude.
In five studies, I investigated the diving response and splenic contraction during apnea in a range of groups, including recreational trekkers, elite climbers, Sherpa (living high and low) and endurance athletes. My primary finding was striking: the diving response and splenic size were associated with tolerance to high-altitude hypoxia in lowlanders; individuals with a powerful diving response and large spleen showed less symptoms of acute mountain sickness, at high-altitude.
I also found that groups often exposed to high-altitude have larger spleens compared with groups who reside at sea-level. Further studies showed that this spleen enlargement is most likely caused by both genetic- and exposure induced factors. I also found that the spleen is reduced in size by ~14% per 1000 m of ascent in lowlanders, suggesting that its red cell regulating function may be important during short-term high-altitude exposure, before EPO-induced red cell increase occurs, thereby aiding haematological acclimatization.
Collectively, my findings in studies 1-4 indicate that a strong diving response and a large spleen may be characteristics of high-altitude tolerance in lowlanders, and could possibly be used to predict sensitivity to high-altitude hypoxia. In the final study, I also found that endurance athletes, which are dependent on efficient oxygen delivery, have large spleens and a powerful blood-boosting spleen contraction.