Date Published: October 31, 2018
Publisher: Public Library of Science
Author(s): Christopher K. Willie, Michael Stembridge, Ryan L. Hoiland, Michael M. Tymko, Joshua C. Tremblay, Alexander Patrician, Craig Steinback, Jonathan Moore, James Anholm, Prajan Subedi, Shailesh Niroula, Chris J. McNeil, Ali McManus, David B. MacLeod, Philip N. Ainslie, Christopher Torrens.
The University of British Columbia Nepal Expedition took place over several months in the fall of 2016 and was comprised of an international team of 37 researchers. This paper describes the objectives, study characteristics, organization and management of this expedition, and presents novel blood gas data during acclimatization in both lowlanders and Sherpa. An overview and framework for the forthcoming publications is provided. The expedition conducted 17 major studies with two principal goals—to identify physiological differences in: 1) acclimatization; and 2) responses to sustained high-altitude exposure between lowland natives and people of Tibetan descent. We performed observational cohort studies of human responses to progressive hypobaric hypoxia (during ascent), and to sustained exposure to 5050 m over 3 weeks comparing lowlander adults (n = 30) with Sherpa adults (n = 24). Sherpa were tested both with (n = 12) and without (n = 12) descent to Kathmandu. Data collected from lowlander children (n = 30) in Canada were compared with those collected from Sherpa children (n = 57; 3400–3900m). Studies were conducted in Canada (344m) and the following locations in Nepal: Kathmandu (1400m), Namche Bazaar (3440m), Kunde Hospital (3480m), Pheriche (4371m) and the Ev-K2-CNR Research Pyramid Laboratory (5050m). The core studies focused on the mechanisms of cerebral blood flow regulation, the role of iron in cardiopulmonary regulation, pulmonary pressures, intra-ocular pressures, cardiac function, neuromuscular fatigue and function, blood volume regulation, autonomic control, and micro and macro vascular function. A total of 335 study sessions were conducted over three weeks at 5050m. In addition to an overview of this expedition and arterial blood gas data from Sherpa, suggestions for scientists aiming to perform field-based altitude research are also presented. Together, these findings will contribute to our understanding of human acclimatization and adaptation to the stress of residence at high-altitude.
The study of human physiology during acute and chronic exposure to high-altitude informs our understanding of the physical response to reduced oxygen availability. Hypoxemia, such as that experienced at high-altitude, is also a stress common amongst critically and chronically ill patients. There is, however, a markedly heterogeneous response between individuals to the same stimuli [1,2]. At sea-level, simulated hypoxic stress can be achieved through exposure to a reduced inspired oxygen fraction in an enclosed environment (e.g. hypoxic chambers or tents) and is a useful laboratory based approach for the study of acute hypoxic exposure. Such an approach is problematic for the study of acclimatization processes and long-term hypoxic exposure. This is predominately because of the complexities of conducting a lengthy study in the confines of a small chamber. Field expeditions have therefore long been the modus operandi of physiologists interested in the physiological responses to high-altitude . These expeditions are notable, not just for their substantial contributions to the natural sciences, but also for the logistical hurdles and physical hardship of living and conducting research at altitude.
Arterial blood gas data was successfully collected at each altitude on 21 lowlanders and 11 Sherpa. The results are summarized in Table 4. Changes in PaO2 and SaO2 were not different between Sherpa and lowlanders. At each altitude PaCO2 was decreased in both groups (Fig 4); however, PaCO2 was greater in Sherpa at Pheriche and the Pyramid Laboratory (P<0.05 for both). This, coupled with a lower [HCO3-] at Kathmandu and Namche Bazaar for Sherpa (P<0.05 for both), led to a main effect of race for pH (P<0.05). Indeed, the Sherpa were less alkalotic at each altitude than lowlanders. Although there were numerous setbacks over the course of the expedition that ranged from the typical illnesses experienced in developing countries to tanks of pure nitrogen instead of 15% oxygen arriving at 5050m, every planned study was successfully completed. Nevertheless, number of potentially confounding factors still bear consideration to help inform future expeditions to high-altitude. The 2016 UBC Expedition was comprised of seventeen studies on five distinct cohorts: 1) 30 lowlander adults; 2) 12 Sherpa adults who de-acclimatized at 1400m for 5–15 days; 3) 12 Sherpa adults who had not recently descended below 3500m; 4) 57 Sherpa children; 5) 30 age and BMI-matched lowlander children tested in Canada at 344m. Studies were conducted both during a nine-day trekking ascent to 5050m and during three weeks at 5050m, which focused on cardiovascular, cerebrovascular, cardiopulmonary and neuromuscular aspects of human physiological responses to acclimatization. The findings from this study will be reported in approximately seventeen ensuing publications according to their respective a priori hypotheses. Source: http://doi.org/10.1371/journal.pone.0204660