Set rad 5

Cardiorespiratory variables were obtained once at low altitude and every morning at high altitude between 0600 and 0900 local time with participants in a fasted state. All cardiorespiratory variables were obtained in the supine position following a minimum 3-min baseline with the participant resting quietly with their eyes closed and with white noise headphones to reduce external distraction. For cardiovascular measurements, participants were instrumented with an automated brachial blood pressure monitor (model BP786n; Omron, San Ramon, CA) and a peripheral pulse oximeter (Masimo SET Rad-5, Danderyd, Sweden) placed on the left middle finger for heart rate (HR, beats/min). Three brachial blood pressure measurements were obtained and averaged. Mean arterial pressure (MAP, mmHg) was calculated as 1/3 systolic arterial pressure + 2/3 diastolic arterial pressure. Ventilation (V̇_E, L/min) was obtained using a respirometer (nSpire Haoscale, Colorado). Participant weight was also recorded daily.

The exercise protocol used in this study consisted of 20 min of moderate intensity walking exercise at a target HR reserve (HRR). Individual target heart rate ranges were calculated as 40%–60% of HRR using the Karvonen method (Karvonen & Vuorimaa, 1988). Resting HR measures were obtained every morning prior to exercise testing and were recorded via a wireless pulse oximeter. Participants were told their target HR zone and were given wrist‐worn HR monitors (HR; Polar FT1 or FT7, Polar Electro) to self‐monitor their HR during exercise. Exercise was completed at the same time of day within each participant at each elevation. Because of the crowded environment surrounding the guest house in Kathmandu, exercise at low altitude (Kathmandu, 1400 m) was completed on stairs in the hotel, whereas exercise at high altitude (Namche, 3440 m and Pheriche, 4240 m) was completed on walking paths outside near the guest house. HR, perceived physical strain and perceived mental strain were measured during exercise at minutes 5–7 (early) and 14–16 (late) of the 20 min walking test. Arterial oxygen saturation (Masimo SET^® Rad‐5) was recorded pre and post exercise. Core affect was only measured pre exercise to assess changes between altitudes (Venhorst et al., 2018a).

Each morning (06:00–08:00), non-invasive fasted daily measures were made including weight (digital scale; Omron, model OMRHBF514C), Hb concentration (hemoglobinometer; Hemocue HB201+) and hematocrit (hct; heparinized capillary tube, mini-centrifuge; StatSpin, CritSpin microhematocrit system, Model M960). The participant was seated in a private and quiet room and provided with white noise through head phones to minimize distraction. Subsequently, respiratory rate and (P_ET)CO₂ were measured using a portable, calibrated capnograph (Masimo EMMA, Danderyd, Sweden) with a personal mouthpiece and nose clip. HR and SpO₂ were measured with a portable finger pulse oximeter (Masimo SET^® Rad-5, Danderyd, Sweden). Arterial blood pressure (i.e., systolic, diastolic) was measured using an automated blood pressure cuff (Omron, model BP786n) and used to calculate pulse pressure (systolic-diastolic) and MAP (1/3 systolic + 2/3 diastolic). Arterial blood draws were taken and assessed using a blood gas analyzer (Abbott iStat, CG4+ and CHEM 8+ cartridges; Mississauga, Ontario, Canada; blood gasses corrected for altitude and body temperature; see Table 2). Each participant filled out the Lake Louise AMS questionnaire to assess self-reported AMS symptoms (see Table 1).