Cardiovascular function in healthy Himalayan high-altitude dwellers.

BACKGROUND: Residents of the Himalayan valleys uniquely adapted to their hypoxic environment in terms of pulmonary vasculature, but their systemic vascular function is still largely unexplored. The aim of the study was to investigate vascular function and structure in rural Sherpa population, permanently living at high altitude in Nepal (HA), in comparison with control Caucasian subjects (C) living at sea level. METHODS AND RESULTS: 95 HA and 64 C were enrolled. Cardiac ultrasound, flow-mediated dilation (FMD) of the brachial artery, carotid geometry and stiffness, and aortic pulse wave velocity (PWV) were performed. The same protocol was repeated in 11 HA with reduced FMD, after 1-h 100% O2 administration. HA presented lower FMD (5.18 ± 3.10 vs. 6.44  ±  2.91%, p = 0.02) and hyperemic velocity than C (0.61 ± 0.24 vs. 0.75 ± 0.28 m/s, p = 0.008), while systolic pulmonary pressure was higher (29.4 ± 5.5 vs. 23.6 ± 4.8 mmHg, p < 0.0001). In multiple regression analysis performed in HA, hyperemic velocity remained an independent predictor of FMD, after adjustment for baseline brachial artery diameter, room temperature and pulse pressure, explaining 8.7% of its variance. On the contrary, in C brachial artery diameter remained the only independent predictor of FMD, after adjustment for confounders. HA presented also lower carotid IMT than C (0.509 ± 0.121 vs. 0.576 ± 0.122 mm, p < 0.0001), higher diameter (6.98 ± 1.07 vs. 6.81 ± 0.85 mm, p = 0.004 adjusted for body surface area) and circumferential wall stress (67.6 ± 13.1 vs. 56.4 ± 16.0 kPa, p < 0.0001), while PWV was similar. O2 administration did not modify vascular variables. CONCLUSIONS: HA exhibit reduced NO-mediated dilation in the brachial artery, which is associated to reduced hyperemic response, indicating microcirculatory dysfunction. A peculiar carotid phenotype, characterized by reduced IMT and enlarged diameter, was also found.

Respiratory and leg muscles perceived exertion during exercise at altitude.

We compared the rate of perceived exertion for respiratory (RPE,resp) and leg (RPE,legs) muscles, using a 10-point Borg scale, to their specific power outputs in 10 healthy male subjects during incremental cycle exercise at sea level (SL) and high altitude (HA, 4559 m). Respiratory power output was calculated from breath-by-breath esophageal pressure and chest wall volume changes. At HA ventilation was increased at any leg power output by ∼ 54%. However, for any given ventilation, breathing pattern was unchanged in terms of tidal volume, respiratory rate and operational volumes of the different chest wall compartments. RPE,resp scaled uniquely with total respiratory power output, irrespectively of SL or HA, while RPE,legs for any leg power output was exacerbated at HA. With increasing respective power outputs, the rate of change of RPE,resp exponentially decreased, while that of RPE,legs increased. We conclude that RPE,resp uniquely relates to respiratory power output, while RPE,legs varies depending on muscle metabolic conditions.

High-altitude exposure reduces inspiratory muscle strength.

It was the aim of the study to assess the maximal pressure generated by the inspiratory muscles (MIP) during exposure to different levels of altitude (i.e., hypobaric hypoxia). Eight lowlanders (2 females and 6 males), aged 27 - 46 years, participated in the study. After being evaluated at sea level, the subjects spent seven days at altitudes of more than 3000 metres. On the first day, they rode in a cable car from 1200 to 3200 metres and performed the first test after 45 - 60 minutes rest; they then walked for two hours to a mountain refuge at 3600 metres, where they spent three nights (days 2 - 3); on day 4, they walked for four hours over a glacier to reach Capanna Regina Margherita (4559 m), where they spent days 5 - 7. MIP, flow-volume curve and SpO (2) % were measured at each altitude, and acute mountain sickness (Lake Louise score) was recorded. Increasing altitude led to a significant decrease in resting SpO (2) % (from 98 % to 80 %) and MIP (from 134 to 111 cmH (2)O) (baseline to day 4: p < 0.05); there was an improvement in SpO (2) % and a slight increase in MIP during the subsequent days at the same altitude. Expiratory (but not inspiratory) flows increased, and forced vital capacity and FEF (75) decreased at higher altitudes. We conclude that exposure to high altitude hypoxia reduces the strength of the respiratory muscles, as demonstrated by the reduction in MIP and the lack of an increase in peak inspiratory flows. This reduction is more marked during the first days of exposure to the same altitude, and tends to recover during the acclimatisation process.

Hypoxic ventilatory response in successful extreme altitude climbers.

A very high ventilatory response to hypoxia is believed necessary to reach extreme altitude without oxygen. Alternatively, the excessive ventilation could be counterproductive by exhausting the ventilatory reserve early on. To test these alternatives, 11 elite climbers (2004 Everest-K2 Italian Expedition) were evaluated as follows: 1) at sea level, and 2) at 5,200 m, after 15 days of acclimatisation at altitude. Resting oxygen saturation, minute ventilation, breathing rate, hypoxic ventilatory response, maximal voluntary ventilation, ventilatory reserve (at oxygen saturation = 70%) and two indices of ventilatory efficiency were measured. Everest and K2 summits were reached 29 and 61 days, respectively, after the last measurement. Five climbers summited without oxygen, the other six did not, or succeeded with oxygen (two climbers). At sea level, all data were similar. At 5,200 m, the five summiters without oxygen showed lower resting minute ventilation, breathing rate and ventilatory response to hypoxia, and higher ventilatory reserve and ventilatory efficiency, compared to the other climbers. Thus, the more successful climbers had smaller responses to hypoxia during acclimatisation to 5,200 m, but, as a result, had greater available reserve for the summit. A less sensitive hypoxic response and a greater ventilatory efficiency might increase ventilatory reserve and allow sustainable ventilation in the extreme hypoxia at the summit.