Preservation of Neurovascular Coupling to Cognitive Activity in Anterior Cerebrovasculature During Incremental Ascent to High Altitude.

Background: High altitude sojourn challenges blood flow regulation in the brain, which may contribute to cognitive dysfunction. Neurovascular coupling (NVC) describes the ability to increase blood flow to working regions of the brain. Effects of high altitude on NVC in frontal regions undergoing cognitive activation are unclear but may be relevant to executive function in high-altitude hypoxia. This study sought to examine the effect of incremental ascent to very high altitude on NVC by measuring anterior cerebral artery (ACA) and middle cerebral artery (MCA) hemodynamic responses to sustained cognitive activity. Materials and Methods: Eight adults (23 ± 7 years, four female) underwent bilateral measurement of ACA and MCA mean velocity and pulsatility index (PI) through transcranial Doppler during a 3-minute Stroop task at 1400, 3440, and 4240 m. Results: Resting MCA and ACA PI decreased with high-altitude hypoxia (p < 0.05). Cognitive activity at all altitudes resulted in similar increases in MCA and ACA mean velocity, and decreases in ACA and MCA PI (p < 0.05 for MCA, p = 0.07 for ACA). No significant altitude-by-Stroop interactions were detected, indicating NVC was stable with increasing altitude. Conclusions: Ascent to very high altitude (4240 m) using an incremental profile that supports partial acclimatization does not appear to disturb (1) increases in cerebral blood velocity and (2) reductions in pulsatility that characterize optimal NVC in frontal regions of the brain during cognitive activity.

Implications of changing trekker demographics on travel health in the Annapurna region.

OBJECTIVE: The objective is to investigate trekkers' changing demographics, travel patterns and experience of illness in the Annapurna region. STUDY DESIGN: A mixed method study comprising a cross-sectional survey was carried out with trekkers who had completed trekking in the Annapurna region. METHODS: Interviews were carried out with trekkers using a standardised questionnaire from September to December (main trekking season) 2014 and 2016. The interview format included trekkers' demographic characteristics, travel patterns, preparation and logistics and experiences of illness and treatment. RESULTS: The demographic composition of trekkers had changed. Chinese and Nepalese trekkers were the most dominant groups along with other international trekkers from 16 different countries. In terms of the trekking pattern, the Chinese and the Nepalese trekkers spent a median of 7 days each in the trek and trekked to a median altitude of 3500 m, while other international trekkers spent a median of 10 days and trekked to a median altitude of 4000 m. In general, trekkers' food habits and travel patterns were good. They undertook some health preparation by using the Internet, consulting friends and travel guidebooks and consulting a doctor, pharmacist and other healthcare providers and brought medicines accordingly. However, 25% of trekkers, most commonly Chinese, Korean and Nepalese, came without any health preparation and with no medicines. Thirty percent of the trekkers became sick during the trek with common illnesses such as diarrhoea, vomiting, the common cold, headache, fever and altitude-related symptoms. CONCLUSIONS: Trekkers' demographic composition has changed from that found in previous studies, and this was reflected in their trekking pattern. Trekkers' health preparations for high-altitude trekking were still inadequate, especially among the newer groups such as the Nepalese, Chinese and Korean trekkers. Issues such as trekkers' health preparation and practice, eating patterns, the length of trek and altitude and health and safety provision need further improvement, especially in the context of these changing trekker demographics.