The primary objective of the study will be to determine whether rapid remote limb ischemic preconditioning (RIPC) combined with acetazolamide can further reduce the incidence of acute mountain sickness (AMS) during the 6-hour hypoxic chamber.

The current measures to prevent acute mountain sickness (AMS) mainly include drug prevention and non-drug prevention. Acetazolamide is a drug approved by the U.S. FDA for the prevention and treatment of AMS. Remote limb ischemic preconditioning (RIPC) can also reduce the incidence of AMS as a non-durg method, with a strategy of 2 times/day training for 1 week reducing the incidence of AMS in 6 hours from 40% to 30%. The objective of this study is to determine whether rapid RIPC training combined with acetazolamide can further reduce the incidence of AMS. In this study, subjects will be divided into 5 groups: medicine group (acetazolamid 125mg bid, 2 days before entering the hypoxic room), RIPC group (RIPC training twice daily, 6 days before entering the hypoxic room), rapid RIPC group (RIPC training forth daily, 3 days before entering the hypoxic room), combined group (rapid RIPC training plus acetazolamide) and controlled group. RIPC training, completed by Renqiao Remote Ischemic Conditioning Device (Doctormate®), will be comprised of 5 cycles of bilateral upper limb ischemia and reperfusion, which will be induced by 2 cuffs placed around the upper arms respectively and inflated to 200mmHg for 5 minutes followed by 5 minutes of reperfusion by cuff deflation. After the intervention, subjects will be exposed to 4500m altitude in a normobaric hypoxic chamber for 6 hours. The incidence of AMS and other data will be compared between groups.

Inclusion Criteria:

• People who live in plain areas all year round and have not been to an altitude of 1500 meters or more in the past 30 days;
• Sign the informed consent form voluntarily.

Exclusion Criteria:

• Chronic physical or mental diseases, including hypertension, diabetes, coronary heart disease, cerebrovascular disease, chronic obstructive pulmonary disease, migraine, anxiety, depression, insomnia, etc.;
• The female is pregnant or in the period of preparing for pregnancy or breast-feeding;
• Have a history of smoking;
• Have a history of thrombosis in the upper limbs;
• Severe damage to local soft tissues of upper limbs, fractures, etc.;
• Allergic to sulfa;
• Are taking one or more drugs;
• Past laboratory tests suggest hypokalemia, hyponatremia, or liver and kidney damage;
• Patients unsuitable for enrollment in the clinical trial according to investigators decision making.

Due to the nature of the procedure, it was not possible to blind subjects to the intervention of medicine or RIPC.