This study evaluates the safety and efficacy of the voluntary ventilatory response as prophylaxis for acute mountain sickness, measured by the Lake Louise Self-Report Score, comparing to a group using acetazolamide.

Rationale: Acute mountain sickness (AMS) is a common condition among people who go to altitude and stay at altitude. Acclimatization is the most important mechanism in order to reduce the risk of AMS, however, this is not possible or adequate in a large part of the cases. Recently, there are indications that adjustment of respiration by means of a voluntary increase in the respiratory minute volume can have a similar prophylactic effect. The purpose of this study is to measure the effect of the voluntary increase of the minute volume by means of controlled hyperventilation as prophylaxis for acute mountain sickness without prior acclimatization, with AMS being expressed in the Lake Louise Self-Report Score (LLSRS).

Objective: To investigate the safety and efficacy of the voluntary increase in minute ventilation by means of controlled hyperventilation as prophylaxis for AMS, measured by the LLSRS in a randomized controlled trial ascending to 4954m altitude.

Study design: Prospective randomized controlled trial, safety and efficacy.

Study population: 30 healthy subjects

Intervention: The investigational prophylaxis is controlled hyperventilation. Participants in the interventional group will be trained to hyperventilate in a controlled fashion doing a series of exercises during the 4 days prior to the ascent. They will also be taught in a practical way to recognize early clinical signs and symptoms of hypocapnia.

Main study parameters/endpoints: Safety and efficacy measured by comparing the LLSRS between the two groups. Target end-tidal CO2 ( PETCO2) will be measured to objectify adequate hyperventilation. Symptoms of hypocapnia due to the (pre-)intervention as well as any adverse events will be reported and analysed.

Inclusion Criteria:

• Living at lower altitude than 900 meters

Exclusion Criteria:

• Cardiac or pulmonary comorbidity
• Smoking
• Infectious disease during the last 30 days
• BMI> 30
• Pharmaceutical use as diuretics, corticosteroids, acetazolamide, or anti -inflammatory drugs during the 2 weeks prior to the study
• A history of high altitude cerebral edema or high altitude pulmonary edema
• Cardiovascular risk factors such as a personal history of cardiovascular disease, familial history of major adverse cardiovascular events (MACE) at age younger than 45 yrs, hypercholesterolemia and stroke.