The study is examining if an over-the-counter device (Theravent) worn while sleeping can reduce acute mountain sickness upon awakening in a high altitude trekking population.

The specific aim of this study is to evaluate if an inexpensive and disposable end-expiratory pressure device can prevent acute mountain sickness (AMS). AMS is a common disorder found in 25-75% of hikers and trekkers in N. America and Europe who expediently ascend high altitude (>8,000 ft). This environmental malady is insidious in onset and prevention is necessary not just to limit progression to severe or fatal disease, but also to limit physiologic deterioration in those who seek enjoyment or employment at high altitudes. One of the hallmarks of both healthy and sick individuals sleeping at high altitude is an oscillating pattern of respiration marked by periods of hyperventilation alternating with apnea or hypopnea. This distressing "periodic breathing" pattern leads to a feeling of suffocation, prevents restful sleep, and the hypoxic events may well worsen ensuing AMS. Prior studies have found positive end-expiratory pressure (PEEP) an effective non-pharmacologic method to prevent nocturnal desaturations and decreasing both AMS incidence and severity.

Traditionally, PEEP devices are cumbersome and expensive, and while showing promising efficacy, are limited by both cost and portability as a useful non-pharmacologic option for AMS prophylaxis. The SLEEP-AID methodology is designed to prospectively enroll participants, randomized in a double blind placebo-controlled fashion to either the intervention [Theravent (Ventus Medical) which is single use, inexpensive, and very small] or a visually identical "sham" placebo group, and gather physiologic data to accurately reflect sleep patterns of high altitude travelers and objective as well as subjective outcomes of the intervention. The benefit of this approach will be to provide definitive data in a large and diverse cross section of a real hiking population that is generalizable to the majority of tens of millions of hikers, climbers, and high altitude tourists in the United States, Europe, Asia, and South America.

Inclusion Criteria:

• ages 18-65
• Lake Louise Score (LLS) of < 3
• Have not taken NSAIDs, acetazolamide, or corticosteroids in the prior week
• Have not traveled above 4200 m in the prior week.
• First night in Pheriche or Dingboche

Exclusion Criteria:

• Unable to read the consent form
• Taken NSAIDs, acetazolamide, or corticosteroids in the week prior to study enrollment.
• Hazardous medical conditions which precludes the ability to tolerate the experimental device.
• Pregnancy or suspected pregnancy.
• Participants who are younger than 18 years of age and more than 65.
• Travel to or above 4200m in the preceding week.
• Diagnosis of AMS upon enrollment (LLS ≥3 with symptoms of headache)
• Previously diagnosed obstructive sleep apnea
• Current symptoms of nasal congestion, rhinorrhea, sinusitis, upper respiratory infection, asthma, COPD exacerbation, pneumonia, bronchitis, or other disease of the respiratory tract.

2 months (duration of study and intervention)