Sildenafil for Swimming-Induced Pulmonary Edema (SIPE) Prevention

Study Overview
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Brief Summary
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This trial is testing the effectiveness of a single oral dose of sildenafil (50 mg) taken 1 hour before a provocative event on the subsequent development of swimming-induced pulmonary edema.

Detailed Description
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Immersion pulmonary edema (also known as swimming-induced pulmonary edema, SIPE) is a condition in which the lungs fill with fluid (pulmonary edema) during a dive or vigorous swim, causing cough with bloody sputum, shortness of breath and reduced blood oxygen levels. In the Navy this usually occurs in young, healthy individuals such as SEAL and Special Warfare Combatant-Craft trainees. SIPE generally resolves spontaneously within 24 hours but it can be fatal. It is believed that SIPE is responsible for some deaths in civilians during triathlons. This proposal aims to test a drug to prevent SIPE. Depending upon severity, the prevalence of SIPE is reported in up to 60% during 2.4-3.6 km open sea swimming trials in the Israel Defense Force. In SEAL training in the US approximately 40 cases per year (around 3%) have been reported, more commonly during winter, when it is observed in up to 5% of trainees. Return to duty time can be up to 7 days. SIPE also affects other groups of highly fit individuals such as triathletes. In susceptible individuals it tends to recur, thus a preventive medicine would be useful for both Navy SEALs and civilians. The aim of this study will be to provide the Navy an FDA-approved drug that can be used to prevent SIPE. The investigators hypothesize that sildenafil administration to SIPE-susceptible individuals one hour before a swim in cold water will reduce or eliminate the risk of SIPE. The method to be used to test this hypothesis will be a 40-minute period of exercise immersed to the neck in 20°C water, a test that results in SIPE symptoms in the majority of susceptible individuals. The investigators plan to study 20 individuals who have previously experienced SIPE. Each volunteer will be tested twice. Either sildenafil or an inactive drug (placebo) administered in random order will be given prior to each exercise. For each participant exercise periods will be performed at least 7 days apart. The identity of the drug and placebo will be concealed from the investigators and the volunteers until the end of the study. The number of instances in which SIPE manifestations after sildenafil and placebo will then be compared. Availability of a drug that can prevent SIPE would provide the Navy with a useful tool that could be administered to SEALs who have experienced SIPE prior to critical missions. It would also be useful for civilians who have experienced SIPE but wish to continue with the precipitating exercise such as swimming or competing in triathlons, and also for patients with heart failure for whom swimming induces shortness of breath or pulmonary edema.

Official Title
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Sildenafil for Prevention of Swimming-Induced Pulmonary Edema (SIPE)

Conditions
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Immersion, Edema, Pulmonary, Diving

Intervention / Treatment
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* Drug: Sildenafil Citrate
* Drug: Placebo Oral Tablet


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Healthy volunteers between 18 and 45 years History of swimming-induced pulmonary edema Exclusion Criteria: Pregnant women Significant heart valve disease Cardiomyopathy Uncontrolled hypertension Coronary artery disease Obstructive lung disease VO2max <25 mL/kg as estimated by the University of Houston Non-Exercise Test Previous adverse reaction to sildenafil Use of antihypertensives or other drugs that are known to interact adversely with sildenafil (e.g. nitrates, alpha adrenergic blockers)

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 45 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Prevention
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: Double blind, randomized
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Placebo Comparator: Placebo<br>Each participant will be studied with active drug and placebo. | Drug: Placebo Oral Tablet<br>* Placebo<br>|
| Active Comparator: Sildenafil<br>Sildenafil 50 mg orally one hour (once) before immersed exercise | Drug: Sildenafil Citrate<br>* Oral sildenafil, 50 mg<br>* Other names: Revatio;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Number of Participants With Pulmonary Edema | One or more of: hypoxemia, productive cough, pulmonary edema on chest radiograph, wheezing on chest auscultation. | During or immediately after exercise in cold water, approximately one hour and 40 minutes | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Number of Participants With Dyspnea Leading to Voluntary Premature Cessation of Exercise | Voluntary premature cessation of exercise due to shortness of breath. | During or immediately after exercise in cold water, approximately one hour and 40 minutes | 
| Number of Participants With Post-exercise 10% Decrease in Forced Vital Capacity (FVC) or Forced Expiratory Volume in One Second (FEV1) as Measured by Spirometry | Post-exercise 10% decrease in forced vital capacity (FVC) or forced expiratory volume in one second (FEV1). | Immediately after exercise in cold water, approximately one hour and 40 minutes | 
| Number of Participants With Comet Tails Seen on Ultrasound of the Lungs | A comet tail artefact is a short path reverberation artefact that weakens with each reverberation, resulting in a vertical echogenic artefact that rapidly fades as it continues in to the ultrasound image. | Immediately after exercise in cold water, approximately one hour and 40 minutes | 
| Number of Participants Who Found the Exercise Easiest When Given Sildenafil Citrate Versus When Given Placebo |  | Immediately after exercise in cold water, approximately one hour and 40 minutes |