Author Contributions: Dr Alleman had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Drs Scherrer and Seiler contributed equally to this work.
Study concept and design: Allemann, Sartori, Egli, Scherrer, Seiler.
Acquisition of data: Allemann, Hutter, Lipp, Sartori, Duplain, Egli, Cook.
Analysis and interpretation of data: Allemann, Lipp, Sartori, Scherrer, Seiler.
Drafting of the manuscript: Allemann, Sartori, Scherrer, Seiler.
Critical revision of the manuscript for important intellectual content: Hutter, Lipp, Sartori, Duplain, Egli, Cook.
Statistical analysis: Allemann, Sartori, Seiler.
Obtained funding: Sartori, Scherrer.
Administrative, technical, or material support: Hutter, Lipp, Sartori, Egli, Cook.
Study supervision: Allemann, Scherrer, Seiler.
Financial Disclosures: None reported.
Funding/Support: This work was supported by grants from the Swiss National Science Foundation, the International Olympic Comittee, the Fondazione Dottor PierLuigi Crivelli, the Emma Muschamp Foundation, the Dr Max Clöetta Foundation, and the Placide Nicod Foundation. The Hewlett-Packard Corporation provided the echocardiographic equipment at high altitude.
Role of the Sponsors: The funding sources had no role in the design and conduct of the study; in the collection, management, analysis, and interpretation of the data; or in the preparation, review, or approval of the manuscript.
Acknowledgment: We are indebted to the participants in the study; to the Sezione Varallo del Club Alpino Italiano for providing the locations in the Capanna Regina Margherita; to our mountain guides Andrea Enzio, Osvaldo Antonietti, and Bruno Brand for leading the participants safely to the hut; and the Swiss Army for transporting part of the material.