The frequency of preoperative cardiac ischemia and the 30-days postoperative mortality is much higher than previously assumed, with approximately 10 % of patients undergoing non-cardiac surgery suffering from postoperative myocardial injury. A recent danish study furthermore showed that patients treated with a high inspiratory oxygen fraction during surgery had a higher 1 year mortality compared with patients treated with a low inspiratory fraction. This was especially significant among patients undergoing cancer surgery. A possible explanation, is that a high oxygen fraction results in oxidative stress and endothelial dysfunction.

With this randomized cross-over study we wish to investigate the effect of a high inspiratory oxygen fraction on the endothelial function among healthy male volunteers. The primary outcome is the endothelial function assessed by the EndoPat system. Secondary outcomes are changes in oxidative biomarkers. Heart rate variability (HRV) recordings will serve as a measure for the effect of oxygen on the autonomic nervous system.

Inclusion Criteria:

• Healthy male volunteers between 18 and 30 years who has given an oral and written informed consent

Exclusion Criteria:

• Smoking, or ex-smoker Any kind of medication on a daily basis History of atopic dermatitis Known familiar hypercholesterolemia History of arteriosclerotic disease in the first and second-degree relatives Known or unknown arrhythmias, as measured by the baseline HRV-recording