Changes in tissue microcirculation during ischemic conditioning (4 cycles of 5-min ischemia and 5-min reperfusion) has not been well documented. In previous studies, there was difference in changes in microcirculation, such as recovery slope and occlusion slope, between healthy subjects and cardiac surgery patients. Moreover, the occlusion slope, which reflects local tissue oxygen consumption during ischemic period, is anticipated to decrease during repeated ischemia-reperfusion cycle by its protecting effect, however there has not been well-conducted study. The purpose of the study is to evaluate the changes in microcirculation measured by tissue oxygen saturation during ischemic conditioning between healthy volunteers and cardiac surgery patients.

Subjects who are male healthy volunteers (aged 20-45) or who are scheduled to receive cardiac surgery (aged 20-80) will undergo ischemic conditioning, consisting of 4 cycles of 5-min ischemia with pressure of 200 mmHg on upper extremity followed by 5-min reperfusion with no pressure. During ischemic conditioning, changes in tissue microcirculation (baseline tissue saturation, occlusion slope during ischemia, and recovery slope during reperfusion) will be observed using tissue oxygen saturation sensor attached to the thenar muscle of the hand. For cardiac surgery patients, the study will be conducted before anesthesia induction on the surgery day to exclude any potential effect of anesthetics.

<Healthy volunteers>

Inclusion Criteria:

• Age 20-45
• No underlying chronic disease
• Male volunteer

Exclusion Criteria:

• Under taking prescription drugs
• Taking herbal medicines within 2 weeks
• Baseline systolic blood pressure > 150 mmHg or diastolic pressure > 100 mmHg
• Body mass index < 18 kg/m^2 or > 30 kg/m^2
• Vigorous exercise, excessive alcohol, smoking or caffeine within 24 hours
• Any abnormalities on upper extremities
• Do not consent to participate

<Cardiac surgery patients>

Inclusion Criteria:

• Age 20-80
• Scheduled for cardiac surgery

Exclusion Criteria:

• Baseline systolic blood pressure > 150 mmHg or diastolic pressure > 100 mmHg
• Body mass index < 18 kg/m^2 or > 30 kg/m^2
• Uncontrolled diabetes
• Under taking beta-blockers
• Severe renal dysfunction, chronic kidney disease, on hemodialysis
• Any abnormalities on upper extremities (i.e, AV fistula on arms)
• Peripheral vascular disease, peripheral neuropathy, coagulopathy
• Vigorous exercise, excessive alcohol, smoking or caffeine within 24 hours
• Pregnant
• Emergency surgery
• Do not consent to participate