The investigators will study in the possibility of cardiovascular disease, caused by the duty loading, of physician of internal medicine. The investigators will also explore if there {dose response effect} between the duty loading and the stress response of physicians of internal medicine. Therefore, the investigators will compare the stress responses of physicians of internal medicine during with different duty loading ( non-duty day, one duty area with 3 wards, 2 duty areas with 6 wards) in a observational method. Those stress response will be measured by cardiovascular risk indicators, including blood pressure, heart rate variability, blood sampling and urine sampling.

Inclusion Criteria:

• Attending physicians of internal medicine of Taipei municipal hospital, certified by Taiwan society of internal medicine.

Exclusion Criteria:

• thyroid dysfunction
• pregnancy, diabetes mellitus
• history of cardiovascular disease (stroke, coronary arterial disease, or myocardial infraction)
• current smokers, or
• taking sleeping pills or B-blocker

Attending physicians of internal medicine of Taipei municipal hospital, certified by Taiwan society of internal medicine. We will compare those results of outcome variables of different amount of duty area.