This study will enrolled 90 healthy volunteers. The sublingual microcirculation will be examined by sidestreamdark-field videomicroscopy (MicroScan;Microvision Medical, Amsterdam, The Netherlands). Five video sequences (20 s) was obtained from different sublingual sites, and digitally stored the images with code numbers that did not reflect volunteers' information for later offline analysis by automated analysis software (AVA 3.0; Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands).

Inclusion Criteria:

• Healthy volunteers aged from 20 to 79 years old
• BMI ranged from 18.5 to 27 kg/m2

Exclusion Criteria:

• Systolic blood pressure > 140 mm Hg, diastolic blood pressure > 95 mm Hg, or systolic blood pressure < 90 mm Hg at enrollment
• Body temperature > 37.5 ℃ or < 35.5 ℃ at enrollment
• had been diagnose with any one of the following diseases
• hypertension
• diabetes mellitus
• peripheral arterial occlusive disease
• coronary arterial disease
• liver cirrhosis
• chronic kidney disease
• stroke
• anemia
• asthma
• chronic bronchitis
• any metabolic diseases
• any hematologic disease
• uncured cancer
• chronic uncontrolled infection
• other disease may limit daily activities
• non-native speakers

Healthy Volunteers