Human digestive system physiologically ensures the absorption of oral water and hydration of the human body. Water is quickly absorbed by the digestive tract with a peak between 15 and 20 minutes. It has demonstrated that oral water remains the best hydration solution that have an effect on plasma volume expansion and cardiovascular system during exercise. While the cardiovascular effect of fluid expansion by saline serum is well known (venous return, preload and cardiac output), effect of oral water varies in the literature depending on the physiological state of the patient and the clinical state. Thus, the investigators aim to investigate oral water effects on fluid responsiveness, regional blood flow and microcirculatory changes.

Inclusion Criteria:

• Healthy volunteer subject between 18 and 30 years old
• patient with a regular sinus rhythm
• Echogenic subject.
• Fasting of solid and liquid since 8 h
• Subject in regular sinus rhythm.
• Written consent signed.

Exclusion Criteria:

• Any known cardiac, renal or endocrine pathology.
• Arrhythmia rhythm disorder by atrial fibrillation
• Pregnant or nursing woman.
• Pathology versus indicating Nacl administration.
• Person under tutors or curators or deprived of liberty.
• Person not affiliated to a social security scheme.