The main objective of this study is to determine a threshold value of diaphragmatic excursion (ultrasound measures: expiration versus inspiration)that best predicts a 50% collapsibility of the inferior vena cava.

Secondary objectives of this study are:

• to determine a threshold value of diaphragmatic excursion (ultrasound measures: expiration versus inspiration)that best predicts a 40% collapsibility of the inferior vena cava (IVC).
• to determine a threshold value of diaphragmatic excursion (ultrasound measures: expiration versus inspiration)that best predicts a 100% collapsibility of the IVC.
• to determine the location of the cutting plane for the TM analysis of collapsibility of the IVC.
• to evaluate the hemodynamic conditions of normal healthy volunteers.
• to detect any abnormality of cardiac function.

Inclusion Criteria:

• The volunteer must have given his/her informed and signed consent
• The volunteer must be insured or beneficiary of a health insurance plan

Exclusion Criteria:

• The volunteer is participating in another study
• The volunteer is in an exclusion period determined by a previous study
• The volunteer is under judicial protection, under tutorship or curatorship
• The volunteer refuses to sign the consent
• It is impossible to correctly inform the volunteer
• The patient is pregnant, parturient, or breastfeeding
• The volunteer has known heart disease like heart failure, cardiac arrhythmia
• The volunteer takes cardiotropics
• The volunteer has known lung disease: obstructive or restrictive respiratory failure
• The volunteer has clinical signs of COPD (coughing with morning sputum in a smoking subject)
• Any emergency situation