Respiratory Variations in the Diameter of the Inferior Vena Cava With Spontaneous Ventilation

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