Influence of Chronic Vascular Diseases on Transcranial Doppler Profiles in Critically Ill Patients

Inclusion Criteria for entry in the study: * Sedated patient under mechanical respiratory assistance Inclusion criteria for entry in group 1: the patient meets at least one of the following criteria: * The patient is a man over the age of 50 or a woman over the age of 60 * Hypercholesterolemia (LDL \> 1.6 g/L, HDL \< 0.4 g/L) * Arterial hypertension for over 10 years (treated or systolic arterial pressure \> 140 mmHG) * Type 2 diabetes for over 10 years * Active or former smoker in the past 3 years * History of cardiovascular event (peripheral artery disease, heart attack, stroke/transient ischemic attack over 3 months ago) * Chronic renal insufficiency with MDRD \< 30 ml/min/1.73m\^2 Inclusion criteria for entry in group 2: * The included patient is not in group 1 Exclusion Criteria: * acute neurological disorder (brain trauma, infectious or immune meningitis, meningoencephalitis, ischemic or hemorrhagic stroke \<3 months) * pregnant woman * person under guardianship * prisoners * recent carotid surgery (\<1 month)