The primary objective of this study is to show that cardiovascular risk factors associated with the chronic elevation of arterial resistance may be associated with "false" profiles of intracranial hypertension during transcranial doppler ultrasound of the middle cerebral arteries in intensive care unit patients. A "false" profile of intracranial hypertension is defined by a high pulsatility index without any intracranial pathology.

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)

All sedated patients under mechanical respiratory assistance will be included. These are further devided into 2 groups.