Use of intraosseous Doppler ultrasonography to study skeletal physiology ("Echo-Os Study"). Exploratory study before its use in space physiology.

Bones have a complex vascular network providing nutrients and oxygen to bone cells. The physiology of intraosseous blood circulation remains very little known to date, particularly in human. Human bone vascularization studying is very difficult because of a lack of simple tools for functional exploration of bone vascular perfusion. For blood flow studies, ultrasonography is best suited, allowing for dynamic non-invasive measures. Bone has until now been considered to stop ultrasound and therefore prevent any intraosseous measurements. From a physics viewpoint, bones conduct ultrasound waves well, but they are reflected differently compared to soft tissues. A specific analysis of the ultrasound returned by the bone, using specific correction factors, is therefore needed to interpret ultrasound signals, reconstruct an anatomical image, and extract physiological information. The system proposed in this study combines standard conventional low-frequency ultrasound probes with a specific analysis of ultrasound wave reflection. This system makes it possible to reconstruct an anatomical bone image and record the pulsatile signal of intraosseous vascular perfusion. The investigators will use this system to study the vascular reactivity induced by different physiological maneuvers.

This protocol proposes to study the following mechanisms of blood flow regulation at the level of tibia cortical bone: flow-mediated dilation induced by endothelium (with arterial occlusion test), vasoconstriction induced by sympathetic activation (with static handgrip test), and vasoconstriction induced by veno-arteriolar reflex (with venous occlusion test). This is a pilot study in physiology performed with healthy volunteers. This study will verify whether our intraosseous ultrasound system can properly measure physiological responses expected during these maneuvers. This protocol will also establish links between perfusion and bone architecture at tibial level.

Inclusion Criteria for sub-protocol 1:

• Male aged 20-40 years

Inclusion criteria for sub-protocol 2:

• Male aged 20-40 years & 50-70 years
• Body height of at least 180 cm (in order to have tibia length of 43-45 cm allowing the positioning of ultrasonic probe at distal tibia, and occlusive cuff at calf level)
• Bone densitometry with available report performed within 5 last years (if none has been done, possibility to perform densitometry covered by the study at selection or inclusion visit)

Inclusion criteria common for both sub-protocols:

• Healthy volunteer without chronic pathology (in particular no known rhythm disorder) or long-term treatment
• No symptomatic acute medical event requiring treatment on the visit days
• No history of tibia fractures
• Body Mass Index between 19 and 26
• Affiliation to the French Social Security System
• Written informed consent

Non-Inclusion criteria:

• Inability to stay still for 20 minutes (tremor)
• Active smoking (stopped less than 1 year ago)
• History of prolonged corticosteroid treatment
• Deprivation of liberty by legal or administrative decision
• Subject to involuntary psychiatric treatment
• Subject to a legal protection measure
• For sub-study 1: Osteoporosis known at interview

Exclusion Criteria:

• Any abnormality or deviation from the selection criteria identified during the clinical examination at the inclusion visit (non-sinus rhythm in ECG, body temperature > 38°C, blood pressure or heart rate outside the defined standards, etc.)

Data will be shared upon reasonable request. Only de-identified data will be shared. Any data collected during the study may be shared. The protocol will be shared initially. Other documents may be shared at a later date upon request (e.g., the CRF to allow a collaborator to select the data they wish to access). The recipients of the data will be researchers. The data will be available for any purpose deemed relevant by the study investigator, based on a protocol provided by the requester, after verification of the obtaining of regulatory approvals, including the favorable opinion of an ethics committee.

The data will be shared after signing a negotiated data transfer agreement ( data access agreement), for the duration specified in the agreement.

The data will be made available via secure transfer (sharing platform approved by the university hospital: BlueFiles or Oodrive).