Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS) is a cardiovascular risk factor due to intermittent hypoxia phenomena. Several etiological factors are involved in the pathogenesis of OSAS. Among them, the rostro-caudal displacement of fluid during dorsal decubitus has been highlighted. Under the effect of gravity, an accumulation of fluid is possible in the lower limbs, redistributing itself towards the upper parts of the body during the supine position.

This phenomenon of fluid shift is usually evaluated by impedancemetry after a night in the supine position. However, some authors have shown that fluid shift occurs within 90 minutes after supine. Thus, in the perspective of future studies, in order to simplify the implementation of this evaluation and to reduce the time of hospitalization necessary for the subjects participating in the study, we would like to verify the correlation between the impedancemetry measurement at T 90 min and that obtained after one night of supine position. This is a single-center, prospective, open-label study at the Poitiers University Hospital. We will include 30 patients over 18 years of age admitted to the regional sleep pathology center for suspected nocturnal respiratory disorders to receive polysomnography and able to provide written consent.We excluded : patients younger than 18 years of age, A history of vascular surgery of the lower limbs such as varicose vein surgery, vascular bypass surgery, carcinological surgery with lymph node dissection, the presence of metallic implants in the lower limbs or spine or implantable cardiac devices, those not receiving Social Securitý or not receiving it through a third party, persons receiving enhanced protection, namely minors, and persons deprived of libertý by a judicial or administrative decision, persons staying in a health or social institution, and adults under legal protection.we will perform an impedance measurement at T0, T30, T90, and after overnight supine. Impedance measurement is performed using electrodes delivering a low intensity current of known frequency allowing the study of the liquid volume.

Inclusion Criteria:

• Patients 18 years of age or older
• Patients requiring polysomnography at the regional sleep pathology center for suspected nocturnal breathing disorders
• Patients able to give their non-opposition

Exclusion Criteria:

• The presence of metallic implants in the lower limbs or spine or implantable pacemakers because of possible interference with the impedance signals
• A history of amputation of both lower limbs
• Persons benefiting from reinforced protection, namely minors, persons deprived of libertý by a judicial or administrative decision, persons staying in a health or social institution and adults under legal protection, persons in emergency situations.