, Ces résultats sont concordants avec ceux rapportés dans la littérature : une première étude physiologique randomisée en cross--over sur 17 patients (77) rapportait une diminution du volume courant de 443 mL avec l'O 2 --MHC à 429 mL avec l'OHDN à 60 L/min. Une autre étude physiologique sur 15 patients (53) retrouvait une diminution de 5% du volume courant avec l'OHDN par rapport à l, oxygénothérapie standard au masque à haute concentration : 440 ± 352 mL avec l'O 2 --MHC, versus 414 ± 333 mL avec l'OHDN (p=0.005) et 377 ± 297 mL avec la CPAP (p=0.005), p.2

, La diminution du volume courant avec l'OHDN observée dans notre étude sur banc pourrait être un des mécanismes ayant participé à la diminution de la mortalité dans le bras OHDN dans l'étude FLORALI (32), en regard du concept du PSILI, bien que cela reste pour le moment très théorique. En effet, d'autres effets physiologiques de l'ODHN peuvent également expliquer les bénéfices cliniques rapportés dans certaines études. Ainsi, en améliorant l'oxygénation et limitant la ré--inhalation de CO 2 par lavage de l'espace mort, l'OHDN entraine une diminution du besoin en ventilation, avec diminution du travail respiratoire et des variations de pressions oesophagiennes, et donc une diminution des variations de pression transpulmonaire (53). L'OHDN permet également de maintenir une pression expiratoire positive (PEP) (48,50,54), entrainant une diminution de l'inhomogénéité du parenchyme pulmonaire par recrutement des zones dépendantes. Cet du mannequin était fermée, soit légèrement inférieure aux valeurs de PEP rapportées dans les études physiologiques (3.81 ± 1.33 à 50 L/min dans l'étude de Parke et al (54) par exemple). 2.2. Explications physiopathologiques Cette diminution du volume courant par rapport à l'état de base avec l'OHDN et la CPAP s'explique par une chute à l'inspiration de la pression des voies aériennes au niveau proximal (mesurée à la bouche), Les données sur le volume courant avec l'OHDN sont rares dans la littérature car il n'est pas mesurable en pratique clinique (ses variations peuvent être estimées au moyen de la tomographie d'impédance électrique)

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, Méthodes : Dans une étude sur banc d'essai (ASL 5000), nous avons testé ces six supports d'oxygénation non invasifs, en simulant trois mécaniques respiratoires (normale, obstructive et restrictive) et trois niveaux d'effort respiratoire différents (faible, modéré et détresse respiratoire). Résultats : Par rapport à l'O 2 -MHC (VT=440 ± 352 mL), la VNI-M (VT=690 ± 321 mL) et la VNI-H (VT=652 ± 366 mL) étaient associées à une augmentation significative du volume courant, tandis que la CPAP (VT=377 ± 297 mL) et l'OHDN (VT=414 ± 333 mL) étaient associées à une réduction significative du volume courant (p<0.001). Ces variations de volume courant étaient corrélées aux variations de pression des voies aériennes proximales (mesurée à la bouche) générées par le support d'oxygénation. Conclusion : Le support d'oxygénation utilisé influence, Effet des différents supports d'oxygénation non invasifs sur le volume courant : une étude sur banc. Résumé : Introduction : Il existe de multiples supports d'oxygénation non invasifs : l'oxygénothérapie standard au masque (O 2 -MHC), l'oxygénothérapie à haut débit nasal humidifiée (OHDN)

, Mots clés : ventilation non invasive, volume courant, détresse respiratoire aiguë. Influence of different non-invasive oxygenation support devices on tidal volume: a bench study