Fig. 1

Experimental procedure. A: Enrolment flowchart. Of note, 12 of the 28 COVID-19 patients were recruited prior to trial registration, but with ethics approval; B: experimental equipment and monitoring of (1) Helmet’s pressure (P_aw) and (2) esophageal pressure (P_es) through OptiVent^™ monitor, (3) arterial blood gases (ABG) through radial line, (4) blood pressure (BP), cardiac output (CO) and heart rate (HR) through CNAP^® monitor consisting of a finger cuff and a brachial cuff; Panel C: experimental protocol