Non-invasive Ventilation and High-speed Oxygen Therapy Effects on Heart Function - HiFlow-Heart Study

The investigators propose to carry out a prospective randomized cross-over prospective physiological study comparing, Non-Invasive Ventilation and High Flow Oxygen Therapy in patients with chronic uncompensated heart failure. This stable population would make it possible to easily study variations in a physiological parameter without any added risk for the patient, but with all the pathophysiological parameters transposable to the situation of decompensated heart failure. Indeed, it is accepted that the existence of heart failure with decreased left ventricular ejection fraction (LVEF) (\< 40%) exposes patients to a high risk of congestive cardiac decompensation due to the associated presence of diastolic dysfunction1. The study will be conducted using an alternating design, where a patient receives the two treatments one after the other ("cross-over"), because the alternating design, compared to the two parallel arm design, reduces the number of patients needed to show a given difference between High Flow Oxygen Therapy and Non-Invasive Ventilation at equal power, if there is neither an order-of-prescription effect ("period") nor a residual effect of the first treatment on the second treatment ("carry-over"). In order to avoid a residual effect on changes in pressure or oxygenation, a wash-out period on conventional oxygen therapy (O2C) should be set between the two treatments (High Flow Oxygen Therapy and Non-Invasive Ventilation) administered to the same patient.