Insuffisance respiratoire grave : du sommeil à la physiopathologie du ventricule droit

Right ventricular dysfunction including an increase of right ventricular afterload and a decrease of cardiac output can be assessed by the pressure-volume relationship of the right ventricle (RV). Systolic function or contractility or end-systolic elastance can be measured as the ratio of end-systolic pressure over end-systolic volume. Afterload or arterial elastance can be measured as the ratio of end-systolic pressure over stroke volume. Ventriculo-arterial coupling is the ratio of end-systolic elastance over arterial elastance. The optimal coupling is 1.5-2. The maintenance of stroke volume in the presence of overload depends on systolic function adaptation, with secondary diastolic changes. During pulmonary hypertension, consequences of right ventricular decoupling are: 1- Insufficient homeometric adaptation to afterload leads to heterometric adaptation i.e. increased preload as a cause of upstream congestion, 2- Flow output cannot be maintained in the face of increased peripheral oxygen demand, as a cause of decreased aerobic exercise capacity, chronically, circulatory shock acutely. Echocardiography is an efficient tool to evaluate right ventricular function. Echocardiographic indices include : cardiac output, tricuspid annular plane systolic excursion or TAPSE, inferior vena cava diameter, pericardial effusion. Treatment of right ventricular failure aims at decreasing (after) load, improve RV contractility and optimize systolic and diastolic interactions.