Cardiopulmonary interactions

Positive-pressure ventilation (PPV) alters ventricular loading conditions and compliance. In patients who are hypovolemic, the effects of positive airway pressure on the right heart predominate, whereas in patients who have systemic ventricular systolic dysfunction, the effects of PPV on left ventricular afterload predominate. Large changes in arterial pulse pressure over the respiratory cycle help to identify mechanically ventilated patients who may have a favorable response to the administration of fluid or who may not tolerate high levels of positive end-expiratory pressure without fluid administration. PPV raises juxtacardiac pressure, thereby reducing left ventricular afterload. Respiratory effort imposes critical loads on the heart, and respiratory muscle failure from inadequate oxygen delivery is a final common pathway to death from shock..