• Spontaneous ventilation is a form of cardiovascular stress.
• Spontaneous inspiratory efforts will, by decreasing intrathoracic pressure, augment systemic venous return, increasing right ventricular volumes.
• Spontaneous inspiratory efforts will, by decreasing intrathoracic pressure, increase the pressure gradient for left ventricular ejection, impeding left ventricular emptying. In heart failure states and if the swings in intrathoracic pressure are great, this effect can precipitate acute heart failure.
• In patients with obstructive lung disease, rapid spontaneous ventilation can induce marked hyperinflation which can cause hemodynamic compromise by (a) increasing pulmonary vascular resistance and (b) decreasing systemic venous return to the heart even if intrathoracic pressure decreases.
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