Effects of interactions between pulmonary and systemic circulation and cardiac function
The framework
- The heart and lungs share a rigid thoracic cavity, a common circulation and a shared pericardial space
- -> intrathoracic pressure is a determinant of cardiac loading, and cardiac filling pressure is a determinant of lung mechanics
- The single most useful framework: transmural pressure, not intracavitary pressure, is the true load on the ventricle
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LV transmural pressure = LV intracavitary pressure - intrathoracic pressure
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- Raising intrathoracic pressure (positive pressure ventilation) dec preload AND dec LV afterload
- Lowering intrathoracic pressure (forceful spontaneous inspiration, obstructive apnoea) inc preload AND inc LV afterload
- -> a patient in respiratory distress is doing the opposite of what their failing LV needs
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