Increased intrathoracic pressure (such as from PEEP) typically causes PCWP readings to do which of the following?

Increased intrathoracic pressure (such as from PEEP) typically causes PCWP readings to do which of the following?

• A. Be unaffected by intrathoracic pressure.
• B. Decrease due to reduced venous return.
• C. Increase artificially due to higher thoracic pressure.
• D. Become an exact measure of LVEDP.

Answer: (C)

Increased intrathoracic pressure from PEEP raises the external pressure around the heart and pulmonary vessels, and that pressure is transmitted into the pulmonary capillaries and left atrium. The pulmonary capillary wedge pressure is an indirect measure of left atrial pressure (and thus LV end-diastolic pressure), but when thoracic pressure is elevated, the reading is driven up by this external pressure rather than by a true rise in left-sided preload. So the wedge pressure increases artificially with higher thoracic pressure. It’s not unaffected, not a reliable decrease, and it’s not an exact measure of LVEDP—it's confounded by intrathoracic pressure.

Increased intrathoracic pressure from PEEP raises the external pressure around the heart and pulmonary vessels, and that pressure is transmitted into the pulmonary capillaries and left atrium. The pulmonary capillary wedge pressure is an indirect measure of left atrial pressure (and thus LV end-diastolic pressure), but when thoracic pressure is elevated, the reading is driven up by this external pressure rather than by a true rise in left-sided preload. So the wedge pressure increases artificially with higher thoracic pressure. It’s not unaffected, not a reliable decrease, and it’s not an exact measure of LVEDP—it's confounded by intrathoracic pressure.