During which maneuver does cephalad flow diminish in normal patients according to LEV Doppler assessment?

The correct answer pertains to the physiological changes that occur during the respiratory cycle, particularly with respect to venous flow in the lower extremities as assessed by LEV Doppler. In normal patients, during expiration, the diaphragm moves upward, reducing the intrathoracic pressure. This pressure change affects venous return, leading to a diminished cephalad flow in the lower extremities. The venous blood flow is influenced significantly by the respiratory phases, and during expiration, the reduced abdominal pressure combined with the upward movement of the diaphragm causes a decrease in the flow dynamics towards the heart.

In contrast, during inspiration, venous return typically increases due to decreased pressure in the thoracic cavity, allowing for better cephalad flow. The Valsalva maneuver comprises forced expiration against a closed airway, leading to significant changes in pressure, but it does not result in constant flow; rather, it often reduces venous return due to elevated intrathoracic pressure. Proximal compression generally aids in redirecting blood flow towards the heart, thereby increasing flow rather than diminishing it.