In the lateral position, blood flow to the dependent lung of the anesthetized patient most represents which zone of flow?

In the lateral position, the dependent lung experiences the greatest blood flow due to the influence of gravity on pulmonary circulation. When a patient is in the lateral position, the lung that is down (dependent lung) is subjected to higher hydrostatic pressure compared to the upper lung (non-dependent lung). This positioning leads to a preferential distribution of blood flow to the dependent lung, aligning with the characteristics of Zone 3 of pulmonary blood flow.

In Zone 3, the arterial pressure is greater than both the venous pressure and the alveolar pressure. This allows for continuous blood flow during the respiratory cycle. The dependent lung in the lateral position corresponds to this area of greater blood flow because the pressure gradients favor perfusion, resulting in enhanced blood flow in that region.

Understanding this helps in recognizing the physiological changes that occur due to positioning in anesthetized patients, which can significantly impact ventilation-perfusion relationships and overall oxygenation.