Abstract :
In the awake patient, breathing spontaneously in the lateral decubitus position (LDP), gravity results in a higher pleural pressure around the dependent lung which places the dependent lung on the steep part of the compliance (pressure-volume) curve. Also, gravity results in a higher pulmonary blood flow to the dependent lung than the blood flow to the nondependent lung. In the awake patient breathing spontaneously, and probably during natural sleep, the dependent lung receives more perfusion matched with more ventilation during the lateral decubitus position than the nondependent lung. Thus, adequate ventilation-perfusion matching is insured in both the dependent and the nondependent lungs of the awake patient during the LDP.
