A central mechanism augments ventilation of the dependent lung in the lateral decubitus position
Fukuda, M.; Yamamura, T.; Harada, K.; Enya, T.; Komura, Y.
Masui. Japanese Journal of Anesthesiology 37(6): 646-654
1988
ISSN/ISBN: 0021-4892 PMID: 3216460 Document Number: 306243
Spontaneously increased ventilation of the dependent lung in the lateral decubitus position compensates for the gravitational shift of the pulmonary blood flow to this side. The present study indicates that the hemilateral predominant ventilation is centrally controlled, though it was previously attributed to the peripheral mechanisms with simple relative changes in the mechanical properties of the two lungs. Expired minute ventilation (.ovrhdot.VE), peak inspiratory pressure (PIP) and airway occlusion pressure (P0.1) were measured in each of the lungs separated with an endobronchial tube in 14 subjects. At light levels of halothane anesthesia (0.2 .apprx. 0.4% in oxygen), .ovrhdot.VE of the dependent lung was larger than that of the nondependent lung by 56%. PIP and P0.1 were also larger in the dependent side by 61% and 36%, respectively. At deeper levels of anesthesia (halothane 1.4 .apprx. 2.2%), the predominant ventilation of the dependent lung was absent and .ovrhdot.VE, PIP P0.1 no longer differed significantly between the lungs. We consider that the more extendedly stretched diaphragm on the dependent side sends stronger muscle afferent signals to increase excitability of the phrenic neurons producing augmented inspiratory driving force. The absence of predominant ventilation of the dependent lung at deeper levels of anesthesia could be due to the reduced gain of the diaphragmatic stretch reflex.