Spatial distribution of ventilation and perfusion in anesthetized dogs in lateral postures

Abstract

We aimed to assess the influence of lateral decubitus postures and positive end-expiratory pressure (PEEP) on the regional distribution of ventilation and perfusion. We measured regional ventilation (VA) and regional blood flow (Q) in six anesthetized, mechanically ventilated dogs in the left (LLD) and right lateral decubitus (RLD) postures with and without 10 cmH(2)O PEEP. Q was measured by use of intravenously injected 15-microm fluorescent microspheres, and VA was measured by aerosolized 1-microm fluorescent microspheres. Fluorescence was analyzed in lung pieces approximately 1.7 cm(3) in volume. Multiple linear regression analysis was used to evaluate three-dimensional spatial gradients of Q, VA, the ratio VA/Q, and regional PO(2) (Pr(O(2))) in both lungs. In the LLD posture, a gravity-dependent vertical gradient in Q was observed in both lungs in conjunction with a reduced blood flow and Pr(O(2)) to the dependent left lung. Change from the LLD to the RLD or 10 cmH(2)O PEEP increased local VA/Q and Pr(O(2)) in the left lung and minimized any role of hypoxia. The greatest reduction in individual lung volume occurred to the left lung in the LLD posture. We conclude that lung distortion caused by the weight of the heart and abdomen is greater in the LLD posture and influences both Q and VA, and ultimately gas exchange. In this respect, the smaller left lung was the most susceptible to impaired gas exchange in the LLD posture.

A system for open‐access 3He human lung imaging at very low field

“…Such a system would permit orientationally dependent studies that are impossible by clinical MRI scanners, where subjects can only be imaged in the supine position. This research is driven by current interest in the pulmonary physiology community, where the effect of gravity, posture, and body orientation on pulmonary ventilation and perfusion is a subject under much debate (15,16,17). A major limitation in this area is the lack of a method to obtain quantitative, high-resolution maps of lung ventilation and perfusion with the subject in different orientations.…”

Influência da variação dos decúbitos laterais na deposição pulmonar de aerossol

“…This preferential ventilation may result from a combination of three mechanical elements: gravity, the relative lowering of the mediastinum toward the support plane and the cranial position of the inferolateral hemidiaphragm caused by the hydrostatic pressure of the viscera on its lower face [5][6][7][8][9] .…”

“…Lateral decubitus is the corporal position that results in the greatest changes regarding static volume, regional ventilation, perfusion and pulmonary diffusion capacity [5][6][7][8] . This occurs due to the craniocaudal direction of the gravity vector and results in a hydrostatic pressure gradient between lungs [5][6][7][8] .…”

“…This occurs due to the craniocaudal direction of the gravity vector and results in a hydrostatic pressure gradient between lungs [5][6][7][8] .…”

“…This behavior is due to the vertical pleural pressure gradient, which causes a decrease in lung volume and high compliance in the dependent lung [5][6][7][8][9][10] .…”