Function Perioperative Medicine and Intensive Care, Karolinska University Hospital Solna, Stockholm, Sweden;
Department of Physiology and Pharmacology, Section of Anesthesiology and Intensive Care Medicine, Karolinska Institutet, Stockholm, Sweden; and.
J Appl Physiol (1985). 2017 Jun 1;122(6):1445-1451. doi: 10.1152/japplphysiol.00887.2015. Epub 2017 Mar 23.
Previous studies in humans have shown that gravity has little influence on the distribution of lung blood flow while changing posture from supine to prone. This study aimed to evaluate the maximal influence of posture by comparison of regional lung blood flow in the upright and head-down posture in 8 healthy volunteers, using a tilt table. Regional lung blood flow was marked by intravenous injection of macroaggregates of human albumin labeled with Tc or In, in the upright and head-down posture, respectively, during tidal breathing. Both radiotracers remain fixed in the lung after administration. The distribution of radioactivity was mapped using quantitative single photon emission computed tomography (SPECT) corrected for attenuation and scatter. All images were obtained supine during tidal breathing. A shift from upright to the head-down posture caused a clear redistribution of blood flow from basal to apical regions. We conclude that posture plays a role for the distribution of lung blood flow in upright humans, and that the influence of posture, and thereby gravity, is much greater in the upright and head-down posture than in horizontal postures. However, the results of the study demonstrate that lung structure is the main determinant of regional blood flow and gravity is a secondary contributor to the distribution of lung blood flow in the upright and head-down positions. Using a dual-isotope quantitative SPECT method, we demonstrated that although a shift in posture redistributes blood flow in the direction of gravity, the results are also consistent with lung structure being a greater determinant of regional blood flow than gravity. To our knowledge, this is the first study to use modern imaging methods to quantify the shift in regional lung blood flow in humans at a change between the upright and head-down postures.
先前在人类中的研究表明，当从仰卧位变为俯卧位时，重力对肺血流分布的影响很小。本研究旨在通过比较 8 名健康志愿者在倾斜台上直立和头低位时的区域性肺血流，来评估体位的最大影响。在直立和头低位时，分别通过静脉注射 Tc 或 In 标记的人白蛋白的大聚合体，在潮式呼吸期间对区域性肺血流进行标记。放射性示踪剂在给药后仍固定在肺部。使用衰减和散射校正的定量单光子发射计算机断层扫描（SPECT）对放射性分布进行映射。所有图像均在仰卧位时进行潮式呼吸获得。从直立位到头低位的转变导致血流从基底到顶部分布明显重新分布。我们得出结论，体位对直立人体肺血流分布起作用，并且在直立和头低位时，体位的影响（因此重力）比水平体位时大得多。然而，该研究的结果表明，肺结构是区域性血流的主要决定因素，而重力是直立和头低位时肺血流分布的次要决定因素。使用双同位素定量 SPECT 方法，我们证明，尽管体位的改变使血流向重力方向重新分布，但结果也与肺结构对区域性血流的决定作用大于重力的结果一致。据我们所知，这是首次使用现代成像方法定量研究人体在直立和头低位之间的区域肺血流转移。
