Vertical gradients in regional lung density and perfusion in the supine human lung: the Slinky effect
Vertical gradients in regional lung density and perfusion in the supine human lung: the Slinky effect
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DOI：
10.1152/japplphysiol.01289.2006
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发表时间：
2007-07-01
影响因子：
3.3
通讯作者：
Prisk, G. Kim
中科院分区：
文献类型：
--
作者：
Hopkins, Susan R.;Henderson, A. Cortney;Prisk, G. Kim
体内放射性示踪剂和微球研究对于重力对肺血流分布的影响程度有不同的结论。我们假设体内一些明显的垂直灌注梯度是由于依赖肺的压缩，增加了局部肺密度，从而增加了灌注量/体积。为了验证这一点，6名正常受试者接受了功能性磁共振成像，在屏气时进行动脉自旋标记，并在覆盖右肺大部分的不重叠的15 mm矢状面切片上定量灌注量。在相同的切片上使用短回声2D-快速低角度激发(闪光)序列测量肺质子密度。平均灌注量为1.7ml.min-1.cm(-3)，并与依赖肺上方的垂直高度相关(斜率=-3%/cm，P<；0.0001)。肺密度平均为0.34+/-0.08g/cm(3)，并与垂直高度相关(斜率=-4.9%/cm，P<；0.0001)。相反，当灌注按区域肺密度归一化时，高度-灌注关系的斜率与零相比没有显著差异(P=0.2)。这表明，活体内肺密度的变化会影响对肺血流垂直梯度的解释，并与一个简单的概念模型一致：肺的行为像Slinky(Slinky是Poof-Slinky Inc.的注册商标)，是在自身重量下变形的弹簧。肺的从属区域的肺组织密度较大，类似于垂直定向弹簧的从属部分有更多的线圈。这意味着活体血流灌注的测量将受到密度分布的影响，并与切除的肺组织不同，后者的密度梯度通过处理而减小。
In vivo radioactive tracer and microsphere studies have differing conclusions as to the magnitude of the gravitational effect on the distribution of pulmonary blood flow. We hypothesized that some of the apparent vertical perfusion gradient in vivo is due to compression of dependent lung increasing local lung density and therefore perfusion/volume. To test this, six normal subjects underwent functional magnetic resonance imaging with arterial spin labeling during breath holding at functional residual capacity, and perfusion quantified in nonoverlapping 15 mm sagittal slices covering most of the right lung. Lung proton density was measured in the same slices using a short echo 2D-Fast Low-Angle SHot (FLASH) sequence. Mean perfusion was 1.7 +/- 0.6 ml(.)min(-1.)cm(-3) and was related to vertical height above the dependent lung (slope = - 3%/cm, P < 0.0001). Lung density averaged 0.34 +/- 0.08 g/cm(3) and was also related to vertical height (slope = -4.9%/cm, P < 0.0001). By contrast, when perfusion was normalized for regional lung density, the slope of the height-perfusion relationship was not significantly different from zero (P = 0.2). This suggests that in vivo variations in regional lung density affect the interpretation of vertical gradients in pulmonary blood flow and is consistent with a simple conceptual model: the lung behaves like a Slinky (Slinky is a registered trademark of Poof-Slinky Incorporated), a deformable spring distorting under its own weight. The greater density of lung tissue in the dependent regions of the lung is analogous to a greater number of coils in the dependent portion of the vertically oriented spring. This implies that measurements of perfusion in vivo will be influenced by density distributions and will differ from excised lungs where density gradients are reduced by processing.