Ford Nancy L, McCaig Lynda, Jeklin Andrew, Lewis James F, Veldhuizen Ruud A W, Holdsworth David W, Drangova Maria
Department of Oral Biological and Medical Sciences, The University of British Columbia, Vancouver, British Columbia, Canada
Department of Physics and Astronomy, The University of British Columbia, Vancouver, British Columbia, Canada.
Physiol Rep. 2017 Jan;5(2). doi: 10.14814/phy2.13074.
In this study, we aim to quantify the differences in lung metrics measured in free-breathing and mechanically ventilated rodents using respiratory-gated micro-computed tomography. Healthy male Sprague-Dawley rats were anesthetized with ketamine/xylazine and scanned with a retrospective respiratory gating protocol on a GE Locus Ultra micro-CT scanner. Each animal was scanned while free-breathing, then intubated and mechanically ventilated (MV) and rescanned with a standard ventilation protocol (56 bpm, 8 mL/kg and PEEP of 5 cm HO) and again with a ventilation protocol that approximates the free-breathing parameters (88 bpm, 2.14 mL/kg and PEEP of 2.5 cm HO). Images were reconstructed representing inspiration and end expiration with 0.15 mm voxel spacing. Image-based measurements of the lung lengths, airway diameters, lung volume, and air content were compared and used to calculate the functional residual capacity (FRC) and tidal volume. Images acquired during MV appeared darker in the airspaces and the airways appeared larger. Image-based measurements showed an increase in lung volume and air content during standard MV, for both respiratory phases, compared with matched MV and free-breathing. Comparisons of the functional metrics showed an increase in FRC for mechanically ventilated rats, but only the standard MV exhibited a significantly higher tidal volume than free-breathing or matched MV Although standard mechanical ventilation protocols may be useful in promoting consistent respiratory patterns, the amount of air in the lungs is higher than in free-breathing animals. Matching the respiratory patterns with the free-breathing case allowed similar lung morphology and physiology measurements while reducing the variability in the measurements.
在本研究中，我们旨在使用呼吸门控微型计算机断层扫描技术，量化自由呼吸和机械通气啮齿动物肺部测量指标的差异。将健康雄性斯普拉格-道利大鼠用氯胺酮/赛拉嗪麻醉，并在GE Locus Ultra微型CT扫描仪上采用回顾性呼吸门控方案进行扫描。每只动物在自由呼吸时进行扫描，然后插管并进行机械通气（MV），再采用标准通气方案（56次/分钟，8毫升/千克，呼气末正压为5厘米水柱）以及近似自由呼吸参数的通气方案（88次/分钟，2.14毫升/千克，呼气末正压为2.5厘米水柱）再次进行扫描。以0.15毫米的体素间距重建代表吸气和呼气末的图像。对基于图像测量的肺长度、气道直径、肺容积和空气含量进行比较，并用于计算功能残气量（FRC）和潮气量。在MV期间采集的图像在气腔中显得更暗，气道显得更大。基于图像的测量结果显示，与匹配的MV和自由呼吸相比，在标准MV期间，两个呼吸阶段的肺容积和空气含量均增加。功能指标的比较显示，机械通气大鼠的FRC增加，但只有标准MV的潮气量显著高于自由呼吸或匹配的MV。尽管标准机械通气方案可能有助于促进一致的呼吸模式，但肺部的空气量高于自由呼吸的动物。将呼吸模式与自由呼吸情况相匹配，可在减少测量变异性的同时，实现相似的肺部形态和生理测量。
