BACKGROUND Body position can be optimized for pulmonary ventilation/perfusion matching during surgery and intensive care. However, positional effects upon distribution of pulmonary blood flow and vascular distensibility measured as the pulmonary blood volume variation have not been quantitatively characterized. In order to explore the potential clinical utility of body position as a modulator of pulmonary hemodynamics, we aimed to characterize gravitational effects upon distribution of pulmonary blood flow, pulmonary vascular distension, and pulmonary vascular distensibility. METHODS Healthy subjects (n = 10) underwent phase contrast cardiovascular magnetic resonance (CMR) pulmonary artery and vein flow measurements in the supine, prone, and right/left lateral decubitus positions. For each lung, blood volume variation was calculated by subtracting venous from arterial flow per time frame. RESULTS Body position did not change cardiac output (p = 0.84). There was no difference in blood flow between the superior and inferior pulmonary veins in the supine (p = 0.92) or prone body positions (p = 0.43). Compared to supine, pulmonary blood flow increased to the dependent lung in the lateral positions (16-33%, p = 0.002 for both). Venous but not arterial cross-sectional vessel area increased in both lungs when dependent compared to when non-dependent in the lateral positions (22-27%, p ≤ 0.01 for both). In contrast, compared to supine, distensibility increased in the non-dependent lung in the lateral positions (68-113%, p = 0.002 for both). CONCLUSIONS CMR demonstrates that in the lateral position, there is a shift in blood flow distribution, and venous but not arterial blood volume, from the non-dependent to the dependent lung. The non-dependent lung has a sizable pulmonary vascular distensibility reserve, possibly related to left atrial pressure. These results support the physiological basis for positioning patients with unilateral pulmonary pathology with the "good lung down" in the context of intensive care. Future studies are warranted to evaluate the diagnostic potential of these physiological insights into pulmonary hemodynamics, particularly in the context of non-invasively characterizing pulmonary hypertension.

中文翻译：

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仰卧、俯卧、左右重力对人体肺循环的影响。


背景技术可以针对手术和重症监护期间的肺通气/灌注匹配来优化身体位置。然而，位置对肺血流量分布和作为肺血容量变化测量的血管扩张性的影响尚未得到定量表征。为了探索身体位置作为肺血流动力学调节剂的潜在临床效用，我们旨在表征重力对肺血流分布、肺血管扩张和肺血管扩张的影响。方法 健康受试者 (n = 10) 在仰卧位、俯卧位和右/左侧卧位下接受相差心血管磁共振 (CMR) 肺动脉和静脉流量测量。对于每个肺，通过每个时间范围内的动脉流量减去静脉流量来计算血容量变化。结果 身体位置不会改变心输出量 (p = 0.84)。仰卧位 (p = 0.92) 或俯卧位 (p = 0.43) 时，上肺静脉和下肺静脉之间的血流量没有差异。与仰卧位相比，侧卧位时流向依赖肺的肺血流量增加（16-33%，两者 p = 0.002）。与非依赖侧卧位时相比，依赖侧卧时双肺的静脉而非动脉横截面血管面积有所增加（22-27%，两者均 p ≤ 0.01）。相反，与仰卧位相比，侧卧位非依赖性肺的扩张性增加（68-113%，两者 p = 0.002）。结论 CMR 表明，在侧卧位时，血流分布以及静脉血量（而非动脉血量）从非依赖性肺转移到依赖性肺。 非依赖性肺具有相当大的肺血管扩张储备，可能与左心房压力有关。这些结果支持了在重症监护背景下将单侧肺部病变患者定位为“良好的肺向下”的生理学基础。未来的研究有必要评估这些对肺血流动力学的生理学见解的诊断潜力，特别是在非侵入性表征肺动脉高压的情况下。