School of Medical Instrumentation, Shanghai University of Medicine & Health Sciences, Shanghai, China; NMPA Key Laboratory for Respiratory and Anaesthetic Equipment, Shanghai, China.
Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai, China.
Clin Biomech (Bristol). 2021 Jul;87:105407. doi: 10.1016/j.clinbiomech.2021.105407. Epub 2021 Jun 5.
Computational fluid dynamic simulations have showed that the elevated viscosity of pulmonary fluids may increase the likelihood of airway closure, thus exacerbating inhomogeneity of regional lung ventilation. Unfortunately, there have been few studies directed toward measurements of viscosity of pulmonary fluids and its effect on airway opening pressure and regional distribution of lung ventilation in acute respiratory distress syndrome.
In this study, pulmonary fluids from 8 ARDS patients were measured using a cone and plate rheometer on days 1, 3, 7 and 14 in the treatment of the disorder. Ventilator settings were simultaneously recorded, including tidal volume, positive end-expiratory pressure, fraction of inspired oxygen (FiO), and so on. The regional distribution of lung ventilation was monitored by a bedside electrical impedance tomography system.
The results showed that rheological properties of pulmonary fluids behaved as either Newtonian or non-Newtonian across all patients studied. Significant intersubject and intrasubject variations in measured viscosities were observed, spanning ranges from approximately 1 cP to 7 × 10 cP at shear rates between 0.075-750 s. The product of the positive end-expiratory airway pressure and fraction of inspired oxygen was well correlated with fluid viscosity in patients with high viscosity pulmonary fluids. Furthermore, lung ventilation in these patients was highly inhomogeneous and influenced by rheology of pulmonary fluids.
The current findings provided the direct clinical data for theoretical models of airway reopening and may have important clinical implications in explaining inhomogeneity of lung ventilation and selecting initial levels of positive end-expiratory pressure in mechanically ventilated patients.
计算流体动力学模拟表明，肺液的高粘度可能会增加气道关闭的可能性，从而加剧区域性肺通气的不均匀性。不幸的是，针对肺液粘度及其对急性呼吸窘迫综合征中气道开放压和区域性肺通气分布的影响的测量，研究甚少。
在这项研究中，使用锥板流变仪在治疗该疾病的第 1、3、7 和 14 天测量了 8 名 ARDS 患者的肺液。同时记录了呼吸机设置，包括潮气量、呼气末正压、吸入氧分数（FiO）等。通过床边电阻抗断层成像系统监测肺通气的区域性分布。
结果表明，所有研究患者的肺液流变特性均表现为牛顿型或非牛顿型。在测量的粘度中观察到显著的个体间和个体内变化，在 0.075-750 s 的剪切速率范围内，范围约为 1 cP 至 7×10 cP。高粘度肺液患者的呼气末正压与吸入氧分数的乘积与肺液粘度密切相关。此外，这些患者的肺通气高度不均匀，并受到肺液流变学的影响。
目前的研究结果为气道重新开放的理论模型提供了直接的临床数据，并且在解释肺通气的不均匀性和选择机械通气患者的初始呼气末正压水平方面可能具有重要的临床意义。
