Background

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.

Methods

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 (FiO₂), and so on. The regional distribution of lung ventilation was monitored by a bedside electrical impedance tomography system.

Findings

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 × 10⁴ cP at shear rates between 0.075–750 s⁻¹. 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.

Interpretation

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.

中文翻译：

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肺液粘度对急性呼吸窘迫综合征患者呼气末正压和肺通气区域分布的潜在影响

背景

计算流体动力学模拟表明，肺液粘度升高可能会增加气道闭合的可能性，从而加剧局部肺通气的不均匀性。不幸的是，很少有研究针对肺液粘度的测量及其对气道开放压力和急性呼吸窘迫综合征肺通气区域分布的影响。

方法

在这项研究中，在疾病治疗的第 1、3、7 和 14 天，使用锥板流变仪测量了 8 名 ARDS 患者的肺液。同时记录呼吸机设置，包括潮气量、呼气末正压、吸入氧浓度 (FiO ₂ ) 等。通过床边电阻抗断层扫描系统监测肺通气的区域分布。

发现

结果表明，在所有研究的患者中，肺液的流变学特性表现为牛顿或非牛顿。 观察到测得的粘度在受试者间和受试者内有显着变化，剪切率在 0.075–750 s ^-1之间时，范围从大约 1 cP 到 7 × 10 ⁴ cP 。呼气末气道正压和吸入氧分数的乘积与高粘度肺液患者的液体粘度密切相关。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。

解释

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，并且可能对解释肺通气的不均匀性和选择机械通气患者呼气末正压的初始水平具有重要的临床意义。