Potential effect of pulmonary fluid viscosity on positive end-expiratory pressure and regional distribution of lung ventilation in acute respiratory distress syndrome

Zhenglong Chen; Zhaoyan Hu; Ming Zhong; Linhong Deng; Jiale Tao; Yuanlin Song

doi:10.1016/j.clinbiomech.2021.105407

Potential effect of pulmonary fluid viscosity on positive end-expiratory pressure and regional distribution of lung ventilation in acute respiratory distress syndrome

Clin Biomech (Bristol, Avon). 2021 Jul:87:105407. doi: 10.1016/j.clinbiomech.2021.105407. Epub 2021 Jun 5.

Authors

Zhenglong Chen¹, Zhaoyan Hu¹, Ming Zhong², Linhong Deng³, Jiale Tao⁴, Yuanlin Song⁵

Affiliations

¹ School of Medical Instrumentation, Shanghai University of Medicine & Health Sciences, Shanghai, China; NMPA Key Laboratory for Respiratory and Anaesthetic Equipment, Shanghai, China.
² Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai, China. Electronic address: zhong_ming@fudan.edu.cn.
³ Institute of Biomedical Engineering and Health Sciences, Changzhou University, Changzhou, China.
⁴ Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai, China.
⁵ Department of Pulmonary Medicine, Zhongshan Hospital, Fudan University, Shanghai, China. Electronic address: ylsong70@163.com.

Abstract

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.

Keywords: Acute respiratory distress syndrome; Airway opening pressure; Lung mechanics; Pulmonary fluid; Viscosity.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Humans
Lung
Positive-Pressure Respiration
Respiration, Artificial
Respiratory Distress Syndrome* / therapy
Viscosity