Does Regional Lung Strain Correlate With Regional Inflammation in Acute Respiratory Distress Syndrome During Nonprotective Ventilation? An Experimental Porcine Study*

Abstract Background Lung strain, defined as the ratio between end-inspiratory volume and functional residual capacity, is a marker of the mechanical load during ventilation. However, changes in lung volumes in response to pressures may occur in injured lungs and modify strain values. The objective of this study was to clarify the role of recruitment in strain measurements. Methods Six oleic acid–injured pigs were ventilated at positive end-expiratory pressure (PEEP) 0 and 10 cm H2O before and after a recruitment maneuver (PEEP = 20 cm H2O). Lung volumes were measured by helium dilution and inductance plethysmography. In addition, six patients with moderate-to-severe acute respiratory distress syndrome were ventilated with three strategies (peak inspiratory pressure/PEEP: 20/8, 32/8, and 32/20 cm H2O). Lung volumes were measured in computed tomography slices acquired at end-expiration and end-inspiration. From both series, recruited volume and lung strain (total, dynamic, and static) were computed. Results In the animal model, recruitment caused a significant decrease in dynamic strain (from [mean ± SD] 0.4 ± 0.12 to 0.25 ± 0.07, P < 0.01), while increasing the static component. In patients, total strain remained constant for the three ventilatory settings (0.35 ± 0.1, 0.37 ± 0.11, and 0.32 ± 0.1, respectively). Increases in tidal volume had no significant effects. Increasing PEEP constantly decreased dynamic strain (0.35 ± 0.1, 0.32 ± 0.1, and 0.04+0.03, P < 0.05) and increased static strain (0, 0.06 ± 0.06, and 0.28 ± 0.11, P < 0.05). The changes in dynamic and total strain among patients were correlated to the amount of recruited volume. An analysis restricted to the changes in normally aerated lung yielded similar results. Conclusion Recruitment causes a shift from dynamic to static strain in early acute respiratory distress syndrome.

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Regional lung viscoelastic properties in supine and prone position in a porcine model of acute respiratory distress syndrome

Journal of Applied Physiology ◽

10.1152/japplphysiol.00104.2021 ◽

2021 ◽

Author(s):

Claude Guerin ◽

Sam Bayat ◽

Norbert Noury ◽

Martin Cour ◽

Laurent Argaud ◽

...

Keyword(s):

Acute Respiratory Distress Syndrome ◽

Respiratory Distress Syndrome ◽

Respiratory Distress ◽

Chest Wall ◽

Prone Position ◽

Viscoelastic Properties ◽

Airway Pressure ◽

Distress Syndrome ◽

Impedance Tomography ◽

Regional Lung

Regional viscoelastic properties of thoracic tissues in acute respiratory distress syndrome (ARDS) and their change with position and positive end-expiratory pressure (PEEP) are unknown. In an experimental porcine ARDS, dorsal and ventral lung (R2,L and E2,L) and chest wall (R2,cw and E2,cw) viscoelastic resistive(R) and elastic(E) parameters were measured at 20, 15, 10 and 5 cmH2O PEEP in supine and prone position. E2 and R2 were obtained by fitting the decay of pressure after end-inspiratory occlusion to the equation: Pviscmax(t)=R2 e(-t/τ2), where t is length of occlusion and τ2 time constant. E2 was = R2/τ2. R2,cw and E2,cw were measured from esophageal, dorsal and ventral pleural pressures. Global R2,L and E2,L were obtained from the global trans-pulmonary pressure (airway pressure-esophageal pressure), and regional R2,L and E2,L from the dorsal and ventral airway pressure-pleural pressure difference. Lung ventilation was measured by electrical impedance tomography (EIT). Global R2,cw and E2,cw did not change with PEEP or position. Global R2,L (median(Q1-Q3)) was 37.1(11.0-65.1), 5.1(4.3-5.5), 12.1(8.4-19.5), and 41.0 (26.6-53.5) cmH2O/L/s in supine, and 15.3 (9.1-41.9), 7.9 (5.7-11.0), 8.0 (5.1-12.1) and 12.9 (6.4-19.4) cmH2O/L in prone from 20 to 5 cmH2O PEEP (P=0.06 for PEEP and P=0.06 for position). Dorsal R2,L significantly and positively correlated with amount of collapse measured with EIT. Global and regional lung and chest wall viscoelastic parameters can be described by a simple rheological model. Regional E2 and R2 were uninfluenced by PEEP and position except for PEEP on dorsal E2,L and position on dorsal E2,cw.

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The EIT-based global inhomogeneity index is highly correlated with regional lung opening in patients with acute respiratory distress syndrome

BMC Research Notes ◽

10.1186/1756-0500-7-82 ◽

2014 ◽

Vol 7 (1) ◽

Cited By ~ 35

Author(s):

Zhanqi Zhao ◽

Sven Pulletz ◽

Inéz Frerichs ◽

Ullrich Müller-Lisse ◽

Knut Möller

Keyword(s):

Acute Respiratory Distress Syndrome ◽

Respiratory Distress Syndrome ◽

Respiratory Distress ◽

Distress Syndrome ◽

Regional Lung ◽

Highly Correlated ◽

Inhomogeneity Index

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Effects of Positive End-Expiratory Pressure and Spontaneous Breathing Activity on Regional Lung Inflammation in Experimental Acute Respiratory Distress Syndrome

Critical Care Medicine ◽

10.1097/ccm.0000000000003649 ◽

2019 ◽

Vol 47 (4) ◽

pp. e358-e365 ◽

Cited By ~ 11

Author(s):

Thomas Kiss ◽

Thomas Bluth ◽

Anja Braune ◽

Robert Huhle ◽

Axel Denz ◽

...

Keyword(s):

Acute Respiratory Distress Syndrome ◽

Respiratory Distress Syndrome ◽

Respiratory Distress ◽

Spontaneous Breathing ◽

Lung Inflammation ◽

Distress Syndrome ◽

Positive End Expiratory Pressure ◽

Regional Lung ◽

Spontaneous Breathing Activity

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Dynamics of regional lung aeration determined by electrical impedance tomography in patients with acute respiratory distress syndrome

Multidisciplinary Respiratory Medicine ◽

10.4081/mrm.2012.631 ◽

2012 ◽

Vol 7 ◽

Author(s):

Sven Pulletz ◽

Matthias Kott ◽

Gunnar Elke ◽

Dirk Schädler ◽

Barbara Vogt ◽

...

Keyword(s):

Acute Respiratory Distress Syndrome ◽

Respiratory Distress Syndrome ◽

Respiratory Distress ◽

Electrical Impedance Tomography ◽

Electrical Impedance ◽

Distress Syndrome ◽

Impedance Tomography ◽

Time Constants ◽

Lung Aeration ◽

Regional Lung

Background: Lung tissue of patients with acute respiratory distress syndrome (ARDS) is heterogeneously damaged and prone to develop atelectasis. During inflation, atelectatic regions may exhibit alveolar recruitment accompanied by prolonged filling with air in contrast to regions with already open alveoli with a fast increase in regional aeration. During deflation, derecruitment of injured regions is possible with ongoing loss in regional aeration. The aim of our study was to assess the dynamics of regional lung aeration in mechanically ventilated patients with ARDS and its dependency on positive end-expiratory pressure (PEEP) using electrical impedance tomography (EIT). Methods: Twelve lung healthy and twenty ARDS patients were examined by EIT during sustained step increases in airway pressure from 0, 8 and 15 cm H2O to 35 cm H2O and during subsequent step decrease to the corresponding PEEP. Regional EIT waveforms in the ventral and dorsal lung regions were fitted to bi-exponential equations. Regional fast and slow respiratory time constants and the sizes of the fast and slow compartments were subsequently calculated. Results: ARDS patients exhibited significantly lower fast and slow time constants than the lung healthy patients in ventral and dorsal regions. The time constants were significantly affected by PEEP and differed between the regions. The size of the fast compartment was significantly lower in ARDS patients than in patients with healthy lung under all studied conditions. Conclusion: These results show that regional lung mechanics can be assessed by EIT. They reflect the lower respiratory system compliance of injured lungs and imply more pronounced regional recruitment and derecruitment in ARDS patients.

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