Stress–strain curve and elastic behavior of the fibrotic lung with usual interstitial pneumonia pattern during protective mechanical ventilation

Tonelli, R., Rizzoni, R., Grasso, S. et al. Stress–strain curve and elastic behavior of the fibrotic lung with usual interstitial pneumonia pattern during protective mechanical ventilation. Sci Rep 14, 13158 (2024). https://doi.org/10.1038/s41598-024-63670-z

Summary of "Stress–Strain Curve and Elastic Behavior of the Fibrotic Lung with Usual Interstitial Pneumonia Pattern During Protective Mechanical Ventilation"

Abstract

Patients with acute exacerbation of lung fibrosis with a usual interstitial pneumonia (UIP) pattern are vulnerable to ventilator-induced lung injury (VILI) during mechanical ventilation (MV). This study aimed to create a mechanical model to describe the deformation of UIP lungs during lung-protective MV, comparing stress-strain behavior and specific elastance with those in acute respiratory distress syndrome (ARDS) and healthy lungs. The model integrates partitioned lung and chest wall mechanics and evaluates the contributions of elastin and collagen, key components of lung extracellular matrix (ECM), to lung deformation during MV.

Key Points of the Article

Mechanical Model for UIP-Lung Deformation:

- The study develops a novel constitutive mathematical model to describe lung deformation during mechanical ventilation based on the mechanical properties of UIP lungs compared to ARDS and healthy lungs.

- The model highlights the distinct contributions of elastin and collagen in UIP-lung, particularly during mechanical inflation.

Specific Elastance and Stress–Strain Behavior:

- Specific elastance (a measure of lung stiffness) was significantly higher in UIP patients compared to ARDS patients (28.9 cmH2O vs. 11.4 cmH2O). This reflects the stiffer nature of UIP lungs.

- The UIP-lung showed a steeper stress–strain curve, indicating that even low levels of strain could lead to VILI.

- Collagen plays a dominant role in UIP lung stiffness at higher strain levels, while elastin's contribution is more prominent at lower strain levels.

Increased Risk of VILI in UIP-Lung:

- The study suggests that even when lung-protective MV settings are applied, UIP-lung patients are at high risk of developing VILI due to their altered mechanical properties.

- UIP-lung deformation reaches harmful levels at strain values greater than 0.5, compared to ARDS lungs which tolerate strains up to 1.5 or higher before reaching injury thresholds.

Comparison with ARDS and Healthy Lungs:

- While ARDS lungs share some heterogeneity in elasticity, UIP-lungs exhibit more intrinsic structural changes due to ECM alterations, particularly in the composition and function of collagen and elastin.

- UIP patients show different respiratory mechanics during mechanical ventilation, particularly in terms of lung stiffness and strain response, compared to both ARDS and healthy lungs.

Clinical Implications and Future Directions:

- The findings indicate that UIP-lung patients require tailored MV strategies to avoid VILI. Traditional lung-protective ventilation strategies used for ARDS may not be sufficient for UIP patients.

- Further research is needed to optimize ventilatory support for UIP patients, possibly through ultra-protective ventilation strategies or extracorporeal membrane oxygenation (ECMO).

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Discussion Questions:

1. How can clinicians adapt mechanical ventilation settings for UIP patients to reduce the risk of VILI based on their unique stress–strain behavior?

2. What role could alternative therapies, such as ECMO, play in managing acute exacerbations of UIP, particularly when traditional lung-protective strategies are insufficient?

3. How can the findings from this study influence the development of personalized ventilatory strategies for patients with UIP undergoing mechanical ventilation?

Javier Amador-Casta?eda, BHS, RRT, FCCM

Interprofessional Critical Care Network (ICCN)

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