Functional respiratory imaging, regional strain, and expiratory time constants at three levels of positive end expiratory pressure in an ex vivo pig model

Abstract

Heterogeneity in regional end expiratory lung volume (EELV) may lead to variations in regional strain (ε). High ε levels have been associated with ventilator‐associated lung injury (VALI). While both whole lung and regional EELV may be affected by changes in positive end‐expiratory pressure (PEEP), regional variations are not revealed by conventional respiratory system measurements. Differential rates of deflation of adjacent lung units due to regional variation in expiratory time constants (τ E) may create localized regions of ε that are significantly greater than implied by whole lung measures. We used functional respiratory imaging (FRI) in an ex vivo porcine lung model to: (i) demonstrate that computed tomography (CT)‐based imaging studies can be used to assess global and regional values of ε and τ E and, (ii) demonstrate that the manipulation of PEEP will cause measurable changes in total and regional ε and τ E values. Our study provides three insights into lung mechanics. First, image‐based measurements reveal egional variation that cannot be detected by traditional methods such as spirometry. Second, the manipulation of PEEP causes global and regional changes in R, E, ε and τ E values. Finally, regional ε and τ E were correlated in several lobes, suggesting the possibility that regional τ E could be used as a surrogate marker for regional ε.

Regional expiratory time constants in severe respiratory failure estimated by electrical impedance tomography: a feasibility study

“…Our study shows the physiological influence of different PEEP levels on regional airflow limitations. These data are in line with current animal experiments, demonstrating that whole lung measures of strain do not accurately represent regional pulmonary mechanics [ 40 ]. Furthermore, Pulletz et al demonstrated different time constants measured by EIT in patients with ARDS, comparable to the example given in Fig.…”

From 4D Medical Images (CT, MRI, and Ultrasound) to 4D Structured Mesh Models of the Left Ventricular Endocardium for Patient-Specific Simulations

“…Nowadays, applied biomechanical research has moved into the direction of medical and patient-specific applications; thus the coupling between clinical images and computational modeling can play a fundamental role in this regard. Several examples of commercially available simulation-based services can be mentioned: Medis [ 3 ] and HeartFlow [ 4 ] use CFD as diagnostic tool for Fractional Flow Reserve (FRR) by means of angio-based and CT-based images, respectively, while from a treatment perspective FluidDA [ 5 ] and FEops [ 6 , 7 ] developed commercial tools to support clinicians in respiratory diseases cases and in TAVI applications. Lastly, SIMULIA created an integrative predictive biophysical model of the human heart to extract clinical parameters and guide device design and treatment planning in cardiac diseases [ 8 ].…”