Measurement of Regional Deformation and Volume Change of Donor Lungs during Ex Vivo Lung Perfusion Using a Stereo Vision Method
Creators: Der, Jason R.
Publisher: name: University of Alberta Library
Year: 2022

<p>Lung transplant is a critical treatment that remains the only option for patients with end-state pulmonary illness. This treatment is underutilized because of a shortage of suitable donor lungs, leading to patients succumbing to illness while on the waitlist. Supply is limited by overly conservative rejections of possible donors. Also, transplantation is limited by hypothermic storage, the conventional preservation method, which is restricted to transplant windows of six hours. Shorter preservation periods ensure rates of primary graft dysfunction do not rise exponentially, possibly leading to recipient fatality. However, this limits transplant services to regional operations and can lead to last minute rejections as the donor lung degrade over time. </p>

<p>Ex-vivo lung perfusion (EVLP) preserves and monitors donor lungs at a near physiological state through mechanical ventilation, blood perfusion, and pharmaceutical treatment. The technique has the potential to improve donor lung utilization. Its measurements can accurately determine transplant viability to prevent conservative rejections. In studies, it has been shown to revitalize previously rejected donor lungs into a transplant viable condition. Also, maintaining the donor lung with mechanical ventilation and blood perfusion prevents ischemia and increases preservation periods. However, EVLP could be improved as it could host additional diagnostic sensors. </p>

<p>EVLP introduces the risk of ventilation induced lung injury (VILI) that could injury the lung and jeopardize transplant viability. Also, conventional EVLP diagnostic system measurements are scalar, thus are unable to differentiate the individual performance of the left and right lung, or measure asynchrony. Also, these systems would be unable to measure localized over-inflation due to heterogeneity in the donor lung’s compliance. </p>

<p>A non-invasive camera-based processing scheme was developed to evaluate donor lung performance during EVLP treatment. The camera sensor methodology was evaluated by comparing its measurements to clinical diagnostic systems. A commercial active stereo vision system was used to measure the surface deformation of three donor lung surrogates during positive pressure mechanical ventilation at different tidal volumes. The camera system’s depth measurements were used to reconstruct the lung surfaces to calculate plethysmography metrics, such as tidal volume through surface integration. Also, these metrics were derived from measurements that were simultaneously captured with a combined MEMS, or a Venturi flow rate and pressure sensor that are integrated into the clinical ventilation units. These paired measurements were used to compare the two methods, which were found to have high correlation, but poor agreement with significant systematic and proportional error relative to ventilation tidal volume. The camera-based system performed other calculations.</p>

<p>The camera-based system measured the left and right lung separately using image segmentation. Also, the surface deformation was scanned for peaks or troughs that would correlate with localized over-inflation and under-inflation. Peak detection was performed on surface measurements analogous to tidal volume and dynamic compliance. Lastly, the surface shape of the donor lung surrogates was characterized over one respiratory cycle by averaging all sampled cycles.<br>
These results suggest that the camera-based method is measuring changes in donor lung surface shape with respects to respiratory cycles, however, it is currently unsuitable for plethysmography measurement. Also, a limitation of the study was that the surface deformation measurements and detected peaks were not directly validated, since the reference method did not measure regional performance. However, the left and right lung measurements matched observations that the left lung failed to distend. Furthermore, in several cases the plethysmography systematic and proportional error of the camera method was linearly modelled with high coefficient of determination. With improvements, the method could be utilized as an additional evaluation tool to assess donor lung surface condition and health. </p>