Dynamic digital radiography for monitoring pulmonary function before and after a single lung transplant: a case description

Introduction

Patients with end-stage lung disorders show abnormal ventilation and perfusion of the lungs, which leads to the development of a compensatory respiratory mode. The diaphragm experiences chronic overexertion as the condition worsens, finally developing diaphragm dysfunction. Lung transplantation (LT) has been proven a well-established treatment for clinical end-stage lung disease. The improvement of the diaphragmatic function goes in parallel with the respiratory function following LT (1). Although pulmonary function tests (PFTs) are frequently used to evaluate pulmonary function, they are often not feasible for LT candidates. Recent studies have reported the utility of dynamic chest radiography (DCR) in assessing pulmonary ventilation and perfusion function through visualization of diaphragm motion and lung area change during breath. Here, we report a case of single-lung transplantation (SLT), highlighting the use of DCR to investigate the alteration in pulmonary function and underlying respiratory mechanics after this procedure.

Imaging protocols

DCR was implemented by the AeroDR C80 Digital Radiography X-ray System (Konica Minolta, Tokyo, Japan) with the following X-ray exposure settings: tube voltage, 110 kV; tube current, 100 mA; pulse duration, 5 ms; frame rate, 15 fps. The images were post-processed with a workstation (IWS Dynamic Image Processing Workstation Software DI-X1, Ver.1.2, Konica Minolta).

The patient underwent examination in a functional position, either standing or sitting. Prior to the examination, the radiologist conducted breathing training with the patient. Imaging was performed during tidal breathing, forced breathing, and breath-holding with exposure times of approximately 10, 6, and 7 s, respectively. The patient underwent a DCR examination before transplantation with low-flow nasal cannula oxygen ventilation during tidal breathing and forced breathing, and the ventilation was switched off during breath-holding. The patient underwent DCR examinations after transplantation without the need for ventilation. To assess diaphragm movement on DCR, edge detection algorithms, such as the Prewitt Filter, were employed to automatically identify lung field areas. Template matching technology was utilized to automatically mark the positions of the diaphragm apex and the apices of both lungs, as well as to outline the contours of the lung fields on both sides. The blood flow changes with the cardiac cycle, the X-ray transmission changes, and lung blood flow were analyzed by detecting subtle changes in lung field pixel values during breath-holding, without the administration of contrast media (2,3). DCR quantitative evaluation was carried out to assess the maximum diaphragm excursion and mean speed, the change in lung field area, and pulmonary blood flow perfusion.

Perfusion scintigraphy was performed on the GE860ECT. The patient was ventilated in the supine position and injected with ^99mTc-macroaggregated albumin (^99mTc-MAA). Planar multi-position imaging was performed at eight standard positions, including anterior, posterior, left lateral, right lateral, left posterior oblique at 45°, right posterior oblique at 45°, left rear oblique at 45°, and right rear oblique at 45°. It was followed by the tomographic imaging, with a peak energy of 140 keV and a window width of 20%, using a matrix of 128×128. The probe rotated 360°, collecting data for 15 s per frame for a total of 60.

Case presentation

A 65-year-old man was referred to our hospital with a history of productive cough for 16 years and exacerbated for one month. The patient worked in the coal mine for more than 10 years before being diagnosed with pneumoconiosis (stage III) and chronic obstructive pulmonary disease (COPD). The patient was a heavy smoker with a history of diabetes. Physical examination revealed decreased breath sounds in both lungs, as well as a few moist rales in the right lower lung. The potential of hydrogen (pH) value was 7.349 (normal 7.350–7.450), the partial pressure of carbon dioxide (pCO₂) was 57.1 mmHg (normal 35–48 mmHg), the partial pressure of oxygen (pO₂) was 119 mmHg (normal 83–108 mmHg), and HCO₃ was 30.7 mmol/L (normal 21.4–27.3 mmol/L) under 55% oxygen supplementation. Chest computed tomography (CT) demonstrated diffuse small nodules, perihilar conglomerated masses with multiple calcifications, and emphysema. The patient was intubated and required mechanical ventilation before the left SLT.

PFT before transplantation was not feasible for this patient. The DCR lung blood flow (right lung 64.79%, left lung 35.21%) was comparable with perfusion scintigraphy (right lung 60.00%, left lung 40.00%). Moreover, DCR revealed reduced diaphragm motion, lung area changes, and lung blood flow during tidal and forced breathing (Figure 1, A1-A3; Video S1).

Figure 1 DCR of the patient before and after SLT. The vertical axis represents the extrusion of the diaphragm, the horizontal axis represents the time frame (right side, purple line; left side, green line). Forced breathing DCR pre-transplantation (A1,A2) showed lung hyperinflation and flattened diaphragms with reduced diaphragmatic excursion on both sides, and the lung blood flow fraction in the left was lower than that in the right side (A3). Forced breathing DCR at 6 months post-transplantation showed improved diaphragm excursion (B1,B2) and increased lung blood flow fraction (B3) on the transplantation side. DCR, dynamic chest radiography; SLT, single-lung transplantation.

The patient’s symptoms improved significantly after left SLT. The patient was dismissed from mechanical ventilation and oxygen supplementation. Follow-up DCR was performed at 1-, 2-, and 6-month (Figure 1, B1-B3; Video S2). The DCR-derived parameters at different timepoints, including a maximum excursion of the diaphragm, mean expiratory motion speed of the diaphragm, maximum projected lung area−minimum projected lung area (PLA_max−PLA_min), and percentage of lung blood flow on the transplanted side were higher than those before the transplant (Figure 2A-2D). The mean inspiratory motion speed of the diaphragm on the transplanted side was lower than that before the transplant (Figure 2E). The maximum diaphragm excursion, the PLA_max−PLA_min, the total percent of pulmonary blood flow, and the diaphragm inspiratory motion speed on the native side were lower than those pre-transplantation. The mean diaphragm expiratory motion speed on the native side was higher than pre-transplantation during forced breathing (Figure S1).

Figure 2 The temporal change of DCR parameters on the transplanted side during tidal and forced breathing. DCR-derived parameters including maximum diaphragm excursion (A), mean diaphragm expiratory motion speed (B), the PLA_max−PLA_min (C), and the total percent of pulmonary blood flow (D) on the transplanted side were higher than pre-transplantation. The mean diaphragm inspiratory motion speed (E) on the transplanted side was lower than pre-transplantation. DCR, dynamic chest radiography; PLA_max−PLA_min, maximum projected lung area-minimum projected lung area.

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Recently, chest DCR using a flat panel detector (FPD) with a large field of view has seen increasing clinical use. This novel technique enables one to obtain a time-resolved quantitative evaluation of diaphragm motion and lung field area change during tidal or forced respiration (2,4). Moreover, it can produce images of lung blood flow at a radiation dose as low as one-tenth that of lung perfusion scintigraphy, without the use of contrast media or radionuclides (5).

Over the past twenty years, the SLT procedure has become a therapeutic option for treating end-stage lung diseases (6). SLT substantially improves patients’ lung function and exercise tolerance due to improvement in alveolar gas exchange and inspiratory muscle function (7). The diaphragm is the main inspiratory muscle, which accounts for 70% of the inspired air volume during quiet breathing (1). Therefore, the status of diaphragm function is an important predictor of pulmonary function recovery. In this case, the patient showed decreased extrusion, PLA_max−PLA_min, and mean inspiratory and expiratory motion speed of the diaphragm on both tidal and force breath before SLT, which is consistent with a previous study (8). The aforementioned metrics and lung blood flow demonstrated a significant improvement after SLT. The increase of lung blood flow on the transplanted side is reasonable since the transplanted lung has normal structure and function, with a balanced ventilation/perfusion (V/Q) ratio, whereas the contralateral native lung suffers from pneumoconiosis (stage III) and COPD, leading to an imbalanced V/Q ratio. As a result, the transplanted side inherently has a higher lung blood flow perfusion fraction than the native side. It is intriguing, though, that the mean diaphragm inspiratory motion speed following transplanting was lower than it was prior to the procedure. Our hypothesis was that the diaphragm, which had been in intrinsic hyperpnea before treatment, reverted to normal morphology and function following SLT (9,10). We think that another possible reason for the decrease in average movement speed during inhalation after transplantation may be due to pleural adhesions. Another surprising finding was that the improvements in the transplanted lung had a negative impact on the contralateral impaired lung function. We hypothesize that the observed decrease in diaphragm motion and pulmonary perfusion in the impaired lung is an adaptive response of the human body to the imbalance between the impaired right lung and the normal left lung (11). Another possibility is that after SLT, there is an imbalance in respiratory mechanics between the two sides, which exacerbates compensatory fatigue of the respiratory muscles of the native lungs, and the diaphragm’s work is declining.

Conclusions

To the best of our knowledge, this is the first report demonstrating the dynamic change of pulmonary function and respiratory mechanics pre- and post-SLT utilizing the DCR technique. DCR may play an important role in the monitoring of treatment response of lung diseases in the aspect of pulmonary function.

Acknowledgments

None.

Footnote

Funding: This study was supported by the Guangzhou Municipal Science and Technology Bureau City-University (Institute) Joint Funding Project.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-2424/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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