The role of bronchial artery revascularization in lung transplantation

Alterations in Pulmonary Physiology with Lung Transplantation

Lung transplant is a treatment option for patients with end-stage lung diseases; however, survival outcomes continue to be inferior when compared to other solid organs. We review the several anatomic and physiologic changes that result from lung transplantation surgery, and their role in the pathophysiology of common complications encountered by lung recipients. The loss of bronchial circulation into the allograft after transplant surgery results in ischemia-related changes in the bronchial artery territory of the allograft. We discuss the role of bronchopulmonary anastomosis in blood circulation in the allograft posttransplant. We review commonly encountered complications related to loss of bronchial circulation such as allograft airway ischemia, necrosis, anastomotic dehiscence, mucociliary dysfunction, and bronchial stenosis. Loss of dual circulation to the lung also increases the risk of pulmonary infarction with acute pulmonary embolism. The loss of lymphatic drainage during transplant surgery also impairs the management of allograft interstitial fluid, resulting in pulmonary edema and early pleural effusion. We discuss the role of lymphatic drainage in primary graft dysfunction. Besides, we review the association of late posttransplant pleural effusion with complications such as acute rejection. We then review the impact of loss of afferent and efferent innervation from the allograft on control of breathing, as well as lung protective reflexes. We conclude with discussion about pulmonary function testing, allograft monitoring with spirometry, and classification of chronic lung allograft dysfunction phenotypes based on total lung capacity measurements. We also review factors limiting physical exercise capacity after lung transplantation, especially impairment of muscle metabolism. © 2023 American Physiological Society. Compr Physiol 13:4269-4293, 2023.

Incidence, risk factors, and clinical characteristics of airway complications after lung transplantation

Airway complications may occur after lung transplantation and are associated with considerable morbidity and mortality. We investigated the incidence, risk factors, and clinical characteristics of these complications. We retrospectively reviewed the medical records of 137 patients who underwent lung transplantation between 2008 and 2021. The median follow-up period was 20 months. Of the 137 patients, 30 (21.9%) had postoperative airway complications, of which 2 had two different types of airway complications. The most common airway complication was bronchial stenosis, affecting 23 patients (16.8%). Multivariable Cox analysis revealed that a recipient's body mass index ≥ 25 kg/m² (hazard ratio [HR], 2.663; p = 0.013) was a significant independent risk factor for airway complications, as was postoperative treatment with extracorporeal membrane oxygenation (ECMO; HR, 3.340; p = 0.034). Of the 30 patients who had airway complications, 21 (70.0%) were treated with bronchoscopic intervention. Survival rates did not differ significantly between patients with and without airway complications. Thus, our study revealed that one fifth of patients who underwent lung transplantation experienced airway complications during the follow-up period. Obesity and receiving postoperative ECMO are risk factors for airway complications, and close monitoring is warranted in such cases.

Bilateral sequential lung transplantation: technical aspects

The surgical technique for lung transplantation has evolved dramatically over the last three decades. Significant improvements in short term outcomes in the early years of lung transplantation were due, in large part, to techniques developed to reduce airway anastomotic complications in single lung transplantation. Following development of the technique of en bloc double lung transplantation, evolution to the bilateral sequential technique further reduced airway complications for double lung transplantation. More recently, some programs have utilized the en bloc double lung transplant technique with bronchial artery revascularization to aid airway healing and potentially improve short- and long-term outcomes. The experience with bronchial artery revascularization remains limited to a few series, with the technique having not been widely adopted by most lung transplant programs. With the implementation of priority allocations schemes in many countries, patients with higher risk profiles are being prioritized for transplantation which results in more complex procedures in fragile recipients with multiple comorbidities. This includes the increased need for concomitant cardiac procedures as well as performing lung transplantation after prior cardiothoracic surgery. Different surgical approaches have been described for bilateral sequential lung transplantation with or without intra-operative mechanical circulatory support (MCS), such as sternotomy, clamshell (bilateral anterior thoracotomies with transverse sternotomy), and bilateral thoracotomy incisions. Herein, we aim, not only to describe the various surgical approaches for double lung transplantation, but to provide a comprehensive review of other aspects related to the recipient pathology and different anatomical variants as well as handling technical challenges that might be encountered during the procedure.

Airway complications in lung transplantation

Airway complications (ACs) after lung transplantation remain an important source of morbidity and mortality despite significant advances in the surgical technics, leading to increased cost, and decrease quality of life. The incidences of ACs after lung transplantation range from 2% to 33%, even though most transplant centers have reported rates in the range of 7% to 8%. However, the reported rate of ACs has been inconsistent as a result of a lack of standardized airway definitions and grading protocols before the recent 2018 International Society for Heart and Lung Transplantation (ISHLT) proposed consensus guidelines on ACs after lung transplantation. The ACs include stenosis, perioperative and postoperative bronchial infections, bronchial necrosis and dehiscence, excess granulation tissue, and tracheobronchomalacia (TBM). Anastomosis infection, necrosis, or dehiscence typically develops within the first month after lung transplantation. The most frequent AC after lung transplantation is bronchial stenosis. Several risk factors have been proposed to the development of ACs after lung transplantation, including surgical anastomosis techniques, hypoperfusion, infections, donor and recipient factors, immunosuppression agents, and organ preservation. ACs might be prevented by early recognition of the airway pathology, using advance medical management, and interventional bronchoscopy procedures. Balloon bronchoplasty, cryotherapy, laser photo resection, electrocautery, high-dose endobronchial brachytherapy, and bronchial stents placement are the most frequent interventional bronchoscopic procedures utilized for the management of ACs.

Hemoptysis after Lung Transplantation Caused by Bronchial Arterial Neovascularization: Angiographic Analysis and Successful Embolization

This report discusses 3 bilateral lung transplant recipients (2 female, 1 male) who presented with late hemoptysis (10 y, 18 y, and 19 y after transplantation). All patients had a history of pulmonary infections, bronchiectasis, and/or Aspergillus infection. Arteriography, through catherization of the common femoral artery, demonstrated spontaneous bronchial and systemic neovascularization arising from the thyrocervical trunk, internal thoracic artery, intercostal arteries, and dorsal scapular artery. Embolization was performed with microspheres, polyvinyl alcohol microparticles, and/or glue and effectively terminated hemoptysis. One patient died 10 d later as a result of fungal infection, and the 2 others remained in stable condition (18- and 26-mo postembolization follow-up available).

Consecutive Hypoxia Decreases Expression of NOTCH3, HEY1, CC10, and FOXJ1 via NKX2-1 Downregulation and Intermittent Hypoxia-Reoxygenation Increases Expression of BMP4, NOTCH1, MKI67, OCT4, and MUC5AC via HIF1A Upregulation in Human Bronchial Epithelial Cells

Previous studies have shown that the experimental models of hypoxia-reoxygenation (H/R) mimics the physiological conditions of ischemia-reperfusion and induce oxidative stress and injury in various types of organs, tissues, and cells, both in vivo and in vitro, including human lung adenocarcinoma epithelial cells. Nonetheless, it had not been reported whether H/R affected proliferation, apoptosis, and expression of stem/progenitor cell markers in the bronchial epithelial cells. In this study, we investigated differential effects of consecutive hypoxia and intermittent 24/24-h cycles of H/R on human bronchial epithelial (HBE) cells derived from the same-race and age-matched healthy subjects (i.e., NHBE) and subjects with chronic obstructive pulmonary disease (COPD) (i.e., DHBE). To analyze gene/protein expression during differentiation, both the NHBE and DHBE cells at the 2nd passage were cultured at the air-liquid interface (ALI) in the differentiation medium under normoxia for 3 days, followed by either culturing under hypoxia (1% O₂) for consecutively 9 days and then returning to normoxia for another 9 days, or culturing under 24/24-h cycles of H/R (i.e., 24 h of 1% O₂ followed by 24 h of 21% O₂, repetitively) for 18 days in total, so that all differentiating HBE cells were exposed to hypoxia for a total of 9 days. In both the normal and diseased HBE cells, intermittent H/R significantly increased HIF1A, BMP4, NOTCH1, MKI67, OCT4, and MUC5AC expression, while consecutive hypoxia significantly decreased NKX2-1, NOTCH3, HEY1, CC10, and FOXJ1 expression. Inhibition of HIF1A or NKX2-1 expression by siRNA transfection respectively decreased BMP4/NOTCH1/MKI67/OCT4/MUC5AC and NOTCH3/HEY1/CC10/FOXJ1 expression in the HBE cells cultured under intermittent H/R to the same levels under normoxia. Overexpression of NKX2-1 via cDNA transfection caused more than 2.8-fold increases in NOTCH3, HEY1, and FOXJ1 mRNA levels in the HBE cells cultured under consecutive hypoxia compared to the levels under normoxia. Taken together, our results show for the first time that consecutive hypoxia decreased expression of the co-regulated gene module NOTCH3/HEY1/CC10 and the ciliogenesis-inducing transcription factor gene FOXJ1 via NKX2-1 mRNA downregulation, while intermittent H/R increased expression of the co-regulated gene module BMP4/NOTCH1/MKI67/OCT4 and the predominant airway mucin gene MUC5AC via HIF1A mRNA upregulation.

Domino heart transplant following heart-lung transplantation: a systematic review and meta-analysis

Background

The domino-donor operation occurs when a "conditioned" heart from the heart-lung transplant (HLT) recipient is transplanted into a separate heart transplant (HT) recipient. The purpose of this systematic review was to investigate the indications and outcomes associated with the domino procedure.

Methods

An electronic search was performed to identify all prospective and retrospective studies on the domino procedure in the English literature. Eight studies reported 183 HLT recipients and 263 HT recipients who were included in the final analysis.

Results

HLT indications included cystic fibrosis in 58% (95% CI: 27-84%) of recipients, primary pulmonary hypertension (PPH) in 17% (95% CI: 12-24%), bronchiectasis in 5% (95% CI: 3-10%), emphysema in 5% (95% CI: 0-45%), and Eisenmenger's syndrome in 4% (95% CI: 2-8%). HT indications included ischemic heart disease in 40% (95% CI: 33-47%), non-ischemic disease in 39% (95% CI: 25-56%), and re-transplantation in 10% (95% CI: 1-59%). The pooled mean pulmonary vascular resistance (PVR) in HT recipients was 3.05 Woods units (95% CI: 0.14-5.95). The overall mortality in the HLT group was 28% (95% CI: 18-41%) at an average follow-up of 15.68 months (95% CI: 0.82-30.54), and 35% (95% CI: 17-58%) in the HT group at an average follow-up of 37.26 months (95% CI: 6.68-67.84). Freedom from rejection in HT was 94% (95% CI: 75-99%) at 1 month, 77% (95% CI: 30-96%) at 6 months, and 41% (95% CI: 33-50%) at 1 year.

Conclusions

The domino procedure appears to be a viable option in properly selected patients that can be performed safely with acceptable outcomes.

Bioengineering the Blood-gas Barrier

The pulmonary blood-gas barrier represents a remarkable feat of engineering. It achieves the exquisite thinness needed for gas exchange by diffusion, the strength to withstand the stresses and strains of repetitive and changing ventilation, and the ability to actively maintain itself under varied demands. Understanding the design principles of this barrier is essential to understanding a variety of lung diseases, and to successfully regenerating or artificially recapitulating the barrier ex vivo. Many classical studies helped to elucidate the unique structure and morphology of the mammalian blood-gas barrier, and ongoing investigations have helped to refine these descriptions and to understand the biological aspects of blood-gas barrier function and regulation. This article reviews the key features of the blood-gas barrier that enable achievement of the necessary design criteria and describes the mechanical environment to which the barrier is exposed. It then focuses on the biological and mechanical components of the barrier that preserve integrity during homeostasis, but which may be compromised in certain pathophysiological states, leading to disease. Finally, this article summarizes recent key advances in efforts to engineer the blood-gas barrier ex vivo, using the platforms of lung-on-a-chip and tissue-engineered whole lungs. © 2020 American Physiological Society. Compr Physiol 10:415-452, 2020.

Lung transplant with bronchial arterial revascularization: review of surgical technique and clinical outcomes

Lung transplantation (LTx) is routinely performed with sacrifice of the bronchial arterial circulation. We review bronchial artery anatomy and surgical technique for LTx with direct bronchial arterial revascularization (BAR). We also update the published clinical experience, including from our center, of LTx with BAR. Published series of LTx with BAR are from single centers, and all cite high technical success rates and good short-term outcomes. Technically, double LTx (DLTx) with BAR is almost always possible if a deliberate review of bronchial artery anatomy is performed. For single LTx (SLTx), BAR is feasible in about 50% of cases. The combined Copenhagen and Cleveland Clinic experience (with BAR procedures performed or supervised by Dr. Gosta B. Pettersson) includes 131 LTx with BAR with a technical success rate >95%. Procedural success is uniformly associated with normal airway healing. Five-year survival in LTx with BAR is superior to the 5-year survival of LTx patients in the ISHLT registry. LTx with BAR is feasible and safe, and technical success ensures normal airway healing. The experience with BAR at experienced centers suggests possible long-term survival benefit. A multicenter study is needed to define the role of BAR in LTx.

The Bronchial Arterial Circulation in Lung Transplantation: Bedside to Bench to Bedside, and Beyond

Chronic allograft dysfunction (CLAD) remains a major complication, causing the poor survival after lung transplantation (Tx). Although strenuous efforts have been made at preventing CLAD, surgical approaches for lung Tx have not been updated over the last 2 decades. The bronchial artery (BA), which supplies oxygenated blood to the airways and constitutes a functional microvasculature, has occasionally been revascularized during transplants, but this technique did not gain popularity and is not standard in current lung Tx protocols, despite the fact that a small number of studies have shown beneficial effects of BA revascularization on limiting CLAD. Also, recent basic and clinical evidence has demonstrated the relationship between microvasculature damage and CLAD. Thus, the protection of the bronchial circulation and microvasculature in lung grafts may be a key factor to overcome CLAD. This review revisits the history of BA revascularization, discusses the role of the bronchial circulation in lung Tx, and advocates for novel bronchial-arterial-circulation sparing approaches as a future direction for overcoming CLAD. Although there are some already published review articles summarizing the surgical techniques and their possible contribution to outcomes in lung Tx, to the best of our knowledge, this review is the first to elaborate on bronchial circulation that will contribute to prevent CLAD from both scientific and clinical perspectives: from bedside to bench to bedside, and beyond.

Airway hypoxia in lung transplantation

Lung transplantation is a life-saving operation for patients with advanced lung disease. Pulmonary allografts eventually fail because of infection, thromboembolism, malignancy, airway complications, and chronic rejection, otherwise known as chronic lung allograft dysfunction (CLAD). Emerging evidence suggests that a highly-compromised airway circulation contributes to the evolution of airway complications and CLAD. There are two significant causes of poor perfusion and airway hypoxia in lung transplantation: an abnormal bronchial circulation which causes airway complications and microvascular rejection which induces CLAD. At the time of transplantation, the bronchial artery circulation, a natural component of the airway circulatory anatomy, is not surgically connected, and bronchi distal to the anastomosis become hypoxic. Subsequently, the bronchial anastomosis is left to heal under ischemic conditions. Still later, the extant microvessels in transplant bronchi are subjected to alloimmune insults that can further negatively impact pulmonary function. This review describes how airway tissue hypoxia evolves in lung transplantation, why depriving oxygenation in the bronchi and more distal bronchioles contributes to disease pathology and what therapeutic interventions are currently emerging to address these vascular injuries. Improving anastomotic vascular healing at the time of transplantation and preventing microvascular loss during acute rejection episodes are two steps that could limit airway hypoxia and improve patient outcomes.

Lung Ischaemia-Reperfusion Injury: The Role of Reactive Oxygen Species

Lung ischaemia-reperfusion injury (LIRI) occurs in many lung diseases and during surgical procedures such as lung transplantation. The re-establishment of blood flow and oxygen delivery into the previously ischaemic lung exacerbates the ischaemic injury and leads to increased microvascular permeability and pulmonary vascular resistance as well as to vigorous activation of the immune response. These events initiate the irreversible damage of the lung with subsequent oedema formation that can result in systemic hypoxaemia and multi-organ failure. Alterations in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) have been suggested as crucial mediators of such responses during ischaemia-reperfusion in the lung. Among numerous potential sources of ROS/RNS within cells, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidases, nitric oxide synthases and mitochondria have been investigated during LIRI. Against this background, we aim to review here the extensive literature about the ROS-mediated cellular signalling during LIRI, as well as the effectiveness of antioxidants as treatment option for LIRI.

ISHLT Consensus Statement on adult and pediatric airway complications after lung transplantation: Definitions, grading system, and therapeutics

Airway complications remain a major cause of morbidity and mortality after cardiothoracic transplantation. The reported incidence of airway ischemic complications varies widely, contributed to by the lack of a universally accepted grading system and standardized definitions. Furthermore, the majority of the existing classification systems fail to integrate the wide range of possible bronchial complications that may develop after lung transplant. Hence, a Working Group was created by the International Society for Heart and Lung Transplantation with the aim of elaborating a universal definition of adult and pediatric airway complications and grading system. One such area of focus is to understand the problem in the context of a more standardized consensus of classifying airway ischemia. This consensus definition will have major clinical, therapeutics, and research implications.

History of lung transplantation

Lung transplantation nowadays is a well-accepted and routine treatment for well selected patients with terminal respiratory disease. However, it took several decades of experimental studies and clinical attempts to reach this success. In this paper, we describe the early experimental activity from the mid-forties until the early sixties. The first clinical attempt in humans was reported by Hardy and Webb in 1963 followed by others with short survival only except for one case by Derom et al. who lived for 10 months. Long-term successes were not reported until after the discovery of cyclosporine as a new immunosuppressive agent. Successful heart-lung transplantation (HLTx) for pulmonary vascular disease was performed by the Stanford group starting in 1981 while the Toronto group described good outcome after single-lung transplantation (SLTx) for pulmonary fibrosis in 1983 and after double-lung transplantation for emphysema in 1986. Further evolution in surgical techniques and in transplant type for the various forms of end-stage lung diseases are reviewed. The evolution in lung transplantation still continues nowadays with the use of pulmonary allografts coming from living-related donors, from donors after circulatory death, or after prior assessment and reconditioning during ex vivo lung perfusion (EVLP) in an attempt to overcome the critical shortage of suitable organs. Early outcome has significantly improved over the last three decades. Better treatment and prevention of chronic lung allograft dysfunction will hopefully result in further improvement of long-term survival after lung transplantation.

Effect of positive perioperative donor and recipient respiratory bacterial cultures on early post-transplant outcomes in lung transplant recipients

BACKGROUND

It is standard practice to administer prophylactic antibiotics post lung transplantation. However, no studies have evaluated the impact of culture positivity. The purpose of this study was to evaluate early post-transplant outcomes of culture-positive and culture-negative lung transplant (LT) recipients and the appropriateness of the empiric regimens used.

METHODS

Adult patients who received an LT at Emory University Hospital between January 1, 2010 and August 31, 2015 were reviewed and stratified into three groups: (i) culture-positive appropriate empiric treatment, (ii) culture-positive inappropriate empiric treatment, and (iii) culture-negative. Antibiotics were defined as appropriate if bacteria were sensitive to the empiric regimen. The primary endpoint was 30-day mortality. Secondary endpoints included hospital length of stay (LOS), intensive care unit (ICU) LOS, percent neutrophil count in a bronchoalveolar lavage (BAL) sample, presence of airway ischemia, and appropriateness of the empiric antibiotic regimen.

RESULTS

Nine, zero, and four patients died within 30 days in the culture-positive appropriate (n = 113), culture-positive inappropriate (n = 5), and culture-negative groups (n = 29) (P = .564) respectively. The median hospital LOS was 19, 16, and 15 days respectively. Median ICU LOS was 6, 5, and 7 respectively. The respective percent neutrophil counts in the BAL fluid were 79, 83, and 65. The presence of airway ischemia was only documented in eight patients, all in the culture-positive appropriate group.

CONCLUSION

We did not identify an association between antibiotic appropriateness and 30-day mortality, hospital LOS, or ICU LOS in post-LT recipients.

Safety of hyperbaric oxygen therapy for management of central airway stenosis after lung transplant

BACKGROUND

Central airway stenosis (CAS) is common after lung transplantation and causes significant post-transplant morbidity. It is often preceded by extensive airway necrosis, related to airway ischemia. Hyperbaric oxygen therapy (HBOT) is useful for ischemic grafts and may reduce the development of CAS.

METHODS

The purpose of this study was to determine whether HBOT could be safely administered to lung transplant patients with extensive necrotic airway plaques. Secondarily, we assessed any effects of HBOT on the incidence and severity of CAS. Patients with extensive necrotic airway plaques within 1-2 months after lung transplantation were treated with HBOT along with standard care. These patients were compared with a contemporaneous reference group with similar plaques who did not receive HBOT.

RESULTS

Ten patients received HBOT for 18.5 (interquartile range, IQR 11-20) sessions, starting at 40.5 (IQR 34-54) days after transplantation. HBOT was well tolerated. Incidence of CAS was similar between HBOT-treated patients and reference patients (70% vs 87%, respectively; P=.34), but fewer stents were required in HBOT patients (10% vs 56%, respectively; P=.03).

CONCLUSIONS

This pilot study is the first to demonstrate HBOT safety in patients who develop necrotic airway plaques after lung transplantation. HBOT may reduce the need for airway stent placement in patients with CAS.

Revascularization of decellularized lung scaffolds: principles and progress

There is a clear unmet clinical need for novel biotechnology-based therapeutic approaches to lung repair and/or replacement, such as tissue engineering of whole bioengineered lungs. Recent studies have demonstrated the feasibility of decellularizing the whole organ by removal of all its cellular components, thus leaving behind the extracellular matrix as a complex three-dimensional (3D) biomimetic scaffold. Implantation of decellularized lung scaffolds (DLS), which were recellularized with patient-specific lung (progenitor) cells, is deemed the ultimate alternative to lung transplantation. Preclinical studies demonstrated that, upon implantation in rodent models, bioengineered lungs that were recellularized with airway and vascular cells were capable of gas exchange for up to 14 days. However, the long-term applicability of this concept is thwarted in part by the failure of current approaches to reconstruct a physiologically functional, quiescent endothelium lining the entire vascular tree of reseeded lung scaffolds, as inferred from the occurrence of hemorrhage into the airway compartment and thrombosis in the vasculature in vivo. In this review, we explore the idea that successful whole lung bioengineering will critically depend on 1) preserving and/or reestablishing the integrity of the subendothelial basement membrane, especially of the ultrathin respiratory membrane separating airways and capillaries, during and following decellularization and 2) restoring vascular physiological functionality including the barrier function and quiescence of the endothelial lining following reseeding of the vascular compartment. We posit that physiological reconstitution of the pulmonary vascular tree in its entirety will significantly promote the clinical translation of the next generation of bioengineered whole lungs.