Ambulatory 7-day mechanical circulatory support in sheep model of pulmonary hypertension and right heart failure

Transplantation, bridging, and support technologies in pulmonary hypertension

Despite the progress made in medical therapies for treating pulmonary hypertension (PH), a subset of patients remain susceptible to developing a maladaptive right ventricular phenotype. The effective management of end-stage PH presents substantial challenges, necessitating a multidisciplinary approach and early identification of patients prone to acute decompensation. Identifying potential transplant candidates and assessing the feasibility of such a procedure are pivotal tasks that should be undertaken early in the treatment algorithm. Inclusion on the transplant list is contingent upon a comprehensive risk assessment, also considering the specific type of PH and various factors affecting waiting times, all of which should inform the decision-making process. While bilateral lung transplantation is the preferred option, it demands expert intra- and post-operative management to mitigate the heightened risks of pulmonary oedema and primary graft dysfunction in PH patients. Despite the availability of risk assessment tools, the occurrence of acute PH decompensation episodes can be unpredictable, potentially leading to refractory right ventricular failure even with optimal medical intervention, necessitating the use of rescue therapies. Advancements in right ventricular assist techniques and adjustments to graft allocation protocols for the most critically ill patients have significantly enhanced the survival in intensive care, affording the opportunity to endure while awaiting an urgent transplant. Given the breadth of therapeutic options available, specialised centres capable of delivering comprehensive care have become indispensable for optimising patient outcomes. These centres are instrumental in providing holistic support and management tailored to the complex needs of PH patients, ultimately enhancing their chances of a successful transplant and improved long-term prognosis.

Progress towards permanent respiratory support

PURPOSE OF REVIEW

Although lung transplantation stands as the gold standard curative therapy option for end-stage lung disease, the scarcity of available organs poses a significant challenge in meeting the escalating demand. This review provides an overview of recent advancements in ambulatory respiratory assist systems, selective anticoagulation therapies that target the intrinsic pathway, and innovative surface coatings to enable permanent respiratory support as a viable alternative to lung transplantation.

RECENT FINDINGS

Several emerging ambulatory respiratory assist systems have shown promise in both preclinical and clinical trials. These systems aim to create more biocompatible, compact, and portable forms of extracorporeal membrane oxygenation that can provide long-term respiratory support. Additionally, innovative selective anticoagulation strategies, currently in various stages of preclinical or clinical development, present a promising alternative to currently utilized nonselective anticoagulants. Moreover, novel surface coatings hold the potential to locally prevent artificial surface-induced thrombosis and minimize bleeding risks.

SUMMARY

This review of recent advancements toward permanent respiratory support summarizes the development of ambulatory respiratory assist systems, selective anticoagulation therapies, and novel surface coatings. The integration of these evolving device technologies with targeted anticoagulation strategies may allow a safe and effective mode of permanent respiratory support for patients with chronic lung disease.

A Dynamic Sheep Model to Induce Pulmonary Hypertension and Right Ventricular Failure

Decompensated right ventricular failure (RVF) in pulmonary hypertension (PH) is fatal, with limited medical treatment options. Developing and testing novel therapeutics for PH requires a clinically relevant large animal model of increased pulmonary vascular resistance and RVF. This manuscript describes the method to induce an ovine PH-RVF model that utilizes left pulmonary artery (LPA) ligation, progressive main pulmonary artery (MPA) banding, and insertion of an RV pressure line for monitoring. The PA cuff and RV pressure tubing are connected to subcutaneous access ports. This model of PH-RVF is a versatile platform to control not only the disease severity, but also the RV's phenotypic response. Subjects undergo progressive PA band adjustments twice per week for approximately 9 weeks with sequential measures of RV pressure, PA cuff pressures, and mixed venous blood gas (SvO2). Subjects can further be exercised on a livestock treadmill while hemodynamic parameters are captured. At the initiation and endpoint of this model, ventricular function and dimensions are assessed using echocardiography. In this model, RV mean and systolic pressure increased to 28 ± 5 and 57 ± 7 mmHg at week 1, and further to 44 ± 7 and 93 ± 18 mmHg by week 9, respectively. Echocardiography demonstrates characteristic findings of PH-RVF, notably RV dilation, increased wall thickness, and septal bowing. The rate of PA banding has a significant impact on SvO2 and thus the model can be titrated to elicit varying RV phenotypes. When the PA cuff is tightened rapidly, it can lead to a precipitous decline in SvO2, leading to RV decompensation, whereas a slower, more paced strategy leads to an adaptive RV stress-load response that maintains physiologic SvO2. A faster rate of PA banding will also lead to more severe liver fibrosis. The addition of controlled exercise provides a useful platform for assessing the effects of physical exertion in a PH-RVF model. This chronic PH-RVF model provides a valuable tool for studying molecular mechanisms, developing diagnostic biomarkers, and evaluating mechanical circulatory support systems.