An Ambulatory Pulmonary and Right Heart Assist Device (OxyRVAD) in an Ovine Survival Model

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

BACKGROUND

Right heart failure is the major cause of death in pulmonary hypertension. Lung transplantation is the only long-term treatment option for patients who fail medical therapy. Due to the scarcity of donor lungs, there is a critical need to develop durable mechanical support for the failing right heart. A major design goal for durable support is to reduce the size and complexity of devices to facilitate ambulation. Toward this end, we sought to deploy wearable mechanical support technology in a sheep disease model of chronic right heart failure.

METHODS

In 6 sheep with chronic right heart failure, a mechanical support system consisting of an extracorporeal blood pump coupled with a gas exchange unit was attached in a right atrium-to-left atrium configuration for up to 7 days. Circuit performance, hematologic parameters, and animal hemodynamics were analyzed.

RESULTS

Six subjects underwent the chronic disease model for 56 to 71 days. Three of the subjects survived to the 7-day end-point for circulatory support. The circuit provided 2.8 (0.5) liter/min of flow compared to the native pulmonary blood flow of 3.5 (1.1) liter/min. The animals maintained physiologically balanced blood gas profile with a sweep flow of 1.2 (1.0) liter/min. Two animals freely ambulated while wearing the circuit.

CONCLUSIONS

Our novel mechanical support system provided physiologic support for a large animal model of pulmonary hypertension with right heart failure. The small footprint of the circuit and the low sweep requirement demonstrate the feasibility of this technology to enable mobile ambulatory applications.

In Vivo 5 Day Animal Studies of a Compact, Wearable Pumping Artificial Lung

Recent studies show improved outcomes in ambulated lung failure patients. Ambulation still remains a challenge in these patients. This necessitates development of more compact and less cumbersome respiratory support specifically designed to be wearable. The Paracorporeal Ambulatory Assist Lung (PAAL) is being designed for providing ambulatory support in lung failure patients during bridge to transplant or recovery. We previously published in vitro and acute in vivo results of the PAAL. This study further evaluates the PAAL for 5 days. Five-day in vivo studies with the PAAL were conducted in 50-60 kg sheep after heparinization (activated clotting time range: 190-250 s) and cannulation with a 27 Fr. Avalon Elite dual-lumen cannula. The animals were able to move freely in a stanchion while device flow, resistance, and hemodynamics were recorded hourly. Oxygenation and hemolysis were measured daily. Platelet activation, blood chemistry, and comprehensive blood counts are reported for preoperatively, on POD 0, and POD 5. Three animals survived for 5 days. No study termination resulted from device failure. One animal was terminated on POD 0 and one animal was terminated at POD 3. The device was operated between 1.93 and 2.15 L/min. Blood left the device 100% oxygenated. Plasma-free hemoglobin ranged 10.8-14.5 mg/dl. CD62-P expression was under 10%. Minimal thrombus was seen in devices at explant. Chronic use of the PAAL in awake sheep is promising based on our study. There were no device-related complications over the study course. This study represents the next step in our pathway to eventual clinical translation.

A Model of Pediatric End-Stage Lung Failure in Small Lambs <20 kg

One in five children with end-stage lung failure (ESLF) die while awaiting lung transplant. No suitable animal model of ESLF exists for the development of artificial lung devices for bridging to transplant. Small lambs weighing 15.7 ± 3.1 kg (n = 5) underwent ligation of the left anterior pulmonary artery (PA) branch, and gradual occlusion of the right main PA over 48 hours. All animals remained hemodynamically stable. Over seven days of disease model conditions, they developed pulmonary hypertension (mean PA pressure 20 ± 5 vs. 33 ± 4 mm Hg), decreased perfusion (SvO2 66 ± 3 vs. 55 ± 8%) with supplemental oxygen requirement, and severe tachypneic response (45 ± 9 vs. 82 ± 23 breaths/min) (all p < 0.05). Severe right heart dysfunction developed (tricuspid annular plane systolic excursion 13 ± 3 vs. 7 ± 2 mm, fractional area change 36 ± 6 vs. 22 ± 10 mm, ejection fraction 51 ± 9 vs. 27 ± 17%, all p < 0.05) with severe tricuspid regurgitation and balloon-shaped dilation of the right ventricle. This model of pediatric ESLF reliably produces pulmonary hypertension, right heart strain, and impaired gas exchange, and will be used to develop a pediatric artificial lung.

Percutaneous Mechanical Circulation Support Combined with Extracorporeal Membrane Oxygenation (oxyRVAD) in Secondary Right Heart Failure

Right heart failure (RHF) because of pulmonary hypertension (PH) is a frequently encountered clinical problem with high mortality. The last resort, if pharmacological therapy fails, is mechanical circulatory support. There is a lack of percutaneous systems to support the right ventricle (RV). Venoarterial extracorporeal membrane oxygenation is widely used as a bailout in acute RHF in non-left ventricular assist device patients. Venoarterial extracorporeal membrane oxygenation does not unload the left ventricle and may cause failure of the left ventricle if used for a longer period of time. We report the long-term use of an ECMO-based percutaneous right ventricular assist system (oxyRVAD) capable to deliver up to 6 L/min of blood flow with a returning cannula placed in the main pulmonary artery used in RHF originating from PH with poor oxygenation. We present a series of four patients on oxyRVAD (mean treatment duration 15 ± 7.6 days). Patients benefited from the system clinically; however, two patients eventually died while on oxyRVAD. Nevertheless, we provide a proof-of-concept of this system in PH patients, which is feasible and might provide a useful "bridge-to-recovery" or "bridge-to-transplant" option in the management of patients with severe RHF because of PH.

Right ventricular unloading and respiratory support with a wearable artificial pump-lung in an ovine model

BACKGROUND

Device availability of mechanical circulatory or respiratory support to the right heart has been limited. The purpose of this study was to investigate the effect of right heart unloading and respiratory support with a wearable integrated artificial pump-lung (APL).

METHODS

The APL device was placed surgically between the right atrium and pulmonary artery in 7 sheep. Anti-coagulation was performed with heparin infusion. The device's ability to unload the right ventricle (RV) was investigated by echocardiograms and right heart catheterization at different bypass flow rates. Hemodynamics and echocardiographic data were evaluated. APL flow and gas transfer rates were also measured at different device speeds.

RESULTS

Hemodynamics remained stable during APL support. There was no significant change in systemic blood pressure and cardiac index. Central venous pressure, RV pressure, RV end-diastolic dimension and RV ejection fraction were significantly decreased when APL device flow rate approached 2 liters/min. Linear regression showed significant correlative trends between the hemodynamic and cardiac indices and device speed. The oxygen transfer rate increased with device speed. The oxygen saturation from the APL outlet was fully saturated (>95%) during support. The impact of APL support on blood elements (plasma free hemoglobin and platelet activation) was minimal.

CONCLUSIONS

APL device support significantly unloaded the RV with increasing device speed. The device also provided stable hemodynamics and respiratory support in terms of blood flow and oxygen transfer. The right heart unloading performance of this wearable device needs to be evaluated further in an animal model of right heart failure with long-term support.

Long-term support with an ambulatory percutaneous paracorporeal artificial lung

BACKGROUND

Conventional extracorporeal membrane oxygenation is bulky and non-ambulatory and requires multiple blood transfusions. We hypothesized that a percutaneous, paracorporeal artificial lung (PAL) could be established through a single venous cannulation to provide long-term ambulatory respiratory support.

METHODS

Our PAL system was tested in 11 healthy sheep. An Avalon Elite dual-lumen cannula (DLC), inserted through the right jugular vein into the superior vena cava, right atrium, and inferior vena cava, was connected to a CentriMag pump and compact hollow-fiber gas exchanger, forming a short-circuit PAL system. All sheep were moved to intensive care unit and were ambulatory after anesthesia recovery. Hemodynamics and device performance were measured daily.

RESULTS

The ambulatory PALs were successfully established in all sheep. The sheep were awake, ate, and moved freely in the metabolic cage, with no need of artificial nutrition or blood transfusion. All sheep had stable hemodynamics, with 2 liters/min of average circuit flow and hemoglobin levels exceeding 9.2 g/dl throughout the experiment. A progressive decrease of oxygen transfer and carbon dioxide removal capacity was observed. Sheep were euthanized between 10 and 24 days for bleeding (n = 2), gas exchanger failure (n = 6), and DLC issues (n = 3).

CONCLUSIONS

We successfully established long-term ambulatory PAL for up to 24 days in 11 animals using our patented DLC through a single-site percutaneous venous cannulation. Critical bleeding/thrombosis formation and gas exchanger durability remain two major challenges for long-term-ambulatory PAL.

Venovenous extracorporeal membrane oxygenation for acute lung failure in adults

BACKGROUND

Acute lung failure (ALF) is an increasing problem that can be treated with venovenous extracorporeal membrane oxygenation (vv-ECMO). This report summarizes prospectively collected data of an institutional experience with vv-ECMO.

METHODS

From January 2007 to December 2010, 176 patients (mean age, 48 ± 16; range, 14-78 years) with ALF refractory to conventional therapy were supported with vv-ECMO. The general indication for vv-ECMO was a partial oxygen pressure/fraction of inspired oxygen (Fio(2)) < 80 mm Hg under a Fio(2) of 1.0, a positive end-expiratory pressure of 18 cm H(2)O, and refractory respiratory acidosis (pH < 7.25), despite optimization of conservative therapy.

RESULTS

All patients underwent peripheral cannulation. In 59 cases, vv-ECMO was placed in another facility with ECMO transport by helicopter or ambulance. The mean vv-ECMO support interval was 12 ± 9.0 days (range, 1-67 days). During ECMO, 12 patients (7%) could be extubated and stepwise mobilized. Cannula-related complications during long-term support occurred in 14%, which was mostly minor bleeding. Overall survival was 56%: 58 patients (33%) died during mechanical support, and 20 (11%) died after weaning from the system. The best outcome was noted in trauma patients. Risk factors were mainly advanced age and multiorgan failure.

CONCLUSION

Modern vv-ECMO is an excellent treatment in patients with severe ALF and should be more liberally used.

Wang-Zwische double lumen cannula-toward a percutaneous and ambulatory paracorporeal artificial lung

We are developing a high performance double lumen cannula (DLC) for a minimally invasive, ambulatory and percutaneous paracorporeal artificial lung (PAL). The Wang-Zwische (W-Z) DLC was designed for percutaneous insertion into the Internal Jugular (IJ) vein with a drainage lumen open to both the superior vena cava (SVC) and the inferior vena cava (IVC) maximizing venous drainage. A separate collapsible but nondistensible membrane infusion lumen open to the right atrium (RA) achieves minimal recirculation allowing for total gas exchange. The W-Z DLC prototypes are made by a proprietary dip molding process with the "molded in" flat wire spiral stainless steel spring resulting in a flexible yet kink resistant thin wall (0.1 mm) outer cannula with one piece construction. With the ultra thin membrane infusion lumen collapsed, an introducer shaft fits tightly within the drainage lumen to facilitate insertion with placement at the SVC-RA-IVC junction. The W-Z DLC prototypes were tested while connected to a compact pump-gas exchanger circuit in three sheep (2 acute and one 15 day performance study). Insertion was simple, using standard percutaneous insertion techniques. Recirculation was as low as 2%. The 15 day performance study demonstrated our prototype 26 Fr W-Z DLC can achieve 2 L/min blood flow with minimal recirculation. The W-Z DLC design minimizes recirculation rate, maximizes flow lumen cross-sectional area, and maximizes achievable blood flow to enhance gas exchange performance allowing for one site percutaneous venovenous support.