Twelve-hour canine heart preservation with a simple, portable hypothermic organ perfusion device

Proof of Concept Study for a Closed Ex-Vivo Limb Perfusion System for 24-hour Subnormothermic Preservation Using Acellular Perfusate

BACKGROUND

The two approaches to vascularized tissue machine perfusion utilize either the open (non-pressurized) or closed (pressurized) perfusion system. Most studies describing isolated limb perfusion preservation rely on open perfusion systems and report tissue edema exceeding 40% after 12-14 hours of preservation.A variant of machine perfusion places the limb and perfusate into a reservoir closed to atmosphere. It is hypothesized that the reservoir pressure, acting as a transmural pressure, has the advantage of reducing edema formation by counteracting the hydrostatic pressure gradient from the perfusion pressure.This proof-of-concept study aim was to demonstrate feasibility of the ULiSSESTM device (closed, vertical perfusion system) to preserve forelimbs of Sus Scrofa swine for 24 hours of subnormothermic perfusion compared to an open, horizontal perfusion system. The ULiSSES™ is a compact, practical device that applies pulsatile, pressurized perfusion through the novel use of a diaphragm pump powered by compressed oxygen.

METHODS

Forelimbs from swine were preserved in ULiSSES™ device (closed perfusion system) (n = 9) and in an open perfusion system (n = 4) using sub-normothermic modified Krebs-Henseleit Solution. Physiological parameters were measured at the start and every 3 hours for 24 hours. Limbs were weighed prior to and post perfusion to compare weight gain. Edema and cellular integrity were evaluated using histopathology pre and post perfusion.

RESULTS

Closed perfusion system showed superiority compared to the open perfusion system in terms of oxygen consumption, reduction in vascular resistance, and overall tissue integrity. The closed perfusion system demonstrated a 21% reduction in weight gain compared to the open perfusion system and significantly reduced intracellular edema.

CONCLUSION

The ULiSSES™ closed, pressurized perfusion technology has translatable military applications with the potential to preserve porcine limbs for 24 hours with improved results compared to an open perfusion system.

LEVEL OF EVIDENCE

N/A.

Oxygen consumption during oxygenated hypothermic perfusion as a measure of donor organ viability

Hypothermic machine perfusion (HMP) for the preservation of kidneys, recovered from extended criteria organ donors (ECDs), presents the opportunity for assessing ex vivo parameters that may have value in predicting postimplantation organ viability. Organ perfusion and vascular resistance are the parameters most frequently cited as the basis for the decision to use or discard a donor kidney. The limitation of these measures is emphasized by the observation that a significant percentage of ECD kidneys with poor perfusion parameters can provide life-sustaining function after transplantation. It has been suggested that whole organ oxygen consumption (OC) during oxygenated HMP may better reflect the proportion of viable tissue in the organ and more reliably predict posttransplant organ function. Our study correlates renal OC and renal vascular resistance (RVR) during oxygenated HMP with postpreservation glomerular filtration rates (GFRs) in rodent kidneys after 24 hours of oxygenated HMP. Kidneys from adult rodents were preserved for 24 hours using oxygenated HMP and static cold storage (SCS). During oxygenated HMP preservation, organ OC, renal organ flow rates, and RVR were serially measured. After the preservation period, organs were mounted onto a Langendorff device for warming to normal body temperature and measurement of GFR. Oxygen consumption and RVR during HMP were correlated with postpreservation GFR. Oxygen consumption during oxygenated HMP was significantly correlated (r2 = 0.871; p < 0.05) with postpreservation GFR, suggesting that higher OC predicts better postpreservation GFR. In contrast, RVR was poorly correlated with postpreservation GFR (r2 = 0.258; p = 0.199). Glomerular filtration rate in SCS kidneys was 0.002 ± 0.003 ml/min/g. We demonstrate that measurement of organ OC during oxygenated HMP may have significant value in predicting postpreservation organ function.

Intermittent antegrade cardioplegia: isolated heart preservation with the Asporto heart preservation device

BACKGROUND

A major problem in procurement of donor hearts is the limited time a donor heart remains viable. After cardiectomy, ischemic hypoxia is the main cause of donor heart degradation. The global myocardial ischemia causes a cascade of oxygen radical formation that cumulates in an elevation in hydrogen ions (decrease in pH), irreversible cellular injury, and potential microvascular changes in perfusion.

OBJECTIVE

To determine the changes of prolonged storage times on donor heart microvasculature and the effects of intermittent antegrade perfusion.

MATERIALS AND METHODS

Using porcine hearts flushed with a Ribosol-based cardioplegic solution, we examined how storage time affects microvascular myocardial perfusion by using contrast-enhanced magnetic resonance imaging at a mean (SD) of 6.1 (0.6) hours (n = 13) or 15.6 (0.6) hours (n = 11) after cardiectomy. Finally, to determine if administration of cardioplegic solution affects pH and microvascular perfusion, isolated hearts (group 1, n = 9) given a single antegrade dose, were compared with hearts (group 2, n = 8) given intermittent antegrade cardioplegia (150 mL, every 30 min, 150 mL/min) by a heart preservation device. Khuri pH probes in left and right ventricular tissue continuously measured hydrogen ion levels, and perfusion intensity on magnetic resonance images was plotted against time.

RESULTS

Myocardial perfusion measured via magnetic resonance imaging at 6.1 hours was significantly greater than at 15.6 hours (67% vs 30%, P = .00008). In group 1 hearts, the mean (SD) for pH at the end of 6 hours decreased to 6.2 (0.2). In group 2, hearts that received intermittent antegrade cardioplegia, pH at the end of 6 hours was higher at 6.7 (0.3) (P = .0005). Magnetic resonance imaging showed no significant differences between the 2 groups in contrast enhancement (group 1, 62%; group 2, 40%) or in the wet/dry weight ratio.

CONCLUSION

Intermittent perfusion maintains a significantly higher myocardial pH than does a conventional single antegrade dose. This difference may translate into an improved quality of donor hearts procured for transplantation, allowing longer distance procurement, tissue matching, improved outcomes for transplant recipients, and ideally a decrease in transplant-related costs.

Intermittent Antegrade Cardioplegia: Isolated Heart Preservation with the Asporto Heart Preservation Device

Background

A major problem in procurement of donor hearts is the limited time a donor heart remains viable. After cardiectomy, ischemic hypoxia is the main cause of donor heart degradation. The global myocardial ischemia causes a cascade of oxygen radical formation that cumulates in an elevation in hydrogen ions (decrease in pH), irreversible cellular injury, and potential microvascular changes in perfusion.

Objective

To determine the changes of prolonged storage times on donor heart microvasculature and the effects of intermittent antegrade perfusion.

Materials and Methods

Using porcine hearts flushed with a Ribosol-based cardioplegic solution, we examined how storage time affects microvascular myocardial perfusion by using contrast-enhanced magnetic resonance imaging at a mean (SD) of 6.1 (0.6) hours (n=13) or 15.6 (0.6) hours (n=11) after cardiectomy. Finally, to determine if administration of cardioplegic solution affects pH and microvascular perfusion, isolated hearts (group 1, n=9) given a single antegrade dose, were compared with hearts (group 2, n=8) given intermittent antegrade cardioplegia (150 mL, every 30 min, 150 mL/min) by a heart preservation device. Khuri pH probes in left and right ventricular tissue continuously measured hydrogen ion levels, and perfusion intensity on magnetic resonance images was plotted against time.

Results

Myocardial perfusion measured via magnetic resonance imaging at 6.1 hours was significantly greater than at 15.6 hours (67% vs 30%, P=.00008). In group 1 hearts, the mean (SD) for pH at the end of 6 hours decreased to 6.2 (0.2). In group 2, hearts that received intermittent antegrade cardioplegia, pH at the end of 6 hours was higher at 6.7 (0.3) ( P=.0005). Magnetic resonance imaging showed no significant differences between the 2 groups in contrast enhancement (group 1, 62%; group 2, 40%) or in the wet/dry weight ratio.

Conclusion

Intermittent perfusion maintains a significantly higher myocardial pH than does a conventional single antegrade dose. This difference may translate into an improved quality of donor hearts procured for transplantation, allowing longer distance procurement, tissue matching, improved outcomes for transplant recipients, and ideally a decrease in transplant-related costs.

Optimizing Donor Heart Outcome After Prolonged Storage With Endothelial Function Analysis and Continuous Perfusion

BACKGROUND

By minimizing tissue ischemia, continuous perfusion (CP) during organ transport may increase the safety of "marginal donors." My colleagues and I investigated whether an analysis of donor heart viability predicts recovery of grafts challenged with a 24-hour preservation interval.

METHODS

Dog hearts underwent cold static storage (CS) for 8 hours (n = 8) or 24 hours (n = 2) or CP for 24 hours with cold asanguinous, oxygenated solution (n = 8). Myocardial systolic and diastolic function and oxygen and lactate consumption were assessed at base line, during CP, and after Langendorff blood reperfusion. Base line endothelial function was evaluated by the percentage transcoronary change ([coronary sinus - aorta]/aorta) in myeloperoxidase and by platelet function and coronary flow reserve after 20 seconds of coronary artery occlusion. During CP, the endothelium was assessed by transcoronary protein release and coronary resistance. Edema was assessed by weight gain and histology.

RESULTS

Base line systolic and metabolic functions showed no relation to post-Langendorff function. Compared with CS, CP resulted in a greater recovery in systolic function (87% +/- 35% vs 65% +/- 15% of baseline; p = 0.05) and a shorter interval required for lactate consumption to exceed production (7.0 +/- 6.8 minutes vs 15.0 +/- 8.9 minutes; p = 0.06). Endothelial function was heterogeneous: coronary flow reserve, 2.7 +/- 0.7; percentage change in myeloperoxidase, -8.4% +/- 6.8%; and change in platelet function, 4.3% +/- 3.5%, as determined by thromboelastography angle at base line. Protein release during CP for 24 hours was 8.3 +/- 7.1 g. Two factors predicted more than 75% systolic pressure generation recovery: use of CP and normal endothelial function (p = 0.05; Fisher's exact test). However, CP led to edema according to histology, weight gain (72 +/- 29 g), and impaired diastolic function versus CS (end-diastolic pressure-volume relationship, 1.4 +/- 0.4 mm Hg/mL vs 0.8 +/- 0.3 mm Hg/mL; p = 0.08).

CONCLUSIONS

Better systolic function despite 16 hours' more preservation than cold storage corroborates the idea that CP supports aerobic metabolism at physiologically important levels. Viability analysis focused on endothelial function and identified organs that were able to tolerate this 24-hour preservation interval.

Perfusion preservation of rodent kidneys in a portable preservation device based on fluidics technology

BACKGROUND

Technology that can implement the basic requirements for successful organ preservation in a portable configuration has yet to be realized.

METHODS

This work evaluates kidney preservation in a new class of portable organ preservation technology based on fluidics principles. During hypothermic pulsatile perfusion preservation (HPPP), oxygen consumption, renal vascular resistance (RVR), pH, pCO2, and perfusion pressure were measured. After 24 hr of preservation, perfusate distribution was assessed, and oxygen consumption, RVR, and glomerular filtration rate (GFR) were compared in perfused, statically stored, and freshly harvested kidneys.

RESULTS

During HPPP, perfusion pressure was 5.8+/-3.3 mmHg with oxygen delivery to the organs in excess of 3.5 times the organ metabolic requirement. During function measurements, RVR was not statistically different in the three groups; however, both oxygen consumption and GFR in the statically stored organs were significantly lower than in HPPP stored or freshly harvested kidneys.

CONCLUSIONS

Our findings suggest that full portability in a hypothermic perfusion preservation device seems feasible utilizing fluidics-based technology.

Preservation of metabolic reserves and function after storage of myocytes in hypothermic UW solution

Isolated rat myocytes cold stored anaerobically up to 24 h in University of Wisconsin solution lost 95% of their ATP and 100% of their glycogen. They underwent contracture when rewarmed in a Krebs-Henseleit (KH) medium that contained Ca unless Ca addition was delayed. In the latter case, cell function, measured by stimulation-induced cell shortening, was surprisingly well retained. Aerobically stored cells were resistant to Ca on rewarming, although 96% of glycogen was still lost, along with 46% of ATP. Cells that were incubated for 48 h aerobically with the substrates glucose and pyruvate at pH 6.2 retained 77% of their ATP and 59% of their glycogen, with good cell morphology. At pH 6.2, the demand for ATP was only 55% of that at pH 7.4. However, after rewarming, these cells functioned no better than anaerobically stored cells, although their inotropic response to isoproterenol was improved. We conclude that 1) aerobic conditions with substrates at low pH preserve myocyte metabolic reserves well for 48 h, partly by reducing the demand for ATP; 2) rewarming conditions are critical for anaerobically stored cells with metabolic stores that are severely depleted; and 3) unloaded cell function is surprisingly insensitive to a period of severe metabolic deprivation.

Cardiac transplantation following a 24-h preservation using a perfusion apparatus

BACKGROUND

We developed a new apparatus for heart preservation and have already reported successful transplantation following 12 h of preservation using this apparatus. The efficacy of coronary perfusion with an oxygenated Celsior solution was investigated through transplantation following 24 h of preservation using the apparatus.

MATERIALS AND METHODS

After being harvested, grafts were preserved with a combination of immersion in a 4 degrees C Celsior solution and perfusion with an oxygenated Celsior solution using the apparatus in the coronary perfusion (CP) group and simply immersed in a 4 degrees C Celsior solution in the simple immersion(SI) group. beta-Adenosine triphosphate (beta-ATP), phosphocreatine (Pcr), and inorganic phosphate (P(i)) levels and myocardial pH (pH(i)) were measured immediately after the heart was excised and at 12 and 24 h after preservation. Following preservation, orthotopic transplantation was performed. Cardiac function was measured 2 h after weaning from cardiopulmonary bypass (CPB).

RESULTS

beta-ATP/P(i), Pcr/P(i), and pH(i) levels were significantly higher in the CP group than in the SI group at 12 and 24 h after preservation. Four of six animals in the CP group and two of six in the SI group were successfully weaned from CPB. The recovery rates of cardiac function were better in the CP group than in the SI group.

CONCLUSION

Twenty-four hours of heart preservation may be possible with a combination of immersion in a 4 degrees C Celsior solution and perfusion with an oxygenated Celsior solution using the perfusion apparatus.

The Effect of Coronary Perfusion with an Oxygenated Celsior Solution on 12-hour Cardiac Preservation

Celsior is a new extracellular-type cardiac preservation solution. We recently developed an apparatus for preservation using low-pressure continuous coronary perfusion. The purpose of this study was to investigate the efficacy of coronary perfusion with an oxygenated Celsior solution using the new apparatus for prolonged cardiac preservation. Adult mongrel dogs weighing 9-13 kg were divided into two groups: the coronary perfusion group (CP; n = 5) and the simple immersion group (SI; n = 7). The coronary vascular beds were washed out with a 4 degrees C Celsior solution following cardiac arrest using the same solution, and their hearts were excised. In the CP group, the graft was immersed in a 4 degrees C Celsior solution and perfused with the same oxygenated solution. In the SI group, the graft was simply immersed in a 4 degrees C Celsior solution. beta-adenosine triphosphate (beta-ATP), phosphocreatine (Pcr), inorganic phosphate (Pi) levels and myocardial pH (pHi) were measured immediately after excising the heart, and at 3, 6, and 12 hours after preservation. beta-ATP, Pcr, and Pi values were expressed as a percentage of control values, which were measured immediately after excising the heart. beta-ATP/Pi and Pcr/Pi levels were significantly higher in the CP group than in the SI group at 6 and at 12 hours after preservation. The pHi levels during preservation were significantly higher in the CP group than in the SI group. Low-pressure hypothermic coronary perfusion with an oxygenated Celsior solution is effective for long-term heart preservation. </hea

Extending myocardial viability during heart preservation with cyclosporine A

BACKGROUND AND AIM OF STUDY

Hypothermic preservation (PRES) of donor hearts is limited to 12-14 hours for complete functional recovery after reperfusion. In a canine heterotopic heart transplant model, 50% to 60% functional recovery returned after 18 hours of PRES with University of Wisconsin (UW) solution. Concomitant with functional changes were marked increases in apoptotic cells at 2 (2.69%) and 6 (5.98%) hours of reperfusion with a concomitant decrease in lamin B1 (2% and 7.6%, respectively) with no evidence of necrotic cells. These results suggested that blockade of apoptosis may prolong myocardial viability during PRES and reperfusion.

METHODS

Donor hearts were subjected to 18 and 24 hours of PRES (2 degrees C to 4 degrees C) with and without cyclosporine A (CyS) treatment (apoptosis blocker). CyS was given to the donor animal (10 mg/kg), in the PRES solution (10(-5) mol/L), slowly infused during the PRES period (1 mL/min), and also to the recipient animal (2.5 mg/kg).

RESULTS

After 18 hours of PRES with CyS, function returned to 100% within 1 hour and stayed at this level throughout a 6-hour recovery period. Apoptotic myocytes were reduced (55%) after 18 hours PRES with CyS treatment, and 6-hour reperfusion lamin B1 was reduced to only 3.7%. Twenty-four hour PRES in UW resulted in no functional recovery. However, after CyS treatment, functional recovery returned to 100% after 4 hours of reperfusion. Adenosine triphosphate (ATP) and creatine phosphate (CP) concentrations were surprisingly the same with or without CyS treatment at 18 hours and lower with 24 hours.

CONCLUSIONS

Use of CyS in the PRES solution prolongs myocardial viability during donor heart PRES. The mechanism of action may be associated with the mitochondrial permeability transition (MPT) pore via cyclophilin D binding.

Ex vivo cardiac allograft preservation by continuous perfusion techniques

The current technique of cardiac preservation for clinical transplantation by infusion of cold cardioplegia and immersion of the heart in an isotonic saline bath at 4 degrees C limits safe tissue preservation time to 4 to 6 hours. The myriad of benefits to be gained by extending cardiac preservation time has prompted the search for alternatives to hypothermic immersion of the heart, the most promising of which involves techniques of coronary artery perfusion. Countless studies have shown the benefits of long-term storage of donor hearts by perfusion rather than the immersion technique. Continuous perfusion preservation has three basic advantages over simple immersion. Perfusion preservation with oxygen carrying solutions has the advantage of preventing ischemia, anaerobic metabolism, and reperfusion injury. Second, nutritional supplementation and provision of substrate can be more effectively delivered to myocardial cells. Third, continuous perfusion preservation effects the clearance of metabolic waste products from the coronary circulation. The composition of the ideal perfusion solution and optimal preservation conditions remain incompletely defined.

Long-term heart preservation using a new portable hypothermic perfusion apparatus

OBJECTIVE

Perfusion storage is not often used clinically compared with simple immersion because of complicated circuits and demanding management. We developed a new apparatus for preservation combined with simple immersion and continuous coronary perfusion.

METHODS

The main characteristics of this apparatus are as follows: (1) hypothermic storage, (2) does not require any energy source, (3) variable perfusion pressure, and (4) portability. The perfusion apparatus is composed of a storage chamber, a cooling chamber, and metal bars from which a perfusate bag is suspended. Adult mongrel dogs were divided into two groups: the coronary perfusion group (CP, n = 6) and the simple immersion group (SI, n = 6). Coronary vascular beds of the dog were washed out with a University of Wisconsin (UW) solution following cardiac arrest obtained using a GIK solution. The hearts were then excised. In the CP group, the heart graft, which was immersed in a 4 degrees C UW solution, was perfused with the same solution at a flow rate of 35 approximately 50 ml/hr. In the SI group, the heart graft was immersed in a 4 degrees C UW solution only. The heart graft was preserved for 12 hours in both groups. Beta-adenosine triphosphate (beta-ATP), phosphocreatine (Pcr), and inorganic phosphate (Pi) levels were measured immediately after excision of the heart, and at 3, 6, and 12 hours after preservation. Beta-ATP, Pcr, and Pi values were expressed as a percentage of control values, which had been obtained immediately after excision of the heart. Water content of the myocardium was measured prior to and after 12-hour preservation. The preserved graft was then evaluated through orthotopic transplantation.

RESULTS

Beta-ATP/Pi levels at 6 and 12 hours after preservation were significantly higher in the CP group than in the SI group (62 +/- 5 versus 39 +/- 7%, 48 +/- 5 versus 22 +/- 8%, respectively, p < 0.05). Pcr/Pi levels at 6 and 12 hours after preservation were 30 +/- 9% and 22 +/- 8%, respectively in the CP group, while Pcr/Pi levels in the SI group were detected in only one case. There was no significant difference in water content either prior to or after 12-hour preservation between the two groups. Histopathologically, irregular expansion and/or contraction of myocardial fibers were more severe in the SI group than in the CP group. The recovery rate of hemodynamic parameters 2 hours after heart transplantation was significantly (p < 0.05) higher in the CP group than in the SI group.

CONCLUSION

Stable and safe long-term canine heart preservation with continuous coronary perfusion associated with immersion is possible using this new apparatus, and may have broad clinical application.

Twenty-four-hour heart preservation using continuous cold perfusion and copper (II) complexes

BACKGROUND

During long-term in vitro heart preservation and subsequent reperfusion, irreversible tissue damage occurs in part due to reactive oxygen species. Therefore, inhibition of generation of oxygen-derived free radicals and the related oxidative damage of ischemic tissue may be useful in maintaining heart function after long-term preservation. Complexes of Cu(II) may cause disproportionation of superoxide and thus may function as an inhibitor of the effects of oxygen-derived free radicals.

METHODS

In this study, 24-h preservation of isolated rat hearts was performed. Using the Langendorff technique, hearts were perfused for 24 h with a hypothermic, moderately hyperkalemic (15 mM KCl) solution containing various metabolic and membrane-stabilizing additives at constant low pressure. In addition, the potential benefit of the addition of two Cu(II) compounds (Cu(II) Cl2 and Cu(II)2Asp4) to the perfusion solution was examined.

RESULTS

The Cu(II)Cl2-treated hearts were significantly better preserved than control hearts after 24 h of preservation with regard to recovery of systolic pressure, coronary flow, max +dP/dt, and max -dP/dt. Lipid peroxidation as estimated by myocardial malonaldehyde (both P < 0. 001) and myocardial creatine kinase release (both P < 0.05 vs control) were significantly reduced in the Cu(II)Cl2 and Cu(II)2Asp4 groups. Overall, Cu(II)Cl2 best preserved the heart after 24 h of cold preservation with respect to indices of functional recovery, whereas Cu(II)2Asp4 did not significantly improve functional recovery compared to control.

CONCLUSION

Low-pressure, cold perfusion with an enhanced solution is a potential method to preserve donor hearts in preparation for transplantation. The beneficial effect of Cu(II)Cl2 was attributed to (i) SOD activity of the Cu2+ species and/or (ii) termination of chain carriers in the lipid peroxidations by aqueous Cu2+ and Cu+ species. The negation of some of the positive effects of Cu2+ species by the introduction of acetylsalicylate was tentatively assigned to potentiation of the Ca2+ modality for reperfusion injury.

Continuous perfusion of donor hearts in the beating state extends preservation time and improves recovery of function

OBJECTIVES

Improving methods of donor heart preservation may permit prolonged storage and remote procurement of cardiac allografts. We hypothesized that continuous, sanguineous perfusion of the donor heart in the beating, working state may prolong myocardial preservation.

METHODS

We developed a portable perfusion apparatus for use in donor heart preservation. Contractile, metabolic, and vasomotor functions were monitored simultaneously in an isolated swine heart. The metabolic state was monitored by myocardial tissue pH. Vasomotor function was assessed in isolated coronary ring chambers. Hearts were randomized into 3 groups: group I (n = 5), cardioplegic arrest, 12-hour storage at 4 degrees C with modified Belzer solution, and 2-hour sanguineous reperfusion in the working state; group II (n = 6), 12-hour continuous perfusion in the beating working state, 30 minutes of arrest (to simulate re-implantation time), and 2 hours of reperfusion, as above; group III (n = 7), coronary ring control hearts.

RESULTS

At 2 hours of reperfusion, left ventricular developed pressure in group II was higher than in group I (mean +/- standard deviation: 90 +/- 6 mm Hg, 53 +/- 15 mm Hg, P = .005). Significantly less myocardial edema was observed in group II than in group I (73% +/- 4%, 80% +/- 1% water content, P = .01). Significantly less myocardial acidosis was noted in group II than in group I during preservation (pH 7.3 +/- 0.01, 6.1 +/- 0.03, P < .001) and reperfusion (pH 7.3 +/- 0.008, 6.8 +/- 0.05, P < .001). Coronary endothelial vasomotor function was better preserved in group II than in group I as evidenced by dose-response relaxation of coronary rings to 10(-8) mol/L bradykinin (37%, 55% delta baseline, P = .01).

CONCLUSION

This new method extends the current preservation limit and avoids time-dependent ischemic injury, thereby allowing for distant procurement of donor organs.

Assessment of left ventricular compliance during heart preservation

There is critical need for a greater number of donor hearts for transplantation. The demand can be relieved, in part, by an extension of preservation time. This necessitates new methods of preservation and development of means to assess the functional condition of the preserved heart. We report a heart-preservation system designed for long-term preservation support and discuss issues specifically related to extended heart preservation. This article presents methodology to assess ventricular compliance and to quantify coronary flow distribution during the use of microperfusion preservation. Ventricular adenosine triphosphate (ATP) concentrations are directly related to the immediate post-preservation function: however, direct measurement of ATP is not clinically available. Based on the premise that ventricular compliance relates directly to the ventricular ATP concentrations, we performed sequential ventricular compliance measurements using a simple left ventricular balloon during a 24 h preservation period. A porcine heart model was employed using a continuous, hypothermic, antegrade, microperfusion system for 24 h and measurements were made at specific intervals during the preservation time. The compliance measurements were ascertained by pressure-volume curves using a flaccid balloon inserted into the left ventricle through the mitral valve. In addition, to assess microvascular function during the preservation interval, regional coronary flow measurements were performed using a microsphere technique. We report that after 12 h of preservation there was a twofold reduction in ventricular compliance which decreased further by fivefold at 18 h. In contrast, there was a time-dependent decrease in left ventricular coronary flow, especially with the left-ventricular subendocardial region significantly decreasing by 50% at 12 h. In conclusion, a simple ventricular-compliance balloon provided a direct measurement of ventricular compliance of the preserved heart which may provide an indirect estimate of the ventricular high-energy phosphates of the preserved heart prior to transplantation.