Creation of an Ex Vivo Renal Perfusion Model to Investigate Microwave Ablation.

This study hypothesized that an ex vivo renal perfusion model can create smaller microwave ablation (MWA) measurements during perfused states compared with nonperfused states across multiple device settings. Nine bovine kidneys, a fluoroscopic compatible perfusion model, and a commercially-available clinical MWA system were used to perform 72 ablations (36 perfused and 36 nonperfused) at 9 different device settings. Comparing perfused and nonperfused ablations at each device setting, significant differences in volume existed for 6 of 9 settings (P < .05). Collapsed across time settings, the ablation volumes by power were the following (perfused and nonperfused, P value): 60 W, 2.3 cm3 ± 1.0 and 7.2 cm3 ± 2.7, P < .001; 100 W, 5.4 cm3 ± 2.1 and 11.5 cm3 ± 5.6, P < .01; and 140 W, 11.2 cm3 ± 3.7 and 18.7 cm3 ± 6.3, P < .01. Applied power correlated with ablation volume: perfused, 0.021 cm3/W and R = 0.462, P = .004, and nonperfused, 0.029 cm3/W and R = 0.565, P < .001. These results support that an ex vivo perfused organ system can evaluate MWA systems and demonstrate heat sink perfusion effects of decreased ablation size.

Novel portable hypothermic machine perfusion preservation device enhances cardiac viability of donated human hearts.

Introduction: Heart transplant remains the gold standard treatment for patients with advanced heart failure. However, the list of patients waiting for a heart transplant continues to increase. We have developed a portable hypothermic oxygenated machine perfusion device, the VP.S ENCORE®, to extend the allowable preservation time. The purpose of this study was to test the efficacy of the VP.S. ENCORE® using deceased donors derived hearts. Methods: Hearts from brain-dead donors not utilized for transplant (n = 11) were offered for research from the Texas Organ Sharing Alliance (TOSA), South and Central Texas' Organ Procurement Organization (OPO) and were preserved in the VP.S ENCORE® for 4 (n = 2), 6 (n = 3), and 8 (n = 3) hours or were kept in static cold storage (SCS) (n = 3). After preservation, the hearts were placed in an isolated heart Langendorff model for reperfusion and evaluated for cardiac function. Results: The mean donor age was 37.82 ± 12.67 with the youngest donor being 19 and the oldest donor being 58 years old. SCS hearts mean weight gain (%) was -1.4 ± 2.77, while perfused at 4 h was 5.6 ± 6.04, perfused at 6 h 2.1 ± 6.04, and 8 h was 7.2 ± 10.76. Venous and arterial lactate concentrations were less than 2.0 mmol/L across all perfused hearts. Left ventricular contractility (+dPdT, mmHg/s) for 4 h (1,214 ± 1,064), 6 (1,565 ± 141.3), and 8 h (1,331 ± 403.6) were within the range of healthy human heart function. Thus, not significant as compared to the SCS group (1,597 ± 342.2). However, the left ventricular relaxation (mmHg/s) was significant in 6-hour perfused heart (p < 0.05) as compared to SCS. Gene expression analysis of inflammation markers (IL-6, IL-1ß) showed no significant differences between SCS and perfused hearts, but a 6-hour perfusion led to a downregulated expression of these markers. Discussion: The results demonstrate that the VP.S ENCORE® device enhances cardiac viability and exhibits comparable cardiac function to a healthy heart. The implications of these findings suggest that the VP.S ENCORE® could introduce a new paradigm in the field of organ preservation, especially for marginal hearts.

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 use either the open (nonpressurized) 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 to 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 Universal Limb Stasis System for Extended Storage (ULiSSES) device (closed, vertical perfusion system) to preserve forelimbs of Sus scrofa swine for 24 hours of subnormothermic perfusion compared with 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 subnormothermic modified Krebs-Henseleit solution. Physiological parameters were measured at the start and every 3 hours for 24 hours. Limbs were weighed before and after perfusion to compare weight gain. Edema and cellular integrity were evaluated using histopathology pre and post perfusion. RESULTS: Closed perfusion system showed superiority compared with 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 with 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 with an open perfusion system.

Characterizing and Tuning Perfusion Parameters Within an Innovative, Versatile Oxygenating Perfusion System.

The advantages of oxygenated perfusion are continuing to be demonstrated by many groups focused on improving the efficacy of tissue preservation for transplant, bioreactors for studies of basic tissue physiology, and closed-loop resuscitation. This work presents a novel and portable device that supplies oxygenated and pulsatile perfusion, both of which are regulated by a single pump-oxygenator component comprised of silicone tubes that are cyclically inflated/deflated with compressed oxygen. In this study, pump variables (oxygen supply pressure and length of a silicone tube) were evaluated against hydraulic elements that mimicked the vascular resistance of kidneys, livers, and hearts. The perfusion pressures, flow rates, and oxygenation rates produced by the device were characterized for all configurations of pump variables, and the pulse rates were tuned to improve performance. The device supplied perfusion pressures ranging from 3.5 to 109 mmHg, flow rates ranging from 1.4 to 71.8 mL min-1, and oxygenation rates up to 316.6 µmol min-1. From those results, it was determined that the device was capable of achieving perfusion parameters used in previous kidney, liver, and heart preservation studies. Ultimately, this research demonstrated the efficacy of a novel device that is designed to supply oxygenated perfusion across a range of applications.

Failure Pressures of Dural Repairs in a Porcine Ex Vivo Model: Novel Use of Titanium Clips Versus Tissue Glue.

OBJECTIVE: Endoscopic skull base surgery is advancing, and it is important to have reliable methods to repair the resulting defect. The objective of this study was to determine the failure pressures of 2 commonly used methods to repair large dural defects: collagen matrix underlay with fibrin glue and collagen matrix underlay with polyethylene glue, as well as a novel repair method: fascia lata with nonpenetrating titanium vascular clips. METHODS: The failure pressure of the 3 dural repairs was determined in a closed testing apparatus. Defects in porcine dura were created and collagen matrix grafts were used as an underlay followed by either fibrin glue (FG/CMG) or polyethylene glycol glue (PEG/CMG). A third condition using a segment of fascia lata was positioned flush with the edges of the dural defect and secured with titanium clips (TC/FL). Saline was infused to simulate increasing intracranial pressure (ICP) applied to the undersurface of the grafts until the repairs failed. RESULTS: The mean failure pressure of the PEG/CMG repair was 34.506 ± 14.822 cm H2O, FG/CMG was 12.413 ± 5.114 cm H2O, and TC/FL was 8.330 ± 3.483 cm H2O. There were statistically significant differences in mean failure pressures among the 3 repair methods. CONCLUSION: In this ex vivo model comparing skull base repairs' ability to withstand cerebrospinal fluid leak, the repairs that utilized PEG/CMG tolerated the greatest amount of pressure and was the only repair that exceeded normal physiologic ICP's. Repair methods utilizing glues generally tolerated higher pressures compared to the novel repair using clips alone.

Immediate Auditory Feedback is Superior to Other Types of Feedback for Basic Surgical Skills Acquisition.

OBJECTIVE: We examined the effect of timing and type of feedback on medical students' knot-tying performance using visual versus auditory and immediate versus delayed feedback. We hypothesized that participants who received immediate auditory feedback would outperform those who received delayed and visual feedback. METHODS: Sixty-nine first- and second-year medical students were taught to tie 2-handed knots. All participants completed 3 pretest knot-tying trials without feedback. Participants were instructed to tie a knot sufficiently tight to stop the "blood" flow while minimizing the amount of force applied to the vessel. Task completion time was not a criterion. Participants were stratified and randomly assigned to 5 experimental groups based on type (auditory versus visual) and timing (immediate versus delayed) of feedback. The control group did not receive feedback. All groups trained to proficiency. Participants completed 3 posttest trials without feedback. RESULTS: There were fewer trials with leak (p < 0.01) and less force applied (p < 0.01) on the posttest compared to the pretest, regardless of study group. The immediate auditory feedback group required fewer trials to achieve proficiency than each of the other groups (p < 0.01) and had fewer leaks than the control, delayed auditory, and delayed visual groups (p < 0.02). CONCLUSIONS: In a surgical force feedback simulation model, immediate auditory feedback resulted in fewer training trials to reach proficiency and fewer leaks compared to visual and delayed forms of feedback.

Method for three-dimensional visualization of neurodegeneration in cupric-silver stained serial rat brain slices.

The spatial distribution of neurodegeneration in brains is difficult to visualize when working from 2-D serial slices. In studies where repetitive operant behavior measurements are made over several weeks following organic solvent exposure, definitive evidence of degeneration in brain structures may have been significantly cleared by the time the tissue is prepared histologically. The only remaining evidence that injury has occurred may be nothing more than neuronal and cellular debris. By choosing stains that are specific for this type of residual and/or indicative of specific pathology, a 3-D representation of the spatial distribution of the neuronal and cellular debris fields within the organ can be highlighted and displayed. We present a method for visualizing the spatial distribution of neuronal degeneration that can result from low-level organic solvent exposure scenarios. A cupric-silver stain highly specific for neuronal degeneration is used to identify neuronal debris fields in 73 serial slices of brains of rodents that were exposed to toluene vapors. Serial brain sections stained with cupric-silver are scanned at 600 dpi using a gray-scale protocol. Using commercially available software, scans are assembled into 3-D images showing both topographical and internal anatomical details. The reassembled images are further processed into stereo pairs. Gray-scale scans are compared to the original sections to establish gray-scale ranges for healthy and damaged tissue and artifact staining.

Failure pressures of three rhinologic dural repairs in a porcine ex vivo model.

BACKGROUND: The objective of this work was to determine the failure pressures of 3 commonly performed repair techniques of 5-mm dural defects in a controlled setting. METHODS: This was a pig dura ex vivo study. A testing apparatus was fabricated to study failure pressures of 3 different repairs in a porcine model. Five-millimeter (5-mm) dural defects were created and plugged with autologous mucosa/Tisseel (MT) (Baxter International Inc.), fat graft (FG), and bath plug (BP) techniques. Saline solution was infused at 30 mL/hour to apply unidirectional pressure to the repair until failure occurred. Five dural repairs were performed for each arm of the trial, for a total of 15 trials. RESULTS: The mean failure pressure of the MT repair was 4.3 ± 1.9 cmH2 O, of the FG repair was 10.9 ± 4.2 cmH2 O, and of the BP repair was 20.7 ± 2.2 cmH2 O. Differences among mean failure pressures were statistically significant. CONCLUSION: The BP repair showed significantly higher tolerances for pressure than the other 2 repairs. The BP repair was the only technique that withstood adult physiologic supine cerebrospinal fluid (CSF) pressure.

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.

The application of fluidics technology for organ preservation.

A prototype design of a portable, pulsatile, perfusion preservation device based on a novel application of fluidics technology was tested to evaluate its ability to oxygenate preservation solution and to examine the relationship between organ resistance, perfusion pressure, and perfusion flow characteristics. The effects of organ resistance on pulse rate, perfusion pressure, and perfusion flow were modeled. Interstitial PO2 in canine hearts stored at 4 degrees C for 12 hours in the fluidics device (n = 5) and in static hypothermic storage (n = 5) was also compared. Increasing outflow resistance did not have an effect on operating frequency of the fluidics actuator. Perfusion pressure rose as outflow resistance was increased, and the flow of preservation solution decreased proportionately. The PO2 of the preservation solution increased to 300 mm Hg in two hours and reached a plateau that exceeded 400 mm Hg within six hours. The aortic flow profile during pulsatile perfusion resembled a square wave function with a mean pulse duration of 0.30 +/- 0.05 seconds. Oxygen delivery by the fluidics perfusion device exceeded the oxygen requirements of the hypothermically preserved organs at all resistance levels. Initial interstitial PO2 in the hearts of both groups was greater than 150 mm Hg. In perfused hearts, PO2 declined 30% by the 12th hour, whereas complete depletion of oxygen was noted in the static storage group within six hours. The fluidics organ perfusion/transport apparatus weighs less than 18 kg, uses no electrical power, and can operate continuously for 10 to 12 hours expending 780 L of oxygen.

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.

Novel portable hypothermic pulsatile perfusion preservation technology: Improved viability and function of rodent and canine kidneys.

BACKGROUND: A reliable, portable, cost effective device for perfusion preservation of donor organs remains elusive. A portable, organ perfusion device design for hypothermic, machine perfusion (HMP) that successfully supported rodent kidneys for 24 hours was evaluated in canine kidneys. MATERIAL/METHODS: Freshly recovered rodent and canine kidneys were subjected to 24 hours of HMP or static storage (SS). Organ perfusion and cell membrane integrity were examined in HMP and SS rodent kidneys. Canine kidney function was evaluated in an isolated organ preparation. Oxygen consumption (OC), renal vascular resistance (RVR), and glomerular filtration rates (GFR) were compared. RESULTS: Perfusion pressure during HMP averaged 16 mmHg with oxygen delivery roughly 4 fold greater than the canine kidney's metabolic requirements. Following 24 hours of preservation, RVR was significantly elevated while OC and GFR were significantly lower in the SS organs compared to the HMP stored or freshly recovered kidneys. CONCLUSIONS: This organ preservation technology appears to provide an excellent preservation environment for kidneys such that post-transplant delayed graft function is minimized. Additionally, compared to current machine perfusion systems, the preservation system described in this work is significantly reduced in size, weight, and complexity, such that total portability may be possible.