In an effort to bring total liquid ventilation (TLV) to clinical application, a prototype ventilator with 4 single piston pumps and 4 conventional membrane oxygenators, simply designed and easily controlled, was tested in an in vivo ful- sized sheep model. TLV was performed in 3 anesthetized and paralyzed sheep (weight range 54–56 Kg). Once all the inclusion criteria were met during gas ventilation (PaO2 > 400mmHg, PaCO2 between 30–45mmHg, and MAP 60 mmHg), liquid ventilation process was started giving an initial fill volume of 30 ml/kg of pre-warmed PFC (FC77), followed by a liquid tidal volume. Respiratory rate was set as 5 breaths per minute, and an I:E ratio of 1:2 using a square wave flow pattern during both phases of ventilation was used; Arterial blood gas; hemoglobin; oxygen saturation; SvO2; cardiac output; systemic and pulmonary arterial blood pressure; heart rate; ventilator pressure, tidal volume, and airway pressure data w assessed and recorded at the beginning of TLV and then every hour. The ventilator's CO2 removal efficiency was assessed by sampling the PFC before and after the oxygenators and calculating the normalized CO2 removal efficiency by the formula: [PPFCCO2in-PPFCCO2out]/ [PPFCCO2in]. This system was tested for 3 hours with stable PaCO2 and PaO2 (see figures below) and no hemodynamic impairment. An averaged CO2 removal efficiency of 80% and an averaged level of 676 mmHg of PFC PO2 were obtained by the 4 membrane oxygenators with a countercurrent sweep gas of 100% oxygen at 5 L/min. No evidence of fluorothorax was observed at the chest gross examination at the end of the experiments; These data suggest the potential of this prototype to support removing CO2 and oxygenating perfluorocarbons during total liquid ventilation in a full sized animal model.Figure

The preparation, characterization, and preliminary biomedical application of various nitric oxide (NO)-releasing fumed silica particles (0.2-0.3 microm) are reported. The tiny NO-releasing particles are synthesized by first tethering alkylamines onto the surface of the silica using amine-containing silylation reagents. These amine groups are then converted to corresponding N-diazeniumdiolate groups via reaction with NO(g) at high pressure in the presence of methoxide bases (e.g., NaOMe). N-Diazeniumdiolate groups were found to form more readily with secondary amino nitrogens than primary amino nitrogens tethered to the silica. Different alkali metal cations of the methoxide bases, however, have little effect on the degree of N-diazeniumdiolate formation. The N-diazeniumdiolate moieties attached on the silica surface undergo a primarily proton-driven dissociation to NO under physiological conditions, with an "apparent" reaction order somewhat greater than 1 owing to local increases in pH at the surface of the particles as free amine groups are generated. The rates of N-diazeniumdiolate dissociation are further related to the parent amine structures and the pH of the soaking buffer. The N-diazeniumdiolate groups also undergo slow thermal dissociation to NO, with zero-order dissociation observed at both -15 and 23 degrees C. It is further shown that the resulting NO-releasing fumed silica particles can be embedded into polymer films to create coatings that are thromboresistant, via the release of NO at fluxes that mimic healthy endothelial cells (EC). For example a polyurethane coating containing 20 wt % of NO-releasing particles prepared with pendant hexane diamine structure (i.e., Sil-2N[6]-N(2)O(2)Na) is shown to exhibit improved surface thromboresistivity (compared to controls) when used to coat the inner walls of extracorporeal circuits (ECC) employed in a rabbit model for extracorporeal blood circulation.

Introduction: NO flux for normal endothelium is 4.0 × 10−10mol/min*cm2. Diazeniumdiolates are typical NO release agents that when incorporated into d matrix polymer prevent platelet adherence and consumption during extracorporeal circulation (ECC). Determining the NO flux necessary to prevent platelet activation during ECC would obviate the need for systemic heparinization. Methods: Two experimental models were used to test a diamino-silica NO donor compound. Initial studies were performed using our rabbit model of ECC. Once efficacy of the coating was demonstrated a 24 hr swine model was used to determine the relationship between circuit NO flux and platelet consumption. Blood samples for both studies included arterial blood gases, platelet counts and platelet aggregometry. NO fluxes and SEMs were performed on all circuits.Figure: Fumed Slica Controls vs ND-Doped in Rabbit model of ECCFigure: Platelet Consumption vs NO Flux in a 24 hr Swine ModelResults: In the rabbit model, the NO-doped circuits demonstrated a trend toward less platelet consumption while SEMs showed less adhesion In the 24 hr swine model platelet consumption was less than expected for the first 12 hours until NO flux fell close to 4.0 × 10−10mol/min*cm2. Conclusion: Maintenance of NO flux greater than endothelial level is a critical component in the development of thromboresistive biomaterials for extracorporeal circulation.

Nitric oxide (NO) releasing silicone rubbers (SR) are prepared via a three-step reaction scheme. A diamino triaminoalkyltrimethoxysilane crosslinker is used to vulcanize hydroxyl terminated polydimethylsiloxane (PDMS) in the presence of ambient moisture and a dibutyltin dilaurate catalyst so that the respective diamine triamine groups are covalently linked to the cured SR structure. These amine sites are then diazeniumdiolated, in situ, when the cured SR is reacted with NO at elevated pressure (80 psi). Although nitrite species are also formed during the NO addition reaction, in most cases the diazeniumdiolated polymer is the major product within the final SR matrix. Temperature appears to be the major driving force for the dissociation of the attached diazeniumdiolate moieties, whereas the presence of bulk water bathing the SR materials has only minimal effect on the observed NO release rate owing to the low water uptake of the SR matrices. The resulting SR films/coatings release NO at ambient or physiological temperature for up to 20 d with average fluxes of at least 4 x 10(10) mol x cm(-2) x min(-1) (coating thickness > or = 600 microm) over first 4 h, comparable to the NO fluxes observed from stimulated human endothelial cells. The NO loading and concomitant NO release flux of the SR material are readily adjustable by altering the diamine triamine loading and film/coating thickness. The new NO releasing SR materials are shown to exhibit improved thromboresistance in vivo, as demonstrated via reduced platelet activation on the surface of these polymers when used to coat the inner walls of SR tubings employed for extracorporeal circulation in a rabbit model.

Purpose: Nitric oxide (NO) release from vascular endothelium plays a role in preventing both platelet activation and aggregation. NO-releasing polymers represent one strategy for preventing platelet activation and adhesion to artificial surfaces. One class of NO-releasing polymer relies on a surface-bound diamino-cross linking agent (DACA) onto which NO has been coupled. Our goal was to demonstrate that this agent when applied to an extracorporeal circuit would reduce thrombosis and platelet consumption. Methods: Unheparinized New Zealand white rabbits were cannulated in the superior vena cava. Venovenous extracorporeal circulation was carried out for 4 hours at flow rates of 100–120ml/min. Three surfaces were evaluated: untreated silicone rubber (n=2), silicone rubber coated with NO-loaded DACA (n=3), and silicone rubber coated with DACA in the absence of NO (n=4). Platelet counts and fibrinogen levels were performed hourly. The experiment concluded at the end of 4 hours or upon thrombosis of the circuit. The circuits were rinsed and preserved for scanning electron microscopy (SEM). Results: No circuit thrombosis or platelet consumption occurred in the NO-releasing tubing. Furthermore, SEM's of these circuits showed adherent but morphologically normal, non-activated platelets. All DACA-coated non-NO and plain silicone circuits were associated with significant platelet consumption and displayed greater platelet aggregates with fibrin stranding on SEM. Additionally, all four DACA coated non-NO loaded circuits thrombosed prior to the conclusion of the experiment. Fibrinogen consumption occurred irrespective of surface type. The use of nitric oxide releasing compounds in extracorporeal circuits reduces artificial surface-associated platelet consumption. It also reduces the rate of circuit thrombosis, potentially decreasing the need for systemic heparinization.

Purpose: We have reported the nonthrombogenic properties of surface NO in a system which leached the active molecule. A new polymer, which releases only NO, relies on a surface-bound diamino-cross linking agent (DACA) onto which NO has been coupled. We evaluated this surface in our standard model. Methods: Unheparinized New Zealand white rabbits were cannulated in the superior vena cava. Venovenous extracorporeal circulation was carried out for 4 hours at flow rates of 100–120ml/min. Three silicone rubber surfaces were evaluated: untreated (n=2), DACA coated alone (n=4), and DACA loaded with NO (n=3). Platelet counts and fibrinogen were measured hourly. The experiment concluded at the end of 4 hours or upon thrombosis of the circuit. The circuits were rinsed and preserved for scanning electron microscopy (SEM). Results: No circuit thrombosis or platelet consumption occurred in the NO-releasing tubing. SEM's of these circuits showed adherent but morphologically normal, non-activated platelets. All control circuits caused significant platelet consumption and displayed greater platelet aggregates with fibrin stranding on SEM. All four DACA coated controls thrombosed prior to the conclusion of the experiment. Fibrinogen consumption occurred irrespective of surface type. This polymer has the nonthrombogenic properties of NO release without leaching other molecules.