D. De

Electroreduction of Nitrate and Nitrite Ion on a Platinum‐Group‐Metal Catalyst‐Modified Carbon Fiber Electrode Chronoamperometry and Mechanism Studies

The mechanisms of nitrate and nitrite ion electroreduction on a carbon fiber electrode modified with platinum group metal catalyst are studied. Chronoamperometry studies reveal that two different mechanisms exist in two cathodic regions. A plot of log i vs. E reveals the presence of adsorption pseudocapacitance and is supported by impedance measurement at the electrode/solution interface. In the −600 to −800 mV (Ag/AgCl) potential region, the Tafel slope for nitrate ion reduction varies between ca. 221 and 236 mV/dec, while in the −925 to −1000 mV (Ag/AgCl) region, the slope was ca. 80 to 85 mV/dec. For nitrite ion reduction, the Tafel slope was ca. 232 to 250 mV/dec in the −500 to −700 mV (Ag/AgCl) potential region, and between −925 and −1000 mV (Ag/AgCl), the slope was between 80 and 86 mV/dec. The adsorption of nitrogen dioxide on the electrode surface was determined to be the rate‐limiting step in both potential regions. The present results indicate that although the first step of nitrate reduction in neutral solution takes a similar path as nitrate/nitrite ion reduction in alkaline solution, the rest of the mechanistic pathways are different in alkaline or acidic solution.

Cyclic Voltammetric Studies of Nitrate and Nitrite Ion Reduction at the Surface of Iridium‐Modified Carbon Fiber Electrode

The electroreduction of nitrate and nitrite on iridium-deposited carbon fiber electrode in aqueous sodium perchlorate solutions of pH 7 was studied using cyclic voltammetric techniques. Results obtained on the modified electrode support a two-step nitrate reduction mechanism in which nitrate is first reduced to nitrite at E peak = -800 mV (Ag/AgCl) during the negative scan and further reduced to ammonia at E peak = -775 mV (Ag/AgCl) during the anodic scan. An oxidation peak for the unreduced nitrite was observed at -300 mV (Ag/AgCl). A Tafel slope of approximately 178 mV/dec and a pseudo-first-order rate constant of k° = 4.18 x 10 -7 cm s -1 were determined for the cathodic reduction peak while Tafel slope of 18.9 mV/dec and k° = 2.62 X 10 -23 cm s -1 were obtained for the anodic reduction peak. The Tafel slopes obtained also support the two-step mechanism. The results obtained strongly suggest a minimal effect of pH on nitrate reduction in the pH range of 2.0-13.0 in NaClO 4 solution at the surface of iridium-coated carbon fiber electrode.

Emboli from an extraluminal blood Flow hollow fiber oxygenator with and without an arterial filter during cardiopulmonary bypass in a pig model

&NA; The effect of an arterial filter on visceral emboli was quantified with autologous indium‐111 labeled platelets (INPLT) during cardiopulmonary bypass (CPB) in Yorkshire pigs. Biodistribution of INPLT was determined in 12 control pigs (30‐35 kg, unoperated control [n = 6] and sham operated control [n = 6]). CPB was carried out with (n = 6) and without (n = 6) an arterial filter in 12 pigs at a flow rate of 2.5‐3.5 L/min. Platelets labeled with In‐111 tropolone (650‐780 &mgr;Ci) were injected intravenously 24 hr before CPB. All pigs were systemically heparinized (activated coagulation time > 400 sec); CPB was instituted with a roller pump, an extraluminal blood flow oxygenator (Bentley Univox, 1.8 m2), and an arterial filter (0.25 m2) and continued for 3 hr. Platelet kinetics, pooling, and counts were monitored by a Geiger probe and a Coulter counter. The thrombi in the oxygenator and arterial filter and emboli in viscera and brain were imaged with a gamma camera and measured with an ion chamber and gamma counter. Percentage of INPLT (mean ± SD) in organs, tissues, and components of the circuit in four groups of pigs was calculated. Flow cytometry with antibodies to CD61 (GPIIIa) and CD62P (GMP‐140: control) of porcine platelets was carried out with blood samples taken before, during, and after CPB for estimation of circulating platelet aggregates and platelet microparticles. Pulmonary, renal, cardiac, and cerebral emboli in pigs undergoing CPB with and without a filter were similar (p < 0.1). The amount of filter adherent thrombi was small (0.04 ± 0.01%); oxygenator adherent thrombus in both groups was similar (p < 0.1). Emboli were found in the cerebral medulla, hippocampus, and posterior cerebral cortex in both groups. During CPB, the arterial filter functioned minimally as a trap for platelet thrombi detached from the oxygenator and circulating emboli. Flow cytometry of blood demonstrated the shift of equilibria from single platelets to platelet aggregates and microparticles during CPB and their gradual reversal to single platelets after CPB; the loosely adherent emboli dis‐aggregated and further shifted these equilibria to single platelets and smaller aggregates, probably through the action of endogenous nitric oxide and prostacyclin. The emboli were trapped in organs and tissues and microparticles were sequestered by the reticuloendothelial system. ASAIO Journal 1996;42:1010‐1018.

Reduction of neutrophil margination by L-arginine during hypothermic cardiopulmonary bypass in a pig model.

Nitric oxide generation by L-arginine (2 mg/kg/min) infusion during cardiopulmonary bypass (CPB) increases blood flow to all organs and reduces cytokine induced organ damage by reducing the level of marginating neutrophils (Ns). The N-trapping in the oxygenator (OX), arterial filter (AF), cardiotomy reservoir (CR), and N-margination were quantified with indium 111 labeled autologous neutrophils (INN) in nine groups of 40 Yorkshire pigs (30-35 kg). Cardiopulmonary bypass (180 min or 90 min CPB, 90 min reperfusion) was carried out at 2.5-3.5 L/min and at two temperatures (18 degrees C, 28 degrees C). The INN (650-780 microCi) was administered intravenously 15 mins before CPB. All pigs received heparin systemically (activated coagulation time > 400 secs); CPB was instituted with a roller pump, OX (Univox 1.8 m2), AF (0.25 m2), and CR (BCR-3500, Bentley Lab, Irvine, CA). The INN distribution in the device (OX, AF, CR) and organs was imaged with a gamma camera and measured with an ion chamber and a gamma counter. The LA infusion decreased N-trapping, estimated as the percent of injected INN (mean +/- standard deviation), in OX from control (2.7 +/- 2.02)% to (0.94 +/- 0.29)%, and margination in lung from control (48 +/- 4)% to minimal levels (23 +/- 2)% (p < 0.01). In the CPB reperfusion group, a beneficial effect was observed at LA low dose and toxicity of higher N-margination at 15 mg/ kg/min. Neither CPB temperature nor Leumedin affected N-margination significantly.

Reduction of platelet thrombi and emboli by L-arginine during cardiopulmonary bypass in a pig model

We wanted to test the hypothesis that NO generation by L-arginine (LA) infusion will be beneficial in increasing blood flow to all organs to counteract the process of global ischemia during cardiopulmonary bypass (CPB) and to reduce platelet emboli by platelet inhibition. The effect of LA infusion on NO formation, vasodilation, and reduction of thromboembolic burden in organs and tissues after CPB was quantified with In-111-labeled autologous platelets in two major groups: 180 minutes CPB (CPB) and 90 minutes CPB plus 90 minutes reperfusion (RP). Platelets labeled with In-111 tropolone (650–780 μCi) were administered 24 hours before CPB and LA infusion (bolus, 10 mg/kg and infusion at 2 mg/kg/min, 21 pigs for 180 minutes CPB) in 8 groups of 30 Yorkshire pigs (30–35 kg, 6 pigs; LA 2 mg/kg/min, 3 pigs; sham-thoracotomy control, 6 pigs; unoperated control, 6 pigs). Two groups of 9 pigs (control CPB, 6 pigs; LA 2 mg/ kg/min, 3 pigs) underwent 90 minutes of CPB and 90 minutes of reperfusion. All pigs were heparinized (ACT >400 seconds); CPB was instituted with a roller pump, an oxygenator (OX: Bentley Univox, 1.8 m2), and an arterial filter (AF: 0.25 m2, Bentley) at a blood flow of 2.5–3.5 1/min. Radioactive thrombi in OX and AF and emboli in viscera, brain, and connective tissues were imaged with a gamma camera and were finally measured with an ion chamber and a gamma counter. The percent of injected platelets (mean ± SD) in the organs and tissues of all pigs was calculated. Cerebral emboli were mapped in 25 regions of both hemispheres of pig brain. Flow cytometry with antibodies to CD61 (GPIIIa) and CD62P (GMP-140: control) of porcine platelets was carried out with blood samples taken before, during, and after CPB. Coronary bypass with LA infusion decreased the amount of adherent thrombi in OX and AF (p < 0.07). The embolic burden in brain and lung also decreased. Regional cerebral mapping of In-111 platelets showed reduced emboli in almost all regions, including the medulla, hippocampus, and posterior cerebral cortex in both LA-treated groups. Flow cytometry of blood samples demonstrated the shift of equilibria from single platelet to platelet-aggregate-microparticle during CPB and steady-state level after the first 5–10 minutes of initiation of CPB. The L-arginine infusion reduced thrombi and emboli during CPB in the pig model.