A new feedback neural network with supervised learning

A model is introduced for continuous-time dynamic feedback neural networks with supervised learning ability. Modifications are introduced to conventional models to guarantee precisely that a given desired vector, and its negative, are indeed stored in the network as asymptotically stable equilibrium points. The modifications entail that the output signal of a neuron is multiplied by the square of its associated weight to supply the signal to an input of another neuron. A simulation of the complete dynamics is then presented for a prototype one neuron with self-feedback and supervised learning; the simulation illustrates the (supervised) learning capability of the network.

Arterialization of the liver. III. Influence of systemic and portal pressure gradients following heterotopic partial liver transplantation

An acute study was designed to compare blood pressures across a heterotopically transplanted partial liver graft using arterialized and nonarterialized models. Eight partial liver transplants (PLT) were done in each group, using Wistar rats. The data gathered from them are the basis for the results obtained herein. Whereas there was no significant difference (P greater than 0.01) in inflow, outflow, or the pressure difference across the PLT between nonarterialized and arterialized groups, host portal venous pressures were significantly higher (P less than 0.01) in the arterialized group. A 1 mm arteriovenous fistula (AVF) was used to arterialize the PLTs in this study. It was proved that arterializing a PLT using a 1 mm AVF did not alter the pressure difference across the transplanted liver compared with the situation in the nonarterialized setting.

Arterialization of the liver. II. Systemic pressure gradients in rats following variously sized arteriovenous fistulae

Four groups (I, II, III, and IV) of six Wistar rats each were studied to elucidate the blood pressure changes following creation of arteriovenous fistulae (AVF) of diameters 1, 2, and 3 mm (groups II, III, and IV, respectively). Group I comprised normal rats with no AVF. Blood pressures were recorded in the carotid and femoral arteries, the femoral and portal veins, the right atrium, and the inferior vena cava (IVC) at renal vein (RV) and common iliac vein (CIV) levels. We found that AVF size did not disturb baseline carotid arterial or portal venous pressures (P greater than 0.01), but the femoral arterial pressures fell increasingly (P less than 0.01). On the other hand, right atrial pressure and that of IVC at RV and CIV levels rose substantially with increasing diameters of AVF (P less than 0.01). It was concluded that an AVF of 1 mm diameter least upset the normal blood pressures in the vessels examined.

Effect of arteriovenous fistula size on arterialized and host livers in rats

In studying the hemodynamic relationship and behavior of peak blood flow indexes at different sizes of arteriovenous fistulas (AVF) using arterialized partial liver transplants (PLT), 96 male Wistar rats served as donors and recipients of heterotopic PLT in an acute phase study using ether anesthesia. AVF of 1, 2, and 3 mm were compared with a control group (0 mm) along the "index of peak perfusion rate" of blood flow, the dependent variable. We found that with increasing AVF sizes, a progressive fall in the peak blood flow in the host livers (P less than 0.01, r = -0.51) and a similar rise in the same index in the graft livers (P less than 0.01, r = +0.76) were documented. Also noted was a gradual fall in the cardiac pulsatility component of perfusion to both host and graft livers at AVF sizes of 2 and 3 mm. The same component of perfusion to host and graft livers was best at AVF size of 1 mm. It was concluded that a 1-mm AVF provided the best degree of arterialization to a PLT.

Sufentanil disposition during cardiopulmonary bypass

In order to investigate the ability of a computer-assisted continuous infusion (CACI) system to maintain constant plasma levels of sufentanil during cardiopulmonary bypass (CPB) using pharmacokinetic data derived from healthy surgical patients to determine the infusion rate, ten patients were anaesthetized with diazepam, enflurane and oxygen until ten minutes prior to the expected time of initiation of CPB. At that point, an infusion of sufentanil, aimed to reach a central compartment concentration of 5 ng.ml-1, was started via CACI. Plasma concentrations of sufentanil, haematocrit, total protein and albumin concentrations, and nasopharyngeal and CPB inflow temperatures were obtained at predetermined intervals before and up to 90 min after the initiation of CPB. Plasma concentrations of sufentanil reached 3.8 +/- 0.4 ng.ml-1 before CPB and approached the 5.0 ng.ml-1 set point (4.7 +/- 0.4 ng.ml-1) over the 90 min of CPB. In conclusion, our results show that it is possible to obtain stable plasma levels of sufentanil on CPB using a pharmacokinetically driven infusion scheme; however, our data suggest that use of such a system may lead to accumulation of drug during CPB.

Effects of preoperative calcium entry blocker therapy on alpha-adrenergic responsiveness in patients undergoing coronary revascularization

Calcium entry blocking drugs (CaEBs) produce vasodilation and, in high doses, modify alpha adrenergic receptor function. Previous laboratory data suggested that CaEBs might alter the response to alpha-adrenergic stimulation. The authors tested the hypothesis that CaEB therapy altered alpha-adrenergic responsiveness in patients chronically treated with CaEBs. Twenty-six consenting patients with coronary artery disease were given a phenylephrine challenge before anesthesia induction and during cardiopulmonary bypass while the aorta was cross-clamped. A log dose response curve was constructed for each patient, and the ED30 (dose producing 30% increase in systemic vascular resistance) was calculated. Nine patients not treated with CaEB served as controls, and 17 patients were treated with nifedipine (n = 7) or diltiazem (n = 10). Mean ED30 was increased approximately three-fold in the CaEB treated groups compared to the control group. However, there was no statistical difference in the ED30 or phenylephrine dose response slopes between CaEB treated and untreated patients. In awake patients, ED30 correlated with nifedipine levels (R = 0.953, P = 0.01). There was a significant (P less than .02) shift in the ED30 from prior to anesthesia to during aortic cross-clamp and cardiopulmonary bypass; ED30 was approximately 50% less and correlated with CaEB level (R = 0.713, P = 0.03). Hemodynamic variables were not different between groups at any interval. Our data suggest that vascular responsiveness to phenylephrine in patients treated with CaEBs is diminished, but similar to that in untreated patients. Vascular responsiveness decreases in awake patients with increasing nifedipine levels.

Regulation of bovine adipose tissue metabolism during lactation. 3. Adaptations of hormone-sensitive and lipoprotein lipases

Activity of lipases in adipose tissue during pregnancy and lactation was investigated in Holstein cows producing 5950 to 10,000 kg milk per 305 d. Activity of cytoplasmic lipoprotein lipase per gram of tissue was 97, 78, 140, 162, 179, and 235% of 30 d prepartum at -15, 15, 30, 60, 180, and 349 d about calving in yr 1. In yr 2, lipoprotein lipase per gram was 100, 259, 838, 791, and 430% of -30 d at -15, 30, 60, 120, and 180 d. Adaptations in activity per milligram cytoplasm protein were similar to those per gram tissue. Hormone-sensitive lipase per milligram protein was 161, 251, 114, 126, and 252% of -30 d when measured at 30, 60, 120, 180, and 240 d postpartum. Activity per gram of tissue responded similarly to the lactation state. Lipoprotein lipase is thus not a large contributor to the peripartum bovine adipose adaptation but is important in reattainment of body composition in mid and late lactation. Hormone-sensitive lipase is also increased during peak and midlactation. The pattern of elevated activity of these oppositely directed lipases reflects the dichotomous forces of milk fat production and body fat recovery acting on adipose tissue of lactating heifers.