Extracorporeal liver perfusion using human and pig livers for acute liver failure.

BACKGROUND: Patients with fulminant hepatic failure (FHF) often die awaiting liver transplantation. Extracorporeal liver perfusion (ECLP) has been proposed as a method of "bridging" such patients to transplantation. We report the largest experience to date of ECLP using human and porcine livers in patients with acute liver failure. METHODS: Patients with FHF unlikely to survive without liver transplantation were identified. ECLP was performed with human or porcine livers. Patients underwent continuous perfusion until liver transplantation or withdrawal of support. Two perfusion circuits were used: direct perfusion of patient blood through the extracorporeal liver and indirect perfusion with a plasma filter between the patient and the liver. FINDINGS: Fourteen patients were treated with 16 livers in 18 perfusion circuits. Nine patients were successfully "bridged" to transplantation. ECLP stabilized intracranial pressure (ICP) and cerebral perfusion pressure (CPP). Arterial ammonia levels fell from a median of 146 to 83 micromol/liter within 12 hr and this reduction was maintained at least 48 hr. Pig and human ECLP lowered ammonia levels equally. Serum bilirubin levels also fell from a median of 385 to 198 micromol/liter over the first 12 hr but the response was not sustained as well with porcine livers. There was no immunological benefit to using the the filtered perfusion circuit. INTERPRETATION: These data demonstrate that ECLP is safe and can provide metabolic support for comatose patients with fulminant hepatic failure for up to 5 days. While labor and resource intensive, this technology is available to centers caring for patients with acute liver failure and deserves wider evaluation and application.

Extracorporeal support with a cadaver liver as a bridge to transplantation.

Extracorporeal liver perfusion (ECLP) has been used for detoxifying blood in patients in class IV hepatic encephalopathy. Palliation of the moribund patient utilizing extracorporeal devices with cross-circulation of a cadaver liver has been documented for over three decades. Common problems associated with this procedure which appear in the literature include cadaver liver distention, increased resistance to blood flow, and limited time of extracorporeal support due to cadaver liver failure. This report summarizes the experiences of the perfusion team in utilizing an extracorporeal circuit with an otherwise nontransplantable cadaveric liver, to support the decompensating hepatic patient as a bridge to transplantation. Between January and July 1992, three patients were supported for hepatic failure with ECLP. Two patients were placed on ECLP with a modified circuit containing two positive displacement pumps and one centrifugal pump. The third patient was placed on ECLP with a circuit that contained two centrifugal pumps and one positive displacement pump. Patient age ranged from 6 to 38 years and length of support ranged from 24 to 72 hours. In all three patients, a centrifugal pump was placed in the suprahepatic inferior vena cava line to facilitate cadaver liver drainage and decompression. Intensive monitoring of both patient and cadaver liver hemodynamics, hepatic function, and hematological status was performed. All three patients were successfully weaned from ECLP. Two patients received successful orthotopic liver transplantation. The third died of complications unrelated to ECLP after support was discontinued.(ABSTRACT TRUNCATED AT 250 WORDS)

Variants of self-organizing maps.

Self-organizing maps have a bearing on traditional vector quantization. A characteristic that makes them more closely resemble certain biological brain maps, however, is the spatial order of their responses, which is formed in the learning process. A discussion is presented of the basic algorithms and two innovations: dynamic weighting of the input signals at each input of each cell, which improves the ordering when very different input signals are used, and definition of neighborhoods in the learning algorithm by the minimal spanning tree, which provides a far better and faster approximation of prominently structured density functions. It is cautioned that if the maps are used for pattern recognition and decision process, it is necessary to fine tune the reference vectors so that they directly define the decision borders.

What Perturbs the ggrdgr Rings of Uranus?

The gamma and delta rings have by far the largest radial perturbations of any of the nine known Uranian rings. These two rings deviate from Keplerian orbits, having typical root-mean-square residuals of about 3 kilometers (compared to a few hundred meters for the other seven known rings). Possible causes for the perturbations include nearby shepherd satellites and Lindblad resonances. If shepherd satellites are responsible, they could be as large as several tens of kilometers in diameter. The perturbation patterns of the gamma and delta rings have been examined for evidence of Lindblad resonances of azimuthal wave number m = 0, 1, 2, 3, and 4. The beta ring radial residuals are well matched by a 2:1 Lindblad resonance. If this represents a real physical phenomenon and is not an artifact of undersampling, then the most plausible interpretation is that there is an undiscovered satellite orbiting 76,522 +/- 8 kilometers from Uranus, with an orbital period of 15.3595 +/- 0.0001 hours and a radius of 75 to 100 kilometers. Such a satellite would be easily detected by the Voyager spacecraft when it encounters Uranus. The 2:1 resonance location is 41 +/- 9 kilometers inside the delta ring, which makes it unlikely that the resonance is due to a viscous instability within the ring. In contrast, no low-order Lindblad resonance matches the gamma ring perturbations, which are probably caused by one or more shepherd satellites large enough to be clearly visible in Voyager images.