Development of a central matching system for the allocation of cadaveric kidneys: a simulation of clinical effectiveness versus equity

OBJECTIVES

1) To develop a computer-based simulation to prospectively study the impacts of explicitly incorporating different equity criteria into the process of allocating kidneys to recipients, given the scarcity of this resource. 2) To assess the tradeoffs between systems that allocate kidneys based only on medical criteria, systems that allocate kidneys based only on equity criteria, and systems that consider both medical and equity criteria.

METHODS

A computer-based simulation was developed that describes the flows of patients and kidneys. This model provides information at various time points about the number of patients in the system who are awaiting transplants, the number of kidneys available for transplantation, the number of transplantations performed for each matching algorithm, and the number of kidneys discarded (when applicable), as well as the means and standard deviations of the HLA-match scores, number of days from registration to transplantation, and number of days (from registration) of those who are still waiting for transplants. Five different matching algorithms were compared, ranging from determination of the allocation by a single medical criterion (i.e, HLA match) to determination by a single equity criterion (i.e., relative position in the waiting queue). The remaining algorithms represent different strategies of weighting these two considerations. Estimates regarding the main parameters of the model were derived utilizing data collected through the Multiple Organ Retrieval and Exchange Programme of Ontario, Canada.

RESULTS

The simulation was set to run for a period of ten years. A tradeoff between graft survival (or improved HLA matching) and equal treatment of patients regardless of their likelihood to benefit was found. It is clear that an algorithm that allocates kidneys based only on temporal location of patient on the waiting list is likely to be unacceptable because of the very poor average HLA-match scores that it yields. Pool size was found to be a major determinant in the attainment of optimal matching from a medical perspective.

CONCLUSIONS

1) The final choice about any allocation algorithm to be used requires that a value judgment be made, i.e., how great a reduction in HLA-match score should be traded in order to improve equity score (or vice versa). 2) A computer-based simulation model is a feasible way to prospectively test the impact of any given allocation algorithm on any given system.

Selection of guide sequences that direct efficient cleavage of mRNA by human ribonuclease P

Any RNA, when in a complex with another oligoribonucleotide known as an external guide sequence (EGS), can become a substrate for ribonuclease P. Simulation of evolution in vitro was used to select EGSs that bind tightly to a target substrate messenger RNA and that increase the efficiency of cleavage of the target by human ribonuclease P to a level equal to that achieved with natural substrates. The most efficient EGSs form transfer RNA precursor-like structures with the target RNA, in which the analog of the anticodon stem has been disrupted, an indication that selection for the optimal substrate for ribonuclease P yields an RNA structure different from that of present-day transfer RNA precursors.

66A-078:a kappa-opiate receptor agonist for amelioration of spinal spasticity

The effect and mechanism of kappa opiate receptor agonist and high-frequency electrostimulation of acupoints in treating spinal spasticity were studied. The spinal spastic models were made by gradual mechanical compression on the cervical spinal cord of rabbits. 24 prepared rabbits were divided into 3 groups randomly, and each group with 8 rabbits was given intrathecally kappa-receptor agonist 66A-078, kappa-receptor antagonist +66A-078 and normal saline respectively. The degree of spasticity was quantified by both clinical score and electrophysiological examinations. The result showed that the spasticity was markedly inhibited by intrathecal injection of 66A-078 and that the kappa-receptor antagonist (naloxone) reversed this effect. We can infer that the antispastic effect of 66A-078 is mediated by kappa-receptors. This result is helpful in explaining the immediate antispastic mechanism of high-frequency electrostimulation of acupoints discussed in previous study.

Human RNaseP RNA and nucleolar 7-2 RNA share conserved 'To' antigen-binding domains

RNase P in both prokaryotes and eukaryotes is a ribonucleoprotein that cleaves tRNA precursors to generate the 5' termini of the mature tRNAs. Many patients with autoimmune diseases produce antibodies against a 40 kDa protein (designated To or Th antigen) which is an integral component of eukaryotic RNaseP as well as nucleolar 7-2 RNP which is identical to the mitochondrial RNA processing (MRP) RNP. Interestingly, the To antigen found in human cells and the C5 protein, the only protein component of E. coli RNaseP, are antigenically related. In this study, we show that a 56 nucleotide-long sequence, corresponding to nucleotides 20-75 near the 5' end of human RNaseP RNA, is sufficient to bind the To antigen. We previously showed that the human To antigen binds to a short distinct structural domain near the 5' end of human 7-2/MRP RNA. There is no obvious primary sequence homology between the To antigen binding sites in RNaseP RNA and 7-2/MRP RNA; however, these sequences are capable of assuming a similar secondary structure which corresponds to the recently proposed 'cage' structure for RNaseP RNAs and 7-2/MRP RNA (Forster and Altman (1989) Cell 62: 407-409). These data are supportive of the idea that these two RNAs may have evolved from a common progenitor molecule.

Transcutaneous electrical nerve stimulation for treatment of spinal spasticity

Thirty-two patients with spinally originated muscle spasticity were treated with a transcutaneous electrical nerve stimulator, the Han's acupoint nerve stimulator (HANS) via skin electrodes placed over the acupoints on the hand and leg. High frequency (100 Hz), but not the low frequency (2 Hz), stimulation was effective in ameliorating muscle spasticity. While the therapeutic effect lasted for only 10 minutes in the first treatment, it became consolidated after consecutive daily treatment for 3 months. The anti-spastic effect induced by high frequency electrical stimulation can be partially reversed by a high dose of naloxone. The results suggest that the anti-spastic effect elicited by peripheral electrical stimulation is mediated, at least in part, by the endogenous opioid ligand interacting with the kappa opiate receptors, most probably dynorphin, in the central nervous system.

Sports causing most injuries in Hong Kong

A prospective survey was carried out on 2293 patients attending the Sports Injury Clinic in the Prince of Wales Hospital between May 1984 and December 1990. A Sports Injury Report Form was completed for each patient. Subjects in this study represent a group of nonprofessional and non-élite athletes in a metropolitan area. Soccer, basketball, volleyball, long-distance running and cycling in descending order were the five most common sports causing injury. Different sports produced different injury patterns. In four of the five sports, the knee (27.27-50.47%) and the ankle (16.78-24.67%) were the commonest sites of injury. In cycling, the face (19.46%) was the commonest site of injury. There was a higher injury rate to the lower than the upper limb in soccer, basketball, volleyball and long-distance running, with a ratio of upper- to lower-limb injury ranging from 1:1.13 to 1:46.10. In cycling, upper limb injury was more frequent (upper- to lower-limb injury ratio was 1:0.53). Sprain was the commonest injury overall (44.60%). It was also the commonest injury condition in volleyball (55.15%), basketball (55.34%), soccer (51.41%) and long-distance running (39.33%). In cycling, abrasion (24.83%) was commonest.

[Research on anti-idiotypic antibodies to bovine abortus]

Based on the establishment of McAbs to a local Brucella strain S85A, the McAb A7 was selected and tested as a protective one. Using A7 to immunize rabbits, we got high titer anti-idiotypic antibodies which were then proved to possess internal image by competitive inhibiting ELISA and catch blocking ELISA. The anti-idiotypic antibodies were then purified and mixed with glycerin to immunize guinea pigs and mice. The results showed that: immunized guinea pigs and mice had produced certain titer antibodies to Brucella. 79.2% of immunized guinea pigs had been protected from the challenge of 544A 4 months later from primary immunization. The number of T ANAE+ in peripheral blood of immunized mice had increased significantly compared to controls. These results suggest that the anti-idiotypic antibodies not only possess the antigen internal image but have the available immunogenicity stimulate animals producing Ab3 and make them get free from the infection.

Permeability to albumin in isolated coronary venules

This study reports measurements of albumin permeability in isolated coronary venules. The isolated microvessel technique allows the quantification of transmural exchange of macromolecules under tightly controlled physical and chemical conditions. Transvenular exchange of albumin was studied in isolated coronary venules during alterations in filtration rate caused by changes in intravascular pressure. The apparent permeability coefficient of albumin (Pa) at an intraluminal pressure of 11 cmH2O was 3.92 +/- 0.43 x 10(-6) cm/s. Elevating intraluminal pressure to 16 and 21 cmH2O increased Pa to 5.13 +/- 0.57 x 10(-6) and 6.78 +/- 0.66 x 10(-6) cm/s, respectively. Calculation of the true diffusive permeability coefficient of albumin (Pd) at zero filtration rate was 1.54 x 10(-6) cm/s. The product of hydraulic conductance (Lp) and (1 - sigma), where sigma is the solute reflection coefficient, was 3.25 x 10(-7) cm.s-1 x cmH2O-1. At a net filtration pressure of 4-5 cmH2O, diffusion accounts for > 60% of total albumin transport across the venular wall. Transmural albumin flux is very sensitive to filtration rate, rising 6.7% for each cmH2O elevation of net filtration pressure. At 11 cmH2O net filtration pressure, convection accounts for nearly 70% of net albumin extravasation from the venular lumen. We suggest that the isolated coronary venule is a suitable preparation for the study of solute exchange in the heart.

Purification and characterisation of a snake venom phospholipase A2: a potent inhibitor of platelet aggregation

An inhibitor of human platelet aggregation was identified from the venom of an Australian Copperhead snake, Austrelaps superba, as a novel phospholipase A2. The inhibitor was purified to homogeneity by chromatography on Q-Sepharose, S-Sepharose and C8 reverse phase HPLC. The purified phospholipase A2 has a molecular weight of 15 kDa as assessed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). N-terminal sequence analysis of the platelet inhibitor revealed 70-80% sequence identity to other previously described secretory phospholipase A2. Phospholipase activity of the purified protein was confirmed by the ability of the enzyme to hydrolyse lecithin. Pretreatment of the purified protein with the specific phospholipase A2 inhibitor p-bromophenacyl bromide, resulted in abrogation of both its enzyme and platelet inhibitory activity. The phospholipase A2 inhibited platelet aggregation and serotonin release, induced by a variety of platelet agonists, in a time and dose dependent manner.

Hong Kong Sports Institute: sports medicine and science from theory to practice

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Disruption by methylmercury of membrane excitability and synaptic transmission of CA1 neurons in hippocampal slices of the rat

In order to examine the effects of methylmercury (MeHg) on central synaptic transmission, field potentials were recorded in the CA1 neurons of hippocampal slices by using extracellular microelectrode recording techniques. After stimulation of Schaffer collaterals at low frequency (0.25 Hz), population spikes and excitatory postsynaptic potentials (EPSPs) were recorded at the cell bodies and apical dendrites of CA1 pyramidal cells, respectively. Antidromically activated population spikes were also recorded at the cell bodies of CA1 pyramidal cells by stimulating the alveus. Long-term potentiation (LTP) was induced by application of brief high-frequency stimulation (15 trains of four stimuli per train at 100 Hz) after 25 min of population spike baseline recordings. MeHg was applied to slices acutely by bath perfusion with artificial cerebrospinal fluid (ACSF). At 20-500 microM, MeHg significantly increased and then decreased the amplitudes of, or blocked, the population spikes, EPSPs, and antidromically activated population spikes. Time to increase and time to block of these field potentials were concentration-dependent. Exposure of slices to 4 microM MeHg for 180 min increased but did not reduce the amplitudes of population spikes, EPSPs, or antidromically activated population spikes. The effects of MeHg on population spikes induced by either orthodromic or antidromic stimulation were similar. In the absence of MeHg, application of high-frequency stimulation increased population spike amplitudes by 60-100%. This effect (LTP) could be sustained for more than 2 hr in the absence of MeHg. When 100 microM MeHg was applied concomitantly with high-frequency stimulation, the population spike amplitudes were increased by an additional 20-50% based on the already elevated population spike amplitude by high-frequency stimulation. Subsequently, population spike amplitudes were reduced and finally blocked in a manner similar to the effect of MeHg on population spikes recorded without high-frequency stimulation. Application of MeHg (100 microM) for 20 min prior to high-frequency stimulation did not prevent induction of LTP even though the population spike amplitudes had been decreased by more than 10% of the control level, suggesting that MeHg may not alter induction of LTP. Reversibility of the effects of MeHg was examined by washing slices with MeHg-free ACSF or 1 mM D-penicillamine for 60-120 min after MeHg treatment. Washing slices with MeHg-free ACSF caused at best partial reversal of effects of MeHg. D-Penicillamine, a chelator of MeHg, completely reversed the effects of MeHg on EPSPs but only partially reversed the effects of MeHg on population spikes, antidromically activated population spikes, and LTP.(ABSTRACT TRUNCATED AT 400 WORDS)

Histamine increases venular permeability via a phospholipase C-NO synthase-guanylate cyclase cascade

In this study, we hypothesized that histaminergic increases in venular permeability result from a cascade triggered by activation of phospholipase C (PLC), inducing the synthesis of nitric oxide (NO) and activating guanylate cyclase. The apparent permeability coefficient to albumin (Pa) was measured in isolated porcine coronary venules subjected to constant flow and hydrostatic and oncotic pressures. Histamine (2.5, 5, and 10 microM) transiently and progressively increased Pa. The PLC inhibitor 2-nitro-4-carboxyphenyl N,N-diphenylcarbamate (NCDC; 100 microM) decreased baseline permeability and abolished the effect of histamine. The NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA; 10 microM) and the guanylate cyclase inhibitor 6-anilinoquinoline-5,8-quinone (LY 83583; 10 microM) also blocked the histamine-induced hyperpermeability. L-Arginine (3 mM) reversed the inhibition by L-NMMA. NG-monomethyl-D-arginine did not influence the effect of histamine. Furthermore, sodium nitroprusside (10 microM) augmented Pa by two- to threefold; this effect was blocked in the presence of LY 83583 but not altered in the presence of NCDC. The results suggest that histamine increases coronary venular permeability by a direct action on the venular endothelial cells through a PLC-NO synthase-guanylate cyclase-signaling cascade.

Real-time coherent image differentiation using a self-pumped phase conjugator with Cu:KNSBN

A technique for real-time coherent image differentiation is described in a device consisting of a self-pumped phase conjugator that uses a copper-doped potassium sodium strontium barium niobate crystal. We demonstrate the proposed technique.

The Johnson antishear device and standard shin pad in the isokinetic assessment of the knee

Isokinetic training and assessment of the knee joint has been the mainstay of rehabilitation, especially in patients with anterior cruciate ligament deficiency. Besides the original shin pad used, the antishear device was introduced by Johnson in 1982. This device has been shown biomechanically to prevent excessive anterior translation of force on the tibia during training. However, there is a need to compare the antishear device and the standard shin pad in the isokinetic assessment. Hence, the major objective of this study is to define, if any, the difference in patient assessment between the new double pad device and the old single shin pad. Ten subjects with no previous history of injury on either knee were tested with the Cybex Isokinetic Dynamometer. There were four men and six women and the mean age was 25.2 years. They were randomized into different test sequences with different shin pads at different speeds. Correlation and paired t tests (P) were performed to find out the correlation and difference between the two devices. There was significant difference in performance assessment between the two devices in knee extension (P < 0.05) but no significant difference in knee flexion (P > 0.05). There was also a high correlation (r > 0.75) between the two devices. It is concluded that because of the significant difference of data generated between the two devices, it is important to select one single device with each patient during a series of testings.

Enhanced self-pumped phase conjugation from 16 degrees -cut KNSBN:Cu

With the maximum coupling coefficient and high internal reflection conditions, the self-pumped phase-conjugation reflectivity of copper-doped potassium sodium strontium barium niobate (KNSBN:Cu) is increased with 16 degrees -cut samples. The response time is also shortened. The resolution property of 16 degrees -cut KNSBN:Cu is determined and a distorted image is corrected by using the 16 degrees -cut sample.

Targeted cleavage of mRNA by human RNase P

Ribonuclease P from Escherichia coli can cleave RNAs in simple, hydrogen-bonded complexes of two oligoribonucleotides that resemble the aminoacyl stem and 5' leader sequence of tRNA precursors. RNase P from human (HeLa) cells cannot catalyze the cleavage in vitro of the 5'-proximal oligoribonucleotide that contains the leader sequence in such simple complexes but can do so when the 3'-proximal oligoribonucleotide (external guide sequence) is altered to resemble three-quarters of a tRNA molecule. In such a complex, the efficiency of cleavage of the mRNA for chloramphenicol acetyltransferase, as the 5'-proximal oligoribonucleotide, depends on the structural details of the external guide sequence and on the choice of target site within the mRNA. The presence of the appropriately designed external guide sequence in cells in tissue culture reduces chloramphenicol acetyltransferase activity and the level of the corresponding intact mRNA in the cells. Thus, it appears that the use of such external guide sequences may provide a general technique for gene inactivation.

[Pulmonary function disturbances in patients with hepatic cirrhosis]

The results of five pulmonary function tests on 52 patients with uncompensated hepatic cirrhosis were presented. Compared with matched healthy adults, the patients had decreased values of VC, TLC and DLCO, and their RV/TLC increased (P < 0.05-0.001). Possible pathogenic factors were investigated. The ascites showed evident influences on pulmonary function. In addition to the disorders detected by the above 4 tests, FRC decreased in the patients with ascites. A comparison between the patients with albumin below 30g/L and the patients with albumin above 30g/L revealed that reduced plasma albumin also played role in decreasing VC, TLC and DLCO. Besides the effects of ascites, severe varices of esophagus should have relation to the increase of RV/TLC and the decrease of DLCO.

Flow modulates coronary venular permeability by a nitric oxide-related mechanism

This study demonstrates that flow velocity modulates coronary venular permeability to albumin. Apparent permeability coefficients of albumin (Pa) were measured in isolated cannulated coronary venules ranging from 30 to 70 microns in diameter. Hydrostatic and oncotic pressures were controlled while the intraluminal flow velocity was varied. Pa at an intraluminal hydrostatic pressure of 12 cmH2O and a flow velocity of 7 mm/s was 4.01 +/- 0.53 x 10(-6) cm/s. Increasing flow velocity to 10 and 13 mm/s augmented the permeability by 33 +/- 14 and 48 +/- 14%, respectively. The nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA) (10(-5) M), decreased baseline Pa and abolished the flow-induced permeability changes. Administration of L-arginine (3 x 10(-3) M), a physiological precursor of nitric oxide which reverses the effect of L-NMMA, restored the relationship between flow and permeability. From these results we conclude that 1) flow velocity should be considered as a physical force that potentially modulates permeability of venular exchange vessels in the heart and 2) flow modulates coronary venular permeability via the production of nitric oxide.

[Studies of Rehmannia glutinosa Libosch. f. hueichingensis as a blood tonic]

We have studied the function of dried and prepared Rehmannia glutinosa f. hueichingensis in treating hemorrhagic anemic mice and in fostering bone marrow hematopoietic cells CFU-S, CFU-E. The results show that Rehmannia glutinosa f. hueichingensis can promote the recovery of blood deficient animals, RBC. Hb expedite the multiplication and differentiation of CFU-S, CFU-E, and thus proves markedly helpful to the generation of blood.