Distributed Reservation Control Protocols for Random Access Broadcasting Channels

Two distributed reservation control protocols are described, analyzed, and simulated for the transmission of datagramtype messages, encoded into fixed length packets, over a synchronous communication satellite channel. These protocols are of a hybrid form between pure random access contention protocols of the ALOHA variety and reservation control protocols such as CPODA. Simulations have shown that certain versions of these protocols can support throughput rates in excess of 97 percent of the channel capacity, maintain stability even under overload conditions, and incur waiting time delays ranging from 0.5 s under light traffic load to 0.88 s for saturated traffic conditions.     

Multiple Risk Expert Systems Interventions: Impact of Simultaneous Stage-Matched Expert System Interventions for Smoking, High-Fat Diet, and Sun Exposure in a Population of Parents.

Three stage-based expert system interventions for smoking, high-fat diet, and unsafe sun exposure were evaluated in a sample of 2,460 parents of teenagers. Eighty-four percent of the eligible parents were enrolled in a 2-arm randomized control trial, with the treatment group receiving individualized feedback reports for each of their relevant behaviors at 0, 6, and 12 months as well as a multiple behavior manual. At 24 months, the expert system outperformed the comparison condition across all 3 risk behaviors, resulting in 22% of the participants in action or maintenance for smoking (vs. 16% for the comparison condition), 34% for diet (vs. 26%), and 30% for sun exposure (vs. 22%). Proactive, home-based, and stage-matched expert systems can produce significant multiple behavior changes in at-risk populations where the majority of participants are not prepared to change. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of metabolic alterations on the accumulation of technetium-99m-labeled d,l-HMPAO in slices of rat cerebral cortex

It is widely recognized that the distribution of technetium-99m-labeled d,l-hexamethylpropylene amine oxime (99mTc-HMPAO) in the brain is determined by the regional blood flow. However, other factors may affect this process including the metabolism of the brain tissue. To examine this possibility we studied the effects of metabolic alterations on 99mTc-HMPAO uptake in rat brain cortex slices, with concurrent measurement of oxygen consumption (QO2). 99mTc-HMPAO uptake was determined by incubating slices of rat cerebral cortex at 37 degrees C in Krebs-Ringer phosphate glucose medium containing 99mTc-HMPAO with and without test substances. Differential gradients for 99mTc activity between the tissue and the suspending medium (T/M ratio) were derived from the equation T/M[99mTc] = counts per gram of tissue/counts per milliliter of medium. The QO2 of the brain slices was measured using a biological oxygen monitor equipped with a polarographic oxygen probe. Inhibitors affecting oxidative phosphorylation caused parallel suppression of the T/M ratio and QO2. Agents that uncouple oxidation from phosphorylation increased the QO2 and decreased the T/M ratio. Incubation of slices at 22 degrees C depressed the T/M ratio and QO2. The presence of inhibitors of oxidative phosphorylation in the incubation medium increased the release of 99mTc activity from slices that had been prelabeled with 99mTc-HMPAO. These findings suggest that the altered metabolic status of the brain tissue modulates the kinetics and net accumulation of 99mTc-HMPAO at the cellular level by either depressing uptake, increasing back-diffusion, or both.     

Noninvasive assessment of cardiac diabetic neuropathy by carbon-11 hydroxyephedrine and positron emission tomography

OBJECTIVES: The purpose of this investigation was to evaluate the sympathetic nervous system of the heart by positron emission tomographic (PET) imaging in patients with diabetes mellitus with and without diabetic autonomic neuropathy. BACKGROUND: The clinical assessment of cardiac involvement in diabetic autonomic neuropathy has been limited to cardiovascular reflex testing. With the recent introduction of radiolabeled catecholamines such as carbon (C)-11 hydroxyephedrine, the sympathetic innervation of the heart can be specifically visualized with PET imaging. METHODS: Positron emission tomographic imaging was performed with C-11 hydroxyephedrine and rest myocardial blood flow imaging with nitrogen-13 ammonia. Three patient groups were studied, including healthy volunteers as control subjects, diabetic patients with normal autonomic function testing and diabetic patients with varying severity of autonomic neuropathy. Homogeneity of cardiac tracer retention as well as absolute tracer retention was determined by relating myocardial tracer retention to an arterial C-11 activity input function. RESULTS: Abnormal regional C-11 hydroxyephedrine retention was seen in seven of eight patients with autonomic neuropathy. Relative tracer retention was significantly reduced in apical, inferior and lateral segments. The extent of the abnormality correlated with the severity of conventional markers of autonomic dysfunction. Absolute myocardial tracer retention index measurements showed a 45 +/- 21% decrease in distal compared with proximal myocardial segments in autonomic neuropathy (0.069 +/- 0.037 min-1 vs. 0.13 +/- 0.052 min-1, p = 0.02). CONCLUSIONS: This study demonstrates a heterogeneous pattern of neuronal abnormalities in patients with diabetic cardiac neuropathy. The extent of this abnormality correlated with the severity of neuropathy assessed by conventional tests. Future studies in larger groups of patients are required to define the relative sensitivity of this imaging approach in detecting cardiac neuropathy and to determine the clinical significance of these scintigraphic findings in comparison with conventional markers of autonomic innervation.     

Implementation of a low-cost Interim 21CFR11 compliance solution for laboratory environments

In the recent past, compliance with 21CFR11 has become a major buzzword within the pharmaceutical and biotechnology industries. While commercial solutions exist, implementation and validation are expensive and cumbersome. Frequent implementation of new features via point releases further complicates purchasing decisions by making it difficult to weigh the risk of non-compliance against the costs of too frequent upgrades. This presentation discusses a low-cost interim solution to the problem. While this solution does not address 100% of the issues raised by 21CFR11, it does implement and validate: (1) computer system security; (2) backup and restore ability on the electronic records store; and (3) an automated audit trail mechanism that captures the date, time and user identification whenever electronic records are created, modified or deleted. When coupled with enhanced procedural controls, this solution provides an acceptable level of compliance at extremely low cost.