Biomedical subjects

R Littlefield

Publications and source records attributed to R Littlefield.

5 recordsLinked to original sources

PubMed2001

Methodology for identifying patients at high risk for osteoporotic fracture.

BACKGROUND: Osteoporotic fractures are associated with significant morbidity, mortality, and health care costs. OBJECTIVE: The purpose of this paper is to present and validate a mathematical model that managed care organizations can apply to administrative claims data to help locate members at risk for osteoporotic fracture and estimate future fracture rates. METHODS: Using known risk factors from previous clinical studies, 92,000 members of a large Midwest health plan were placed in 1 of 4 risk categories based on historical claims markers: demographic/lifestyle (age, sex, smoking, alcoholism); steroid use; medical history (previous osteoporotic fracture, ordinary bone fracture, osteoporosis diagnosis, bone mineral density test); or steroid use with medical history. Logistic regression was used to assign a probability of fracture for the 4 groups over the next 2 years. These predictions were compared with actual fracture rates, and refined models were produced. The models were then validated by applying them to current data and comparing the predicted fracture rate for each group to known results. RESULTS: The model predicted that 1.26% of the study members would experience osteoporotic fracture over the next 2 years; the actual result was 1.27%. Within the 4 risk groups, the predicted fracture rates were lower than the actual rates for the demographic risk group (0.87% predicted vs 0.97% actual) and higher than the actual rates for the steroid use (1.78% predicted vs 1.58% actual), medical history (5.90% predicted vs 4.94% actual), and the steroid use with medical history groups (7.80% predicted vs 6.42% actual). CONCLUSION: The application of this risk model to an administrative claims database successfully identified plan members at risk for osteoporotic fracture.

Aged↗

PubMed2001

Actin dynamics at pointed ends regulates thin filament length in striated muscle.

Regulation of actin dynamics at filament ends determines the organization and turnover of actin cytoskeletal structures. In striated muscle, it is believed that tight capping of the fast-growing (barbed) ends by CapZ and of the slow-growing (pointed) ends by tropomodulin (Tmod) stabilizes the uniform lengths of actin (thin) filaments in myofibrils. Here we demonstrate for the first time that both CapZ and Tmod are dynamic on the basis of the rapid incorporation of microinjected rhodamine-labelled actin (rho-actin) at both barbed and pointed ends and from the photobleaching of green fluorescent protein (GFP)-labelled Tmod. Unexpectedly, the inhibition of actin dynamics at pointed ends by GFP-Tmod overexpression results in shorter thin filaments, whereas the inhibition of actin dynamics at barbed ends by cytochalasin D has no effect on length. These data demonstrate that the actin filaments in myofibrils are relatively dynamic despite the presence of capping proteins, and that regulated actin assembly at pointed ends determines the length of thin filaments.

Actin Cytoskeleton↗

PubMed1998

Defining actin filament length in striated muscle: rulers and caps or dynamic stability?

Actin filaments (thin filaments) are polymerized to strikingly uniform lengths in striated muscle sarcomeres. Yet, actin monomers can exchange dynamically into thin filaments in vivo, indicating that actin monomer association and dissociation at filament ends must be highly regulated to maintain the uniformity of filament lengths. We propose several hypothetical mechanisms that could generate uniform actin filament length distributions and discuss their application to the determination of thin filament length in vivo. At the Z line, titin may determine the minimum extent and tropomyosin the maximum extent of thin filament overlap by regulating alpha-actinin binding to actin, while a unique Z filament may bind to capZ and regulate barbed end capping. For the free portion of the thin filament, we evaluate possibilities that thin filament components (e.g. nebulin or the tropomyosin/troponin polymer) determine thin filament lengths by binding directly to tropomodulin and regulating pointed end capping, or alternatively, that myosin thick filaments, together with titin, determine filament length by indirectly regulating tropomodulin's capping activity.

Actins↗

PubMed1997

TeleInViVo: a collaborative volume visualization application.

Converging technologies in the areas of networks, volume visualization algorithms, and computer performance have made possible the development of a new tool for collaboration, which extends the reach of health professionals, and other consumers of volumetric data around the world. TeleInViVo(tm) is a three-dimensional (3D) collaborative volume visualization tool for medical applications. It extends the capabilities of InViVo(tm), a fast volume visualization tool developed at the Fraunhofer IGD, Darmstadt, Germany [1-3], with efficient and intuitive network collaboration features for remote consultation and new modes of interaction. The software runs on both UNIX and Windows NT platforms. TeleInViVo provides a high degree of interactivity for the medical professional when interacting with the patient data, facilitates explanation and communication between field personnel and medical experts located far from the field, and permits viewing of the data in a multitude of ways designed to support rapid and accurate diagnosis. Current efforts involve architectural enhancements to support multiuser, distributed telemedical scenarios. The application includes the following features: Volume and subvolume data transmission at user specified resolution, Synchronization cues, Integration of Immersion Probe(tm), a 6 degree-of-freedom input device, for ergonomic 3D data exploration, Tools for measuring distances, Tools for planning instrument path, Arbitrary cutting planes in real time, Interactive segmentation tools, Virtual video recorder and playback (cine loops), 3D stereo mode. TeleInViVo is an essential part of the MUSTPAC-1 portable 3D ultrasound system developed by Battelle Pacific Northwest Labs, Richland, WA.

Computer Communication Networks↗

PubMed1984

Simple method for locating the optical center of a lens.

This article evaluates an old and little used method, which involves holding a small light in front of the lens and marking the spot where the centers of the images reflected from the front and rear surfaces overlap. The location of the center found this way correlates very well with the marking lensometer method. This method may also be used while the patient is wearing the spectacle. Thus, the examiner may easily see the patient's pupillary center and the optical center simultaneously. Induced prismatic effects from inaccurate lens centering can easily be diagnosed without removing the spectacle from the patient's face.

Eyeglasses↗