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Biomedical subjects

John A Davis

Publications and source records attributed to John A Davis.

5 recordsLinked to original sources
PubMed2006

Deterministic hydrodynamics: taking blood apart.

We show the fractionation of whole blood components and isolation of blood plasma with no dilution by using a continuous-flow deterministic array that separates blood components by their hydrodynamic size, independent of their mass. We use the technology we developed of deterministic arrays which separate white blood cells, red blood cells, and platelets from blood plasma at flow velocities of 1,000 microm/sec and volume rates up to 1 microl/min. We verified by flow cytometry that an array using focused injection removed 100% of the lymphocytes and monocytes from the main red blood cell and platelet stream. Using a second design, we demonstrated the separation of blood plasma from the blood cells (white, red, and platelets) with virtually no dilution of the plasma and no cellular contamination of the plasma.

Blood Platelets↗
PubMed2006

Critical particle size for fractionation by deterministic lateral displacement.

The fractionation of small particles in a liquid based on their size in a micropost array by deterministic lateral displacement was recently demonstrated with unprecedented resolution (L. R. Huang, E. C. Cox, R. H. Austin and J. C. Sturm, Science, 2004, 304, 987-990, ). In this paper, we present a model of how the critical particle size for fractionation depends on the micropost geometry, depending specifically on the gap between posts, the offset of posts in one row with respect to another, and whether the fluid is driven by hydrodynamics or by electroosmosis. In general the critical particle diameter is much smaller than the gap, which prevents clogging. The model is supported by data with particles from 2.3 to 22 microm.

Chemical Fractionation↗
PubMed2004

Performance of epimysial stimulating electrodes in the lower extremities of individuals with spinal cord injury.

This study describes the performance of surgically-implanted epimysial stimulating electrodes in the muscles of the lower extremities for use in functional neuromuscular stimulation (FNS) systems for standing after spinal cord injury. A total of 86 epimysial electrodes were implanted in 13 volunteers with low tetraplegia or paraplegia receiving the Case Western Reserve University/Veteran Affairs (CWRU/VA)-implanted standing/transfer neuroprosthesis. The neuroprosthesis consisted of bilateral epimysial electrodes in the knee and hip extensors (vastus lateralis, gluteus maximus, and adductor magnus or semimembranosus) and intramuscular electrodes at the T12/L1 or L1/L2 spinal roots for trunk extension. Recruitment properties, stimulated knee and hip extension moments, standing performance, and mechanical integrity over time were measured for a period up to four years post-implantation. Stimulated thresholds were stable and recruitment was sufficient to generate joint moments adequate for standing, with up to 97% body weight supported by the legs. Four mechanical failures were observed, all in the posterior muscles of the thigh, leaving 95% of all electrodes operational at all followup intervals. Probability of 24-month survival is estimated to be 93% plateauing to a steady state of 90% at four years. These results indicate that epimysial designs are appropriate for long-term clinical use in the large muscles of the lower extremities with implanted motor system neuroprostheses.

Adult↗
PubMedDate not supplied

Long-term user perceptions of an implanted neuroprosthesis for exercise, standing, and transfers after spinal cord injury.

This study was completed to understand the usage patterns, system performance, degree of satisfaction, complications, and health benefits as perceived by recipients of a surgically implanted neuroprosthesis for exercise, standing, and transfers in individuals with low-cervical or thoracic spinal cord injury (SCI). A standardized telephone survey was administered to 11 recipients of the Case Western Reserve University/Veterans Affairs (CWRU/VA) implanted standing neuroprosthesis with more than 12 months of experience with the functional electrical stimulation (FES) system. Nine implant recipients were using the neuroprosthesis regularly for standing and/or exercising at the time of the survey. All 11 implant recipients noted improved health and a reduced incidence of pressure sores, leg spasms, and urinary tract infections (UTIs). No incidents of deep-vein thrombosis, infection, cellulitis, or electrical burns because of the neuroprosthesis were noted. System recipients uniformly felt that the neuroprosthesis resulted in better overall health and general well-being. Subjects were moderately to very satisfied with the performance of the neuroprosthesis and unanimously expressed a willingness to repeat the surgery and rehabilitation to obtain the same clinical outcome. All implant recipients reported the system to be safe, reliable, and easy to use. The implanted standing neuroprosthesis appears to be a clinically acceptable and effective means of providing the ability to exercise, stand, and transfer to selected individuals with paraplegia or low tetraplegia.

Activities of Daily Living↗