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Biomedical subjects

L R Williams

Publications and source records attributed to L R Williams.

At least 109 records · Page 6Linked to original sources
PubMed1986

A model for the kinetics of potassium in healthy humans.

A model is developed to describe the distribution and excretion of potassium at arbitrary times during or after intake by ingestion or injection. The movement of K is tracked in greater detail than in previous models and is described in terms of anatomical compartments rather than the hypothetical, mathematically derived pools often considered. Parameter values are derived for a typical resting healthy adult male. Because of its anatomically realistic framework, the model may be used as a point of departure for modelling the behaviour of K in various subgroups of the population under less ideal conditions.

Adult↗
PubMed1986

Result of bypass grafting for upper limb ischemia.

Bypass grafting in the treatment of upper extremity ischemia is required far less frequently than it is in the lower extremity. The present study was undertaken to evaluate functional results and long-term patency of such grafts. Between 1978 and 1984, 33 bypass grafts were performed to relieve hand and forearm ischemia in 27 patients. The indication for bypass was neglected trauma (violent or iatrogenic) in 12 cases, primary arteriopathy in nine patients, and vascular complications of thoracic outlet compression in six patients. A reversed saphenous vein graft was used in 22 cases, and polytetrafluoroethylene was used in the remaining 11 procedures. Proximal anastomoses were from the aortic arch (one), subclavian artery (five), axillary artery (11), carotid artery (seven), and brachial artery (nine). Distal reconstructions were to the subclavian (three), axillary (three), brachial (16), radial (four), ulnar (two), and interosseous (five) arteries. Complete pre- and postoperative Doppler pressure measurements were available in 19 cases and demonstrated a significant increase in forearm systemic pressure index, from 0.51 before bypass to 0.86 postoperatively (p less than 0.001). Finger systolic pressure measurement in 10 patients also showed a significant improvement after operation. Follow-up of 31 grafts from 6 to 72 months (mean, 35.5 months) revealed an overall patency rate of 73% at 2 years and 67% at 3 years. Similar to lower extremity revascularization, more proximal grafts fared better; the 2-year patency rate was 83% for grafts at or above the brachial artery but only 53% for bypass distal to the brachial bifurcation. Major amputation was not required in any case, even after graft occlusion.

Adolescent↗
PubMed1986

Extended use of computed tomography in the management of complex aortic problems: a learning experience.

Eighty-nine patients with clinical problems arising from the thoracic or abdominal aorta had computed tomography (CT) scans with contrast enhancement in addition to standard aortograms. Forty-four patients had aneurysms, 22 had aortic graft complications, and 23 had aortoiliac occlusion. CT scanning provided diagnostic information not apparent by conventional angiography in 39 patients (43.8%). This additional information did not significantly alter the operative management in 13 patients (14.6%). The helpful information provided by CT in these patients included demonstration of gallstones, renal cysts, anomalous venous structures, horseshoe kidney, and femoral anastomotic aneurysms. However, in 26 of 89 patients (29%), the additional data obtained by CT significantly changed the timing or approach to operative management. Management was altered in 12 of 44 patients (28%) with aneurysms, 7 of 22 patients (32%) with aortic graft complications, and 7 of 23 patients (30%) with aortoiliac occlusive disease or suspected distal thromboembolism. Specific information provided by CT included contained aortic aneurysm rupture, aortic dissection, laminated intraluminal thrombus or pseudointima, extent of perigraft infection, aortic atherosclerosis, anastomotic false aneurysm, and thrombus as a source of distal embolization. Thus, CT had a significant impact on operative management. It serves as a valuable adjunct to aortography in patients with complex aortic problems.

Aged↗
PubMed1986

Popliteal artery entrapment: diagnosis by computed tomography.

Popliteal artery entrapment by an anomalous band of the gastrocnemius muscle is uncommon. In cases where popliteal artery occlusion has occurred, the diagnosis is difficult to establish. A case is presented in which computed axial tomography of the popliteal space established the diagnosis of popliteal artery thrombosis caused by entrapment when other diagnostic modalities were inconclusive. Computed axial tomography provides precise anatomic display of the muscle structure of the popliteal fossa and should be an important diagnostic tool in patients suspected to have popliteal artery entrapment.

Adult↗
PubMed1985

Central nervous system-directed neuronotrophic activity present in red blood cells.

A new neuronotrophic factor has been identified in extracts of vertebrate red blood cells. The factor supports the survival in culture of neurons from vertebrate central nervous systems, and does not support the survival of several peripheral ganglionic neurons. The active molecule appears to be a slightly acidic protein of 30,000-100,000 daltons.

Animals↗
PubMed1985

Modification of fibrin matrix formation in situ enhances nerve regeneration in silicone chambers.

The spatial-temporal progress of nerve regeneration was examined in silicone chambers of three different volume capacities: 11, 25, and 75 microliter. In all chambers, the stumps of a transected rat sciatic nerve were sutured into the ends of the chamber leaving a 10 mm gap between the stumps. Chambers were implanted empty (E chambers) or prefilled with saline (PF chambers). A coaxial and continuous fibrin matrix had formed in all chambers by 1 week. In E chambers, the matrices had a proximal-distal taper that was more pronounced in E25 and E75 chambers due to significantly larger matrix diameters in the proximal region. At 3 weeks, vascular and Schwann cell migration and axonal regeneration were less advanced in the E25 and E75 than in the control E11 chambers. The retardation correlated with the presence of an avascular organization of circumferential cells. Saline prefilling affected the caliber and density of fibrin fibers in the 1 week matrices of PF25 and PF75 chambers. The matrices did not have a prominent taper and diameters were progressively larger with increasing chamber volume. Saline prefilling did not affect regeneration progress in 3 week PF11 chambers but did enhance regeneration in the PF25 chambers; a 1.5-fold larger diameter nerve formed at 3 weeks that contained 2.6-fold more axons. Progress in the PF75 chamber was retarded. We conclude that the volume, timing, and nature of the fluid filling a silicone chamber have significant influence on the formation of fibrin matrices. Alterations in matrix formation correlate with substantial changes in the subsequent progress of intrachamber regeneration events.

Animals↗
PubMed1985

Serial movement timing and musical experience.

Musicians and non-musicians were compared on a serial movement-timing task incorporating six continuous 11-cm segments. The serial pattern was structured for both spatial and temporal symmetry. There were seven subjects in each group and 50 test trials were analyzed for timing error. The non-musicians were less accurate and more variable for certain parts of the pattern. The findings supported the view that musical practice can assist the process of mapping internal representations of serial relations to novel spatio-temporal patterns of movement.

Adult↗
PubMed1985

Effects of exercise on choice reaction latency and movement speed.

Performance and learning of an 8-choice RT-MT task was investigated as a function of two levels of interpolated arm exercise. Following a pretest under control nonexercise conditions, 90 subjects were given 60 trials under one of three experimental conditions (low intensity, high intensity, and vowel-cancelling). This was followed on a second day by a further 18 trials under control conditions. Predictions from the theory of exercise-induced activation received only limited support by the indication that the highly intense condition impaired RT. Exercise of low intensity did not facilitate RT. For MT no differential effects were found. Similarly, learning RT and MT was unaffected by exercise. These findings indicate that the theory of exercise-induced activation needs to be developed further to account for response situations that have high demand for attention.

Adult↗
PubMed1984

Competence of nerve tissue as distal insert promoting nerve regeneration in a silicone chamber.

A new peripheral nerve forms across a 10 mm gap within a silicone chamber regeneration model when the distal segment of a transected sciatic nerve, connected to its end organs, is sutured into the distal end of the chamber. We have tested the ability of other tissue inserts to support axonal regeneration in the chamber. When an isolated 2 mm piece of sciatic nerve was sutured into the distal end, fibrin matrix formation, cell immigration and axonal regeneration were identical to those occurring in the control. When the distal nerve insert was replaced with a 2 mm piece of skin or a ligation, a matrix did not form and subsequent cell immigration and axonal regeneration did not occur. When a 2 mm piece of tendon was inserted, a matrix did form at 1 week, but a structure across the gap was observed at later time periods in only 2 out of 7 chambers. The matrix either dissolved before cells could enter the chamber or did not promote cellular immigration and subsequent axonal regeneration. When the distal end was left open, a matrix formed and cells from the reactive tissue outside the chamber entered the matrix and formed a granulation tissue bridge across the gap. This tissue failed to support axonal regeneration; at 3 weeks, axons stopped 1 mm beyond the proximal stump at the interface with the granulation tissue. Thus, matrix formation and a cellular bridge are necessary but not sufficient to ensure regeneration. Successful regeneration across the silicone chamber gap requires humoral and/or cellular contributions available from peripheral nervous tissue and not from the other tested tissues.

Animals↗
PubMed1984

The Collaborative Lipid Research Clinics Program Family Study: detection of major genes influencing lipid levels by examination of heterogeneity of familial variances.

Age, sex-adjusted, and transformed lipid and lipoprotein data on over 1,200 white North American sibships in the Collaborative Lipid Research Clinics Family Study were analyzed for possible major genes causing high or low levels of these traits. The sibships were stratified on the basis of parents' trait values, and within-sibship variance in the high (or low) families was compared to that in the normal families via an F-test. The null hypothesis of multifactorial transmission was strongly rejected for low LDL, low total cholesterol, and high HDL families. An analysis of spouse-pair variance gave similar results. This may reflect the presence of dominant genes for hyperalpha- and hypobetalipoproteinemia. There was weaker evidence for single genes causing hyperbetalipoproteinemia. There was no evidence for major genes influencing triglyceride levels. Methodological issues with significant bearing on these results and those of other studies are discussed.

Biometry↗
PubMed1984

Alterations in femoral artery hemodynamics associated with femoropopliteal bypass.

Subcritical iliac artery stenoses become critical stenoses if common femoral artery (CFA) flow rates increase sufficiently. Infrainguinal bypasses done in the presence of subcritical iliac artery stenoses may be in jeopardy on the basis of inadequate inflow if critical iliac stenoses are produced by increased CFA flow resulting from the bypasses. This study was undertaken to define the CFA hemodynamic changes seen with femoropopliteal bypass and to determine the relative effects of subcritical iliac artery stenoses on these pressure and flow changes. The iliac and femoral arteries of five canine hindlimbs were isolated for placement of a constricting microcaliper, intraarterial pressure cannula, and electromagnetic flow probe. Systemic pressure was monitored via the contralateral CFA. CFA pressure and flow were measured at incremental iliac artery stenoses with the superficial femoral artery (SFA) occluded and with the SFA patent, simulating femoropopliteal bypass. Indices of CFA pressure/systemic pressure (FAI) and percentage increases in CFA flow with open versus occluded SFAs were calculated. CFA flow rates were significantly higher with open versus occluded SFAs, with and without iliac artery stenoses present. Despite these increases in CFA flow, CFA pressure indices were unchanged when comparing open with occluded SFAs even in the presence of subcritical iliac artery stenoses. These findings suggest that femoropopliteal bypass does not result in increases in CFA flow rates sufficient enough to cause decreased graft perfusion pressures in the presence of subcritical iliac artery stenoses. Therefore, the patency of an infrainguinal bypass done in the presence of a subcritical iliac artery stenosis should not be adversely affected in the early postoperative period on the basis of inflow.

Animals↗
PubMed1984

Prediction of improvement in ankle blood pressure following arterial bypass.

Percutaneous femoral artery pressures and lower extremity segmental Doppler-derived blood pressures in 116 lower extremities were analyzed to determine if postbypass ankle/brachial indices (ABIs) could be predicted based on preoperative pressures. Predicted ABIs were calculated by increasing the prebypass ABI by the same percentage that the extremity/brachial index at the distal end of the bypass would be increased, assuming a postbypass index of 1.0 at the distal graft. The correlation between predicted ABI and actual postbypass ABI was strong for aortofemoral bypass (r = 0.8735) and moderate for infrainguinal bypass (r = 0.5961), with 75% of the postinfrainguinal bypass ABIs being greater than predicted. Minimum postoperative increases in ABI can be predicted based on preoperative hemodynamic measurements, thus providing important information relative to choosing the appropriate level of revascularization in patients with multisegmental disease.

Ankle↗
PubMed1984

Aortofemoral or femoropopliteal revascularization? A prospective evaluation of the papaverine test.

Proper selection of suprainguinal vs. infrainguinal arterial revascularization in patients with multilevel disease requires hemodynamic assessment. In such patients hemodynamic evaluation of the aortoiliac system cannot be made accurately with either arteriography or current noninvasive techniques. One hundred six lower extremities underwent preoperative triplane arteriography, measurement of Doppler-derived segmental blood pressures, measurement of common femoral intra-arterial pressure, and intra-arterial injection (30 mg) of the vasodilator papaverine hydrochloride prior to arterial bypass. Common femoral intra-arterial pressure was monitored continuously before and after papaverine injection. The resting femoral/brachial pressure index (FBI) and the maximum change in this index (% delta FBI) following papaverine injection were calculated. To be considered improved postoperatively, claudicants required an increase in treadmill walking time of greater than or equal to 50%, whereas patients operated on for limb salvage required an increase in the thigh/brachial pressure index (TBI) of greater than or equal to 0.15 for suprainguinal revascularizations and an increase of TBI to greater than or equal to 0.9 for infrainguinal revascularizations. In the first 41 extremities (phase I), receiver operator characteristic analysis revealed a % delta FBI greater than or equal to 15% to be optimal in the detection of hemodynamically significant aortoiliac disease. In phase II (65 limbs) this discriminant value for % delta FBI was assessed prospectively. In phase I, in which the choice of supra- vs. infrainguinal bypass was determined arteriographically, only 80% of the extremities were improved; in phase II, in which supra- vs. infrainguinal bypass was determined by the papaverine test, 98% of extremities were improved (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Aorta↗
PubMed1984

A measure of model reliability.

A method for evaluating predictive models is developed by giving a precise and statistically meaningful interpretation to the statement that a model is accurate within a factor of k. This method is applicable to any model for which there is a set [y1,..., yn] of observations corresponding to a set [x1,..., xn] of model predictions. We define a geometrically intuitive measure of model reliability kg in terms of the ratios yi/xi and a statistically rigorous measure ks in terms of 1n (yi/xi). For reasonably accurate models, kg and ks are in virtual agreement and thus can be used interchangeably as a reliability index. The index ks estimates a model parameter of the form exp[(V1 + V2)1/2], where V1 describes an observational variance and V2 is related to an uncertainty associated with the model itself. The computed value for ks is not unique but depends on the sample of observations. The probability distribution of ks can be characterized provided the observational distributions are lognormal, independent, and satisfy a homoscedasticity condition. These requirements are often satisfied by quantities of interest in radiation risk analyses. The reliability indices kg and ks may be applied even if the underlying observational distributions are not lognormal, although the probability distribution of ks cannot be characterized in this case.

Animals↗
PubMed1983

Spatial-temporal progress of peripheral nerve regeneration within a silicone chamber: parameters for a bioassay.

The spatial-temporal progress of peripheral nerve regeneration across a 10-mm gap within a silicone chamber was examined with the light and electron microscope at 2-mm intervals. A coaxial, fibrin matrix was observed at 1 week with a proximal-distal narrowing that extended beyond the midpoint of the chamber. At 2 weeks, Schwann cells, fibroblasts, and endothelial cells had migrated into the matrix from both nerve stumps. There was a delay of 7-14 days after nerve transection and chamber implantation before regenerating axons appeared in the chamber. At 2 weeks, nonmyelinated axons were seen only in the proximal 1-5 mm of the chamber in association with Schwann cells. Axons reached the distal stump by 3 weeks and a proximal-distal gradient of myelination was observed. These observations define the parameters of a morphologic assay for regeneration in this chamber model which can be used to investigate cellular and molecular mechanisms underlying the success of peripheral nerve regeneration.

Animals↗
PubMed1983

Retrograde transport of goldfish optic nerve proteins labeled by N-succinimidyl [3H]propionate.

Following injection of the acylating reagent N-succinimidyl [3H]propionate into the optic nerve of goldfish, labeled protein appeared in the ipsilateral retina and contralateral tectum in a time-dependent manner. Autoradiography indicated the presence of the labeled material in the neuroplasm of the retinal ganglion cells and their projections. While most of the recoverable injected radioactivity was confined to the injection site even after 1 week, labeled proteins arriving in the retina by retrograde flow or in the tectum by anterograde flow had distinctly different patterns, a result suggesting specific transport processes rather than diffusion. In contrast to reported studies with the labeling agent in other species, a prominent 68,000 molecular weight component was not seen. The results are discussed in relation to the role of retrograde transport in regeneration.

Animals↗
PubMed1983

Early experience with popliteal to infrapopliteal bypass for limb salvage.

In an attempt to improve graft patency and limb salvage in patients with isolated tibial vessel and/or popliteal-tibial vessel occlusive disease, bypass grafts from the popliteal or distal superficial femoral artery to infrapopliteal arteries were used in patients requiring bypass for limb salvage. During a 2 1/2-year period, 23 patients with patent axial vessels and hemodynamically normal inflow to the level of the knee underwent such bypasses. Cumulative graft patency and limb salvage rates at 31 months were 84% and 70%, respectively. Five of the six patients who required below-knee amputation did so because of progressive gangrene in the presence of a patent bypass. Short bypasses between the popliteal and infrapopliteal arteries can significantly contribute to limb salvage in patients with tibial vessel occlusive disease and may be particularly useful in patients with saphenous veins too short for longer bypasses.

Adult↗