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Biomedical subjects

W Hoff

Publications and source records attributed to W Hoff.

18 recordsLinked to original sources
PubMed2000

Long-lived amide I vibrational modes in myoglobin.

Pump-probe experiments in the infrared measure vibrational relaxation rates. Myoglobin, which is almost entirely alpha helix in secondary structure, has an unusually long, nonexponential excited state relaxation generated by optically pumping at the blue side ( 5. 85 microm) of the amide I band. The amino acid alanine and the predominantly beta sheet protein photoactive yellow protein do not have such a long-lived state, suggesting that the alpha helix in proteins can support nonlinear states of 15 ps characteristic times.

Amides↗
PubMed1999

An interactive system for kinematic analysis of artificial joint implants.

The objective of this project was to develop and test a software system for the kinematic analysis of total joint arthroplasty (TJA) implants. Using a supervised iterative optimization algorithm (simulated annealing), the system iteratively adjusts the pose of an implant model to maximize correlation between the model's pose and the pose of an actual implant in a x-ray image. A graphical user interface (GUI) was developed that provides visualization of the model-fitting process, and permits human guidance for error correction. The resulting system was evaluated to determine its accuracy and repeatability. On synthetic images, the mean translational and rotational errors were found to be 0.005 mm and 0.0015 degrees, respectively. On in vitro images, the repeatability was found to be 0.15 mm of translation and 0.17 degrees of rotation. The outcome is a working joint-measurement software system and quantitative data to support comparison with other methods.

Arthroplasty, Replacement, Knee↗
PubMed1997

Meta-analysis of randomized, double-blind, placebo-controlled, efficacy and safety studies of mirtazapine versus amitriptyline in major depression.

A meta-analysis was performed on efficacy and safety data from 4 randomized, double-blind, 6-week, single-center studies comparing mirtazapine (n = 194; 5-35 mg/day) with amitriptyline (n = 193, 40-280 mg/day) and placebo (n = 193) in outpatients with a DSM-III diagnosis of major depressive episode. On all the main efficacy variables both active drugs consistently produced significantly greater improvements and significantly greater percentages of responders or remitters than placebo. The meta-analysis of adverse events shows that mirtazapine was better tolerated than amitriptyline, particularly with respect to anticholinergic and cardiac adverse events. There were no differences between mirtazapine and placebo regarding the incidence of serotonergic adverse events. In conclusion, the results of this meta-analysis demonstrate that mirtazapine is as effective as amitriptyline but has a better tolerability profile.

Adolescent↗
PubMed1997

Traditional health practitioners as primary health care workers.

The author conducted a field study in 1993 to evaluate the effectiveness of four projects that were training traditional health practitioners (THPs) to provide primary health care (PHC) services in Ghana, Mexico, and Bangladesh. The study, funded by a grant from the World Health Organization, Division of Strengthening Health Services, concluded that incorporating trained THPs in PHC programmes can be cost effective in providing essential and culturally relevant health services to communities. The main objective of the study was to evaluate how effective the training projects were and to determine what impacts they might have upon the communities served. A qualitative field evaluation was performed using data collected from project documents, observations, and field interviews with a selection of health agency staff, THPs, and community members. A summary of results is presented from the four field studies. For details refer to the full report.

Adult↗
PubMed1996

"In vivo" pose estimation of artificial knee implants using computer vision.

This paper describes an algorithm to estimate the position and orientation (pose) of artificial knee implants from fluoroscopy images using computer vision. The resulting information is used to determine contact position from " in vivo" bone motion in implanted knees. This determination can be used to support the development of improved prosthetic knee implants. Current generation implants have a limited life span due to premature wear of the polyethylene material at the joint surface. To get "in vivo" motion, fluoroscopy videos were taken of implant patients performing deep knee bends. Our algorithm determines the full 6 degree of freedom translation and rotation of knee components. This is necessary for artificial knees which have shown significant rotation out of the sagittal plane, in particular internal/external rotations. By creating a library of images at known orientation and performing a matching technique, the 3-D pose of the femoral and tibial components are determined. By transforming the coordinate systems into one common system contact positions can be determined. The entire process, when used at certain knee angles, will give a representation of the positions in contact during normal knee motion.

Algorithms↗
PubMed1992

Traditional healers and community health.

A review of projects in various countries suggests that traditional healers, if properly trained, can contribute significantly to the work of primary care teams. Recommendations are offered with a view to making the best possible use of this valuable resource.

Developing Countries↗
PubMed1988

Haemodynamic effects of intravenous and oral alifedrine in patients with cardiac failure.

A randomized, double-blind, double-crossover, placebo-controlled haemodynamic study was undertaken in patients with Grade II/III (NYHA) cardiac failure to examine the acute effects of intravenous alifedrine, 20 mg and 40 mg (17 patients), and oral 40 mg alifedrine (8 of these patients). Patients received single doses of alifedrine and placebo on separate days, with invasive monitoring. Alifedrine resulted in a significant (p less than 0.001), dose-dependent increase in cardiac output. The peak effect (+23% with 20 mg i.v., +42% with 40 mg i.v. and +29% with 40 mg orally) was seen approximately 1 hour after intravenous administration (with about half of these increases still apparent at 3 hours) but developed progressively over 3 hours after oral administration. There were significant reductions (p less than 0.001) in peripheral resistance (peak mean changes -21% with 20 mg i.v., -31% with 40 mg i.v. and -23% with 40 mg orally), but little (less than +/- 6%) observed change in arterial pressure. With intravenous alifedrine, there were significant increases in stroke volume (+19% with 20 mg, +35% with 40 mg, p less than 0.001) with little (5%) change in heart rate (+3% and +7%, respectively, N.S.). With the 40 mg oral dose, there was a small increase in heart rate (+12%, p less than 0.005) associated with a 19% (N.S.) increase in stroke volume. Peak haemodynamic responses to 40 mg alifedrine orally were 50% to 75% of those seen after administration of the same dose intravenously. When assessed 3 hours after administration, responses to the two routes of administration were similar. There were no clinically or statistically significant changes in arterial (non-invasive), pulmonary artery, pulmonary capillary or right atrial pressures with any dose of alifedrine. No significant arrhythmias were noted clinically with the doses studied. Alifedrine, therefore, is an interesting agent, available both orally and intravenously, which is well tolerated and appears to produce marked acute increases in cardiac output with little change in heart rate or blood pressure. Further studies should determine whether these effects are maintained during longer-term therapy and clarify the relative contributions of positive inotropic and peripheral vasodilator activity to the effects observed.

Administration, Oral↗
PubMed1985

Stricter selection criteria improve the results of shunt surgery.

Between October, 1976 and December, 1982, 176 patients with full-blown liver cirrhosis were referred to us either with Acute oesophageal variceal bleeding, or after having had such a haemorrhage. Eight of these patients died of a haemorrhage that did not respond to conservative treatment, or of hepatic failure after emergency surgery. After receiving initial conservative treatment, 168 patients were classified in accordance with clinical, biochemical and haemodynamic selection criteria, particular importance being attached to the haemodynamic criteria. One-hundred-and-one of these patients in whom a shunt operation was not justifiable, were treated conservatively by means of repeated sclerotherapy. In the cases of acute bleeding, a balloon tamponade was performed in 3, an emergency shunt procedure in 1 and palliative dissection surgery in 4. Twenty-three patients in a non-bleeding state were treated conservatively without sclerotherapy. Shunt surgery was performed in 44 patients; out of the 42 patients shown by our selection criteria to be suitable for shunt surgery, only 1 patient died, 5 days after the operation, of cardiac failure with underlying toxic cardiomyopathy. In view of the low early mortality rate in selectively operated patients, a major argument against the use of the shunt for the treatment of portal hypertension is no longer valid, and it should again be considered whether the surgical procedure might not provide better long-term results than does conservative sclerotherapy alone.

Gastrointestinal Hemorrhage↗
PubMed1978

Sodium and chloride transport in the isolated human cornea.

22Na and 36Cl fluxes in isolated human cornea preparations were measured under short-circuited conditions. At pH 7.3-PH 7.6 sodium net flux was directed from aqueous humour to tear side, chloride net flux was statistically not different from zero. Alkalinization of the bathing solution to pH 8.6 stimulated unidirectional sodium and chloride fluxes from aqueous humour to tear side resulting in net sodium and chloride fluxes towards the tear side which both were statistically different from zero. Cyclic AMP (10(-3) M) was found to stimulate sodium and chloride unidirectional fluxes from aqueous humour to tear side, thus leading to significant net sodium and chloride fluxes in the same direction. Epinephrine (10(-4) M) increased the unidirectional chloride flux from aqueous humour to tear side more pronounced than in the opposite direction, producing a significant net chloride flux towards the tear side. The results are consistent with the hypothesis that the electrolyte pumps may under certain conditions contribute to the dehydration of the stroma.

Biological Transport, Active↗