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Biomedical subjects

M W Johnson

Publications and source records attributed to M W Johnson.

At least 55 records · Page 3Linked to original sources

Payer status, but not race, affects the cost of liver transplantation.

Prior studies evaluating the impact of race and payer on cost of liver transplantation did not adjust for clinical factors known to increase cost. We analyzed the impact of race and payer on the cost of liver transplantation after controlling for clinical factors. We analyzed data obtained on patient and graft survival, cost, race, age, sex, payer, and United Network for Organ Sharing (UNOS) status from 153 consecutive liver transplants in 130 patients performed at University of North Carolina Hospitals from September 1991 through December 1996. Race was classified as white or nonwhite, and payer status was classified as commercial or Medicare/Medicaid. Multivariate linear regression was used to compare costs, adjusting for age, sex, race, payer, and UNOS status. For the 130 patients, 1-year patient and graft survival rates were 88% and 82%, respectively. There were no significant differences in patient and graft survival or in the unadjusted average cost of liver transplantation by race or payer. After adjusting for demographic and clinical factors, the cost of transplantation was $28,494 more for Medicare/Medicaid recipients compared with the commercial insurance recipients (P = .02). The Medicare/Medicaid group had higher intensive care unit costs compared with the commercial insurance group ($17,807 and $9,359, respectively; P = .03), and a longer length of stay (41 and 31 days, respectively; P = .04). There was no significant difference in cost between whites and nonwhites adjusting for these factors. Medicare or Medicaid patients had a higher cost of transplantation compared with those with commercial insurance. The cost of liver transplantation was similar for whites and nonwhites.

Adolescent↗

Clinical considerations in the use of missing tissue compensators for head and neck cases.

The irregular shape or contour of the patient's surface in the treatment field can alter the dose distribution resulting in non-uniformity of dose in the treatment volume. Missing tissue compensators have been most commonly used to improve this non-uniformity, especially in head & neck, breast, lung and supraclavicular regions. Two or three dimensional compensators have been typically designed to make the dose uniform at a specific depth. This compensation shifts the dose distribution within the treatment volume so that some structures may be under or over compensated. This study will examine how various sites in head and neck cases are affected by compensators. We have also analyzed the uncertainty in compensated dose due to the daily variations in patient repositioning. Computer isodose plans using Cobalt-60 gamma rays and 6 and 18 MV x-rays were generated using coronal contours. Results show that the dose uniformity is improved for the treatment sites, especially for the thinner sites, like the larynx and the anterior cervical neck nodes. Finally, patient movement or positioning errors of +/-1.0 cm will cause a change in dose distribution.

Head and Neck Neoplasms↗

Perfluorocarbon liquid manipulation of high-density intraocular foreign bodies.

BACKGROUND: Perfluorocarbon liquids (PFCLs) are useful for floating various materials off the posterior retina during vitreoretinal surgery. It is generally assumed that buoyancy forces restrict this use to objects with specific gravity lower than that of PFCLs. METHODS: We tested potential intraocular foreign body materials with specific gravities ranging from 1.1-8.7. The relative affinities of each material for saline and PFCL (specific gravity 1.94) were determined. For each material, we then tested the ability of several specimens of increasing surface/volume ratio to float at the saline-PFCL interface in a glass beaker. RESULTS: All materials with specific gravity higher than PFCL demonstrated a greater affinity for saline than for PFCL. Specimens of each of these dense materials floated at the saline-PFCL interface, provided that the surface/volume ratio of the specimen was above a critical value. The critical surface/volume ratio for each material was directly proportional to its specific gravity. CONCLUSIONS: PFCLs may be useful for manipulating a variety of intraocular foreign bodies, even those with specific gravities higher than PFCL. Surface forces, in addition to buoyancy, govern the disposition of small foreign bodies at the saline-PFCL interface.

Eye Foreign Bodies↗

Surgical management of posteriorly dislocated silicone plate intraocular lenses.

Silicone plate intraocular lenses do not adhere to the lens capsule and are placed under tension by postoperative contraction of the capsular bag. Recent reports suggest that a defect anywhere in the capsular bag can potentially lead to delayed posterior dislocation of silicone plate intraocular lenses. These implants are more difficult to grasp and manipulate inside the eye than traditional polymethylmethacrylate lenses and therefore, require special microsurgical techniques. Given sufficient anterior capsular support, posteriorly dislocated silicone plate implants can be repositioned in the ciliary sulcus and do not necessarily require intraocular lens exchange. With proper vitreoretinal surgical techniques, posteriorly dislocated silicone plate intraocular lenses can be repositioned or exchanged with excellent visual results and an acceptably low complication rate.

Foreign-Body Migration↗

An externally powered, multichannel, implantable stimulator-telemeter for control of paralyzed muscle.

An implantable integrated stimulator and telemetry system has been developed. The system is capable of fulfilling the stimulus and telemetry needs of advanced functional neuromuscular stimulation (FNS) applications requiring multiple channels of stimulation and multiple channels of sensor or biopotential sensing. This system provides a command control structure, an inductive radio frequency link providing power to the implant device as well as two-way transcutaneous communication, an ASIC for decoding the command and for providing functional control within the implant, and modular circuitry providing the application specific implant functions. Biocompatible hermetic packaging, lead systems, and in-line connectors suitable for long-term implantation, provide encapsulation for the circuitry and access to the electrodes and sensors used in the application. The first implant configuration realized from this modular system is targeted for clinical implementation in persons with tetraplegia at the C6 level for restoration of hand function, using wrist position as the command control source. The implant device realized has ten channels of stimulation and telemetry used to control and sense a joint angle transducer implanted in the radio-carpal joint of the wrist. A prototype device has been fabricated and is undergoing testing in an animal.

Algorithms↗

The etiology and treatment of macular detachment associated with optic nerve pits and related anomalies.

PURPOSE: Up to two thirds of patients with optic disc pits develop a sight-limiting maculopathy. There is confusion regarding the etiology and nature of the maculopathy in these cases. We present 7 cases of serous macular detachment occurring in association with optic pits or related cavitary anomalies and identify a rhegmatogenous etiology. METHODS: We reviewed the records of 7 patients with optic nerve anomalies and macular detachment. Patients were treated with observation, barricade laser, vitrectomy, and/or gas tamponade. RESULTS: Seven patients were noted to have serous macular detachment associated with an optic nerve pit or other cavitary anomaly. A hole or tear in the diaphanous tissue overlying the optic pit was identified in all cases. None of the patients had a posterior vitreous detachment. Two were treated with photocoagulation only, and 5 underwent pars plana vitrectomy with fluid-gas exchange with or without photocoagulation. Pretreatment visual acuity ranged from 20/30 to 6/200. Posttreatment acuity ranged from 20/25 to 20/100. Five of 7 eyes had final acuities of 20/30 or better, and all treated eyes improved. CONCLUSIONS: A tear in the diaphanous tissue overlying the optic nerve pit is responsible for the development of serous macular detachment and is consistent with findings in similar conditions, such as retinal detachment in association with chorioretinal coloboma. These tears may be quite subtle, and careful biomicroscopic examination is required to appreciate them. The treatment of this condition remains controversial. However, because of the relatively poor prognosis, we believe treatment should include the formation of a barricade to fluid movement as well as sealing and relief of traction from the hole. The value of laser treatment may be increased by the early identification of a defect in the diaphanous membrane prior to the development of macular detachment. Consideration of prophylactic laser might then reduce the need for later, more invasive measures, and improve the prognosis.

Adolescent↗

Isolation and characterization of synaptoneurosomes from single rat hippocampal slices.

A technique for recovering functional synaptoneurosomes containing vesicularized elements of the presynapse and postsynapse into an enriched fraction has been modified to allow for small amounts of starting brain tissue. Single 400 microm rat hippocampal slices were homogenized and sequentially filtered in a 1 cc tuberculin syringe to produce an enriched synaptoneurosome fraction. Data from Western immunoblots for specific synaptic proteins suggest that these fractions are neurochemically similar to synaptosome fractions generated by sucrose gradients. Electron micrographs show that the 'small scale' preparations contain an abundant population of fused presynaptic and postsynaptic vesicularized bodies as previously published for synaptoneurosome fractions prepared from relatively large amounts of starting tissue. The single slice synaptoneurosome preparation is a quick, easy and reliable method for use in the study of synaptic function.

Animals↗

Familial internal limiting membrane dystrophy. A new sheen retinal dystrophy.

OBJECTIVE: To describe the clinicopathologic features of a previously unreported retinal dystrophy. METHODS: Fourteen members of a single family were examined. The medical records of 2 additional family members were reviewed. Pathologic examination was performed on 2 eyes of 1 affected patient. RESULTS: Five individuals were identified with a retinal dystrophy characterized by a glistening inner retinal surface throughout the posterior pole. Visual loss occurred in 3 affected patients in later life owing to superficial polycystic retinal edema and retinal folds. Electroretinographic testing revealed a selective diminution of the b wave. Pathologic examination revealed an abnormal internal limiting membrane with schisis cavities in the inner retina. Endothelial cell swelling, pericyte degeneration, and basement membrane thickening were present in retinal capillaries. CONCLUSIONS: A previously unreported sheen retinal dystrophy is described. Pedigree analysis suggests an autosomal dominant mode of inheritance. A primary defect in Müller cells is the suspected, but unproved, cause. No effective treatment for the associated visual loss is known. The term familial internal limiting membrane dystrophy is proposed to describe this condition.

Adult↗

Sustained closure of surgically repaired macular holes after retinal detachment with submacular fluid.

PURPOSE: To examine the behavior of surgically repaired macular holes when subsequent retinal detachment with submacular fluid develops and to correlate these observations with current theories of macular hole formation and closure. METHODS: We reviewed the medical records of four patients who underwent successful surgical closure of macular holes and subsequently developed rhegmatogenous retinal detachment with macular involvement. RESULTS: No reopening of the original macular hole occurred in any of the four patients. No focal macular attachment was seen that would suggest firm adherence of the macular hole edges to the underlying retinal pigment epithelium. CONCLUSIONS: When retinal detachment with submacular fluid develops in patients with a successfully closed macular hole, sustained closure of the macular dehiscence is typically seen. These findings support reapproximation of the hole edges with an associated retinal wound healing response as the mechanism of hole closure.

Aged↗

A new approach to the surgical management of idiopathic uveal effusion syndrome.

PURPOSE: To describe a new method for managing retinal detachment associated with idiopathic uveal effusion syndrome. METHODS: A 73-year-old man with idiopathic uveal effusion syndrome and total retinal detachment in the right eye underwent quadrantic partial-thickness sclerectomies in conjunction with pars plana vitrectomy, internal drainage of subretinal fluid, and fluid-gas exchange. RESULTS: In the right eye, the patient's retina remained attached for 1 year after the procedure, and visual acuity improved to 20/70 on final follow-up. CONCLUSION: Internal drainage of subretinal fluid performed in conjunction with quadrantic partial-thickness sclerectomies may be a preferred method of treating secondary retinal detachment in idiopathic uveal effusion syndrome. This procedure hastens reattachment of the neurosensory retina and may thereby improve the visual outcome.

Aged↗

Surgical management of posteriorly dislocated silicone plate haptic intraocular lenses.

PURPOSE: To report a large series of delayed posterior dislocation of silicone plate haptic intraocular lenses after Nd:YAG laser capsulotomy and discuss the surgical management of this complication. METHODS: We reviewed the records of 11 consecutive patients (11 eyes) with delayed onset of posterior dislocation of a plate haptic silicone intraocular lens. The cause of the posterior capsular defect, time to dislocation, surgical management techniques, complications, and visual outcome were recorded. RESULTS: In eight of the 11 eyes, the silicone plate haptic intraocular lens dislocated an average of 1.8 months (range, 0 to 6.5 months) after Nd:YAG posterior capsulotomy. The other three eyes had surgical complications at the time of cataract extraction that compromised posterior capsular or zonular integrity and led to silicone plate haptic intraocular lens dislocation from 9 weeks to 6 months (mean, 3.6 months) postoperatively. Surgical management consisted of pars plana vitrectomy with intraocular lens repositioning (six eyes) or exchange (five eyes). The average follow-up period after intraocular lens repositioning or exchange was 6.5 months (range, 1 to 14 months). Best-corrected visual acuity at the last follow-up examination measured 20/40 or better in all but one eye that had preexisting macular disease. CONCLUSIONS: Cataract surgeons and patients should be aware of the potential for plate haptic silicone intraocular lenses to undergo delayed posterior dislocation through capsular defects. This complication can be managed effectively with vitrectomy and either repositioning or exchange of the implant. Postoperative visual acuity is generally excellent, and complications are minimal.

Adult↗

The Endophthalmitis Vitrectomy Study. Relationship between clinical presentation and microbiologic spectrum.

PURPOSE: The authors determine if specific features of the clinical presentation of acute postoperative endophthalmitis correlated with the microbiologic culture results. METHODS: A total of 420 patients who had clinical evidence of endophthalmitis within 6 weeks after cataract surgery or secondary intraocular lens implantation were evaluated as part of a randomized clinical trial. Results of cultures performed on aqueous and vitreous specimens obtained at presentation were categorized as follows: gram-positive coagulase-negative micrococci, "other" gram-positive, gram-negative, and equivocal/no growth. RESULTS: Eleven features of the initial clinical presentation were associated with significant differences in the microbiologic spectrum (P < 0.05). Baseline factors correlating with higher rates of both gram-negative and other gram-positive isolates were: corneal infiltrate, cataract wound abnormalities, afferent pupillary defect, loss of red reflex, initial light perception-only vision, and symptom onset within 2 days of surgery. Gram-negative organisms did not grow in any eyes in which a retinal vessel could be visualized, and 61.9% of these eyes had equivocal or no growth. Diabetes mellitus was associated with a higher yield of gram-positive, coagulase-negative micrococci. Eye pain was not a discriminator for culture results. CONCLUSIONS: The presenting characteristics of acute endophthalmitis after cataract surgery may be helpful in predicting the most likely culture results. Such predictions do not appear sufficiently strong to guide the initial empiric choice of intravitreal antibiotics.

Acute Disease↗

Atypical, severe toxoplasmic retinochoroiditis in elderly patients.

BACKGROUND: The diagnosis of toxoplasmic retinochoroiditis is based primarily on characteristic ocular findings, with supportive serologic evidence. Clinical recognition of atypical presentations is critical for timely antiparasitic drug therapy. METHODS: Case histories were reviewed for seven presumed immunocompetent elderly patients with atypically severe (multifocal or diffuse or both) toxoplasmic retinochoroiditis. Three cases initially were misdiagnosed as acute retinal necrosis syndrome. The correct diagnosis was confirmed in each case by response to antiparasitic drug therapy, polymerase chain reaction studies of intraocular specimens, or histopathologic analysis. RESULTS: The patients ranged in age from 69 to 82 years (median, 74 years). Only three patients had intercurrent medical conditions that may be associated with subtle immune dysfunction (diabetes mellitus and hepatitis C). The extensive necrotizing retinochoroiditis in each patient was nonhemorrhagic and not associated with occlusive retinal arteritis. Despite prompt response to antiparasitic drug therapy, prolonged treatment usually was required, and four patients had retinitis reactivation after discontinuing treatment. Significant visual loss accompanied the infection in most eyes. CONCLUSION: Toxoplasmosis should be considered as a cause of multifocal or diffuse necrotizing retinitis or both in elderly patients. Older patients may be more susceptible to severe ocular Toxoplasma infections because of age-related decline in cell-mediated immunity and chronic underlying diseases.

Aged↗

Clinical considerations in the use of missing tissue compensators for thoracic cases.

The irregular shape or contour of the patient's surface in the treatment field can alter the dose distribution resulting in non-uniformity of dose in the treatment volume. Missing tissue compensators have been most commonly used to improve this non-uniformity, especially in head and neck, breast, lung and supraclavicular regions. Two or three dimensional compensators have been typically designed to make the dose uniform at a specific depth. This compensation shifts the dose distribution within the treatment volume so that some structures may be under or over compensated. This study will examine how various thoracic sites are affected by compensators, with and without heterogeneity corrections. We have also analyzed the uncertainty in compensated dose due to the daily variations in patient repositioning. Computer isodose plans using Cobalt-60 gamma rays and 6 and 18 MV X-rays were generated using sagittal contours. Results show that superficial sites, like the supraclavicular nodes and the spinal cord, do not receive as consistent a dose compensation as the midplane sites. In addition, the compensated lung dose increases. Finally, patient movement or positioning errors of +/- 1.0 cm causes only a slight change in dose distribution.

Humans↗

Complement-induced retinal arteriolar occlusions in the cat.

PURPOSE: To develop an animal model of complement-induced retinal vasculopathy and determine whether it resembles Purtscher's retinopathy. METHODS: Intravenous cobra venom factor was used to achieve intravascular activation of the complement system in cats. After a single bolus of cobra venom factor (75 units/kg), retinal blood flow was monitored at regular intervals by fluorescein angioscopy and angiography. RESULTS: Multiple small retinal arteriolar occlusions were present during the initial fluorescein transit of the immediate postinjection fluorescein study in 12 of 12 animals. Small, rapidly moving gaps in the fluorescein column were seen in two thirds of the animals observed continuously by fluorescein angioscopy. Angiographically, the obstructions were transient, and filling of the associated patches of capillary nonperfusion occurred within 3 minutes. Purtscher's-like ischemic retinal infarcts did not develop in any eye. Histopathologic analysis failed to demonstrate the nature of the transient vascular obstructive lesions, but indirect evidence suggested the possibility of granulocyte aggregates. CONCLUSION: Intravascular activation of the complement system produces transient microembolic retinal arteriolar occlusions in the cat. Although this model may represent a mild form of Purtscher's retinopathy, factors in addition to complement activation appear necessary to induce ischemic retinal infarcts.

Angioscopy↗

Hepatitis C viral infection in liver transplantation.

OBJECTIVE: To study the outcomes of patients who underwent liver transplantation for the primary diagnosis of chronic active hepatitis secondary to hepatitis C virus (HCV). DESIGN AND SETTING: Retrospective review within a university medical center. PATIENTS: Seventy-four adult recipients who received 78 orthotopic liver allografts for the primary diagnosis of chronic active hepatitis secondary to HCV between January 1990 and December 1994. Sixty-seven patients (91%) survived more than 2 months and were analyzed further for recurrent HCV infection. MAIN OUTCOME MEASURE: Recurrence of HCV infection, hepatitis, or cirrhosis and survival rates for patients who were undergoing orthotopic liver transplantation for chronic active hepatitis secondary to HCV. RESULTS: Actuarial survival rates for the entire group were 79.3%, 70.9%, and 64.5% at 1,2, and 3 years, respectively. Four patients (5% underwent retransplantation with an actuarial survival rate of 14.3% at 1 year (P<.05). Thirty-eight patients (57%) had evidence of posttransplant HCV infection, 31 patients (46%) showed histologic evidence of viral hepatitis, and 11 patients (16%) experienced portal fibrosis or cirrhosis. Seven (33%) of the deaths and all retransplantations were secondary to recurrent HCV infection. There were no significant differences in age, sex, United Network of Organ Sharing status, associated diagnoses, intraoperative packed red blood cell requirements, OKT3 use, or 1-, 2-, and 3-year survival rates in the recurrent vs nonrecurrent HCV infection groups. A higher incidence of posttransplant cirrhosis was observed in patients who were treated with tacrolimus (FK 506) (31.8% vs 8.9%, P<.05). Twenty-one patients (70%) received interferon alfa antiviral therapy with a significant benefit in the liver function test results during therapy (P<.01). CONCLUSIONS: Despite recurrence of HCV infection in most patients after transplantation, survival following primary orthotopic liver transplantation for chronic active hepatitis secondary to HCV infection remains favorable, and these patients should continue to be candidates for liver transplantation. In contrast, survival following retransplantation for HCV infection is poor and should be reconsidered. There is an apparent association between the intensity of immunosuppression and recurrent HCV infection and cirrhosis that warrants continued evaluation. Interferon therapy appears to afford benefit to patients in whom recurrent HCV hepatitis develops after transplantation.

Actuarial Analysis↗