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Biomedical subjects

T John

Publications and source records attributed to T John.

At least 37 records · Page 2Linked to original sources
PubMed1999

Paediatric intracranial aneurysms: results of a surgical series and literature review of Guglielmi detachable coil embolization.

It is known that the profile of aneursyms in the paediatric age group demonstrates a different biology and epidemiology than those in the adult population in terms of size, sex, location, multiplicity and complications such as vasospasm and rebleeding. As a consequence of their different behaviour, timing of surgery does not appear to be such a critical issue in their management decision. Surgical clipping is still the treatment of choice, however, with our growing experience of endovascular techniques, these might prove to be a suitable alternative in the future. We report the results of our surgical series of 17 paediatric and adolescent patients harbouring 18 arterial intracranial aneurysms (age range 7-18 years). Systemic diseases traditionally known to be associated with this entity were excluded. In order to assess endovascular techniques as a potential treatment alternative for this group of patients, we reviewed the current literature, dealing with Guglielmi detachable coil (GDC) embolization of arterial cerebral aneurysms in this age group. No current series deals purely with paediatric aneurysms; we have reviewed paediatric cases reported as part of large adult series. Copyright 1999 Harcourt Publishers Ltd.

Journal Article↗
PubMed1998

Simplified anesthesia technique for scleral tunnel phacoemulsification.

A simplified anesthesia technique for sutureless scleral tunnel, small incision, one-port phacoemulsification is described. Step 1: Mild intravenous sedation is achieved with 1 mg of midazolam and 10 mg of propofol. Step 2: A tetracaine- or preservative-free-lidocaine-soaked Weck cell sponge is applied to the superior bulbar conjunctiva and the superior episcleral tissue for localized anesthesia. Step 3: Preservative-free lidocaine 1%, 0.75 cc, is injected into the anterior chamber for intraocular anesthesia. This technique can be used in the presence of all types of cataracts, requires about 10 seconds to complete, and can be used with all phacoemulsification techniques. Results of the technique in a study population are reported.

Adult↗
PubMed1997

Mitomycin C-augmented trabeculectomy in refractory congenital glaucoma.

OBJECTIVE: The purpose of the study is to determine the safety and efficacy of mitomycin C-augmented trabeculectomy in children with developmental glaucoma treated previously by conventional procedures. DESIGN: Retrospective review of all cases of developmental glaucoma with previously failed conventional procedures that underwent mitomycin C-augmented trabeculectomy between January 1992 and December 1994. PARTICIPANTS: A total of 19 eyes of 13 patients were included in the study. Nineteen eyes included primary congenital glaucoma (15 eyes) with documented failure of primary trabeculotomy, Axenfeld-Reiger syndrome (2 eyes) and aniridia (2 eyes). INTERVENTION: Mitomycin C-augmented (0.4 mg/ml for 3 minutes) trabeculectomy was the chosen intervention. MAIN OUTCOME MEASURES: Preoperative and postoperative intraocular pressures (IOPs), visual acuities, success rate, bleb characteristics, time of surgical failure, and complications were the main outcome measures. RESULTS: The mean IOP was reduced from a preoperative level of 33.74 +/- 10.70 mmHg to 11.89 +/- 1.33 mmHg (P < 0.0001) with the percentage reduction in IOP being 64.75. The mean follow-up was 19.52 +/- 2.65 months. Visual acuity was maintained in all the cases after surgery. Complete success as defined in the authors' study was achieved in 18 eyes (94.74%). Only one patient was classified as a qualified success. The bleb was characterized by its large elevated, avascular, transparent appearance in all the eyes. The only significant complication was retinal detachment in an eye with buphthalmos, aphakia, and large axial length. However, the retina was reattached successfully by retinal reattachment surgery, and visual acuity improved to the preoperative level of 20/200. It was not possible to determine the cause of retinal detachment or to assess the possible role of mitomycin C in this complication. CONCLUSIONS: Mitomycin C-augmented trabeculectomy is a viable option in eyes with failed conventional trabeculotomy surgery.

Adolescent↗
PubMed1996

Surveillance imaging of the operated artery does not alter clinical outcome following carotid endarterectomy.

Clinical outcome was studied in 243 patients undergoing 260 carotid endarterectomies; 166 of these patients underwent serial postoperative surveillance imaging. Including perioperative events, cumulative freedom from ipsilateral stroke was 86 and 82 per cent at 5 and 10 years respectively; the mean incidence of ipsilateral stroke was 1.8 per cent per annum. Twenty patients (8 per cent) suffered cerebral ischaemic events in the hemisphere of the operated side during follow-up: eight transient ischaemic attacks (TIA) and 12 strokes (only two preceded by TIA). Two symptomatic patients were found to have occluded the operated artery but the remainder had no evidence of significant recurrent disease. Cumulative freedom from occlusion or severe (greater than 70 per cent) recurrent stenosis was 87 and 78 per cent at 5 and 10 years respectively; the mean incidence of recurrence of significant disease was 2.2 per cent per annum. No revisional surgery was performed on the operated arteries. In its current format, neither clinical nor surveillance imaging could have prevented any of the strokes observed during follow-up.

Angiography, Digital Subtraction↗
PubMed1995

Fate of the non-operated carotid artery after contralateral endarterectomy.

The long-term fate of the non-operated internal carotid artery (ICA) in 219 patients undergoing contralateral carotid endarterectomy was studied; 151 patients underwent serial postoperative imaging of the vessel. Cumulative freedom from stroke in the non-operated hemisphere was 99, 96 and 86 per cent at 1, 5 and 10 years respectively, giving a mean incidence of stroke of 1 per cent per annum. Only one stroke was preceded by a transient ischaemic attack and no stroke was associated with severe (70 per cent or greater) stenosis of the ICA. Ten patients (7 per cent) with initially mild or moderate disease of the non-operated ICA progressed to severe stenosis during follow-up, but only three became symptomatic and, in each case, the onset of symptoms preceded recognition of disease progression. The long-term risk of stroke in the non-operated ICA territory is very small. Of practical importance is that none of the observed strokes could have been prevented by postoperative surveillance of this type.

Carotid Artery Diseases↗
PubMed1995

Corneal sensation after small incision, sutureless, one-handed phacoemulsification.

Corneal sensitivity was measured in 60 eyes preoperatively and at one day, one week, and one month after small incision, sutureless, one-handed phacoemulsification performed by the same surgeon using the same technique. Corneal sensation remained normal at the center and the 3, 6, and 9 o'clock positions. Decreased corneal sensation was found over the width of the scleral tunnel incision at the limbus, extending in a wedge-shaped sector not encompassing the central cornea.

Aged↗
PubMed1993

Device use patterns and clinical outcome of implantable cardioverter defibrillator patients with moderate and severe impairment of left ventricular function.

The beneficial effects of implanted cardioverter defibrillator (ICD) therapy in patients with malignant ventricular tachyarrhythmias and variable degrees of left ventricular (LV) dysfunction are debated. ICD use and patient survival were examined in 128 patients with malignant ventricular arrhythmias and moderate or severe LV dysfunction. Group I included 64 patients with moderate LV dysfunction (LV ejection fraction of > 30%) and group II, 64 patients with severe LV dysfunction (LV ejection fraction of < or = 30%). Follow-up period ranged from 1 to 78 months. The two groups were similar in age, incidence of coronary artery disease and presenting arrhythmia. The mean LV ejection fraction in group I was 44% +/- 8% and group II was 22% +/- 5% (P < 0.0001). At 4 years of follow-up, 66% of patients from group I and 62% from group II (P = NS) had ICD activation for presumed ventricular tachyarrhythmia. Survival was calculated using actuarial analysis. Arrhythmic or sudden death mortality at 4 years of follow-up was 4% in group I and 7% in group II (P = NS). Cardiac mortality was for group I, 7% (P < 0.05), 12% (P < 0.01), 15% (P < 0.01), and 15% (P < 0.01) for follow-up years 1, 2, 3, and 4, respectively. For group II, cardiac mortality was 27%, 36%, 41%, and 41% for follow-up years for 1, 2, 3, and 4, respectively. The majority of cardiac deaths in both groups was observed in the first 2 years of follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗
PubMed1992

Prospective comparison of biphasic and monophasic shocks for implantable cardioverter-defibrillators using endocardial leads.

Bidirectional shocks using 2 current pathways have been used in endocardial lead systems for implantable cardioverter-defibrillators, but the optimal shock waveform for endocardial defibrillation is unknown. The clinical efficacy and electrical characteristics of bidirectional monophasic and biphasic shocks for endocardial cardioversion-defibrillation of fast monomorphic or polymorphic ventricular tachycardia (VT), or ventricular fibrillation (VF) were evaluated. Thirty-three patients (mean age 60 +/- 12 years, and mean left ventricular ejection fraction 34 +/- 13%) were studied. Defibrillation catheter electrodes were located in the right ventricular apex and superior vena cava/right atrial junction. A triple-electrode configuration including the 2 catheter electrodes and a left thoracic patch was used to deliver bidirectional shocks from the right ventricular cathode to an atrial anode (pathway 1) and the thoracic patch (pathway 2). The shock waveforms examined were sequential and simultaneous monophasic, and simultaneous biphasic. The efficacy of 580 V (20 J) shocks for fast monomorphic VT were comparable for the 3 waveforms (73% for sequential monophasic, 73% for simultaneous monophasic, and 100% for simultaneous biphasic). However, for polymorphic VT and VF, 580 V sequential monophasic shocks had a significantly lower efficacy (25%) than did simultaneous monophasic (75%; p = 0.01) or biphasic (89%; p less than 0.001) shocks. Single-shock defibrillation thresholds with simultaneous biphasic shocks were significantly lower (9 +/- 5 J) than were those with simultaneous monophasic shocks (15 +/- 4 J; p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Electric Countershock↗
PubMed1991

A technique for the determination of center of gravity and rolling resistance for tilt-seat wheelchairs.

A balance platform setup was defined for use in the determination of the center of gravity in the sagittal plane for a wheelchair and patient. Using the center of gravity information, measurements from the wheelchair and patient (weight, tire coefficients of friction), and various assumptions (constant speed, level-concrete surface, patient-wheelchair system is a rigid body), a method for estimating the rolling resistance for a wheelchair was outlined. The center of gravity and rolling resistance techniques were validated against criterion values (center of gravity error = 1 percent, rolling resistance root mean square error = 0.33 N, rolling resistance Pearson correlation coefficient = 0.995). Consistent results were also obtained from a test dummy and five subjects. Once the center of gravity is known, it is possible to evaluate the stability of a wheelchair (in terms of tipping over) and the interaction between the level of stability and rolling resistance. These quantitative measures are expected to be of use in the setup of wheelchairs with a variable seat angle and variable wheelbase length or when making comparisons between different wheelchairs.

Biomechanical Phenomena↗
PubMed1991

Adherence of Acanthamoeba castellanii to new daily wear, extended wear, and disposable soft contact lenses.

We studied the adherence of Acanthamoeba to three types of new, unworn soft contact lenses: daily wear; extended wear; and disposable contact lenses. We used a human corneal isolate of Acanthamoeba castellanii in commercially prepared saline. Unworn lenses were exposed to Acanthamoeba cysts or trophozoites with stirring. After exposure the numbers of Acanthamoeba adhering were determined by light microscopy and confirmed by scanning electron microscopy. In general, the adherence of Acanthamoeba cysts and trophozoites to disposable lenses was less than that to daily wear and extended wear lenses. However, any adherence of Acanthamoeba to soft contact lenses is a potential source of corneal infection.

Acanthamoeba↗
PubMed1990

Bacterial adherence to extended wear soft contact lenses.

The authors studied the adherence of Pseudomonas aeruginosa and Staphylococcus aureus to extended wear soft contact lenses (EWSCLs) with and without focal deposits using both a radiolabeling technique and electron microscopy. P. aeruginosa showed significant adherence to contact lenses in vitro. In contrast, S. aureus failed to show significant adherence to contact lenses in vitro (i.e., the radioactive uptake was not significantly above background). The extent of adherence of Pseudomonas was proportional to the number of focal deposits on the lenses. Results of electron microscopic examination showed the bacteria to be adherent primarily to large focal deposits (greater than or equal to 150 microns). There was no pseudomonal adherence to the small focal deposits (less than or equal to 50 microns) and little adherence to the areas in between the focal deposits. The authors hypothesize that worn lenses, especially those with large focal deposits, serve as a vehicle for the transport of P. aeruginosa to the cornea. This hypothesis could be a partial explanation for the high incidence of keratitis caused by P. aeruginosa in EWSCL patients.

Bacterial Adhesion↗
PubMed1990

Acanthamoeba keratitis successfully treated with prolonged propamidine isethionate and neomycin-polymyxin-gramicidin.

We report a case of Acanthamoeba castellanii keratitis that was successfully treated with intense propamidine isethionate and neomycin-polymyxin-gramicidin over 11 and nine days, respectively. The frequency with which the medications were applied, once every 30 minutes with each medication, has been surpassed only once before in reported cases. Additional medical treatment included topical miconazole 1% drops for five days and clotrimazole 1% drops for one day; the latter was discontinued due to corneal epithelial toxicity. Intense treatment of Acanthamoeba keratitis with these medications has not been reported before for as long as 11 days. Our aggressive approach was successful, and no clinically detectable significant side effects were observed. There has been no recurrence to date.

Acanthamoeba Keratitis↗