Biomedical subjects

Christopher Stone

Publications and source records attributed to Christopher Stone.

3 recordsLinked to original sources

PubMed2004

Reverse digital artery island flap in the elderly.

The following case report illustrates the successful use of the reverse digital artery island flap in elderly patients. The reverse digital artery island flap is a recognised method of providing good quality soft tissue cover to the amputated fingertip. First described in 1986 by Kojima, Lai and Han have reported their experience of 52 and 120 of these flaps, respectively. The majority of patients in the literature are less than 50 years old, with ages ranging from 3 to 62 years. The flap is based upon reversed flow in the digital artery via a communicating branch from the contralateral artery at a point 5mm proximal to the distal interphalangeal joint crease. In the two cases reported below, we have shown that the indications for this type of homodigital flap reconstruction for fingertip amputations can be safely extended to elderly patients.

Aged↗

PubMed2003

Thoracoscopic extracardiac obliteration of the left atrial appendage for stroke risk reduction in atrial fibrillation.

OBJECTIVES: We evaluated left atrial appendage obliteration in high-risk patients with atrial fibrillation (AF). BACKGROUND: Left atrial appendage thrombosis and embolization is the principal mechanism of stroke in AF. Anticoagulation is underutilized and often contraindicated. METHODS: Thoracoscopic Left Appendage, Total Obliteration, No cardiac Invasion (LAPTONI) was undertaken with a loop snare in eight patients and a stapler in seven patients, median age 71 years, with clinical risk factors for stroke and with an absolute contraindication to or failure of prior thrombosis prevention with warfarin. Eleven patients had a history of prior thromboembolism. One patient took sustained warfarin during follow-up. RESULTS: The LAPTONI procedure was completed in 14 of 15 patients, and 1 patient required urgent conversion to open thoracotomy because of bleeding. Patients have been followed up for 8 to 60 months, mean 42 +/- 14 months. One fatal stroke occurred 55 months after surgery, and one non-disabling stroke three months after surgery. Two other deaths occurred, one after coronary bypass surgery and the other from hepatic failure. The subgroup of 11 patients with prior thromboembolism had an annualized rate of stroke of 5.2% per year (95% confidence interval [CI] 1.3 to 21) after LAPTONI, which compares to a rate of 13% per year (95% CI 9.0 to 19) for similar aspirin-treated patients from the Stroke Prevention in Atrial Fibrillation trials (p = 0.15). CONCLUSIONS: The LAPTONI procedure appears technically feasible without immediate disabling neurologic morbidity or mortality, and it demonstrates low post-operative event rates and a statistical trend toward thromboembolic risk reduction in high-risk AF patients.

Adult↗

PubMed2003

For real! XCS with continuous-valued inputs.

Many real-world problems are not conveniently expressed using the ternary representation typically used by Learning Classifier Systems and for such problems an interval-based representation is preferable. We analyse two interval-based representations recently proposed for XCS, together with their associated operators and find evidence of considerable representational and operator bias. We propose a new interval-based representation that is more straightforward than the previous ones and analyse its bias. The representations presented and their analysis are also applicable to other Learning Classifier System architectures. We discuss limitations of the real multiplexer problem, a benchmark problem used for Learning Classifier Systems that have a continuous-valued representation, and propose a new test problem, the checkerboard problem, that matches many classes of real-world problem more closely than the real multiplexer. Representations and operators are compared using both the real multiplexer and checkerboard problems and we find that representational, operator and sampling bias all affect the performance of XCS in continuous-valued environments.

Classification↗