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N Burgess

Publications and source records attributed to N Burgess.

10 recordsLinked to original sources
PubMed1994

A constructive algorithm that converges for real-valued input patterns.

A constructive algorithm is presented which combines the architecture of Cascade Correlation and the training of perceptron-like hidden units with the specific error-correcting roles of Upstart. Convergence to zero errors is proved for any consistent classification of real-valued pattern vectors. Addition of one extra element to each pattern allows hyper-spherical decision regions and enables convergence on real-valued inputs for existing constructive algorithms. Simulations demonstrate robust convergence and economical construction of hidden units in the benchmark "N-bit parity" and "twin spirals" problems.

Algorithms↗
PubMed1993

The frusemide test: simple screening test for renal acidification defect in urolithiasis.

Urinary pH was first labelled as a risk factor for patients with recurrent calcium stone disease of the renal tract in 1978. The standard diagnostic test for patients with a history of stones, who appear to have urinary acidification defects is the ammonium chloride test. However, the performance of this test results in significant morbidity, particularly nausea and vomiting, and as a result there is little enthusiasm for screening for such defects. We describe a screening test that may be used to determine which patients require more definitive testing. It involves an oral dose of frusemide (40 mg) followed by half-hourly urine sampling for pH. For the detection of a renal tubular acidification defect, the frusemide test had sensitivity = 100%, specificity = 82%, predictive value of a positive result = 40%, predictive value of a negative result = 100%, screening efficiency = 84%, and there was no morbidity. During the ammonium chloride test 80% of the patients vomited or felt very nauseated.

Ammonium Chloride↗
PubMed1991

Earmoulds: some benefits from horn fitting.

The narrow bore of conventional hearing aid earmoulds restricts the transmission of higher auditory frequencies. For subjects with moderate to severe high-frequency hearing loss this is likely to have an adverse effect on the perception and recognition of phonemes with high-frequency components. Twenty-two subjects with predominantly high-frequency hearing loss underwent a series of tests to compare the performance of earmoulds having conventional 1.9 mm through-tubing with earmoulds fitted with a smooth horn with a final internal diameter of 4 mm. The test battery comprised free-field Békésy audiometry, in-the-ear pressure measurement, speech audiometry using AB word lists and semantic differential rating of the relative sound quality of the two systems. Subjectively the horn fitting was rated as clearer, more natural, undistorted and acoustically comfortable. Objectively, by both Békésy audiometry and in-the-ear pressure measurement, the horn gave more gain in the higher auditory frequencies. With the horn there was improved recognition of phonemes, especially fricatives and affricatives.

Adult↗
PubMed1985

Improved intraoperative evaluation of mitral valve operations utilizing two-dimensional contrast echocardiography.

Whenever possible, precise mitral valve repair is preferable to valve replacement. Present methods for intraoperative detection of mitral regurgitation, primarily hemodynamic measurements and direct palpation, may underestimate or not detect the presence and severity of regurgitation. We have investigated two-dimensional contrast echocardiography as a means of improving our intraoperative assessment of mitral valve function both before and after repair or replacement. After exposure of the heart, a baseline two-dimensional echocardiogram (in modified long- and short-axis planes) is performed using a hand-held 5 mHz mechanical transducer. Five milliliters of agitated 5% dextrose in water is injected into the left ventricle through a transseptal needle to generate detectable microbubbles. In the absence of mitral regurgitation, virtually all microbubbles exit through the aorta; in the presence of regurgitation, a mass of microbubbles reflux into the left atrium. After repair of the mitral valve and immediately after bypass, the contrast echocardiogram is repeated and hemodynamic measurements are obtained. Forty-three patients (37 with mitral valve disease and six additional patients without mitral disease) undergoing cardiac operations were evaluated. Experience with intraoperative two-dimensional contrast echocardiography has accurately demonstrated relatively small degrees of mitral regurgitation when conventional techniques failed to do so and has allowed more precise repair of the residual regurgitation. Two commissurotomy and two annuloplasty patients who were thought to have satisfactory repairs underwent immediate second procedures because of significant residual mitral regurgitation demonstrated solely by this echocardiographic microbubble technique. No complications associated with this technique have developed. We conclude that intraoperative two-dimensional contrast echocardiography is a sensitive and safe technique that allows intraoperative detection of even small degrees of mitral regurgitation and provides a basis for precise repair of mitral valve lesions.

Adult↗
PubMed1984

Intraoperative contrast echocardiography to evaluate mitral valve operations.

Intraoperative two-dimensional contrast echocardiography was performed on 29 patients undergoing open heart surgery to determine the presence of mitral regurgitation before and immediately after the operative procedure: 14 patients had predominant mitral stenosis, 9 had severe mitral regurgitation and 6 had no mitral valve disease (control subjects). Two-dimensional echocardiography was performed by applying a 5 MHz transducer directly on the heart during injection of saline solution through an apical ventricular sump or transseptal needle, generating contrast microbubbles, with imaging in two planes. Baseline studies were performed after thoracotomy and pericardiotomy before cardiopulmonary bypass, and a second study was done after the operative procedure, with the patient off cardiopulmonary bypass with hemodynamic stabilization before chest closure. No control subject had contrast evidence of mitral regurgitation before or after cardiopulmonary bypass. Two of three patients with mitral valvuloplasty and two of five with commissurotomy required a second operative procedure before chest closure because of persistent mitral regurgitation detected by intraoperative two-dimensional contrast echocardiography. Thirteen of the 15 patients with valve replacement had no mitral regurgitation after cardiopulmonary bypass. Intraoperative two-dimensional echocardiographic findings correlated with data from postoperative clinical examinations and two-dimensional echocardiography-Doppler studies. It is concluded that two-dimensional echocardiography with contrast is an important intraoperative tool for assessing the presence and relative severity of mitral regurgitation after mitral commissurotomy, valvuloplasty or valve replacement. This technique may allow surgeons to be more aggressive in combining reparative operative procedures (that is, commissurotomy and valvuloplasty) in an attempt to retain native valves.

Adult↗