Search PubMed⌕ Search

Biomedical subjects

W M Smith

Publications and source records attributed to W M Smith.

At least 235 records · Page 13Linked to original sources
PubMed1978

Error propagation in quantitative biplane cineroentgenography.

The propagation of errors in quantitative biplane cineroentgenography was investigated to see which variables were the most critical. The analysis was carried out both for the propagation of root-mean-square errors and for errors as derived by a Taylor expansion of the reconstruction equations. The reconstruction is most sensitive to the measured values of the coordinates, as opposed to the parameters of the physical system. It was found that decreasing the error in one parameter to zero does not significantly affect the accuracy of the reconstruction; it is more efficient to reduce the errors for all of the parameters simultaneously.

Animals↗
PubMed1978

Characteristics of atrioventricular conduction and the spectrum of arrhythmias in lown-ganong-levine syndrome.

Electrophysiological characteristics of atrioventricular (A-V) conduction and refractoriness were examined in 12 patients with Lown-Ganong-Levine (LGL) syndrome referred for assessment of the following arrhythmias: (group I) regular narrow QRS tachycardia 6/12 (50%), (group II) atrial fibrillation (AF) 2/12 (17%), group III) ventricular tachycardia (VT) 4/12 (33%). A-V node refractory periods were shorter, and enhanced A-V conduction more frequent (7/12, 58% vs 7/28, 25%) in LGL patients compared to similar studies in 28 normal controls. During laboratory study reciprocating tachycardia (RT) due to re-entry within the A-V node occurred in 4/12 (33%) LGL patients, and exhibited a shorter cycle length (294 +/- 60.4 msec) than did the same arrhythmia in 11/28 (39%) controls 372 +/- 51.8 msec, P less than 0.05). Similarly, RT utilizing a concealed accessory pathway had a shorter cycle length (228 +/- 3.5 msec) in 2/12 (17%) LGL patients than in 11/28 (39%) controls (314 +/- 24.3 msec, P less than 0.001). In AF, the shortest R-R intervals in 4/12 (33%) LGL patients (2 group I, 2 group II) were shorter than in 15/28 (54%) control patients (254 +/- 42.2 msec vs 325 +/- 64.2 msec, P less than 0.05). The mean R-R internvals did not differ significantly (LGL 372 +/- 89 msec vs control 428 +/- 82.6 msec). This study suggests that the characteristics of A-V conduction and refractoriness may permit development of more rapid heart rates during certain arrhythymias in LGL patients compared to normal controls. Furthermore, the occurrence of VT in patients with LGL sydrome indicates that symptomatic arrhythmias require specific diagnosis.

Adolescent↗
PubMed1978

Determinants of antegrade echo zone in the Wolff-Parkinson-White syndrome.

Forty-five patients with the Wolff-Parkinson-White syndrome and reciprocating tachycardia which utilized the atrioventricular (A-V) node for antegrade conduction and an accessory pathway for ventriculo-atrial (retrograde) conduction were studied. The extrastimulus technique in the right atrium and coronary sinus at multiple pacing cycle lengths was used. Three types of "echo zones" were defined by the relationship of the antegrade effective refractory period (ERP) of the accessory pathway, the longest coupling interval accompanied by an atrial echo, the ERP of the A-V node, and the functional refractory period of the atrium. Eighteen of 45 patients (40%) had more than one type of echo zone demonstrated by changing either pacing site or pacing cycle length or both. Pacing site and intraventricular conduction delay were found to have important effects on the longest coupling interval accompanied by an atrial echo in those echo zones in which the longest coupling interval accompanied by an atrial echo was less than the antegrade ERP of the accessory pathway. The echo zone is a useful concept to explain the physiology of the common reciprocating tachycardia in patients with the Wolff-Parkinson-White syndrome. However, the echo zone is profoundly affected by pacing site and pacing cycle length. When these variables are changed, many patients can be shown to have more than one type of echo zone. Studies of the echo zone have limited value as therapeutic guides.

Cardiac Pacing, Artificial↗
PubMed1978

Separation testing of hemodialysis shunts using dynamic and static forces in a controlled environment.

Analytical methods are presented for determining the longitudinal dynamic and static forces needed to overcome the transverse frictional forces and effect the separation of hemodialysis shunt connections under controlled environmental conditions. Results for different types of shunts and their associated connectors are reported along with the factors that affect the separation force and separation times.

Biomedical Engineering↗
PubMed1977

Treatment of mild hypertension: results of a ten-year intervention trial.

Three hundred and eighty-nine subjects, ages 21-55, with diastolic blood pressures between 90 and 115 mm Hg were studied prospectively for 7-10 years in a controlled intervention trial to determine whether pressure lowering reduces the incidence of cardiovascular complications and death. The assignment to therapy, either a combination of a diuretic and rauwolfia serpentina, or an identical placebo, was random. Adverse effects required termination in only 23 (5.9%) cases. Diastolic blood pressure (DBP) was reduced an average of 10 mm Hg (systolic equals 16 mm Hg) in the active treatment group with no change in the placebo group. The major end points of death, myocardial infarction, and stroke totaled 17 and were nearly equally divided between treatment and placebo. Other manifestations of coronary disease were also equally distributed. Complications such as electrocardiographic hypervoltage, left ventricular hypertrophy, radiogrpahic cardiomegaly, and retinopathy occurred in the placebo group at a rate of 53.1 per 100 subjects compared to 23.8 per 100 in those on active drugs. Treatment failure occurred in 24 placebo-treated cases and none of the active group. The overall effectiveness of pressure lowering in reducing these complications and treatment failure was 60%. It is concluded that given the lower level of excess risk in mild uncomplicated hypertension, and the failure of active drug therapy to protect against coronary disease, systematic follow-up without drugs while attempting hygienic intervention and control of other risk factors may be a reasonable alternative for this large group.

Adult↗
PubMed1977

Collaborative study of a spectrofluorometric assay for Rauwolfia serpentina tablets and powdered root, using a vanadium pentoxide-phosphoric acid determinative step.

Reserpine-rescinnamine group alkaloids are extracted from Rauwolfia serpentina preparations into dimethylsulfoxide (DMSO)-methanol and diluted with 0.5N H2SO4. The chloroform extract of this solution is passed through a 0.1N NaOH-Celite column and then through a silica gel column. The weakly basic alkaloids trapped on the latter column are eluted with chloroform-methanol; a portion of the eluate is treated with a vanadium pentoxide-phosphoric acid solution, and the reserpine-rescinnamine content is determined by measuring the intensity of the resulting fluorescence. The following means and standard deviations (11 collaborators) were obtained for the determination of reserpine-rescinnamine group alkaloids in 4 samples of Rauwolfia serpentina (NF reference powder, 100 and 50 mg commercial tablets, and 45 mg synthetic tablet formation): 0.173%, 0.0050; 0.128%, 0.0030; 0.150%, 0.0069; and 0.142%, 0.0032; respectively. The method has been adopted as official first action.

Indicators and Reagents↗
PubMed1976

Collaborative study of a spectrofluorometric assay for Rauwolfia serpentina tablets and powdered root.

Reserpine-rescinnamine group alkaloids are extracted from Rauwolfia serpentina preparations into a dimethylsulfoxide (DMSO)-methanol mixture and diluted with 0.5N H2SO4. The chloroform extract of this solution is passed through a 0.1N NaOH-Celite column and then through a silica gel column. The weakly basic alkaloids trapped on the latter column are eluted with a methanol mixture; a portion of the eluate is treated with nitrous acid and the reserpine-rescinnamine content is determined by measuring the intensity of fluorescence of the oxidation product. The following means and standard deviations (11 collaborators) were obtained for the determination of reserpine-rescinnamine group alkaloids in 4 samples of Rauwolfia serpentina (NF reference powder, 100 mg and 50 mg commercial tablets, and a 45 mg synthetic tablet formulation) : 0.174% +/- 0.0112, 0.131% +/- 0.0047, 0.160% +/- 0.0100, and 0.153% +/- 0.0083, respectively.

Indicators and Reagents↗
PubMed1975

Long-term therapy for chronic bacteriuria in men. U.S. Public Health Service cooperative study.

Response to therapy, renal function, and mortality were analyzed in a prospective study of 249 men with bacteriuria followed for up to 10 years. All patients received initial organism-specific antibiotic therapy followed by 2 years of continuous treatment with sulfamethizole, nitrofurantoin, methenamine mandelate, or placebo. Continuous therapy with active drugs delayed recurrence of bacteriuria and reduced acute clinical exacerbations of infection. Patients with pure Escherichia coli bacteriuria, normal intravenous pyelogram, no previous therapy, and a normal prostate had a good prognosis with short-term antibiotic therapy alone. The presence of prostatic or upper urinary tract calculi, pyelonephritic scars, or mixed or enterococcal infections predicted a poor bacteriologic prognosis. In the absence of severe urologic disease or concomitant noninfectious renal disease no patients with persistent bacteriuria developed renal failure. Continuous antibiotic therapy is of value in selected male patients with bacteriuria in reducing recurrence and acute clinical exacerbations of urinary tract infection.

Adult↗
PubMed1972

Feedback: real-time delayed vision of one's own tracking behavior.

When a televised display of a person's owni behavior in pursuit tracking is delayed, his performance, as measured by time on target, is seriously degraded. Data for six subjects on two trackitng pattertns under seven delay values reveal a linear inverse relationship between the logarithm of the time on target and the magnitude of delay.

Feedback↗