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Biomedical subjects

D E Gibson

Publications and source records attributed to D E Gibson.

16 recordsLinked to original sources
PubMed1999

Valve orifice area alone is an insufficient index of aortic stenosis severity: effects of the proximal and distal geometry on transaortic energy loss.

BACKGROUND AND AIMS OF THE STUDY: Standard measures of hemodynamic severity of aortic valve stenosis vary widely among patients with and without clinical symptoms. Our hypothesis is that valve orifice area alone is not the sole determinant of adverse clinical outcome. Stenotic orifice area ratio is ratio of the cross-sectional stenotic orifice area to the down-stream, ascending aorta cross-sectional area. Determination of workload together with aortic valve orifice area ratio might improve risk stratification among asymptomatic patients with critical aortic stenosis. Accordingly, application of both parameters together might be useful in guiding management decisions in this condition. METHODS: In this study the dependency of transaortic fluid mechanical energy transfer (one component of left ventricular workload) on aortic valve orifice area is shown using modeling and experimental techniques. RESULTS: For a stroke volume of 62 ml at a heart rate of 60 beats/min, the piston work (analogous to left ventricular work) increased by 17% as the stenotic orifice area ratio decreased from 0.60 to 0.25, by 35% as the ratio fell from 0.25 to 0.20, and by 73% as the ratio fell from 0.20 to 0.10. CONCLUSIONS: As predicted by the fundamental fluid mechanical theory, simulated left ventricular work and energy loss in aortic stenosis are influenced not only by the effective stenotic valve orifice area, but also by the geometry of the inflow and outflow conduits, proximal and distal to the valve. These findings might explain clinically observed discrepancies between valve orifice area and the onset of the classical symptoms of severe aortic stenosis that reflect the left ventricular workload. Consideration of the left ventricular work in addition to the effective valve orifice area should enhance clinical evaluation, prognostication and risk stratification among patients with severe aortic stenosis.

Aorta↗
PubMed1998

The hemodynamic effects of mechanical prosthetic valve type and orientation on fluid mechanical energy loss and pressure drop in in vitro models of ventricular hypertrophy.

BACKGROUND AND AIMS OF THE STUDY: When choosing a prosthetic replacement for a natural heart valve, one objective should be to minimize the workload placed on the heart. This workload can be raised by fluid mechanical energy losses imposed by the valve. For a patient with left ventricular hypertrophy, certain aortic valve types and orientations could be hemodynamically superior to others. METHODS: This study used a control volume analysis to investigate the effects of prosthetic mechanical aortic valve type and orientation on fluid mechanical energy losses in four in vitro models of the left ventricular outflow/aortic inflow tract in various degrees of hypertrophy. Flow visualization studies were performed to qualitatively validate this analysis. The two most commonly used mechanical valve designs were studied: the St. Jude Medical (SJM) bileaflet valve and the Medtronic Hall (MH) tilting disk valve. Experiments were performed in pulsatile flow at a constant heart rate of 60 beats per min for five valve type/orientation combinations. The stroke volume was varied between 40 and 120 ml in five increments for each model and valve/orientation studied. RESULTS: Valve type and orientation was found to have a significant effect on energy losses in these models (p < 0.05). Valve/orientation combinations with leaflets or disks approximately parallel to the proximal flow direction created lower energy losses than others. The MH valve in the 180 degrees orientation caused significantly less energy losses and pressure drops (orifice and recovered) than any of the SJM valve/orientations studied (p < 0.05). The SJM and MH valves in the 0 degree orientation were responsible for significantly more energy loss than other valve/orientations studied (p < 0.05). An aortic inflow tract model with severe (45 degrees) curvature created significantly more energy loss (p < 0.05) than those with less curvature (15 and 30 degrees). However, the insertion of an obstruction simulating a hypertrophic tissue outgrowth caused much more energy loss than increasing the severity of outflow tract curvature from 15 to 45 degrees. Both orifice pressure drop and recovered pressure drop had excellent linear correlations with energy losses found in these models. CONCLUSIONS: These results imply that: (i) prosthetic valve type and orientation should be considered when replacing the aortic valve of a hypertropic patient; (ii) removal of obstructions within the aortic inflow tract will decrease ventricular workload; and (iii) the Doppler-estimated pressure gradients commonly use by cardiologists to assess the performance of a prosthetic valve, correlate very well with left ventricular energy loss and work load.

Aortic Valve↗
PubMed1989

Camphor ingestion.

Camphor ingestion is a toxic ingestion that is seen infrequently in the emergency department. It is remarkable for its rapidity of action and toxicity. A case of camphor ingestion that displayed toxic effects is presented. The pharmacology, manifestations, and management of this readily available substance are discussed.

Administration, Oral↗
PubMed1987

Dentistry in the emergency department.

Dental problems are commonly seen in the emergency department. Although most emergency physicians have had little formal training in dentistry, the majority of these problems can be diagnosed and treated without the need for emergent dental consultation. The necessary procedures may require initial instruction by a cooperative consultant but are easily learned and well within the scope of practice of the emergency physician. Time invested in familiarization with the diagnosis and treatment of the more common dental problems will be rewarded with patient satisfaction.

Anesthesia, Dental↗