Biomedical subjects

J Heethaar

Publications and source records attributed to J Heethaar.

4 recordsLinked to original sources

PubMed1997

Flexible (Polyactive) versus rigid (hydroxyapatite) dental implants.

In a beagle dog study, the peri-implant bone changes around flexible (Polyactive) and rigid hydroxyapatite (HA) implants were investigated radiographically by quantitative digital subtraction analysis and by assessment of marginal bone height, with the aid of a computerized method. A loss of approximately 1 mm of marginal bone height was observed for both the dense Polyactive and the HA implants, after 6 months of loading. This value appeared to be stable from 12 weeks of loading onward. Along the total length of the implant during the first 6 weeks of loading, both the flexible (dense Polyactive) and the rigid (HA) implants showed a decrease in density. However, after this 6-week period, the bone density around the implants increased, and after 18 weeks the original bone density was reached. The flexible Polyactive implants provoked less decrease in density than the rigid HA implants, although not to a statistically significant level. This finding sustains the hypothesis that flexible implant materials may transfer stresses to the surrounding bone more favorably.

Alveolar Bone Loss↗

PubMed1993

Comparison of effects of dopamine hydrochloride and dopexamine hydrochloride on abdominal and femoral hemodynamics in anesthetized dogs.

The effects of dopamine and dopexamine administered in graded intravenous bolus injections (0.1-51.2 micrograms.kg-1) were compared in the renal and femoral, and in a number of splanchnic vessels at the organ level simultaneously in anesthetized dogs. Hemodynamic data are presented for each artery as conductance, which was obtained by dividing mean flow by mean arterial pressure. The data were analyzed in two different ways: 1) by responses at intervals of 3 sec to 12.8 micrograms dopamine or dopexamine during 1 min, and 2) by dose-response curves. Additionally, urine volume was measured during dopamine and dopexamine administration. During a period of 1 min after an injection of dopamine, early and late effects could be distinguished, while heart rate was unaltered. In the superior mesenteric, inferior mesenteric, splenic, common hepatic, renal, and femoral arteries, an early (at 18-21 sec) reduction in conductance was seen. The early reduction was often followed by an increase above the preinjection level. After dopexamine, the early reduction in conductance was not seen, except in the left gastric artery. In contrast to the effect of dopamine, dopexamine induced a more pronounced increase during the late phase. Contrary to dopamine, dopexamine increased the conductance in the common hepatic artery bed. It remains questionable whether dopaminergic receptors are present in this vascular bed. Dopamine raised blood pressure and urine production dose-dependently. Dopexamine decreased aortic pressure. Low dosages of dopexamine increased urine production, without raising renal blood flow. An advantage of dopexamine over dopamine could be that dopexamine does not stimulate alpha-adrenergic receptors.

Blood Flow Velocity↗

PubMed1982

Cardiac function, fiber shortening, and dynamic geometry.

Many models for the study of the pump function of the heart emphasize the importance of cardiac geometry and detailed dimensional data. Because of the lack of accurate measuring techniques, approximate geometries such as shells of revolution have been applied. In this study, methods are presented that measure the dynamic geometry of the working, isolated canine heart by means of ultrasound-velocity tomography techniques. In addition, cardiac dimensions, intramural deformations, and fiber shortening have been measured dynamically in the in situ canine heart throughout the cardiac cycle with implanted radiopaque markers and biplane roentgen techniques. Results of regional contraction and relaxation patterns are presented. Epicardial fiber shortening between apex and base were computed and found to be dependent on the duration of the preceding RR interval.

Animals↗

PubMed1981

Ultrasound velocity tomography, an imaging method.

Analysis of the geometry of the beating heart may yield important information about its condition and function, and may reveal physiologically and clinically relevant information about the influence of regional malfunctioning on the integral heart performance. In this study, a method has been developed which will ultimately allow the determination of the three-dimensional geometry of an isolated working dog-heart throughout the cardiac cycle. The technique will be called 'ultrasound velocity tomography'. Ultrasound velocity tomograms are reconstructions of the spatial distribution of the ultrasound velocity in cross-sections of the object under study. This velocity is to a certain extent characteristic for a tissue, so that various tissues and structures can be identified in a tomogram. The velocities are mathematically reconstructed from thousands of measured times-of-flight of ultrasound pulses which have travelled along different path-ways through the object. By detecting the blood-heart muscle transitions in a tomogram and by combining tomograms from different cross-sections of the heart, a three-dimensional heart-geometry may be obtained. Preliminary results on a formalin-fixed heart are shown and discussed.

Animals↗