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Biomedical subjects

M W Meyer

Publications and source records attributed to M W Meyer.

At least 19 recordsLinked to original sources
PubMed1992

The platelet interactivity phenotype of Streptococcus sanguis influences the course of experimental endocarditis.

A strain of Streptococcus sanguis that induced rabbit platelets to aggregate in vitro (Agg+ phenotype) was hypothesized to be a more virulent pathogen than an Agg- strain in experimental endocarditis in rabbits. A left ventricular catheter was implanted, and then an Agg+ or Agg- strain was inoculated intravenously. Vegetations formed on the aortic semilunar valves but were unaffected by the duration of implantation of the catheter. Vegetations enlarged by accumulating platelets and their mass increased directly with the duration of endocarditis. Inoculation of the Agg+ strain consistently caused endocarditis with significantly larger vegetations, a more severe clinical course (including febrile episodes, hematological changes, and signs of myocardial ischemia), more gross lesions in major organs, and greater mortality than inoculation with the Agg- strain, saline, or the Agg+ strain pretreated with monospecific rabbit immunoglobulin G or Fab fragments against its platelet aggregation-associated protein (PAAP; class II). In experimental endocarditis, PAAP expressed by Agg+ S. sanguis appeared to be an important virulence factor.

Animals↗
PubMed1992

[Functional structures of the aorta as a predilection area of the earliest atherosclerotic changes].

Marked lipid deposits selectively localized in the grooves of so-called aortic functional structures were found in a 5-month-old infant who died of rapidly progressing crescentic glomerulonephritis. A prominent nephrotic syndrome comprising hypercholesterolemia and triglyceridemia was present and led to extensive lipid infiltration of the aortic intima. Development of the intimal lesions was probably enhanced by hypertension found in final phase of the illness. Spontaneously enhanced permeability of the intima in the "grooves" and a special constellation of haemodynamic forces along the functional structures were probably responsible for the peculiarly selective localization of lipid deposits that has so far not been described in the literature.

Aorta, Abdominal↗
PubMed1991

The kinetics of diastereomeric amino acids with o-phthaldialdehyde.

The kinetics of the reaction of the amino acid epimers L-isoleucine, D-allo-isoleucine, L-threonine, and D-allo-threonine with o-phthaldialdehyde and mercaptoethanol were determined at 25 degrees C. L-Isoleucine reacts faster than its D-epimer whereas L-threonine reacts slightly slower than its D-epimer. In the case of isoleucine, the consequence can be an allo/iso ratio which in the worst case is 25% too low if these amino acids are quantified by liquid chromatography and o-phthaldialdehyde fluorescence detection. The effect on dating of fossils by amino acid racemization is discussed.

Amino Acids↗
PubMed1986

Umbilical blood pressures and utero-placental blood flow in spontaneously hypertensive rats.

Some substrains of spontaneously hypertensive rats (SHR) are hypertensive at birth, suggesting the possibility of pre-natal hypertension. Fetal haemodynamics are sensitive to utero-placental blood flow changes. Thus, we used micropuncture to measure umbilical vein blood pressure (BP) in SHR and Wistar-Kyoto rats (WKY) at 18 and 20 days post-conception. We determined utero-placental blood flow (UPBF) at 17 and 20 days post-conception by the microsphere method. Results showed that SHR fetuses were hypertensive only at 20 days. Fetal heart:body weight ratio was higher in SHR, decreased with age and was not associated with BP or heart rate. Utero-placental weight was not affected by either age or strain. However, utero-placental blood flow was low in SHR at 20 days. Thus, in SHR pre-natal hypertension occurs between 18 and 20 days post-conception; pre-natal hypertension is associated with low utero-placental blood flow.

Animals↗
PubMed1984

Mechanisms of recovery from aphasia: evidence from serial xenon 133 cerebral blood flow studies.

In 21 patients who suffered aphasia resulting from left hemisphere ischemic infarction, the xenon 133 inhalation cerebral blood flow technique was used to measure cerebral blood flow within 3 months and 5 to 12 months after stroke. In addition to baseline measurements, cerebral blood flow measurements were also carried out while the patients were performing purposeful listening. In patients with incomplete recovery of comprehension and left posterior temporal-inferior parietal lesions, greater cerebral blood flow occurred with listening in the right inferior frontal region in the late studies than in the early studies. In patients with nearly complete recovery of comprehension and without left posterior temporal-inferior parietal lesions, early listening studies showed diffuse right hemisphere increases in cerebral blood flow. Later listening studies in this latter patient group showed greater cerebral blood flow in the left posterior temporal-inferior parietal region. The study provides evidence for participation of the right hemisphere in language comprehension in recovering aphasics, and for later return of function in left hemisphere regions that may have been functionally impaired early during recovery.

Adult↗
PubMed1983

Flap design and the LeFort III osteotomy: blood flow investigation.

The effect on local blood flow of flap design in a LeFort III osteotomy was examined in this study. The radioactive microsphere technique was used to make serial flow determinations in two groups of macaque monkeys. The use of seven skin and mucosal incisions was compared with a coronal flap procedure. Significant blood flow reductions to the midface segment where measured when a coronal incision was the sole access in performance of the osteotomies. The findings indicate that the multiple incision approach is more biologically sound than the coronal incision approach in the LeFort III osteotomy. Important information about the surgical techniques can be determined from the data and applied to a more successful performance of the LeFort III osteotomy.

Animals↗
PubMed1982

Regional cerebral blood flow correlates of auditory processing.

To study the regional cerebral blood flow (rCBF) correlates of auditory processing, we performed rCBF measurements in young, normal right-handed volunteers engaged in listening tasks. Using the xenon Xe 133 inhalation technique, rCBF was measured in 11 regions in each hemisphere. Compared with a baseline condition, significant rCBF increases in the left posterior Sylvian regions were associated with both verbal phonologic processing and nonverbal acoustic processing. Verbal semantic processing was associated with unilateral increased rCBF in the posterior Sylvian region contralateral to the hand used for response signaling. Comparison of rCBF from homologous regions of the two hemispheres also confirmed a clear difference between the rhyme detection and meaning detection tasks, with the former strongly lateralized to the left hemisphere. Thus, changes in rCBF were related to the nature of the listening task.

Acoustic Stimulation↗
PubMed1981

Evaluation of local blood flow after total maxillary osteotomy.

The radioactive microsphere method was used to quantitate blood flow to selected maxillary tissues before and during left-side cervical sympathetic stimulation in a group of 15 macaque monkeys, nine of which received Le Fort osteotomies. The sympathetic system to regulate blood flow appears to have been modified and has not returned to its normal regulatory status six weeks after the operation.

Animals↗
PubMed1978

Blood flow and oxygen consumption in steroid-treated dental pulps.

This study examined pulpal blood flow and oxygen consumption by the dental pulps of dogs. Blood flow was measured by the radioactive microsphere method and oxygen uptake was determined by the indirect Warburg approach. These variables were assessed 2 days after the canine teeth had been exposed and treated with either a cotton pellet impregnated with 1 per cent prednisolone or normal saline. The analysis indicated that the pulpal blood flow as well as the oxygen consumption did not differ between the steriod-treated tooth and the corresponding saline-treated tooth in the same jaw.

Animals↗
PubMed1978

Quantitation of blood flow after anterior maxillary osteotomy: investigation of three surgical approaches.

The radioactive microsphere method was used to quantitate preoperative and postoperative blood flows in macaque monkeys when three different surgical approaches for anterior maxillary osteotomy were performed. Despite distinct variations in flap designs among the experimental groups, preoperative and postoperative determinations of blood flow were essentially unchanged. Results of the study suggest that a palatal, labial, or combined mucoperiosteal pedicle should be adequate to preserve the flow of blood to tissues in the osteotomized segment.

Animals↗
PubMed1977

Tonometric measurement of dental pulpal and mandibular marrow blood pressures.

Dental pulpal and mandibular marrow vascular pressures were studied with a tonometric method under conditions of autoperfusion and step flow controlled perfusion. The tonometric pulpal and marrow pressures averaged 17 +/- 5 mm Hg and 20 +/- 6 mm Hg, respectively. The venous end pressure was 16 +/- 8 mm Hg at a perfusion pressure of 156 +/- 28 mm Hg. The tonometric pulpal pressures were lower and were less variable than the comparable canulation pulpal pressures.

Animals↗
PubMed1977

Quantification of pulpal blood flow in developing teeth of dogs.

Pulpal blood flow was determined in 32 dogs ranging in age from 6 weeks to 18 months by the isotope fractionation method incorporating diffusible and nondiffusible tracers. Dogs were placed into selected age groups by the developmental status of the canine teeth. For the teeth sampled, the maxillary first, second, and third incisors along with the canines and first molars, pulpal blood flow was determined to be not different in teeth at various developmental stages. For some dental pulps, alveolar mucosa, and bone, the tracers were not determining equivalent blood flows. Because of incomplete trapping of the 7- to 10 mu microspheres and the flow limitation of 86Rb, the 15 mu spheres would appear to be a reliable indicator of "total" blood flow to pulpal tissues. However, in alveolar mucosa and bone, and 15 mu microspheres may not be completely trapped and thus, may underestimate blood flow to these tissues. Within the age range of these dogs, tissue blood flow was not dependent upon the stages of oral development.

Age Factors↗
PubMed1977

Quantitation of blood flow after Le Fort I osteotomy.

Le Fort I maxillary osteotomies were performed on ten macaque monkeys. The particle distribution method (nondiffusible radioactive microspheres) was used to quantitate local blood flow before and after surgery. Significant reduction in blood flow to the osteotomized maxillary segment was noted in those animals (group S) where the descending palatine vessels were transected. Those animals in which the vascular pedicle was intact (group I) showed decreased blood flow to the attached gingiva and alveolar bone, but palatal tissue blood flow was unchanged or increased. The results reinforce the precept of the importance of maintaining an adequate nutrient pedicle when performing orthognathic surgical procedures.

Alveolar Process↗
PubMed1977

Blood flow changes after sagittal split of the mandibular ramus.

Blood flows to various cephalic tissues were determined by the microsphere method before and after unilateral sagittal split of the mandible in macaque monkeys. Significant blood flow decreases were found in certain bony regions of the osteotomized mandible while blood flow to the masseter and medial pterygoid muscles on theosteotomized side was significantly increased. Judicious stripping of the mucoperiosteum and pterygomassteric sling may be an important consideration when planning the sagittal split approach to correct certain mandibular anomalies.

Animals↗