Biomedical subjects

L L Demer

Publications and source records attributed to L L Demer.

60 records · Page 4Linked to original sources

PubMed1987

Relation between geometric dimensions of coronary artery stenoses and myocardial perfusion reserve in man.

To determine the relation between stenosis anatomy and perfusion in man, 31 patients had quantitative coronary arteriography and positron imaging (PET) with Rb-82 or N-13 ammonia at rest and after dipyridamole-handgrip stress. 10 patients were also studied after angioplasty (total stenoses = 41). Percent narrowing and absolute cross-sectional luminal area were related through a quadratic function to myocardial perfusion reserve determined with PET. Arteriographically determined coronary flow reserve was linearly related to relative myocardial perfusion reserve as expected, based on the derivation of equations for stenosis flow reserve. All of the correlations had considerable scatter, indicating that no single measurement derived by coronary arteriography was a good indicator of perfusion reserve by PET in individual patients. This study provides the relation between all anatomic dimensions of coronary artery stenoses and myocardial perfusion reserve in man, and suggests that PET indicates the functional significance of coronary artery stenoses for clinical purposes.

Arterial Occlusive Diseases↗

PubMed1987

Changes in myocardial perfusion reserve after PTCA: noninvasive assessment with positron tomography.

The effect of percutaneous transluminal coronary angioplasty (PTCA) on myocardial perfusion reserve has not been previously determined. Accordingly, 11 patients underwent positron imaging with [13N]ammonia or 82Rb at rest and following dipyridamole + handgrip stress before and after PTCA. The ratio of stress to rest activity (S:R) was determined for each region of interest. Relative myocardial perfusion reserve by positron tomography (RMPR) was calculated by dividing S:R of the stenotic area by a corresponding value from a normal reference area of the same patient. Automated quantitative coronary arteriography was used to objectively measure the percent diameter (%D) and the percent area narrowing (%A) of the stenoses. In nine patients with successful PTCA, %D and %A improved (68 +/- 10 to 49 +/- 15% and 92 +/- 3 to 72 +/- 5%) and RMPR increased from 0.79 +/- 0.07 to 0.96 +/- 0.05. In the two patients in whom PTCA was unsuccessful, RMPR was unchanged. Changes in RMPR correlated inversely with changes in %D (r = -0.68) and %A (r = -0.92) and directly with improved coronary flow reserve derived from all stenosis measurements (r = 0.73, p less than 0.001 for each). This study suggests that dipyridamole + handgrip stress imaging with PET can be used to assess changes in myocardial perfusion reserve before and after PTCA with the potential for determining restenosis noninvasively.

Adult↗

PubMed1987

The use of pressure-volume curves to assess the mechanism and adequacy of stenosis dilatation by balloon angioplasty.

This report introduces a new technique for monitoring and understanding the mechanical events taking place during coronary balloon angioplasty. A standard inflation syringe is instrumented with transducers to record intra-balloon pressure and volume during stenosis dilatation. The theoretical and practical aspects of obtaining and interpreting PTCA "pressure-volume" curves are described. Based on mechanical principles, this method may provide the PTCA operator with information regarding the stiffness and resilience of each stenosis, the mechanism of dilatation, and a measure of adequacy of lumen enlargement even before the balloon is deflated.

Angioplasty, Balloon↗

PubMed1986

Effect of inflation pressures on coronary angioplasty balloons.

It is a common conception that the balloons used in percutaneous transluminal coronary angioplasty will inflate to a certain designated diameter and maintain this diameter over the wide range of inflation pressures. With use of an optical magnification system, the diameters of multiple angioplasty dilating catheters made of polyvinyl chloride (USCI) and polyethylene (Advanced Cardiovascular System, Inc.) were measured with designated balloon diameter sizes of 2.0 to 3.7 mm. All balloons had a linear increase in diameter over a range of pressures from 2 to 10 atm. The average increase in diameter over this pressure range was 15% (range 7 to 18%). Polyvinyl chloride balloons reached their specified diameter at less than 5 atm and exceeded it at higher inflation pressures. Polyethylene balloons reached their specified diameter at 8 to 10 atm, and were below specified diameters at lower pressures. There was slight variation in size and only a minimal difference in compliance between balloons of the same material and size. A given balloon achieved the same diameter at a given pressure even after multiple inflations and maintained a stable diameter during prolonged inflations.

Angioplasty, Balloon↗

PubMed1983

Passive biaxial mechanical properties of isolated canine myocardium.

Excised sheets of canine myocardium were subjected to cyclic loading and unloading in the predominant fibre and cross-fibre directions to determine passive mechanical properties. Myocardium under biaxial loading exhibits both non-linear elasticity and viscoelasticity with some strain-rate dependence in the position of the stress-strain relations, but very little rate dependence in the area enclosed by the loading and unloading portions of the stress-strain loops. Fibre and cross-fibre directions demonstrate anisotropic behaviour, with both the degree and direction of the anisotropy being dependent upon the region of the heart from which specimens are obtained. In the same specimen biaxial as compared with uniaxial loading yields different interpretations as to the material properties.

Animals↗

PubMedDate not supplied

Differential accumulation of intimal monocyte-macrophages relative to lipoproteins and lipofuscin corresponds to hemodynamic forces on cardiac valves in mice.

We have studied the distribution of monocyte-macrophages, lipids, and lipoproteins in sections of aorta and aortic valves from mice fed an atherogenic diet. By immunocytochemical analysis with Mac-1 and F4/80 antibodies, apolipoprotein B antibody, and oil red O staining, three discrete regions were identified: 1) the aortic wall of the sinus of Valsalva, which contained deposits of lipid that colocalized with lipoproteins and monocyte-macrophages; 2) the sides of the aortic valve leaflets facing the ventricle, which did not contain lipids or lipoproteins but which were lined with macrophages that colocalized with lipofuscin; and 3) the sides of the leaflets facing the aorta, which did not contain lipids, lipoproteins, monocyte-macrophages, or lipofuscin deposits. This pattern of distribution resembles the expected distribution of mechanical forces, especially those of systolic blood flow, which in the three areas are predominantly 1) low-shear disturbed flow, 2) high-shear laminar flow, and 3) low-shear laminar flow, respectively. These findings suggest that lesions in the mouse closely resemble early atherosclerotic lesions in humans and other primates with respect to monocyte-macrophage and lipoprotein accumulation. The results also strikingly demonstrate that the accumulation of monocyte-macrophages and lipoproteins can occur independently, with spatial differences corresponding to the distribution of hemodynamic forces.

Animals↗