Biomedical subjects

S Weinbaum

Publications and source records attributed to S Weinbaum.

76 records · Page 5Linked to original sources

PubMedDate not supplied

1997 Whitaker Distinguished Lecture: Models to solve mysteries in biomechanics at the cellular level; a new view of fiber matrix layers.

Three different fundamental cellular level transport models are presented to explore current or recently solved mysteries in what appear to be three unrelated problem areas: (i) Starling's hypothesis for lymph formation in the microcirculation; (ii) the cellular level transduction and transmission mechanisms for sensing and communicating mechanical strain in bone; and (iii) the growth of cellular level macromolecular leakage spots in the arterial intima and their relation to the formation of subendothelial liposomes. This trilogy of what appear to be unrelated problems is shown to have a common link, the thin layer of specialized matrix that cells produce at the surface of their plasmalemma membranes in part to regulate the water and solute transport that surrounds them. In each case unexpected model predictions have led to new hypotheses and the design of new experiments which have helped explain long-standing fundamental questions in biomechanics.

Adaptation, Physiological↗

PubMedDate not supplied

Microvascular thermal equilibration in rat spinotrapezius muscle.

The current study investigates heat exchange in the thermally significant countercurrent paired vessels of the rat spinotrapezius muscle. Detailed tissue surface temperatures under normal (after the microvascular surgery) and pharmacologically vasodilated states were measured using high-resolution infrared thermography. During vasodilation, a measurable thermal disturbance was observed above the first-order feeding vessel pair. The measured tissue temperatures were compared with those predicted by modifying the theoretical model for two-dimensional muscle preparations given by Zhu et al. (Zhu, L., D. E. Lemons, and S. Weinbaum. Ann. Biomed. Eng. 24:109-123, 1996). They were found in good agreement. The Weinbaum-Jiji k(eff) theory (Weinbaum, S., and L. M. Jiji. J. Biomech. Eng. 107:131-139, 1985) for heat exchange between the paired vessels and their surrounding tissue was also examined in this muscle. A close agreement was obtained between the theoretically predicted k(eff) and the measured value calculated using a fin approximation for the tissue layer. This experimental study revealed for the first time the nonequilibration between blood vessels and the surrounding tissue, where the enhancement in k(eff) due to the incomplete countercurrent heat exchange is comparable to the tissue axial conduction.

Animals↗

PubMedDate not supplied

Effects of oscillatory mechanical disturbance on macromolecular uptake by arterial wall.

Transport of 125I-albumin by isolated segments of canine common carotid arteries was studied in vitro at zero transmural pressure. Sinusoidal oscillatory variations in length (peak change 4%) for 15 minutes at frequencies of 5 and 10 Hz caused 40% increase in 125I-albumin uptake, and also a 30% increase in the apparent luminal surface area. Changes in the duration and frequency of oscillation indicate that the total number of oscillations (= frequency X duration) was the critical parameter in causing these effects. The increase in apparent luminal surface area was correlated with regional flattening of the internal elastic lamina and the overlying endothelial cells, as demonstrated by transmission and scanning electron microscopy. Endothelial vesicles were counted with the aid of ruthenium red as a postfixation extracellular marker. The ratio of unstained free vesicles to total vesicles averaged 0.083 in the control state and decreased slightly to 0.070 after oscillation. Although the decrease in free vesicle population indicated an acceleration of vesicle diffusion, our theoretical computations showed that the resulting increase in vesicle flux was negligible. The increase in 125I-albumin uptake by the artery following mechanical oscillation is mainly attributable to the increase in apparent luminal surface area.

Animals↗

PubMedDate not supplied

Transendothelial transport of low density lipoprotein in association with cell mitosis in rat aorta.

Atherosclerosis is characterized by focal areas of lipid accumulation and intimal smooth muscle cell proliferation in large arteries. In vivo studies on rat aorta with Evans blue-albumin conjugate (EBA) have shown that there are preferential sites of increased permeability with an increased uptake of the conjugate. It has been shown that these blue areas are associated with a high endothelial cell turnover rate and an enhanced permeability to lipids. In a previous study, we demonstrated that 99% of endothelial cells in the mitotic (M) phase as identified by hematoxylin staining of the dividing nuclei exhibited EBA leakage and that these dividing cells accounted for 30% of all leakage sites. In the present study, experiments were performed on the thoracic aortas of 10 adult male Sprague-Dawley rats to determine the statistical frequency of isolated leaks to Lucifer yellow-low density lipoprotein conjugate (LY-LDL) at the level of individual cells and to assess the relationship of such leaks to the cell turnover processes. Leakage of LY-LDL around individual endothelial cells was visualized by fluorescence microscopy, and cells in mitosis on the same specimens were identified by hematoxylin staining. Although endothelial cell mitosis is infrequent (0.034%), 80% of dividing cells in the M phase were associated with LY-LDL leakage. These dividing cells accounted for 45% of all leakage spots. These findings lend support to our recent hypothesis that transiently open junctions surrounding the endothelial cells undergoing cell turnover provide pathways through which LDL enters the subendothelial space, resulting in lipid accumulation.

Animals↗