Elevated disks.
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Diagnosis, Differential↗
Biomedical subjects
J E Holte
Publications and source records attributed to J E Holte.
Contribution of collagen, elastin, and smooth muscle to in vivo human brachial artery wall stress and elastic modulus.
BACKGROUND: The contributions of collagen, elastin, and smooth muscle to arterial mechanical properties in the in vivo human artery are not known. METHODS AND RESULTS: We used a recently developed intravascular ultrasound technique to measure total brachial artery wall stress and incremental elastic modulus (Einc) in seven normal human subjects at baseline and after intra-arterial norepinephrine (1.2 micrograms) and nitroglycerin (100 micrograms). Then we applied a modified Maxwell model to estimate the elastic modulus of elastin (EE); the recruitment of collagen fibers supporting wall stress; and the differential contributions of collagen, elastin, and smooth muscle to wall stress and Einc over a wide range of pressure and smooth muscle tone. With this model, EE was 3 x 10(6) dynes/cm2. Collagen fibers were recruited increasingly as transmural arterial pressure increased and reached a value of approximately 5% to 6% at 100 mm Hg under each of the conditions studied. Isobaric smooth muscle contraction resulted in a small decrease in total wall stress and no significant change in total Einc while shifting the predominant element contributing to these mechanical parameters from collagen in parallel with the smooth muscle to collagen in series with the smooth muscle. In contrast, isometric smooth muscle contraction produced large increases in total wall stress (from 0.11 x 10(6) dynes/cm2 after nitroglycerin administration to 1.35 x 10(6) dynes/cm2 after norepinephrine administration) and Einc (from 3.84 x 10(6) dynes/cm2 after nitroglycerin administration to 57.8 x 10(6) dynes/cm2 after norepinephrine administration) entirely as a result of the additional contribution of the smooth muscle and its associated series collagen. CONCLUSIONS: This study describes a technique for determining arterial elastic properties and a model that can be used to estimate a number of mechanical parameters of the human brachial artery in vivo. This technique may be useful in studies of the arterial elastic properties of arteries in patients with vascular pathology.
Adult↗
Direct effects of smooth muscle relaxation and contraction on in vivo human brachial artery elastic properties.
The direct effect of smooth muscle relaxation on arterial elastic properties is controversial. Studies in animals show both a decrease and an increase in elastic modulus. In human subjects, the contribution of smooth muscle to arterial elastic mechanics has been limited by difficulty in separating the direct effects of a vasodilator drug on the arterial wall from the indirect effects due to reduced blood pressure. The purpose of the present study was to assess the direct contribution of vascular smooth muscle to brachial artery elastic mechanics in normal human subjects in vivo. We measured brachial artery compliance and incremental elastic modulus (Einc) in eight normal subjects (age, 22 to 51 years) by using intravascular ultrasound. A 3.5F 30-MHz intravascular ultrasound catheter was placed through a sheath into the brachial artery, and intraarterial pressure, cross-sectional area, and wall thickness were measured simultaneously under baseline conditions and after the administration of intra-arterial nitroglycerin (100 micrograms) and norepinephrine (1.2 micrograms). A pressurized cuff surrounding the brachial artery was inflated to reduce transmural brachial artery pressure. Using this technique, we were able to measure the following arterial characteristics for the first time in human subjects in vivo: (1) the effective unstressed arterial radius and (2) the pressure-area, stress-strain, and pressure-Einc relations over a wide pressure range (0 to 100 mm Hg). Intra-arterial nitroglycerin increased brachial artery area by 22% and intraarterial norepinephrine decreased brachial artery area by 17% at 100 mm Hg transmural pressure (P < .001 versus baseline).(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Computationally two-dimensional finite-difference model for hollow-fibre blood-gas exchange devices.
The goal of this research is to develop a predictive model with good absolute accuracy for blood-gas exchange devices. The proposed model, unlike existing models, is able to predict gas transfer to blood flowing outside oxygenating fibres without experimental data. The proposed model uses a finite-difference numerical technique to solve computationally two-dimensional gas exchange problems such as gas transfer to blood outside hollow fibres. The model is compared to bovine and human experimental data from the small test cells with microporous polypropylene fibres. The test cell flow rates range from 1 m litre min-1 to 5 m litre min-1 for a 72-fibre device. Shear-augmented oxygen diffusion appears to be present, although good accuracy is obtained with a nonaugmented diffusion model, particularly at lower flows. The maximum deviation of oxygen saturation predicted by a shear-augmented bovine blood model from the experimental regression line was 1.7 per cent.
Animals↗
The binocular corneal reflex in infants.
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Blinking↗