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Biomedical subjects

C G Caro

Publications and source records attributed to C G Caro.

61 records · Page 4Linked to original sources
PubMed1966

The dispersion of indicator flowing through simplified models of the circulation and its relevance to velocity profile in blood vessels.

1. The distribution of velocity (velocity profile) was studied in water flowing through simple models of the circulation. Dye was injected and the distribution of velocity was assessed from indicator concentration-time curves recorded with a photomultiplier.2. Observations were made on straight and curved tubes and on a tube containing a short region with an elliptical cross-section. With steady flow, the rate was varied over the range 24-870 ml./min (Reynolds number 102-3690). Sinusoidal pulsations were imposed on the steady flow in some experiments.3. Bends gave rise to large secondary flows. These caused mixing across the flow and a marked reduction in the variation of velocity over the cross-section of the tube. The effect of bends on velocity distribution was maximal at a Reynolds number of ca. 1000. Similar, but far smaller, effects were seen in a region with an elliptical cross-section and when the flow was made pulsatile. Secondary motion due to bends was capable of preventing a heavier-than-water indicator (sp.gr. 1.375) from settling out of the flow.4. The experimental findings suggest that there may be secondary flows in vascular beds. Under certain conditions, these would prevent the establishment of Poiseuille type laminar flow. The possible physiological importance of the findings is discussed.

Blood Circulation↗
PubMedDate not supplied

Diffusion coefficients for protein molecules in blood serum.

A new technique is described for the measurement of the self-diffusion coefficients of protein macromolecules in solution. The method makes use of the phenomenon of Taylor dispersion of a solute introduced into a solvent flowing in the laminar regime through a tube of circular section. Results are reported for the self-diffusion coefficient of cholesterol associated with lipoprotein molecules in dogs' serum at pH 7.4 in the temperature range 18-37 degrees C. The diffusivity of bovine serum albumin in serum has also been studied as a function of temperature at pH 7.4 and 4.7. In the more basic solution, measurements of the diffusivity as a function of protein concentration substantially agree with earlier work. For all the systems studied the diffusivity varies rapidly with temperature. The pH of the solution, in the case of bovine serum albumin, also has a significant effect on the diffusivity of the macromolecule. The latter observation is related to the amount of water bound to the protein molecule in solution.

Animals↗
PubMedDate not supplied

Simultaneous detection of multiple components of motion with MRI.

OBJECTIVE: Simultaneous detection of two or more components of motion using new magnetic resonance pulse sequences was investigated. MATERIALS AND METHODS: The technique employs Fourier phase encoding to encode the first component, and phase contrast detection to encode the second. Although the technique can be generalized to any number of spatial dimensions and motional orders, applications in which one or two spatial dimensions are obtained with a single Fourier velocity or acceleration dimension are most likely to be useful. For example, Fourier-encoded velocity and phase-contrasted acceleration information can be combined into the same image. RESULTS: Several variations of the pulse sequence were investigated in phantoms and human volunteers. The first variation acquired images having an appearance similar to that of Fourier velocity-encoded images in which signal displacement is proportional to velocity, but with pixel intensity determined by acceleration. In another variation two spatial dimensions were acquired with a third dimension that uses Fourier velocity encoding to measure axial velocity within a curved tube. Radial velocity components were determined simultaneously with a second velocity-encoding gradient pulse. CONCLUSION: The phantom and in vivo results presented here suggest that simultaneous detection of two or more components of motion is feasible.

Adult↗
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↗