Biomedical subjects

J Brandon Dixon

Publications and source records attributed to J Brandon Dixon.

4 recordsLinked to original sources

PubMed2006

Image correlation algorithm for measuring lymphocyte velocity and diameter changes in contracting microlymphatics.

Efforts have recently been made to estimate wall shear stress throughout the contractile cycle of mesenteric rat lymphatics with a high speed video microscopy system. This was prompted by reports in the literature that lymphatic pumping is related to wall shear stress. While one can estimate wall shear stress by tracking lymphocyte velocity, it is prohibitively tedious to manually track particles over a reasonable time frame for a good number of experiments. To overcome this, an image correlation method similar to digital particle imaging velocimetry was developed and tested on contracting lymphatics to measure both vessel diameter and fluid velocity. The program tracked temporal fluctuations in spatially averaged velocity with a standard error of prediction of 0.4 mm/s. From these studies we have measured velocities ranging from -2 to 4 mm/s. Diameter changes were also measured with a standard error of 7 microm. These algorithms and techniques could be beneficial for investigating various changes in contractile behavior as a function of changes in velocity and wall shear stress.

Algorithms↗

PubMedDate not supplied

Lymph flow, shear stress, and lymphocyte velocity in rat mesenteric prenodal lymphatics.

OBJECTIVE: To measure lymphocyte velocity, lymphatic contraction, and shear stress in phasically contracting lymphatics in situ. METHODS: A high-speed video system was used to capture multiple contraction cycles in rat mesenteric lymphatic preparations. The images were analyzed to determine fluid velocity, volume flow rate, wall shear stress, and retrograde flow. RESULTS: Lymphocyte density and flux varied from 326 to 35,500 cells/microL and 206 to 2,030 cells/min, respectively. Lymphatics contracted phasically, with a mean diameter 91 +/- 9.0 microm and amplitudes of 39%. Lymph velocity varied with the phasic contractions in both direction and magnitude with an average of 0.87 +/- 0.18 and peaks of 2.2-9.0 mm/s. The velocity was approximately 180 degrees out of phase with the contraction cycle. The average lymph flow was 13.95 +/- 5.27 microL/h with transient periods of flow reversal. This resulted in an average shear of 0.64 +/- 0.14 with peaks of 4-12 dynes/cm(2). CONCLUSIONS: High-speed lymphocyte tracking provided the spatial and temporal resolution to measure lymphocyte flux throughout the phasic contraction. Poiseuille flow was a reasonable model for estimating wall shear stress through most of the phasic contraction cycle of the intervalvular lymphatic segments. Shear rate was low but had large variations in magnitude compared to that seen in blood vessels.

Animals↗

PubMedDate not supplied

Dual-wavelength polarimetry for monitoring glucose in the presence of varying birefringence.

In a continuing effort to develop a noninvasive means of monitoring glucose levels using the aqueous humor of the eye, a dual-wavelength system is developed to show that varying birefringence, similar to what is seen with a moving cornea, can be compensated. In this work, a dual-wavelength, closed-loop system is designed and a model is developed to extract the glucose concentration information. The system and model are tested using various concentrations of glucose in a birefringent test cell subject to motion artifact. The results show that for a static, nonmoving sample, glucose can be predicted to within 10 mg/dl for the entire physiologic range (0 to 600 mg/dl) for either laser wavelength (523 or 635 nm). In the presence of moving birefringence, each individual wavelength produces standard errors on the order of a few thousand mg/dL. However, when the two wavelengths are combined into the developed model, this error is less than 20 mg/dL. The approach shows that multiple wavelengths can be used to drastically reduce the error in the presence of a moving birefringent sample and thus may have the potential to be used to noninvasively monitor glucose levels in vivo in the presence of moving corneal birefringence.

Artifacts↗

PubMedDate not supplied

Measuring microlymphatic flow using fast video microscopy.

Despite advances in the measurement of lymphatic function, little is known about the actual velocities of flow in microlymphatic ( approximately 100 mum diam) vessels. In this work, video microscopy and particle tracking methods are adapted and integrated with an ultra-high-speed imaging camera to obtain measurements of lymph velocities throughout the entire lymphatic contraction cycle in the ratmesentery, something that previous systems were incapable of measuring. To determine the system's accuracy, calibration experiments are conducted across the hypothesized physiologically significant range of velocities for microlymphatic flow (up to 15 mmsec). The system shows high accuracy, less than 2% error, when comparing actual with measured velocities. Microspheres flowing through 140-mum-diam tubing are imaged to demonstrate the system's ability to determine flow rates in these small vessels by measuring particle velocities. To demonstrate biological applicability, mesenteric microlymphatics in loops of the small intestine of three male Sprague-Dawley rats are exteriorized and imaged with the high-speed system at a rate of 500 framessec for several contraction sequences. Lymph velocity fluctuates cyclically with the vessel wall contractions, ranging from -1 to 7 mmsec. These rates are higher than would be possible with standard video microscopy (3.75 mmsec maximum).

Animals↗