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Development of Experimental Lymphedema in a New Animal Model
by Dr. V. P. Zharov
Contributing authors include: E.I. Galanga, V.V. Tuchin, A.V. Solov'eva, and T.V. Stepanova
Arkansas Cancer Research Center, University of Arkansas for Medical Sciences,
Little Rock, AR; Saratov State University and Saratov State Medical University,
Saratov, Russia
There is a clear need for a better understanding of the pathogenesis1 of post-mastectomy lymphedema (PML) and the principle
and mechanism treatment of PML. The goal of this work was to create a new PML
experimental model in order to study the pathogenesis of lymphatic disturbances
and their response to different therapeutic interventions.
The experimental model was created by the ligation2
of collecting vein or extirpation3 of lymph nodes on
rat mesentery4. The creation of lymphedema in an
animal model such as rat mesentery, may offer the optimal possibility of
measuring lymph microvessel function. Because of its unique anatomic structure
consisting of thin, transparent, duplex connective tissue with a single layer of
blood and lymph microvessels, the rat mesentery has been successfully used in
biological experiments focusing on the lymph microvascular system. A further
advantage of rat mesentery for modeling of lymphedema is its single layer of
vessels, which reduces the opportunity for the fast development of collateral
lymph flow and hence the state of collateral outflow.
White rats weighing 150-200 g were anesthetized by Nembutal for all
experimental study. After laparotomy the intestine mesentery was exposed on a
heating stage (370C). The analysis of lymph microcirculation was performed using
transmission microscopy with a digital video camera in real time. Diameters,
phasic contraction5, valve function and lymph flow
of small lymphatics were registered. When measurements of intact parameters were
finished, rats were taken for the creation of lymphedema by the ligation of
collecting vein or extirpation of lymph nodes (experimental groups). Some rats
were used as control groups (surgery without ligation or dissection). So, the
mesenteric microcirculation of rats in the control and experimental groups was
dynamically recorded 30 minutes after the ligation of collecting vein and at
three intervals after dissection of lymph nodes: 30 minutes, one week, and four
weeks.
Simultaneously the amount of water in mesenteric tissue (grams of H2O/1 g of
dry tissue) of each rat was evaluated by direct measurement and involved
excising the mesentery, drying and weighing it. Comparison of the amount of
water and microvascular changes in experimental and control groups for each time
interval allowed determining the degree of edema and disturbances of
microcirculation. Microlymphatic parameters were recorded before the surgery to
obtain initial data and then compared with results after surgery in the same
region of lymphangion.
After ligation of the collecting vein the amount of water in the tissue of
mesentery was increased almost three times giving evidence of development of
acute lymphedema. The mean diameter of lymphatics was decreased, phasic activity
was inhibited, lymph flow velocity was slowed to the stasis, many hemorrhages
appeared around venules, slow blood flow and stasis was observed and
erythrocytes6 appeared in lymphatics. Thirty minutes
after extirpation of regional lymph nodes the amount of water in tissue was
markedly raised in 50% of the animals. The pathologic changes in lymph and blood
microcirculation included constriction of all lymphatic on 25-35%, slowing of
lymph and blood flow. Lymphatic constriction was still increased over normal
conditions ever after normal water volumes in the mesentery tissue were
restored. This fact may be the sign and evidence of a latent period for the
disturbances in lymphedema (lymphedema may still be present w/o observable
symptoms even after observable symptoms have dissipated). The group that had no
lymph node dissection showed no observable changes in microcirculation 30
minutes after surgery.
The measurements of the degree of edema one week after surgery revealed
significant signs of lymphedema: the amount of water after lymph node dissection
was raised in all cases by 100-150% (p 0.005) in comparison with the mean amount
of water in the tissue in the control group. The diameter of the majority of
lymphatics increased from initial measurements. Regions of dilation and
constriction along the lymphangion were observed in one case. In addition, blood
microvessels were dilated significantly, and many new microvessels opened and/or
appeared.
Four weeks after the removal of lymph nodes edema was registered in a
majority of lymphatics (83%) but the degree of edema varied from 30% to 140%.
The investigated lymphangions7 kept the same
lymphatic dilation or progressed. In one case the dilation increased to 79%. The
density of blood microvascular net was markedly less than after the first week
of node extirpation but dilation of blood microvessels remained. In addition
after four weeks many commissures8 developed in
experimental and control groups, but after dissection of lymph nodes the amount
of commissures was visually greater. This fact seems to be at least partially a
result of fibrosis due to increase of oncotic pressure and the amount of protein
in the interstitium.
Thus, experimental lymphedema was created on the rat mesentery by ligation of
collecting vein and dissection of mesenteric lymph nodes. Analysis of temporal
dynamic changes after removal of lymph nodes showed that the greatest degree of
edema was found the first week after surgery. Moreover the presented animal
model allows studying the dynamics of microcirculation disturbances in the
development of lymphedema in greater detail. The marked and specific dynamics of
lymphatic disturbances found:
- constriction of lymphatics immediately after surgery (as ligation of
vein, as dissection of lymph nodes)
- moderate dilation one week after dissection
- tendency to progress to vessel dilation later (after four weeks)
Whether the reason for the observed disturbances after four weeks is the
result of the decrease in acute edema or the start of the chronic stage is not
understood. This issue needs further study.
Terminology:
1 Origin or cause of disease
2 Surgical tie-off of a vessel, ibid.
3 Complete removal or eradication of an organ or tissue.
Miller-Keane Medical Dictionary 2000, www.webmd.com
4 a membranous fold attaching various organs to the body
wall, especially the peritoneal fold attaching the small intestine to the dorsal
body wall. Miller-Keane Medical Dictionary 2000, www.webmd.com
5 Contraction which occurs as a result of stimulus or
adjustment to stimulus. On-Line Medical Dictionary, Dept. of Medical Oncology,
University of Newcastle on Tyne, http://cancerweb.ncl.ac.uk/omd/
6 red blood cells, ibid.
7 lymphatic vessels which carry fluid through tissues.
On-Line Medical Dictionary, Dept. of Medical Oncology, University of Newcastle
on Tyne, http://cancerweb.ncl.ac.uk/omd/
8 a point or line of union or junction between two anatomical
parts (as the lips at their angles or adjacent heart valves). Aetna IntiliHealth:
Merriam-Webster Medical Dictionary at http://www.intelihealth.com/cgi-bin/dictionary.cgi
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About the Author:
Dr. V. P. Zharov
 Dr. Zharov was graduated from two universities in Moscow and earned a PhD in 1977. As a professor from 1988-2000, he headed the Biomedical Engineering Department at Moscow State University of Technology. He came to the USA in 2001 as the director of laser research and Philips Classic Laser Laboratory of the University of Arkansas for Medical Sciences (UAMS). He was the State Prize Winner (the most prestigious award in Russia) and honored by the Laser Center of America with the International Maiman Award. He has published four books and over 150 papers-most of them in peer-review journals in English-and has presented his results over 60 times to international conferences.
Dr. Zharov has 30 years of experience in development of new combined biomedical technologies, especially laser, microwave temperature feedback, and photothermal imaging. In the last six years he has focused on the study of pathogenesis and new therapeutic treatment for post-mastectomy lymphedema (PML), running experiments and clinical trials in cooperation between Bauman Moscow State Technical University and Moscow State University of Medicine and Dentistry. He has continued this research in the Lymphedema Clinic of the Arkansas Cancer Research Center at University of Arkansas for Medical Sciences.
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