Contractions of the Lymphatics and Lymph Flow

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Contractions of the Lymphatics and Lymph Flow

Postby patoco » Mon Mar 19, 2007 9:18 pm

Contractions of the Lymphatics and Lymph Flow

The lymphatics move lymph fluid, not only by muscular actions, as we have usually been told, but also through a series of contractions with the lymph system itself. Indeed, one of the reasons NSAID's should not be taken by people with lymphedema is that they have been shown to actually slow down or stop the lymphatic contractions, thereby causing worse edema. I thought these article would be interesting in presenting information on how lymph moves through our body.

Article One

Lymphatic Vessels Transition to State of Summation above a Critical Contraction Frequency.

Am J Physiol Regul Integr Comp Physiol. 2007 Mar 15

Meisner JK, Stewart RH, Laine GA, Quick CM.
Biomedical Engineering, Dwight Look College of Engineering, Texas A&M University, College Station, Texas, United States; Michael E. DeBakey Institute, Texas A&M University, College Station, Texas, United States.

* To whom correspondence should be addressed. E-mail: cquick@cvm.tamu.edu.

Although lymphatic vessel behavior is analogous to ventricles, which completely relax between contractions, and blood vessels, which maintain a tonic constriction, the mixture of contractile properties can yield behavior unique to lymphatic vessels. In particular, because lymphatic vessels possess a limited refractory period and a slow rate of relaxation, they lack the contractile properties that minimize summation in ventricles. We, therefore, hypothesized that lymphatic vessels transition to a state of summation when lymphatic vessel contraction frequency exceeds a critical value. We used an isovolumic, controlled-flow preparation to compare the time required for full relaxation and the time available to relax during diastole. We measured transmural pressure and diameter on segments of spontaneously contracting bovine mesenteric lymphatic vessels during 10 isovolumic volume steps. We found that beat-to-beat period (frequency(-1)) decreased with increases in diameter, and total contraction time is constant or slightly increases with diameter. We further found that the convergence of beat-to-beat period and contraction cycle duration predicted a critical transition value, beyond which the vessel does not have time to fully relax. This incomplete relaxation and resulting mechanical summation significantly increases active tension in diastole. Because this transition occurs within a physiological range, contraction summation may represent a fundamental feature of lymphatic vessel function. Key words: lymph flow, lymphatic wall tension, mechanics, active lymph pump, edema.

http://ajpregu.physiology.org/cgi/reprint/00468.2006v1

Article Two

INTRINSIC PUMP-CONDUIT BEHAVIOR OF LYMPHANGIONS.

Am J Physiol Regul Integr Comp Physiol. 2006 Nov

Quick CM, Venugopal AM, Gashev AA, Zawieja DC, Stewart R.
Michael E. DeBakey Institute, Texas A&M University, College Station, Texas, United States; Physiology & Pharmacology, Texas A&M University, College Station, Texas, United States; Biomedical Engineering, Texas A&M University, College Station, Texas, United States.

* To whom correspondence should be addressed. E-mail: cquick@tamu.edu.

Lymphangions, segments of lymphatic vessels bounded by valves, have characteristics of both ventricles and arteries. They can act primarily like pumps when actively transporting lymph against a pressure gradient. They can also act as conduit vessels when passively transporting lymph down a pressure gradient. This duality has implications for clinical treatment of several types of edema, since the strategy to optimize lymph flow may depend on whether it is most beneficial for lymphangions to act as pumps or conduits. To address this duality, we employed a simple computational model of a contracting lymphangion and predicted the flows at both positive and negative axial pressure gradients, and validated the results with in vitro experiments on bovine mesenteric vessels. This model illustrates that contraction increases flow for normal axial pressure gradients. With edema, limb elevation, or external compression, however, the pressure gradient might reverse, and lymph may flow passively down a pressure gradient. In such cases, the valves may be forced open during the entire contraction cycle. The vessel thus acts as a conduit, and contraction has the effect of increasing resistance to passive flow, thus inhibiting flow rather than promoting it. This analysis may explain a possible physiologic benefit of the observed flow-mediated inhibition of the lymphatic pump at high flow rates.

Key words: lymphangion, time-varying elastance, shear stress induced dilation.

http://ajpregu.physiology.org/cgi/conte ... 258.2006v1

Article Three

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

Microcirculation. 2006 Oct-Nov

Brandon Dixon J, Greiner ST, Gashev AA, Cote GL, Moore JE, Zawieja DC.
Department of Biomedical Engineering, Texas A&M University, College Station, 77843-1114, USA.

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.

Keywords: lymphatic, lymph pump, lymph flow, lymph shear stress, lymphocyte trafficking

http://taylorandfrancis.metapress.com/c ... 779223v7q/

Article Four

Inhibition of active lymph pump by simulated microgravity in rats.

Am J Physiol Heart Circ Physiol. 2006 Jun

Gashev AA, Delp MD, Zawieja DC.
Department of Medical Physiology, College of Medicine, Cardiovascular Research Institute Division of Lymphatic Biology, Texas A&M University System Health Science Center, 336 Reynolds Medical Bldg., College Station, TX 77843-1114, USA. gashev@tamu.edu

During spaceflight the normal head-to-foot hydrostatic pressure gradients are eliminated and body fluids shift toward the head, resulting in a diminished fluid volume in the legs and an increased fluid volume in the head, neck, and upper extremities. Lymphatic function is important in the maintenance of normal tissue fluid volume, but it is not clear how microgravity influences lymphatic pumping.

We performed a detailed evaluation of the influence of simulated microgravity on lymphatic diameter, wall thickness, elastance, tone, and other measures of phasic contractility in isolated lymphatics. Head-down tail suspension (HDT) rats were used to simulate the effects of microgravity. Animals were exposed to HDT for 2 wk, after which data were collected and compared with the control non-HDT group.

Lymphatics from four regional lymphatic beds (thoracic duct, cervical, mesenteric, and femoral lymphatics) were isolated, cannulated, and pressurized. Input and output pressures were adjusted to apply a range of transmural pressures and flows to the lymphatics. Simulated microgravity caused a potent inhibition of pressure/stretch-stimulated pumping in all four groups of lymphatics. The greatest inhibition was found in cervical lymphatics.

These findings presumably are correlated to the cephalic fluid shifts that occur in HDT rats as well as those observed during spaceflight. Flow-dependent pump inhibition was increased after HDT, especially in the thoracic duct. Mesenteric lymphatics were less strongly influenced by HDT, which may support the idea that lymph hydrodynamic conditions in the mesenteric lymphatic during HDT are not dramatically altered.

Keywords: lymphatic vessels; thoracic duct; lymphatics

http://ajpheart.physiology.org/cgi/cont ... 90/6/H2295

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