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1 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
2 Michael E. DeBakey Institute, Texas A&M University, College Station, Texas, United States; Physiology & Pharmacology, College of Veterinary Medicine, Texas A&M University, College Station, Texas, United States
3 Michael E. DeBakey Institute, Texas A&M University, College Station, Texas, United States; Physiology & Pharmacology, College of Veterinary Medicine, Texas A&M University, United States
4 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; Physiology & Pharmacology, College of Veterinary Medicine, Texas A&M University, United States
* To whom correspondence should be addressed. E-mail: cquick{at}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.
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  C. M. Quick, B. L. Ngo, A. M. Venugopal, and R. H. Stewart Lymphatic pump-conduit duality: contraction of postnodal lymphatic vessels inhibits passive flow Am J Physiol Heart Circ Physiol, March 1, 2009; 296(3): H662 - H668. [Abstract] [Full Text] [PDF]
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C. M. Quick, A. M. Venugopal, R. M. Dongaonkar, G. A. Laine, and R. H. Stewart First-order approximation for the pressure-flow relationship of spontaneously contracting lymphangions Am J Physiol Heart Circ Physiol, May 1, 2008; 294(5): H2144 - H2149. [Abstract] [Full Text] [PDF]
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