Hypothermic machine preservation in liver transplantation revisited:Concepts and criteria in the new millennium

To overcome the present shortage of liver donors by expansion of the existing donor pool and possibly lengthening of the storage time, hypothermic machine perfusion of the liver as a dynamic preservation method is revisited. The three most important aspects are defined to be the type of preservation solution, the characteristics of perfusion dynamics, and the oxygen supply. Reviewing hypothermic liver machine perfusion experiments, the University of Wisconsin machine preservation solution is the solution most used. It is also found that nothing conclusive can be said about the optimal perfusion characteristics, since either perfusion pressure or perfusion flow is reported. The best estimation is perfusion of the liver in a physiological manner, i.e. pulsatile arterial perfusion and continuous portal venous perfusion. The applied pressures could be chosen to be somewhat lower than physiological pressures to prevent possible endothelial cell damage. Oxygen supply is necessary to achieve optimal preservation of the liver. The minimal amount of partial oxygen pressure required is inversely related to the normalized flow. Incorporating these features in a system based on existing standard surgical and organ sharing procedures and which is able to work stand-alone for 24 It, weighing less than 23 kg, could successfully implement this technique into every day clinical practise.</p

Hypothermic machine preservation in liver transplantation revisited: Concepts and criteria in the new millennium

To overcome the present shortage of liver donors by expansion of the existing donor pool and possibly lengthening of the storage time, hypothermic machine perfusion of the liver as a dynamic preservation method is revisited. The three most important aspects are defined to be the type of preservation solution, the characteristics of perfusion dynamics, and the oxygen supply. Reviewing hypothermic liver machine perfusion experiments, the University of Wisconsin machine preservation solution is the solution most used. It is also found that nothing conclusive can be said about the optimal perfusion characteristics, since either perfusion pressure or perfusion flow is reported. The best estimation is perfusion of the liver in a physiological manner, i.e. pulsatile arterial perfusion and continuous portal venous perfusion. The applied pressures could be chosen to be somewhat lower than physiological pressures to prevent possible endothelial cell damage. Oxygen supply is necessary to achieve optimal preservation of the liver. The minimal amount of partial oxygen pressure required is inversely related to the normalized flow. Incorporating these features in a system based on existing standard surgical and organ sharing procedures and which is able to work stand-alone for 24 It, weighing less than 23 kg, could successfully implement this technique into every day clinical practise

Design and in vitro testing of a voice-producing element for laryngectomized patients

A voice-producing element has been developed to improve speech qualify after laryngectomy. The design process started with the formulation of a list of requirements. The lip principle has the best potential for fulfilling the requirements. A numerical model was made to find the optimal geometry of an element based on the lip principle. Extensive in vitro tests were performed to check all requirements. For this a test set-up with realistic acoustic and aerodynamic properties was developed. Results show that the protruding lip length dominates fundamental frequency, cross-sectional area dominates flow resistance and relation between flow and fundamental frequency. Most requirements have been fullfilled; both for males and females a potentially good functioning prototype could be selected. Clinical experiments will be performed to confirm the quality of the voice-producing prosthesis

An In-vitro test set-up for evaluation of a voice-producing element under physiologic acoustic conditions

To improve the voice quality of laryngectomised patients, a voice-producing element has been developed. Prior to in vivo testing we constructed and validated an in-vitro test set-up, consisting of a physical model of the subglottal tract and three physical models of the vocal tract, for the vowels /a/, /i/ and /u/ to evaluate the voice-producing element under physiologic acoustic conditions. To meet acoustic conditions described in the literature, we determined the appropriate dimensions of these physical models, using a numerical model of the pressure perturbation in rigid tubes. The numerical model showed that an acoustic equivalent of the subglottal tract could be obtained with a three-tube system and an end impedance. Vocal tract models could be constructed using two- and four-resonator tubes. The physical models were built and successfully validated according to the human acoustic properties. The developed in-vitro set-up can now be applied to test voice-producing elements or vocal fold models under physiologic acoustic conditions