[en] lntroduction: Since the 80's, the control of the infusion mechanisms has been a main goal in arder to fulfill different necessities, e.g. control of the plasmatic levels or the concentration at the target organ. To this end, three possibilities have been explored, namely: computer assisted infusion bombs - Target Controlled lnfusion (TCI)-, manual protocols -Manually Controlled lnfusion (MCI)-, which emulate what infusion bombs do, and control of the infusion through static mixing -Physically Controlled lnfusion (PhCI)-, the later not used due to the lack of information on it. At present we can consider the mixing mechanisms to be understood, but not so the influence, on these mixers, of the air chamber inside of the container in the way it has been used so far. Objective: The general goal is the study of the influence of the thermodynamic variables on the behavior of static mixture mixing devices containing two phases: liquid and gas. Material and methods: Experiments with continuous gravimetry, dynamic pycnometry, have been designad and conducted to quantify the weight and volume changes caused by the variation of both the static and dynamic pressure of the infusion system. After this experimental phase, we developed calibration procedures for the mixer, understood as a pycnometer, in arder to work without the gas phase and to be able to evaluate the density variations during the mixing process. Results: For the different variations on the pressure, we have obtained, without variation of the density; weight curves with kinetic behavior of arder one. In the pycnometric experiments we measured the variations of the density with time, resulting in a kinetic behavior of arder one as well, but not in accordance with the stablished theoretical model. Discussion: Thermodynamically, this system has been classified as isothermal, with a gaseous phase behaving as an ideal gas. We checked the existence of influences because of the existence of the gaseous phase and evaluated their physical and clinic implications, stating the necessary conditions for the design and development of devices for the intravenous administration of drugs with physical control of the infusion. One of the facts proven is that the hypothesis (that is, that this kind of systems work in a stationary state), assumed from the beginning and by the scientific community, is clearly flawed, since the weight and volume exponentials do not agree in the pycnometric experiments. Hence, the necessity of understanding better this fact with new experiments; these devices work in pseudostationary state and the concentration is not the only variable that is modified, but also the density. Conclusions: We have proven the influence of the kinematics of the mixture in the existence of a gaseous phase and the necessity of excluding it. These devices work in a pseudostationary state, so we have to study the behavior of the concentration and the density, as well as their behavior when the mixture contains several salutes and the solution is multicomponent.

[gl] Antecedentes: Dende a década dos oitenta inténtanse desenvolver dispositivos de infusión intravenosa co fin de administrar de forma óptima fármacos e así poder controlar a súa concentración no sangue o u no órgano diana. Para alcanzar este obxectivo, estanse a explorar tres posibles camiños: as bombas de infusión asistidas por ordenador, ou Target Controlled lnfusion (TCI); os procedementos manuais, ou Manually Controlled lnfusion (MCI), que emulan o que fan as bombas, e o control da infusión mediante sistemas físicos de mestura estática, ou Physically Controlled lnfusion (PhCI), sendo esta última alternativa un método pouco empregado por estar pouco estudado. Actualmente podemos considerar aclarados os mecanismos de mestura, pero non a influencia, sobre estes mesturadores, da cámara de aire dentro do recipiente tal e como tense empregado até o de agora. Obxectivo: O fin xeral é o estudo da influencia das variables termodinámicas no comportamento dos dispositivos de mestura estática cando estes conteñen dúas fases: líquida e gasosa. Material e métodos: Deseñáronse e leváronse a cabo experimentos de gravimetría continua, a densidade constante, para cuantificar os cambios de peso e volume provocados nos mesturadores polas variacións nas presións estática e dinámica do sistema de infusión. Rematada esta fase experimental, desenvolvéronse procedementos de calibración do mesturador, entendido coma un picnómetro, para poder traballar con exclusión absoluta da fase gasosa e avaliar as variacións da densidade no transcurso da mestura. Resultados: Para as diversas modificacións da presión, sen variación da densidade, obtivéronse curvas de peso con comportamento cinético de arde un. Nos experimentos de picnometría medíronse as variacións da densidade no tempo, resultando tamén un comportamento cinético de arde 1, pero non acorde co modelo teórico establecido. Discusión: Termodinámicamente, o sistema clasificouse como isotérmico, coa fase gasosa con comportamento de gas ideal. Comprobouse a presenza de influencias pala existencia da fase gasosa, e avaliáronse as súas implicacións físicas e clínicas, establecendo as condicións necesarias para o deseño e desenvolvemento de dispositivos para a administración intravenosa de fármacos con control físico da infusión. Un feíto evidenciado é que a hipótese, asumida dende o comezo e por todos os investigadores, de que estes sistemas traballan en estado estacionario queda claramente en evidencia ao non concordar as exponenciais de peso e volume obtidas nos experimentos picnométricos. Tense, polo tanto, que afondar con novos experimentos no que claramente estase a evidenciar: estes dispositivos traballan en estado pseudo-estacionario e a concentración non é a única variable que resulta modificada, senón tamén a densidade. Conclusións: Demostrouse a influencia que ten na cinética de mestura a exixencia da fase gasosa e a necesidade de excluíla. Estes dispositivos traballan en estado pseudoestacionario e tense que estudar en profundidade a disociación do comportamento da concentración e da densidade, así coma o seu proceder cando a mestura é de varios solutos e a disolución multicompoñente.