Any patient affected by chronicle renal insufficiency has to undergo a therapy which effectively substitutes the physiological renal functions. The low availability of organs from donors has lead to the development of an alternative therapy to the transplant: the dialysis. This treatment though does not entirely substitute the kidneys in their functions and it implicates negative aspects upon the life of the patient and his family. A lot of attentions are constantly placed upon those innovation aiming at improving the quality of the dialytic treatment, hence the quality of life of the patient. The Two Pool Virtual Simulator (TPVS) is a test bench which aims to replicate the behaviour of a patient during a dialysis session (solutes and liquid exchanges); it allows to monitor some parameters, to test new components of the dialysis machine and various treatments. It is composed of two compartments, replicating the interstitial and the plasmatic compartments of the real patient, between which the exchanges of liquids and solutes take place during the dialytic session. The goal of the present work is the redesign of some of the components of the TPVS, starting from the correct understanding of the problems of the existing version of the simulator. Once the best design solution was found in order to overcome the issues of air bubbles removal and hydraulic sealing of the cover of the main pools of the simulator, computational simulations were performed under the working conditions, as to verify the suitability of the solution. The values of the parameters required by the FE software were obtained from experimental tests performed directly on the materials. Once the solution was proved to be consistent, the component was realised and assembled. Further elements of the TPVS were modified as their efficiency was too low. The second part of the work was focused on the experimental characterisation of the renewed simulator; namely fluid-dynamic effects were considered, in terms of pressures and flow rates. First of all, the hydraulic sealing and the bubble removal were evaluated. Then preliminary tests were performed on the isolated TPVS, in order to evaluate the following aspects: the influence of the working conditions upon the behaviour of some of the components of the setup, the quantifications of the pressure drops along the circuit, the distribution of the flow rates in elements set in parallel. Then the filters of the simulator were characterised; the working point of the simulator was identified as a function of the external pressure acting on them and eventually the resistance they oppose to the circuit was evaluated. The simulator was then characterised under the ideal working conditions as it was connected to the dialysis machine for the whole dialytic treatment. Tests were performed using demineralised water in the first place, while then water was substituted with fluids specifically prepared to replicate the composition and the rheological features (viscosity and density) of blood and interstitial fluid. The modifications applied to the circuit resulted in a device which is easier to use and to control. The characterisation of the simulator allowed to describe the trend of the hydraulic parameters of interest in specific sections of the virtual patient, by detecting the proper flow rate (as a function of the external pressure acting on the filters) to be imposed to the roller pump, in order to have a dynamic balance of the fluids exchange between the two compartments. Simulations performed using demineralised water and proper fluids lead to identify the correct set of the monitorable parameters of the simulator as to guarantee a functional replication of the real behaviour of a patient undergoing dialysis. The comparison between these two working groups lead to a better understanding of the influence of having fluids which replicate the characteristics of the blood and the interstitial fluid upon the exchanges between different compartments during the dialytic session.
Un paziente affetto da insufficienza renale cronica necessita di una terapia che sostituisca in maniera efficiente le funzioni renali. La scarsa disponibilità di organi da donatore ha reso necessario lo sviluppo di una terapia alternativa al trapianto: la dialisi. Quest’ultima non assolve interamente al compito di sostituzione della funzione renale e presenta importanti ripercussioni negative su molti aspetti della vita dell’individuo e dei suoi familiari. Costante è quindi l’interesse verso innovazioni tecniche che possano migliorare la qualità del trattamento dialitico e la qualità di vita del paziente. Il simulatore di paziente è un banco prova che mira a replicare il comportamento di un paziente durante una seduta dialitica (scambio di fluidi e soluti) permettendo di controllare parametri di interesse, di testare nuovi componenti della macchina di dialisi e nuovi tipi di trattamento. Esso è costituito da due compartimenti, che replicano quelli interstizio-cellulare e plasmatico del paziente reale, tra i quali avviene uno scambio di fluidi e soluti nel corso della seduta dialitica. Il presente progetto si pone come obiettivo la riprogettazione di alcuni componenti del simulatore. Il punto di partenza è la comprensione delle problematiche presenti nel vecchio simulatore. A seguito dell’individuazione della miglior soluzione progettuale per risolvere i problemi di debollaggio e tenuta idraulica dei coperchi delle vasche principali del simulatore, sono state sviluppate delle simulazioni computazionali del comportamento del nuovo coperchio nelle condizioni di lavoro, al fine di verificare l’adeguatezza della soluzione. I valori dei parametri necessari da fornire al software sono stati ricavati grazie a prove sperimentali direttamente realizzate sui materiali in questione. Una volta verificata la consistenza della soluzione adottata, il componente è stato realizzato e assemblato. Sono stati infine modificati alcuni componenti del set-up che risultavano poco efficienti. Successivamente si è effettuata la caratterizzazione sperimentale del rinnovato simulatore; in particolare sono stati presi in considerazione gli aspetti fluidodinamici, in termini di pressioni e portate. Sono state inizialmente valutate la tenuta idraulica del nuovo coperchio e l’efficienza di debollaggio del simulatore rinnovato. Sono state effettuate delle prove preliminari sul simulatore isolato, per studiare la dipendenza del comportamento di alcuni elementi dalle condizioni di lavoro, la quantificazione delle perdite di carico nel circuito, la distribuzione della portata in elementi posti in parallelo. Successivamente, gli elementi filtranti del simulatore sono stati caratterizzati ed è stato individuato il punto di lavoro del simulatore, al variare della pressione agente esternamente agli stessi ed è stata stimata la resistenza da loro opposta. Il simulatore è stato quindi studiato nelle condizioni di lavoro ideali, collegato alla macchina di dialisi in funzione, per tutta la durata di un trattamento dialitico. Le prove sono state effettuate in una prima fase utilizzando acqua demineralizzata, successivamente utilizzando fluidi appositamente preparati per riprodurre la composizione e le caratteristiche reologiche (viscosità e densità) del sangue e del fluido interstizio-cellulare. Le modifiche apportate al simulatore hanno consentito di ottenere un dispositivo più facilmente controllabile ed utilizzabile. La caratterizzazione del simulatore ha permesso la descrizione dell’andamento di pressioni e portate in sezioni significative del paziente virtuale, individuando al variare della pressione agente esternamente ai filtri il valore di portata, da impostare sulla pompa, per avere una condizione di equilibrio, ossia di scambio netto nullo di fluidi tra i due compartimenti. Le simulazioni di dialisi eseguite con acqua demineralizzata e soluti hanno permesso di individuare la regolazione ottimale dei parametri del simulatore, per garantire una replica funzionale del comportamento reale di un paziente in dialisi. Il confronto tra questi due gruppi di prove ha consentito inoltre di comprendere in maniera più completa il comportamento del fluidi analoghi del sangue e del fluido interstizio- cellulare negli scambi tra compartimenti durante la seduta dialitica.
Riprogettazione e caratterizzazione sperimentale di un simulatore fisico di paziente in dialisi
CAPUCCI, RICCARDO;GIUDICI, ALESSANDRO
2015/2016
Abstract
Any patient affected by chronicle renal insufficiency has to undergo a therapy which effectively substitutes the physiological renal functions. The low availability of organs from donors has lead to the development of an alternative therapy to the transplant: the dialysis. This treatment though does not entirely substitute the kidneys in their functions and it implicates negative aspects upon the life of the patient and his family. A lot of attentions are constantly placed upon those innovation aiming at improving the quality of the dialytic treatment, hence the quality of life of the patient. The Two Pool Virtual Simulator (TPVS) is a test bench which aims to replicate the behaviour of a patient during a dialysis session (solutes and liquid exchanges); it allows to monitor some parameters, to test new components of the dialysis machine and various treatments. It is composed of two compartments, replicating the interstitial and the plasmatic compartments of the real patient, between which the exchanges of liquids and solutes take place during the dialytic session. The goal of the present work is the redesign of some of the components of the TPVS, starting from the correct understanding of the problems of the existing version of the simulator. Once the best design solution was found in order to overcome the issues of air bubbles removal and hydraulic sealing of the cover of the main pools of the simulator, computational simulations were performed under the working conditions, as to verify the suitability of the solution. The values of the parameters required by the FE software were obtained from experimental tests performed directly on the materials. Once the solution was proved to be consistent, the component was realised and assembled. Further elements of the TPVS were modified as their efficiency was too low. The second part of the work was focused on the experimental characterisation of the renewed simulator; namely fluid-dynamic effects were considered, in terms of pressures and flow rates. First of all, the hydraulic sealing and the bubble removal were evaluated. Then preliminary tests were performed on the isolated TPVS, in order to evaluate the following aspects: the influence of the working conditions upon the behaviour of some of the components of the setup, the quantifications of the pressure drops along the circuit, the distribution of the flow rates in elements set in parallel. Then the filters of the simulator were characterised; the working point of the simulator was identified as a function of the external pressure acting on them and eventually the resistance they oppose to the circuit was evaluated. The simulator was then characterised under the ideal working conditions as it was connected to the dialysis machine for the whole dialytic treatment. Tests were performed using demineralised water in the first place, while then water was substituted with fluids specifically prepared to replicate the composition and the rheological features (viscosity and density) of blood and interstitial fluid. The modifications applied to the circuit resulted in a device which is easier to use and to control. The characterisation of the simulator allowed to describe the trend of the hydraulic parameters of interest in specific sections of the virtual patient, by detecting the proper flow rate (as a function of the external pressure acting on the filters) to be imposed to the roller pump, in order to have a dynamic balance of the fluids exchange between the two compartments. Simulations performed using demineralised water and proper fluids lead to identify the correct set of the monitorable parameters of the simulator as to guarantee a functional replication of the real behaviour of a patient undergoing dialysis. The comparison between these two working groups lead to a better understanding of the influence of having fluids which replicate the characteristics of the blood and the interstitial fluid upon the exchanges between different compartments during the dialytic session.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/133410