Redesign and performance evaluation of a cardiac pulse duplicator

Rodriguez, Reynaldo Adrian (2017-12)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The worldwide demand for prosthetic heart valve (PHV) replacements is increasing rapidly. Although developing countries have the largest demand due to the high incidence of rheumatic heart disease, the mismatch between the available resources and the cost of PHVs often renders them inaccessible in these locations. This raises the need for lower cost PHVs which calls for reduced development costs. A cardiac pulse duplicator (CPD) plays a crucial role in the PHV design process and CPDs built in-house can represent large savings over commercial alternatives. However, they are complex devices and without the appropriate level of expertise their development can result in a time consuming, expensive process which offsets any benefits derived from building it in-house. This thesis documents the redevelopment of a PHV testing device and the methods used to evaluate its performance, providing guidelines to assist those interested in developing a CPD. This was also done to enable the Biomedical Engineering Research Group at Stellenbosch University to test, in accordance to the ISO5840 standard, the PHV it developed. A literature survey confirmed the increasing importance of CPDs in PHV development and in a variety of other cardiovascular research topics but also indicated that there are no established guidelines to quantify or directly assess a CPD’s performance. Due to the difficulty of distinguishing between the hydrodynamic performance of the PHV and that of the device used to test it, the standardisation of methods to assess the performance of CPDs is proposed. The concept of fidelity is presented as a first step towards a means of quantifying CPD performance which can improve the quality of PHV test data. A high performance system was designed and implemented to control the motion of the pump used to generate pulsatile flow. Various other aspects of the CPD were designed and implemented or manufactured. This included control, acquisition and analysis software as well as a number of connected hydraulic elements making up a flexible platform for testing PHVs. Rigorous tests were devised to assess the performance of the CPD’s control system. Commercially available PHVs were tested to evaluate the electrical and hydrodynamic performance of the CPD. To compare the overall performance of the CPD to that of a widely cited counterpart, further tests were carried out so that the results obtained could be compared directly against those found in the literature. Analysis of the results showed the control system to be highly dynamic, accurate (0.019 ±0.006 mm deviation from setpoint at 70 bpm) and repeatable (2.426 ±1.335 mmHg RMSE cycle-to-cycle). The hydrodynamic performance achieved with the hydraulic components that were designed was satisfactory. The measured pressure data showed good agreement with published data for the available reference PHV, although some deviations were noted. These deviations were used to investigate some phenomena that ought to be taken into consideration during the design phase of CPDs. Some shortcomings present in the final implementation of the CPD were identified and recommendations made to address them. Despite its limitations and a cost of R 160 951, the CPD offers similar performance to a commercial system eight times this cost.

AFRIKAANSE OPSOMMING: Die wêreldwye aanvraag na prostetiese hartklep (PHK) plaasvervangers neem vinnig toe. Alhoewel ontwikkelende nasies die grootste aanvraag het as gevolg van die hoë voorkoms van rumatiese hartsiekte, veroorsaak die wanverhouding tussen die beskikbare hulpbronne en die koste van PHKs dat hulle dikwels ontoeganklik in hierdie lande is. Dit gee aanleiding tot die behoefte aan 'n goedkoper PHK wat verminderde ontwikkelingskostes vereis. ‘n Hartpolsnabootser (HPN) speel 'n belangrike rol in die PHK ontwerpsproses en HPNe wat plaaslik gebou word kan grooter besparings inhou as kommersiële alternatiewe. Hulle is egter ingewikkelde toestelle en sonder die toepaslike kundigheid kan hul ontwikkeling tot 'n tydrowende, duur proses lei wat enige voordele wat uit die plaaslike proses voortspruit neutraliseer. Dié tesis dokumenteer die herontwikkeling van 'n PHK toetsapparaat en die metodes wat gebruik is om die werkverrigting te evalueer, om sodoende riglyne te verskaf aan diegene wat belangstel in die ontwikkeling van 'n HPN. Bowendien, is die Biomediese Ingenieurswese Navorsings Groep aan die Universiteit van Stellenbosh in staat gestel om die HPN wat daar ontwikkel is in ooreenstemming met die ISO5840 standaard te toets. 'n Literatuur studie bevestig die toenemende belangrikheid van HPNe in PHK ontwikkeling, sowel as in 'n verskeidenheid van ander kardiovaskulêre-navorsingsonderwerpe, maar het ook aangedui dat daar geen gevestigde riglyne om die werkvirrigting van ‘n HPN te kwantifiseer of direk te evalueer bestaan nie. As gevolg van die probleme om te onderskei tussen die hidrodinamiese prestasie van die PHK en dié van die toestel gebruik om dit te toets, is die standaardisering van metodes om die prestasie van HPNe te evalueer voorgestel. Die konsep van getrouheid word aangebied as 'n eerste stap na 'n wyse om die prestasie van ‘n HPN te kwantifiseer, wat die gehalte van PHK toetsdata kan verbeter. 'n Hoë-prestasie stelsel is ontwerp en geïmplementeer om die beweging van die pomp wat gebruik word om polsmatige vloei te genereer te beheer. Verskeie ander aspekte van die HPN is ontwerp en geïmplementeer of vervaardig. Dit sluit in beheer-, verkryging- en analisesagteware, sowel as 'n aantal gekoppelde hidrouliese elemente wat 'n buigsame omgewing vir die toets van HPNe skep. Streng toetse is ontwerp om die werkverrigting van die HPN se beheerstelsel te evalueer. Komersiële PHKs is getoets om die elektriese en hidrodinamiese werkverrigting van die HPN te evalueer. Om die algehele werkverrigting van die HPN met dié van 'n wyd aangehale ewebeeld te vergelyk, is verdere toetse uitgevoer sodat die resultate wat verkry is direk teen dié wat in die literatuur voorkom vergelyk kon word. Ontleding van die resultate het getoon dat die beheerstelsel hoogs dinamies en akkuraat is (0.019 ±0.006 mm afwyking om ‘n stelpunt teen 70 spm) met herhaalbare uitkomste (2.426 ±1.335 mmHg WGKF siklus-tot-siklus). Die hidrodinamieseprestasie behaal met die hidrouliese komponente wat ontwerp is was bevredigend. Die data vir die gemete druk het goeie ooreenkoms getoon met gepubliseerde data vir die beskikbare verwysings PHK, hoewel sommige afwykings opgemerk is. Hierdie afwykings is gebruik om 'n paar verskynsels wat tydens die ontwerpsfase van HPNe in ag geneem behoort te word te ondersoek. Sommige tekortkominge teenwoordig in die finale implementering van die HPN is geïdentifiseer en aanbevelings is gemaak om hulle aan te spreek. Ten spyte van sy beperkinge en koste van R160 951, is die werkverigting van die HPN soortgelyk aan kommersiële stelsels wat agt keer duurder is.

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