Tesi sul tema "Central aortic"

With the rise in prevalence of cardiovascular (CV) disease, risk stratification is becoming increasingly important. Accurate characterization of the CV system is required, for which central aortic blood pressure (BP) parameters form an integral part. However, invasive measurement of central aortic BP parameters (aP) is difficult. Therefore, non-invasive methods to estimate aP from the radial pressure pulse (rPulse) have been proposed. To analyze accuracy of estimated aP (aPhat) and applicability in risk stratification and diagnosis, this study presents: (1) a novel representation of the rPulse with minimal loss of information, (2) a framework for strict definition and statistical analysis of aPhat, and (3) a dynamic analysis of effects of mean BP (MP) and heart rate (HR) in the rPulse shape. Methods: (1) 2671 rPulse s measured by applanation tonometry were represented using the first eight principal components (PC) scores after standard PC transformation. rPulse shapes were compared in three subpopulations. (2) The concept of "estimation option" (EO) for aP estimation was presented. A framework for strict definition of aPhat and the comparison of EOs was proposed, and 7 different EOs compared. (3) A sequence of rPulse s was analyzed during soft exhalation maneuver (SEM) %, a mild Valsalva type maneuver, in eight healthy subjects. Radial BP and respiration pressure were continuously measured. The effects of MP and HR in the rPulse parameters were analyzed by standard linear regression for each subject. Results: (1) PC representation of the rPulse improves accuracy of the estimation of aPhat compared with the simple use of rPulse parameters. Subpopulations have distinctive rPulse shapes. (2) No single EO was better for the estimation of all aPhat. Inclusion of MP improves estimation accuracy. Despite further improvement when rPulse is included, the general transfer function EO is a biased estimator. (3) The dynamic analysis of the rPulse provides information of the effects of MP and HR in the rPulse not available in static analysis. The effects were specific for each individual and different from the results obtained from a general population. Conclusions: For accurate CV risk stratification, future studies should include a dynamic measurement of calibrated radial pressure pulse during SEM maneuver. Risk analysis and diagnosis should be based on representations of the rPulse with minimum loss of information. aPhat should be used for better understanding of the underlying physiological principles.

Abstract During cardiac and aortic surgery, disturbance of the blood supply in the central nervous system occurs when the repair of aortic pathologies is performed or a bloodless operation field is needed in complex cardiac surgery. To enable the suitable operation environment, the technique named hypothermic circulatory arrest (HCA) has been utilized via heart-lung machine. In this method, the core temperature is lowered to the target temperature, after which blood circulation is halted for a certain period of time. A challenge is that the successful usage of HCA, however still involves the risks of postoperative neurological complications and mortality. In cardiac and aortic arch surgery, the brain is at the highest risk for deficits, whereas in the repair of thoracoabdominal aortic aneurysms (TAAAs), spinal cord injury remains the most severe adverse outcome. Adjunctive protective strategies are required to reduce ischemic injury in these settings. In this thesis, Studies I and II focused on the spinal cord and the Study III on the brain. The studies were performed using acute (II, III) or subacute (I) experimental porcine models, primarily aiming to assess the effectiveness of remote ischemic preconditioning (RIPC) in spinal cord protection along with the aim of studying the underlying mechanisms of RIPC in neuroprotection. Studies I and II demonstrated enhanced motor evoked potential (MEP) responses in both hind limbs, indicating spinal cord protection by RIPC. The faster recovery of brain damage marker S100B along with higher cardiac index and lower systemic lactate levels confirmed the cardio- and neuroprotective properties of RIPC in Study III. The protective mechanism of RIPC was associated with increased antioxidant response (II, III)
Tiivistelmä Sydän- ja aorttakirurgiassa, keskushermoston verenkiertoa joudutaan häiritsemään toteutettaessa aortan korjausleikkauksia tai vaikeissa sydänkirurgisissa toimenpiteissä verettömän leikkausalueen saavuttamiseksi. Sydän-keuhkokoneen avulla toteutettava täydellinen verenkierron pysäytys mahdollistaa vaaditut olosuhteet. Tässä menetelmässä ydinlämpötilaa lasketaan ja verenkierron pysäytys toteutaan tavoitellussa kohdelämpötilassa tietyssä aikaikkunassa. Kyseisen menetelmän onnistunut käyttö sisältää kuitenkin riskejä operaatioiden jälkeisiin neurologisiin komplikaatioihin ja kuolleisuuteen. Sydämen ja aortankaaren kirurgiassa aivot ovat suurimmassa vaarassa vaurioille. Rinta- ja vatsa-aortan aneurysmien eli pullistumien korjausleikkauksiin liittyvä selkäydinvaurio on puolestaan yksi vakavimmista ja vaikeimmista seurauksista. Lisäsuojausmenetelmiä tarvitaan vähentämään iskeemistä vauriota näissä asetelmissa. Väitöskirjan osatyöt I ja II keskittyivät selkäytimeen. Osatyö III käsitteli puolestaan aivojen suojausta. Osatyöt toteutettiin akuutteina (II, III) ja subakuutteina (I) kokeellisina porsasmalleina. Tutkimusten tavoitteina oli arvioida esialtistavan perifeerisen raajaiskemian vaikuttavuutta selkäytimen suojauksessa sekä tutkia raajaiskemian taustalla olevia mekanismeja hermokudoksen suojauksessa. Osatöissä I, II havaittiin motoristen herätepotentiaalien parantuneita vasteita molemmissa takajaloissa osoittaen esialtistavan raajaiskemian suojaavan selkäydintä simuloidussa rinta-aortan korjaustoimenpiteessä. Osatyö III keskittyi alhaisessa lämpötilassa toteutettavaan täydelliseen verenkierron pysäytykseen. Tässä tutkimuksessa todetut aivovauriomarkkeri S100B tason nopeampi lasku, korkeampi sydänindeksi ja alhaisemmat laktaattitasot varmistivat raajaiskemian sydän- ja hermokudossuojausvaikutusta. Esialtistavan perifeerisen raajaiskemian suojaava mekanismi voidaan liittää parantuneeseen solujen antioksidanttivasteeseen (II, III)

This research utilizes CFD to analyze blood flow through pathways representative of central shunts, commonly used as part of the Fontan procedure to treat cyanotic heart disease. In the first part of this research, a parametric study of steady, Newtonian blood flow through parabolic pathways was performed to demonstrate the effect that flow pathway curvature has on wall shear stress distribution and flow energy losses. In the second part, blood flow through two shunts obtained via biplane angiograms is simulated. Pressure boundary conditions were obtained via catheterization. Results showed that wall shear stresses were of sufficient magnitude to initiate platelet activation, a precursor for thrombus formation. Steady results utilizing time-averaged boundary conditions showed excellent agreement with the time-averaged results obtained from pulsatile simulations. For the points of interest in this research, namely wall shear stress distribution and flow energy loss, the Newtonian viscosity model was found to yield acceptable results.

Abstract The repair of thoracoabdominal aortic aneurysms carries a substantial risk of ischaemic perioperative spinal cord injury. Although several protective methods have been developed, the risk of paraplegia has not been eliminated. Moreover, aortic aneurysms, including arch aneurysms, are complex clinical challenges requiring cerebral protection with hypothermic circulatory arrest (HCA). Hypothermia lowers the rate of cerebral metabolism and allows a temporary halt of the systemic circulation. However, there is still a risk for cerebral damage and a need for additional neuroprotective methods. During the last 15 years, our research group has used a porcine model to investigate a variety of neuroprotective tools. In this thesis, an animal model was utilized to study the efficacy of remote ischaemic preconditioning (RIPC) to ameliorate ischaemic damage to the central nervous system, and to shed light on the potential mechanism. Moreover, diazoxide, the pharmacological mimetic of RIPC, was tested in the HCA animal model. In the first Study (I), RIPC showed beneficial effect on the spinal cord against ischaemic insult as recorded with motor-evoked potentials. Strikingly, the beneficial effect of RIPC was observed even before the ischaemia. In the second Study (II), some beneficial effect of RIPC was seen in the immunohistochemical analysis of the spinal cord ischemia but the result remains inconclusive. Similarly, the diazoxide-treated animals had better hemodynamic status postoperatively and mildy better antioxidant activity of the brain in the third Study (III). The fourth study (IV) was a review of the current knowledge of RIPC from the cardiovascular point of view. Our studies indicate that RIPC might be a potential adjunct for preventing neuronal ischaemic injury in the setting of thoracoabdominal aortic surgery. Our result indicates that further preclinical studies with diazoxide are required before studies can be conducted in humans
Tiivistelmä Torakoabdominaalisen aortan aneurysman kirurginen korjaaminen sisältää riskin iskeemiselle selkäytimen vauriolle. Vaikka useita suojaavia tekniikoita on kehitetty, paraplegian riskiä ei ole saatu poistettua kokonaan. Kirurgisen korjaamisen haasteellisuus moninkertaistuu, jos aneurysma on laajentunut myös aortan kaareen. Tällöin vaaditaan hypotermista verenkierron pysäytystä (HCA). Hypotermia alentaa aivojen metabolista aktiivisuutta merkittävästi ja siten verenkierron väliaikainen pysäytys on mahdollista. Tästä huolimatta hypotermiseen verenkierron pysäytykseen liittyy riski aivokudoksen vauriolle. Meidän tutkimusryhmämme on tutkinut useita keskushermostoa suojaavia tekniikoita ja lääkeaineita viimeisen 15 vuoden aikana. Käytämme sikaa koe-eläin mallina, jota on tämänkin väitöskirjan osajulkaisuissa käytetty. Tämän väitöskirjatyön tarkoituksena on ollut tutkia sekä esialtistavan raajaiskemian (RIPC) että farmakologisen mimeetin, diazoxiden, keskushermostoa suojaavia vaikutuksia sekä niiden mahdollista vaikutusmekanismia. Ensimmäisessä osajulkaisussa esialtistava raajaiskemia paransi selkäytimen iskemian sietokykyä, mikä näkyi alaraajojen motorisissa herätepotentiaaleissa. Merkittävintä tutkimuksessa oli, että esialtistavan raajaiskemian edulliset vaikutuksen selkäytimeen oli nähtävissä jo ennen iskemiaa. Toisessa osajulkaisussa esialtistava raajaiskemialla oli nähtävissä edullisia, mutta ei varauksettomia, vaikutuksia selkäytimen iskemian immunohistokemiallisessa analyysissä. Kolmannessa osatyössä diazoxidin vaikutukset iskemiaa vastaan nähtiin parempana hemodynaamisena tilana ja antioksidatiivisen aktiivisuuden lisääntymisenä aivoissa, mutta tulos on myös tulkinnanvarainen. Neljäs osajulkaisu kokosi tämän hetken tietämyksen esialtistavasta raajaiskemiasta. Tutkimuksissamme osoitimme, että esialtistava raajaiskemiassa on potentiaalia tulla yhdeksi välineeksi keskushermoston iskemiaa vastaan torakoabdominaalisen aortan kirurgiassa. Lisäksi diazoxidin mahdolliset neuroprotektiiviset vaikutukset vaativat lisää koe-eläintutkimuksia ennen ihmiskokeisiin siirtymistä

Includes abstract.
Includes bibliographical references.
In Sub-Saharan Africa, the prevalence of vascular calcification (VC) in CKD-5D is unknown. We undertook to determine the effect of ethnicity on VC, the risk factors for VC, the utility of abdominal X-ray (AXR) in predicting coronary calcium score (CCS) and the effect of VC on central aortic systolic pressure (CASP) and left ventricular mass index (LVMI) in South African dialysis patients. ... Black race significantly protects from VC in South African CKD-5D patients and warrants further study. The AXR is a useful screening tool for CCS in our population. VC does not appear to influence CASP in our population.

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A insuficiência aórtica (IAo) é uma patologia que cursa com sobrecarga cardíaca de volume e consequente hipertrofia tipo excêntrica. As principais causas são febre reumática e forma degenerativa senil. O paciente com IAo se mantém assintomático por décadas e quando há falha nos mecanismos compensatórios, ocorre aparecimento de disfunção sistólica e sintomas. Vários fatores neurohumorais contribuem no desenvolvimento da IAo, entre eles o sistema renina-angiotensina IIaldosterona, o principal sistema envolvido no controle da ingestão de água e sódio. Contudo, o comportamento de ingestão de água e sódio, bem como as vias centrais relacionadas a este comportamento, ainda não foram explorados na IAo. Os objetivos da presente dissertação foram verificar em ratos submetidos a IAo subcrôncia (4 semanas; IAo4), e crônica (8 semanas; IAo8), a: a) ingestão de água e NaCl 0.3M diárias; b) ingestão de água e NaCl 0.3M após o tratamento combinando Furosemida (Furo, 10mg/kg pc) associado a baixa dose do inibidor da enzima conversora da angiotensina II, captopril (Cap, 5 mg/kg pc); e c) possível alteração da expressão para a proteína c-fos em estruturas prosencefálicas, pontinas e bulbares após o tratamento combinando Furo/Cap. Para tanto foram utilizados dois grupos de ratos Wistar (280 - 300g) submetidos à IAo ou controle. A cirurgia da indução de IAo foi realizada através da punção retrógrada dos folhetos valvares. Exames de ecocardiogramas (ECO) foram realizados 4 (IAo4) e 8 (IAo8) semanas após a cirurgia para IAo. Durante este período a ingestão de água e NaCl 0,3Mfoi acompanhada doravante. Dois dias após os ECOs os animais receberam o tratamento Furo/Cap para a quantificação do volume ingerido. Quatro dias após os animais foram novamente submetidos ao tratamento Furo/Cap para a coleta...
Aortic regurgitation (AR) is a condition that courses with volume overload and excentric hypertrophy. Main causes are rheumatic fever and degenerative vascular disease. Patients remain asymptomatic for decades and only when there is failure of compensatory mechanisms, systolic dysfunction and symptoms appear. Several neurohural factors contribute to the development of AR, among them the reninangiotensin- aldosterone system, the main system involved in the control of sodium and water intake. However, water and sodium intake, as well as the central pathways related to this behavior, were not yet explored in AR model. The aims of the present dissertation were to verify in rats following a sub chronic (4 weeks; AR4), and chronic (8 weeks; AR8): a) the daily water and 0.3M NaCl intake; b) the water and 0.3M NaCl intake after the combined treatment of Furosemide (Furo, 10mg/kg bw) associated to low dose of the inhibitor of the enzyme conversor of the angiotensin II, captopril (Cap, 5 mg/kg bw); and c) the possible alteration of c-fos protein expression in fore- and hindbrain structures by following Furo/Cap treatment. We used two groups of Wistar rats (280 - 300g) submitted to AR or sham. AR procedure was shaped by retrograde puncture of the aortic valve leaflets. Transthoracic echocardiograms (ECO) were performed in AR4 and AR8 weeks after surgery. During this period of time, daily water and 0.3M NaCl intake were measured. Two days after the ECO the animals received the combined treatment of Furo/Cap for the quantification of the volume intake. Four days later, the animals were again submitted to Furo/Cap treatment to collect the brains to imunohistochemical procedures. As results, either for AR4 and AR8, the ECO revealed decrease in fractioned shortened (AR4: 50.7 ± 2.8... (Complete abstract click electronic access below)

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Introduction: The surgical treatment of the aneurysm of descending thoracic and thoracoabdominal aorta are related with risk of spinal cord ischemic, as well as, coagulation and renal function disorders. Among the spinal cord protection methods, there are liquor drainage, temporary bypass, intercostal arteries implant, deep hypothermia, selective cooling of spinal cord and drugs. Objective: The goal of this paper is to show the viability of using extracorporeal circulation from left atrium to ascending aorta with deep hypotermia for surgical treatment of the thoracic and thoracoabdominal aneurysms. Material and Methods: From January 1994 to July 2001, thirty eight patients were operated, 26 male with mean age of 54.6±12.7. Twelve patients (31.6%) were submitted to correction of thoracoabdominal aneurysm and twenty six to correction of descending aorta aneurysm. The etiologies were: post-trauma in one patient, dilatation after correction of coarctation of the aorta in four patients, syphilitic aortite in two , atherosclerotic in ten patients and aortic dissection in twenty one patients. After extracorporeal circulation installed, the patients were cooled, the faryngeal temperature ranged from 15° and 25°C (20.6±3.2°C). The total circulatory arrest time from nine to thirty six minutes (21.3±6.7). The aortic diameter ranged from 4 to 10.5 cm (8.1±1.5 cm). Results: As neurological complications, paraplegia ocurred in two cases (5.3%) and in one of them there was stroke associated. One patient had paraparesis in inferior members and one, had seizure. The respiratory complications ocurred in twelve (31.6%) patients and tracheostomy was necessary in two cases por delayed ventilaroty support. Two patients from this group (16.7%) died. Two patients had transitory elevation of creatinine but dialysis was not necessary. Emergency operation was performed in two cases and both died. The overall mortality was seven patients (18.4%) and the causes were: bleeding in one patient, respiratory insufficiency in two patients, sudden death in two, heart failure in one and failure of weaning from extracorporeal circulation. Conclusion: Surgical correction of descending thoracic aorta and thoracoabdominal aneurysms during deep hypothermia using extracorporeal circulation with cannulation of left atrium and ascending aorta is a safe method, with low mortality. The complications such as neurologic, respiratory and renal were according to the literature.
O tratamento cirúrgico dos aneurismas da aorta torácica descendente e toracoabdominal estão associados com risco de isquemia medular, como também, a distúrbios de coagulação e alterações da função renal. Dentre os métodos de proteção medular estão, a drenagem do líquido cefalorraquidiano, o bypass temporário, o reimplante das artérias intercostais, a hipotermia profunda, o esfriamento seletivo da medula espinhal e o uso de agentes farmacológicos. Objetivo: O objetivo deste trabalho é demonstrar a viabilidade do uso da circulação extracorpórea (CEC) estabelecida entre o átrio esquerdo e aorta ascendente para indução da hipotermia profunda na correção dos aneurismas torácicos e/ou toracoabdominais. Casuística e Método: No período de janeiro de 1994 a julho de 2001, foram operados 38 pacientes, sendo 26 do sexo masculino, com média de idade 54,6±12,7 anos. Doze pacientes (31,6%) foram submetidos a correção de aneurisma toracoabdominal e 26, a aneurismas torácicos descendentes. O diagnóstico etiológico foi pós-trauma em um paciente; pós-coarctação da aorta (corrigida ou não) em quatro; aortite sifilítica em dois; aterosclerótico, dez pacientes e dissecção de aorta em 21 pacientes. Os pacientes foram induzidos a hipotermia profunda por meio de CEC, com temperatura faríngea variando entre 15 e 25°C (20,6±3,2°C). O tempo de parada circulatória variou de nove a trinta e seis minutos (21,3±6,1 minutos). O diâmetro da aorta dos pacientes variou de quatro a 10,5 cm (8,1±1,5 cm). Resultados: Dentre as complicações neurológicas, a paraplegia ocorreu em dois casos (5,3%), sendo que em um paciente houve quadro associado de acidente vascular cerebral. Um paciente evoluiu com paraparesia de membros inferiores e um, com quadro de convulsão. As complicações respiratórias estiveram presentes em 12 pacientes (31,6%), sendo que dois (5,3%) necessitaram de traqueostomia por necessidade de ventilação mecânica por tempo prolongado, com mortalidade de 16,7% (dois pacientes). Dois pacientes apresentaram elevação transitória nos níveis de creatinina, sem indicação de diálise. Dois pacientes foram operados em caráter de urgência, evoluindo para óbito. A mortalidade total da casuística foi de sete pacientes (18,4%), sendo um por sangramento, dois por complicações respiratórias, dois por morte súbita, um por insuficiência cardíaca e um por dificuldade de saída de CEC. Conclusão: A correção dos aneurismas da aorta torácica descendente e toracoabdominal com o emprego da hipotermia profunda de indução interna pela circulação extracorpórea estabelecida entre o átrio esquerdo e a aorta ascendente, demonstrou ser um método viável para o tratamento cirúrgico dos aneurismas torácicos e toracoabdominais apresentando: mortalidade, complicações neurológicas, renais e respiratórias compatíveis com os achados da literatura da época.

En este trabajo de investigación se intenta saber el grado de interés y preocupación de los pacientes diagnosticados con aneurisma y disección aórtica en cuanto a su patología y su tratamiento. Es por ello que tiene como objetivo general determinar el tipo de educación y cuáles fueron las fuentes de información que recibieron dichos pacientes durante su fase de internación en el servicio de unidad coronaria del Hospital Central durante el año 2003, sobre cuidados y cambios de hábitos para evitar complicaciones y secuelas. Es un estudio cuantitativo y descriptivo, de corte transversal. Se trabajó con una muestra de 18 pacientes internados a los cuales se les realizó una encuesta estructurada con preguntas cerradas.
Fil: Almonacid, Jorge Bruno. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Escuela de Enfermería..
Fil: Rodríguez, Irma Jaquelina. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Escuela de Enfermería..

Bakgrund: I Sverige avlider varje år cirka 600 män och 200 kvinnor till följd av ett brustet abdominalt aortaaneurysm. Mellan 1.5 och 4.0 procent av alla män över 65 år drabbas av ett abdominalt aortaaneurysm och sedan år 2015 erbjuds samtliga 65-åriga män screening för aortaaneurysm. De som diagnostiseras är således vanligen äldre personer, och i takt med stigande ålder ökar även risken att drabbas av andra sjukdomar. Patientgruppen kan därför vårdas på olika typer av vårdavdelningar, vilket gör att den grundutbildade sjuksköterskan kan möta dessa patienter på många olika vårdinstanser. För att kunna ge en god och personcentrerad vård krävs en förståelse för patienternas upplevelser relaterat till sitt aneurysm samt hur det påverkar det dagliga livet för patienterna.  Syfte: Litteraturöversiktens syfte var att beskriva vuxna patienters upplevelser relaterat till deras abdominala aortaaneurysm, både under konservativ behandling samt postoperativt och hur det påverkar det dagliga livet. Metod: Litteraturöversikten är baserad på tolv vetenskapliga artiklar med kvalitativ studiedesign. Artiklarna hämtades från tre olika databaser med medicin- och omvårdnadsfokus och analyserades därefter induktivt med en förenklad form av metasyntes. Resultat: Fem huvudkategorier och sju underkategorier av upplevelser hos patienter identifierades. Huvudkategorierna var: upplevelser kring behovet av information; upplevelser av att kunna lita på hälso- och sjukvården; oro, rädsla och ångest relaterat till AAA; AAAs påverkan på det dagliga livet; och möjlighet att vara delaktig i vårdprocessen. Konklusion: Litteraturöversikten visade att AAA upplevs med stor variation av patienter. Men framförallt upplever patienter en brist i information och kunskap om sitt AAA där ytterligare stöd, information och kunskap önskas av patienter.  Nyckelord: Abdominalt aortaaneurysm, Dagligt liv, Patienter, Personcentrerad vård, Upplevelser
Background: In Sweden, approximately 600 men and 200 women die each year as a result of a ruptured abdominal aortic aneurysm. Between 1.5 and 4.0 percent of all men over the age of 65 years suffer from an abdominal aortic aneurysm and since year 2015, all 65-years-old men have been offered a screening for aortic aneurysm. Those who are diagnosed are thus elderly and alongside an increasing age, the risk of being subject to other diseases also increases. The patient group can therefore be cared for in different types of care wards, which means that the undergraduate nurse can meet these patients in many different care institutions. In order to be able to provide good and person-centred care, an understanding of the patients' experiences of their aneurysm, and how it affects their daily lives, is required. Aim: The aim of this literature study was to describe adult patients' experiences related to abdominal aortic aneurysm, both during conservative treatment and postoperatively and how it affects daily life. Method: A literature study which is based on twelve scientific articles with qualitative study design. The articles were retrieved from three different databases with a focus on medicine and nursing and were thereafter analysed inductively with a simplified form of metasynthesis. Result: Five main categories and seven subcategories of patient experiences were identified. The main categories were: experiences around the need for information; experiences of being able to trust the health care; worry, fear and anxiety related to AAA; AAA's impact on daily life; and the possibility to be involved in the care process. Conclusion: The literature review shows that AAA is experienced with a large variety of patients. But above all, patients experience a lack of information and knowledge about their AAA where further support, information and knowledge is desired by patients.  Keywords: Abdominal aortic aneurysm, Daily life, Experiences, Patients, Person-centred care.

One quarter of any community may have normal (normal/high-normal) as opposed to optimal or hypertensive blood pressures (BP). These individuals may be at risk for a BP-related cardiovascular event, but do not qualify for BP-lowering therapy as those at risk are difficult to identify. In the present thesis I sought to determine whether aspects of non-invasively determined aortic BP may refine BPrelated cardiovascular risk assessment in those with brachial BP values within normotensive ranges. In 1169 participants from a community sample of African ancestry, 319 (27%)

The central aortic blood pressure signal is an important source of information that contains cues about the cardiovascular system condition. Measuring this pulse wave clinically is burdensome as it can be only measured invasively with a catheter. As a result, many mathematical tools have been proposed in the past few decades to reconstruct the aortic pressure signal from the peripheral pressure signals that are usually easier to obtain noninvasively. At the distal level, the blood pressure signal is not directly useful since factors, such as length and stiffness of the arteries, play roles in changing the shape of the pressure signal significantly. In this thesis, multi-channel blind system identification techniques are proposed to estimate the central pressure waveform which vary in their accuracy and complex- ity. First, a simple linear method is applied by approximating the nonlinear arterial system as a linear time-invariant system and applying the cross-relation approach. Next, a more complicated nonlinear Wiener system is proposed to model the nonlinear arterial tree. Along with the channel’s coefficients, the nonlinear functions are estimated using cross-relation and kernel methods. Data-driven machine learning methods are tested to estimate the aortic pressure signals. In many cases, they suffer from underfitting problems. As a remedy, a hybrid machine learning and cross-relation approach is also proposed to add more robustness to the machine learning models. This hybrid approach is implemented by combining the cross-relation with any machine learning method, including deep learning approaches. The various methods are tested using pre-validated virtual databases. The results show that the linear method produces root mean squared errors between 3.40 mmHg and 6.24 mmHg depending on the cross-relation constraint and the equalization tech- nique. On the other hand, the root mean squared errors associated with the nonlinear methods are between 3.76 mmHg and 4.22 mmHg and hence more stable. For the hybrid machine learning and cross-relation approach, applying the cross-relation and the dictionary learning reduce the root mean squared errors up o 67% comparing with the pure machine learning models.

博士
中原大學
生物醫學工程研究所
100
Central ascending aortic systolic (SBP-C) and pulse (PP-C) blood pressure are the most important indexes for cardiovascular mortality in humankind. Currently commercial devices for assessing SBP-C and PP-C non-invasively are almost dependent on an expensively high-fidelity tonometer and an experienced operator for obtaining a wrist pressure waveform, such as SphygmoCor and HEM-9000AI. Then, the wrist pressure waveform was calculated by several different mathematic model for yielding SBP-C and PP-C. The accuracy of gener-alized transfer function (GTF) for predicting SBP-C was quite good. However, according to limitations mentioned above, it was still not popular. This study brought a hypothesis that a pulse volume recording (PVR) waveform obtained easily from a common non-invasive blood pressure monitor could replaced the peripheral pressure waveform to estimate SBP-C non-invasively and with a convenient methodology and at lower cost. The result of this hy-pothesis was compared with other SBP-C prediction models, such as pulse wave analysis (PWA) and N-point moving average (NIBP). The PVR waveform was presented as a surrogate for invasive brachial pressure waveform in this study. This waveform is easily obtained from a commercial noninvasive blood pressure monitor when the cuff pressure is fixed at a constant pressure. Then, the predicted SBP-C was yielded from the obtained PVR waveform using GTF, PWA and NPMA prediction model. Two study groups were used in the present study. The control group was used to create the parameters of these three prediction models by using WatchBP Office, Microlife. Forty subjects were joined in this group, and the average age was 64.1 ± 14.0 years. Another one hundred subjects were joined the other testing group, and the average age was 61.9 ± 13.2 years. This testing group was used to assess the accuracy of three prediction models to esti-mate SBP-C noninvasively that was using VP-2000, Colin. All the invasive aortic pressure waveform, invasive brachial pressure waveform and non-invasive PVR waveform were rec-orded simultaneously in the catheterization laboratory at Taipei Veterans General Hospital. This study demonstrated that PVR waveform which calibrated to oscillometric base SBP and DBP from two different noninvasive blood pressure monitors was suited to predict SBP-C by using GTF prediction model. The accuracy of PVR waveform with GTF prediction model was -2.1 ± 7.7 mmHg, the result was similar to other benchmark of SBP-C prediction model. PWA prediction model was 1.7 ± 7.9 mmHg and with NPMA prediction model was -0.6 ± 7.7 mmHg in the testing group. These results were all compared with invasively measured SBP-C. Although a brachial cuff-based PVR waveform was lack of sufficient high-frequency signals in comparison in a brachial waveform, it is good enough to estimate SBP-C using GTF. And it is accurate as well as PWA and NPMA with either an aortic-to-brachial or aor-tic-to-PVR transfer functions. This study successfully applied PVR waveform from two non-invasive blood pressure monitors in three kinds of SBP-C prediction models, and proved the accuracy compared with the standard invasively measured SBP-C.

abstract: Background. Despite research aimed at understanding the mechanisms of essential hypertension, instances of this condition continue to rise. Recent findings indicate that the administration of dietary nitrates, in the form of beetroot juice and other nitrate-rich vegetables, may offer anti-hypertensive effects in various study populations. Objective. This randomized, placebo-controlled, crossover trial sought to compare the effects of high-nitrate vegetable salads to the effects of low-nitrate canned vegetables on plasma nitrate/nitrite concentration, peripheral and central-aortic systolic and diastolic blood pressures, pulse wave velocity, and flow-mediated dilation. Methods. Healthy, post-menopausal women (n=5; 80% Caucasian; 52.6 ± 5.7 years) with mildly elevated blood pressure (mean blood pressure ≥ 115/70 mm Hg and < 140/80 mm Hg) were randomly assigned to ingest a fresh, high-nitrate vegetable salad or a low-nitrate vegetable medley, twice per day, for a total of 10 consecutive days. Given the crossover design of the trial, participants observed a two to three week washout period followed by reassignment to the opposite condition. Findings were considered significant at a p-value < 0.05, and Wilcoxon Signed-Rank tests compared mean differences between conditions. Results. Plasma nitrate/nitrite concentration was significantly higher following consumption of the high-nitrate versus the low-nitrate condition (p = 0.043). Conversely, the differences in peripheral systolic and diastolic blood pressures were not statistically significant (p = 0.345 and p = 0.684 for systolic and diastolic pressures, respectively) nor were the differences in central-aortic systolic and diastolic blood pressures statistically significant (p = 0.225 and p = 0.465 for systolic and diastolic pressures, respectively). Similarly, when comparing the effects of the high-nitrate condition to the low-nitrate condition, the difference in pulse wave velocity was not statistically significant (p = 0.465). Finally, flow-mediated dilation tended to improve following consumption of the high nitrate condition (p = 0.080). Conclusion. Twice daily consumption of a fresh, high-nitrate vegetable salad significantly increased plasma nitrate/nitrite concentration. Although the trial was underpowered, there was a trend for improved flow-mediated dilation. Finally, twice daily consumption of a fresh, high-nitrate vegetable salad did not significantly lower peripheral or central-aortic systolic or diastolic blood pressures or pulse wave velocity.
Dissertation/Thesis
Masters Thesis Nutrition 2017