Simulation tools for the analysis of single electronic systems

Developments in theory and experiment have raised the prospect of an electronic technology based on the discrete nature of electron tunnelling through a potential barrier. This thesis deals with novel design and analysis tools developed to study such systems. Possible devices include those constructed from ultrasmall normal tunnelling junctions. These exhibit charging effects including the Coulomb blockade and correlated electron tunnelling. They allow transistor-like control of the transfer of single carriers, and present the prospect of digital systems operating at the information theoretic limit. As such, they are often referred to as single electronic devices. Single electronic devices exhibit self quantising logic and good structural tolerance. Their speed, immunity to thermal noise, and operating voltage all scale beneficially with junction capacitance. For ultrasmall junctions the possibility of room temperature operation at sub picosecond timescales seems feasible. However, they are sensitive to external charge; whether from trapping-detrapping events, externally gated potentials, or system cross-talk. Quantum effects such as charge macroscopic quantum tunnelling may degrade performance. Finally, any practical system will be complex and spatially extended (amplifying the above problems), and prone to fabrication imperfection. This summarises why new design and analysis tools are required. Simulation tools are developed, concentrating on the basic building blocks of single electronic systems; the tunnelling junction array and gated turnstile device. Three main points are considered: the best method of estimating capacitance values from physical system geometry; the mathematical model which should represent electron tunnelling based on this data; application of this model to the investigation of single electronic systems. (DXN004909)

Studies of antihypertensive drug persistence and adherence in the Glasgow Blood Pressure Clinic

Hypertension (HTN) is a major risk factor for cardiovascular diseases including stroke, coronary heart disease (CHD), chronic renal failure, peripheral vascular disease, myocardial infarction, congestive heart failure and premature death. The prevalence of HTN in Scotland is very high and although a high proportion of the patients receive antihypertensive medications, blood pressure (BP) control is very low. Recommendations for starting a specific antihypertensive class have been debated between various guidelines over the years. Some guidelines and HTN studies have preferred to start with a combination of an antihypertensive class instead of using a single therapy, and they have found greater BP reductions with combination therapies than with monotherapy. However, it has been shown in several clinical trials that 20% to 35% of hypertensive patients could not achieve the target BP, even though they received more than three antihypertensive medications. Several factors were found to affect BP control. Adherence and persistence were considered as the factors contributing the most to uncontrolled hypertension. Other factors such as age, sex, body mass index (BMI), alcohol intake, baseline systolic BP (SBP), and the communication between physicians and patients have been shown to be associated with uncontrolled BP and resistant hypertension. Persistence, adherence and compliance are interchangeable terms and have been used in the literature to describe a patient’s behaviour with their antihypertensive drugs and prescriptions. The methods used to determine persistence and adherence, as well as the inclusion and exclusion criteria, vary between persistence and adherence studies. The prevalence of persistence and adherence have varied between these studies, and were determined to be high in some studies and low in others. The initiation of a specific antihypertensive class has frequently been associated with an increase or decrease in adherence and persistence. The tolerability and efficacy of the initial antihypertensive class have been the most common methods of explaining this association. There are also many factors that suggest a relationship with adherence and persistence. Some factors in previous studies, such as age, were frequently associated with adherence and persistence. On the other hand, relationships with certain factors have varied between the studies. The associations of age, sex, alcohol use, smoking, baseline systolic blood pressure (SBP) and diastolic BP (DBP), the presence of comorbidities, an increase in the number of pills and the relationship between patients and physicians with adherence and persistence have been the most commonly investigated factors. Most studies have defined persistence in terms of a patient still taking medication after a period of time. A medication possession ratio (MPR) ≥ 80 has been used to define compliance. Either of these terminologies, or both, have been used to estimate adherence. In this study, I used the same definition for persistence to identify patients who have continued with their initial treatment, and used persistence and MPR to define patients who adhered to their initial treatment. The aim of this study was to estimate the prevalence of persistence and adherence in Scotland. Also, factors that could have had an effect on persistence and adherence were studied. The number of antihypertensive drugs taken by patients during the study and factors that led to an increase in patients being on a combination therapy were also evaluated. The prevalence of resistance and BP control were determined by taking the BP after the last drug had been taken by persistent patients during five follow-up studies. The relationship of factors such as age, sex, BMI, alcohol use, smoking, estimated glomerular filtration rate (eGFR), and albumin levels with BP reductions for each antihypertensive class were determined. Information Services Division (ISD) data, which includes all antihypertensive drugs, were collected from pharmacies in Scotland and linked to the Glasgow Blood Pressure Clinic (GBPC) database. This database also includes demographic characteristics, BP readings and clinical results for all patients attending the GBPC. The case notes for patients who attended the GBPC were reviewed and all new antihypertensive drugs that were prescribed between visits, BP before and after taking drugs, and any changes in the hypertensive drugs were recorded. A total of 4,232 hypertensive patients were included in the first study. The first study showed that angiotensin converting enzyme inhibitor (ACEI) and beta-blockers (BB) were the most prescribed antihypertensive classes between 2004 and 2013. Calcium channel blockers (CCB), thiazide diuretics and angiotensin receptor blockers (ARB) followed ACEI and BB as the most prescribed drugs during the same period. The prescription trend of the antihypertensive class has changed over the years with an increase in prescriptions for ACEI and ARB and a decrease in prescriptions for BB and diuretics. I observed a difference in antihypertensive class prescriptions by age, sex, SBP and BMI. For example, CCB, thiazide diuretics and alpha-blockers were more likely to be prescribed to older patients, while ACEI, ARB or BB were more commonly prescribed for younger patients. In a second study, 4,232 and 3,149 hypertensive patients were included to investigate the prevalence of persistence in the Scottish population in 1- and 5-year studies, respectively. The prevalence of persistence in the 1-year study was 72.9%, while it was only 62.8% in the 5-year study. Those patients taking ARB and ACEI showed high rates of persistence and those taking diuretics and alpha blockers had low rates of persistence. The association of persistence with clinical characteristics was also investigated. Younger patients were more likely to totally stop their treatment before restarting their treatment with other antihypertensive drugs. Furthermore, patients who had high SBP tended to be non-persistent. In a third study, 3,085 and 1,979 patients who persisted with their treatment were included. In the first part of the study, MPR was calculated, and patients with an MPR ≥ 80 were considered as adherent. Adherence rates were 29.9% and 23.4% in the 1- and 5-year studies, respectively. Patients who initiated the study with ACEI were more likely to adhere to their treatments. However, patients who initiated the study with thiazide diuretics were less likely to adhere to their treatments. Sex, age and BMI were different between the adherence and non-adherence groups. Age was an independent factor affecting adherence rates during both the 1- and 5-year studies with older patients being more likely to be adherent. In the second part of the study, pharmacy databases were checked with patients' case notes to compare antihypertensive drugs that were collected from the pharmacy with the antihypertensive prescription given during the patient’s clinical visit. While 78.6% of the antihypertensive drugs were collected between clinical visits, 21.4% were not collected. Patients who had more days to see the doctor in the subsequent visit were more likely to not collect their prescriptions. In a fourth study, 3,085 and 1,979 persistent patients were included to calculate the number of antihypertensive classes that were added to the initial drug during the 1-year and 5-year studies, respectively. Patients who continued with treatment as a monotherapy and who needed a combination therapy were investigated during the 1- and 5-year studies. In all, 55.8% used antihypertensive drugs as a monotherapy and 44.2% used them as a combination therapy during the 1-year study. While 28.2% of patients continued with treatment without the required additional therapy, 71.8% of the patients needed additional therapy. In all, 20.8% and 46.5% of patients required three different antihypertensive classes or more during the 1-year and 5-year studies, respectively. Patients who started with ACEI, ARB and BB were more likely to continue as monotherapy and less likely to need two more antihypertensive drugs compared with those who started with alpha-blockers, non-thiazide diuretics and CCB. Older ages, high BMI levels, high SBP and high alcohol intake were independent factors that led to an increase in the probability of patients taking combination therapies. In the first part of the final study, BPs were recorded after the last drug had been taken during the 5 year study. There were 815 persistent patients who were assigned for this purpose. Of these, 39% had taken one, two or three antihypertensive classes and had controlled BP (controlled hypertension [HTN]), 29% of them took one or two antihypertensive classes and had uncontrolled BP (uncontrolled HTN), and 32% of the patients took three antihypertensive classes or more and had uncontrolled BP (resistant HTN). The initiation of an antihypertensive drug and the factors affecting BP pressure were compared between the resistant and controlled HTN groups. Patients who initiated the study with ACEI were less likely to be resistant compared with those who started with alpha blockers and non-thiazide diuretics. Older patients, and high BMI tended to result in resistant HTN. In the second part of study, BP responses for patients who initiated the study with ACEI, ARB, BB, CCB and thiazide diuretics were compared. After adjusting for risk factors, patients who initiated the study with ACEI and ARB were more respondent than those who took CCB and thiazide diuretics. In the last part of this study, the association between BP reductions and factors affecting BP were tested for each antihypertensive drug. Older patients responded better to alpha blockers. Younger patients responded better to ACEI and ARB. An increase in BMI led to a decreased reduction in patients on ACEI and diuretics (thiazide and non-thiazide). An increase in albumin levels and a decrease in eGFR led to decreases in BP reductions in patients on thiazide diuretics. An increase in eGFR decreased the BP response with ACEI. In conclusion, although a high percentage of hypertensive patients in Scotland persisted with their initial drug prescription, low adherence rates were found with these patients. Approximately half of these patients required three different antihypertensive classes during the 5 years, and 32% of them had resistant HTN. Although this study was observational in nature, the large sample size in this study represented a real HTN population, and the large pharmacy data represented a real antihypertensive population, which were collected through the support of prescription data from the GBPC database. My findings suggest that ACEI, ARB and BB are less likely to require additional therapy. However, ACEI and ARB were better tolerated than BB in that they were more likely to be persistent than BB. In addition, users of ACEI, and ARB have good BP response and low resistant HTN. Linkage patients who participated in these studies with their morbidity and mortality will provide valuable information concerning the effect of adherence on morbidity and mortality and the potential benefits of using ACEI or ARB over other drugs.

Effect of remote ischaemic preconditioning in cardiac dysfunction and end-organ injury following cardiac surgery with cardiopulmonary bypass in children: A translational approach investigating clinical outcome and myocardial molecular biology

Congenital heart disease (CHD) is the most common birth defect, causing an important rate of morbidity and mortality. Treatment of CHD requires surgical correction in a significant percentage of cases which exposes patients to cardiac and end organ injury. Cardiac surgical procedures often require the utilisation of cardiopulmonary bypass (CPB), a system that replaces heart and lungs function by diverting circulation into an external circuit. The use of CPB can initiate potent inflammatory responses, in addition a proportion of procedures require a period of aortic cross clamp during which the heart is rendered ischaemic and is exposed to injury. High O2 concentrations are used during cardiac procedures and when circulation is re-established to the heart which had adjusted metabolically to ischaemia, further injury is caused in a process known as ischaemic reperfusion injury (IRI). Several strategies are in place in order to protect the heart during surgery, however injury is still caused, having detrimental effects in patients at short and long term. Remote ischaemic preconditioning (RIPC) is a technique proposed as a potential cardioprotective measure. It consists of exposing a remote tissue bed to brief episodes of ischaemia prior to surgery in order to activate protective pathways that would act during CPB, ischaemia and reperfusion. This study aimed to assess RIPC in paediatric patients requiring CHD surgical correction with a translational approach, integrating clinical outcome, marker analysis, cardiac function parameters and molecular mechanisms within the cardiac tissue. A prospective, single blinded, randomized, controlled trial was conducted applying a RIPC protocol to randomised patients through episodes of limb ischaemia on the day before surgery which was repeated right before the surgery started, after anaesthesia induction. Blood samples were obtained before surgery and at three post-operative time points from venous lines, additional pre and post-bypass blood samples were obtained from the right atrium. Myocardial tissue was resected during the ischaemic period of surgery. Echocardiographic images were obtained before the surgery started after anaesthetic induction and the day after surgery, images were stored for later off line analysis. PICU surveillance data was collected including ventilation parameters, inotrope use, standard laboratory analysis and six hourly blood gas analysis. Pre and post-operative quantitation of markers in blood specimens included cardiac troponin I (cTnI) and B-type natriuretic peptide (BNP), inflammatory mediators including interleukins IL-6, IL-8, IL-10, tumour necrosis factor (TNF-α), and the adhesion molecules ICAM-1 and VCAM-1; the renal marker Cystatin C and the cardiovascular markers asymmetric dymethylarginine (ADMA) and symmetric dymethylarginine (SDMA). Nitric oxide (NO) metabolites and cyclic guanosine monophosphate (cGMP) were measured before and after bypass. Myocardial tissue was processed at baseline and after incubation at hyperoxic concentration during four hours in order to mimic surgical conditions. Expression of genes involved in IRI and RIPC pathways was analysed including heat shock proteins (HSPs), toll like receptors (TLRs), transcription factors nuclear factor κ-B (NF- κ-B) and hypoxia inducible factor 1 (HIF-1). The participation of hydrogen sulfide enzymatic genes, apelin and its receptor were explored. There was no significant difference according to group allocation in any of the echocardiographic parameters. There was a tendency for higher cTnI values and inotropic score in control patients post-operatively, however this was not statistically significant. BNP presented no significant difference according to group allocation. Inflammatory parameters tended to be higher in the control group, however only TNF- α was significantly higher. There was no difference in levels of Cystatin C, NO metabolites, cGMP, ADMA or SDMA. RIPC patients required shorter PICU stay, all other clinical and laboratory analysis presented no difference related to the intervention. Gene expression analysis revealed interesting patterns before and after incubation. HSP-60 presented a lower expression at baseline in tissue corresponding to RIPC patients, no other differences were found. This study provided with valuable descriptive information on previously known and newly explored parameters in the study population. Demographic characteristics and the presence of cyanosis before surgery influenced patterns of activity in several parameters, numerous indicators were linked to the degree of injury suffered by the myocardium. RIPC did not reduce markers of cardiac injury or improved echocardiographic parameters and it did not have an effect on end organ function; some effects were seen in inflammatory responses and gene expression analysis. Nevertheless, an important clinical outcome indicator, PICU length of stay was reduced suggesting benefit from the intervention. Larger studies with more statistical power could determine if the tendency of lower injury and inflammatory markers linked to RIPC is real. The present results mostly support findings of larger multicentre trials which have reported no cardiac benefit from RIPC in paediatric cardiac surgery.