Doctor of Philosophy

dissertationHeart disease is the leading cause of death in the United States. Mechanical circulatory support by ventricular assist devices (VADs) is a means by which deteriorating heart function can be supplemented, and is a leading therapy for latestage heart failure patients. The devices are commonly connected to the apex of the left ventricle (LV) to move oxygenated blood to the body via the aorta. Recent developments have made continuous-flow pumps commonplace in the clinical environment when compared to their pulsatile-flow predecessors. Typically, continuous-flow VADs are designed with axial- or centrifugal- (radial) configurations. The pressures and flow rates vary dramatically in the native heart as blood is moved from the LV to the aorta. This dissertation presents pressure-flow characteristics for both axial- and centrifugal-flow VADs within a wide range of pressure differential values under uniform conditions, by means of a novel, open-loop flow system. Current techniques employ a closed-loop system to determine pump performance. A closed-loop system does not allow pressure differentials less than or equal to zero to be achieved. The native heart experiences pressure gradients near zero across the aortic valve during systole, which is essentially where the VAD is placed. Thus, an open-loop flow system with independently adjustable preload and afterload pressures is required to reach physiologically-relevant pressure differential regions that approximate the pressure gradient across the aortic valve during systole. Additional modifications made to the open-loop flow system generate pulsatile flow type conditions, which mimic those of the native LV. With this type of in vitro test system, not only can general hydrodynamic performance and hydraulic efficiency of VADs be measured, but also off-design operational performance under dynamic flow conditions can be characterized. This research explores hydrodynamic performance characteristics of axial- and centrifugal-flow VADs to determine design advantages that each have. Device characteristics include pressure-flow performance curves, pressure sensitivity, pulsatility index, and pulsatility ratio. Performance curves and other relevant attributes are investigated at previously unreported pressure-flow regions. Performance is evaluated theoretically, computationally, and experimentally under both steady-state, continuous-flow and pulsatile-flow circumstances

The application of a human factors approach to the evaluation of a novel outpatient parenteral antimicrobial therapy service in Malta.

The application of a human factors approach to healthcare has been gaining traction ever since its first mention in the early 1960s. The need for this synergistic collaboration stems from the poor safety and quality outcomes that have been plaguing the history of healthcare, despite continuous efforts by stakeholders to offer patient-centred care at all costs. In recent years, healthcare practitioners have positively contributed to bridging the gap between clinical practices and systems-based approaches. To this end, this research project sets out to apply a human factors approach to the evaluation of a specific niche in healthcare - the newly launched Maltese OPAT service. Considering the high quality attributed to systematic literature reviews (SLRs) in evidence-based medicine, the first phase of this study featured a dual-discipline PROSPERO-registered SLR. Data were critically appraised, synthesised and presented to deduce whether human factors approaches were amenable to OPAT pathways. Data synthesis using the SEIPS 2.0 model successfully extracted facilitators and barriers to OPAT services across the globe, indicating how systems needed to be redesigned to improve service outcomes. At this point during the research journey, the absence of a singular reference source about OPAT episodes made benchmarking and auditing against international service provisions impractical. The second phase addressed this lacuna by conducting a prospective observational cohort study about OPAT episodes, whilst concomitantly compiling a repository (October 2016 to October 2019). Details about the patient cohort and OPAT episodes, completion statuses, OPAT durations and the cost to run the service were inferred. Over the study timeframe, a total of 132 episodes were rendered to 117 patients, equating to a total of 3287 hospital bed days saved. Of these, only 23 episodes resulted in a readmission and so the overall success rate was 82.6%. The OPAT duration was significantly influenced by the presenting infection (p = 0.021), VAD (p < 0.001) and occurrence of a readmission (p = 0.05). Despite the importance of these findings, they offered little knowledge about the patients' and professionals' experiences as end users of the service. This reasoning guided the pursuit of identifying facilitators and barriers attributable to the service from the perspective of these end-users. A cross-sectional questionnaire and a focus group session were conducted to gather data from patients and the OPAT team respectively. Quantitative and qualitative analysis were supplemented by human factors strategies - namely hierarchical task analysis and SEIPS-based modelling. Following quantitative data analysis, a general positive trend in patient satisfaction scores (satisfaction rate of 95.8%) was recorded, therefore favouring the service and the high standard it managed to maintain through the years of provision. Thematic analysis supported this finding and advised caution in terms of focusing on the patient's wellbeing, standardisation of practices, availability of resources and the involvement of informal caregivers. Certain themes were also reiterated from the analysis of the focus group discourse, whereby the OPAT team also stressed the importance of standardising procedures (with specific reference to the referral process and training/education methods), and the team's flexibility and adaptability prior to expanding the service further. SEIPS-based modelling conducted on data collected during the cross-sectional survey and focus group contributed to the mapping of a systems based model applicable to the local service. Comparisons between this and the model created during the SLR about global OPAT services shed light on the requirements for system redesigns of local practices. This doctoral research has contributed both to the practice of OPAT nationally and to the general application of systems-based strategies for the betterment of healthcare outcomes. Future work should focus on the use of new methods to gather more data about the local service, including more robust pharmacoeconomic studies and an in-depth ethnography study from the perspective of the end-users through fieldwork, which could then supplement further human factor approaches such as workflow analysis, thereby ensuring further triangulation of data. On a larger scale, the findings of this research shed light on the amenability of human factors approaches to healthcare practices in general and therefore should be applied across the institution beyond the boundaries set by this case study research

'Being' a ventricular assist device recipient :a liminal existence

PhD ThesisThe purpose of this thesis is to illuminate the experience of living with a ventricular assist device (VAD) from the perspective of the recipients themselves, specific focus is given to the implications of the device on recipients’ day-to-day lives. VADs are mechanical circulatory devices that support or replace the function of a failing heart. In the UK, they are used to bridge patients to heart transplantation. This study adopts an interpretive phenomenological approach using the ‘lived experiences’ of VAD recipients as the basis of the investigation. The study comprised of twenty patients living with VADs, seventeen men and three women, aged 21 to 68, all of whom had been living on VAD support for varying amounts of time. A central tenet of this thesis is that the experience of ‘Being’ a VAD recipient is underpinned by a high degree of liminality (Turner, 1969). Life, for these individuals appears to be placed on hold whilst living with the device. Liminality creeps into the experience of ‘Being’ a VAD recipient at different time points, influencing how the individual views themselves and their future, the practices employed by VAD recipients to manage this uncertainty are considered. The impact of the materiality of the VAD is also discussed, with reference to literature from science and technology studies, exploring how recipients make sense of having a piece of technology implanted into the body and the resultant impacts on identity and surroundings following this merging of the ‘self’ and ‘not-self’. The impact of the VAD on recipients’ social roles and responsibilities are explored, along with the role of VAD communities in learning to live with the device. Ultimately, this thesis suggests that the essence of ‘Being’ a VAD recipient is a pervading sense of liminality as these individuals live under the lingering shadow of heart failure

'Pinholes in my arms': The vicious cycle of vascular access

BACKGROUND: Vascular Access Devices (VAD) are essential for the delivery of intravenous therapies. As patients often live with these devices in place for many months, it is important to understand how patients with cancer make sense of living with these devices.AIM: To explore, in-depth, the lived experience of patients with a Vascular Access Device (VAD). DESIGN / METHODS: This study followed a qualitative approach using Interpretive Phenomenological Analysis (IPA) principles. A purposive sampling technique was used to identify eleven patients with cancer who had a vascular access device in situ and were willing to share their experiences. Semi-structured interviews were the data collection tool. Interviews were digitally recorded, transcribed, and analysed using IPA principles.FINDINGS: Four superordinate themes emerged from the interview data: The self under attack; Being rescued / Being robbed; Protection of self / Protection of others; and Bewilderment and dismay at the lack of staff competence. The study discovered that the insertion of a long-term VAD changes the self and affects the psychological, social, and personal self and impacts on self-esteem and self-image. The insertion of a VAD results in restrictions and limitations to life and can lead to living with distrust and fear. Despite this, VADs are accepted and are eventually embodied. These findings add to existing knowledge by developing the meaning of living with a VAD. To illuminate this understanding and articulate the new knowledge, a conceptual framework entitled the Vicious Cycle of Vascular Access was developed.DISCUSSION: When the decision is made to insert a long-term VAD, both the body and mind should be considered. Steps should be taken to improve the lives of people living with a VAD through improved education and training for Health Care Professionals and by increasing support for people with VAD

Inflow cannula design for biventricular assist devices

Cardiovascular diseases are a leading cause of death throughout the developed world. With the demand for donor hearts far exceeding the supply, a bridge-to-transplant or permanent solution is required. This is currently achieved with ventricular assist devices (VADs), which can be used to assist the left ventricle (LVAD), right ventricle (RVAD), or both ventricles simultaneously (BiVAD). Earlier generation VADs were large, volume-displacement devices designed for temporary support until a donor heart was found. The latest generation of VADs use rotary blood pump technology which improves device lifetime and the quality of life for end stage heart failure patients. VADs are connected to the heart and greater vessels of the patient through specially designed tubes called cannulae. The inflow cannulae, which supply blood to the VAD, are usually attached to the left atrium or ventricle for LVAD support, and the right atrium or ventricle for RVAD support. Few studies have characterized the haemodynamic difference between the two cannulation sites, particularly with respect to rotary RVAD support. Inflow cannulae are usually made of metal or a semi-rigid polymer to prevent collapse with negative pressures. However suction, and subsequent collapse, of the cannulated heart chamber can be a frequent occurrence, particularly with the relatively preload insensitive rotary blood pumps. Suction events may be associated with endocardial damage, pump flow stoppages and ventricular arrhythmias. While several VAD control strategies are under development, these usually rely on potentially inaccurate sensors or somewhat unreliable inferred data to estimate preload. Fixation of the inflow cannula is usually achieved through suturing the cannula, often via a felt sewing ring, to the cannulated chamber. This technique extends the time on cardiopulmonary bypass which is associated with several postoperative complications. The overall objective of this thesis was to improve the placement and design of rotary LVAD and RVAD inflow cannulae to achieve enhanced haemodynamic performance, reduced incidence of suction events, reduced levels of postoperative bleeding and a faster implantation procedure. Specific objectives were: * in-vitro evaluation of LVAD and RVAD inflow cannula placement, * design and in-vitro evaluation of a passive mechanism to reduce the potential for heart chamber suction, * design and in-vitro evaluation of a novel suture-less cannula fixation device. In order to complete in-vitro evaluation of VAD inflow cannulae, a mock circulation loop (MCL) was developed to accurately replicate the haemodynamics in the human systemic and pulmonary circulations. Validation of the MCL’s haemodynamic performance, including the form and magnitude of pressure, flow and volume traces was completed through comparisons of patient data and the literature. The MCL was capable of reproducing almost any healthy or pathological condition, and provided a useful tool to evaluate VAD cannulation and other cardiovascular devices. The MCL was used to evaluate inflow cannula placement for rotary VAD support. Left and right atrial and ventricular cannulation sites were evaluated under conditions of mild and severe heart failure. With a view to long term LVAD support in the severe left heart failure condition, left ventricular inflow cannulation was preferred due to improved LVAD efficiency and reduced potential for thrombus formation. In the mild left heart failure condition, left atrial cannulation was preferred to provide an improved platform for myocardial recovery. Similar trends were observed with RVAD support, however to a lesser degree due to a smaller difference in right atrial and ventricular pressures. A compliant inflow cannula to prevent suction events was then developed and evaluated in the MCL. As rotary LVAD or RVAD preload was reduced, suction events occurred in all instances with a rigid inflow cannula. Addition of the compliant segment eliminated suction events in all instances. This was due to passive restriction of the compliant segment as preload dropped, thus increasing the VAD circuit resistance and decreasing the VAD flow rate. Therefore, the compliant inflow cannula acted as a passive flow control / anti-suction system in LVAD and RVAD support. A novel suture-less inflow cannula fixation device was then developed to reduce implantation time and postoperative bleeding. The fixation device was evaluated for LVAD and RVAD support in cadaveric animal and human hearts attached to a MCL. LVAD inflow cannulation was achieved in under two minutes with the suture-less fixation device. No leakage through the suture-less fixation device – myocardial interface was noted. Continued development and in-vivo evaluation of this device may result in an improved inflow cannulation technique with the potential for off-bypass insertion. Continued development of this research, in particular the compliant inflow cannula and suture-less inflow cannulation device, will result in improved postoperative outcomes, life span and quality of life for end-stage heart failure patients