Showing papers by "Paul Morris published in 2023"

Validation of a novel numerical model to predict regionalized blood flow in the coronary arteries

Abstract: Abstract Aims Ischaemic heart disease results from insufficient coronary blood flow. Direct measurement of absolute flow (mL/min) is feasible, but has not entered routine clinical practice in most catheterization laboratories. Interventional cardiologists, therefore, rely on surrogate markers of flow. Recently, we described a computational fluid dynamics (CFD) method for predicting flow that differentiates inlet, side branch, and outlet flows during angiography. In the current study, we evaluate a new method that regionalizes flow along the length of the artery. Methods and results Three-dimensional coronary anatomy was reconstructed from angiograms from 20 patients with chronic coronary syndrome. All flows were computed using CFD by applying the pressure gradient to the reconstructed geometry. Side branch flow was modelled as a porous wall boundary. Side branch flow magnitude was based on morphometric scaling laws with two models: a homogeneous model with flow loss along the entire arterial length; and a regionalized model with flow proportional to local taper. Flow results were validated against invasive measurements of flow by continuous infusion thermodilution (Coroventis™, Abbott). Both methods quantified flow relative to the invasive measures: homogeneous (r 0.47, P 0.006; zero bias; 95% CI −168 to +168 mL/min); regionalized method (r 0.43, P 0.013; zero bias; 95% CI −175 to +175 mL/min). Conclusion During angiography and pressure wire assessment, coronary flow can now be regionalized and differentiated at the inlet, outlet, and side branches. The effect of epicardial disease on agreement suggests the model may be best targeted at cases with a stenosis close to side branches.

Measuring and misrepresenting the missing millions: the OECD’s assessment of out-of-school youth in PISA for Development

Abstract: PISA for Development (PISA-D) was a pioneering pilot project designed to make PISA, which compares the performance of 15-year-olds in school, more suitable for low- and middle-income countries. This would allow the OECD to move beyond its traditional focus on more affluent nations and to play a central role in monitoring the Sustainable Development Goals. PISA-D was declared a success by the OECD, and its most innovative feature was that, unlike PISA, its assessment included out-of-school youth (OOSY). We analyse that strand of the assessment focussing on who was assessed. We argue that the inclusion of OOSY has been misrepresented by the OECD. Building on the literature serving as the OECD’s sources of legitimacy and applying Suchman’s framework for analysing organisational legitimacy, we portray its shifting definitions of OOSY as a tactical move that allowed it to ensure the project’s success and resolve problems that challenged its sources of legitimacy.

Sex differences in coronary microvascular resistance measured by a computational fluid dynamics model

Abstract: Background Increased coronary microvascular resistance (CMVR) is associated with coronary microvascular dysfunction (CMD). Although CMD is more common in women, sex-specific differences in CMVR have not been demonstrated previously. Aim To compare CMVR between men and women being investigated for chest pain. Methods and results We used a computational fluid dynamics (CFD) model of human coronary physiology to calculate absolute CMVR based on invasive coronary angiographic images and pressures in 203 coronary arteries from 144 individual patients. CMVR was significantly higher in women than men (860 [650–1,205] vs. 680 [520–865] WU, Z = −2.24, p = 0.025). None of the other major subgroup comparisons yielded any differences in CMVR. Conclusion CMVR was significantly higher in women compared with men. These sex-specific differences may help to explain the increased prevalence of CMD in women.

Quantifying Myocardial Blood Flow and Resistance Using 4D-Flow Cardiac Magnetic Resonance Imaging

Abstract: Background Ischaemia with nonobstructive coronary arteries is most commonly caused by coronary microvascular dysfunction but remains difficult to diagnose without invasive testing. Myocardial blood flow (MBF) can be quantified noninvasively on stress perfusion cardiac magnetic resonance (CMR) or positron emission tomography but neither is routinely used in clinical practice due to practical and technical constraints. Quantification of coronary sinus (CS) flow may represent a simpler method for CMR MBF quantification. 4D flow CMR offers comprehensive intracardiac and transvalvular flow quantification. However, it is feasibility to quantify MBF remains unknown. Methods Patients with acute myocardial infarction (MI) and healthy volunteers underwent CMR. The CS contours were traced from the 2-chamber view. A reformatted phase contrast plane was generated through the CS, and flow was quantified using 4D flow CMR over the cardiac cycle and normalised for myocardial mass. MBF and resistance (MyoR) was determined in ten healthy volunteers, ten patients with myocardial infarction (MI) without microvascular obstruction (MVO), and ten with known MVO. Results MBF was quantified in all 30 subjects. MBF was highest in healthy controls (123.8 ± 48.4 mL/min), significantly lower in those with MI (85.7 ± 30.5 mL/min), and even lower in those with MI and MVO (67.9 ± 29.2 mL/min/) (P < 0.01 for both differences). Compared with healthy controls, MyoR was higher in those with MI and even higher in those with MI and MVO (0.79 (±0.35) versus 1.10 (±0.50) versus 1.50 (±0.69), P=0.02). Conclusions MBF and MyoR can be quantified from 4D flow CMR. Resting MBF was reduced in patients with MI and MVO.

Rapid virtual fractional flow reserve using 3-D computational fluid dynamics

Abstract: Over the last ten years, virtual Fractional Flow Reserve (vFFR) has improved the utility of Fractional Flow Reserve (FFR), a globally recommended assessment to guide coronary interventions. Although the speed of vFFR computation has accelerated, techniques utilising full 3D computational fluid dynamics (CFD) solutions rather than simplified analytical solutions still require significant time to compute. This study investigated the speed, accuracy and cost of a novel 3D-CFD software method based upon a graphic processing unit (GPU) computation, compared with the existing fastest central processing unit (CPU)-based 3D-CFD technique, on 40 angiographic cases. The novel GPU simulation was significantly faster than the CPU method (median 31.7 s (IQR 24.0-44.4 s) vs 607.5 s (490-964 s), P < 0.0001). The novel GPU technique was 99.6% (IQR 99.3-99.9) accurate relative to the CPU method. The initial cost of the GPU hardware was greater than the CPU (£4080 vs £2876), but the median energy consumption per case was significantly less using the GPU method (8.44 (6.80-13.39) Wh vs 2.60 (2.16-3.12) Wh, P < 0.0001). This study demonstrates that vFFR can be computed using 3D CFD with up to 28-fold acceleration than previous techniques with no clinically significant sacrifice in accuracy.

Remote evaluation of risk and physiological response to therapeutic escalation and clinical worsening in patients with pulmonary hypertension

Abstract: Background International guidelines for the treatment of patients with pulmonary arterial hypertension (PAH) recommend the use of risk stratification to optimise therapy to achieve and maintain a low risk profile. However, recommended methods require hospital-based investigations. We sought to develop a method for daily, remote risk evaluation. Methods Consecutive patients (5820) with pulmonary hypertension (PH) were identified from the ASPIRE registry and stepwise Cox regression was applied to identify parameters associated with survival. A physiological risk score was applied to all patients and survival was assessed by the Kaplan-Meier method. Physical activity was measured in patients with PAH implanted with insertable cardiac monitors (ICM, 80) to provide a remote measure of exercise capacity. In patients with PAH and implanted pulmonary artery pressure (PAP) monitor and ICM (28) we undertook a time-stratified bidirectional case crossover study to determine the physiology of therapeutic escalation (TE) and clinical worsening and a remote physiological risk score applied to the data. Results Aage, male sex, PH aetiology, WHO functional class (FC), incremental shuttle walk distance (ISWD), heart rate reserve (HRR) and total pulmonary resistance (TPR) as independent predictors of survival. Mortality increased with each decile of baseline physiological risk. In patients with PAH, thresholds of physiological risk were used to classify patients into low-, intermediate low, intermediate high , and high risk groups for one-year mortality, which were well matched to COMPERA2.0 score-stratified groups. ICM-measured physical activity decreased with indicators of increased clinical risk (WHO-FC, NT-proBNP, ISWD, COMPERA2.0). Following TE, remote monitored mean PAP and TPR were reduced, and cardiac output (CO) and physical activity increased at days seven, four, 22 and 42 respectively. Clinical worsening events (CWE) were preceded by an increase remote monitored mean PAP and TPR and reduced CO and physical activity. Change in emote physiological risk score identifiable six days after TE and twelve days prior to a CWE. Conclusion Remote risk evaluation may facilitate personalised medicine and proactive management. The physiological risk score accurately stratifies patients with PH and may be applied to remote monitoring data for early evaluation of clinical efficacy and detection of clinical worsening.

Modelling The Hemodynamics of Coronary Ischemia

Abstract: Acting upon clinical patient data, acquired in the pathway of percutaneous intervention, we deploy hierarchical, multi-stage, data-handling protocols and interacting low- and high-order mathematical models (chamber elastance, state-space system and CFD models), to establish and then validate a framework to quantify the burden of ischaemia. Our core tool is a compartmental, zero-dimensional model of the coupled circulation with four heart chambers, systemic and pulmonary circulations and an optimally adapted windkessel model of the coronary arteries that reflects the diastolic dominance of coronary flow. We guide the parallel development of protocols and models by appealing to foundational physiological principles of cardiac energetics and a parameterisation (stenotic Bernoulli resistance and micro-vascular resistance) of patients’ coronary flow. We validate our process first with results which substantiate our protocols and, second, we demonstrate good correspondence between model operation and patient data. We conclude that our core model is capable of representing (patho)physiological states and discuss how it can potentially be deployed, on clinical data, to provide a quantitative assessment of the impact, on the individual, of coronary artery disease.