Development of a diagnostic sensor for measuring blood cell concentrations during haemoconcentration

Background: HemoSep® is a commercial ultrafiltration and haemoconcentration device for the concentration of residual bypass blood following surgery. This technology is capable of reducing blood loss in cardiac and other types of "clean site" procedures, including paediatric surgery. Clinical feedback suggested that the device would be enhanced by including a sensor technology capable of discerning the concentration level of the processed blood product. We sought to develop a novel sensor that can, using light absorption, give an accurate estimate of packed cell volume (PCV). Materials and methods: A sensor-housing unit was 3D printed and the factors influencing the sensor's effectiveness – supply voltage, sensitivity and emitter intensity - were optimised. We developed a smart system, using comparator circuitry capable of visually informing the user when adequate PCV levels (⩾35%) are attained by HemoSep® blood processing, which ultimately indicates that the blood is ready for autotransfusion. Results: Our data demonstrated that the device was capable of identifying blood concentration at and beyond the 35% PCV level. The device was found to be 100% accurate at identifying concentration levels of 35% from a starting level of 20%. Discussion: The sensory capability was integrated into HemoSep's® current device and is designed to enhance the user’s clinical experience and to optimise the benefits of HemoSep® therapy. The present study focused on laboratory studies using bovine blood. Further studies are now planned in the clinical setting to confirm the efficacy of the device

Development of a portable blood salvage and autotransfusion technology to enhance survivability of personnel requiring major medical interventions in austere or military environments

Introduction - Uncontrolled haemorrhage is the leading cause of death on the battlefield, and two-thirds of these deaths result from non-compressible haemorrhage. Blood salvage and autotransfusion represent an alternative to conventional blood transfusion techniques for austere environments, potentially providing blood to the casualty at point of injury. The aim of this paper is to describe the design, development and initial proof-of-concept testing of a portable blood salvage and autotransfusion technology to enhance survivability of personnel requiring major medical interventions in austere or military environments. Method - A manually operable, dual-headed pump was developed that removes blood from site of injury to a collection reservoir (upper pump) and back to casualty (lower pump). Theoretical flow rate calculations determined pump configuration and a three-dimensionally printed peristaltic pump was manufactured. Flow rates were tested with fresh bovine blood under laboratory conditions representative of the predicted clinical environment. Results - Mathematical modelling suggested flow rates of 3.6 L/min and 0.57 L/min for upper and lower pumps. Using fresh bovine blood, flow rates produced were 2.67 L/min and 0.43 L/min. To mimic expected battlefield conditions, upper suction pump flow rate was calculated using a blood/air mixture. Conclusion - The authors believe that this technology can potentially enhance survivability for casualties in austere and deployed military settings through autotransfusion and cell concentration. It reduces negative effects of blood donation on the conventional donor pool, and potentially negates the logistical constraints associated with allogenic transfusions

Investigating the suitability of carbon nanotube reinforced polymer in transcatheter valve applications

The current delivery size of transcatheter aortic valves, limited by the thickness of their pericardial leaflets, correlates with a high prevalence of major vascular complications. Polyurethane valves can be developed to a fraction of the thickness of pericardial valves through the addition of carbon nanotubes to reinforce their leaflets. This study investigates the suitability of a novel carbon nanotube reinforced leaflet to reduce the delivery profile of transcatheter aortic valves. Carbon nanotube polyurethane composites were developed with thicknesses of 50 μm and their mechanical properties were determined in relation to various environmental effects. The composites demonstrated improvements to the material stiffness, particularly at increasing strain rates compared to the neat polymer. However, increasing nanotube concentrations significantly decreased the fatigue life of the composites. Key findings highlighted a potential for carbon nanotube reinforcement in valve replacement which experience very high strain rates during the cardiac cycle. Further testing is needed to achieve a strong nanotube-matrix interface which will prolong the cyclic fatigue life and further strengthen tensile properties. Testing on the durability and haemocompatibility of these composite heart valves are ongoing

Comparative evaluation of blood salvage techniques in patients undergoing cardiac surgery with cardiopulmonary bypass

Background: The primary objective of this study was to test and compare the efficacy of currently available intraoperative blood salvage systems via a demonstration of the level of increase in percentage concentration of red blood cells (RBC), white blood cells 9WBC) and platelets (Plt) in the end product. Methods: In a prospective, randomized study, data of 80 patients undergoing elective cardiac surgery with cardiopulmonary bypass in a 6-month period was collected, of which the volume aspirated from the surgical field was processed by either the HemoSep Novel Collection Bag (Advancis Surgical, Kirkby-in-Ashfield, Notts, UK) (N=40) (Group 1) or a cell- saver (C.A.T.S Plus Autotransfusion System, Fresenius Kabi, Bad Homburg, Germany) (N=40) (Group 2). Results: Hematocrit levels increased from 23.05%±2.7 to 43.02%±12 in Group 1 and from 24.5±2 up to 55.2±9 in Group 2 (p=0.013). The mean number of platelets rose to 225200±47000 from 116400 ±40000 in the HemoSep and decreased from 125200±25000 to 96500±30000 in the cell-saver group (p=0.00001). The leukocyte count was concentrated significantly better in Group 1 (from 10100±4300 to 18120±7000; p=0.001). IL-6 levels (pg/dL) decreased from 223±47 to 83±21 in Group 1 and from 219±40 to 200±40 in Group 2 (p=0.001). Fibrinogen was protected significantly better in the HemoSep group (from 185±35 to 455±45; p=0.004). Conclusions: Intraoperative blood salvage systems functioned properly and the resultant blood product was superior in terms of red blood cell species. The HemoSep group had significantly better platelet and leukocyte concentrations and fibrinogen content

Blood flow simulations in the pulmonary bifurcation for the assessment of valve replacement in adult patients with congenital heart disease

Adult patients with congenital heart disease comprise a growing population with complex cardiac conditions, among other ageing-associated diseases. This particular group of patients may undergo multiple surgical procedures in their lifetime, a significant number of which involves pulmonary valve replacement (PVR). The clinical decision for such surgical intervention is currently relying on symptoms, including arrhythmias, and measures of right ventricular dilatation, at e.g. 80-90 mL/m2 end-systolic and 150-160 mL/m2 end-diastolic volumes [1,2]. However, there is no common consensus on the reliability of these criteria, and more accurate and timely assessment for PVR treatment is necessary. The overall objective of this work is to investigate the altered haemodynamic environment in the adult with congenital heart defect, including pre- and post-operative conditions. Here, we show computational results in the pulmonary bifurcation with the scope to establish a novel and reliable metric for pulmonary valve replacement

Haemodynamic analysis in arterial models in relation to pulmonary valve treatment in adults with congenital heart disease

Introduction Pulmonary artery stenting and valve replacement (PVR) are common interventions in an increasing population of adult patients with previously repaired congenital heart disease [1]. Indications for intervention include assessing regional haemodynamics and effects on right ventricular volume and function [2]. The criterion for intervention remains largely empirical and the optimal timing remains unknown. This work aims to investigate the altered haemodynamic environment of adults with congenital heart disease, pre- and post- operative PVR to establish a computational fluid dynamic (CFD) derived metric for determining the optimal requirement for PVR and stenting. In this initial work, we present CFD results in simplified geometries representing the proximal pulmonary artery and bifurcation. Methods Blood flow simulations were performed using an implementation of the finite volume method. The flow was assumed to be incompressible and governed by the Newtonian Navier-Stokes equations. Physiological vessel dimensions and boundary conditions were used in the models. Local velocities and wall shear stress values were evaluated numerically. Results and Discussion Blood flow in the pulmonary bifurcation is strongly dependent on the local geometrical characteristics and haemodynamic conditions. An increase in the flow separation is observed when the angle of the bifurcation increases. In addition, the geometry has a significant effect on the velocities and shear stresses developed on the vessel wall. Future work will involve anatomically-correct reconstructions from CT and MRI image data of adult congenital heart patients that have or are about to undergo pulmonary valve replacement. Numerical studies of these models will provide an insight into the underlying flow mechanisms of more complex 3D patient-specific geometries

Assessment of microcirculation on sternal woundhealing after coronary artery bypass graft surgical diabetic and non-diabetic patients using laser Doppler imaging system

Background/Introduction: In this study we propose to investigate the effect of the neovascularisation and blood flow to the sternum and sur-rounding tissues in diabetic & non-diabetic patients by using a laser Doppler imager. The reasons for the delayed healing are not entirely clear, but are thought to include both mechanical factors such as poor wiring of the breast-bone during surgery, and biological factors related to the interruption to the blood supply to the sternum and sur-rounding tissues associated with the procedure. Aims/Objectives: To assess the role of neovascularisation in diabetic & non-diabetic following coronary artery bypass graft (CABG) surgery using Laser Doppler Imager. Method: Patients were divided into two groups as diabetic & non-diabetic had undergone CABG (30 patients). Sternal microcirculation measurements were taken by using a Moor LDI laser Doppler imaging system, at ten timepoints (pre-induction to 96 hours after bypass). The regional blood flow was estimated by measuring the Doppler shift of laser light caused by blood cells passing within the laser light field. Blood samples were taken for the analysis of number of factors. Results: The neovascularisation and wound healing were comparatively faster in non-diabetic surgical patients than diabetic group. New vessel formation from the right internal thoracic and intercostal arteries to the left side confirmed that the vascular supply of the sternum on the left side following CABG surgery was not entirely depended upon the left internal thoracic arteries. This is due to secondary changes in diabetic patients on vascular system. Discussion/Conclusion: There was a formation of new vessels from right side of the sternum following the mobilization of left internal thoracic artery in CABG surgical patients. The healing process was faster in non-diabetic CABG surgical patients. comparatively faster in non-diabetic surgical patients than diabetic group. New vessel formation from the right internal thoracic and intercostal arteries to the left side confirmed that the vascular supply of the sternum on the left side following CABG surgery was not entirely depended upon the left internal thoracic arteries. This is due to secondary changes in diabetic patients on vascular system. Discussion/Conclusion: There was a formation of new vessels from right side of the sternum following the mobilization of left internal thoracic artery in CABG surgical patients. The healing process was faster in non-diabetic CABG surgical patients

In vitro assessment of the lenz effect on heart valve prosthesis at 1.5T

Increasing numbers of patients with cardiac valve prostheses are being referred for magnetic resonance imaging (MRI) despite concerns about the potential for functional valve impedance due to Lenz forces. This study aims to determine, in vitro, the occurrence of Lenz forces on 9 heart valve prostheses at 1.5 T and assess the risk of impedance of valve function. A specially designed hydro-pneumatic system was used to record pressure changes across the valve indicative of any MR induced alteration in leaflet performance. Nine cardiac valve prostheses were exposed to the B0 field at 1.5 T. Each valve was advanced through the B0 field and continuous signals from high frequency pressure transducers were recorded and pressure drops across the valve were assessed using time correction superimposition. The delta p across the valve was assessed as a marker of any MRI induced alteration in leaflet performance. All prostheses produced sinusoidal waveforms. Profiles were asymmetrical and there was no consistency in complex shape and valve type/sub-group. Irregularities in pressure profiles of 4 prostheses were detected indicating resistance of the occluder to the B0 field. This study provides empirical evidence of the Lenz Effect on cardiac valve prostheses exposed to the MR B0 field causing functional valve impedance and increasing the risk of valvular regurgitation and reduced cardiac output. Thus, it is essential to consider the potential for the Lenz Effect when scanning cardiac valve implant patients in order to safeguard their wellbeing