Design and numerical simulation for the development of an expandable paediatric heart valve.

Current paediatric valve replacement options cannot compensate for somatic growth, leading to an obstruction of flow as the child outgrows the prosthesis. This often necessitates an increase in revision surgeries, leading to legacy issues into adulthood. An expandable valve concept was modelled with an inverse relationship between annulus size and height, to retain the leaflet geometry without requiring additional intervention. Parametric design modelling was used to define certain valve parameter aspect ratios in relation to the base radius, Rb, including commissural radius, Rc, valve height, H and coaptation height, x. Fluid-structure simulations were subsequently carried out using the Immersed Boundary method to radially compress down the fully expanded aortic valve whilst subjecting it to diastolic and systolic loading cycles. Leaflet radial displacements were analysed to determine if valve performance is likely to be compromised following compression. Work is ongoing to optimise valvular parameter design for the paediatric patient cohort.

Blood flow simulations in the pulmonary bifurcation in relation to adult patients with repaired tetralogy of Fallot.

Understanding the haemodynamic environment of the pulmonary bifurcation is important in adults with repaired conotruncal congenital heart disease. In these patients, dysfunction of the pulmonary valve and narrowing of the branch pulmonary arteries are common and can have serious clinical consequences. The aim of this study was to numerically investigate the underlying blood flow characteristics in the pulmonary trunk under a range of simplified conditions. For that, an in-depth analysis was conducted in idealised two-dimensional geometries that facilitate parametric investigation of healthy and abnormal conditions. Subtle variations in morphology influenced the haemodynamic environment and wall shear stress distribution. The pressure in the left pulmonary artery was generally higher than that in the right and main arteries, but was markedly reduced in the presence of a local stenosis. Different downstream pressure conditions altered the branch flow ratio, from 50:50% to more realistic 60:40% ratios in the right and left pulmonary artery, respectively. Despite some simplifications, this study highlights some previously undocumented aspects of the flow in bifurcating geometries, by clarifying the role of the stagnation point location on wall shear stress and differential branch pressures. In addition, measurements of the mean pressure ratios in the pulmonary bifurcation are discussed in the context of a new haemodynamic index which could potentially contribute to the assessment of left pulmonary artery stenosis in tetralogy of Fallot patients. Further studies are required to confirm the results in patient-specific models with personalised physiological flow conditions.

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.

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.

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.

In vitro assessment of the Lenz effect on heart valve prostheses at 1.5 T.

PURPOSE: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Novel Split Chest Tube Improves Post-Surgical Thoracic Drainage.

OBJECTIVE: Conventional, separate mediastinal and pleural tubes are often inefficient at draining thoracic effusions. DESCRIPTION: We developed a Y-shaped chest tube with split ends that divide within the thoracic cavity, permitting separate intrathoracic placement and requiring a single exit port. In this study, thoracic drainage by the split drain vs. that of separate drains was tested. METHODS: After sternotomy, pericardiotomy, and left pleurotomy, pigs were fitted with separate chest drains (n=10) or a split tube prototype (n=9) with internal openings positioned in the mediastinum and in the costo-diaphragmatic recess. Separate series of experiments were conducted to test drainage of D5W or 0.58 M sucrose, an aqueous solution with viscosity approximating that of plasma. One litre of fluid was infused into the thorax, and suction was applied at -20 cm H2O for 30 min. RESULTS: When D5W was infused, the split drain left a residual volume of 53 ± 99 ml (mean value ± SD) vs. 148 ± 120 for the separate drain (P=0.007), representing a drainage efficiency (i.e. drained vol/[drained + residual vol]) of 95 ± 10% vs. 86 ± 12% for the separate drains (P = 0.011). In the second series, the split drain evacuated more 0.58 M sucrose in the first minute (967 ± 129 ml) than the separate drains (680 ± 192 ml, P<0.001). By 30 min, the split drain evacuated a similar volume of sucrose vs. the conventional drain (1089 ± 72 vs. 1056 ± 78 ml; P = 0.5). Residual volume tended to be lower (25 ± 10 vs. 62 ± 72 ml; P = 0.128) and drainage efficiency tended to be higher (98 ± 1 vs. 95 ± 6%; P = 0.111) with the split drain vs. conventional separate drains. CONCLUSION: The split chest tube drained the thoracic cavity at least as effectively as conventional separate tubes. This new device could potentially alleviate postoperative complications.

Novel ultrafiltration technique for blood conservation in cardiac operations.

PURPOSE: The performance characteristics and clinical outcome of a novel hemoconcentrator, the HemoSep (Brightwake, Nottingham, United Kingdom), for reusing salvaged blood postoperatively were evaluated. DESCRIPTION: HemoSep concentrates blood by removing the fluid component from a pooled volume of blood salvaged at the end of the operation from the heart-lung machine. During a 6-month period, 102 patients were prospectively randomized into two groups. In group 1 (n = 52), salvaged blood in the venous reservoir after the cessation of cardiopulmonary bypass was reused by the HemoSep device and the processed blood was retransfused to the patients. In group 2 (n = 50), the control group, the operation proceeded using conventional method without using the hemoconcentrator. EVALUATION: The mean amount of processed blood was 775 ± 125 mL. The efficacy of the HemoSep device was confirmed by the percentage concentration of the hematocrit at 15 and 40 minutes. Serum albumin and factor VII levels were concentrated more than threefold at 40 minutes vs baseline measurements. Patients who received processed blood had significantly less need for an allogeneic transfusion. CONCLUSIONS: The HemoSep device functions as designed and without technical failures, offering a complementary technique in blood management during cardiac operations.

A technical review of flexible endoscopic multitasking platforms.

BACKGROUND: Further development of advanced therapeutic endoscopic techniques and natural orifice translumenal endoscopic surgery (NOTES) requires a powerful flexible endoscopic multitasking platform. METHODS: Medline search was performed to identify literature relating to flexible endoscopic multitasking platform from year 2004-2011 using keywords: Flexible endoscopic multitasking platform, NOTES, Instrumentation, Endoscopic robotic surgery, and specific names of various endoscopic multitasking platforms. Key articles from articles references were reviewed. RESULTS: Flexible multitasking platforms can be classified as either mechanical or robotic. Purely mechanical systems include the dual channel endoscope (DCE) (Olympus), R-Scope (Olympus), the EndoSamurai (Olympus), the ANUBIScope (Karl-Storz), Incisionless Operating Platform (IOP) (USGI), and DDES system (Boston Scientific). Robotic systems include the MASTER system (Nanyang University, Singapore) and the Viacath (Hansen Medical). The DCE, the R-Scope, the EndoSamurai and the ANUBIScope have integrated visual function and instrument manipulation function. The IOP and DDES systems rely on the conventional flexible endoscope for visualization, and instrument manipulation is integrated through the use of a flexible, often lockable, multichannel access device. The advantage of the access device concept is that it allows optics and instrument dissociation. Due to the anatomical constrains of the pharynx, systems are designed to have a diameter of less than 20 mm. All systems are controlled by traction cable system actuated either by hand or by robotic machinery. In a flexible system, this method of actuation inevitably leads to significant hysteresis. This problem will be accentuated with a long endoscope such as that required in performing colonic procedures. Systems often require multiple operators. To date, the DCE, the R-Scope, the IOP, and the Viacath system have data published relating to their application in human. CONCLUSION: Alternative forms of instrument actuation, camera control and master console ergonomics should be explored to improve instrument precision, sphere of action, size and minimize assistance required.

A prospective randomized study to evaluate the renal impact of surgical revascularization strategy in diabetic patients.

Acute kidney injury (AKI) is a major postoperative complication following cardiac surgery. Diabetes mellitus is a major cause of nephropathy and end-stage renal failure. We aimed to evaluate the occurrence of adverse renal outcomes, in diabetic patients, between on-pump (CPB) and off-pump (OPCAB) coronary artery bypass graft (CABG). Seventy-one diabetic patients (36 and 35 patients in the CPB and OPCAB groups, respectively) were enrolled in a prospective randomized study. Renal tubular and glomerular functions, were monitored preoperatively and over five consecutive days. There was no significant difference between the groups in terms of age, gender, New York Heart Association class, Canadian Cardiovascular Society functional classification of angina grade and number of CABG. Intensive care unit stay, duration of intubation, hospital stay and bleeding were significantly higher in the CPB group. No significant differences in plasmatic creatinine, urinary creatinine, creatinine clearance, proteinuria or osmolality were detected. A significant rise in urinary albumine excretion occurred in both groups peaking on the operative day; for the on-pump CABG group (10±5 vs. 48±57; P=0.015) and for the OPCAB group (11±6 vs. 37±59; P=0.04). Values were less important in the OPCAB group and return to the baseline was faster than in the CPB group. OPCAB attenuates sub-clinical AKI, in diabetic patients.

The influence of cannulation technique on blood flow to the brain in rats undergoing cardiopulmonary bypass: a cautionary "tail".

Recently, there has been an increase in the use of rat models of cardiopulmonary bypass (CPB) for research purposes. Much of this work has focused on cerebral injury associated with CPB. Many of these studies employ a peripheral cannulation approach, often utilizing the caudal artery and internal or external jugular vein. The aim of the present study was to establish whether there is any alteration in blood flow to the brain associated with the use of different cannulation routes. Twenty-four adult male Sprague Dawley rats were allocated to one of three study groups: Group 1- caudal artery return, Group 2 -open-chest aortic return, and Group 3- nonbypass control group. Colored microspheres were injected into all animals at four time points (postinduction, initiation of bypass, midbypass, and end bypass). After the termination of each experiment, the brains were excised, the tissue was digested, the microspheres were harvested, and the global blood flow to the brain was assessed using the reference flow method. There was a significant reduction in blood flow to the brain between both bypass groups and the control group. Additionally, cerebral blood flow was significantly lower in the caudal return group than in the aortic return group. There is a significant drop in blood flow to the brain associated with the initiation and continuation of CPB when compared to non-CPB controls. These results also confirm a considerable cerebral hypoperfusion associated with the peripheral cannulation technique, and suggest that peripheral bypass may exaggerate the influence CPB has on cerebral injury. This technique must therefore be employed with caution.

Simple surface sulfonation retards plasticiser migration and impacts upon blood/material contact activation processes.

BACKGROUND: The use of Di-2-ethylhexyl phthalate (DEHP) plasticised polyvinyl chloride (DEHPPPVC) in medical devices persists despite evidence suggesting that DEHP migration can be harmful. Researchers have shown that a simple surface sulfonation process can retard the migration of DEHP, which may reduce the associated inflammatory response. The present study is designed to investigate the effects of surface sulfonation on DEHP migration and blood contact activation using in vitro and rodent models. METHODS: The study was carried out in two phases: phase 1, in which the migration rate of DEHP from DEHPPPVC and sulfonated DEHP plasticised PVC (SDEHPPPVC) was measured; phase 2 of the study, in which the materials were incorporated into a rat recirculation biomaterial test model and blood samples taken to assess CD11b expression on neutrophils, IL-6 and Factor XIIa. RESULTS: The initial DEHP concentration washed from the surface after storage was 37.19 +/- 1.17 mg/l in the PPVC group and 5.89 +/- 0.81 mg/l in the SPPVC group (p<0.0001). The post-wash migration rate was 3.07 +/- 0.32 mg/l/hour in the PPVC group compared to 0.46 +/- 0.038 mg/l/hour in the SPPVC group (p<0.0001). In phase 2 of the study, CD11b expression increased by 228.9% +/- 37% over the test period in the PPVC group compared to 118.3% +/- 46% in the SPPVC group (p<0.01). IL-6 levels rose from 3.1 +/- 1.4 pg/ml to 263 +/- 26 pg/ml in the PPVC group and 2.2 +/- 1.6 pg/ml to 161 +/- 29 pg/ml in the SPPVC group (p<0.01). Factor XIIa levels rose from 0.22 +/- 0.13 g/ml to 3.7 +/- 0.32 microg/ml and 0.28 +/- 0.09 to 2.71 +/- 0.21 microg/ml in the PPVC and SPPVC groups, respectively (p<0.05 at 90 minutes). CONCLUSIONS: The simple sulfonation process significantly retards the migration of DEHP and is associated with the moderation of contact activation processes.

Clinical efficacy of two-phase leukocyte filtration in high-risk patients undergoing coronary revascularization with cardiopulmonary bypass.

The purpose of this study was to investigate the clinical outcome, inflammatory response and myocardial function in high-risk patients undergoing three different leukocyte depletion strategies. Over a four-month period, forty patients (EuroSCORE 6+) undergoing coronary revascularization were prospectively randomized to one of the four perfusion protocols: Group 1 (N=10): Conventional circuits (ECC) + two leukocyte filters (LG6B, Pall, USA) with the method of two-phase (continuous + strategic) leukofiltration; Group 2 (N=10): ECC + single leukocyte filter with the method of continuous leukofiltration; Group 3 (N=10): ECC + single leukocyte filter with the method of strategic leukofiltration; Group 4 (N=10) CONTROL: ECC without leukocyte filtration. Blood samples were collected at T1: Baseline, T2: On CPB, T3: X-Clamp, T4: Off CPB, T5: ICU24 and T6: ICU48. Perioperative follow-up was thoroughly monitored. Leukocyte counts in double filter and strategic filtration groups demonstrated significant differences at T4 (p < .05 vs. control). TNFalpha levels were significantly lower in Group 1 at T4 and procalcitonin levels at T5 and T6 (p < .05 vs. control). CKMB levels demonstrated well preserved myocardium in double filter group (p < .05 vs. control). Brain natriuretic peptide levels in double filter group were significantly lower at T5 and T6 with respect to Group 2 (p <.05) and control (p <.001). Matrixmetallopeptidase 9 and D-Dimer levels in double filter group were significantly lower at T5 and T6 (p <.05 vs. control).Two-phase leukofiltration is associated with some compound benefit over continuous deployment in high-risk patients. A larger more powerful study than this pilot one is warranted for further evaluation.

The effect of priming solutions and storage time on plasticizer migration in different PVC tubing types--implications for wet storage of ECMO systems.

The wet priming of extracorporeal membrane oxygenation systems and storage of these systems for rapid deployment is common practice in many clinical centers. This storage policy is, however, seen by many to be controversial due to the potential adverse effects associated with the migration of the di(2-ethylhexyl) phthalate plasticizer (DEHP) from the polyvinyl chloride (PVC) circuit tubing and issues surrounding the maintenance of sterility. This study was performed to evaluate the effects of both short and long-term storage and priming fluid type on plasticizer migration from four commonly used PVC tubes in extracorporeal membrane oxygenation therapy circuits. The four tubes incorporating three plasticizers, two DEHP, one tri(2-ethylhexyl) trimellitate (TOTM), and one dioctyl adipate (DOA) were exposed to each of the three priming fluids for a period of 28 days. Samples were taken at time intervals of 1, 4, 8, 24, and 48 hours, followed by samples at 7, 14, and 28 days. Each sample was processed using a spectrophotomer and the concentration of plasticizer leaching into each solution at each time-point determined. There was a time dependent increase in plasticizer leached from each tube. The migration was greatly affected by both the priming fluid and tubing type. The migration of DEHP was higher than that of TOTM and DOA over both the short and long-term exposure levels. Plasticizer migration occurs from all of the tubes tested over the long term. The TOTM and DOA tubes performed better than the DEHP counterparts in the short term. Selection of priming fluid has a major bearing on plasticizer migration with significant lipid and protein containing fluids promoting higher migration than simple sodium chloride .9% solution prime. The results suggest that DOA tubing and sodium chloride. 9% solution priming fluid should be selected if wet primed perfusion circuits are to be used over short terms of storage.

The effectiveness of scoring and bipolar diathermy on ear cartilage behavior: ex vivo study.

A common unsatisfactory long-term outcome of otoplasty is undercorrection and residual deformity. Aggressive scoring with a scalpel blade can cause unattractive and painful ridging, especially in older patients with stiffer cartilage. We developed an ex vivo pig ear model to compare the effectiveness of bipolar diathermy with blade scoring for cartilage warping. Strips of cartilage harvested from Landrace pig ears were subjected to bipolar diathermy (group A), blade scoring (group B), and blade scoring combined with reverse-side bipolar diathermy (group C). The strip deflection and cartilage tension were measured for each group. No statistical difference (P

Quantification of fat mobilization in patients undergoing coronary artery revascularization using off-pump and on-pump techniques.

Fat mobilization during cardiopulmonary bypass (CPB) is a recognized risk of the procedure. Intravascular mobilization of fat emboli subsequent to CPB has been implicated in some of its recognized pathophysiologies, particularly with regard to cerebral embolic injury. The aim of this study was to investigate whether fat mobilization is still a real issue in modern perfusion practice and to determine whether off pump coronary artery bypass techniques minimize this risk. Thirty patients undergoing routine elective coronary artery bypass graft (CABG) surgery were divided into two groups. Group 1 patients underwent off pump coronary artery bypass (OPCAB) procedures, and group 2 underwent CABG supported with CPB. Blood samples were taken from the CPB patients at the beginning, middle, and end of the procedure, from the suction line, from the arterial line, and from the venous line for measurement of fat emboli present. Samples were taken at corresponding time-points from the OPCAB patients for similar measurements. Fat emboli were counted manually using Oil red O staining and light microscopy. The fat emboli were sized using calibrated microspheres as a visual size contrast. No fat emboli were observed in any of the blood samples taken from the OPCAB patients. There were fat emboli present in all samples taken during CPB from all sources. The count was highest in the suction system and lowest in the venous blood and tended to increase during CPB. There was an absence of large fat emboli in the venous blood, which tends to indicate that the larger fat emboli lodge in the microvasculature. OPCAB surgery eliminates the risk of fat embolization in patients undergoing coronary revascularization. The suction system is the major source of fat emboli during CPB, and despite the multiple filtration components of the CPB system, fat emboli of various and significant sizes do reach the patient. Fat embolization remains a risk in routine elective CABG surgery. Cardiotomy suction should be eliminated where possible.