Simulation study of a selective cerebral perfusion system with a single centrifugal pump

We previously successfully developed a simple nonroller extracorporeal circulation system (NRECC). In aortic arch surgery, more than two pumps are generally used for systemic perfusion and selective cerebral perfusion (SCP); we developed a new pressure-dependent perfusion system for SCP based on our NRECC and operated by a single centrifugal pump. The cerebral perfusion line was branched from the main perfusion line, and one 15 French and two 12 French cannulae were used for SCP. The perfusion pressure was regulated with a tube occluder. Afterload was changed from 30 to 80 mm Hg, the pressure of the SCP line was increased from 80 to 200 mm Hg, and flow volume was measured. When the afterload was set at 50 mm Hg, according to the increase of perfusion from 80 to 200 mm Hg, the flow volume of the 15 French cannula increased from 280 to 950 ml/min. Under the same conditions, flow volume of the 12 French cannula increased from 160 to 560 ml/min. Sufficient flow volume of the SCP lines was obtained when the SCP line pressure was over 80 mm Hg. As a result of the increased perfusion pressure, the flow volume showed a direct increase. These findings suggest that aortic arch surgery is possible using this SCP system.     

Assessment of temporary dialysis catheter performance on the basis of flow and pressure measurements in vivo and in vitro

The efficiency of hemodialysis treatments depends on catheter performance and, consequently, on effective blood flow that can be achieved at maximum extracorporeal pressures. Differences in effective and displayed flow were determined with ultrasound dilution technology, and a mathematical correction function for the MultiFiltrate hemodialysis machine was developed. This algorithm was used to calculate effective blood flow during treatment from displayed flow and arterial pressure. To assess catheter performance over time, we measured effective blood flow as function of extracorporeal pressure in 11 uncuffed, tunneled hemodialysis catheters with shotgun design. Pressure and flow profiles of the catheters were determined, and pressure symmetry was measured. To assess flow resistance over time, pressure trends of the catheters at different blood flow rates were measured for each patient over a mean period of 6.1 +/- 3.0 days. Increases in flow resistance during the study period were found to be small. Mean arterial pressure decreased from -185 mm Hg to -200 mm Hg, and mean venous pressure increased from 197 mm Hg to 215 mm Hg. Effective flow did not change significantly during the study. In conclusion, all catheters investigated easily provided effective flows above 450 mL/min over the study period at maximum extracorporeal pressures below +/-300 mm Hg.     

Precise quantification of pressure flow waveforms of a pulsatile ventricular assist device

Unreliable quantification of flow pulsatility has hampered many efforts to assess the importance of pulsatile perfusion. Generation of pulsatile flow depends upon an energy gradient. It is necessary to quantify pressure flow waveforms in terms of hemodynamic energy levels to make a valid comparison between perfusion modes during chronic support. The objective of this study was to quantify pressure flow waveforms in terms of energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE) levels in an adult mock loop using a pulsatile ventricle assist system (VAD). A 70 cc Pierce-Donachy pneumatic pulsatile VAD was used with a Penn State adult mock loop. The pump flow rate was kept constant at 5 L/min with pump rates of 70 and 80 bpm and mean aortic pressures (MAP) of 80, 90, and 100 mm Hg, respectively. Pump flows were adjusted by varying the systolic pressure, systolic duration, and the diastolic vacuum of the pneumatic drive unit. The aortic pressure was adjusted by varying the systemic resistance of the mock loop EEP (mm Hg) = (integral of fpdf)/(integral of fdt) SHE (ergs/cm3) = 1,332 [((integral of fpdt)/(integral of fdt))--MAP] were calculated at each experimental stage. The difference between the EEP and the MAP is the extra energy generated by this device. This difference is approximately 10% in a normal human heart. The EEP levels were 88.3 +/- 0.9 mm Hg, 98.1 +/- 1.3 mm Hg, and 107.4 +/- 1.0 mm Hg with a pump rate of 70 bpm and an aortic pressure of 80 mm Hg, 90 mm Hg, and 100 mm Hg, respectively. Surplus hemodynamic energy in terms of ergs/cm3 was 11,039 +/- 1,236 ergs/cm3, 10,839 +/- 1,659 ergs/cm3, and 9,857 +/- 1,289 ergs/cm3, respectively. The percentage change from the mean aortic pressure to EEP was 10.4 +/- 1.2%, 9.0 +/- 1.4%, and 7.4 +/- 1.0% at the same experimental stages. Similar results were obtained when the pump rate was changed from 70 bpm to 80 bpm. The EEP and SHE formulas are adequate to quantify different levels of pulsatility for direct and meaningful comparisons. This particular pulsatile VAD system produces near physiologic hemodynamic energy levels at each experimental stage.     

Effects of graded pulsatile pressure on the reflex vasomotor responses elicited by changes of mean pressure in the perfused carotid sinus-aortic arch regions of the dog

1. In the anaesthetized dog, the carotid sinuses and aortic arch were isolated from the circulation and separately perfused with blood by a method which enabled the mean pressure, pulse pressure and pulse frequency to be varied independently in each vasosensory area. The systemic circulation was perfused at constant blood flow by means of a pump and the systemic venous blood was oxygenated by an extracorporeal isolated pump-perfused donor lung preparation.2. We have confirmed our previous observations that under steadystate conditions the vasomotor responses elicited reflexly by changes in mean carotid sinus pressure are modified by alterations in carotid sinus pulse pressure, whereas those evoked by changes of mean aortic arch pressure are only weakly affected by modifications of aortic pulse pressure.3. When the carotid sinus and aortic arch regions are perfused in combination at constant pulse frequency (110 c/min), the relationship between mean carotid sinus-aortic arch pressure and systemic arterial perfusion pressure is dependent on the size of the pulse pressure.4. Increasing the pulse pressure alters the curve relating the mean carotid sinus-aortic arch pressure to systemic arterial perfusion pressure in such a way that the perfusion pressure is lower at a given carotid sinus-aortic arch pressure within the range 80-150 mm Hg. The larger the pulse pressure, up to about 60 mm Hg, the greater the fall in systemic arterial perfusion pressure. Above a mean carotid sinus-aortic arch pressure of about 150 mm Hg, alterations of pulse pressure have little effect.5. There is a family of curves representing the relation between mean carotid sinus-aortic arch pressure and systemic vascular resistance, depending on the pulse pressure.     

The effects of pulsatile flow upon renal tissue perfusion during cardiopulmonary bypass: a comparative study of pulsatile and nonpulsatile flow

This study was conducted to directly compare the effects of pulsatile and nonpulsatile blood flow in the extracorporeal circulation upon renal tissue perfusion by using a tissue perfusion measurement system. A total cardiopulmonary bypass circuit was constructed to accommodate twelve Yorkshire swine, weighing 20 approximately 30 kg. Animals were randomly assigned to group 1 (n = 6, nonpulsatile centrifugal pump) or group 2 (n = 6, pulsatile T-PLS pump). A tissue perfusion measurement probe (Q-Flow 500) was inserted into the renal parenchymal tissue, and the extracorporeal circulation was maintained for an hour at a pump flow rate of 2 L/min after aortic cross-clamping. Tissue perfusion flow in the kidney was measured before bypass and every 10 minutes after bypass. Renal tissue perfusion flow was substantially higher in the pulsatile group throughout bypass (ranging 48.5-64.1 ml/min/100 g in group 1 vs. 51.0-88.1 ml/min/100 g in group 2). The intergroup difference was significant at 30 minutes (47.5 +/- 18.3 ml/min/100 g in group 1 vs. 83.4 +/- 28.5 ml/min/100 g in group 2; p = 0.026). Pulsatile flow achieves higher levels of tissue perfusion of the kidney during short-term extracorporeal circulation. A further study is required to observe the effects of pulsatile flow upon other vital organs and its long-term significance.     

Minimal sensor count approach to fuzzy logic rotary blood pump flow control

A rotary blood pump fuzzy logic flow controller without flow sensors was developed and tested in vitro. The controller, implemented in LabView, was set to maintain a flow set point in the presence of external pressure disturbances. Flow was estimated as a function of measured pump's delta P and speed, using a steady-state, nonlinear approximation. The fuzzy controller used the pump's flow estimate and delta P as feedback variables. The defuzzified control output manipulated the pump speed. Membership functions included flow error, delta P, and pump speed. Experimental runs in a mock loop (water/glycerin 3.5 cPs, 37 degrees C), using the estimated flow, were compared with those using a Transonic flow meter for nine conditions of flow and delta P (4 to 6 L/min, 150 to 350 mm Hg). Pressure disturbances generated by a servo pinch valve ranged from +/-23 to +/-47 mm Hg. Results indicated that the fuzzy controller ably regulated the flow set point to within +/-10% of the baseline even under large swings in pressure. There was no difference in controller performance between the ultrasonic flow measurement and the estimated flow calculation scenarios. These tests demonstrated that the fuzzy controller is capable of rejecting disturbances and regulating flow to acceptable limits while using a flow estimate.     

Hemodynamic effects of a new percutaneous circulatory support device in a left ventricular failure model

We have tested a new percutaneous circulatory support device in seven anesthetized calves with induced left ventricular failure. The device is based on a flexible catheter with a foldable propeller and cage at the distal end. The rotation of the propeller (1,000-15,000 rpm) is transmitted from a drive unit at the proximal end to the propeller by way of a rotating wire inside the catheter. This also contains an umbrella-like mechanism to open the pump head from the folded (diameter 4.6 mm) to the active position. The rotation of the propeller creates a pressure drop in front of the propeller and a pressure rise behind. Heart failure was induced with metoprolol and verapamil in combination with a VVI pacemaker to create a left atrial pressure greater than 20 mm Hg. A centrifugal pump was used to bypass the right ventricle and to ensure a sufficient filling of the left ventricle. After baseline recordings, the pump was run at 14,000 rpm, and the hemodynamic response was compared with the baseline. A 24 +/- 10 mm Hg pressure gradient was generated across the pump, resulting in a drop in the right carotid artery mean pressure from 80 +/- 11 to 71 +/- 13 mm Hg (p = 0.008) and a drop in the left ventricular systolic pressure from 109 +/- 17 to 100 +/- 19 mm Hg (p = 0.004). The pressure in the left atrium decreased from 25 +/- 3 to 20 +/- 5 mm Hg (p = 0.008). The mean femoral pressure increased from 78 +/- 10 to 95 +/- 20 mm Hg (p = 0.005). A moderate reduction in the right carotid flow was observed (15%, p = 0.029), whereas no significant changes were found in the coronary flow, the flow in the right femoral artery, or in the left kidney. The device showed a significant unloading of the left ventricle and an increased perfusion pressure for the lower part of the body. The moderate changes in flow were probably caused by still active autoregulation, and this needs to be tested with more pronounced circulatory failure.     

A coronary active perfusion system for off-pump coronary artery bypass: advantage over passive perfusion regarding the physiology of the coronary artery

To avoid myocardial ischemia during off-pump coronary artery bypass, we developed a coronary active perfusion system (CAPS) that perfuses arterial blood to the coronary artery at the diastolic phase of the cardiac cycle by a syringe pump system. We report herein the details and compare CAPS with a passive shunt circuit from the femoral artery (FA shunt), regarding the physiology of the coronary artery. Six pigs were used for this study. After CAPS or FA shunt perfusion was established, coronary flow and coronary pressure were measured. The coronary flows in the native coronary artery, FA shunt perfusion, and CAPS perfusion with syringe pump stroke volume settings ranging from 0.1 to 0.4 ml were 27.2+/-3.0, 4.1+/-1.5, 12.7+/-1.2, 24.8+/-1.9, 33.3+/-1.6, and 42.2+/-1.9 ml/min, respectively. Mean coronary pressures under FA shunt perfusion and CAPS perfusion with stroke settings from 0.1 to 0.4 ml were 23.7+/-4.6, 48.8+/-5.0, 61.3+/-7.5, 70.8+/-5.4, and 82.3+/-5.2 mm Hg, respectively. CAPS had an advantage over the FA shunt regarding coronary flow with safe coronary pressure. Using CAPS, an off-pump coronary artery bypass can be performed safely without myocardial ischemia.     

A performance evaluation of eight geometrically different 10 Fr pediatric arterial cannulae under pulsatile and nonpulsatile perfusion conditions in an infant cardiopulmonary bypass model

This investigation compared pressure drops and surplus hemodynamic energy (SHE) levels in eight commercially available pediatric aortic cannulae (10 Fr) with different geometries during pulsatile and nonpulsatile perfusion conditions in an in vitro infant model of cardiopulmonary bypass. For each trial, the cannula was placed at the distal end of the arterial line, and the insertion tip was fixed to the inlet of the simulated patient. The pseudo patient was subjected to seven pump flow rates ranging from 400 to 1000 ml/min (at 100 ml/min increments), and the mean arterial pressure was set at a constant 40 mm Hg via Hoffman clamp. Of the eight cannulae, the Surgimedics and THI models had significantly larger pressure drops (48.8 +/- 0.3 mm Hg and 48.3 +/- 1.4 mm Hg, respectively; 600 ml/min pulsatile) compared with the RMI cannula (27.6 +/- 1.2 mm Hg; 600 ml/min pulsatile), which created, on average, half of the pressure drop seen in the poorest performing cannulae. When perfusion mode was switched from nonpulsatile to pulsatile, there was a 7-9 fold increase in delivery of SHE recorded at both the pre- and postcannulae sites, regardless of which cannula was being tested. Despite being classified under the same size (10 Fr), these eight cannulae were found to vary considerably in length, inner diameter, and geometrical design. The results suggest that these differences can have a significant impact on pressure drops, as well as generation and delivery of SHE. Furthermore, it was found that pulsatile perfusion produced more "extra" hemodynamic energy when compared with nonpulsatile perfusion, regardless of cannula model.     

Timing and reproducibility of access flow measurements using extracorporeal temperature gradients

The duration, accuracy, and reproducibility of a new access flow measuring technique was analyzed in a series of in vitro experiments using an extracorporeal line switch that allowed for almost instantaneous reversal of extracorporeal blood flow without disconnecting the blood lines. Access flow was modeled from the magnitude and time course of extracorporeal temperature changes caused by switching the blood lines. Ten tests were done with access flows covering a range from 410 to 1500 ml min. The coefficient of variation of triplicate access flow identifications was 3.8 +/- 1.5%. The mean bias between measured and modeled access flows was 54 +/- 54 ml min and independent of the range of measured access flows. The average time constant for temperatures to stabilize after switching the blood lines was 0.68 +/- 0.11 min. These results show that the instantaneous change in the direction of blood flow in proximal parts of the extracorporeal circulation produces a smooth change in extracorporeal temperatures that can be explained by a mathematical model incorporating access flow and that a reproducible measure for access blood flow can be obtained as one of the model parameters from that fit within a few minutes of switching the blood lines without the injection of indicator.     

Foetal placental blood flow in the lamb

1. Fifteen sheep foetuses of 1.5-5.2 kg body weight were prepared with indwelling arterial and venous catheters for experimentation one to six days later.2. Unanaesthetized foetuses were found to have mean arterial and central venous blood pressures of 40 +/- 1.5 (S.E. of mean) and 2.0 +/- 0.3 (S.E. of mean) mm Hg respectively, compared to intra-uterine pressure. Intra-uterine pressure was 16 +/- 0.8 (S.E. of mean) mm Hg with respect to atmospheric pressure at mid-uterine level.3. Mean placental blood flow of the foetuses was 199 +/- 20 (S.E. of mean) ml./(min.kg body wt.). Mean cardiac output in eleven of the foetuses was 658 +/- 102 (S.E. of mean) ml./(min.kg).4. Mean foetal and maternal colloid osmotic pressures were 17.5 +/- 0.7 (S.E. of mean) and 20.5 +/- 0.6 (S.E. of mean) mm Hg respectively at 38 degrees C.5. Intravenous infusions into six ewes of 1.8 mole of mannitol and 0.4 mole of NaCl resulted in significant increases in foetal plasma osmolarity, sodium, potassium, and haemoglobin concentrations, without detectable transfer of mannitol to the foetal circulation.6. In the sheep placenta there is osmotic and hydrostatic equilibration of water. As a consequence, there should be an interaction between foetal placental blood flow and foetal water exchange with the maternal circulation. It was concluded that this interaction tends to stabilize foetal placental blood flow.     

Pulsatile perfusion improves regional myocardial blood flow during and after hypothermic cardiopulmonary bypass in a neonatal piglet model

Pediatric myocardial related morbidity and mortality after cardiopulmonary bypass (CPB) are well documented, but the effects of pulsatile perfusion (PP) versus nonpulsatile perfusion (NPP) on myocardial blood flow during and after hypothermic CPB are unclear. After investigating the effects of PP versus NPP on myocardial flow during and after hypothermic CPB, we quantified PP and NPP pressure and flow waveforms in terms of the energy equivalent pressure (EEP) for direct comparison. Ten piglets underwent PP (n = 5) or NPP (n = 5). After initiation of CPB, all animals underwent 15 minutes of core cooling (25 degrees C), 60 minutes of hypothermic CPB with aortic cross-clamping, 10 minutes of cold reperfusion, and 30 minutes of rewarming. During CPB, the mean arterial pressure (MAP) and pump flow rates were 40 mm Hg and 150 ml/kg per min, respectively. Regional flows were measured with radiolabeled microspheres. During normothermic CPB, left ventricular flow was higher in the PP than the NPP group (202+/-25 vs. 122+/-20 ml/l 00 g per min). During hypothermic CPB, no significant intragroup differences were observed. After 60 minutes of ischemia and after rewarming (276+/-48 vs. 140+/-12 ml/100 g per min; p < 0.05) and after CPB (271+/-10 vs. 130+/-14 ml/100 g per min; p < 0.05), left ventricular flow was higher in the PP group. Right ventricular flow resembled left ventricular flow. The pressure increase (from MAP to EEP) was 10+/-2% with PP and 1% with NPP (p < 0.0001). The increase in extracorporeal circuit pressure (ECCP) (from ECCP to EEP) was 33+/-10% with PP and 3% with NPP (p < 0.0001). Pulsatile flow generates significantly higher energy, enhancing myocardial flow during and after hypothermic CPB and after 60 minutes of ischemia in this model.     

Uncoupling the systemic circulation and the Ex Vivo circuit during experimental isolated liver perfusion

Performing an ex vivo liver perfusion as a transient liver support requires perfusing the liver with a flow of 1 ml/min per kg of liver, which could reach 25% of the cardiac output when a human liver is used. This high flow could be detrimental in patients with acute liver failure. Therefore, in an ischemic-induced liver failure pig model, we developed a circuit allowing low flows going out of and into the systemic circulation, whereas the flow going through the ex vivo liver is maintained at a high value. This was obtained by uncoupling the ex vivo circuit from the systemic circulation. Ex vivo liver perfusion was performed in a closed circuit with a flow averaging 1 ml/min per kg of ex vivo liver (700 to 800 ml/min, according to the weight of the livers we used). It was linked to the systemic circulation with input and output flows equal to that used during hemodialysis (200 ml/min). Compared with previously reported direct circuits, this perfusion system was well tolerated from a circulatory point of view. After the induction of ischemic liver failure, the ex vivo liver perfusion led to an increase in urea, branched amino acids to aromatic amino acid ratio, and fractional clearance of indocyanine green and galactose and to a decrease in ammonia and lactic acid. This system allowed the ex vivo liver to keep its clearing properties despite a low extracorporeal flow. It represents an extracorporeal circuit that could be used in place of the direct extracorporeal high-flow liver perfusion.     

Hemodynamic energy generated by a combined centrifugal pump with an intra-aortic balloon pump

We examined the pulsatility generated by an intra-aortic balloon pump/centrifugal pump (IABP/CP) combination in terms of energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE). In five cardiac-arrested pigs, the outflow cannula of the CP was inserted into the ascending aorta, the inflow cannula in the right atrium. A 30-ml IABP was subsequently placed in the descending aorta. Extracorporeal circulation was maintained for 30 minutes using a pump flow of 75 ml/kg per minute by CP alone or by IABP/CP with pressure and flow measured in the right internal carotid artery. The IABP/CP combination converted the flow to pulsatile and increased pulse pressure significantly from 9.1 +/- 1.3 mm Hg to 54.9 +/- 6.1 mm Hg (p = 0.012). It also significantly increased the percent change from mean arterial pressure to EEP from 0.2 +/- 0.3% to 23.3 +/- 6.1% (p = 0.012) and SHE from 133.2 +/- 234.5 erg/cm to 20,219.8 +/- 5842.7 erg/cm3 (p = 0.012). However, no statistical difference was observed between CP and IABP/CP in terms of mean carotid artery pressure (p = NS). In a cardiac-arrested animal model, pulsatility generated by a IABP/CP combination may be effective in terms of energy equivalent pressure and surplus hemodynamic energy.     

Device and technique for extracorporeal blood volume sequestration during hemodialysis

We developed a technique for a controlled and reversible volume perturbation of the cardiovascular system during hemodialysis. The capacitance of the extracorporeal circulation was modified by an expansion bag, using separate filling and draining lines connected to postpump and prepump sections of the arterial line segment, respectively. The connection to this bag was manually operated by three-way valves. The volume sequestered into the blood bag was continuously measured by a weighing scale. Filling and draining of the expansion bag was measured in eight patients in two subsequent routine dialysis treatments. Four volume shifts were done in each treatment. Filling and draining rates and times depended on extracorporeal blood flow as well as arterial and venous line pressures. Bag inflow and outflow volumes were 215.8 +/- 28.5 ml/min and 221.6 +/- 37.0 ml/min, respectively. The total volume transiently sequestered in the bag was 479.8 +/- 61.3 ml. The duration of the whole test was 4.5 +/- 0.8 minutes. During filling, residual dialyzer blood flow was transiently reduced to 58.5 +/- 21.6 ml/min and the filtration fraction reached 30 +/- 13%. There were no adverse events such as clotting in the blood bag or in the dialyzer. The method provides rapid, reversible, and safe volume shifts between the patient and the extracorporeal circulation with the potential to elicit a hemodynamic response for characterizing the patient during each dialysis treatment.     

Subperineurial demyelination associated with reduced nerve blood flow and oxygen tension after epineurial vascular stripping

Using laser Doppler measurements of nerve blood flow and electron microscopy, we determined that removal of the vasa nervorum from the surface of rat peripheral nerve results in an immediate 58.4% +/- (SD) 12.6% reduction in nerve blood flow (p less than 0.017) and subsequent subperineurial demyelination. To further assess the role of ischemia in demyelination, a second group of Sprague-Dawley rats (250 to 300 gm) was anesthetized and oxygen tensions were recorded with platinum microelectrodes in the tibial epineurial and endoneurial spaces before and 30 minutes after epineurial devascularization. Normal epineurial oxygen tension was 40.4 +/- (SD) 6.5 mm Hg before devascularization and 26.3 +/- 12.3 mm Hg after (p less than 0.012). Normal endoneurial oxygen tension was 22.9 +/- 6.0 mm Hg before devascularization and 14.3 +/- 5.4 mm Hg after (p less than 0.003). The topography of nerve fiber injury in this experimental model is identical with the changes induced in the sciatic nerve by circumferential compression at 30 mm Hg which is also thought to impede epineurial circulation. This subperineurial pattern of demyelination and axonal degeneration is associated with experimental interference with the epineurial circulation and may be contrasted with the central fascicular degeneration caused by microsphere embolization of the vasa nervorum via the common iliac artery. The data suggest that ischemia is the mechanism for subperineurial fiber injury after epineurial devascularization and highlight the importance of the transperineurial vessels which connect the epineurial anastomotic circulation and endoneurial capillary network.     

Development of an artificial placenta IV: 24 hour venovenous extracorporeal life support in premature lambs

An extracorporeal artificial placenta would change the paradigm of treating extremely premature infants. We hypothesized that a venovenous extracorporeal life support (VV-ECLS) artificial placenta would maintain fetal circulation, hemodynamic stability, and adequate gas exchange for 24 hours. A near-term neonatal lamb model (130 days; term = 145 days) was used (n = 9). The right jugular vein was cannulated for VV-ECLS outflow, and an umbilical vein was used for inflow. The circuit included a peristaltic roller pump and a 0.5 m(2) hollow fiber oxygenator. Lambs were maintained on VV-ECLS in an "amniotic bath" for up to 24 hours. Five of nine fetuses survived for 24 hours. In the survivors, average mean arterial pressure was 69 ± 10 mm Hg for the first 4 hours and 36 ± 8 mm Hg for the remaining 20 hours. The mean fetal heart rate was 202 ± 30. Mean VV-ECLS flow was 94 ± 20 ml/kg/min. Using a gas mixture of 50% O(2)/3% CO(2) and sweep flow of 1-2 L/min, the mean pH was 7.27 ± 0.09, with Po(2) of 35 ± 12 mm Hg and Pco(2) of 48 ± 12 mm Hg. Necropsy revealed a patent ductus arteriosus in all cases, and there was no gross or microscopic intracranial hemorrhage. Complications in failed attempts included technically difficult cannulation and multisystem organ failure. Future studies will enhance stability and address the factors necessary for long-term support.     

Development of "plug and play" TransApical to aorta VAD

Our TransApical to Aorta pump, a simple and minimally invasive left ventricular (LV) assist device, has a flexible, thin-wall conduit connected by six struts to a motor with ball bearings and a turbine extending into the blood path. Pulsatile flow is inherent in the design as the native heart contraction preloads the turbine. In six healthy sheep, the LV apex was exposed by a fifth intercostal left thoracotomy. The pump was inserted from the cardiac apex through the LV cavity into the ascending aorta. Aortic and LV pressure waveforms, pump flow, motor current, and pressure were directly measured. All six cannula pumps were smoothly advanced on the first attempt. Pump implantation was <15 minutes (13.6 +/- 1.8 minutes). Blood flow was 2.8 l/min to 4.4 l/min against 86 +/- 8.9 mm Hg mean arterial blood pressure at maximum flow. LV systemic pressure decreased significantly from 102.5 +/- 5.55 mm Hg to 58.8 +/- 15.5 mm Hg at the fourth hour of pumping (p = 0.042), and diastolic LV pressure decreased from 8.4 +/- 3.7 to 6.1 +/- 2.3 mm Hg (p > 0.05). The pump operated with a current of 0.4 to 0.7 amps and rotation speed of 28,000 to 33,000 rpm. Plasma free hemoglobin was 4 +/- 1.41 mg/dl (range, 2 to 5 mg/dl) at termination. No thrombosis was observed at necropsy.A left ventricular assist device using the transapical to aorta approach is quick, reliable, minimally invasive, and achieves significant LV unloading with minimal blood trauma.     

Computational design and experimental performance testing of an axial-flow pediatric ventricular assist device

The Virginia Artificial Heart Institute continues to design and develop an axial-flow pediatric ventricular assist device (PVAD) for infants and children in the United States. Our research team has created a database to track potential PVAD candidates at the University of Virginia Children's Hospital. The findings of this database aided with need assessment and design optimization of the PVAD. A numerical analysis of the optimized PVAD1 design (PVAD2 model) was also completed using computational fluid dynamics (CFD) to predict pressure-flow performance, fluid force estimations, and blood damage levels in the flow domain. Based on the PVAD2 model and after alterations to accommodate manufacturing, a plastic prototype for experimental flow testing was constructed via rapid prototyping techniques or stereolithography. CFD predictions demonstrated a pressure rise range of 36-118 mm Hg and axial fluid forces of 0.8-1.7 N for flows of 0.5-3 l/min over 7000-9000 rpm. Blood damage indices per CFD ranged from 0.24% to 0.35% for 200 massless and inert particles analyzed. Approximately 187 (93.5%) of the particles took less than 0.14 seconds to travel completely through the PVAD. The mean residence time was 0.105 seconds with a maximum time of 0.224 seconds. Additionally, in a water/glycerin blood analog solution, the plastic prototype produced pressure rises of 20-160 mm Hg for rotational speeds of 5960 +/- 18 rpm to 9975 +/- 31 rpm over flows from 0.5 to 4.5 l/min. The numerical results for the PVAD2 and the prototype hydraulic testing indicate an acceptable design for the pump, represent a significant step in the development phase of this device, and encourage manufacturing of a magnetically levitated prototype for animal experiments.     

Splenic blood flow and intrasplenic flow distribution in rats

Summary In 75 rats, anesthetized with pentobarbital and breathing spontaneously, regional splenic blood flow (rSBF) was measured by means of the⁸⁵Kr(β)-clearance technique after an intraaortic slug injection of the dissolved indicator. In the normal and undisturbed spleen in situ rSBF is linearly related to the mean arterial blood pressure (MABP) within the range of 30–140 mm Hg. Mean rSBF is 0.71 ml/g/min, the mean arterial blood pressure being 105 mm Hg. In normal rats rSBF decreases significantly with increasing body weight or age. After total obstruction of the open circulation by application of rigid spherocytes, mean rSBF is reduced to 0.26 ml/g/min and is independent of the mean arterial blood pressure within the same range. In splenomegaly, due to enhanced reticuloendothelial activity and intensified immunological responses after tumor implantation, an increase in total splenic blood flow is found. However, related to 1 g of splenic wet weight, rSBF is diminished. In splenomegaly, rSBF also linearly depends on MABP within a wide range. Mean rSBF is 0.51 ml/g/min, the mean arterial blood pressure being 91 mm Hg. The distribution of intrasplenic blood flow between open and closed circulation depends on the size of the mean arterial blood pressure. The perfusion rate of the open circulation, compared with rSBF amounts to 72–93% (MABP=80–130 mm Hg).