Akif Ündar

A microfluidic device for continuous, real time blood plasma separation

A microfluidic device for continuous, real time blood plasma separation is introduced. The principle of the blood plasma separation from blood cells is supported by the Zweifach-Fung effect and was experimentally demonstrated using simple microchannels. The blood plasma separation device is composed of a blood inlet, a bifurcating region which leads to a purified plasma outlet, and a concentrated blood cell outlet. It was designed to separate blood plasma from an initial blood sample of up to 45% inlet hematocrit (volume percentage of cells). The microfluidic network was designed using an analogous electrical circuit, as well as analytical and numerical studies. The functionality of this device was demonstrated using defibrinated sheep blood. During 30 minutes of continuous blood infusion through the device, all the erythrocytes (red blood cells) traveled through the device toward the concentrated blood outlet while only the plasma was separated at the bifurcating regions and flowed towards the plasma outlet. The device has been operated continuously without any clogging or hemolysis of cells. The experimentally determined plasma selectivity with respect to blood hematocrit level was almost 100% regardless of the inlet hematocrit. The total plasma separation volume percent varied from 15% to 25% with increasing inlet hematocrit. Due to the devices simple structure and control mechanism, this microdevice is expected to be used for highly efficient continuous, real time cell-free blood plasma separation from blood samples for use in lab on a chip applications.

Extracorporeal Life Support Registry Report 2008: neonatal and pediatric cardiac cases.

Each year thousands of patients require extracorporeal life support (ECLS) for a variety of respiratory, cardiac, and emergency reasons. The ECLS registry, a Federal Drug Administration approved control group, provides a database of approximately 37,000 ECLS patients from domestic and international hospitals, with details about demographic factors, diagnosis, treatment, and complications. The report is circulated to Extracorporeal Life Support Organization members with the goal of providing feedback on each center’s practices relative to the performance of all of the centers, and to the general public with the goal of enhancing research and improving patient care. In this report, the ECLS Registry Report International Summary for July 2008 is analyzed with a specific focus on neonatal and pediatric cardiac patients. From the data, it is evident that cardiac ECLS patients have a lower chance of survival than respiratory ECLS patients, and furthermore, younger patients have a lower chance of survival. Requirement for inotropes while on ECLS is by far the most common complication, followed by surgical site bleeding, necessitating hemofiltration. The major mechanical complications facing cardiac ECLS patients are oxygenator failure and clots in the circuit. Databases such as this one provide powerful tools for institutions, clinicians, and researchers.

An evaluation of the benefits of pulsatile versus nonpulsatile perfusion during cardiopulmonary bypass procedures in pediatric and adult cardiac patients.

The controversy over the benefits of pulsatile and nonpulsatile flow during cardiopulmonary bypass procedures continues. The objective of this investigation was to review the literature in order to clarify the truths and dispel the myths regarding the mode of perfusion used during open-heart surgery in pediatric and adult patients. The Google and Medline databases were used to search all of the literature on pulsatile vs. nonpulsatile perfusion published between 1952 and 2006. We found 194 articles related to this topic in the literature. Based on our literature search, we determined that pulsatile flow significantly improved blood flow of the vital organs including brain, heart, liver, and pancreas; reduced the systemic inflammatory response syndrome; and decreased the incidence of postoperative deaths in pediatric and adult patients. We also found evidence that pulsatile flow significantly improved vital organ recovery in several types of animal models when compared with nonpulsatile perfusion. Several investigators have also shown that pulsatile flow generates more hemodynamic energy, which maintains better microcirculation compared with nonpulsatile flow. These results clearly suggest that pulsatile flow is superior to nonpulsatile flow during and after open-heart surgery in pediatric and adult patients.

Effects of perfusion mode on regional and global organ blood flow in a neonatal piglet model

BACKGROUND Organ injury (brain, kidney, and heart) has been reported in up to 30% of pediatric open heart surgery patients after conventional hypothermic non-pulsatile cardiopulmonary bypass (CPB) support with or without deep hypothermic circulatory arrest (DHCA). The effects of pulsatile (with a Food and Drug Administration approved modified roller pump) versus non-pulsatile perfusion on regional and global cerebral, renal, and myocardial blood flow were investigated during and after CPB with 60 minutes of DHCA in a neonatal piglet model. METHODS Piglets, mean weight 3 kg, were used in both pulsatile (n = 7) and non-pulsatile (n = 7) groups. After initiation of CPB, all animals were subjected to hypothermia for 25 minutes, reducing the rectal temperatures to 18 degrees C, 60 minutes of DHCA followed by 10 minutes of cold reperfusion and 40 minutes of rewarming with a pump flow of 150 mL/kg/min. During cooling and rewarming, alpha-stat acid-base management was used. Differently labeled radioactive microspheres were injected pre-CPB, on normothermic CPB, pre-DHCA, post-DHCA, and after CPB to measure the regional and global cerebral, renal, and myocardial blood flows. RESULTS Global cerebral blood flow was significantly higher in the pulsatile group compared to the non-pulsatile group at normothermic CPB (100.4 +/- 6.3 mL/100 gm/min versus 70.2 +/- 8.1 mL/100 gm/min, p < 0.05) and pre-DHCA (77.2 +/- 5.2 mL/100 gm/min versus 56.1 +/- 6.7 mL/100 gm/min, p < 0.05). Blood flow in cerebellum, basal ganglia, brain stem, and right and left cerebral hemispheres had an identical pattern with the global cerebral blood flow. Renal blood flow appeared higher in the pulsatile group compared to the non-pulsatile group during CPB, but the results were statistically significant only at post-CPB (94.8 +/- 9 mL/100 gm/min versus 22.5 +/- 22 mL/100 gm/min, p < 0.05). Pulsatile flow better maintained the myocardial blood flow compared to the non-pulsatile flow after CPB (316.6 +/- 45.5 mL/100 gm/min versus 188.2 +/- 19.5 mL/100 gm/min, p < 0.05). CONCLUSIONS Pulsatile perfusion provides superior vital organ blood flow compared to non-pulsatile perfusion in this model.

Comparison of pH-stat and alpha-stat cardiopulmonary bypass on cerebral oxygenation and blood flow in relation to hypothermic circulatory arrest in piglets.

Background Deep hypothermic circulatory arrest is used in neonatal cardiac surgery. Recent work has suggested improved neurologic recovery after deep hypothermic arrest with pH-stat cardiopulmonary bypass (CPB) compared with alpha-stat CPB. This study examined cortical oxygen saturation (ScO(2)), cortical blood flow (CBF), and cortical physiologic recovery in relation to deep hypothermic arrest with alpha-stat or pH-stat CPB. Methods Sixteen piglets were cooled with pH-stat or alpha-stat CPB to 19 [degree sign]C (cortex) and subjected to 60 min of circulatory arrest, followed by CPB reperfusion and rewarming and separation from CPB. Near infrared spectroscopy and laser Doppler flowmetry were used to monitor ScO(2) and CBF. Cortical physiologic recovery was assessed 2 h after the piglets were separated from CPB by cortical adenosine triphosphate concentrations, cortical water content, CBF, and ScO(2). Results During CPB cooling, ScO(2) increased more with pH-stat than with alpha-stat bypass (123 +/- 33% vs. 80 +/- 25%); superficial and deep CBF were also greater with pH-stat than with alpha-stat bypass (22 +/- 25% vs. -56 +/- 22%, 3 +/- 19% vs. -29 +/- 28%). During arrest, ScO(2) half-life was greater with pH-stat than with alpha-stat bypass (10 +/- 2 min vs. 7 +/- 2 min), and cortical oxygen consumption lasted longer with pH-stat than with alpha-stat bypass (36 +/- 8 min vs. 25 +/- 8 min). During CPB reperfusion, superficial and deep CBF were less with alpha-stat than with pH-stat bypass (-40 +/- 22% vs. 10 +/- 39%, -38 +/- 28% vs. 5 +/- 28%). After CPB, deep cortical adenosine triphosphate and CBF were less with alpha-stat than with pH-stat bypass (11 +/- 6 pmole/mg vs. 17 +/- 8 pmole/mg, -24 +/- 16% vs. 16 +/- 32%); cortical water content was greater with alpha-stat than with pH-stat bypass (superficial: 82.4 +/- 0.3% vs. 81.8 +/- 1%, deep: 79.1 +/- 2% vs. 78 +/- 1.6%). Conclusions Cortical deoxygenation during hypothermic arrest was slower after pH-stat CPB. pH-stat bypass increased the prearrest ScO(2) and arrest ScO(2) half-life, to increase the cortical oxygen supply and slow cortical oxygen consumption. Improved cortical physiologic recovery after hypothermic arrest was suggested with pH-stat management.

Bioglue surgical adhesive impairs aortic growth and causes anastomotic strictures

BACKGROUND BioGlue surgical adhesive (CryoLife, Inc, Kennesaw, GA) is currently being used to secure hemostasis at cardiovascular anastomoses in adults. Interference with vessel growth would preclude its use during congenital heart surgery. The purpose of this study was to determine if BioGlue reinforcement of aortic anastomoses impairs vessel growth and causes strictures. METHODS Ten 4-week-old piglets (8.0 +/- 1.4 kg) underwent primary aorto-aortic anastomoses. Five piglets were randomly assigned to anastomotic reinforcement with BioGlue. After a 7-week growth period, the aortas were excised for morphometric analysis and histopathology. RESULTS Weight gains were similar in both groups. In BioGlue animals, however, aortic circumference increased only 1.5 +/- 0.8 mm (versus 2.7 +/- 0.8 mm in controls; p = 0.054). BioGlue animals developed a 33.9% stenosis of the aortic lumen area (versus 3.7% in controls, p = 0.038). Adventitial changes reflecting tissue injury and fibrosis were present in all BioGlue animals versus none of the control animals (p = 0.008). CONCLUSIONS BioGlue reinforcement impairs vascular growth and causes stricture when applied circumferentially around an aorto-aortic anastomosis. This adhesive should not be used on cardiovascular anastomoses in pediatric patients.

Pulsatile and nonpulsatile flows can be quantified in terms of energy equivalent pressure during cardiopulmonary bypass for direct comparisons.

The purpose of this study was to quantify and compare pulsatile and nonpulsatile pressure and flow waveforms in terms of energy equivalent pressure (EEP) during cardiopulmonary bypass in a neonatal piglet model. EEP is the ratio of the area under the hemodynamic power curve and the flow curve. Piglets, mean weight of 3 kg, were used in physiologic pulsatile pump (n = 7), pulsatile roller pump (n = 6), and nonpulsatile roller pump (n = 7) groups. Data (waveforms of the femoral artery pressure, pump flow, and preaortic cannula extracorporeal circuit pressure) were collected during normothermic cardiopulmonary bypass at 35 degrees C (15 minutes on-pump), before deep hypothermic circulatory arrest (pre-DHCA) at 18 degrees C, and after cold reperfusion and rewarming (post-DHCA) at 36 degrees C. The pump flow rate was 150 ml/kg/min in all three groups. During pulsatile perfusion, the pump rate was 150 bpm in both pulsatile groups. Although there was no difference in mean pressures in all groups, EEP and the percentage increase of pressure (from mean pressure to EEP) of mean arterial pressure and preaortic cannula extracorporeal circuit pressure were higher with pulsatile perfusion compared with nonpulsatile perfusion (p < 0.001). In particular, the physiologic pulsatile pump group produced significantly higher hemodynamic energy compared with the other groups (p < 0.001). These results suggest that pulsatile and nonpulsatile flows can be quantified in terms of EEP for direct comparisons, and pulsatile flow generates higher energy, which may be beneficial for vital organ perfusion during cardiopulmonary bypass.

Decrease in red blood cell deformability caused by hypothermia, hemodilution, and mechanical stress: Factors related to cardiopulmonary bypass

During extracorporeal circulation in cardiopulmonary bypass (CPB) surgery, blood is exposed to anomalous mechanical and environmental factors, such as high shear stress, turbulence, decreased oncotic pressure caused by dilution of plasma, and moderate and especially deep hypothermia widely applied during CPB in infants. These factors cause damage to the red blood cells (RBCs), which is manifest by immediate and delayed hemolysis and by changes in the mechanical properties of RBCs. These changes include, in particular, decrease in RBC deformability impeding the passage of RBCs through the microvessels and may contribute to the complications associated with CPB surgery. We investigated in vitro the independent and combined effects of hypothermia, plasma dilution, and mechanical stress on deformability of bovine RBCs. Our studies showed each of these factors to cause a significant decrease in the deformability of RBCs, especially acting synergistically. The impairment of RBC deformability caused by hypothermia was found to be more pronounced for RBCs suspended in phosphate buffered saline (PBS) than for RBCs suspended in plasma. The decrease in RBC deformability caused by mechanical stress was significantly exacerbated by dilution of plasma with PBS. In summary, results of our in vitro study strongly point to a possible detrimental consequence of conventional CPB arising from increased RBC rigidity, which may lead to impaired microcirculation and tissue oxygen supply.

Viscoelasticity of pediatric blood and its implications for the testing of a pulsatile pediatric blood pump.

Red blood cell hematocrit, aggregation and deformability, and plasma protein concentration influence the viscosity and elasticity of whole blood. These parameters affect the flow properties, especially at low shear rates (< 50 s–1). In particular, we have previously shown that the viscoelasticity of fluid affects the inlet filling characteristics and regions of flow separation in small pulsatile blood pumps. Although the viscosity of pediatric blood has been thoroughly studied, its elasticity has not been previously measured. Here we present the viscosity and elasticity of pediatric blood against shear rate for hematocrits from 19–56, measured using an oscillatory rheometer. There is little effect of patient age on blood viscoelasticity. A statistical analysis showed that when compared at constant hematocrit, blood from adult and pediatric patients had similar viscoelastic properties. We present blood analog solutions, as a function of hematocrit, constructed on the basis of the pediatric measurements. Flow field results for viscoelastic analogs of 20, 40 and 60% hematocrit and a Newtonian analog will be compared in the initial, in vitro testing of the Penn State pediatric blood pump, to determine the importance of incorporating a viscoelastic analog into the desigh interaction.

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.