Bubble tracking through computational fluid dynamics in arterial line filters for cardiopulmonary bypass

Investigation of cardiopulmonary bypass parameters on embolus transport in a patient-specific aorta

Neurological complexities resulting from surgery requiring cardiopulmonary bypass (CPB) remain a major concern, encompassing a spectrum of complications including thromboembolic stroke and various cognitive impairments. Surgical manipulation during CPB is considered the primary cause of these neurological complications. This study addresses the overall lack of knowledge concerning CPB hemodynamics within the aorta, employing a combined experimental-computational modeling approach, featuring computational fluid dynamics simulations validated with an in vitro CPB flow loop under steady conditions. Parametric studies were systematically performed, varying parameters associated with CPB techniques (pump flow rate and hemodiluted blood viscosity) and properties related to formed emboli (size and density). This represents the first comprehensive investigation into the individual and combined effects of these factors. Our findings reveal critical insights into the operating conditions of CPB, indicating a positive correlation between pump flow rate and emboli transport into the aortic branches, potentially increasing the risk of stroke. It was also found that larger emboli were more often transported into the aortic branches at higher pump flow rates, while smaller emboli preferred lower flow rates. Further, as blood is commonly diluted during CPB to decrease its viscosity, more emboli were found to enter the aortic branches with greater hemodilution. The combined effects of these parameters are captured using the non-dimensional Stokes number, which was found to positively correlate with emboli transport into the aortic branches. These findings contribute to our understanding of embolic stroke risk factors during CPB and shed light on the complex interplay between CPB parameters.

Can a low prime volume arterial filter be used as an alternative for a venous bubble trap in minimal extracorporeal circulation? An in vitro investigation

BACKGROUND

During cardiac surgery the use of a minimal extracorporeal circulation (MiECC) system may reduce the adverse effects for the patient. This is probably caused by reduced inflammation and hemodilution. For the use of a MiECC circuit, a venous bubble trap (VBT) is warranted for safety reasons. The aim of this study was to assess if an arterial filter with a small prime volume has the same (or better) air removal capacities as a VBT in a MiECC circuit and subsequentially may be used as an alternative.

METHODS

In an in vitro study, air removal properties were compared between the arterial filter and three VBT's on the market, VBT160 (Getinge), VBT 8 (LivaNova and VARD (Medtronic). In a MiECC circuit, the filter devices were placed in a venous position and challenged with massive and micro air. Gaseous microemboli (GME) were measured with a bubble counter proximal and distal of the VBT device.

RESULTS

More than 99.9 % of the air was removed after a bolus air challenge by all VBT's. Both the VARD and the AF100 showed better GME removal properties (not significant for the AF100) compared to the other devices. All filters showed GME generation after a challenge with massive air. Compared to the other filters, only the VARD showed no passing of larger bubbles when a volume of 50 mL of air was present in the filter.

CONCLUSIONS

The AF100 seems to be a safe and low prime alternative for use in a MiECC system as a venous air trap. A word of caution, placement of the AF100 arterial filter in the venous line is off label use.

Computational modeling of drug dissolution in the human stomach: Effects of posture and gastroparesis on drug bioavailability

The oral route is the most common choice for drug administration because of several advantages, such as convenience, low cost, and high patient compliance, and the demand and investment in research and development for oral drugs continue to grow. The rate of dissolution and gastric emptying of the dissolved active pharmaceutical ingredient (API) into the duodenum is modulated by gastric motility, physical properties of the pill, and the contents of the stomach, but current in vitro procedures for assessing dissolution of oral drugs are limited in their ability to recapitulate this process. This is particularly relevant for disease conditions, such as gastroparesis, that alter the anatomy and/or physiology of the stomach. In silico models of gastric biomechanics offer the potential for overcoming these limitations of existing methods. In the current study, we employ a biomimetic in silico simulator based on the realistic anatomy and morphology of the stomach (referred to as "StomachSim") to investigate and quantify the effect of body posture and stomach motility on drug bioavailability. The simulations show that changes in posture can potentially have a significant (up to 83%) effect on the emptying rate of the API into the duodenum. Similarly, a reduction in antral contractility associated with gastroparesis can also be found to significantly reduce the dissolution of the pill as well as emptying of the API into the duodenum. The simulations show that for an equivalent motility index, the reduction in gastric emptying due to neuropathic gastroparesis is larger by a factor of about five compared to myopathic gastroparesis.

In-Vitro Evaluation of Two Types of Neonatal Oxygenators in Handling Gaseous Microemboli and Maintaining Optimal Hemodynamic Stability During Cardiopulmonary Bypass

Objective

Usually only FDA-approved oxygenators are subject of studies by the international scientific community. The objective of this study is to evaluate two types of neonatal membrane oxygenators in terms of transmembrane pressure gradient, hemodynamic energy transmission and gaseous microemboli capture in simulated cardiopulmonary bypass systems.

Methods

We investigated the Braile Infant 1500 (Braile Biomédica, São José do Rio Preto, Brazil), an oxygenator commonly used in Brazilian operating rooms, and compared it to the Dideco Kids D100 (Sorin Group, Arvada, CO, USA), that is an FDA-approved and widely used model in the USA. Cardiopulmonary bypass circuits were primed with lactated Ringer's solution and packed red blood cells (Hematocrit 40%). Trials were conducted at flow rates of 500 ml/min and 700 ml/min at 35ºC and 25ºC. Real-time pressure and flow data were recorded using a custom-based data acquisition system. For gaseous microemboli testing, 5cc of air were manually injected into the venous line. Gaseous microemboli were recorded using the Emboli Detection and Classification Quantifier.

Results

Braile Infant 1500 had a lower pressure drop (P<0.01) and a higher total hemodynamic energy delivered to the pseudopatient (P<0.01). However, there was a higher raw number of gaseous microemboli seen prior to oxygenator at lower temperatures with the Braile oxygenator compared to the Kids D100 (P<0.01).

Conclusion

Braile Infant 1500 oxygenator had a better hemodynamic performance compared to the Dideco Kids D100 oxygenator. Braile had more gaseous microemboli detected at the pre-oxygenator site under hypothermia, but delivered a smaller percentage of air emboli to the pseudopatient than the Dideco oxygenator.

Validation of an open source framework for the simulation of blood flow in rigid and deformable vessels

We discuss in this paper the validation of an open source framework for the solution of problems arising in hemodynamics. The proposed framework is assessed through experimental data for fluid flow in an idealized medical device with rigid boundaries and a numerical benchmark for flow in compliant vessels. The core of the framework is an open source parallel finite element library that features several algorithms to solve both fluid and fluid-structure interaction problems. The numerical results for the flow in the idealized medical device (consisting of a conical convergent, a narrow throat, and a sudden expansion) are in good quantitative agreement with the measured axial components of the velocity and pressures for three different flow rates corresponding to laminar, transitional, and turbulent regimes. We emphasize the crucial role played by the accuracy in performing numerical integration, mesh, and time step to match the measurements. The numerical fluid-structure interaction benchmark deals with the propagation of a pressure wave in a fluid-filled elastic tube. The computed pressure wave speed and frequency of oscillations, and the axial velocity of the fluid on the tube axis are close to the values predicted by the analytical solution associated with the benchmark. A detailed account of the methods used for both benchmarks is provided.

Computational evaluation of the thrombogenic potential of a hollow-fiber oxygenator with integrated heat exchanger during extracorporeal circulation

The onset of thromboembolic phenomena in blood oxygenators, even in the presence of adequate anticoagulant strategies, is a relevant concern during extracorporeal circulation (ECC). For this reason, the evaluation of the thrombogenic potential associated with extracorporeal membrane oxygenators should play a critical role into the preclinical design process of these devices. This study extends the use of computational fluid dynamics simulations to guide the hemodynamic design optimization of oxygenators and evaluate their thrombogenic potential during ECC. The computational analysis accounted for both macro- (i.e., vortex formation) and micro-scale (i.e., flow-induced platelet activation) phenomena affecting the performances of a hollow-fiber membrane oxygenator with integrated heat exchanger. A multiscale Lagrangian approach was adopted to infer the trajectory and loading history experienced by platelet-like particles in the entire device and in a repetitive subunit of the fiber bundles. The loading history was incorporated into a damage accumulation model in order to estimate the platelet activation state (PAS) associated with repeated passes of the blood within the device. Our results highlighted the presence of blood stagnation areas in the inlet section that significantly increased the platelet activation levels in particles remaining trapped in this region. The order of magnitude of PAS in the device was the same as the one calculated for the components of the ECC tubing system, chosen as a term of comparison for their extensive diffusion. Interpolating the mean PAS values with respect to the number of passes, we obtained a straightforward prediction of the thrombogenic potential as a function of the duration of ECC.

Evaluation of the Quadrox-I neonatal oxygenator with an integrated arterial filter

Cardiopulmonary bypass (CPB) can be a potential cause of morbidity in patients for several reasons, including significantly higher gaseous microemboli (GME) formation than extracorporeal life support (ECLS) and physiological circulation, diverted blood flow from the patient via an open purge line of the arterial filter, and pressure drop across the oxygenator that is used in the circuit. Using a combined oxygenator and arterial filter may minimize these harmful factors and can effectively reduce the chances for postoperative morbidity. This study investigated the new QUADROX-i Neonatal Oxygenator (D-72145, Maquet, Hirrlingen, Germany) with an integrated arterial filter in terms of the hemodynamic properties and ability to clear GME in response to hypothermic versus normothermic conditions, open versus closed arterial filter purge line, and varying flow rates in a simulated CPB circuit identical to that of the clinical setting. A flow probe, pressure transducer, and Emboli Detection and Classification (EDAC) quantifier transducer were placed upstream and downstream to the oxygenator to measure changes in each parameter. The circuit was primed with fresh human blood with an hematocrit (Hct) of 26% diluted with Ringer’s lactate solution. Five milliliters of air were injected proximal to the venous cardiotomy reservoir, under non-pulsatile perfusion, with flow rates of 500 ml/min, 750 ml/min, and 1000 ml/min. A total of 8 air bolus injections were made at each individual set of conditions for a total of 96 injections. Results showed that the QUADROX-i Neonatal Oxygenator with an integrated filter has excellent hemodynamic properties with extremely low pressure drops and blood flow diverted from the patient, as well as high rates of GME capturing. The arterial filter purge line has a significant effect on the degree of blood flow diverted from the patient (p < 0.001), but does not affect pressure drop across the oxygenator.

Pre-clinical laboratory evaluation of the new 'AF' arterial line filter range

INTRODUCTION

The presence of emboli was recognised relatively early in the history of open heart surgery. The emboli produced during cardiopulmonary bypass have the predisposition to distribute into, and ultimately obstruct, microvessels of all tissues. The Sorin Group has recently developed a new range of arterial line filters. Before the Sorin AF range of filters was released for pre-launch clinical trials, our group performed in vitro laboratory testing of the AF range against a selection of commercially available filters on the global market.

RESULTS

The Sorin AF620 and AF640 demonstrate both the smallest prime volume and smallest surface contact area (92ml and 290 cm(2), respectively).The results of the GME Handling Efficiency experiments ranged by 39.6%, from 95.9% to 56.3%. In terms of an air bolus handling, the results of the Limit Bolus experiment ranged by 97 ml, from 147.5 ml down to 50 ml. The pressure drop across all the filters was measured under steady state experimental conditions. All of the above investigations were considered against surface area and prime volume.

CONCLUSION

It is clear from the results that some commercially available arterial line filters perform better than others, not only in overall performance, but also with regard to individual characteristics. Evaluating arterial line filters for hospital-specific use has to balance pressure drop, surface area, micro air handling, prime volume and gross air handling; all points need to be considered. In the AF620 and AF640, Sorin boast that they are the two smallest prime and smallest surface area filters commercially available on the global market. The Sorin AF filter range performs well in all of the areas we investigated and will be a competitive option for centres, irrespective of which characteristics they use to evaluate and select their arterial line filter.