Peritoneal dialysis (PD) is an effective renal replacement strategy for patients with end-stage renal disease utilizing the peritoneum as the filter and PD catheter as access. A survey of PD patients showed that some felt uncomfortable with the length of current catheters and would be interested to explore newer, shorter designs. We redesigned the transfer set and external portion of the catheter, addressing this barrier as a part of our multi-institutional design project led by a nephrologist from the University of Arkansas for Medical Sciences (UAMS) and an engineering design team from the biomedical engineering department at the University of Arkansas. Multiple designs were considered, including spiral, retractable, and collapsible bulbs, with an accordion-style mechanism being selected for prototyping. We created several prototypes, first by 3D printing as well as by silicone casting. Computational fluid analysis showed the design to be fully capable of delivering clinically relevant flows. The final design of our PD transfer set has a flexible accordion section that is 7 cm when extended and collapses to substantially shorten this length. We propose that the design can also be extended to the extra-abdominal section of the PD catheter.

This paper proposes a novel mathematical modeling framework for peripheral arterial and peripheral venous blood pressure signals from porcine experiments. Peripheral blood pressure signals can be acquired using regular catheters during standard patient treatment. The minimally invasive nature and ubiquitous availability of catheters render it an ideal candidate for various applications. However, there is no analytical model for peripheral blood pressure signals in the literature. We address this issue by proposing a model for these signals under the integral pulse frequency modulation (IPFM) framework. The model incorporates the impacts of physiological phenomena, such as the heartbeat pulse shape variation, heart rate variability, respiratory rate, etc. The model parameters are obtained by applying the IPFM model to experimental data collected from four pigs under different anesthetic dosages. The proposed model can fit the experimental data with Pearson correlation coefficients greater than 0.99 and 0.90 for arterial and venous blood pressure signals, respectively. The performance of model-synthesized data on the classification of two different anesthesia is comparable with experimental data. Parameters like pulse shape and duration can also work as distinguishable features under different anesthesia. We also proposed a way to distinguish respiratory-induced heart rate variability from other causes. Increasing doses of vasodilating anesthesia is similar to going from dehydration to hydration. Thus the results obtained in this study can be extended in distinguishing hydrated and dehydrated subjects. This model can be extended to similar biomedical signals like photoplethysmography, cerebral blood flow velocity, and Doppler waveforms.

OBJECTIVE Current cystotomy methods often implement the use of off-label devices, resulting in urocystolith extraction difficulty and potentially leading to postoperative complications and discomfort for the patient. The objective of this study was to create 3 novel 3-D printed cystotomy spoons that offer a dedicated solution for removing urocystoliths from a patient's urinary bladder. ANIMALS Clinical use of the 3 novel 3-D printed cystotomy spoons were ultimately evaluated in 4 dogs and 1 cat that presented for urocystotlith removal at 3 different veterinary hospitals in northwest Arkansas. METHODS The novel cystotomy spoons were designed using SolidWorks, 3-D printed with a Dental Surgical Guide resin, and underwent prototype testing that included chlorhexidine soaking, autoclave sterilization, 3-point bend testing, and Finite Element Analysis. The efficiency of the spoons was then evaluated through a limited proof-of-concept study utilizing a postoperative questionnaire for the participating clinicians. RESULTS Practitioner feedback indicated positive experiences using 1 or more of the novel 3-D printed cystotomy spoons while performing a cystotomy surgery. However, successful use of the spoons was ultimately limited to dogs in the 23 to 34 kg weight range. CLINICAL RELEVANCE Novel 3-D printed cystotomy spoons have the potential to mediate urocystolith extraction difficulty and reduce postoperative complications. Additionally, this research demonstrates how veterinarians might develop custom 3-D models and prints to meet patient-specific needs. As such, further development could impact the standard of healthcare and the veterinary industry by promoting the use of additive manufacturing in veterinary medicine.

Strokes are among the leading causes of death worldwide. Ischemic stroke, due to plaque or other buildup blocking blood flow to the brain, is the most common type. Although ischemic stroke is treatable, current methods have severe shortcomings with high mortality rates. Clot retrieval devices, for example, can result in physically damaged vessels and death. This study aims to create blood clots that are representative of those found in vivo and demonstrate a new method of removing them. Static blood clots were formed using a 9:1 ratio of whole sheep blood and 2.45% calcium chloride solution. This mixture was heated in a water bath at 37 °C for approximately one hour until solidified. Following clot solidification, human plasmin was introduced by various methods, including soaking, injection, and membrane perfusion, and the resulting dissolution percentages were determined. Different clot types, representative of the wide range found physiologically, were also manufactured and their dissolution characteristics evaluated. A method to reproducibly create blood clots, characteristic of those found in vivo, is essential for the production of stroke retrieval devices that can efficiently and effectively remove clots from patients with low mortality rates and little/no damage to the surrounding vessels.

Supravalvar aortic stenosis (SVAS) severity guides management, including decisions for surgery. Physiologic and technical factors limit the determination of SVAS severity by Doppler echocardiography and cardiac catheterization in Williams syndrome (WS). We hypothesized SVAS severity could be determined by the sinotubular junction-to-aortic annulus ratio (STJ:An). We reviewed all preintervention echocardiograms in patients with WS with SVAS cared for at our center. We measured STJ, An, peak and mean Doppler gradients, and calculated STJ:An. We created 2 mean gradient prediction models. Model 1 used the simplified Bernoulli's equation, and model 2 used computational fluid dynamics (CFD). We compared STJ:An to Doppler-derived and CFD gradients. We reviewed catheterization gradients and the waveforms and analyzed gradient variability. We analyzed 168 echocardiograms in 54 children (58% male, median age at scan 1.2 years, interquartile range [IQR] 0.5 to 3.6, median echocardiograms 2, IQR 1 to 4). Median SVAS peak Doppler gradient was 24 mm Hg (IQR 14 to 46.5). Median SVAS mean Doppler gradient was 11 mm Hg (IQR 6 to 21). Median STJ:An was 0.76 (IQR 0.63 to 0.84). Model 1 underpredicted clinical gradients. Model 2 correlated well with STJ:An through all severity ranges and demonstrated increased pressure recovery distance with decreased STJ:An. The median potential variability in catheterization-derived gradients in a given patient was 14.5 mm Hg (IQR 7.5 to 19.3). SVAS severity in WS can be accurately assessed using STJ:An. CFD predicts clinical data well through all SVAS severity levels. STJ:An is independent of physiologic state and has fewer technical limitations than Doppler echocardiography and catheterization. STJ:An could augment traditional methods in guiding surgical management decisions. (C) 2021 Elsevier Inc. All rights reserved.

PURPOSE:Peripheral venous pressure (PVP) waveform analysis is a novel, minimally invasive, and inexpensive method of measuring intravascular volume changes. A porcine cohort was studied to determine how venous and arterial pressure waveforms change due to inhaled and infused anesthetics and acute hemorrhage.METHODS:Venous and arterial pressure waveforms were continuously collected, while each pig was under general anesthesia, by inserting Millar catheters into a neighboring peripheral artery and vein. The anesthetic was varied from inhaled to infused, then the pig underwent a controlled hemorrhage. Pearson correlation coefficients between the power of the venous and arterial pressure waveforms at each pig's heart rate frequency were calculated for each variation in the anesthetic, as well as before and after hemorrhage. An analysis of variance (ANOVA) test was computed to determine the significance in changes of the venous pressure waveform means caused by each variation.RESULTS:The Pearson correlation coefficients between venous and arterial waveforms decreased as anesthetic dosage increased. In an opposing fashion, the correlation coefficients increased as hemorrhage occurred.CONCLUSION:Anesthetics and hemorrhage alter venous pressure waveforms in distinctly different ways, making it critical for researchers and clinicians to consider these confounding variables when utilizing pressure waveforms. Further work needs to be done to determine how best to integrate PVP waveforms into clinical decision-making.

The ability to customize the size and shape of angioplasty balloons may be useful in many clinical and research applications of coronary and endovascular intervention. Fully customizable balloons are outside the reach of most researchers due to their prohibitive cost. A small-scale balloon-forming machine was developed to produce fully customizable balloons. This study describes the creation of this customizable balloon-forming machine and identifies the key components of manufacturing a patient-specific balloon. Using a standard balloon-shaped mold created with a novel application of 3D stereolithography-printed resin, 104 PET balloon formation tests were conducted. A statistical study was conducted in which molding temperature and inflation air pressure were independent variables ranging from 100 to 130 °C and from 3.7 to 6.8 atm, respectively. The criteria for balloon-forming success were defined; pressure and temperature combined were found to have a significant impact on the success ( p = 0.011), with 120 °C and 4.76 atm resulting in the highest chance for success based on a regression model.

Current in vitro models of the left heart establish the pressure difference required to close the mitral valve by sealing and pressurizing the ventricular side of the valve, limiting important access to the subvalvular apparatus. This paper describes and evaluates a system that establishes physiological pressure differences across the valve using vacuum on the atrial side. The subvalvular apparatus is open to atmospheric pressure and accessible by tools and sensors, establishing a novel technique for experimentation on atrioventricular valves. Porcine mitral valves were excised and closed by vacuum within the atrial chamber. Images were used to document and analyze closure of the leaflets. Papillary muscle force and regurgitant flow rate were measured to be 4.07 N at 120 mmHg and approximately 12.1 ml/s respectively, both of which are within clinically relevant ranges. The relative ease of these measurements demonstrates the usefulness of improved ventricular access at peak pressure/force closure.

Purpose Flow phantoms are used in experimental settings to aid in the simulation of blood flow. Custom geometries are available, but current phantom materials present issues with degradability and/or mimicking the mechanical properties of human tissue. In this study, a method of fabricating custom wall-less flow phantoms from a tissue-mimicking gel using 3D printed inserts is developed. Methods A 3D blood vessel geometry example of a bifurcated artery model was 3D printed in polyvinyl alcohol, embedded in tissue-mimicking gel, and subsequently dissolved to create a phantom. Uniaxial compression testing was performed to determine the Young’s moduli of the five gel types. Angle-independent, ultrasound-based imaging modalities, Vector Flow Imaging (VFI) and Blood Speckle Imaging (BSI), were utilized for flow visualization of a straight channel phantom. Results A wall-less phantom of the bifurcated artery was fabricated with minimal bubbles and continuous flow demonstrated. Additionally, flow was visualized through a straight channel phantom by VFI and BSI. The available gel types are suitable for mimicking a variety of tissue types, including cardiac tissue and blood vessels. Conclusion Custom, tissue-mimicking flow phantoms can be fabricated using the developed methodology and have potential for use in a variety of applications, including ultrasound-based imaging methods. This is the first reported use of BSI with an in vitro flow phantom.

Assessment of supravalvar aortic stenosis (SVAS) severity in Williams syndrome (WS) is often complicated by the discrepancy in pressure drops obtained via peak-instantaneous Doppler and peak-to-peak cardiac catheterization measurements. With SVAS, static pressure in the left ventricle is converted to kinetic energy, maximal at the vena contracta, some of which is recovered through pressure energy and some of which is lost through thermal energy and deformation. The phenomenon …

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Fluid Structure Interaction (FSI) models are an essential tool in understanding the complex coupling of blood flow in the heart. The objective of this study is to establish a method of comparing data obtained from FSI models and benchtop measurements from phantoms to identify sources of flow changes for use in intraventricular flow analysis. Two geometries are considered: 1) a vascular model consisting of a straight channel with an ellipsoidal swell and 2) an idealized left ventricle (LV) model representative "acorn" shape. Two phantoms are created for each of the two geometries: 3D printed rigid phantoms from a resin and custom-made tissuemimicking phantoms from a medical gel. Benchtop measurements are made using the phantoms within a custom flow loop setup with pulsatile flow. Computational Fluid Dynamics (CFD) simulations are conducted with a Smoothed Particle Hydrodynamics (SPH) model. The two flow channel geometries utilized in the experiments are replicated for the simulations. The cavity walls are defined by ghost particles that are rigidly fixed. Maximum pressure drops were 57 mmHg and 196 mmHg for the rigid swell and rigid LV, respectively, whereas maximum pressure drops were 155 mmHg for the gel swell and 140 mmHg for the gel LV. Calculations from the simulations resulted in a maximum pressure drop of 55 mmHg for the swell and 110 mmHg for the LV. This data serves as a first step in corroborating our methodology to utilize the information obtained from both methods to identify and better understand mutual sources of changes in flow patterns.

Objective: Computational models of the mitral valve (MV) have the potential to accurately predict behavior of tissues and devices, but require high quality imagery for validation. Of particular technical difficulty, is imaging the closed valve, which requires both precise positioning as well as constant control of the trans-mitral pressure. This study describes an alternative approach that utilizes surgical adhesive. Methods: The relative locations of six descriptive anchor points of the annulus and the center of the papillary muscle tips in porcine MVs were defined. The valves were then explanted and mounted in a dedicated 3D printed annulus clamp and papillary muscle holder designed using the measurements to mimic physiological systolic geometry. The mounted valves were closed using air pressure and the closed leaflets fixed in the systolic configuration using surgical grade adhesive. Once fully dried the air pressure is removed and the valves imaged in a μCT scanner. Results: Scan time of approximately 1.5 hours yielded a 33μm voxel resolution. It was found that the glue held the leaflets in a securely and physiologically correct closed configuration throughout the scan and the chordae tendineae were maintained taut. The glue did not interfere with imaging. Further work on optimizing the imaging apparatus and segmentation will be presented. Conclusions: Creating robust and reliable computational models of the mitral valve requires high quality 3D imagery. By utilizing a surgical adhesive to seal the leaflets shut, the mitral valve can be scanned by μCT without the added complexity of maintaining constant pressure difference across the valve during the scan. This makes scanning closed valves substantially easier and quicker, facilitating further imaging and bench-top measurements required for computational validation.

Imaging techniques of the mitral valve have improved tremendously during the last decade, but challenges persist. The delicate changes in annulus shape and papillary muscle position throughout the cardiac cycle have significant impact on the stress distribution in the leaflets and chords, thus preservation of anatomically accurate positioning is critical. The aim of this study was to develop an in vitro method and apparatus for obtaining high-resolution 3D MRI images of porcine mitral valves in both the diastolic and systolic configurations with physiologically appropriate annular shape, papillary muscle positions and orientations, specific to the heart from which the valve was harvested. Positioning and mounting was achieved through novel, customized mounting hardware consisting of papillary muscle and annulus holders with geometries determined via pre-mortem ultrasonic intra-valve measurements. A semi-automatic process was developed and employed to tailor Computer Aided Design models of the holders used to mount the valve. All valve mounting hardware was 3D printed using a stereolithographic printer, and the material of all fasteners used were brass for MRI compatibility. The mounted valves were placed within a clear acrylic case, capable of holding a zero-pressure and pressurized liquid bath of a MRI-compatible fluid. Obtaining images from the valve submerged in liquid fluid mimics the natural environment surrounding the valve, avoiding artefacts due to tissue surface tension mismatch and gravitational impact on tissue shape when not neutrally buoyant. Fluid pressure was supplied by reservoirs held at differing elevations and monitored and controlled to within ±1mmHg to ensure that the valves remained steady. The valves were scanned in a 7 Tesla MRI system providing a voxel resolution of at least 80μm. The systematic approach produced 3D datasets of high quality which, when combined with physiologically accurate positioning by the apparatus, can serve as an important input for validated computational models.