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Research Papers

J. Med. Devices. 2018;13(1):011001-011001-9. doi:10.1115/1.4041414.

Mechanical circulatory support (MCS) options are limited for patients with dysfunctional single ventricle physiology. To address this unmet clinical need, we are developing an axial-flow blood pump to provide mechanical assistance to the cavopulmonary circulation. In this study, we investigate the use of high-resolution cardiac magnetic resonance imaging (MRI) to visualize the complex fluid flow conditions of mechanical circulatory assist in two patient-specific Fontan anatomies. A three-bladed axial-flow impeller coupled to a supportive cage with a four-bladed diffuser was positioned in the inferior vena cava (IVC) of each Fontan anatomy. Cardiac magnetic resonance (CMR) imaging and power efficiency studies were conducted at physiologic relevant parameters with cardiac outputs of 2, 3, and 4 L/min with impeller rotational speeds of 2000 and 4000 rpm. The axial-flow impeller was able to generate improved flow in the total cavopulmonary connection (TCPC). The higher rotational speed was able to redistribute flow in the TCPC anastomosis aiding in removing stagnant blood. No retrograde flow was observed or measured in the superior vena cava (SVC). As an extension of the CMR data, a scalar stress analysis was performed on both models and found a maximum scalar stress of approximately 42 Pa for both patient anatomies. The power efficiency experiments demonstrated a maximum energy gain of 8.6 mW for TCPC Anatomy 1 and 12.58 mW for TCPC Anatomy 2 for a flow rate of 4 L/min and at 4000 rpm. These findings support the continued development of axial blood pumps for mechanical cavopulmonary assist.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;13(1):011002-011002-7. doi:10.1115/1.4041336.

Attendant wheelchairs provide a means to transport patients or mobility to people with walking disability. They can be attendant propelled, which are highly maneuverable in confined spaces, but offer no power assistance. Also, they can be electric powered with joystick control interface, which provides power assistance, but not as maneuverable as the attendant propelled wheelchair. With the objective of providing power assistance and having excellent maneuverability, this paper presents a motorized attendant wheelchair with haptic interface. Its control approach is based on virtual/desired dynamics, which is not the true dynamics of the wheelchair, but a mathematical model describing the motion behavior of a desired system. The desired dynamics takes the user's applied force/torque and yields desired velocities of the wheelchair. In the evaluation, tasks in confined spaces that require a lot of maneuvers were given and performed using the motorized wheelchair with haptic and joystick control interfaces. The results in terms of task completion times showed that motorized wheelchair with haptic significantly outperformed the motorized wheelchair with joystick interface. In addition, the performance of the motorized with haptic interface and attendant propelled wheelchairs were evaluated at two different loads. At heavy load, the task completion times of motorized wheelchair with haptic interface were comparable to the attendant propelled wheelchair.

Topics: Haptics , Wheelchairs
Commentary by Dr. Valentin Fuster

Technical Brief

J. Med. Devices. 2018;13(1):014501-014501-6. doi:10.1115/1.4041190.

Pectus carinatum (PC) presents itself as a protrusion on the chest wall of adolescent individuals. Current treatment for PC is performed with a Pectus carinatum orthosis (PCO) that applies a compressive force to the protrusion. While this treatment is accepted, the magnitude of compressive forces applied remains unknown leading to excessive or deficient compression. Although the need for this quantitative data is recognized, no studies reporting the data or methods are available. The purpose of this study was to design an accurate force measurement system (FMS) that could be incorporated into a PCO with minimal bulk. Components of the FMS were three-dimensional (3D)-printed and incorporated into an existing PCO design. The FMS was calibrated using a custom indenter that applied forces to the FMS in a controlled manner. Evaluation of the FMS on five human participants was also performed. A reliability measure of the FMS was calculated for analysis. The FMS was implemented into the PCO and able to withstand the applied forces. The calibration revealed an increase in load cell error with increased magnitude of applied force (mean error [SD] = 5.59 N [6.48 N]). Participants recruited to evaluate the FMS demonstrated reliable forces (R = 96%) with smaller standard deviations than those during the calibration. The FMS was shown capable of measuring PCO forces but requires further testing and improvement. This system is the foundational component in a wireless, minimalistic sensor system to provide real time force feedback to both the clinician and patient.

Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Med. Devices. 2018;13(1):015001-015001-9. doi:10.1115/1.4041335.

Error and uncertainty in needle placement can drastically impact the clinical outcome of both diagnostic and therapeutic needle-based procedures. In this work, we aim to estimate the shape of a bent needle during insertion and provide a prototype design of a needle whose deflection is tracked in real time. We calculate slope along a needle by measuring the movement of fixed wires running along its length with a compact image-based sensor. Through the use of the Euler–Bernoulli beam theory, we calculate shape and trajectory of a needle. We constructed a prototype needle with two wires fixed along its length and measured wire-movement using a vertical-cavity surface-emitting laser (VCSEL) mouse sensor. This method was able to estimate needle tip deflection within 1 mm in a variety of deflection scenarios in real time. We then provide a design of a needle with real-time deflection tracking in 3D, providing the user with a simple display to convey needle deflection in tissue. This method could be applied to needle-based biopsy or therapy procedures to improve the diagnostic accuracy or treatment delivery quality.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;13(1):015002-015002-4. doi:10.1115/1.4041337.

Cardiovascular assessment and fitness training are often overlooked in physical rehabilitation. Many current rehabilitation exercise devices do not allow for the recording and exportation of variables related to cardiovascular fitness. Therefore, the purpose of this work was to design, prototype, and validate a data logger that measures, records, and exports time, heart rate (HR), and speed data with the commercially available rehabilitation device called the Intelligently Controlled Assistive Rehabilitation Elliptical (ICARE). Validation involved using the data logger device in parallel with devices currently used in research environments for measuring HR (TrueOne 2400 metabolic cart with polar HR monitoring chest strap) and speed (ICARE's console). Ten healthy individuals without known disability impacting walking or ability to use the ICARE, exercised on the ICARE while HR and ICARE speed were measured. It was found that the data logger can be used to accurately measure, record, and export HR (linear regression: P < 0.001; R2 = 0.892) and speed (linear regression: P < 0.001; R2 = 0.997) data when used with the ICARE.

Commentary by Dr. Valentin Fuster

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