Accepted Manuscripts

David A. Prim, Jay Potts and John/F Eberth
J. Med. Devices   doi: 10.1115/1.4040648
Intricate patterns of blood pressure and flow are generated by the cyclic contraction and relaxation of the heart and the coordinated opening and closing of valves. These pulsatile waves are augmented by the resistance, compliance, and inertance properties of the vasculature, resulting in unique hemodynamic characteristics present at distinct anatomically locations. In vivo these hemodynamically generated loads, transduced as physical signals into resident vascular cells, are crucial to the maintenance and preservation of healthy vascular physiology. Failure to recreate biomimetic loading in vitro however, can lead to pathological gene expression and aberrant remodeling. As a generalized approach to improve native and engineered blood vessels, we have designed, built, and tested a pulsatile perfusion bioreactor based on the concept of biomimetic impedances. Here the elements of an incubator-based culture system were formulaically designed to match the vascular impedance of a brachial artery using a 5-element electrohydraulic analog that incorporates both inherent (systemic) and added elements. Using freshly harvested saphenous veins, the relative expression of seven known mechanically sensitive remodeling genes were analyzed using a quantitative polymerase chain reaction (qPCR). Of these, we found plasminogen activator inhibitor-1 (SERPINE1) and fibronectin 1 (FN1) to be highly sensitive to differences between arterial- and venous-like culture conditions after 6 hours in our bioreactor. The analytical approach and biological confirmation provide a framework towards the general design of hemodynamic-mimetic vascular culture systems.
Jinhua Li, Zemin Zhang, Shuxin Wang, Zufeng Shang and G. K. Zhang
J. Med. Devices   doi: 10.1115/1.4040638
Natural orifice translumenal endoscopic surgery (NOTES) has offered significant advantages of less pain, reduced recovery time and minimized scar after operation, demonstration a promising development prospect. However, the large-size specimen extraction remains challenging for NOTES, due to the narrow space of the human natural orifices. To address such difficulties, a specimen extraction method that utilizes the braided fiber tube (BFT) structure with excellent retractility to accommodate and bind the bulky specimen has been proposed. Based on the theory of helical spring, the geometric model and the mechanical model of the BFT are established, and experiments have been performed to verify the accuracy of the derived mechanical model. In addition, a tensile test of using the BFT to extract large specimens via a small channel is carried out, which verifies the stable extraction performance of the proposed design. The BFT will not be damaged when extracting the specimen with a diameter less than 1.75 times of the channel diameter. A NOTES-specific specimen extraction instrument is designed according to the characteristics of NOTES, and it has 3 degrees of freedom and is able to actively capture different specimen by using a suction cup. Finally, specimen extraction experiments on NOTES multitasking platform phantom have been conducted using the prototyped instrument to validate its feasibility and effectiveness.
Marco Giovannini, Xingsheng Wang, Jian Cao and Kornel Ehmann
J. Med. Devices   doi: 10.1115/1.4040635
Skin cancer represents one of the most common forms of cancer in the United States. This and other skin disorders can be effectively diagnosed by performing a punch biopsy to obtain full-thickness skin specimens. The quality of the skin samples depends from the forces exerted by the punch cannula during the cutting process. The reduction of these forces is critical in the extraction of high quality tissue samples from the patient. During the skin biopsy, the biopsy punch (BP) is advanced into the lesion while it is rotated clockwise and counterclockwise generating, therefore, a rotary vibrational motion. No previous studies analyze whether this motion is effective in soft tissue cutting and if it could be improved. In this paper, the BP procedure is investigated in detail. First, the steady cutting motion of the BP is analyzed. Then, the superimposition of several vibrational motions onto the rotary motion of the BP is investigated. A analytical models, based on a fracture mechanics approach, are adopted to predict the cutting forces. Experimental studies are performed on phantom tissue to demonstrate that the application of vibrational motions can lead to the reduction of cutting forces. The outcome of this study can benefit several clinical procedures in which a cannula device is adopted to cut and collect soft tissue samples.
Technical Brief  
Mohammad Sahlabadi and Parsaoran Hutapea
J. Med. Devices   doi: 10.1115/1.4040637
Surgical needles are commonly used to reach target locations inside of the body for percutaneous procedures. The major issues in needle steering in tissues are the insertion force which causes tissue damage and the tissue deformation that causes the needle path deviation (i.e., tip deflection) resulting in the needle missing the intended target. In this study, honeybee-inspired needle prototypes were proposed and studied to decrease the insertion force and to reduce the tissue deformation. Three-dimensional (3D) printing technology was used to manufacture scaled-up needle prototypes. Needle insertion tests on tissue-mimicking polyvinyl chloride (PVC) gel were performed to measure the insertion force and the tip deflection. Digital image correlation study was conducted to determine the tissue deformation during the insertion. It was demonstrated that the bioinspired needles can be utilized to decrease the insertion force by 24% and to minimize the tip deflection. It was also observed that the bioinspired needles decrease the tissue deformation by 17%. From this study, it can be concluded that the proposed bee-inspired needle design can be used to develop and manufacture innovative surgical needles for more effective and less invasive percutaneous procedures.
Design Innovation Paper  
Aimee Sakes, Awaz Ali, Jovana Janjic and Paul Breedveld
J. Med. Devices   doi: 10.1115/1.4040636
Even though technological advances have increased the application area of Minimally Invasive Surgery (MIS), there are still hurdles to allow for widespread adoption for more complex procedures. The development of steerable instruments, in which the surgeon can alter the tip orientation, has increased the application area of MIS, but they are bulky, which limits their ability to navigate through narrow environments, and complex, which complicates miniaturization. Furthermore, they do not allow for navigating through complex anatomies. In an effort to improve the dexterity of the MIS instruments, while minimizing the outer dimensions, the previously developed cable-ring mechanism was redesigned, resulting in the thinnest, Ø2 mm (Ø1 mm lumen), 8 Degrees Of Freedom (DOF) multisteerable tip for MIS to date. The multisteerable tip consists of 4 steerable segments of 2-DOF stackable elements allowing for ±90° articulation, as well the construction of complex shapes, actuated by 16 Ø0.2 mm stainless steel cables. In a proof-of-principle experiment, an ultrasound transducer and optical shape sensing fiber were inserted in the lumen and the multisteerable tip was used to perform scanning motions in order to reconstruct a wire frame in 3D. This configuration could in future be used to safely navigate through delicate environments and allow for tissue characterization. Therefore, the multisteerable tip has the potential to increase the application area of MIS in future, as it allows for improved dexterity, the ability to guide several tip tools towards the operation area, and the ability to navigate through tight anatomies.
Design Innovation Paper  
Nathan Knighton, Brian Cottle, Veronique Dentan, Tom Vercauteren, Ahsan Akram, Annya Bruce, Kevin Dhaliwal and Robert Hitchcock
J. Med. Devices   doi: 10.1115/1.4040639
Optical molecular imaging is an emerging field and high resolution optical imaging of the distal lung parenchyma has been made possible with the advent of clinically approved fiber based imaging modalities. However, currently, there is no single method of allowing the simultaneous imaging and delivery of targeted molecular imaging agents. We describe the rationale, development, and validation to near clinical readiness of a triple lumen bronchoscopy catheter that allows concurrent imaging and fluid delivery, with the aim of clinical use to deliver multiple fluorescent compounds to image alveolar pathology.
Samuel / A Miller, William / R Heineman, Alison A. Weiss and Rupak K. Banerjee
J. Med. Devices   doi: 10.1115/1.4040563
Efficient detection of pathogens is essential to the development of a reliable point-of-care diagnostic device. Magnetophoretic separation, a technique used in microfluidic platforms, utilizes magnetic microbeads coated with specific antigens to bind and remove targeted biomolecules using an external magnetic field. For better reliability and accuracy in the device, the efficient capture of these magnetic microbeads is important. The aim was to analyze the effect of an electroosmotic flow switching on the capture efficiency of magnetic microbeads in a microfluidic device and demonstrate viability of bacteria capture. This analysis was performed at microbead concentrations of 2x106 and 4x106 beads/mL, electroosmotic flow voltages of 650 and 750 volts, and under constant and switching flow protocols. Images were taken using an inverted fluorescent microscope and the pixel count was analyzed to determine fluorescent intensity. A capture zone was used to distinguish between captured and uncaptured beads. The capture efficiency range was 31% - 42% for constant flow and 71% to 85% for switching flow. Compared to constant flow, the relative percentage increase due to the switching flow was ~2 times (p<0.05). Initial testing using bacteria-bead complexes was also performed in which these complexes were captured under the constant flow to create a calibration curve based on fluorescent pixel count. The calibration curve was linear on a log-log plot (R2 = 0.96). The significant increase in capture efficiency highlights the effectiveness of flow switching for magnetophoretic separation in microfluidic devices and prove its viability in bacterial analysis.
TOPICS: Flow (Dynamics), Microfluidics, Bacteria, Electroosmosis, Calibration, Separation (Technology), Electrical measurement, Magnetic fields, Reliability, Microscopes, Testing
Patrícia Filipa Pinheiro Silva, Alexandros Drakidis, Silvana Gomes and Torben Lenau
J. Med. Devices   doi: 10.1115/1.4040492
Polymer needles for medical injections offer a range of opportunities like compatibility with magnetic resonance scanning and simultaneous delivery of more than one drug. However, the lower stiffness property of polymers compared to steel is a challenge for penetration. This paper explores strategies for higher penetration success, which include impulse insertion, tissue stretching and different tip geometries. The strategies are experimentally examined using artificial skin models. It is demonstrated that polymer needles have higher penetration rates when the strategies are applied. Penetration rates were only 10-20% when using slow speed insertion (0.2mm/s) but 100% penetration rates was achieved using impulse insertion. Penetration forces are similar for slow insertion speed and high speed (impulse insertion) and for needles made out of different material (polymer or steel). Animals like the mosquito and the woodpecker inspired the strategies. Conical and pyramidal tips were studied for polymer needles and a commercial bevel steel needle tip. The result was lower penetration forces and 100% penetration success was possible using the pyramidal polymer needles. For the model in study was observed a similar behaviour considering penetration force and rate of penetration success for steel and polymer pyramidal needles. An Anova statistical analysis show significance when using springs and strain, as well for the combination of both.
TOPICS: Impulse (Physics), Biological tissues, Polymers, Geometry, needles, Steel, Magnetic resonance, Springs, Statistical analysis, Stiffness, Biomedicine, Artificial skin, Drugs
Expert View  
Vasum Peiris, Kui Xu, Heather Agler, Eric Chen, Rashmi Gopal-Srivastava, Brian Lappin, Debra Lewis and Gayatri Rao
J. Med. Devices   doi: 10.1115/1.4040489
Rare diseases (RD) affect approximately 30 million Americans, half of whom are children. This study is the first to comprehensively evaluate their medical device needs via a survey of physicians. The study sought to identify and document the presumed unmet diagnostic and therapeutic device needs for RD management; clarify the magnitude of the potential unmet need; and generate meaningful data to inform medical device stakeholders. A cross-sectional non-probability survey was conducted. The study population was drawn from the membership files of four groups: FDA Medical Devices Advisory Committee, Pediatric Advisory Committee, Pediatric Device Consortia, and NIH Rare Diseases Clinical Research Network. Only physician respondents with experience or knowledge regarding RD were eligible. Among eligible respondents, 90% confirmed the need for innovative devices to care for people with RD. Over 850 device needs were identified for 436 RD, with 74% of needs related to children. Pediatric physicians (OR=2.11, 95% CI 1.01-4.39, P=.046) and physicians with more RD experience reflected greater dissatisfaction with existing devices (OR =4.49, 95% CI 2.25-8.96, P < 0.0001). Creation of entirely new devices is the top recommendation for mitigating needs. This study demonstrates a major public health need for innovative medical devices to care for children and adults with RD. FDA and NIH support and seek opportunities to accelerate device development for these vulnerable patients.
TOPICS: Medical devices, Diseases, Pediatrics, Frequency-domain analysis, Food and Drug Administration, Probability
Review Article  
Christopher Uhl, Wentao Shi and Yaling Liu
J. Med. Devices   doi: 10.1115/1.4040272
As a necessary pathway to man-made organs, organ-on-chips which simulate the activities, mechanics and physiological responses of a real organs have attracted plenty of attention over the past decade. As the maturity of 3D cell-culture models and microfluidics advances, the study of organ-on-chips has made significant progress. This review article provides a comprehensive overview and classification of organ-on-chip microfluidics. Specifically, the review focuses on organ-on-chip systems capable of being used in pre-clinical drug screening and development. Additionally, the review highlights the strengths and weaknesses of each organ-on-chip system towards the goal of improved drug development and screening. The various organ-on-chip systems investigated throughout the review include, blood vessel, lung, liver, and tumor systems and the potential benefits which each provides to the growing challenge of high-throughput drug screening. Published organ-on-chip systems have been reviewed over the past decade (2007-2017) with focus given mainly to more recent advances and improvements within each organ system. Each organ-on-chip system has been reviewed on how closely and realistically it is able to mimic its physiological counterpart, the degree of information provided by the system towards the ultimate goal of drug development and screening, how easily each system would be able to transition to large scale high-throughput drug screening, and what further improvements to each system would help to improve the functionality, realistic nature of the platform, and throughput capacity.
TOPICS: Drugs, Microfluidics, Physiology, Artificial organs, Blood vessels, Liver, Lung, Tumors
Abhijith Rajiv, Yaxuan Zhou, Jeremy Ridge, Per G. Reinhall and Eric/J Seibel
J. Med. Devices   doi: 10.1115/1.4040271
Forward-viewing catheters and scopes for diagnosing disease and guiding interventions in small ducts (less than 3 mm diameter) require wide-field high-quality imaging since scope tip bending is difficult and ineffective. A high-fidelity electromechanically coupled finite element model of a piezoelectric actuated resonant fiber scanner is presented which enables improvement on the general design of fiber-optic scanner geometry to increase scan frequency and field of view. Using the proposed model, parametric sweeps on the specific design variables achieved by acid etching of glass fiber are analyzed to identify their effect on scanner performance and to choose improved designs. The resulting complex fiber scanner design requires development of unique microfabrication techniques. Comparison of three model simulations and their experimental testing show that our proposed coupled model has prediction error of ≤12% with respect to experimental data, while other uncoupled models have up to 98% error. The model and microfabrication techniques presented in this paper have significance for fiber scanning-based systems in that they demonstrate reliability for model-driven design and also flexibility for fiber scanner design of complex geometries, allowing for improvement on medical imaging performance.
TOPICS: Fibers, Testing, Design, Microfabrication, Errors, Etching, Finite element model, Geometry, Imaging, Engineering simulation, Biomedical imaging, Catheters, Diseases, Ducts, Glass fibers, Reliability, Simulation, Resonance
Ying Ying Wu, Deepshikha Acharya, Camilla Xu, Boyle C. Cheng, Sandeep Rana and Kenji Shimada
J. Med. Devices   doi: 10.1115/1.4040187
Noninvasive ventilator support using BiPAP/CPAP is commonly utilized for chronic medical conditions like sleep apnea and neuromuscular disorders like ALS that lead to weakness of respiratory muscles. Generic masks come in standard sizes and are often perceived by patients as being uncomfortable, ill-fitting and leaky. A significant number of patients are unable to tolerate the masks and eventually stop using their devices. The goal of this project is to develop custom-fit masks to increase comfort, decrease air leakage and thereby improve patient compliance. A single patient case study of a patient with variant ALS was performed to evaluate the custom-fit masks. His high nose bridge and overbite of lower jaw caused poor fit with generic masks, and he was noncompliant with his machine. Using desktop Stereolithography 3D printing and MRI data, a generic mask was extended with a rigid interface such that it was complementary to the patient's unique facial contours. Patient or clinicians interactively select a desired mask shape using a newly developed computer program. Subsequently, a compliant silicone layer was applied to the rigid interface. Ten different custom-fit mask designs were made using computer-aided design software. Patient evaluated the comfort, extent of leakage, and satisfaction of each mask via a questionnaire. All custom-fit masks were rated higher than the standard mask except for two. Our results suggest that modifying generic masks with a 3D-printed custom-fit interface is a promising strategy to improve compliance with BiPAP/CPAP machines.
TOPICS: Additive manufacturing, Leakage, Continuous positive airway pressure, Machinery, Computer software, Fittings, Muscle, Shapes, Silicones, Sleep, Bridges (Structures), Stereolithography, Computer-aided design, Magnetic resonance imaging, Biomedicine
Cailin Ng, Wenyu Liang, Chee Wee Gan, Hsueh Yee Lim and Kok Kiong Tan
J. Med. Devices   doi: 10.1115/1.4040185
An automated surgical device, the Ventilator Tube Applicator (VTA), enables a grommet insertion surgery for patients with otitis media with effusion to be completed in a short time automatically and precisely. However, its current design limits the usefulness of the device as it is restricted by the properties of the eardrum, such as angle, thickness and strength. Therefore, a novel design was conceptualized and the insertion control algorithm was improved to overcome the current challenges of the VTA. This innovative cover-cutter instrument design allows three-dimensional motion on an oblique surface using a single axis actuator. Experimental results on mock membranes showed great improvements in terms of robustness, success rate and insertion force. Finite element analysis on a cadaveric TM model further validated the usefulness of the cover-cutter instrument, and showed some interesting insights in the grommet insertion process.
TOPICS: Instrumentation, Surgery, Design, Ear, Finite element analysis, Actuators, Membranes, Robustness, Control algorithms
Akram Faqeeh, Roger Fales, John Pardalos, Ramak Amjad, Isabella Zaniletti and Xuefeng Hou
J. Med. Devices   doi: 10.1115/1.4040188
Premature infants often require respiratory support with a varying concentration of the fraction of inspired oxygen to keep the peripheral oxygen saturation within the desired range to avoid both hypoxia and hyperoxia. The widespread practice for controlling the fraction of inspired oxygen is by manual adjustment. Automatic control of the oxygen to assist care providers is desired. A novel closed-loop respiratory support device with dynamic adaptability is evaluated non-clinically by using a neonatal respiratory response model. The device demonstrated the ability to improve oxygen saturation control over manual control by increasing the proportion of time where arterial oxygen saturation is within the desired range while minimizing the episodes and periods where arterial oxygen saturation of the neonatal respiratory model is out of the target range.
TOPICS: Control equipment, Oxygen, Automatic control
Kyle Yeates, Ava Segal, Richard Neptune and Glenn K. Klute
J. Med. Devices   doi: 10.1115/1.4040183
To improve balance of individuals with lower limb amputation on coronally-uneven terrain, a coronally-clutching ankle (CCA) was developed to actively adapt through ±15° of free coronal foot rotation during the first ~60 ms of initial contact. Three individuals with lower limb amputations were fit with the CCA and walked across an instrumented walkway with a middle step that was either flush, 15° inverted, or 15° everted. An opaque latex membrane was placed over the middle step, making the coronally-uneven terrain unpredictable. Compared to participants' clinically-prescribed prosthesis, the CCA exhibited significantly more coronal angular adaption during early stance. The CCA also improved participants' center of mass path regulation during the recovery step (reduced variation in mediolateral position) and reduced the use of the hip and stepping recovery strategies, suggesting it improved participants' balance and enabled a quicker recovery from the disturbance. However, use of the CCA did not significantly affect participants' ability to regulate their coronal angular momentum during the disturbance, suggesting the CCA did not improve all elements of dynamic balance. Reducing the distance between the CCA's pivot axis and the base of the prosthetic foot might resolve this issue. These findings suggest actively adapting the coronal plane angle of a prosthetic ankle can improve certain elements of balance for individuals with lower limb amputation who walk on coronally-uneven and unpredictable terrain.
TOPICS: Rotation, Latex, Angular momentum, Center of mass, Prostheses, Artificial limbs, Membranes
Bradley W. Hanks, Mary I Frecker and Matthew Moyer
J. Med. Devices   doi: 10.1115/1.4040184
Radiofrequency ablation (RFA) is an increasingly used, minimally invasive, cancer treatment modality for patients who are unwilling or unable to undergo a major resective surgery. There is a need for RFA electrodes that generate thermal ablation zones that closely match the geometry of typical tumors, especially for endoscopic ultrasound-guided (EUS) RFA. In this paper, the procedure for optimization of an RFA electrode is presented. First, a novel compliant electrode design is proposed. Next, a thermal ablation model is developed to predict the ablation zone produced by an RFA electrode in biological tissue. Then, a multi-objective genetic algorithm is used to optimize two cases of the electrode geometry to match the region of destructed tissue to a spherical tumor of a specified diameter. This optimization procedure is then applied to EUS-RFA ablation of pancreatic tissue. For a target 2.5cm spherical tumor, the optimal design parameters of the compliant electrode design are found for two cases. Case 1 and Case 2 optimal solutions filled 70.9% and 87.0% of the target volume as compared to only 25.1% for a standard straight electrode. The results of the optimization demonstrate how computational models combined with optimization can be used for systematic design of ablation electrodes. The optimization procedure may be applied to RFA of various tissue types for systematic design of electrodes for a specific target shape.
TOPICS: Electrodes, Endoscopic devices, Optimization, Radiofrequency ablation, Ablation (Vaporization technology), Design, Biological tissues, Tumors, Geometry, Shapes, Ultrasound, Surgery, Cancer, Genetic algorithms
Design Innovation Paper  
Jason Green, Richard Glisson, Jane Hung, Mohamed Ibrahim, Alfredo Farjat, Beiyu Liu, Ken Gall and Howard Levinson
J. Med. Devices   doi: 10.1115/1.4040186
Wide mesh or tape sutures are used to close high-tension wounds such as in hernia or tendon repair. However, wide sutures produce large knots that are susceptible to increased palpability, infection, and foreign body response. To prevent such adverse events, we developed a small suture anchor to replace wide suture knots. The suture anchor was iteratively developed using 3D design software and produced via 3D printing. Anchor prototypes underwent monotonic, cyclic fatigue, and stress-life testing in a benchtop soft tissue suture model. Results were compared to a standard of care knot and alternative suture fixation devices. The final anchor design was selected based on minimal size and mechanical performance. The size of the final anchor (200 mm3) was 33% smaller than a tape suture knot and 68% smaller than a mesh suture knot. Monotonic testing of mesh and tape suture revealed a significantly greater anchor failure load compared to knot and alternative fixations (p< 0.05). Additionally, all anchors successfully completed cyclic fatigue testing without failure while other fixations, including knot, failed to complete cyclic fatigue testing multiple times. Stress-life testing demonstrated durable anchor fixation under varying tensile stress. Failure mode analysis revealed anchor fracture and tissue failure as modes of anchor failure, each of which occurred at supraphysiologic forces. We created a small suture anchor that significantly outperforms knot and alternative suture fixations in benchtop testing and addresses concerns of increased palpability, infection, and foreign body response from large suture knots.
TOPICS: Fatigue, Maintenance, Stress, Engineering prototypes, Equipment performance, Fracture (Materials), Biological tissues, Design, Failure mechanisms, Fracture (Process), Testing, Computer software, Failure, Fatigue testing, Tension, Wounds, Soft tissues, Tendons, Additive manufacturing
Design Innovation Paper  
F. Mark Payne, Tony Connell and Jacob Rice
J. Med. Devices   doi: 10.1115/1.4030812
Background: Tissue expanders are used in breast reconstruction after mastectomy to create a space for placement of permanent breast implants. The AeroForm™ Tissue Expander, developed by AirXpanders™ Inc., utilizes carbon dioxide released from an internal reservoir to inflate the expander. The released gas is contained within a high barrier material pre-formed into a breast shaped shell of the desired volume. During patient travel to higher altitude, a partially inflated expander will increase in volume proportionately to the gas fill volume. At volume levels near full, expansion is governed by the compliance of the inner gas barrier and silicone shell. Therefore, the assessment of the expander performance at altitude consists of the analysis of two operating regimes. The first regime is fill levels < 70% full where the implant, when exposed to cabin pressure, expands without significantly stressing the inner gas barrier. The second is fill levels ~>70% where the response of the inner gas barrier is important, both in terms of structural capability and determination of the volume increase. We assessed the impact of pressurized flight on expander performance in both operating regimes. Findings: The volume increase associated with altitude increase to 8000 feet (maximum cabin altitude per FAA) is typically within the range administered during post-operative fills of saline expanders. Although assessment must be conducted by a clinician, a patient can be typically expected to tolerate the increased volume with some minor discomfort, such as a feeling of tightness. At higher fill levels, the structural capability of shell has been demonstrated to withstand the additional pressure loading. At these fill levels, the expander does not expand as much, due to the structural restraint of the shell. To date, 7 subjects have flown with the expander in situ during clinical trials. All subjects were required to temporarily cease dosing up to two weeks prior. Flight travel was completed uneventfully and they reported discomfort levels ranging from none to moderate. The recommendation to cease dosing two weeks prior to flying was made to allow the expected 1 cc per day of CO2 permeation to occur, which will result in slight deflation to accommodate for the expansion of the CO2 when flying. As expected, subjects reported a sensation of pressure upon ascent which subsided on descent.
TOPICS: Biological tissues, Carbon dioxide, Shells, Pressure, Flight, Reservoirs, Silicones

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