28 minute read
Music Interventions for Alzheimer’s Disease Jessica George `24
to carefully monitor changes to the patient’s music performance that would be detected via electrodes placed on the surface of the brain, preoperative and intraoperative monitoring plans with labeled brain regions were composed. In the preoperative preparations, functional magnetic resonance imaging (fMRI) data from finger-tapping, word-reading, and verbal generation tasks were obtained as a baseline reference for comparison with data from the resection period. Preoperative cognitive, language, and motor testing demonstrated that no impairments relative to age were seen within the patient, as he/she exhibited a T-score (how much results vary from the mean) less than the 30th percentile. These low scores indicate low levels of anxiety, as well as depressive states, experienced by the patient prior to the craniotomy. Prior to the procedure, the patient was also asked to familiarize himself/herself with a straightforward piece that could guarantee a near perfect performance during the surgery, so that any changes in music performance would be attributable to intraoperative issues and not the patient’s violin-playing experience. Although the patient experienced an epileptic seizure during cortical stimulation, monitoring his/her complex motor and musical functions as he/she played the violin throughout resection allowed for better analysis of his/her condition. As such, a near complete resection was achieved, showing no postoperative deficits that would lead to future exacerbation of functional impairment. Specifically, 95% of the total tumor was successfully resected, which allowed the patient to resume normal activities as well as professional musical duties after just two weeks (4). While the postoperative results seem promising, it is important to note that they were self-reported by the patient and were not determined via neuropsychological testing, thus affecting the scope of their validity. Another study conducted by a group of clinicians in the Department of Neurosurgery at the Medical University of Warsaw aimed to observe another individual’s ability to perform music. In this evaluation, Dr. Tomasz A. Dziedic and his team examined the performance of a 42-year-old female amateur pianist with transient speech disturbance. An MRI indicated that the presence of a supratentorial cavernoma (a cluster of abnormal blood vessels) was causing symptomatic epilepsy (6). To attempt resection, an awake protocol with anesthesia was initiated, shortly followed by a left-sided temporo-occipital craniotomy. The researchers used a 4 mA current to stimulate the cortex and observe language responses. During the awake craniotomy, the patient was asked to play music that she had memorized solely with her right hand, followed by playing solely with her left hand. The patient appeared to experience extreme difficulty as she could not cognitively process how to continue the movements while playing. Next, the patient was asked to play music from a score, following the same tasks of playing with her right hand, then her left hand. It was found that she was unable to read the music or interpret the scores. This study indicates success in optimizing a technique for intraoperative monitoring of music performance using hand movements. The cortical stimulation revealed that the basal ganglia and cerebellar areas are related to music performance, and that to successfully perform music, feedback from the auditory cortex must not be compromised. In these studies, the use of musicians was crucial as their musical ability served as a complex, cognitively-demanding skill that could be monitored via intraoperative music performance. These studies suggest that musicians acquire extensive benefits from awake craniotomies, as these surgeries can pinpoint the exact areas of the cortex that need to maintain viability for an individual to preserve musical functionality. Moreover, by focusing on these specific areas of the brain as opposed to the brain as a whole, awake craniotomies allow for more focused treatment of one’s condition and a more specific approach to applying MT interventions in areas directly associated with music.
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Maintenance of Cognition
While it is important to ensure that the motor control needed for musical performance is preserved during these awake craniotomies, another aspect to maintain in individuals undergoing these procedures is their cognitive states. Electrical stimulation during awake surgery through brain mapping of the right non-dominant hemisphere has revealed the function of visuospatial and social cognition in this area. While visuospatial cognition refers to one’s perception and cognitive representation of space, social cognition encompassess all the cognitive processes involved in nonverbal social interaction (facial emotion recognition or theory of mind) (6). Historically, brain mapping in relation to cognitive function has been fairly limited due to an underestimation of the cognitive implication in the right hemisphere, as well as its anatomical and structural complexities. However, taking a closer look at the right hemisphere can provide surgeons and researchers alike with a better understanding of the maintenance of cognition during awake craniotomies.
Figure 1 Music therapy has been as a successful non invasive surgical technique in improving overall patient statisfaction as seen through inreased post surgery cognitive function and decreased neurological deficits. During awake craniotomies, attempts have been made to map the right hemispheric cortical areas involved in recognizing facial emotion to understand its relation to preservation of cognition. A study consisting of 18 patients with right hemispheric lesions examined 386 cortical sites using Ekman’s faces (which feature distinctive facial expressions) as a preoperative baseline test. Ekman’s faces involve showing photographs of faces exhibiting one of the 6 facial emotions – anger, happiness, fear, surprise, disgust, and sadness – to patients (6). Of the 386 sites studied during the procedure, researchers identified 5 sites (approximately 1.30%) as responsible for facial emotion recognition in 5 patients (7). These sites consisted of one site in the medial segment of the superior temporal gyrus (STG), one site in the posterior segment of the STG, one site in the posterior segment of the medial temporal gyrus (MTG), and two sites in the supramarginal gyrus. Not only do these findings suggest that the cognitive functions of the right hemisphere are essential for everyday facial emotion recognition, but also that this area of the brain should be a greater focus of study as cortical and subcortical structures involved in visuospatial and social cognition demonstrates marked variability amongst patients. Thus, it can be inferred that cortical and subcortical mapping of the nondominant hemisphere can be used as a gold standard during awake craniotomies to track the development of neuropsychological tasks. Further study is needed to determine the potential of these sorts of mapping to decrease depressive symptoms an individual may experience, measured through levels of emotion and perception.
Psychological and Emotional Outcomes
A study conducted in 2017 by researcher Dr. Pao-Yuan Wu and colleagues at a medical institution in Taiwan investigated the outcomes of MT interventions on the levels of anxiety and other psychological factors experienced by patients before and after an awake craniotomy. The study consisted of 38 patients divided into two groups of 19, where the experimental group selected and listened to music of their preference in the waiting room and the control group received the usual preoperative care (8). Patients were also included based on having brain tumor diagnoses, being at least 20 years of age, having no visual or auditory impairment, and the ability to communicate in either Mandarin, Chinese, or Taiwanese. The MT intervention group was allowed to choose their music from six types of soothing music, including nature, piano, harp, orchestra, jazz, or synthesis music. During the procedure, these individuals were allowed to listen to their preferred music once again as they laid on the operating table. The results indicated that the patients who had exposure to MT intervention experienced a significant decrease in their level of anxiety and that the music intervention significantly reduced average heartbeat rate to 84.5 bpm with a systolic pressure of 42 mmHg and diastolic pressure of 38 mmHg gradually over time as compared to average preoperative readings of 168 bpm heart rate and 166 mmHg systolic and 164 mmHg diastolic pressures. Such decreases in physiology suggests that MT is associated with decreased levels of anxiety and distress after patients have undergone an awake craniotomy. Moreover, these results can revolutionize the way perioperative (around the time of surgery) care is given to patients in high stress situations before undergoing surgery. Providing opportunities to listen to soothing music in the waiting room and during surgery to reduce anxiety can be a viable goal in improving human care and ensuring lasting positive outcomes from invasive procedures. References
Conclusion
Brain mapping in combination with MT can lead to extensive postoperative outcomes such as decreased stress and anxiety, motor control management via implementation of intraoperative music techniques, and maintenance of cognitive conformability by examination of specific brain regions. While MT promotes neuronal repair and decreases pain episodes even after patients have stopped listening, brain mapping can pinpoint critical regions and tumor areas to assist in minimizing cognitive impairment postoperatively. Therefore, both of these disciplines can be used in conjunction to further improve upon the recovery process of patients undergoing complex, high stress procedures. However, while the previous studies demonstrate the promise of MT during neurosurgical procedures, there are still many areas to address in order to confirm high postoperative efficacy. For example, disruption of musical ability should always be compared with a baseline speech or motor task to understand the qualitative origin of the deficit brought on by illness. In other words, patients should always be asked to complete certain tasks preoperatively so that intraoperative and postoperative findings may later be compared to account for any changes in the patient’s state. Musical ability should also be assessed with a standardized objective scoring method from before and after surgery to allow for comparison of the effectiveness of this alternative therapy. Possible future avenues may include using successful brain mapping techniques to further assess and prevent the onset of neurodegenerative diseases or disorders that may not be treatable at the current time.
1. J. Liang, X. Tian, and W. Yang, Application of music therapy in general surgical treatment. Biomed Research International 2021, 1-4 (2021). doi: 10.1155/2021/6169183 2. T. Dziedzic, et al., Awake intraoperative mapping to identify cortical regions related to music performance: technical note. Journal of Clinical Neuroscience 83, 64-67 (2021). doi: 10.1016/j. jocn.2020.11.027. 3. A. Scerrati, et al., Artists playing music while undergoing brain surgery: a look into the scientific evidence and the social media perspective. Clinical Neurology and Neurosurgery 196, 105-111 (2020). doi: 10.1016/j.clineuro.2020.105911. 4. V. Piai, et al., Awake surgery for a violin player: monitoring motor and music performance, a case report. Archives of Clinical Neuropsychology 34, 132-137 (2019). doi: 10.1093/arclin/acy009. 5. F. Bernard, et al., Right hemisphere cognitive functions: from clinical and anatomic bases to brain mapping during awake craniotomy part I: clinical and functional anatomy. World Neurosurgery 118, 348-359 (2018). doi: 10.1016/j.wneu.2018.05.024. 6. F. Bernard, et al., Right hemisphere cognitive functions: from clinical and anatomic bases to brain mapping during awake craniotomy part II: neuropsychological tasks and Brain mapping. World Neurosurgery 118, 360-368 (2018). doi: 10.1016/j.wneu.2018.05.024. 7. P. Wu, et al., Effects of music listening on anxiety and physiological responses in patients undergoing awake craniotomy. Complementary Therapies in Medicine 32, 56-60 (2017). doi: 10.1016/j. ctim.2017.03.007.
Image retrieved from :
1. https://pixabay.com/photos/surgeons-operation-operating-room-6841376/
Graphics Illustrated by Annie Li `22
ART AND MEDICINE: THE EFFECTS OF TECHNICAL DRAWING EXERCISES ON SPATIAL VISUALIZATION OF HUMAN ANATOMY
THUMYAT NOE `23
Spatial visualization, the ability to visualize shapes and the orientations of objects in space, can help medical students learn human anatomy, which many consider a challenging area of study. Past studies suggest that high spatial visualization positively correlates with increased success in scientific disciplines, leading researchers from Kansas City University to believe that enhancing spatial visualization through technical drawing exercises may help medical students successfully learn anatomy. In a recent experiment, researchers from Kansas City University tested the effects of technical drawing exercises on spatial visualization of medical students enrolled in neuroanatomy courses. Researchers hypothesized that technical drawing exercises may improve spatial visualization and thus help medical students perform better in anatomy courses. In order to test their hypothesis, researchers recruited 84 medical students enrolled in a neuroscience course to participate in this experiment. For baseline measurements, participants filled out a pre-questionnaire and took the Mental Rotations Test (MRT), a standard spatial skills test. Afterwards, researchers randomly assigned some participants to attend four art sessions. During each art session, participants worked on technical drawing exercises. Upon completion of these sessions, participants completed a post-questionnaire and took the MRT again. Researchers compared initial and final performances on the test to determine if technical drawing exercises improved spatial visualization skills. Although most participants showed improvement on the final assessment, participants who attended art sessions showed greater improvement
Figure 1 Research suggests that studying anatomy requires high spatial visualization skills.
than those in the control group. Researchers also found that participants with prior artistic experience showed greater improvement on the post-assessments, and participants who noticed an improvement in their spatial visualization skills after attending art sessions showed greater improvement compared to those who did not notice a change in their artistic abilities. Overall, the results imply that technical drawing exercises may enhance spatial visualization and help medical students in their anatomy studies. Those who wish to pursue a career in medical care should consider engaging in technical drawing exercises to improve spatial visualization. A possible direction for future studies is to control for a sample of participants who engage in technical drawing exercises during their free time.
1. Y. Na, et al., Spatial visualization of human anatomy through art using technical drawing exercises. Anatomical Science Education 0, 1-12 (2021). doi: 10.1002/ase.2080. 2. Image retrieved from: https://unsplash.com/photos/drkk_Tqbqq4
CAN A VIRTUAL REALITY SIMULATION WITH A CRIMINAL’S FUTURE SELF DECREASE SELF-DESTRUCTIVE BEHAVIOR?
JOYCE CHEN `23
Many of us have done things that we regret over the course of our lifetime. Some of us develop from our setbacks, while others are imprisoned and ostracized by society. These criminals’ actions were likely impulsive, completely disregarding the consequences that the future may bring. However, poor decisions can be resolved by introspection. Dr. Jean-Louis van Gelder of the Max Planck Institute for the Study of Crime, Security and Law sought to understand how convicted offenders would react if they engaged with an older version of themselves through virtual reality (VR). He and his research team hypothesized that the offenders would reflect on their actions and grow from them instead of engaging in self-destructive behavior. The team studied 24 young male offenders over the course of three months. Prior to this experience, participants had pictures of their faces taken by the researchers. These images were processed to create aged 3D avatars. The participants were asked to answer several survey questions based on their ability to connect with and imagine their future selves, how much they engaged in self-destructive behavior, and their expectations for their future lives. Afterwards, they were immersed in the VR simulation, where they met their older selves in a futuristic environment. The participants reported their emotions and experiences during the simulation immediately after. The researchers noticed that the offenders reported decreased levels of self-defeating behavior after the VR simulation. Behaviors such as “spending more money on something than intended” had decreased from 71.4% to 52.4% and “drinking alcohol” decreased from 52.4% to 28.6%. Based on a linear regression analysis, a significant positive correlation between the offenders’ poor vision of their future and their self-defeating behavior was represented by p = 0.04 with an adjusted of 0.03. Therefore, an increase in an offender’s vividness of the future is linked to the decrease in their self-destructive behavior. However, future studies with larger sample sizes would be necessary to draw more accurate conclusions. Dr. Gelder and his colleagues’ study showed how art, specifically digital media and virtual reality, can be used for psychological research and possibly therapeutic interventions. Although additional research is needed, the researchers believe that this experiment highlights the potential of the arts and technology in decreasing crime rates by changing behaviors in offenders.
1. J. Van Gelder, et al., Interaction with the future self in virtual reality reduces self-defeating behavior in a sample of convicted offenders. Sci Rep 12, 2254 (2022). doi: 10.1038/s41598-02206305-5. 2. Image retrieved from: https://cdn.pixabay.com/photo/2016/08/18/10/02/smartphone-1602486_1280.jpg
VIGNESH SUBRAMANIAN `24
A stroke, or cerebrovascular accident, is a medical emergency in which blood flow to the brain is interrupted or reduced. Strokes are the result of either an ischemic (arterial obstruction) or hemorrhagic (arterial rupture) event and are associated with the arrest of neuronal activity in the brain. However, various regions of the central nervous system (CNS) have demonstrated a capacity for recovering from post-stroke cerebral necrosis by regenerating and reorganizing synaptic connections, an ability known as neuroplasticity. CNS regions that exercise this ability are also among those associated with critical motor skills, visual acuity, and spatial awareness that define an individual’s sensory perception and artistic abilities. A study led by Griffith University researchers aimed to better characterize the relationship between post-stroke neuroplasticity and artistic skills compensation. Researchers conducted a systematic review of fifteen famous artists who each survived a left or right cerebral stroke to assess differences between premorbid and ‘post-stroke’ artistic styles as well as compare clinical outcomes between the two hemispheres. In the ten patients who had right cerebral strokes, particular attention was paid towards evaluating use of elementary bold colors, simplification of images, inability to reproduce chiaroscuro (treatment of light and shade), and left-side neglect. In the five patients who had left cerebral strokes, a loss of tri-dimensionality, perspective, rigidity, and repetitiveness were watched for, as these were previously thought to be perceptual attributes of each hemisphere. Researchers found that in nearly all examined cases, the artists demonstrated statistically significant recovery of artistic skills. Ten artists
Figure 1 Neuroplasticity is the capacity of the brain to develop and reorganize synaptic connections with new experiences or following injury.
adopted new, more expressive designs, while the rest either demonstrated restitutio ad integrum (restoration of premorbid styles) or could not have an attributable style clearly established. Patients with right hemispheric stroke primarily suffered left-side hemineglect, paresis (muscular weakness), visual field omissions, and apraxia (difficulty with skilled movement). Patients with left hemispheric stroke were found to have suffered right-side hemiparesis and aphasia (inability to understand or express speech) as well as having to learn to work with a non-dominant hand. The majority of patients were also found to have developed ischemia (reduced blood flow) in the frontal, temporal-parietal, or occipital cerebral areas associated with the processing and integration of motor functions. These results suggest that in the context of the damage done by stroke-induced lesioning, poststroke neuroplasticity in these artists’ brains was responsible not only for neurological recuperation, but also the development, in some cases, of entirely new artistic sensibilities and styles.
1. E. Petcu, et al., Artistic skills recovery and compensation in visual artists after stroke. Frontiers in Neurology 7, 1–12 (2016). doi: 10.3389/fneur.2016.00076 2. Image retrieved from: https://commons.wikimedia.org/wiki/File:Neuroplasticity.jpg
FEELING THE RAINBOW: ADVANCES IN MULTISENSORY ARTISTIC EXPERIENCES FOR THE VISUALLY IMPAIRED
PETER GILLESPIE `25
Figure 1 A color’s hue, warmth, and intensity can now be expressed by sound and temperature. Is art seen, or is it experienced? Thanks to the work of researchers Jorge Bartolome, Gilsang Cho, and Jun-Dong Cho at Sungkyunkwan University, people with visual impairments can now appreciate artwork through senses other than vision. Previous research in allowing people with visual impairments to experience art has appealed to just one other sense, such as sound or touch. However, Bartolome and his team believe that appealing to multiple senses at once can improve the user’s ability to memorize and integrate artwork. How does one determine the sound of a color or its temperature? To answer this question, Bartolome gave pairs of adjectives to 18 college students with normal vision. They then categorized each pair in relation to brightness or darkness, warmth or coldness, or both of these designations. Later, they rated how strongly related the adjective pair was to these designations. For example, given the adjective pair noisy and quiet, participants may report that the pair relates strongly or weakly to brightness or darkness, but not feelings of warmth or coldness. Participants then rated the adjective pair to a sensory stimulus. For example, when listening to a musical piece, a participant may say the piece relates strongly to the adjective “noisy.” The researchers also weighted the frequency of responses. By creating a link between adjectives and color character and another between adjectives and sensory stimuli, the researchers essentially created a connection between color character and sensory stimuli and used their unifying adjective list to bridge the gap. The researchers found that a higher temperature was best for representing warm colors like red, and colder temperatures for representing colder colors like blue, suggesting the applicability of temperature in communicating hue. Furthermore, because musical pieces were more easily distinguishable than temperature, they were deemed best for communicating aspects like brightness or darkness. When a different group of participants were asked to guess the color related to each stimulus, hue was determined with 71.6% accuracy and color character with 92.5% accuracy. Given the limited practice with this multimodal model and the supposed heightened sensory ability of visually impaired individuals, this methodology suggests a promising lens through which visually impaired individuals may experience fine art.
A REVIEW OF A REVIEW OF A REVIEW OF NITINOL’S NITINOL’S NITINOL’S APPLICATION IN APPLICATION IN APPLICATION IN VASCULAR STENTS VASCULAR STENTS VASCULAR STENTS
ARYAN PATEL `25 ARYAN PATEL `25
Introduction
Vascular stents are surgical implants used in operations to help dilate a narrowed, or stenosed, artery. They are often used to treat the symptoms of severe peripheral arterial disease (PAD), a form of heart disease that affects the limbs as a result of plaque buildup on the arterial walls (1). Stents are commonly fashioned from stainless steel, but the high restenosis and low patency rates of stainless steel stents have led to investigations to find a better material for this device. Restenosis is a phenomenon that occurs after the stent is implanted, where inflammation and growth factors cause the artery to narrow again, causing patency, or the state in which the ar-
Figure 1 Above is a stenosed artery prior to intervention. The yellow is the plaque buildup that reduces blood flow and often causes claudication and symptoms of PAD. tery is fully dilated, to fall. Nitinol, an alloy of nickel and titanium, has become a prime candidate for vascular stent material because it demonstrates high biocompatibility, making the stent more effective than traditionally used materials at lowering restenosis and thus maintaining higher patency rates.
Biocompatibility
Nitinol is an alloy of nickel and titanium, and the specific ratio in which these two elements are combined determines the properties of the alloy. This unique material demonstrates a high degree of biocompatibility, as the combination of nickel and titanium makes it highly resistant to corrosive compounds in human blood. Corrosion resistance is of special concern as corrosion of the implant may cause toxic amounts of nickel from the stent to be released into the bloodstream. However, nitinol exemplifies properties of a self-passivating material, a type of material which can independently create a protective surface layer to shield the material underneath the surface. This surface layer relies on the build up of titanium oxide to reduce the corrosion of the surface of the stent. A comparative study from 2016 conducted by R.E. Lee in association with the National Aeronautics and Space Administration (NASA) tested stainless steel and nitinol for corrosion resistance by placing them in brine solutions
Figure 2 The stent conforms to the natural bends of an artery, dilating the vessel for uninhibited blood flow.
for six and twelve months. After removal from the brine solution, each alloy was thoroughly rinsed and subject to visual and microscopic evaluation to detect corrosion damage. It was found that the general corrosion resistance of nitinol was between 0.49% and 0.50%, while the general corrosion resistance of stainless steel was 1.60%. This study concluded that nitinol exhibited insignificant general corrosion rates and very pronounced surface repassivation (2). By industry standards, this means that nitinol is more corrosion-resistant than stainless steel, which makes nitinol more biocompatible and less likely to release toxic elements like
nickel into the bloodstream. This reduces the chance of inflammation in the artery, which is a key cause of restenosis. A 2015 study conducted by Stacey J. Sullivan of the Oak Ridge Institute further analyzed the anticorrosive properties of nitinol by submerging nitinol stents into a nitric acid solution that mimics the environment of the human body. The stents used in the study also received surface treatments prior to corrosion testing. The study found that a measurable release of nickel ions was detected, but the cumulative nickel release was below 1100 nanograms after the stent was immersed in the solution for 60 days, which is well below the recommended daily intake value of 170 micrograms (3). These studies show that nitinol stents (especially when surface polished) do not release high amounts of toxic material into the bloodstream because of self-passivation and resistance to corrosion. This makes nitinol stents a safe implant option for patients. Since nickel release is associated with arterial inflammation, nitinol’s corrosion resistance and biocompatibility makes nitinol stents more effective at preventing restenosis and maintaining patency.
Clinical Advantages of Nitinol Stents
To test the efficacy of nitinol stents, several patient-centered studies have been conducted in the past decade to measure restenosis and patency rates. In a 2019 study conducted by Dr. Sourav Gur of the University of Arizona, 32 patients were implanted with stents, 22 of which received nitinol stents while the remaining 10 received stainless steel implants. The patients
were monitored for symptoms of PAD. Successful dilation of the artery was defined as the restoration of blood flow through the artery without significant restenosis. Primary patency rate was defined as the number of patients who were free of restenosis without repeat intervention or surgical procedures, and secondary patency rate was defined as the number of patients free of restenosis after two rounds of surgery/intervention. The results of the study reveal that the primary and secondary patency rates of nitinol stents 6 to 12 months after implantation (89% and 80.9%, respectively) are significantly higher than the primary and secondary patency rates of stainless steel stents (78.8% and 38.4%, respectively) (4). This suggests that nitinol stents are much more effective at dilating the artery and restoring blood flow to the extremities, especially in ...Patency rates of nitinol ...Patency rates of nitinol severe cases where surstents are higher than those stents are higher than those geons had to operate on patients of stainless steel...[and] of stainless steel...[and] more than once. This are much more effective are much more effective is likely a result of nitinol’s corat dilating the artery and at dilating the artery and rosion resistance, as restoring blood flow... restoring blood flow... arterial inflammation is less likely to occur in patients with nitinol implants, which leads to lower restenosis and higher patency rates. A 2017 study conducted by Mahmoud F. Elmahdy of Cairo University tested the efficacy of nitinol stents on a much larger patient population to verify the outcomes of previous studies. A total of 213 patients were selected based on a history of PAD and claudication, a symptom of PAD that causes pain in the extremities. The patients were monitored 12, 24, and 36 months after the implantation procedure. To demonstrate the efficacy of nitinol stents, researchers calculated primary patency. This study found that nitinol stents provided safe and effective treatment in symptomatic patients with PAD, as patency rates reached 81.4%, 77.7%, and 74.4% at 12, 24, and 36 months, respectively (5). The results of this study confirm
Figure 3 Nitinol wire is used in the production of nitinol stents, a self-passivating material that facilitates blood flow without releasing a high amount of toxic material into the bloodstream.
the predictions of the researchers that nitinol stents would be effective at dilating the artery and preventing re-narrowing up to three years after the implantation procedure. This study demonstrates that nitinol stents are effective at dilating the artery and preventing restenosis since a majority of patients implanted with nitinol stents recovered from symptoms of PAD and experienced returning functionality to their extremities. This is likely a result of several factors, one of them being nitinol’s biocompatibility. In this case corrosion resistance of nitinol would prevent nickel release and therefore limit arterial inflammation and restenosis while the stent is in the patient’s body. Further evidence on the longer-term efficacy of nitinol stents was gathered in a 2019 study conducted by Dr. Masato Nakamura of Toho University’s Division of Cardiovascular Medicine, which monitored 77 patients implanted with nitinol stents. Patients that were selected were at least 20 years of age and showed symptoms of lifestyle-limiting claudication. Patients were also selected based on arterial health. Only those with stenosed arteries or arterial lesions with lengths less than 150 mm were selected. Researchers determined the endpoints of the study to be the number of patients free from target-limb failure 12 months after implantation. Target limb failure was defined as procedure-related death, limb amputation, or restenosis. To record the results of the study, ultrasonic and X-ray imaging were used to take images of the arteries. Researchers also conducted routine medical visits on each patient at 1, 6, 12, 24, and 26 months after implantation, which included physical examinations and laboratory blood tests. This study revealed that nitinol stents provided patency in 71% of implanted patients one year after surgery, and 67.8% patency in patients after three years (6). These findings confirm that nitinol stents are effective in dilating the artery up to three years after implantation, demonstrating the potential of nitinol stents for longer-term stenting. Not only were patency rates higher, but patients also reported dramatic changes to quality of life as they recovered from claudication and other complications of PAD. The outcomes of these studies reveal that nitinol is well suited to applications in stenting as seen by high patency rates and positive outcomes. The main reason for nitinol stents being so effective at maintaining patency lies in their inherent biocompatibility. As the stent remains in the patient’s body, it is exposed to corrosive compounds in the patient’s blood. Since nitinol is highly resistive to corrosion, nickel release is limited which reduces the chance of arterial inflammation: a key source of restenosis. Therefore, if the chances of the artery narrowing after intervention are mitigated, patency rates will increase as dilation is restored and blood flow is unhindered.
Conclusion
With the advent of new biomaterials such as nitinol, stent technology has progressed greatly due to the unique biochemical properties of such materials. The findings of these studies confirm that nitinol is a material better suited to stent applications than stainless steel because nitinol’s composition allows it to slow the rate of corrosion in the body to minimal levels, which minimizes negative immune response and corrosion, two primary factors that cause restenosis. Nitinol stents are already being manufactured and tested on human patients, and trials have been largely successful, improving the quality of life for many patients suffering from PAD. In 2015, nitinol stents manufactured by Abbot were found to meet the safety and efficacy criteria of the Food and Drug Administration (FDA) (7). As stent technology and vascular intervention become more advanced, the number of patients recovering from PAD will likely increase, and nitinol’s place as a prime material for stents may make it possible to improve hundreds or even thousands of lives in the future. This review aims to explain the unique properties that make nitinol biocompatible and how nitinol stents are improving outcomes for patients with PAD, but further research should be conducted on ideal stent design and manufacturing. Stent design is the most impactful factor in the functionality of the implant, so an experimental study testing novel designs and its long-term patency and restenosis rates should be conducted to help researchers determine the best design for the implant.
References
1. Peripheral artery disease (PAD). Mayo Clinic, (2021). 2. R.E. Lee, Electrochemical, polarization, and crevice corrosion testing of nitinol 60, a supplement to the ECLSS sustaining materials compatibility study. NASA Technical Reports Server, (2016). 3. S. Sullivan et al., Effects of oxide layer composition and radial compression on nickel release in nitinol stents. Shape Memory and Superelasticity 1, 319-327 (2015). doi: https://doi.org/10.1007/ s40830-015-0028-x. 4. S. Gür et al., Central venous occlusion in hemodialysis access: comparison between percutaneous transluminal angioplasty alone and nitinol or stainless-steel stent placement. Diagnostic and Interventional Imaging 100, 485–492 (2019). doi: 10.1016/j.diii.2019.03.011 5. M. Elmahdy, Long-term primary patency rate after nitinol self-expandable stents implantation in long totally occluded femoropopliteal lesions. Heart Lung Circ. 26, 6 (2017). doi: 10.1016/j. hlc.2016.09.011 6. M. Nakamura, Nitinol self-expanding stents for the treatment of obstructive superficial femoral artery disease: three-year results of the reliable Japanese multicenter study. Annals of Vascular Diseases 11, 324–334 (2018). doi: 10.3400/avd.oa.18-00067 7. L. Garcia et al., Wire-interwoven nitinol stent outcome in the superficial femoral and proximal popliteal arteries. Circulation: Cardiovascular Interventions 8, 5 (2015). doi: 0.1161/CIRCINTERVENTIONS.113.000937
