Perfect Resonant Absorption of Guided Water Waves by Autler-Townes Splitting

The control of guided water wave propagation based on the Autler-Townes splitting resonance concept is demonstrated experimentally, numerically, and theoretically. Complete wave absorption is achieved using an asymmetric pointlike scatterer made of two closely spaced resonant side channels connected to a guide and designed so that its energy leakage is in perfect balance with the inherent viscous losses in the system. We demonstrate that the nature of the resonators and guide junction completely controls the positions of the wave numbers at the reflection and transmission zeros on the real axis; the asymmetry of the resonators completely controls their positions on the imaginary axis. Thus, by adjusting these two independent parameters, we obtain a zero reflection and transmission.

A tunable electromagnetic metagrating

We explore electromagnetic (EM) wave incidence upon gratings of reconfigurable metamaterial cylinders, which collectively act as a metagrating, to identify their potential as reconfigurable subwavelength surfaces. The metacylinders are created by a closely spaced, microstructured array of thin plates that, in the limit of small inter-plate spacing, are described by a semi-analytical continuum model. We build upon metacylinder analysis in water waves, translating this to EM for TE polarization (longitudinal magnetic field) for which the metacylinders exhibit anisotropic scattering; this is exploited for the multiple scattering of light by an infinite metagrating of uniform cylinder radius and angle, for which we retrieve the far-field reflection and transmission spectra for plane-wave incidence. These spectra reveal unusual effects including perfect reflection and a negative Goos–Hänchen shift in the transmitted field, as well as perfect symmetry in the far-field scattering coefficients. The metagrating also hosts Rayleigh–Bloch surface waves, whose dispersion is contingent on the uniform cylinder angle, shifting under rotation towards the light-line as the cylinder angle approaches the horizontal. For both plane-wave scattering and the calculation of the array-guided modes, the cylinder angle is the principal variable in determining the wave interaction, and the metagrating is tunable simply through rotation of the constituent metacylinders.

Scattering of surface waves by a vertical truncated structured cylinder

This paper describes the solution to the problem of scattering of plane incident waves on water of constant depth by a bottom mounted circular cylinder, extending partially through the depth, which has an internal structure comprised of closely spaced thin vertical barriers between which fluid is allowed to flow. The problem is solved under full depth-dependent linearized water wave theory using an effective medium equation to describe the fluid motion in cylinder and effective boundary conditions to match that flow to the fluid region outside the cylinder. The interest in this problem lies in the development of novel solution methods for fully three-dimensional water wave interaction with bathymetric plate arrays. Results computed using this theory are compared with a shallow water approximation based on the recent work of Marangos & Porter (2021 Shallow water theory for structured bathymetry. Proc. R. Soc. A477, 20210421.) and with accurate computations of an exact representation of the geometry using a discrete set of plates. Other results highlight the resonant directional lensing effects of this type of cylindrical plate array device.

Shallow water theory for structured bathymetry

A shallow water theory is developed which applies to surface wave propagation over structured bathymetry comprising rapid abrupt fluctuations in depth between two smoothly varying levels. Using a homogenization approach coupled to the depth-averaging process which underpins shallow water modelling, governing equations for the wave elevation are derived which explicitly relate local spatially varying anisotropy of wave speeds to properties of the microstructured bed. The model is applied to two water wave scattering problems both to demonstrate the complex wave propagation characteristics exhibited by structured beds and to provide examples of how to use structured beds to engineer bespoke wave propagation. This includes propagating waves with practically zero reflection and loss of form through circular bends in channels.

125 A Case of Mistaken Identity: An Obsolete Anti-Reflux Device in An Older Patient with Variable Gastrointestinal Symptoms

Background

A frail 93-year-old lady presented with delirium and hypoxia, on a background of heart failure, constipation, cerebrovascular disease, and osteoporosis. A CTPA on admission revealed an unusual appearance of the left hypochondrium, leading to subsequent CT abdomen. This unexpectedly reported the presence of a gastric band. We therefore considered a possible misidentification as this procedure seemed unlikely in someone of her age. Her GP records revealed that she underwent surgical insertion of an Angelchik prosthesis in 1984. It transpired that our patient had experienced several longstanding symptoms, including reflux, bloating and constipation, which have all been observed in patients with Angelchik prostheses in situ.

Discussion

The Angelchik prosthesis is an anti-reflux device for patients with chronic reflux disease with or without hiatus hernia, introduced in 1979. It comprised of an elastomer shell ring filled with silicone gel, that was sited at the lower oesophagus and secured with DACRON tapes. It was initially lauded for its replicable insertion technique and promising early results with around 30,000 being inserted in mainly British and American Hospitals. However, over time it became apparent that a significant proportion of patients reported ongoing gastrointestinal symptoms due to device failure.

Serious complications such as gastric perforations were also recognised. Surgical removal was noted to be technically complex, providing further challenges. The Angelchik prosthesis therefore fell from favour after a period of use of only fifteen years, and is now rarely encountered. We discovered that our patient had experienced multiple long-standing gastrointestinal complaints potentially linked to her prosthesis, though this association had not previously been considered. Whilst her frailty meant that removal would not be pragmatic, it is uncertain if this could have been a possible consideration in the past. This device is relevant to geriatricians as many recipients are now elderly, and may report ongoing symptoms.

A19 HEALTH CARE UTILIZATION DIFFERENCES BETWEEN FIRST NATIONS AND THE GENERAL POPULATION WITH INFLAMMATORY BOWEL DISEASE IN SASKATCHEWAN

Background

Indigenous patients with inflammatory bowel disease (IBD) have expressed concerns about barriers to access IBD care. The limited evidence of IBD among Indigenous people highlights the need for studies evaluating access to IBD care in this population.

Aims

We aimed to compare health care utilization between First Nations (FNs) and individuals from the general population (GP) diagnosed with IBD in Saskatchewan (SK).

Methods

A population-based retrospective cohort study was conducted using administrative health databases of SK from 1998 to 2017 fiscal years. As a patient-oriented research initiative, outcomes of interest were chosen in collaboration with Indigenous patients and family advocates. A validated algorithm requiring multiple health care contacts was applied to identify incident IBD cases. The self-declared FN status variable was used to divide IBD cases between FNs and the general population (GP). To balance the groups, 1:5 age and sex matching was applied. Cox-proportional models were used to estimate hazard ratios (HRs) and 95% confidence intervals (95%CI). Stratified analysis was completed for those diagnosed before and after 2008 (pre- and post-biologic eras).

Results

A matched cohort with 696 IBD incident cases was created (FN=116, GP=580). Comparing health care utilization of FNs and individuals from the GP with IBD, there were no statistically significant differences in outpatient gastroenterology visits (FNs=81.0%, GP=83.6%), colonoscopies (FNs=91.4%, GP=86.9%), and surgeries for IBD (FNs=31.0%, GP=33.5%). We observed differences in prescription claims for any medication for IBD (FNs=79.3%, GP=89.3%) and 5-aminosalicylic acid (5-ASA) claims (FNs=75.9%, GP=81.4%). The HRs adjusted by rural/urban residence and diagnostic type showed differences in prescription claims for any IBD medication (HR=0.52, 95%CI 0.41–0.65) and 5-ASA (HR=0.57, 95%CI 0.45–0.72). In the pre-biologic era, FNs had a lower risk of having a prescription claim for any IBD medication (HR=0.32, 95%CI 0.23–0.45) and 5-ASA (HR=0.33, 95%CI 0.24–0.47), respectively. These differences were not significant in the post-biologic era.

Conclusions

Our study identified an inverse association between FN status and having prescription medication claims for IBD in SK. We considered multiple confounding variables when evaluating this association but could not control by disease severity. Thus, this association might reflect a barrier to access IBD medications or that FNs with IBD might present a milder disease. Further studies should continue evaluating access to IBD care, medication use, and disease severity among FNs living with IBD.

Funding Agencies

Saskatchewan Centre for Patient-Oriented Research (SCPOR), Saskatchewan Health Research Foundation (SHRF), and College of Medicine, University of Saskatchewan.

A4 A FRAMEWORK TO STUDY INFLAMMATORY BOWEL DISEASE AMONG INDIGENOUS PEOPLES AND PRELIMINARY RESULTS FROM SASKATCHEWAN, CANADA

Background

Inflammatory Bowel Disease (IBD) is a chronic condition with significant life-threatening disease-related complications and reductions in quality of life if left untreated. Despite available research about IBD in the general population, there is limited-to-no evidence about IBD among Indigenous peoples in Canada and around the world.

Aims

We aimed to define a collaborative framework, estimate the prevalence and incidence rates of IBD among First Nations in Saskatchewan, Canada, and explore perceptions of IBD among Indigenous peoples in the province.

Methods

This study began when Indigenous patients shared their health experiences with IBD with research team members. An interdisciplinary research team was formed including Indigenous patient and family advocates (IPFAs, Indigenous patients living with IBD and parents of an Indigenous person with IBD), an IBD gastroenterologist, knowledge users, and Indigenous and non-Indigenous researchers. Our research team committed to raise awareness of IBD among Indigenous peoples within Indigenous communities and among health care providers and to advocate for better healthcare and well-being by providing evidence of IBD among Indigenous peoples living with IBD in Saskatchewan. We defined a mixed methodology. The first phase of the study used Saskatchewan administrative health data to estimate the prevalence and incidence rates with 95% confidence intervals (95%CI) of IBD among First Nations. The second phase of the study will use a photovoice methodology to gather “the voices” of Indigenous peoples with IBD, encouraging self-interpretation of pictures, engaging their communities, and empowering them with the study findings.

Results

The IPFAs play a critical role in the project by sharing their experiences and defining the directions of the project, as well as defining our research framework (Figure 1). Preliminary results show that the prevalence of IBD among First Nations in Saskatchewan increased from 66 (95%CI 65–68) per 100,000 population in 1999 to 148 (95%CI 145–151) per 100,000 people in 2015. In contrast, the incidence rates appear to be stable over time, 11/100,000 (95%CI 4–24) in 1999 and 11/100,000 (95%CI 5–20) in 2015. We started recruiting participants for the photovoice study in September 2019.

Conclusions

This ground-breaking patient-driven study is the first stage to improve health among Indigenous peoples living with IBD in Saskatchewan. This project will generate community-engaged knowledge and expertise to inform the development of an Indigenous IBD framework that could promote better and knowledge-based healthcare for Indigenous peoples with IBD in Canada and worldwide.

Funding Agencies

CIHRSaskatchewan Health Research Foundation (SHRF) and Saskatchewan Centre for Patient-Oriented Research (SCPOR)

Transmission and absorption in a waveguide with a metamaterial cavity

The reflection and transmission of acoustic waves along a waveguide of uniform width by a metamaterial cavity is considered. The metamaterial is comprised of a closely spaced array of micro-channels separated by thin plates between which the field may be damped. Exact equations governing the field in the microstructured metamaterial cavity are replaced by an effective field using the homogenisation approach. This allows a solution to be formulated in terms of an integral equation across the interface between the metamaterial cavity and the waveguide. Attention focuses on the resonant and damping effects of a metamaterial cavity of tapered height where rainbow trapping phenomena are encountered. It is shown that near-perfect broadbanded absorption of the incoming wave energy can be achieved.

Treating and Reducing Anxiety and Pain in the Paediatric Emergency Department (The Trapped 2 Survey): Time for Action – A Pediatric Emergency Research Canada (Perc) Project

BACKGROUND: Multiples barriers to appropriate analgesia provision are reported in the paediatric emergency department (PED), including limited accessibility to effective strategies.

OBJECTIVES: To evaluate the improvement in the accessibility of pain and anxiety management strategies in PEDs in Canada, after the creation of a national pediatric pain quality improvement collaborative, through Pediatric Emergency Research Canada.

DESIGN/METHODS: In 2013, the TRAPPED 1 survey was administered across Canadian PEDs, in order to evaluate the resources in place for pain and anxiety management. Subsequent to the TRAPPED 1, a pain Quality Improvement Collaborative was created to stimulate the implementation of new pain and anxiety management strategies through the sharing of information between PEDs. The TRAPPED 2 survey involved a cross sectional survey similar to TRAPPED 1, after a two year interval. Its main focus was to evaluate the improvement in the accessibility of specific, preferred strategies reported by each centre, after participating in this collaborative between December 2014 to November 2015, and then working to implement change within their own PEDs.

RESULTS: All 15/15 Canadian PEDs responded to TRAPPED 1 in 2013. In 2014, 11/15 agreed to participate in the national pain Quality Improvement Collaborative, with a goal of introducing new pain and anxiety management strategies within their own PEDs. An in-person meeting, email communication, and telephone meetings were employed for information sharing regarding experiences/challenges within each of the participating centres. Newly introduced strategies included education, distraction, nurse-initiated protocols, and policies/education to encourage the use of intranasal (IN) medications. 11/11 centres have responded to the interim follow up surveys in 2015. At the end of the project (Fall 2105), 15/15 Canadian PEDs agreed to complete the final TRAPPED 2 survey. When comparing the results of 2015 with 2013, an increased number of PEDs used face-based pain scales (14/15 vs 6/15) and behavioural scales (5/15 vs 1/15) for pain assessment of school-aged children and infants, respectively. Use of assessment room wall decoration for distraction increased from 7/15 to 11/15. Reminder posters for pain management at triage increased from 4/15 to 6/15. Availability of electronic distraction strategies (e.g. using tablets) increased from 4/15 to 10/15 centres. For skin-piercing procedure, nurses initiated protocols to use topical anesthetic creams and oral sucrose was available in 12/15 centres (compared to 10/15 in 2013), and 14/15 (compared to 12/15 in 2013) respectively. Availability of IN medications increased in the last two years: fentanyl 14/15 (9/15 in 2013) and midazolam in at least 10/15 (8/15 in 2013). 10/11 PEDS involved in the QI strategy reported the implementation of at least one of their strategies identified.

CONCLUSION: This study suggests that the use of a pain Quality Improvement Collaborative may improve the introduction of new strategies in multiple PEDs. It can help guide other centres when introducing new strategies to reduce pain and anxiety for children in community EDs. Future research can focus on the sustainability of the strategies, and as well the effect of the collaborative on the introduction of other pain treatment strategies.

Paramedic rapid sequence intubation in patients with non-traumatic coma

INTRODUCTION

Pre-hospital intubation by paramedics is widely used in comatose patients prior to transportation to hospital, but the optimal technique for intubation is uncertain. One approach is paramedic rapid sequence intubation (RSI), which may improve outcomes in adult patients with traumatic brain injury. However, many patients present to emergency medical services with coma of non-traumatic cause and the role of paramedic RSI in these patients remains uncertain.

METHODS

The electronic Victorian Ambulance Clinical Information System was searched for the term 'suxamethonium' between 2008 and 2011. We reviewed the patient care records and included patients with suspected non-traumatic coma who were treated and transported by road-based paramedics. Demographics, intubation conditions, vital signs (before and after drug administration) and complications were recorded. Younger patients (<60 years) were compared with older patients.

RESULTS

There were 1152 paramedic RSI attempts of which 551 were for non-traumatic coma. The success rate for intubation was 97.5%. There was a significant drop in blood pressure in younger patients (<60 years) with the mean systolic blood pressure decreasing by 16 mm Hg (95% CI 11 to 21). In older patients, the systolic blood pressure also decreased significantly by 20 mm Hg (95% CI 17 to 24). Four patients suffered brief cardiac arrest during pre-hospital care, all of whom were successfully resuscitated and transported to hospital.

CONCLUSIONS

Paramedic RSI in patients with non-traumatic coma has a high procedural success rate. Further studies are required to determine whether this procedure improves outcomes.