Single and coupled cavity mode sensing schemes using a diagnostic field.

Precise optical mode matching is of critical importance in experiments using squeezed-vacuum states. Automatic spatial-mode matching schemes have the potential to reduce losses and improve loss stability. However, in quantum-enhanced coupled-cavity experiments, such as gravitational-wave detectors, one must also ensure that the sub-cavities are also mode matched. We propose what we believe to be a new mode sensing scheme, which works for simple and coupled cavities. The scheme requires no moving parts, nor tuning of Gouy phases. Instead a diagnostic field tuned to the HG20/LG10 mode frequency is used. The error signals are derived to be proportional to the difference in waist position, and difference in Rayleigh ranges, between the sub-cavity eigenmodes. The two error signals are separable by 90 degrees of demodulation phase. We demonstrate reasonable error signals for a simplified Einstein Telescope optical design. This work will facilitate routine use of extremely high levels of squeezing in current and future gravitational-wave detectors.

Observing the optical modes of parametric instability.

Parametric instability (PI) is a phenomenon that results from resonant interactions between optical and acoustic modes of a laser cavity. This is problematic in gravitational wave interferometers where the high intracavity power and low mechanical loss mirror suspension systems create an environment where three-mode PI will occur without intervention. We demonstrate a technique for real-time imaging of the amplitude and phase of the optical modes of PI yielding, to the best of the authors' knowledge, the first ever images of this phenomenon which could form part of active control strategies for future detectors.

High-flow nasal oxygen as first-line therapy for COVID-19-associated hypoxemic respiratory failure: a single-centre historical cohort study.

PURPOSE: The optimal noninvasive modality for oxygenation support in COVID-19-associated hypoxemic respiratory failure and its association with healthcare worker infection remain uncertain. We report here our experience using high-flow nasal oxygen (HFNO) as the primary support mode for patients with COVID-19 in our institution. METHODS: We conducted a single-centre historical cohort study of all COVID-19 patients treated with HFNO for at least two hours in our university-affiliated and intensivist-staffed intensive care unit (Jewish General Hospital, Montreal, QC, Canada) between 27 August 2020 and 30 April 2021. We report their clinical characteristics and outcomes. Healthcare workers in our unit cared for these patients in single negative pressure rooms wearing KN95 or fit-tested N95 masks; they underwent mandatory symptomatic screening for COVID-19 infection, as well as a period of asymptomatic screening. RESULTS: One hundred and forty-two patients were analysed, with a median [interquartile range (IQR)] age of 66 [59-73] yr; 71% were male. Patients had a median [IQR] Sequential Organ Failure Assessment Score of 3 [2-3], median [IQR] oxygen saturation by pulse oximetry/fraction of inspired oxygen ratio of 120 [94-164], and a median [IQR] 4C score (a COVID-19-specific mortality score) of 12 [10-14]. Endotracheal intubation occurred in 48/142 (34%) patients, and overall hospital mortality was 16%. Barotrauma occurred in 21/142 (15%) patients. Among 27 symptomatic and 139 asymptomatic screening tests, there were no cases of HFNO-related COVID-19 transmission to healthcare workers. CONCLUSION: Our experience indicates that HFNO is an effective first-line therapy for hypoxemic respiratory failure in COVID-19 patients, and can be safely used without significant discernable infection risk to healthcare workers.

RéSUMé: OBJECTIF: La modalité non invasive optimale pour le soutien en oxygène lors d'insuffisance respiratoire hypoxémique liée à la COVID-19 et son association avec l'infection des travailleurs de la santé restent incertaines. Nous rapportons ici notre expérience avec l'utilisation de canules nasales à haut débit (CNHD) comme principale modalité de soutien pour les patients atteints de COVID-19 dans notre établissement. MéTHODE: Nous avons mené une étude de cohorte historique monocentrique de tous les patients atteints de COVID-19 traités par CNHD pendant au moins deux heures dans notre unité de soins intensifs affiliée à l'université et dotée d'intensivistes (Hôpital général juif, Montréal, QC, Canada) entre le 27 août 2020 et le 30 avril 2021. Nous rapportons leurs caractéristiques cliniques et leurs résultats. Les travailleurs de la santé de notre unité ont soigné ces patients dans des chambres individuelles à pression négative en portant des masques KN95 ou N95 ajustés; ils ont subi un dépistage symptomatique obligatoire de l'infection à la COVID-19, ainsi qu'un dépistage en période asymptomatique. RéSULTATS: Cent quarante-deux patients ont été analysés, avec un âge médian [écart interquartile (ÉIQ)] de 66 [59-73] ans; 71 % étaient des hommes. Les patients avaient un score SOFA (Sequential Organ Failure Assessment) médian [ÉIQ] de 3 [2, 3], un ratio médian [ÉIQ] de saturation en oxygène par oxymétrie de pouls/fraction d'oxygène inspiré de 120 [94-164], et un score 4C (un score de mortalité spécifique à la COVID-19) médian [ÉIQ] de 12 [10­14]. Dans l'ensemble, 48/142 patients (34 %) ont reçu une intubation endotrachéale, et la mortalité hospitalière globale était de 16 %. Un barotraumatisme est survenu chez 21/142 (15 %) patients. Parmi les 27 tests de dépistage symptomatiques et 139 tests asymptomatiques, aucun cas de transmission de COVID-19 liée aux CNHD aux travailleurs de la santé n'a été observé. CONCLUSION: Notre expérience indique que les CNHD constituent un traitement de première intention efficace pour l'insuffisance respiratoire hypoxémique chez les patients atteints de COVID-19 qui peut être utilisé en toute sécurité, sans risque d'infection significatif discernable pour les travailleurs de la santé.

Revealing optical loss from modal frequency degeneracy in a long optical cavity.

Optical loss plays a significant role in optical experiments involving optical cavities such as recycling cavities and filter cavities in laser interferometer gravitational-wave detectors. For those cavities, modal frequency degeneracy, where the fundamental and a higher order mode resonate inside the cavity simultaneously, is a potential mechanism which may bring extra optical loss to the cavity thus degrade detection sensitivity. In this paper, we report observation of modal frequency degeneracy in a large-scale suspended Fabry-Pérot cavity. The cavity g-factor is tuned by a CO2 laser heating one test mass, and the cavity finesse is obtained from a ring-down measurement of the transmitted light. We demonstrate that the modal frequency degeneracy can cause a reduction of the cavity finesse by up to ∼30%, corresponding to a ∼2-fold increase in total optical loss. To minimize optical loss in gravitational-wave detectors, the effect of modal frequency degeneracy needs to be taken into account in the design and operation of the detector.

Two dimensional photonic crystal angle sensor design.

We present a novel design for an angle sensor based on photon coupling to internal optical modes of a two dimensional photonic crystal. We show in simulation that an implementation of this design could achieve sensitivities as high as 1.61 × 106 V/rad, which in principle allows for angle measurements with a noise floor of 2.98 × 10-14 rad$/\sqrt{\textrm{Hz}}$ at the photodiode noise equivalent power. We discuss the limitations of this design and predict the impact these limitations have on the sensitivity as well as the possible ways to further increase the devices sensitivity. As a proof of concept, we demonstrate experimentally a photonic crystal with an angle sensitive mode.

Point absorbers in Advanced LIGO.

Small, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nanometer scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduce the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power buildup in second generation gravitational wave detectors (dual-recycled Fabry-Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and, hence, limit GW sensitivity, but it suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises.

Pump RIN coupling to frequency noise of a polarization-maintaining 2 µm single frequency fiber laser.

We investigated the frequency noise coupling mechanism of a 2 µm polarization-maintaining single frequency fiber laser (SFFL) theoretically and experimentally. The coupling of pump's relative intensity noise (RIN) to frequency noise of a single-frequency high-gain silica fiber laser is shown experimentally to be consistent with a theoretical model where thermal expansion and thermo-optic effect mediate the coupling. The measured and theoretical frequency noise of the 2 µm SFFL with three pump sources is compared. We find using a 1550 nm single frequency laser pump source produces the lowest frequency noise, less than 100 Hz/Hz at frequencies higher than 100 Hz.

Spurious point-of-care lactate elevation in ethylene glycol intoxication: rediscovering a clinical pearl.

A 76-year-old man was found unresponsive and brought to the emergency department. Initial workup showed profound lactic acidosis on a point-of-care arterial blood gas, without clinical signs of hypoperfusion. Investigations for types A and B lactic acidosis revealed no unifying diagnosis to explain both his altered mental status and profound lactic acidosis. A toxicology workup revealed an increased osmolar gap and an elevated ethylene glycol level. The lactic acidosis and his mental status completely normalised within 8 hours of renal replacement therapy initiation and fomepizole administration. Ethylene glycol metabolites have similar molecular structure with L-lactate. Some blood gas analysers are unable to differentiate them, resulting in an artefactual lactate elevation. Our case highlights the importance of recognising a falsely elevated lactate, which should raise clinical suspicion of ethylene glycol poisoning, as the treatment is time-sensitive to prevent complications and mortality.

A Paralyzing Case of Myalgias.

BACKGROUND Myalgia, which describes muscle pain or soreness, is a common presenting complaint encountered in the Emergency Department, in inpatient settings and in outpatient settings. Its differential diagnosis is broad and includes benign as well as more serious clinical entities. Some of the common causes of myalgias include viral infections, strenuous exercise, and medications. Succinylcholine is a well-known neuromuscular blockade agent that is frequently used for rapid sequence intubation and short surgeries. CASE REPORT We present the case of a 70-year-old male who presented to the Emergency Department with a chief complaint of acute, severe onset diffuse myalgia leading to the inability to mobilize. He was being investigated for recent onset generalized lymphadenopathy and had undergone a diagnostic lymph node biopsy under general anesthesia 2 days prior to his presentation. He was diagnosed with presumed succinylcholine-induced myalgias after other etiologies were deemed less likely with thorough history, physical examination, and laboratory investigations. Succinylcholine binds nicotinic acetylcholine receptors of the neuromuscular junction and produces prolonged depolarization during which activation of the muscle is blocked. Initial depolarization of the neuromuscular junction induces hectic fasciculation of the muscle fibers, which in turn may be responsible for the occurrence of post-operative myalgias (POM). This entity can be severe and debilitating and is self-limited. CONCLUSIONS Succinylcholine remains a commonly used agent in anesthesia and succinylcholine-induced myalgia should remain in the differential diagnosis of acute, non-inflammatory myalgia. Its recognition can help avoid unwarranted, possibly invasive investigations and their associated additional healthcare costs.

Modular suspension system with low acoustic coupling to the suspended test mass in a prototype gravitational wave detector.

Low acoustic loss suspension systems are essential components in low thermal noise instruments including gravitational wave detectors. Monolithic fused silica suspensions have been used successfully with fused silica test masses but may not be suitable in next generation detectors that may use sapphire or silicon test masses. Here we report a study of a modular suspension system with high replaceability. The system is based on high pressure gravitationally attached mechanical contacts which have been previously shown to contribute low acoustic losses to sapphire resonators. Here we combine high pressure contacts with cantilevers and fibres to create sets of four suspension modules which are shown to have low loss contributions to fused silica test masses in a 74-m high-finesse optical cavity. Results are combined with finite element simulations to estimate the strain energy distributions of the eigenmodes. By combining the simulations and measurement results, the test mass loss angle due to the coupling to the suspension system was estimated. The modular suspension system is shown to contribute <10% to the total test mass acoustic loss. Such suspension systems could have applications for test masses or subsystems in next generation gravitational wave detectors.

First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO.

Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher-order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15 538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electrostatic actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nN was required to maintain the acoustic mode at its minimum amplitude.

Analytical model for ring heater thermal compensation in the Advanced Laser Interferometer Gravitational-wave Observatory.

Advanced laser interferometer gravitational-wave detectors use high laser power to achieve design sensitivity. A small part of this power is absorbed in the interferometer cavity mirrors where it creates thermal lenses, causing aberrations in the main laser beam that must be minimized by the actuation of "ring heaters," which are additional heater elements that are aimed to reduce the temperature gradients in the mirrors. In this article we derive the first, to the best of our knowledge, analytical model of the temperature field generated by an ideal ring heater. We express the resulting optical aberration contribution to the main laser beam in this axisymmetric case. Used in conjunction with wavefront measurements, our model provides a more complete understanding of the thermal state of the cavity mirrors and will allow a more efficient use of the ring heaters in the Advanced Laser Interferometer Gravitational-wave Observatory.

Novel low-resource intervention reduces urinary catheter use and associated urinary tract infections: role of outcome measure bias?

BACKGROUND: Previous interventions targeting nosocomial urinary tract infections have reduced catheterization and infections, but they require significant resources and may be susceptible to misclassification and surveillance bias. We sought to determine the effectiveness of a novel intervention at reducing catheterization and infections while exploring the potential for bias. METHODS: We conducted a prospective study of a brief monthly in-person educational intervention focusing on appropriate urinary catheter use. RESULTS: We studied 1,335 patients (13,753 patient days) on 1 control and 1 intervention ward. After the intervention, the device utilization rate was significantly reduced, with a relative risk of 0.49 (95% confidence interval [CI], 0.32-0.76; P = .001) versus 1.02 (95% CI, 0.58-1.82; P = .93) for controls. Both wards demonstrated a reduction in catheter-associated infections after intervention, with an intervention relative risk of 0.42 (95% CI, 0.16-1.08; P = .07) and 0.51 (95% CI, 0.22-1.20; P = .12) for controls. There was no change in the rate of all nosocomial urine infections, with an intervention relative risk of 0.79 (95% CI, 0.38-1.65; P = .53) and 0.89 (95% CI, 0.48-1.67; P = .72) for controls. CONCLUSION: Our study demonstrates that our novel educational intervention significantly reduces urinary catheter use in hospitalized patients. The trend towards reduced catheter-associated infections after intervention, coupled with the absence of an improvement in all nosocomial infections supports a potential role of misclassification bias. We suggest that future prospective investigations explore this phenomenon using more robust outcome measures.