Study of middle ear disease using tympanometry in general practice.

Tympanometry was used to provide evidence of middle ear effusions in a prospective study of middle ear disease in 264 children aged 3 months to 6 years in general practice. Adequate measurements on both ears were obtained in 220 children, of whom 68 (31%) had evidence of middle ear effusion in one ear (29 children) or both ears (39 children) at entry to the study. In 28 (42%) of the 68 children persistence of the tympanometric findings was recorded for at least three months. Children of European descent were more likely to have evidence of middle ear effusion at the initial examination compared with African and West Indian children, as were those children whose siblings had a positive history of otitis media compared with those whose siblings had no such history. Children under 3 years were more likely to have evidence of an effusion than older children. Middle ear effusion as shown by tympanometry was not associated with a previous history of otitis media in the child but was associated with recent symptoms of respiratory infection or otalgia. A previous consultation for otitis media was, however, strongly associated with a greater likelihood of a consultation for otitis media during the follow up period. Comparing evidence of effusion by tympanometry with that by pneumatic otoscopy showed that using the appearance of the eardrum alone the sensitivity of otoscopy was 55%; the addition of mobility improved the sensitivity to 76% with little reduction in specificity. Further studies on populations using tympanometry are needed to determine the natural history, aetiology, and indications for referring children with middle ear effusion.     

Functional assessment of moisture influenced cadaveric tympanic membrane using phase shift‐resolved optical Doppler vibrography

An elevated relative moisture in the external ear canal and middle ear cavity may predispose to chronic otorrhea and related infections along with abnormal tympanic membrane (TM) vibration patterns. Therefore, phase shift‐resolved optical Doppler vibrography (ODV) was used for vibration assessments of moisture influenced cadaveric TM. ODV was applied to generate time resolved cross‐sectional and volumetric vibrographs of a cadaveric TM, driven acoustically at several frequencies. In order to analyze the effect of moisture on TM, homogenous moisture conditions were provided by soaking the cadaveric TM specimens in 1× phosphate buffer saline with a pH of 7.4. The TM specimen was exposed to a rapidly switchable frequency generator during the ODV image acquisition. The experiment was conducted for 3 hours and the cadaveric TM was exposed to each frequency with an interval of 30 minutes. Acquired phase shift‐resolved ODV assessments revealed a depth dependent vibration tendency between the applied frequencies, along with a decline in the moisture level of the cadaveric TM specimen. Thus, the ODV method can aid our understanding of sound conduction in the middle ear, thus supporting the diagnosis of TM diseases.     

Smartphone‐based spectral imaging otoscope: System development and preliminary study for evaluation of its potential as a mobile diagnostic tool

We develop a novel smartphone‐based spectral imaging otoscope for telemedicine and examine its capability for the mobile diagnosis of middle ear diseases. The device was applied to perform spectral imaging and analysis of an ear‐mimicking phantom and a normal and abnormal tympanic membrane for evaluation of its potential for the mobile diagnosis. Spectral classified images were obtained via online spectral analysis in a remote server. The phantom experimental results showed that it allowed us to distinguish four different fluids located behind a semitransparent membrane. Also, in the spectral classified images of normal ears (n = 3) and an ear with chronic otitis media (n = 1), the normal and abnormal regions in each ear could be quantitatively distinguished with high contrast. These preliminary results thus suggested that it might have the potentials for providing quantitative information for the mobile diagnosis of various middle ear diseases.     

Non‐invasive optical assessment of viscosity of middle ear effusions in otitis media

Eustachian tube dysfunction can cause fluid to collect within the middle ear cavity and form a middle ear effusion (MEE). MEEs can persist for weeks or months and cause hearing loss as well as speech and learning delays in young children. The ability of a physician to accurately identify and characterize the middle ear for signs of fluid and/or infection is crucial to provide the most appropriate treatment for the patient. Currently, middle ear infections are assessed with otoscopy, which provides limited and only qualitative diagnostic information. In this study, we propose a method utilizing cross‐sectional depth‐resolved optical coherence tomography to noninvasively measure the diffusion coefficient and viscosity of colloid suspensions, such as a MEE. Experimental validation of the proposed technique on simulated MEE phantoms with varying viscosity and particulate characteristics is presented, along with some preliminary results from in vivo and ex vivo samples of human MEEs.

In vivo Optical Coherence Tomography (OCT) image of a human tympanic membrane and Middle Ear Effusion (MEE) (top), with a CCD image of the tympanic membrane surface (inset). Below is the corresponding time‐lapse M‐mode OCT data acquired along the white dotted line over time, which can be analyzed to determine the Stokes–Einstein diffusion coefficient of the effusion.     

The mobility gap: estimating mobility thresholds required to control SARS-CoV-2 in Canada

BACKGROUND:Nonpharmaceutical interventions remain the primary means of controlling severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) until vaccination coverage is sufficient to achieve herd immunity. We used anonymized smartphone mobility measures to quantify the mobility level needed to control SARS-CoV-2 (i.e., mobility threshold), and the difference relative to the observed mobility level (i.e., mobility gap).METHODS:We conducted a time-series study of the weekly incidence of SARS-CoV-2 in Canada from Mar. 15, 2020, to Mar. 6, 2021. The outcome was weekly growth rate, defined as the ratio of cases in a given week versus the previous week. We evaluated the effects of average time spent outside the home in the previous 3 weeks using a log-normal regression model, accounting for province, week and mean temperature. We calculated the SARS-CoV-2 mobility threshold and gap.RESULTS:Across the 51-week study period, a total of 888 751 people were infected with SARS-CoV-2. Each 10% increase in the mobility gap was associated with a 25% increase in the SARS-CoV-2 weekly case growth rate (ratio 1.25, 95% confidence interval 1.20–1.29). Compared to the prepandemic baseline mobility of 100%, the mobility threshold was highest in the summer (69%; interquartile range [IQR] 67%–70%), and dropped to 54% in winter 2021 (IQR 52%–55%); a mobility gap was present in Canada from July 2020 until the last week of December 2020.INTERPRETATION:Mobility strongly and consistently predicts weekly case growth, and low levels of mobility are needed to control SARS-CoV-2 through spring 2021. Mobility measures from anonymized smartphone data can be used to guide provincial and regional loosening and tightening of physical distancing measures.

The global toll of coronavirus disease 2019 (COVID-19) continues to grow, despite the promise of recently approved vaccines. A surge is occurring in many countries in the Northern Hemisphere, including Canada, that may take a considerable toll before vaccination is sufficiently widespread to achieve herd immunity. Nonpharmaceutical public health interventions, including physical distancing, remain the primary population-based means of controlling COVID-19.¹ Since early in the second wave, which started in September 2020, polling has suggested that most people in Canada have supported and adhered to government-directed restrictions,² and many favour strengthened measures to control community transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative viral agent of COVID-19.³SARS-CoV-2 is spread primarily through close contact with people who are infected.⁴ As with any infectious disease, contact rates are a primary driver of SARS-CoV-2 transmission.⁵ Mobility measures capturing human activity through anonymized tracking of smartphones are believed to be reasonable proxies of contact rates outside of one’s own home; these measures can provide more timely and reliable sources of information on contact rates compared with time-use surveys or contact tracing.^6–8Aggregated smartphone mobility data are provided by a number of software developers and have been used to quantify the impact of policy on mobility in Canada,⁹ the effectiveness of lockdowns aiming to reduce the spread of SARS-CoV-2^10–12 and loopholes from excessively localized measures.¹³ Mobility metrics are helpful for gauging the effect of restrictions on behaviour, but do not, on their own, show decision-makers whether restrictions in place at the time are sufficient to curtail the spread of SARS-CoV-2. In this study, we evaluated the association between smartphone mobility measures and the spread of SARS-CoV-2 in Canada, both nationally and provincially, between March 2020 and March 2021. We also sought to quantify the mobility level needed to control COVID-19 (i.e., the mobility threshold), and the difference between observed mobility levels and the threshold (i.e., the mobility gap). We hypothesized that lower mobility levels may be needed in provinces with larger urban populations in the winter compared with more rural provinces in the summer.¹⁴     

Burden of noninfluenza respiratory viral infections in adults admitted to hospital: analysis of a multiyear Canadian surveillance cohort from 2 centres

BACKGROUND:Data on the outcomes of noninfluenza respiratory virus (NIRV) infections among hospitalized adults are lacking. We aimed to study the burden, severity and outcomes of NIRV infections in this population.METHODS:We analyzed pooled patient data from 2 hospital-based respiratory virus surveillance cohorts in 2 regions of Canada during 3 consecutive seasons (2015/16, 2016/17, 2017/18; n = 2119). We included patients aged ≥ 18 years who developed influenza-like illness or pneumonia and were hospitalized for management. We included patients confirmed positive for ≥ 1 virus by multiplex polymerase chain reaction assays (respiratory syncytial virus [RSV], human rhinovirus/enterovirus (hRV), human coronavirus (hCoV), metapneumovirus, parainfluenza virus, adenovirus, influenza viruses). We compared patient characteristics, clinical severity conventional outcomes (e.g., hospital length-of stay, 30-day mortality) and ordinal outcomes (5 levels: discharged, receiving convalescent care, acute ward or intensive care unit [ICU] care and death) for patients with NIRV infections and those with influenza.RESULTS:Among 2119 adults who were admitted to hospital, 1156 patients (54.6%) had NIRV infections (hRV 14.9%, RSV 12.9%, hCoV 8.2%) and 963 patients (45.4%) had influenza (n = 963). Patients with NIRVs were younger (mean 66.4 [standard deviation 20.4] yr), and more commonly had immunocompromising conditions (30.3%) and delay in diagnosis (median 4.0 [interquartile range (IQR) 2.0–7.0] days). Overall, 14.6% (12.4%–19.5%) of NIRV infections were acquired in hospital. Admission to ICU (18.2%, median 6.0 [IQR 3.0–13.0] d), hospital length-of-stay (median 5.0 [IQR 2.0–10.0] d) and 30-day mortality (8.4%; RSV 9.5%, hRV 6.6%, hCoV 9.2%) and the ordinal outcomes were similar for patients with NIRV infection and those with influenza. Age > 60 years, immunocompromised state and hospital-acquired viral infection were associated with worse outcomes. The estimated median cost per acute care admission was $6000 (IQR $2000–$16 000).INTERPRETATION:The burden of NIRV infection is substantial in adults admitted to hospital and associated outcomes may be as severe as for influenza, suggesting a need to prioritize therapeutics and vaccines for at-risk people.

The global burden of lower respiratory tract infections is substantial, leading to many hospital admissions and deaths, especially among young children and older adults.¹ Respiratory viruses are responsible for almost half of such infections in adults that require in-hospital management; previous studies estimate that 28%–62% are caused by noninfluenza respiratory viruses (NIRVs).^2–4 With some geographical and seasonal variations, respiratory syncytial virus (RSV), human rhinovirus (hRV) and human coronavirus (hCoV) are among the most frequently identified NIRV infections.^1–7 Most infected adults develop mild, self-limiting illnesses, but increasing evidence suggest that NIRVs, either alone or with coinfecting bacteria, can result in severe pneumonia and death.^8,9 For instance, RSV has been shown to cause severe respiratory failure, with fatality rates comparable to or exceeding those observed among adults admitted to hospital with influenza.^10–12 Data on hRV, hCoV and other NIRVs are more limited, owing to the lack of accurate diagnostics and systematic case-finding approaches.^7–9 However, with the increasing availability of multiplex polymerase chain reaction (PCR) assays that can simultaneously detect influenza and NIRVs, these infections are now readily diagnosed as part of a syndromic approach in patients who present with acute respiratory illnesses.^2–5,13,14 The burden, clinical significance and impacts of NIRVs on the health care system remain inadequately characterized.To address this gap, we analyzed the relative frequencies, patient characteristics, location of acquisition (community or hospital), severity and clinical outcomes of patients with NIRV and influenza infections diagnosed by multiplex PCR in a cohort of adults admitted to hospital in 2 large Canadian health care centres during a 3-year surveillance period. The associated health care resource use was also estimated.     

Characterization of mucins in human middle ear and Eustachian tube

Mucins are important glycoproteins in the mucociliary transport system of the middle ear and Eustachian tube. Little is known about mucin expression within this system under physiological and pathological conditions. This study demonstrated the expression of MUC5B, MUC5AC, MUC4, and MUC1 in the human Eustachian tube, whereas only MUC5B mucin expression was demonstrated in noninflamed middle ears. MUC5B and MUC4 mucin genes were upregulated 4.2- and 6-fold, respectively, in middle ears with chronic otitis media (COM) or mucoid otitis media (MOM). This upregulation of mucin genes was accompanied by an increase of MUC5B- and MUC4-producing cells in the middle ear mucosa. Electron microscopy of the secretions from COM and MOM showed the presence of chainlike polymeric mucin. These data indicate that the epithelium of the middle ear and Eustachian tube expresses distinct mucin profiles and that MUC5B and MUC4 mucins are highly produced and secreted in the diseased middle ear. These mucins may form thick mucous effusion in the middle ear cavity and compromise the function of the middle ear.     

In vivo noninvasive measurement of spatially resolved corneal elasticity in human eyes using Lamb wave optical coherence elastography

Current elastography techniques are limited in application to accurately assess spatially resolved corneal elasticity in vivo for human eyes. The air‐puff optical coherence elastography (OCE) with an eye motion artifacts correction algorithm is developed to distinguish the in vivo cornea vibration from the eye motion and visualize the Lamb wave propagation clearly in healthy subjects. Based on the Lamb wave model, the phase velocity dispersion curve in the high‐frequency is calculated to obtain spatially resolved corneal elasticity accurately with high repeatability. It is found that the corneal elasticity has regional variations and is correlated with intraocular pressure, which suggests that the method has the potential to provide noninvasive measurement of spatially resolved corneal elasticity in clinical practice.     

中耳胆脂瘤的影像诊断:高分辨率计算机断层成像与磁共振成像的比较研究

目的:评估和比较高分辨率计算机断层成像(high resolution computer tomography,HRCT)与磁共振成像(magnetic resonance imaging,MRI)对中耳胆脂瘤的诊断价值。方法:回顾性分析临床初步诊断为中耳胆脂瘤患者55人(63耳)在术前5天内进行的16排HRCT和1.5T MRI诊断结果,以病理诊断为基础对HRCT和MRI的诊断结果进行对比研究,统计分析HRCT和MRI的灵敏度、特异度、阳性预期值、阴性预期值,以及Kappa检验两者之间的内在观察一致性。结果:63耳中,病理确诊为中耳胆脂瘤40耳。HRCT正确诊断30例,假阳性11例,假阴性10例,灵敏度、特异度、阳性预期值以及阴性预期值分别为75%、52.17%、73.17%、54.55%。MRI正确诊断37例,假阳性和假阴性各为3例,灵敏度、特异度、阳性预期值以及阴性预期值分别为92.5%、86.96%、75%和86.96%。HRCT与MRI诊断结果之间的内在观察一致性Kappa=0.274(P0.05)。剔除既往有手术史的10耳,只针对无手术史的53耳,HRCT与MRI诊断结果之间的内在观察一致性增高,吻合度一般,Kappa=0.462(P0.05)。结论:MRI的总体阳性检出率高于HRCT,尤其是对中耳胆脂瘤手术后复发的诊断;HRCT与MRI两者相结合对于中耳胆脂瘤的明确诊断具有互补作用。     

Retinal cross-section motion correction in three-dimensional retinal optical coherence tomography

Motion correction is an important issue in ophthalmic optical coherence tomography (OCT), and can improve the ability of data sets to reflect the physiological structures of tissues and make visualization and subsequent analysis easier. In this study, we present a novel method to correct the cross-sectional motion artifacts in retinal OCT volumes. Motion along the x-direction (fast-scan direction) is corrected through the normalized cross-correlation algorithm, while axial motion compensation is performed using the polynomial fitting method on the inner segment/outer segment (IS/OS) layer segmented by the shortest path faster algorithm (SPFA). The results of volunteers with central serous chorioretinopathy demonstrate that the proposed method effectively corrects motion artifacts in OCT volumes and may have potential application value in the evaluation of ophthalmic diseases such as diabetic retinopathy, glaucoma and age-related macular degeneration.     

Pneumatization and mesenchyme in the human middle ear

The normal pneumatization in human middle ears from Wittmaack's temporal bone collection (ENT Clinic, University of Hamburg Medical School) is investigated by means of light microscopy and compared with electron-microscopic findings in the rat. The fetal middle ear in man and rats is completely filled with mesenchyme. The compartmentalization of the middle ear by the associated mucosal folds of the ossicular chain and the middle ear pneumatization are results of the resorption of the mesenchyme present. Ultrastructural findings in the rat's middle ear reinforce light-microscopic studies and provide evidence of the fibrillogenesis which characterizes the transformation of the mesenchyme into the tunica propria of the middle ear mucosa. The microtopography of mesenchymal remnants in middle ears of neonates and in children during the first year of life, and their relevance as to the pathogenesis of the primary acquired keratoma (cholesteatoma) are discussed.     

Efficacy and safety of convalescent plasma for severe COVID-19 based on evidence in other severe respiratory viral infections: a systematic review and meta-analysis

BACKGROUND:The safety and efficacy of convalescent plasma in severe coronavirus disease 2019 (COVID-19) remain uncertain. To support a guideline on COVID-19 management, we conducted a systematic review and meta-analysis of convalescent plasma in COVID-19 and other severe respiratory viral infections.METHODS:In March 2020, we searched international and Chinese biomedical literature databases, clinical trial registries and prepublication sources for randomized controlled trials (RCTs) and nonrandomized studies comparing patients receiving and not receiving convalescent plasma. We included patients with acute coronavirus, influenza and Ebola virus infections. We conducted a meta-analysis using random-effects models and assessed the quality of evidence using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach.RESULTS:Of 1099 unique records, 6 studies were eligible, and none of these included patients with COVID-19. One nonrandomized study (n = 40) on convalescent plasma in severe acute respiratory syndrome coronavirus (SARS-CoV) provided uninformative results regarding mortality (relative risk [RR] 0.10, 95% confidence interval [CI] CI 0.01 to 1.70). Pooled estimates from 4 RCTs on influenza (n = 572) showed no convincing effects on deaths (4 RCTs, RR 0.94, 95% CI 0.49 to 1.81), complete recovery (2 RCTs, odds ratio 1.04, 95% CI 0.69 to 1.64) or length of stay (3 RCTs, mean difference −1.62, 95% CI −3.82 to 0.58, d). The quality of evidence was very low for all efficacy outcomes. Convalescent plasma caused few or no serious adverse events in influenza RCTs (RR 0.85, 95% CI 0.56 to 1.29, low-quality evidence).INTERPRETATION:Studies of non-COVID-19 severe respiratory viral infections provide indirect, very low-quality evidence that raises the possibility that convalescent plasma has minimal or no benefit in the treatment of COVID-19 and low-quality evidence that it does not cause serious adverse events.

Coronavirus disease 2019 (COVID-19) has been diagnosed in nearly 3 million individuals around the globe, of whom around 0.2 million have died.¹ Many patients with COVID-19 develop severe acute respiratory illness requiring admission to intensive care units (ICU) and often mechanical ventilation.² The case fatality rate in COVID-19 may be as high as 2.3% overall² and from 10% to 40% among severely affected individuals. ^3,4 There is an urgent need for effective therapies.Emerging epidemiologic and clinical data show both similarities and differences between severe COVID-19 and severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS).⁵ Similarly, treatment strategies for severe influenza infections tested during the H1N1 pandemic and H5N1 and H7N9 outbreaks could inform the care of patients with severe COVID-19.⁶Of the treatment options proposed for COVID-19,⁷ convalescent plasma has evidence suggesting a mortality benefit for Ebola virus infection.⁸ This intervention has also been tested in other severe acute viral respiratory infections.^6,9,10 “Convalescent plasma” refers to plasma obtained from individuals recently recovered from a viral illness, which is expected to contain the highest levels of polyclonal antibodies directed against the virus.¹¹ Similarly, “hyperimmune plasma” is collected from donors exhibiting high titres of neutralizing antibodies, independent of time elapsed since viral illness. Authors have used the terms interchangeably, and because viral neutralization is only one of the postulated mechanisms by which antibodies exert their antiviral effect, the importance of the distinction between the 2 products remains unclear (Figure 1).Open in a separate windowFigure 1:Potential mechanisms of action of anti–severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies in coronavirus disease 2019 (COVID-19). This figure illustrates the normal entry of SARS-CoV-2 in a host cell, in which membrane fusion is mediated by the interaction between the SARS-CoV-2 spike glycoprotein (red) and the angiotensin-converting enzyme 2 (ACE2) receptor (green) on the host cell, either through the cytoplasmic or endosomal route. Antibodies directed against the receptor-binding domain (RBD) of the spike protein can interfere with its interaction with the ACE2 receptor and prevent viral entry in the host cell (panel A). Antibodies directed against epitopes outside the RBD can also exert antiviral functions through other mechanisms (panels B, C and D). The relative importance of these various functions in rescuing patients from an active SARS-CoV-2 infection is unknown. Importantly, neutralization assays generally used to qualify hyperimmune products measure only 1 of the 4 mechanisms depicted here and do not necessarily correlate with the others.Clinicians have typically administered convalescent plasma to patients with viral infections whose condition deteriorated despite supportive care.⁶ Although the primary postulated mechanism of action of convalescent plasma is reduction in viremia (passive immunity),¹² an increase in host immune response (active immunity) has also been proposed.¹³ We describe in Figure 1 the possible mechanisms by which convalescent plasma inhibits severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).Systematic summaries of the available evidence regarding safety and effectiveness can inform the use of convalescent plasma in patients with COVID-19. We therefore conducted a systematic review to summarize the evidence for convalescent plasma to support a guideline on COVID-19 management.¹⁴ Because we anticipated a paucity of direct evidence addressing the use of convalescent plasma in COVID-19, we summarized the available evidence addressing convalescent plasma in the treatment of SARS, MERS and influenza, including H1N1, H7N9 and H5N1, as well as addressing possible adverse effects in patients with Ebola disease.     

Tectorial Membrane Morphological Variation: Effects upon Stimulus Frequency Otoacoustic Emissions

The tectorial membrane (TM) is widely believed to play an important role in determining the ear's ability to detect and resolve incoming acoustic information. While it is still unclear precisely what that role is, the TM has been hypothesized to help overcome viscous forces and thereby sharpen mechanical tuning of the sensory cells. Lizards present a unique opportunity to further study the role of the TM given the diverse inner-ear morphological differences across species. Furthermore, stimulus-frequency otoacoustic emissions (SFOAEs), sounds emitted by the ear in response to a tone, noninvasively probe the frequency selectivity of the ear. We report estimates of auditory tuning derived from SFOAEs for 12 different species of lizards with widely varying TM morphology. Despite gross anatomical differences across the species examined herein, low-level SFOAEs were readily measurable in all ears tested, even in non-TM species whose basilar papilla contained as few as 50-60 hair cells. Our measurements generally support theoretical predictions: longer delays/sharper tuning features are found in species with a TM relative to those without. However, SFOAEs from at least one non-TM species (Anolis) with long delays suggest there are likely additional micromechanical factors at play that can directly affect tuning. Additionally, in the one species examined with a continuous TM (Aspidoscelis) where cell-to-cell coupling is presumably relatively stronger, delays were intermediate. This observation appears consistent with recent reports that suggest the TM may play a more complex macromechanical role in the mammalian cochlea via longitudinal energy distribution (and thereby affect tuning). Although significant differences exist between reptilian and mammalian auditory biophysics, understanding lizard OAE generation mechanisms yields significant insight into fundamental principles at work in all vertebrate ears.     

Inside Cover

Optical Coherence Tomography angiography (OCTA) is widely used to image chorioretinal vasculature, with contrast that derives from scattering and motion of red blood cells (RBCs). In the rat eye, a scattering tracer highlights vertical vessels which are not visualized by intrinsic RBC scattering alone. The dependence of microvessel OCTA on angular orientation, explored in this work, represents a potential artifact that should be considered in the clinical interpretation of OCTA. Further details can be found in the article by Jun Zhu, Marcel T. Bernucci, Conrad W. Merkle, and Vivek J. Srinivasan ( e202000090) .

     

Front Cover: Photoacoustic imaging of the human placental vasculature (J. Biophotonics 4/2020)

Successful therapy of twin‐to‐twin transfusion syndrome requires accurate imaging to guide laser photocoagulation of the anastomosing placental vessels. Photoacoustic (PA) imaging is an alternative imaging method that provides contrast for hemoglobin, and in this study, it was used to visualize chorionic superficial and subsurface vasculature in human placentas. The strong potential of PA imaging to guide minimally invasive fetal therapies was demonstrated. Further details can be found in the article by Efthymios Maneas, Rosalind Aughwane, Nam Huynh, et al. ( e201900167 ).

     

Three approaches for estimating the elastic modulus of the tympanic membrane

The function of the middle ear is to resolve the acoustic impedance mismatch between the air in the ear canal and the fluid of the inner ear. Without this impedance matching, very little acoustic energy would be absorbed into the cochlea. The first step in this process is the tympanic membrane (TM) converting sound in the ear canal into vibrations of the middle ear bones. Understanding how the TM manages its task so successfully over such a broad frequency range should lead to more satisfactory and less variable TM repairs (myringoplasty). In addition, understanding the mechanics of the TM is necessary to improve the coupling between ossicular prostheses and the TM. Mathematical models have played a central role in helping the research community understand the mechanics of the eardrum. However, all models require parameters as inputs. Unfortunately, most of the parameters needed for modeling the TM are not well known. In this work, several approaches for inferring the material properties of the TM are explored. First, constitutive modeling is used to estimate an elastic modulus based on the elastic modulus of collagen and experimentally observed fiber densities. Second, experimental tension and bending test results from the literature are re-interpreted using composite laminate theory. Lastly, dynamic measurements of the cat TM are used in conjunction with a composite shell model to bound the material parameters. Values from the literature, both measurement and modeling efforts, and from the present analysis are brought together to form a coherent picture of the TM's material properties. In the human, the data bound the elastic modulus between 0.1 and 0.3 GPa. In the cat, the data suggest a range of 0.1-0.4 GPa. These values are significantly higher than previous estimates.     

3D finite element model of the chinchilla ear for characterizing middle ear functions

Chinchilla is a commonly used animal model for research of sound transmission through the ear. Experimental measurements of the middle ear transfer function in chinchillas have shown that the middle ear cavity greatly affects the tympanic membrane (TM) and stapes footplate (FP) displacements. However, there is no finite element (FE) model of the chinchilla ear available in the literature to characterize the middle ear functions with the anatomical features of the chinchilla ear. This paper reports a recently completed 3D FE model of the chinchilla ear based on X-ray micro-computed tomography images of a chinchilla bulla. The model consisted of the ear canal, TM, middle ear ossicles and suspensory ligaments, and the middle ear cavity. Two boundary conditions of the middle ear cavity wall were simulated in the model as the rigid structure and the partially flexible surface, and the acoustic-mechanical coupled analysis was conducted with these two conditions to characterize the middle ear function. The model results were compared with experimental measurements reported in the literature including the TM and FP displacements and the middle ear input admittance in chinchilla ear. An application of this model was presented to identify the acoustic role of the middle ear septa—a unique feature of chinchilla middle ear cavity. This study provides the first 3D FE model of the chinchilla ear for characterizing the middle ear functions through the acoustic-mechanical coupled FE analysis.     

Chaperoning transmembrane helices in the lipid bilayer

Elimination of membrane proteins often requires recognition of their transmembrane domains (TMDs) in the lipid bilayer. In this issue, Arines et al. (2020. J. Cell Biol. https://doi.org/10.1083/jcb.202001116) show that in Saccharomyces cerevisiae, the vacuole-associated Rsp5 ubiquitin ligase uses a TMD in substrate adaptor Ssh4 to recognize membrane helices in Ypq1, which targets this lysine transporter for lysosomal degradation during lysine starvation.

In eukaryotic cells, protein quality control (PQC) mediates the degradation of not only aberrant but also unwanted polypeptides, safeguarding both the quality and quantity of the cellular proteome (1). A central goal in PQC research is to delineate the mechanism of substrate selection, which, if inappropriately executed, could lead to undesired destruction of functional proteins and thus the collapse of the proteostasis network. For soluble proteins that succumb to PQC, it is usually the surface exposure of hydrophobic elements that alerts cellular chaperones to potential folding catastrophe (2). Chaperones often serve a dual triaging role: while giving their clients additional time to fold, they can also interface with degradation machineries such as the ubiquitin proteasome system or lysosomes, causing the elimination of terminally misfolded or unwanted polypeptides.Unlike PQC of soluble proteins, substrate recognition for membrane proteins bearing abnormal transmembrane domain (TMD) is largely unknown, even for the best characterized PQC process, ER-associated degradation (ERAD; 3). Early studies on PQC of unassembled T cell receptor α chain (TCRα) showed that the single TMD of TCRα contains two charged residues, which are thermodynamically unfavored in the lipid environment and thus must be shielded when TCRα assembles with CD3σ. Accordingly, unassembled TCRα is eliminated by ERAD via a mechanism dependent on these charged residues (4), but TMD-specific chaperones responsible for recognizing charged residues in the lipid bilayer have not been identified. Likewise, recent investigations into the function of the Hrd1 ubiquitin ligase suggested a role for the TMDs of Hrd1 in recognition of specific aberrant membrane proteins in ERAD (5). Cryo-EM studies further showed two juxtaposed central cavities with a lateral gate poised to receive TMDs in the yeast Hrd1 complex (6), but how aberrant TMDs in ERAD substrates are recognized and retrotranslocated by Hrd1 remains an open question.The issue of substrate recognition becomes even more complex for feedback-regulated degradation of unwanted membrane proteins. In this case, substrates are initially stable and functionally essential, but a change in environmental cues renders them dispensable and results in a short-lived fate. One such example is the sterol-regulated degradation of a sterol-synthesizing enzyme called HMG-CoA reductase (HMGR). HMGR is a stable ER protein when the sterol level is low, but an increase in membrane sterol abundance alters the conformation of a sterol-sensing domain in HMGR, exposing an element functionally equivalent to a degron in short-lived proteasomal substrates (7). Despite extensive studies, the molecular signature of the degron in HMGR is still undefined, let alone the molecular basis of its recognition. In this issue, Arines and colleagues investigate how Ypq1, a multi-spanning lysine transporter of the yeast vacuole, is regulated by lysine availability, a regulated membrane protein turnover event analogous to HMGR degradation. Their study identifies critical residues in Ypq1 TMDs for its turnover and establishes the Rsp5 ubiquitin ligase adaptor Ssh4 as a TMD-specific chaperone that recognizes these elements (8).Ypq1 is a seven-transmembrane, PQ loop–containing lysine transporter localized to the yeast vacuole membrane. Under lysine-replete conditions, Ypq1 is stable as it uses a PQ loop–dependent conformational cycle to import excess lysine into the vacuole. When lysine is depleted, Ypq1 is sorted into the multivesicular body (MVB) for degradation (Fig. 1). This process is initiated once Ypq1 is ubiquitinated by the ubiquitin ligase complex Rsp5–Ssh4, but how Ypq1 is targeted by Rsp5–Ssh4 has been unclear (9).Open in a separate windowFigure 1.Regulated recognition of Ypq1 by Ssh4. When lysine in the cytosol is abundant, Ypq1 undergoes a rapid conformational cycle to transport lysine from the cytosol into the vacuole lumen. Under lysine-depleted conditions, the transporter is trapped in a conformation recognizable by Ssh4, which recruits Rsp5 to catalyze Ypq1 ubiquitination and internalization into the MVB. Ub, ubiquitin.To understand the mechanism of Ypq1 recognition, Arines et al. first engineered a Ypq1 mutant that uncouples ligase-mediated degradation from lysine availability. This Ypq1 mutant is constitutively degraded in an Ssh4-dependent manner even under lysine-replete conditions. With this tool in hand, they performed a random mutagenesis-based suppressor screen, which identified many suppressor mutants. Mapping these mutations revealed several elements in Ypq1 that are critical for ligase recognition, which include two TMDs (TM5 and TM7) and a cytosolic loop. Importantly, when these mutations were introduced back into wild-type Ypq1, they also block Ssh4-dependent, lysine-regulated Ypq1 degradation. As expected, coimmunoprecipitation showed that Ypq1 suppressor mutants have reduced affinity to Ssh4. Since the cytosolic loop contains a previously known Rsp5 recognition motif, they further characterized the role of Ypq1 TMDs in ligase recruitment.Structural modeling suggests that TM5 and TM7 are juxtaposed to each other. Systematic mutagenesis targeting each residue of these two TMDs further consolidated the residues essential for Ssh4-mediated degradation. A similar mutagenesis study on Ssh4 revealed an important role for the Ssh4 TMD in Ypq1 degradation. Interestingly, for both Ssh4 and Ypq1, many identified residues are clustered on one side of the membrane helices. Arines et al. propose that Ssh4 uses its TMD to recognize TM5 and TM7 in Ypq1 based on a charge complementation experiment: a charged residue introduced into TM5 of Ypq1 abolished Ssh4-mediated degradation, but introducing an opposite charge into the TMD of Ssh4 restored lysine-regulated Ypq1 degradation.The recognition of Ypq1 by Ssh4 appears to occur when Ypq1 adopts a specific conformation during lysine transport because charge complementarity–based degradation of Ypq1 depends on the PQ loop, which is required for lysine transport. Additionally, structural modeling of Ypq1 suggested that in the inward-open and occluded conformations, TM5 is packed against TM7, but the two TMDs become distant from each other in the outward-open conformation, which exposes residues critical for Ssh4 recognition. These findings suggest that the rapid conformational cycling during lysine transport may prevent Ssh4 recognition, but lysine depletion stalls Ypq1 in a conformation recognizable by Ssh4 (Fig. 1).The study, together with the recent discovery of the ER membrane protein complex (EMC) in the biogenesis of multi-spanning membrane proteins at the ER, suggests a new class of chaperones that recognize specific features in TMDs. While emerging evidence suggests that the EMC recognizes exposed charged or polar residues in TMDs (10), the molecular basis of Ssh4 substrate interaction remains unclear. Like cytosolic chaperones, the EMC at the ER appears to play a dual role: while initially shielding charged/polar residues to facilitate TMD assembly, it may eventually target misassembled membrane proteins for degradation. By contrast, TMD-specific chaperones in other organelles like Ssh4 may have a more dedicated function in PQC. Clearly, more TMD-specific chaperones await to be discovered. Additionally, future studies will surely reveal not only the range of substrates and functions for each TMD-specific chaperone but also the structural basis of TMD recognition.     

Interplane bulk motion analysis and removal based on normalized cross‐correlation in optical coherence tomography angiography

Bulk motion seriously degrades the image quality of optical coherence tomography angiography (OCTA). Conventional correction methods focus on in‐plane displacement, while the bulk motion component perpendicular to B‐scans also introduces noise. This work first presents an evaluation of this component using a specific scan protocol and an approximate expression derived from peak‐normalized cross‐correlation values, and then quantitatively assesses how interplane bulk motion noise reduce the sensitivity of cross‐sectional angiograms. Finally, we developed a repetitive bulk motion correction method based on the estimated displacements and redundant volume scans. The correction does not require registration and angiogram reconstruction of low flow sensitivity frames, and the results of in vivo mice skin OCTA imaging experiments show that the proposed method can effectively reduce bulk motion noise caused by cardiac and respiratory motion and occasional shaking, and improve OCTA image quality, which has practical significance for clinical OCTA diagnosis and analysis.