Three-dimensional architecture and moment arms of human rotator cuff muscles in vivo: Interindividual, intermuscular, and intramuscular variations.

The human rotator cuff consists of four muscles, each with a complex, multipennate architecture. Despite the functional and clinical importance, the architecture of the human rotator cuff has yet to be clearly described in humans in vivo. The purpose of this study was to investigate the intramuscular, intermuscular, and interindividual variations in architecture and moment arms of the human rotator cuff. Muscle volumes, fascicle lengths, physiological cross-sectional areas (PCSAs), pennation angles, and moment arms of all four rotator cuff muscles were measured from mDixon and diffusion tensor imaging (DTI) scans of the right shoulders of 20 young adults. In accordance with the most detailed dissections available to date, we found substantial intramuscular variation in fascicle length (coefficients of variation (CVs) ranged from 26% to 40%) and pennation angles (CVs ranged from 56% to 62%) in all rotator cuff muscles. We also found substantial intermuscular and interindividual variations in muscle volumes, but relatively consistent mean fascicle lengths, pennation angles, and moment arms (CVs for all ≤17%). Moreover, when expressed as a proportion of total rotator cuff muscle volume, the volumes of individual rotator cuff muscles were highly consistent between individuals and sexes (CVs ≤16%), suggesting that rotator cuff muscle volumes scale uniformly, at least in a younger population without musculoskeletal problems. Together, these data indicate limited interindividual and intermuscular variability in architecture, which may simplify scaling routines for musculoskeletal models. However, the substantial intramuscular variation in architecture questions the validity of previously reported mean architectural parameters to adequately describe rotator cuff function.

The effects of postural support padding modifications to child restraints for children with disability on crash protection.

OBJECTIVE: Many children with physical disabilities need additional postural support when sitting and supplementary padding is used on standards approved child restraints to achieve this when traveling in a motor vehicle. However, the effect of this padding on crash protection for a child is unknown. This study aimed to investigate the effect of additional padding for postural support on crash protection for child occupants in forward facing child restraints. METHODS: Forty frontal sled tests at 49 km/h were conducted to compare Q1 anthropometric test device (ATD) responses in a forward-facing restraint, with and without additional padding in locations to increase recline of the restraint, and/or support the head, trunk and pelvis. Three padding materials were tested: cloth toweling, soft foam, and expanded polystyrene (EPS). The influence of padding on head excursion, peak 3 ms head acceleration, HIC15, peak 3 ms chest acceleration and chest deflection were analyzed. RESULTS: The influence of padding varied depending on the location of use. Padding used under the restraint to increase the recline angle increased head injury metrics. Toweling in multiple locations which included behind the head increased head excursion and chest injury metrics. There was minimal effect on injury risk measures with additional padding to support the sides of the head or the pelvis position. Rigid EPS foam, as recommended in Australian standards and guidelines, had minimal effect on injury metrics when used inside the restraint, as did tightly rolled or folded toweling secured to the restraint at single locations around the body of the child. CONCLUSIONS: This study does not support the use of postural support padding to increase recline of a forward-facing restraint or padding behind the head. Recommendations in published standards and guidelines to not use foam that is spongy, soft or easily compressed, with preference for secured firm foam or short-term use of tightly rolled or folded toweling under the child restraint cover is supported. This study also highlights the importance of considering the whole context of child occupant protection when using additional padding, particularly the change in the child's seated position when adding padding in relation to the standard safety features of the restraint.

Updated population-level estimates of child restraint practices among children aged 0-12 years in Australia, 10 years after introduction of age-appropriate restraint use legislation.

OBJECTIVE: Optimal child passenger protection requires use of a restraint designed for the age/size of the child (appropriate use) that is used in the way the manufacturer intended (correct use).This study aimed to determine child restraint practices approximately 10 years after introduction of legislation requiring correct use of age-appropriate restraints for all children aged up to 7 years. METHODS: A stratified cluster sample was constructed to collect observational data from children aged 0-12 years across the Greater Sydney region of New South Wales (NSW). Methods replicated those used in a similar 2008 study. Population weighted estimates for restraint practices were generated, and logistic regression used to examine associations between restraint type, and child age with correct use accounting for the complex sample. RESULTS: Almost all children were appropriately restrained (99.3%, 95% CI 98.4% to 100%). However, less than half were correctly restrained (no error=27.3%, 95% CI 10.8% to 43.8%, no serious error=43.8%, 95% CI 35.0% to 52.7%). For any error, the odds of error decreased by 39% per year of age (OR 0.61, 95% CI 0.46 to 0.81) and for serious error by 25% per year (OR 0.75, 95% CI 0.60 to 0.93). CONCLUSION: The findings demonstrate high levels of appropriate restraint use among children across metropolitan Sydney approximately 10 years after introduction of legislation requiring age-appropriate restraint use until age 7, however, errors in the way restraints remain common. IMPLICATIONS FOR PUBLIC HEALTH: Given the negative impact incorrect use has on crash protection, continuing high rates of incorrect use may reduce effectiveness of legislative change on injury reduction.

Regional associations between inspiratory tongue dilatory movement and genioglossus activity during wakefulness in people with obstructive sleep apnoea.

Inspiratory tongue dilatory movement is believed to be mediated via changes in neural drive to genioglossus. However, this has not been studied during quiet breathing in humans. Therefore, this study investigated this relationship and its potential role in obstructive sleep apnoea (OSA). During awake supine quiet nasal breathing, inspiratory tongue dilatory movement, quantified with tagged magnetic resonance imaging, and inspiratory phasic genioglossus EMG normalised to maximum EMG were measured in nine controls [apnoea-hypopnea index (AHI) ≤5 events/h] and 37 people with untreated OSA (AHI >5 events/h). Measurements were obtained for 156 neuromuscular compartments (85%). Analysis was adjusted for nadir epiglottic pressure during inspiration. Only for 106 compartments (68%) was a larger anterior (dilatory) movement associated with a higher phasic EMG [mixed linear regression, beta = 0.089, 95% CI [0.000, 0.178], t(99) = 1.995, P = 0.049, hereafter EMG↗/mvt↗]. For the remaining 50 (32%) compartments, a larger dilatory movement was associated with a lower phasic EMG [mixed linear regression, beta = -0.123, 95% CI [-0.224, -0.022], t(43) = -2.458, P = 0.018, hereafter EMG↘/mvt↗]. OSA participants had a higher odds of having at least one decoupled EMG↘/mvt↗ compartment (binary logistic regression, odds ratio [95% CI]: 7.53 [1.19, 47.47] (P = 0.032). Dilatory tongue movement was minimal (>1 mm) in nearly all participants with only EMG↗/mvt↗ compartments (86%, 18/21). These results demonstrate that upper airway dilatory mechanics cannot be predicted from genioglossus EMG, particularly in people with OSA. Tongue movement associated with minimal genioglossus activity suggests co-activation of other airway dilator muscles. KEY POINTS: Inspiratory tongue movement is thought to be mediated through changes in genioglossus activity. However, it is unknown if this relationship is altered by obstructive sleep apnoea (OSA). During awake supine quiet nasal breathing, inspiratory tongue movement, quantified with tagged magnetic resonance imaging (MRI), and inspiratory phasic genioglossus EMG normalised to maximum EMG were measured in four tongue compartments of people with and without OSA. Larger tongue anterior (dilatory) movement was associated with higher phasic genioglossus EMG for 68% of compartments. OSA participants had an ∼7-times higher odds of having at least one compartment for which a larger anterior tongue movement was not associated with a higher phasic EMG than controls. Therefore, higher genioglossus phasic EMG does not consistently translate into tongue dilatory movement, particularly in people with OSA. Large dilatory tongue movements can occur despite minimal genioglossus inspiratory activity, suggesting co-activation of other pharyngeal muscles.

A novel method to quantify perivascular space enlargement near the syrinx in a rodent model of post-traumatic syringomyelia.

Posttraumatic syringomyelia (PTS) is an enigmatic condition characterized by the development of fluid-filled cysts (syrinxes) within the spinal cord. Perivascular spaces (PVS) are a critical component of fluid transport within the central nervous system (CNS), with dilated PVSs variably implicated in the pathogenesis of syringomyelia. The extent and spatial distribution of dilated PVSs in syringomyelia, however, remains unclear. This study aims to develop a method to assess PVS dimensions across multiple spinal cord segments in rats with PTS. Syrinxes were induced in two Sprague-Dawley rats at C6/7 with computer-controlled motorized spinal cord impaction; two control rats underwent sham laminectomies. Spinal cord segments were obtained at C4, C6 and C8, cleared via tissue clearing protocols, stained with immunofluorescent antibodies and imaged under confocal microscopy. Qualitative and quantitative analyses of PVS size were performed. Arteriolar PVSs were enlarged in the perisyringeal region of the spinal cord, compared to the control cord. No PVS enlargement was observed above or below the syrinx. These results confirm previous incidental findings of enlarged PVSs in the perisyringeal region, providing new insights into PVS dimensions across multiple spinal segments, and providing a novel method for quantifying spinal cord perivascular space size distributions.

Differences in participant characteristics and observed child restraint use between population-based and restraint fitting service samples.

OBJECTIVE: To compare characteristics and restraint use between a population-based and fitting service sample of child restraint users. METHOD: Characteristics of the two samples were compared using chi-squared tests. Differences in errors in restraint use observed in the two samples were modeled using logistic regression. RESULTS: There were significant differences in child age (p < 0.001), and restraint types (p < 0.001) between the two samples, with more younger children in the fitting service sample. Controlling for differences in restraint type, the odds that adult participants were female were 61% less in the fitting service sample than in the population-based sample (OR 0.39, 95%CI 0.21-0.71). The odds that adult participants perceived a large risk associated with restraint misuse (OR 3.62, 95%CI 1.33-9.84), had a household income in the highest bracket (OR 3.89, 95%CI 1.20-12.62) and were living in areas of highest socioeconomic advantage (OR 2.72, 95%CI 1.22-6.06) were approximately three times higher in the fitting service sample. Overall, more participants had errors in restraint use in the population-based sample (p = 0.021). However, after controlling for restraint type, securing errors were three times more likely (OR 3.34, 95%CI 1.12-10.2), and serious installation errors were almost twice as likely (OR 1.91, 95% CI 1.09-3.39) in the fitting service sample. CONCLUSIONS: While less resource intensive, convenience and/or fitting service samples may be less representative than population-based samples. Given the need for efficiency, methods that combine randomized population-based invitations to participate in restraint fitting check day events across geographically representative areas may be useful for ongoing surveillance of child restraint use.

Direct optogenetic activation of upper airway muscles in an acute model of upper airway hypotonia mimicking sleep onset.

STUDY OBJECTIVES: Obstructive sleep apnea (OSA), where the upper airway collapses repeatedly during sleep due to inadequate dilator muscle tone, is challenging to treat as current therapies are poorly tolerated or have variable and unpredictable efficacy. We propose a novel, optogenetics-based therapy, that stimulates upper airway dilator muscle contractions in response to light. To determine the feasibility of a novel optogenetics-based OSA therapy, we developed a rodent model of human sleep-related upper airway muscle atonia. Using this model, we evaluated intralingual delivery of candidate optogenetic constructs, notably a muscle-targeted approach that will likely have a favorable safety profile. METHODS: rAAV serotype 9 viral vectors expressing a channelrhodopsin-2 variant, driven by a muscle-specific or nonspecific promoter were injected into rat tongues to compare strength and specificity of opsin expression. Light-evoked electromyographic responses were recorded in an acute, rodent model of OSA. Airway dilation was captured with ultrasound. RESULTS: The muscle-specific promoter produced sufficient opsin expression for light stimulation to restore and/or enhance electromyographic signals (linear mixed model, F = 140.0, p < 0.001) and induce visible tongue contraction and airway dilation. The muscle-specific promoter induced stronger (RM-ANOVA, F(1,8) = 10.0, p = 0.013) and more specific opsin expression than the nonspecific promoter in an otherwise equivalent construct. Viral DNA and RNA were robust in the tongue, but low or absent in all other tissues. CONCLUSIONS: Significant functional responses to direct optogenetic muscle activation were achieved following muscle-specific promoter-driven rAAV-mediated transduction, providing proof-of-concept for an optogenetic therapy for patients with inadequate dilator muscle activity during sleep.

Strain-dependent shear properties of human adipose tissue in vivo.

INTRODUCTION: Human adipose tissue (fat) deforms substantially under normal physiological loading and during impact. Thus, accurate data on strain-dependent stiffness of fat is essential for the creation of accurate biomechanical models. Previous studies on ex vivo samples reported human fat to be nonlinear and viscoelastic. When static compression is combined with magnetic resonance (MR) elastography (an imaging technique used to measure viscoelasticity in vivo), the large deformation properties of tissues can be determined. Here, we use magnetic resonance elastography to quantify fat shear modulus in vivo under increasing compressive strain and compare it to the underlying passive gluteal muscle. METHODS: The right buttocks of ten female participants were incrementally compressed at four levels while MR elastography (50 Hz) and mDixon images were acquired. Maps of tissue shear modulus (G*) were reconstructed from the MR elastography phase images. Tissue strain was estimated from registration of deformed and undeformed mDixon images. Linear mixed models were fit to the natural logarithm of the compressive strain and shear modulus data for each tissue. RESULTS: Shear modulus increased in an exponential relationship with compressive strain in fat: Gfat*=748.5*Cyy-1.18Pa, and to a lesser extent in muscle: Gmuscle*=956.4*Cyy-0.36Pa. The baseline (undeformed) stiffness of fat was significantly lower than that of muscle (mean G*fat = 752 Pa, mean G*muscle = 1000 Pa, paired samples t-test, t = -4.24, p = 0.001). However, fat exhibited a significantly higher degree of strain dependence (characterised by the exponent of the curve, t = -6.47, p = 0.0001). CONCLUSION: Static compression of human adipose tissue results in an increase in apparent viscoelastic shear modulus (stiffness), in an exponentially increasing relationship. The relationships defined here can be used in the development of physiologically realistic computational models for impact, injury and biomechanical modelling.

Aquaporin-4 expression and modulation in a rat model of post-traumatic syringomyelia.

Aquaporin-4 (AQP4) has been implicated in post-traumatic syringomyelia (PTS), a disease characterised by the formation of fluid-filled cysts in the spinal cord. This study investigated the expression of AQP4 around a mature cyst (syrinx) and the effect of pharmacomodulation of AQP4 on syrinx size. PTS was induced in male Sprague-Dawley rats by computerized spinal cord impact and subarachnoid kaolin injection. Immunofluorescence of AQP4 was carried out on mature syrinx tissue 12 weeks post-surgery. Increased AQP4 expression corresponded to larger, multiloculated cysts (R2 = 0.94), yet no localized changes to AQP4 expression in perivascular regions or the glia limitans were present. In a separate cohort of animals, at 6 weeks post-surgery, an AQP4 agonist (AqF026), antagonist (AqB050), or vehicle was administered daily over 4 days, with MRIs performed before and after the completion of treatment. Histological analysis was performed at 12 weeks post-surgery. Syrinx volume and length were not altered with AQP4 modulation. The correlation between increased AQP4 expression with syrinx area suggests that AQP4 or the glia expressing AQP4 are recruited to regulate water movement. Given this, further investigation should examine AQP4 modulation with dose regimens at earlier time-points after PTS induction, as these may alter the course of syrinx development.

Optogenetic Control of Muscles: Potential Uses and Limitations.

Optogenetics is a technique where a cell is transduced with a light-sensitive ion channel. This technique can be used to control muscle cell contraction in conjunction with commonly used viral vectors. However, this technique has not yet become widely applied. In this study, we discuss the mechanisms and techniques involved in opsin transfer to muscle tissue, the clinical applicability of these approaches, and the major limitations facing this technique.

The combined use of DTI and MR elastography for monitoring microstructural changes in the developing brain of a neurodevelopmental disorder model: Poly (I:C)-induced maternal immune-activated rats.

Early neuropathology mechanisms in neurodevelopmental disorders are partially understood because routine anatomical magnetic resonance imaging (MRI) cannot detect subtle brain microstructural changes in vivo during postnatal development. Therefore, we investigated the potential value of magnetic resonance elastography (MRE) and diffusion tensor imaging (DTI) in a rat model of neurodevelopmental disorder induced by maternal immune activation. We studied 12 offspring of mothers injected with polyriboinosinic-polyribocytidylic acid (poly (I:C), 4 mg/kg) on gestational day 15, plus 8 controls. T2-weighted anatomical MR images, MRE (800 Hz) and DTI (30 gradient directions, b = 765.8 s/mm2, 5 images, b = 0 s/mm2) were collected when the rats were 4 and 10 weeks old, and results were compared with histological analysis performed at week 10. Ventricles were ~1.4 fold larger from week 4 in poly (I:C) rats than in controls. No other morphological abnormalities were detected in poly(I:C) rats. At week 4, larger ventricles were correlated with lower external capsule fractional anisotropy and internal capsule radial diffusion (Pearson, r = -0.53, 95% confidence intervals (CI) [-0.79 to -0.12], and r = -0.45, 95% CI [-0.74 to -0.01], respectively). The mean and radial diffusion of the corpus callosum, the mean and axial diffusion of the internal capsule and the radial diffusion properties in the external capsule increased with age for poly (I:C) rats only (Sidak's comparison, P<0.05). Cortical stiffness did not increase with age in poly (I:C) rats, in contrast with controls (Sidak's comparison, P = 0.005). These temporal variations probably reflected abnormal myelin content, decreased cell density and microglia activation observed at week 10 after histological assessment. To conclude, MRE and DTI allow monitoring of abnormal brain microstructural changes in poly (I:C) rats from week 4 after birth. This suggests that both imaging techniques have the potential to be used as complementary imaging tools to routine anatomical imaging to assist with the early diagnosis of neurodevelopmental disorders and provide new insights into neuropathology.

Ex vivo bovine liver nonlinear viscoelastic properties: MR elastography and rheological measurements.

INTRODUCTION: Knowledge of the nonlinear viscoelastic properties of the liver is important, but the complex tissue behavior outside the linear viscoelastic regime has impeded their characterization, particularly in vivo. Combining static compression with magnetic resonance (MR) elastography has the potential to be a useful imaging method for assessing large deformation mechanical properties of soft tissues in vivo. However, this remains to be verified. Therefore this study aims first to determine whether MR elastography can measure the nonlinear mechanical properties of ex vivo bovine liver tissue under varying levels of uniform and focal preloads (up to 30%), and second to compare MR elastography-derived complex shear modulus with standard rheological measurements. METHOD: Nine fresh bovine livers were collected from a local abattoir, and experiments were conducted within 12hr of death. Two cubic samples (∼10 × 10 × 10 cm3) were dissected from each liver and imaged using MR elastography (60 Hz) under 4 levels of uniform and focal preload (1, 10, 20, and 30% of sample width) to investigate the relationship between MR elastography-derived complex shear modulus (G∗) and the maximum principal Right Cauchy Green Strain (C11). Three tissue samples from each of the same 9 livers underwent oscillatory rheometry under the same 4 preloads (1, 10, 20, and 30% strain). MR elastography-derived complex shear modulus (G∗) from the uniform preload was validated against rheometry by fitting the frequency dependence of G∗ with a power-law and extrapolating rheometry-derived G∗ to 60 Hz. RESULTS: MR elastography-derived G∗ increased with increasing compressive large deformation strain, and followed a power-law curve (G∗ = 1.73 × C11-0.38, R2 = 0.96). Similarly, rheometry-derived G∗ at 1 Hz, increasing from 0.66 ± 1.03 kPa (1% strain) to 1.84 ± 1.65 kPa (30% strain, RM one-way ANOVA, P < 0.001), and the frequency dependence of G∗ followed a power-law with the exponent decreasing from 0.13 to 0.06 with increasing preload. MR elastography-derived G∗ was 1.4-3.1 times higher than the extrapolated rheometry-derived G∗ at 60 Hz, but the strain dependence was consistent between rheometry and MR elastography measurements. CONCLUSIONS: This study demonstrates that MR elastography can detect changes in ex vivo bovine liver complex shear modulus due to either uniform or focal preload and therefore can be a useful technique to characterize nonlinear viscoelastic properties of soft tissue, provided that strains applied to the tissue can be quantified. Although MR elastography could reliably characterize the strain dependence of the ex vivo bovine liver, MR elastography overestimated the complex shear modulus of the tissue compared to rheological measurements, particularly at lower preload (<10%). That is likely to be important in clinical hepatic MR elastography diagnosis studies if preload is not carefully considered. A limitation is the absence of overlapping frequency between rheometry and MR elastography for formal validation.

Child restraint headrest and belt routing design features and their association with child passenger behavior and restraint misuse.

OBJECTIVES: Ergonomic design of child restraint systems (CRS) may facilitate optimal travel behavior and crash protection of child passengers during motor vehicle trips. However there have been few studies examining the relationship between CRS design and child passenger travel behavior. The aim of this study was to examine whether associations between CRS design features and child passenger behavior exist during real-world, everyday vehicle trips. METHODS: Video from a naturalistic driving study (NDS) was analyzed in this study. Families drove an instrumented study vehicle for approximately two weeks with at least one child aged between one and eight years traveling in their own forward-facing (FF) CRS or belt positioning booster (BPB). Video for one child passenger was randomly selected from each trip for analysis. Video was coded for five-second epochs at nine time points (5%, 17%, 25%, 30%, 50%, 53%, 75%, 89% and 95% of trip length). Two types of child passenger travel behaviors were identified by manual review of the video and audio recordings: (i) optimal/suboptimal head position and (ii) correct/incorrect use of the internal harness/shoulder belt. Video screenshots were used to characterize CRS design features. Random effects logistic regression models were used to examine the associations between specific CRS design features and the travel behaviors of interest, whilst accounting for clustering of data by child and trip. RESULTS: Suboptimal head position was associated with the absence of a height adjustable headrest and a narrow headrest wing width in FFCRS. Incorrect harness use in a FFCRS was associated with the absence of an adjustable headrest, in addition to headrest features such as wing width and depth. In BPBs, a reduction in suboptimal head position was associated with the absence of a sash belt guide, however no restraint design features were associated with incorrect shoulder belt use. CONCLUSIONS: Some CRS design features may influence undesirable child passenger travel behavior. These early findings support enhanced and user-centric CRS design as a likely important mechanism to improve child passenger safety.

Regional genioglossus reflex responses to negative pressure pulses in people with obstructive sleep apnea.

Tongue and upper airway dilator muscle movement patterns during quiet breathing vary in people with obstructive sleep apnea (OSA). Many patients have inadequate or counterproductive responses to inspiratory negative airway pressure that likely contributes to their OSA. This may be due, at least in part, to inadequate or nonhomogeneous reflex drive to different regions of the largest upper airway dilator, genioglossus. To investigate potential regional heterogeneity of genioglossus reflex responses in OSA, brief suction pulses were applied via a nasal breathing mask and an electromyogram (EMG) was recorded in four regions (anterior oblique, anterior horizontal, posterior oblique, and posterior horizontal) using intramuscular fine wire electrodes in 15 people with OSA. Genioglossus short-latency reflex excitation amplitude had regional heterogeneity (horizontal vs. oblique regions) when expressed in absolute units but homogeneity when normalized as a percentage of the immediate (100 ms) prestimulus EMG. Regional variability in reflex morphology (excitation and inhibition) was present in one-third of the participants. The minimum cross-sectional area (CSA) of the pharyngeal airway was quantified using MRI and may be related to the amplitude of the short-latency reflex response to negative pressure as we found that people with a smaller CSA tended to have a greater reflex amplitude (e.g., horizontal region r2 = 0.41, P = 0.01). These findings highlight the complexity of genioglossus reflex control, the potential for regional heterogeneity, and the functional importance of upper airway anatomy in mediating genioglossus reflex responses to rapid changes in negative pressure in OSA.NEW & NOTEWORTHY Our findings indicate that 30% of participants had regional heterogeneity in reflex morphology (excitation/inhibition) to brief pulses of negative upper-airway pressure across anterior oblique, anterior horizontal, posterior oblique, and posterior horizontal regions of the genioglossus muscle. Reflex excitation amplitude was proportional to prestimulus drive, with increased activation in oblique compared with horizontal regions of the posterior tongue. People with narrower upper-airway anatomy tended to have increased genioglossus reflex amplitude to negative pressure pulses during wakefulness.

Neck Loads During Head-First Entries into Trampoline Dismount Foam Pits: Considerations for Trampoline Park Safety.

Serious cervical spine injuries have been documented from falls into foam pits at trampoline parks. To address the lack of evidence on how foam pits should be designed for mitigating neck injury risk, this study aimed to quantify neck loads during head-first entry into varying foam pit designs. An instrumented Hybrid III anthropomorphic test device was dropped head-first from a height of up to 1.5 m into three differently constructed foam pits, each using a different mechanism to prevent direct contact between the falling person and the floor (foam slab, trampoline or net bed). Measured neck loads were compared to published injury reference values. In the simplest, foam-only pit design, increasing foam depth tended to reduce peak compressive force. At least one injury assessment reference metric was exceeded in all pit conditions tested for 1.5 m falls, most commonly the time-dependent neck compression criterion. The results highlight the importance of adequate foam depth in combination with appropriate pit design in minimizing injury risk. The risk of cervical spine injury may not be reduced sufficiently with current foam pit designs.

Statistical shape models of the posterior cranial fossa and hindbrain volumes may provide a more robust clinical metric for Chiari malformation.

Chiari malformation is characterised by the herniation of the cerebellar tonsils through the foramen magnum. However, tonsillar herniation and other 2D morphometric measurements of the posterior cranial fossa (PCF) have a weak association with patients' symptoms and clinical outcomes. This study aimed to contrast current 2D metrics with a novel 3D shape analysis of the PCF and the hindbrain, to determine if 3D measurements provides further insight into the pathophysiology of Chiari. The cranium of 12 controls and 21 Chiari malformation patients with (N = 9) and without (N = 12) a syrinx were scanned. The morphology of the PCF was quantified with typical 2D measurements. Additionally, a correspondence-based shape model that normalised the PCF volume, was used to find 3D differences in the shape of the PCF, and the distance of the hindbrain from the inner surfaces of the PCF. Shape analysis showed that, compared to controls, the caudal (p = 0.007; 2.3 mm, IQR: 1.6-3.3 mm) and anterior (p = 0.027; 1.3 mm,IQR: 1.1-1.6 mm) surfaces of the hindbrain were closer to the PCF in patients with and without a syrinx, respectively. However, there were negligible differences in the shape of the PCF between patient groups (p > 0.39). Current morphometric measures should be normalised for variation in PCF volume, so that shape measures are not biased. The reduced CSF space between the hindbrain and PCF will alter CSF dynamics, which may compress cerebellar vasculature and contribute to patient symptomatology.

Head excursion in frontal impacts is lower in high back booster seats than in forward facing child seats with internal harnesses designed for children up to 8 years of age.

OBJECTIVE: It is often assumed that a child restraint with a five or six-point internal harness provides greater protection for children in frontal crashes than a booster seat with a lap-sash seat belt. However, most research comparing these restraint types has focused on protection for children aged up to approximately 3-4 years of age. Recently, harnessed child restraints for older children up to approximately 8 years of age have become available, but there is little data on their performance compared to booster seats for children over 4 years of age. This study aimed to compare frontal crash performance of a series of harnessed child restraints for children aged 4-8 years to booster seats. METHODS: Four large harnessed child restraints (Type G in the Australian Standard, AS/NZS 1754:2013) and six high back booster seats (Type E in AS/NZS 1754:2013) were tested in frontal impact on a deceleration sled. Head and pelvis accelerations were recorded and head excursions were measured from high speed video. RESULTS: Head excursion was an average of 92 mm greater in the large harnessed child restraints than the high back booster seats. The initial position of the head in Type G restraints, an average of 58 mm further forward compared to Type E boosters, was the main contributor to the larger head excursion during impact. Conversely, peak head accelerations in the impact phase were, on average, 37.2 g lower in the large harnessed child restraints than the high back booster seats. CONCLUSIONS: These data suggest that recommendations for harnessed restraints and booster seats for children aged 4-8 years is not as obvious as is sometimes assumed. Harnessed restraints allow greater head excursion in frontal impacts, potentially increasing the chances of head impacts, especially in vehicles with limited clearance between the restraint and the seat in front. The likelihood, and types of, incorrect use that occur in each restraint type, the vehicle occupant space, and the restraint's crash performance under ideal conditions should be considered in recommending restraints for these older children.

The relationship between mandibular advancement, tongue movement, and treatment outcome in obstructive sleep apnea.

STUDY OBJECTIVES: To characterize how mandibular advancement enlarges the upper airway via posterior tongue advancement in people with obstructive sleep apnea (OSA) and whether this is associated with mandibular advancement splint (MAS) treatment outcome. METHODS: One-hundred and one untreated people with OSA underwent a 3T magnetic resonance (MRI) scan. Dynamic mid-sagittal posterior tongue and mandible movements during passive jaw advancement were measured with tagged MRI. Upper airway cross-sectional areas were measured with the mandible in a neutral position and advanced to 70% of maximum advancement. Treatment outcome was determined after a minimum of 9 weeks of therapy. RESULTS: Seventy-one participants completed the study: 33 were responders (AHI<5 or AHI≤10 events/hr with >50% AHI reduction), 11 were partial responders (>50% AHI reduction but AHI>10 events/hr), and 27 nonresponders (AHI reduction<50% and AHI≥10 events/hr). Responders had the greatest naso- and oropharyngeal tongue anterior movement (0.40 ± 0.08 and 0.47 ± 0.13 mm, respectively) and oropharyngeal cross-sectional area enlargement (6.41 ± 2.12%) per millimeter of mandibular advancement. A multivariate model that included tongue movement and percentage of airway enlargement per millimeter of mandibular advancement along with baseline AHI correctly classified 69.2% (5-fold cross-validated 62.5%, n = 39) of participants in response categories when the jaw was advanced in the range that would usually be regarded as sufficient for clinical efficacy (> 4 mm). In comparison, a model using only baseline AHI correctly classified 50.0% of patients (5-fold cross-validated 52.5%, n = 40). CONCLUSIONS: Tongue advancement and upper airway enlargement with mandibular advancement in conjunction with baseline AHI improve treatment response categorization to a satisfactory level (69.2%, 5-fold cross-validated 62.5%).

Changes in intrathoracic pressure, not arterial pulsations, exert the greatest effect on tracer influx in the spinal cord.

BACKGROUND: Cerebrospinal fluid (CSF) circulation in the brain has garnered considerable attention in recent times. In contrast, there have been fewer studies focused on the spine, despite the expected importance of CSF circulation in disorders specific to the spine, including syringomyelia. The driving forces that regulate spinal CSF flow are not well defined and are likely to be different to the brain given the anatomical differences and proximity to the heart and lungs. The aims of this study were to determine the effects of heart rate, blood pressure and respiration on the distribution of CSF tracers in the spinal subarachnoid space, as well as into the spinal cord interstitium. METHODS: In Sprague Dawley rats, physiological parameters were manipulated such that the effects of spontaneous breathing (generating alternating positive and negative intrathoracic pressures), mechanical ventilation (positive intrathoracic pressure only), tachy/bradycardia, as well as hyper/hypotension were separately studied. To investigate spinal CSF hydrodynamics, in vivo near-infrared imaging of intracisternally infused indocyanine green was performed. CSF tracer transport was further characterised with in vivo two-photon intravital imaging. Tracer influx at a microscopic level was quantitatively characterised by ex vivo epifluorescence imaging of fluorescent ovalbumin. RESULTS: Compared to mechanically ventilated controls, spontaneous breathing animals had significantly greater movement of tracer in the subarachnoid space. There was also greater influx into the spinal cord interstitium. Hypertension and tachycardia had no significant effect on spinal subarachnoid spinal CSF tracer flux and exerted less effect than respiration on tracer influx into the spinal cord. CONCLUSIONS: Intrathoracic pressure changes that occur over the respiratory cycle, particularly decreased intrathoracic pressures generated during inspiration, have a profound effect on tracer movement after injection into spinal CSF and increase cord parenchymal tracer influx. Arterial pulsations likely drive fluid transport from perivascular spaces into the surrounding interstitium, but their overall impact is less than that of the respiratory cycle on net tracer influx.

Comparative performance of rearward and forward-facing child restraint systems with common use errors: Effect on crash injury risk for a 1-year-old occupant.

OBJECTIVE: To compare how errors in child restraint use influence crash injury risk in rearward and forward-facing restraints for a 1-year old occupant. METHODS: Three convertible child restraint systems (CRS) were subjected to frontal dynamic sled tests at 56 km/h in rearward-facing and forward-facing modes in a correct use (baseline) condition and in five incorrect use conditions: loose securing belt, loose harness, partial harness use, top tether slack, and three minor errors. Excursion, head, and chest 3 ms resultant acceleration, HIC15, and neck forces and moments of a Q1 anthropomorphic test device (ATD) seated in the restraints were measured. The effect of incorrect use on each outcome and restraint type was analyzed. RESULTS: The influence of errors varied across different outcome variables, the three restraints tested and orientation modes. Excursion increased in four of five incorrect use conditions in both rearward and forward-facing orientations. A very loose harness increased four of five outcome variables in at least one forward-facing restraint, whereas only excursion was increased when rearward-facing. Overall, there tended to be a more negative effect of incorrect use (demonstrated through increases in outcome variables compared to the baseline) in the forward-facing orientation. CONCLUSIONS: Overall, errors in use tended to have a larger negative impact on forward-facing restraints than rearward-facing restraints. Given the widespread nature of errors in use, this adds further weight to arguments to keep children rearward-facing to 12 months of age and older. The results also highlight a variation in response to errors across differently designed restraints, suggesting the influence of errors may be minimized by restraint design that is more resistant to errors.