Canceling the elastic Poynting effect with geometry

The Poynting effect is a paragon of nonlinear soft matter mechanics. It is the tendency (found in all incompressible, isotropic, hyperelastic solids) exhibited by a soft block to expand vertically when sheared horizontally. It can be observed whenever the length of the cuboid is at least four times its thickness. Here we show that the Poynting effect can be easily reversed and the cuboid can shrink vertically, simply by reducing this aspect ratio. In principle, this discovery means that for a given solid, say one used as a seismic wave absorber under a building, an optimal ratio exists where vertical displacements and vibrations can be completely eliminated. Here we first recall the classical theoretical treatment of the positive Poynting effect, and then show experimentally how it can be reversed. Using finite-element simulations, we then investigate how the effect can be suppressed. We find that cubes always provide a reverse Poynting effect, irrespective of their material properties (in the third-order theory of weakly nonlinear elasticity).

Pulse-wave velocity assessments derived from a simple photoplethysmography device: Agreement with a referent device

Objective

Pulse-wave velocity (PWV), a common measure of arterial stiffness, can be measured continuously and across multiple body sites using photoplethysmography (PPG). The objective was to determine whether a simple photoplethysmography PPG PWV method agrees with a referent device.

Approach

Photoplethysmography heart-finger PWV (hfPWV) and heart-toe PWV (htPWV) were compared to oscillometric carotid-wrist PWV (cwPWV) and carotid-ankle PWV (caPWV) referent measurements, respectively. In 30 adults (24.6 ± 4.8 years, body mass index 25.2 ± 5.9 kg/m², 18 female), three measurements were made: two supine baseline measurements (Base 1, Base 2) and one measurement (Tilt) 5 min after a modified head-up tilt test (mHUTT). Overall agreement and repeated measures agreement (change in PPG PWV from Base to Tilt vs. change in referent PWV from Base to Tilt) were calculated using linear mixed models. Agreement estimates were expressed as intra-class correlation coefficients (ICC).

Main results

For hfPWV there was strong overall agreement (ICC: 0.77, 95%CI: 0.67-0.85), but negligible and non-significant repeated measures agreement (ICC: 0.10, 95%CI: -0.18 to 0.36). For htPWV, there was moderate overall agreement (ICC:0.50, 95%CI: 0.31-0.65) and strong repeated measures agreement (ICC: 0.81, 95%CI: 0.69-0.89).

Significance

Photoplethysmography can continuously measure PWV at multiple arterial segments with moderate-strong overall agreement. While further work with upper-limb PPG PWV is needed, PPG can adequately capture acute changes in lower-limb PWV.

Social Jetlag and Cardiometabolic Risk in Preadolescent Children

Objective: Childhood cardiometabolic disease risk (CMD) has been associated with short sleep duration. Its relationship with other aspects of sleep should also be considered, including social jetlag (SJL) which represents the difference between a person's social rhythms and circadian clock. This study investigated whether childhood CMD risk is associated with sleep duration, sleep disturbances, and SJL.

Study Design: The observational study included 332 children aged 8–10 years (48.5% female). The three independent variables were sleep duration, sleep disturbances, and SJL. SJL was calculated as the variation in hours between the midpoint of sleep during free (weekend) days and work/school days. Eleven cardiometabolic biomarkers were measured, including central blood pressure, lipids, glycated hemoglobin, arterial wave reflection, and glucose. Underlying CMD risk factors were identified using factor analysis.

Results: Four underlying CMD risk factors were identified using factor analysis: blood pressure, cholesterol, vascular health, and carbohydrate metabolism. Neither sleep disturbances nor sleep duration were significantly associated with any of the four CMD factors following adjustments to potential confounders. However, SJL was significantly linked to vascular health (p = 0.027) and cholesterol (p = 0.025).

Conclusion: These findings suggest that SJL may be a significant and measurable public health target for offsetting negative CMD trajectories in children. Further studies are required to determine biological plausibility.

Cerebrovascular function response to prolonged sitting combined with a high-glycemic index meal: A double-blind, randomized cross-over trial

Acute prolonged sitting leads to cerebrovascular disruptions. However, it is unclear how prolonged sitting interacts with other common behaviors, including high- (HGI) and low-glycemic index (LGI) meals. Using a double-blind randomized cross-over design, this study evaluated the effects of prolonged (3 hr) sitting, with a high- (HGI; GI: 100) or low-glycemic index (LGI; GI: 19) meal on total brain blood flow (Q_Brain ) and executive function. Eighteen young, healthy, active participants (22.6 [3.1] y, 33% F, 24.3 [3.7] kg/m² ) sat for 3 hr after consuming an HGI or LGI meal. Using Doppler ultrasound to measure internal carotid (ICA) and vertebral (VA) artery blood flow, Q_Brain was calculated: (ICA blood flow + VA blood flow) × 2. Executive function was assessed using the Stroop Test and Trail Making Test-Part B. Brain fog was measured using a modified Borg Category Scale with Ratio properties (CR10). Following 3 hr of sitting, there was a significant decrease in Q_Brain with time (p = .001, ES = -0.26), though there were nonsignificant interaction (p = .216) and condition effects (p = .174). Brain fog increased (p = .024, ES = 0.27) and Stroop reaction time worsened with time (p = .001, ES: -0.40), though there were nonsignificant condition effects for brain fog (p = .612) and the Stroop test (p = .445). There was a nonsignificant condition effect (p = .729) for the Trail Making Test-Part B, but completion time improved with time (p = .001, ES = -0.40). In conclusion, 3 hr of prolonged sitting decreases Q_Brain and executive function independent of glycemic index in young, healthy adults.

Prevalence and duration of gastrointestinal symptoms before diagnosis of Inflammatory Bowel Disease and predictors of timely specialist review: a population-based study

BACKGROUND AND AIMS

Lack of timely referral and significant waits for specialist review amongst individuals with unresolved gastrointestinal (GI) symptoms can result in delayed diagnosis of Inflammatory Bowel Disease (IBD).

AIMS

To determine the frequency and duration of GI symptoms and predictors of timely specialist review before the diagnosis of both Crohn's Disease (CD) and ulcerative colitis (UC).

METHODS

Case-control study of IBD matched 1:4 for age and sex to controls without IBD using the Clinical Practice Research Datalink from 1998-2016.

RESULTS

We identified 19,555 cases of IBD, and 78,114 controls. 1 in 4 cases of IBD reported gastrointestinal symptoms to their primary care physician more than 6 months before receiving a diagnosis. There is a significant excess prevalence of GI symptoms in each of the 10 years before IBD diagnosis. GI symptoms were reported by 9.6% and 10.4% at 5 years before CD and UC diagnosis respectively compared to 5.8% of controls. Amongst patients later diagnosed with IBD, <50% received specialist review within 18 months from presenting with chronic GI symptoms. Patients with a previous diagnosis of irritable bowel syndrome or depression were less likely to receive timely specialist review (IBS: HR=0.77, 95%CI 0.60-0.99, depression: HR=0.77, 95%CI 0.60-0.98).

CONCLUSIONS

There is an excess of GI symptoms 5 years before diagnosis of IBD compared to the background population which are likely attributable to undiagnosed disease. Previous diagnoses of IBS and depression are associated with delays in specialist review. Enhanced pathways are needed to accelerate specialist referral and timely IBD diagnosis.

Endothelium function dependence of acute changes in pulse wave velocity and flow-mediated slowing

Flow-mediated slowing (FMS), defined as the minimum pulse wave velocity (PWV_min) during reactive hyperemia, is potentially a simple, user-objective test for examining endothelial function. The purpose of the current study was to determine the effects of a known endothelial dysfunction protocol on arm PWV and PWV_min. Complete data were successfully collected in 22 out of 23 healthy adults (23.8 years [SD 4.1], 16 F, 22.8 kg/m² [SD 2.8]). Local endothelial dysfunction was induced by increasing retrograde shear stress in the upper arm, through inflation of a distal (forearm) tourniquet to 75 mmHg, for 30 min. Pre- and post-endothelial dysfunction, PWV was measured followed by simultaneous assessment of PWV_min and flow-mediated dilation (FMD). PWV was measured between the upper arm and wrist using an oscillometric device, and brachial FMD using ultrasound. FMD (%) and PWV_min (m/s) were calculated as the maximum increase in diameter and minimum PWV during reactive hyperemia, respectively. Endothelial dysfunction resulted in a large effect size (ES) decrease in FMD (∆ = -3.10%; 95% CI: -4.15, -2.05; ES = -1.3), and a moderate increase in PWV (∆ = 0.38 m/s; 95% CI: 0.07, 0.69; ES = 0.5) and PWV_min (∆ = 0.16 m/s; 95% CI: 0.05, 0.28; ES = 0.6). There was a large intra-individual (pre- vs post-endothelial dysfunction) association between FMD and PWV_min (r = -0.61; 95% CI: -0.82, -0.24). In conclusion, acute change in PWV and PWV_min are at least partially driven by changes in endothelial function.

Experimental assessment of clinical MRI-induced global SAR distributions in head phantoms

OBJECTIVE

Accurate estimation of SAR is critical to safeguarding vulnerable patients who require an MRI procedure. The increased static field strength and RF duty cycle capabilities in modern MRI scanners mean that systems can easily exceed safe SAR levels for patients. Advisory protocols routinely used to establish quality assurance protocols are not required to advise on the testing of MRI SAR levels and is not routinely measured in annual medical physics quality assurance checks. This study aims to develop a head phantom and protocol that can independently verify global SAR for MRI clinical scanners.

METHODS

A four-channel birdcage head coil was used for RF transmission and signal reception. Proton resonance shift thermometry was used to estimate SAR. The SAR estimates were verified by comparing results against two other independent measures, then applied to a further four scanners at field strengths of 1.5 T and 3 T.

RESULTS

Scanner output SAR values ranged from 0.42 to 1.52 W/kg. Percentage SAR differences between independently estimated values and those calculated by the scanners differed by 0-2.3%.

CONCLUSION

We have developed a quality assurance protocol to independently verify the SAR output of MRI scanners.

Anaesthetists stress is induced by patient ASA grade and may impair non-technical skills during intubation

BACKGROUND

The aims of this study were to determine if patient ASA grade was associated with increased stress in anaesthetists with a subsequent effect on non-technical skills.

METHODS

Stress was measured using a validated objective (heart rate variability or heart rate) and subjective tool. We studied eight consultant anaesthetists at baseline (rest) and during 16 episodes of intubation with an ASA 1 or 2 patient vs. an ASA 3 or 4 patient. The primary outcome for the study was objective and subjective stress between both patient groups. Secondary outcomes were non-technical skill ratings and the association between stress measurements.

RESULTS

ASA 3 or 4 patients were associated with increases in objective stress when compared to baseline (mean 4.6 vs. 6.7; P = 0.004). However, ASA 1 or 2 patients were not associated with increases in stress when compared to baseline (mean 4.6 vs. 4.7; P = 1). There was no significant difference in subjective stress between the groups (P = 0.18). Objective stress negatively affected situational awareness (P = 0.03) and decision-making (P = 0.03); however, these did not decline to a clinically significant threshold. Heart rate variability (r = 0.60; P = 0.002) better correlated with subjective stress when compared to heart rate (r = 0.30; P = 0.15). Agreement between raters for Anaesthetic Non-Technical Skills (ANTS) scores was acceptable (ICC = 0.51; P = 0.003).

CONCLUSION

This study suggests that higher patient ASA grade can increase stress in anaesthetists, which may impair non-technical skills.

Effects of local radiofrequency denervation on ventricular electrophysiological properties in normal and acute myocardial ischemia heart

OBJECTIVE

To observe the effects of local radiofrequency denervation on ventricular effective refractory periods, electrical alternans and ventricular arrhythmia susceptibility post myocardial infarction.

MATERIALS AND METHODS

Thirty-four mongrel dogs were randomly divided into the normal heart group (n = 16, 8 in sham and 8 in local sympathetic denervation - LSD) and the acute myocardial ischemia (AMI) group (n = 18, 9 in control and 9 in LSD). The left cardiac sympathetic nerve was denervated with irrigated catheter radiofrequency ablation. Left ventricular effective refractory periods (ERP), monophasic action potential duration at 90% (APD90) and APD alternans were measured at baseline and 2 hours after LSD in the normal heart group. AMI was induced by ligating the left anterior descending coronary artery 2 hours after LSD was performed. Then APD90, the occurrence of ventricular arrhythmias (VAs) were measured.

RESULTS

Compared with baseline, LSD significantly prolonged ventricular ERP and APD90 at all sites (p < 0.05 for all) in the LSD group, whereas no significant change was shown in the sham group. But their spatial dispersions did not change in both groups. APD alternans occurred at shorter pacing cycle length at each site after LAD→LSD when compared to the sham group (p < 0.05 for all). After AMI, the occurrence of VAs was significantly lower in the LSD group than in the control group (p < 0.05).

CONCLUSIONS

LSD may have a beneficial impact on ventricular arrhythmias induced by AMI through modulation of autonomic tone.

Variation in the risk of venous thromboembolism following colectomy

Background

Guidelines recommend extended thromboprophylaxis following colectomy for malignant disease, but not for non-malignant disease. The aim of this study was to determine absolute and relative rates of venous thromboembolism (VTE) following colectomy by indication, admission type and time after surgery.

Methods

A cohort study of patients undergoing colectomy in England was undertaken using linked primary (Clinical Practice Research Datalink) and secondary (Hospital Episode Statistics) care data (2001–2011). Crude rates and adjusted hazard ratios (HRs) were calculated for the risk of first VTE following colectomy using Cox regression analysis.

Results

Some 12 388 patients were identified; 312 (2·5 per cent) developed VTE after surgery, giving a rate of 29·59 (95 per cent c.i. 26·48 to 33·06) per 1000 person-years in the first year after surgery. Overall rates were 2·2-fold higher (adjusted HR 2·23, 95 per cent c.i. 1·76 to 2·50) for emergency compared with elective admissions (39·44 versus 25·78 per 1000 person-years respectively). Rates of VTE were 2·8-fold higher in patients with malignant disease versus those with non-malignant disease (adjusted HR 2·84, 2·04 to 3·94). The rate of VTE was highest in the first month after emergency surgery, and declined from 121·68 per 1000 person-years in the first month to 25·65 per 1000 person-years during the rest of the follow-up interval. Crude rates of VTE were similar for malignant and non-malignant disease (114·76 versus 120·98 per 1000 person-years respectively) during the first month after emergency surgery.

Conclusion

Patients undergoing emergency colectomy for non-malignant disease have a similar risk of VTE as patients with malignant disease in the first month after surgery.

Distal revascularisation with interval ligation (DRIL): an experience

INTRODUCTION

The global increase of chronic renal failure has resulted in a growing number of patients on haemodialysis using arteriovenous fistulas (AVFs). By virtue of their very function, AVFs at times shunt blood away from regions distally, resulting in an ischaemic steal syndrome. Distal revascularisation with interval ligation (DRIL) has been described as a procedure to treat symptomatic ischaemic steal. We present our experience in the management of this complication.

PATIENTS AND METHODS

Six patients with severe ischaemic steal were treated using a DRIL procedure between May 2004 and June 2007. There were three males and three females, all with elbow brachiocephalic AVFs. Symptoms ranged from severe rest pain to digital gangrene. Published results from international studies of 135 DRIL procedures were also reviewed.

RESULTS

Vascular access was maintained along with the elimination of ischaemic symptoms in the six patients using an ipsilateral reversed basilic vein graft. Interval ligation of the distal brachial artery was performed at the same time. All patients showed immediate and sustained clinical improvement of symptoms with a demonstrable increase in digital pulse oximetry.

CONCLUSIONS

DRIL is a beneficial treatment option that has proven successful at alleviating ischemic steal symptoms and preserving vascular access. This avoids placement of central lines, its associated risks, and the need to create an alternative sited fistula.

Life expectancy of adult liver allograft recipients in the UK

BACKGROUND

Liver transplantation is a very successful therapy for those with end stage disease. Although there are numerous data on patient and graft survival after liver transplantation, life expectancy and possible loss of life (compared with a normal matched population) in those who survive remains unknown.

AIMS

To assess the life expectancy and life years lost of adult liver allograft recipients, compared with an age and sex matched UK population to provide patients with more information and to improve the use of a scarce resource.

METHODS

Using the National Transplant Database held by UK Transplant, on over 3600 adult liver allograft recipients transplanted between 1985 and 2003, we analysed survival of all adults who survived more than six months after transplantation and compared survival after transplantation with national age and sex matched controls to assess life years lost.

RESULTS

Estimated median survival time of the analysis cohort of 2702 adult liver allograft recipients was 22.2 years (95% confidence interval 19.3-25.6), with an estimated loss of seven life years compared with an age and sex matched population.

CONCLUSIONS

Overall, female recipients have a longer life expectancy and lose fewer life years than male recipients. While younger recipients have a longer life expectancy, they also lose more life years. Those transplanted for cancer, hepatitis C virus infection, and alcoholic liver disease had the greatest loss of life years.

The Happy Seeder enables direct drilling of wheat into rice stubble

Lack of suitable machinery is a major constraint to direct drilling into combine-harvested rice residues due to the heavy straw load, and the presence of loose tough straw deposited by the harvester. Therefore, most rice stubbles are burnt in the mechanised rice–wheat systems of south Asia and Australia, as this is a rapid and cheap option, and allows for quick turn around between crops. As well as loss of organic matter and nutrients, rice stubble burning causes very serious and widespread air pollution in the north-west Indo-Gangetic Plains, where rice–wheat systems predominate. A novel approach with much promise is the Happy Seeder, which combines the stubble mulching and seed drilling functions in the one machine. The stubble is cut and picked up in front of the sowing tynes, which engage bare soil, and deposited behind the seed drill as mulch. Evaluation of the technology over 3 years in replicated experiments and farmers’ fields in Punjab, India, showed that establishment of wheat sown into rice residues with the Happy Seeder was comparable with establishment using conventional methods (straw burnt followed by direct drilling or cultivation before sowing) for sowings around the optimum time into stubbles up to 7.5 t/ha. For late sowings, plant density declined significantly at straw loads above 5 t/ha. The mulch also reduced weed biomass by ~60%, and reduced soil evaporation. Yield of wheat sown around the optimum time into rice residues, using the Happy Seeder, was comparable with or higher than yield after straw removal or burning, in replicated experiments and farmers’ fields, for straw loads up to 9 t/ha. In farmers’ fields there was an average yield increase of 9 and 11% in 2004–05 and 2005–06, respectively, compared with farmer practice. For sowings after the optimum time, yield declined significantly at straw loads greater than 7.5 t/ha. The Happy Seeder offers the means of drilling wheat into rice stubble without burning, eliminating air pollution and loss of nutrients and organic carbon due to burning, at the same time as maintaining or increasing yield.

Salivary IgA response to prolonged exercise in a hot environment in trained cyclists

The aim of this study was to determine the effects of prolonged exercise in hot conditions on saliva IgA (s-IgA) responses in trained cyclists. On two occasions, in random order and separated by 1 week, 12 male cyclists cycled for 2 h on a stationary ergometer at 62 (3)% V(.)O(2 max) [194 (4) W; mean (SEM)], on one occasion (HOT: 30.3 degrees C, 76% RH) and on another occasion (

CONTROL

20.4 degrees C, 60% RH). Water was available ad-libitum. Venous blood samples and 2-min whole unstimulated saliva samples were collected at pre, post and 2 h post-exercise. The s-IgA concentration was determined using a sandwich-type ELISA. Exercising heart rate, rating of perceived exertion, rectal temperature, corrected body mass loss (P<0.01) and plasma cortisol (P<0.05) were greater during HOT. The decrease in plasma volume post-exercise was similar on both trials [HOT: -6.7 (1.1) and

CONTROL

-6.6 (1.3)%; P<0.01]. Saliva flow rate decreased post-exercise by 43% returning to pre-exercise levels by 2 h post-exercise (P<0.05) with no difference between trials. Saliva IgA concentration increased post-exercise (P<0.05) with no difference between trials. Saliva IgA secretion rate decreased post-exercise by 34% returning to pre-exercise levels by 2 h post-exercise (P<0.05) with no difference between trials. These data show that a prolonged bout of exercise results in a reduction in s-IgA secretion rate. Additionally, these data demonstrate that performing prolonged exercise in the heat, with ad libitum water intake, does not influence s-IgA responses to prolonged exercise.

Nonlinear viscoelasticity of concentrated solutions of aggrecan aggregate

Aggrecan, the major cartilage proteoglycan, is the macromolecular species primarily involved in the resiliency of cartilage tissue. Most aggrecan molecules occur in cartilage extracellular matrix as aggregates. Each aggregate has a supramolecular structure, with many highly anionic, brushlike aggrecan subunits noncovalently bound to a hyaluronan chain. To better examine the viscoelastic properties of aggrecan aggregate, contaminating subunits were removed by exclusion chromatography. At physiologic ionic strength, concentrated solutions of purified aggrecan aggregate exhibit predominantly elastic behavior at small shear strains. However, above a critical strain, gamma c, the shear moduli show a pronounced strain-softening transition, where the storage modulus decreases suddenly, and the loss modulus exhibits a maximum. At small stresses, the creep function is also highly elastic, exhibiting an equilibrium compliance and large recoverable compliance. When the stress is amplified, a discrete transition to viscous flow occurs at a yield stress sigma y. These nonlinear responses are similar to previous observations for close-packed colloidal suspensions of soft spheres, such as microgel or emulsion particles, for which a yield transition occurs when the stress and deformation are sufficient to move a particle past its neighbors.

Clinical practice guideline: screening and diagnosing autism

The clinical practice guideline (CPG) reviewed in this month's column concerns the screening and diagnosis of autism. Autism is the third most common developmental disability and affects more than 1 in 500 children, or nearly 400,000 people in the United States, in some form. Primary care providers of children, including pediatric nurse practitioners (PNPs) and family nurse practitioners (FNPs), should reasonably expect to care for at least one child with autism (CWA). The American Academy of Neurology (AAN) has therefore developed guidelines to help healthcare providers facilitate the early identification of children with autism.