Slow Compression Rates Research Articles

High-Performance Hydrogels via Alternate Compression–Decompression

Novel bioapplications of hydrogels draw huge attention to the development of strong and tough hydrogels that are easily obtainable with less chemical additions. Here, we demonstrate that pressure, a basic thermodynamic quantity, could enable poly(vinyl alcohol) (PVA) to effectively form a gel. The resulting hydrogels by alternate compression–decompression (ACD) have tunable superior mechanical properties compared with conventional freeze-thawed (FT) PVA hydrogels. The microstructures of the ACD hydrogels under varying parameters, including compression rate, cycles, and holding time, reveal that either a slow compression rate or cyclic compressions favor the physical cross-linking of such single polymer networks. The mechanical results display a wide range of ultimate tensile strength, tensile strain, and maximum compressive strength of ∼0.3 to 2.5 MPa, ∼200 to 550%, and ∼3 to 7 MPa, respectively. Moreover, the load resistance of such hydrogels can be further trained by low-cyclic strain hardening to a maximum compressive strength of ∼50 MPa, followed by a desirable recovery. Upon cyclic compression, the ACD hydrogels exhibit consistent energy dissipation behaviors. More importantly, the effect of modulation of pressure on the hydrogel’s mechanical properties is very likely universal for other hydrogel systems due to the basic mechanism of pressure-induced gelation for the polymers discussed.

Alternating fast and slow chest compression rates during CPR improved hemodynamics

IntroductionMechanical chest compression devices allow for variation in chest compression (CCs) characteristics from moment to moment, enabling therapy that is not feasible for manual CCs. Effects of varying compressions over time have not been studied. In a randomized trial in an experimental model of prolonged cardiac arrest, we compared time-varying CPR (TVCPR), alternating between 100 and 200 compressions per minute (cpm) every 6 s, to guidelines CPR (Control). MethodsVentricular fibrillation (VF) was electrically induced in 20 anesthetized pigs (28.4–45.8 kg). Following 10 min of untreated VF, cardiopulmonary resuscitation (CPR) began, randomized to TVCPR or Control. Rate of return of spontaneous circulation (ROSC), 4-h survival, and hemodynamics during the first 5 min of CPR were compared between groups. Moment-to-moment hemodynamic effects of changing the CC rate were analyzed. ResultsTVCPR improved the proportion of ROSC over time compared to Control (p < 0.05) but ROSC (9/10 vs. 5/10) and 4-h survival (8/10 vs 5/10) did not differ significantly between groups. During CPR, coronary and cerebral perfusion pressures and femoral artery pressure did not differ between groups; however, end-tidal CO2 and mixed venous O2 saturation were higher, and pulmonary artery pressure was lower (p < 0.05) for TVCPR than Control. During TVCPR, switching to 100 cpm increased coronary perfusion pressure (p < 0.05), and switching to 200 cpm increased cerebral perfusion pressure (p < 0.05). ConclusionsTime-varying CPR significantly improved indicators of net forward blood flow and proportion of ROSC over time without negatively impacting perfusion pressures. Alternating CC rate alternates between perfusion pressures favoring the brain and those favoring the heart. Time-varying CPR represents a new avenue of research for optimizing CPR. Institutional Protocol NumberUniversity of Alabama at Birmingham Institutional Animal Care and Use Committee (IACUC) Protocol Number 140406860.

Investigation of mechanical and microstructural characteristics of Ti–45Nb undergoing transversal ultrasonic vibration-assisted upsetting

Abstract Numbers of researchers have investigated the mechanism of the acoustic softening effect and applied it in the plastic forming field. Inadequacy discussion, nevertheless, softening effect has been focused on the volume effect, seldom considering the surface effect. In this study, a transverse ultrasonic vibration-assisted upsetting system was developed to compress the aeronautical material Ti–45Nb cylinder. A similar acoustic softening effect was obtained comparing with the existing softening mechanism as the amplitude is lower than 34 μm or under slow compression rates, whereas the reduction of flow stress is not only contributed by the volume effect when the amplitude is larger than 34 μm and with higher compression rates, which is co-caused by volume effect and surface effect. Besides, the influences of amplitude and vernation time on residual hardening effect were analyzed. To reveal the effect of the different acoustic softening mechanisms on texture evolution with a higher compression rate, Electron backscatter diffraction (EBSD) was used to disclose the evolution characterizations of grain size, misorientation angle, and texture under different amplitude. The results show that the number of the low angle grain boundary and sub-grain in the tested area has a positive relationship with the deformation and amplitude, especially the specimens under amplitudes of 38 μm and 46 μm. Besides, the acoustic residual hardening effect of Ti–45Nb is caused by the increase of dislocation density and grain refinement under ultrasonic vibration.

Analysis of Basic Life Support Training Provided to Pharmacy Students Using Feedback Device

The quality of chest compression affects survival after sudden cardiac arrest, particularly when it occurs out of hospital. Pharmacy students should acquire basic life support skills as part of the model core curriculum of pharmacy education. Here, we trained first-year students at the Faculty of Pharmacy to deliver cardiopulmonary resuscitation and used a manikin with a real-time feedback device that quantified chest compression skills. Students were classified into shallow compressions (SC; <50 mm) and deep compressions (DC; ≥50 mm) groups based on the depth of chest compressions measured prior to training. After training, the mean compression depth (mm) was significantly shallower for the SC, than the DC group and many students in the SC group did not reach a depth of 50 mm. Similarly, students were classified into slow compression rate (SR; ≤120/min) and rapid compression rate (RR; >120/min) groups based on the results of training in the rate of chest compressions. Significant differences in mean compression rates were not found between the groups. However, correct compression rate (%), the percentage of maintaining 100-120 compression/min was significantly higher in the SR, than in the RR group. Chest compression rates correlated with compression depth, and chest compression tended to be too shallow in group that was too fast. The quality of chest compression might be improved by delivering chest compressions at a constant rate within the recommended range.

Void structure stability in wet granular matter and its application to crab burrows and cometary pits

Cohesive granular matter can support stable void structures, which can universally be found in various scenes from everyday lives to space. To quantitatively characterize the stability and strength of a void structure in cohesive granular matter, we perform a simple tunnel-compression experiment with wet granular matter. In the experiment, a horizontal tunnel in a wet granular layer is vertically compressed with a slow compression rate. The experimental result suggests that the tunnel deformation can be classified into the following three types: (i) shrink, (ii) shrink with collapse, and (iii) subsidence by collapse. Using the experimental result, we estimate the stable limit of various void structures in a cohesive granular layer from crab burrows on a sandy beach to the pits observed on cometary surfaces.

Kinetic effects on the morphology and stability of the pressure-induced extended-solid of carbon monoxide.

In this work, the dependence of the morphology and stability of the extended solid of carbon monoxide (CO) is correlated to the rate of transformation from the molecular CO to extended solid of CO using optical imaging, photoluminescence, Raman spectroscopy, and X-ray diffraction. The analyses show the rate and pressure of the transformation to be strongly controlled by catalytic effects, both chemical and optical. In a larger volume per reaction area, the transformation was found to require either a longer time at an elevated pressure or a higher pressure compared to a sample synthesized in a smaller volume per reaction area, leading to the conclusion that the transformation rate is slower for a sample in a larger volume per reaction area. A faster rate of transformation was also noted when the reaction area of a CO sample was catalyzed with H2SO4. Through variation of the volume per reaction area, pressure or the addition of catalysts, it was possible to control the rate of the phase transition and therefore the morphology. In general, the extended solid of CO synthesized with a faster rate showed a more ordered structure and increased metastability relative to the material formed with a slower compression rate.

Abstract 290: Cardiopulmonary Resuscitation Duty Cycle in Out-of-Hospital Cardiac Arrest

Background: CPR duty cycle is the portion of time spent in compression relative to the total time of the compression-decompression cycle. Guidelines recommend a 50% duty cycle based largely on animal investigation. Little is known about duty cycle in human resuscitation and whether duty cycle correlates with other CPR measures. Methods: We calculated the duty cycle, compression depth, and compression rate during EMS resuscitation of 164 patients with out-of-hospital ventricular fibrillation cardiac arrest. We captured force recordings from a chest accelerometer to measure ten-second CPR epochs that immediately preceded each scheduled rhythm analysis. Duty cycle was calculated using two methods. The effective compression time (ECT) is the time from beginning to end of compression divided by total period for that compression-decompression cycle. The area duty cycle (ADC) is the ratio of area under the force curve divided by total area of one compression-decompression cycle. We evaluated the compression depth and compression rate according to duty cycle quartiles. Results: There were 369 ten-second epochs among 164 patients. The median duty cycle was 38.8% (SD=5.5%) using ECT and 32.2% (SD=4.3%) using ADC. A relatively shorter compression phase (lower duty cycle) was associated with greater compression depth (test for trend &lt; 0.05 for ECT and ADC) and slower compression rate (test for trend &lt; 0.05 for ADC) (Table). Sixty-one patients (37%) survived to hospital discharge. Conclusions: In this system with high survival, duty cycle was well below the 50% recommended guideline, and was associated with compression depth and rate. These findings provide rationale to incorporate duty cycle into future research to evaluate how CPR influences resuscitation.

Cardiopulmonary resuscitation duty cycle in out-of-hospital cardiac arrest

BackgroundDuty cycle is the portion of time spent in compression relative to total time of the compression–decompression cycle. Guidelines recommend a 50% duty cycle based largely on animal investigation. We undertook a descriptive evaluation of duty cycle in human resuscitation, and whether duty cycle correlates with other CPR measures. MethodsWe calculated the duty cycle, compression depth, and compression rate during EMS resuscitation of 164 patients with out-of-hospital ventricular fibrillation cardiac arrest. We captured force recordings from a chest accelerometer to measure ten-second CPR epochs that preceded rhythm analysis. Duty cycle was calculated using two methods. Effective compression time (ECT) is the time from beginning to end of compression divided by total period for that compression–decompression cycle. Area duty cycle (ADC) is the ratio of area under the force curve divided by total area of one compression–decompression cycle. We evaluated the compression depth and compression rate according to duty cycle quartiles. ResultsThere were 369 ten-second epochs among 164 patients. The median duty cycle was 38.8% (SD=5.5%) using ECT and 32.2% (SD=4.3%) using ADC. A relatively shorter compression phase (lower duty cycle) was associated with greater compression depth (test for trend <0.05 for ECT and ADC) and slower compression rate (test for trend <0.05 for ADC). Sixty-one of 164 patients (37%) survived to hospital discharge. ConclusionsDuty cycle was below the 50% recommended guideline, and was associated with compression depth and rate. These findings provider rationale to incorporate duty cycle into research aimed at understanding optimal CPR metrics.

Cost-efficient method and device for the study of stationary tissular gas bubble formation in the mechanisms of decompression sickness.

Current in vivo methods cannot distinguish between the roles of vascular and stationary tissular gas bubbles in the mechanisms of decompression sickness (DCS). To answer this question, we designed a normobaric-hyperbaric chamber for studying specifically the contribution of stationary tissular gas bubbles in the mechanisms of DCS in individually-superfused tissue samples. For validating our method, we investigated in rat brain slices exposed to 0.4MPa air absolute pressure whether fast decompression rate - the most important cause of cerebral DCS - may induce an increase of lactate dehydrogenase (LDH), a marker of cell injury, compared to slow decompression rate. We provide a technical description of our pressure chamber and show that fast decompression rate of 0.3MPamin(-1) induced a rapid and sustained increase of LDH release compared to slow compression rate of 0.01MPamin(-1) (P<0.0001). There is no current method for studying stationary tissular gas bubbles. This report describes the first method for studying specifically in tissue samples the role of stationary tissular gas bubbles in the mechanisms of DCS. Advantageously, according to this method (i) biological markers other than LDH could be easily studied; (ii) tissue samples could be taken not only from the brain but also from any part of the animal's body known of interest in DCS research, allowing performing tissue compartment research, a major question in the physics and theory of decompression research; and (iii) histological studies could be performed from the tissue samples.

Lethality and injuring the effect of compression and decompression rates of high hydrostatic pressure on Escherichia coli O157:H7 in different matrices

The effect of compression and decompression rates of high hydrostatic pressure (HHP) on Escherichia coli O157:H7 was investigated. Samples of orange juice, skimmed milk and Tris buffer were inoculated with E. coli O157:H7 and subjected to 600 MPa for 3 min at 4°C with fast, medium and slow compression and decompression. Analyses immediately after HHP treatment revealed that E. coli in milk and juice treated with fast compression suffered more than slow compression rates. Slow decompression resulted in higher inactivation of E. coli in all matrices. After overnight storage, highest stress-recovery (1.19 log cfu/mL) was observed in Tris buffer. Healthy cells were<1 log cfu/mL in milk and buffer samples, but no growth was detected in orange juice for any of the treatments immediately after HHP. After 15 days at 4°C, E. coli cells in skimmed milk and Tris buffer recovered significantly, whereas the recovery of sublethally injured cells was inhibited in orange juice.

CPR compression depth and rate in relation to physical exertion in paramedic students

The International Liaison Committee on Resuscitation (ILCOR) guidelines suggest rescuers deliver cardiopulmonary resuscitation (CPR) in cycles of 30 chest compressions and 2 ventilations (30:2) at a rate of 100 compressions per minute with a compression depth of 4-5 cm. Given this increase from the previous CPR cycle of 15:2, there is now also greater emphasis on pushing faster and deeper with minimal interruption. This has led to speculation surrounding rescuer fatigue and compression inefficiency. The purpose of this pilot study was to assess the level of work intensity and fatigue among undergraduate students during simulated CPR, including the quality of chest compressions. Methods: this was an observational pilot study investigating second year undergraduate paramedic students’ fatigue levels and quality of chest compressions following 20 minutes of simulated CPR. Data were collected at baseline and after every 2 minutes until conclusion of twenty minutes. Measurements of work intensity and fatigue included heart rate, rating of perceived exertion (Borg), compression depth and compression frequency. Results: a total of 7 subjects participated (2 male, 5 female), with five students aged 21-25 years. Male subjects showed a significantly slower compression rate when compared to females (108.0 vs 125.6 chest compressions per minute, P=0.006). Heart rate was significantly higher than rest (prior to commencing CPR) after 14 minutes of CPR (P=0.045). Perceived exertion was significantly higher than at rest at 2, 6, 10, 14, and 18 minutes, (P&lt;0.01). Conclusion: this pilot study suggests that high levels of fatigue and perceived exertion are present early when undertaking CPR in a controlled setting, with some fatigue attributed to the faster than recommended chest compression rates.

Abstract 220: Analysis of Actual CPR Through a Review of YouTube Video: Poor Performance Is Common in Professional and Lay Rescuers

INTRODUCTION: Numerous studies have shown the performance of CPR in both prehospital and hospital settings often fails to meet recommended standards. We sought to analyze the quality of lay rescuer (LR) and professional rescuer (PR) CPR performance in real resuscitation events captured on video on the website YouTube.com. METHODS: We searched YouTube for videos of actual adult CPR recorded by bystanders. Videos which were staged for teaching, commercial use or entertainment were excluded. A convenience sample of 50 videos of CPR (in and out-of-hospital) was analyzed. Demographics and CPR quality parameters were collected. Compression depth was subjectively evaluated as adequate or inadequate (ie. not forceful enough). RESULTS: The 50 videos collected were uploaded between 12/2009 and 2/2011. They ranged from :07 to 9:57 minutes in length. Forty-two of 50 (84%) were of out-of-hospital arrests. CPR was done by LR in 17 and PR in 43. The mean chest compression (CC) rate was 110/m (SD 30, range 49-200) for all rescuers, 101/m (SD 29, range 46-166) for LR and 113/m (SD 28, range 49-200) for PR. In both groups, 40% of CC were slower than the recommended rate of 100/m. Inadequate release or leaning was seen in 66% of the time overall (11/17 (65%) of LR and 23/43 (53%) of PR). CC depth was adequate in 18/50 (36%) for both groups (3/17 for LR and 17/43 for PR). Depth was inadequate in 31/50 (62%) for both groups (14/17 for LR and 25/43 for PR). Compression depth adequacy was indeterminate in 1 video where the chest could not be seen. The mean time for rescue breath delivery was 7.8s (SD 4.4, range 3.4-25) overall, 6.3s (SD 3.1) for LR, 14.7s (SD 5.2) for PR. For PR, the mean ventilation rate by BVM alone or after intubation was 31/m (SD 17, range 3-66). 88% of ventilations were faster than the recommended 8-10/m. CONCLUSIONS: In actual bystander-recorded CPR, typical measures of CPR quality are often poor. Slow compression rates, excessive ventilation and significant periods of ‘leaning’ are common, in lay as well as professional rescuers. Mean CC rate is close to recommended rates, but with a very wide range making overall compliance poor. Poor compression depth was more common in LR CPR.

Squeeze flow magnetorheology

This paper is concerned with an investigation of the rheological performance of magnetorheological fluids under squeeze flow. Preliminary results on Newtonian fluids are first compared to Stefan’s equation. Then, unidirectional monotonic compression tests are carried out in the presence of uniaxial external magnetic fields at slow compression rates under constant volume operation. Results are compared to Bingham plastic, biviscous, and single chain micromechanical squeeze flow models. Measurements using combined deformation modes (compression+small-strain oscillatory shear) suggest a compression-induced shear strengthen effect up to strains of ∼0.5. Particle-level dynamic simulations are in qualitatively good agreement with experimental observations.

Off-equilibrium response of grafted polymer chains subject to a variable rate of compression

We present Brownian dynamics simulations of single grafted semiflexible chains (i.e., "polymer mushrooms") with varying persistence lengths, intra-chain interactions, and subject to confinement. The results from different rates of compression are presented in the cases of an approaching infinite plane and a paraboloid tip. We discuss the different behaviour observed for grafted chains with strong and weak self-attraction (i.e., "hard" and "soft" polymer mushrooms). In both cases the effect on the size and shape is more pronounced for a slow compression rate, especially for "hard mushrooms". We have also studied the relaxation of the chain while the compressing plane is maintained, and when it is removed suddenly. We find that the response depends strongly on the time allowed for relaxation in the compressed state. When using instead a paraboloid tip, the overall effects are similar yet less pronounced because the chain can dodge the confining object via an "escape transition."

Dynamic Solidification in Nanoconfined Water Films

Mechanical properties of nanoconfined water layers are still poorly understood and continue to create controversy, despite their importance for biology and nanotechnology. We report on dynamic nanomechanical measurements of water films compressed to a few single molecular layers. We show that the mechanical properties of nanoconfined water layers change significantly with their dynamic state. In particular, we observed a sharp transition from viscous to elastic response even at extremely slow compression rates, indicating that mechanical relaxation times increase dramatically once water is compressed to less than 3-4 molecular layers.

Simulation of Mechanically-Assembled Monolayers In Poor Solvent Using Discontinuous Molecular Dynamics

We present and discuss the results of discontinuous molecular dynamics simulations of mechanically assembled polymer layers chemically attached to flexible substrates under poor solvent conditions. Square-well chains of lengths comprising 20 to 100 units end-grafted to a hard surface at low density are compressed laterally at varying rates. Brush thickness depends on the interplay between solvent quality and the substrate compression rate. Brushes formed in poor solvents at fast compression rates are thinner and exhibit more heterogeneity in coverage than brushes formed in good solvents at slow compression rates. End-monomer trapping increases with increasing compression rate and/or decreasing solvent quality. By varying relaxation/compression rate, we can modify the effects of brush thickness hysteresis. Finally, we suggest a general blueprint for efficient formation of defect-free monolayers that might be followed by experimenters.

Jamming transition in emulsions and granular materials

We investigate the jamming transition in packings of emulsions and granular materials via molecular dynamics simulations. The emulsion model is composed of frictionless droplets interacting via nonlinear normal forces obtained using experimental data acquired by confocal microscopy of compressed emulsions systems. Granular materials are modeled by Hertz-Mindlin deformable spherical grains with Coulomb friction. In both cases, we find power-law scaling for the vanishing of pressure and excess number of contacts as the system approaches the jamming transition from high volume fractions. We find that the construction history parametrized by the compression rate during the preparation protocol has a strong effect on the micromechanical properties of granular materials but not on emulsions. This leads the granular system to jam at different volume fractions depending on the histories. Isostaticity is found in the packings close to the jamming transition in emulsions and in granular materials at slow compression rates and infinite friction. Heterogeneity of interparticle forces increases as the packings approach the jamming transition which is demonstrated by the exponential tail in force distributions and the small values of the participation number measuring spatial localization of the forces. However, no signatures of the jamming transition are observed in structural properties, like the radial distribution functions and the distributions of contacts.

The distribution of tetravalent network glasses

A model tetravalent network fluid, crystal and many glasses are studied by molecular dynamics simulation. 171 glasses were made by compressing the fluid with five orders of magnitude variation in the quench rate. The pressure and entropy of each glass are expressed as functions of a single variable, the quench rate dependent limiting density, z 0 of the rigidly jammed state where the pressure diverges. The number of possible glasses with limiting density z0 is approximated by a Gaussian distribution N g(z 0)dz0 = exp{1·2N}exp(-123N(Δz 0)2}dz0, where Δz 0 = z 0 −0·766 and N is the number of molecules. That distribution implies that In {N g(z 0)}/N → 0 as z 0 → 0·864, which suggests that an ideal glass transition would occur to a glass with z 0 = 0·864 with slow compression rates, if the fluid did not freeze. We show that the free energy and pressure of the dense fluid can be simply expressed in terms of the properties of the glasses.

Indentation Analysis of Biphasic Articular Cartilage: Nonlinear Phenomena Under Finite Deformation

The nonlinear indentation response of hydrated articular cartilage at physiologically relevant rates of mechanical loading is studied using a two-phase continuum model of the tissue based on the theory of mixtures under finite deformation. The matrix equations corresponding to the governing mixture equations for this nonlinear problem are derived using a total Lagrangian penalty finite element method, and solved using a predictor-corrector iteration within a modified Newton-Raphson scheme. The stress relaxation indentation problem is examined using either a porous (free draining) indenter or solid (impermeable) indenter under fast and slow compression rates. The creep indentation problem is studied using a porous indenter. We examine the finite deformation response and compare with the response obtained using the linear infinitesimal response. Differences between the finite deformation response and the linear response are shown to be significant when the compression rate is fast or when the indenter is impermeable. The finite deformation model has a larger ratio of peak-to-equilibrium reaction force, and higher relaxation rate than the linear model during the early relaxation period, but a similar relaxation time. The finite deformation model predicts a slower creep rate than the linear model, as well as a smaller equilibrium creep displacement. The pressure distribution below the indenter, particularly near the loaded surface is also larger with the finite deformation model.

Radial flow through deformable porous shells

AbstractThe problem of radially directed fluid flow through a deformable porous shell is considered. General nonlinear diffusion equations are developed for spherical, cylindrical and planar geometries. Solutions for steady flow are found in terms of an exact integral and perturbation solutions are also developed. For unsteady flow, perturbation methods are used to find approximate small-time solutions and a solution valid for slow compression rates. These solutions are used to investigate the deformation of the porous material with comparisons made between the planar and the cylindrical geometries.