Rate Of Stretch Research Articles

Strain rate of stretch affects crossbridge detachment during relaxation of intact cardiac trabeculae.

Mechanical Control of Relaxation refers to the dependence of myocardial relaxation on the strain rate just prior to relaxation, but the mechanisms of enhanced relaxation are not well characterized. This study aimed to characterize how crossbridge kinetics varied with strain rate and time-to-stretch as the myocardium relaxed in early diastole. Ramp-stretches of varying rates (amplitude = 1% muscle length) were applied to intact rat cardiac trabeculae following a load-clamp at 50% of the maximal developed twitch force, which provides a first-order estimate of ejection and coupling to an afterload. The resultant stress-response was calculated as the difference between the time-dependent stress profile between load-clamped twitches with and without a ramp-stretch. The stress-response exhibited features of the step-stretch response of activated, permeabilized myocardium, such as distortion-dependent peak stress, rapid force decay related to crossbridge detachment, and stress recovery related to crossbridge recruitment. The peak stress was strain rate dependent, but the minimum stress and the time-to-minimum stress values were not. The initial rapid change in the stress-response indicates enhanced crossbridge detachment at higher strain rates during relaxation in intact cardiac trabeculae. Physiologic considerations, such as time-varying calcium, are discussed as potential limitations to fitting these data with traditional distortion-recruitment models of crossbridge activity.

Computational modelling of mechano-electric feedback and its arrhythmogenic effects in human ventricular models

The current study aims to investigate the role of mechano-electric feedback (MEF) in healthy cardiac cycles and in cardiac arrhythmia using human ventricular models. The numerical formulation of stretch-activated channels (SACs) in terms of the fibre stretch of the myocardium is incorporated into the modified Hill model that describes the myocardium as an electro-visco-active material. Additionally, we propose models of SACs formulated in terms of the rate of stretch along fibre direction and the stretch along sheet direction. We analyze the effect of the three different models for SACs and different material properties on the regular cycles by using electrocardiogram and volume-time curves, and show that the each model of SACs has regionally different influences on the heart model. Moreover, we simulate ‘commotio cordis’ and ‘precordial thump’ and demonstrate that MEF plays a major role in the occurrence of fibrillation and defibrillation in the absence of the structural cardiac damage. Furthermore, we study the role of MEF in premature ventricular contraction when the blood pressure is disturbed.

A pseudo-strain energy density function for mechanical behavior modeling of visco-hyperelastic materials

In this paper, a constitutive phenomenological framework is proposed for the mechanical behavior of the visco-hyperelastic materials. This phenomenological framework is based on the concept of developing the schemas of the classical linear theory to the nonlinear regime. For this purpose, at first, the structure of the constitutive law of a viscoelastic material is constructed in the linear behavior case. In this construction, it can be observed that the stress can be decomposed into the sum of the elastic part and viscous part with a time function. In generalization of the rebuilt framework of the linear theory to a nonlinear regime to model the mechanical behavior of visco-hyperelastic materials, a pseudo-strain energy density function including elastic and viscous parts is assumed. The hyperelastic behaviors of the developed nonlinear model is organized via a Hookean-type constitutive equation in terms of the power law and exponential strain measures which have a high flexibility for capturing the mechanical behaviors with different trends from the S-shaped to J-shaped forms. The time part of the developed framework is proposed such that it can model the long-term memory fading principle. For this purpose, the new weight functions are used such that they can capture the rate behavior and recognize the relaxation curves with different starting points from stretch and rate of stretch. Finally, in order to do the comprehensive evaluation of the performance of the proposed model, the high strain rate tensile and compression tests, separately and simultaneously; and also, the relaxation tests at different levels from strain and strain rate beside the moderate rate tensile tests are examined to calibrate the model for different mechanical behaviors. It is observed that there is a good accordance between the test data and predictions of the model for the mechanical behavior of visco-hyperelastic materials.

Ion Channels in Biophysics and Physiology: Methods & Challenges to Study Mechanosensitive Ion Channels.

In a seminal work published in 1950, Sir B. Katz showed that the electrical response of the frog muscle spindle varies directly with the rate and amplitude of muscle stretch. This observation led him to propose the existence of a piezoelectric substance in this organ, setting the stage for the field of mechanobiology (Katz, J Physiol 111, 261-282, 1950). Despite this early work, the identity of the molecules responsible for the conversion of mechanical stimuli into biological signals has remained hidden for decades. This delay is often attributed to the inherent difficulty to precisely quantify the mechanical deformations of biological samples. In contrast to other forms of stimuli such as ligand concentration and membrane potential, quantifying mechanical deformations of cell membranes is not trivial. Mechanical forces produce a complex array of membrane deformations including bending, thinning, compression, expansion, and shear, and thus, have components in many strain dimensions. In addition, due to the viscoelastic nature of cells, these deformations may have linear and nonlinear components. In spite of these experimental challenges, Sukharev et al. cloned the first mechanosensitive ion channel from the bacteria E. coli in the mid-1990s (Sukharev et al. Nature, 265-268, 1994). Two decades later, several protein families encompassing dozens of eukaryotic mechanosensitive ion channels have been identified, depicting an astonishing diversity of force-activated molecular machines. In this chapter, we intend to provide an overview of the current state of knowledge and technical challenges to study how cell membranes deform upon mechanical stress and how ion channel proteins detect these deformations to engage homeostatic cellular responses.

Progressive stretch enhances growth and maturation of 3D stem-cell-derived myocardium.

Bio-engineered myocardium has great potential to substitute damaged myocardium and for studies of myocardial physiology and disease, but structural and functional immaturity still implies limitations. Current protocols of engineered heart tissue (EHT) generation fall short of simulating the conditions of postnatal myocardial growth, which are characterized by tissue expansion and increased mechanical load. To investigate whether these two parameters can improve EHT maturation, we developed a new approach for the generation of cardiac tissues based on biomimetic stimulation under application of continuously increasing stretch.Methods: EHTs were generated by assembling cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CM) at high cell density in a low collagen hydrogel. Maturation and growth of the EHTs were induced in a custom-made biomimetic tissue culture system that provided continuous electrical stimulation and medium agitation along with progressive stretch at four different increments. Tissues were characterized after a three week conditioning period.Results: The highest rate of stretch (S3 = 0.32 mm/day) increased force development by 5.1-fold compared to tissue with a fixed length, reaching contractility of 11.28 mN/mm². Importantly, intensely stretched EHTs developed physiological length-dependencies of active and passive forces (systolic/diastolic ratio = 9.47 ± 0.84), and a positive force-frequency relationship (1.25-fold contractility at 180 min-1). Functional markers of stretch-dependent maturation included enhanced and more rapid Ca2+ transients, higher amplitude and upstroke velocity of action potentials, and pronounced adrenergic responses. Stretch conditioned hiPSC-CMs displayed structural improvements in cellular volume, linear alignment, and sarcomere length (2.19 ± 0.1 µm), and an overall upregulation of genes that are specifically expressed in adult cardiomyocytes.Conclusions: With the intention to simulate postnatal heart development, we have established techniques of tissue assembly and biomimetic culture that avoid tissue shrinkage and yield muscle fibers with contractility and compliance approaching the properties of adult myocardium. This study demonstrates that cultivation under progressive stretch is a feasible way to induce growth and maturation of stem cell-derived myocardium. The novel tissue-engineering approach fulfills important requirements of disease modelling and therapeutic tissue replacement.

Continuous vs stepwise anal acoustic reflectometry: An improved technique for physiological measurement of anal sphincter function?

Anal acoustic reflectometry (AAR) is a technique for measuring the physiological profile of the anal canal, primarily the internal anal sphincter. Evaluation of a new continuous method, recently developed for the urethra, would enable its future application for investigation of rectal reflexes. Patients aged 18 and over with fecal incontinence (FI) were included. Stepwise AAR parameters were compared with continuous opening pressure (Op, cmH2 O), opening elastance (Oe, cmH2 O/mm2 ), closing pressure (Cp, cmH2 O), closing elastance (Ce, cmH2 O/mm2 ), hysteresis (Hys, [%]), squeeze opening pressure (SqOp, cmH2 O), and squeeze opening elastance (SqOe, cmH2 O/mm2 ). Vaizey incontinence and Manchester Health Questionnaire scores were also collected. Thirty-two patients, 26 females were analyzed. Median age: 60 (range, 32-75). Median AAR parameters of Op (37.50 vs 35.15, P = .031), Oe (1.31 vs 0.84, P < .0001), Ce (1.11 vs 0.88, P < .0001), Hys (37.75 vs 19.04, P < .0001), and SqOe (1.27 vs 1.06, P = .005) were significantly higher with the continuous method. Cp (22.70 vs 27.22, P = .003) is lower and SqOp (96.87 vs 59.47, P = .71) not significantly different. The continuous technique had superior repeatability between cycles for all AAR parameters except Oe, which was equivalent and continuous SqOp had a stronger negative correlation with Vaizey score than stepwise (-0.46, P = .009 vs -0.37, P = .038). The differences seen between the two techniques are likely to be related to the rate of stretch. The continuous technique appears to represent a more physiological measurement of anal sphincter function than the stepwise technique particularly in the assessment of voluntary squeeze function.

A visco-hyperelastic constitutive model and its application in bovine tongue tissue

Material properties of the human tongue tissue have a significant role in understanding its function in speech, respiration, suckling, and swallowing. Tongue as a combination of various muscles is surrounded by the mucous membrane and is a complicated architecture to study. As a first step before the quantitative mechanical characterization of human tongue tissues, the passive biomechanical properties in the superior longitudinal muscle (SLM) and the mucous tissues of a bovine tongue have been measured. Since the rate of loading has a sizeable contribution to the resultant stress of soft tissues, the rate dependent behavior of tongue tissues has been investigated via uniaxial tension tests (UTTs). A method to determine the mechanical properties of transversely isotropic tissues using UTTs and inverse finite element (FE) method has been proposed.Assuming the strain energy as a general nonlinear relationship with respect to the stretch and the rate of stretch, two visco-hyperelastic constitutive laws (CLs) have been proposed for isotropic and transversely isotropic soft tissues to model their stress-stretch behavior. Both of them have been implemented in ABAQUS explicit through coding a user-defined material subroutine called VUMAT and the experimental stress-stretch points have been well tracked by the results of FE analyses. It has been demonstrated that the proposed laws make a good description of the viscous nature of tongue tissues. Reliability of the proposed models has been compared with similar nonlinear visco-hyperelastic CLs.

Tip-Enhanced Raman Spectromicroscopy on the Angstrom Scale: Bare and CO-Terminated Ag Tips.

The tip is key to the successful execution of tip-enhanced Raman scattering (TERS) measurements in the single molecule limit. We show that nanoscopically smooth silver tips, batch produced through field-directed sputter sharpening, reliably attain TERS with enhancement factors that reach 1013, as measured by the Raman spectra of single CO molecules attached to the tip apex. We validate the bare tips by demonstrating spectromicroscopy with submolecular spatial resolution and underscore that TERS is a near-field effect that does not obey simple selection rules. As a more gainful analytical approach, we introduce TERS-relayed molecular force microscopy using CO-terminated tips. By taking advantage of the large Stark tuning rate of the CO stretch, molecular structure and charges can be imaged with atomic resolution. As illustration, we image a single Ag atom adsorbed on Au(111) and show that the adatom carries +0.2e charge.

Myocardial relaxation is accelerated by fast stretch, not reduced afterload

Fast relaxation of cross-bridge generated force in the myocardium facilitates efficient diastolic function. Recently published research studying mechanisms that modulate the relaxation rate has focused on molecular factors. Mechanical factors have received less attention since the 1980s when seminal work established the theory that reducing afterload accelerates the relaxation rate. Clinical trials using afterload reducing drugs, partially based on this theory, have thus far failed to improve outcomes for patients with diastolic dysfunction. Therefore, we reevaluated the protocols that suggest reducing afterload accelerates the relaxation rate and identified that myocardial relengthening was a potential confounding factor. We hypothesized that the speed of myocardial relengthening at end systole (end systolic strain rate), and not afterload, modulates relaxation rate and tested this hypothesis using electrically-stimulated trabeculae from mice, rats, and humans. We used load-clamp techniques to vary afterload and end systolic strain rate independently. Our data show that the rate of relaxation increases monotonically with end systolic strain rate but is not altered by afterload. Computer simulations mimic this behavior and suggest that fast relengthening quickens relaxation by accelerating the detachment of cross-bridges. The relationship between relaxation rate and strain rate is novel and upends the prevailing theory that afterload modifies relaxation. In conclusion, myocardial relaxation is mechanically modified by the rate of stretch at end systole. The rate of myocardial relengthening at end systole may be a new diagnostic indicator or target for treatment of diastolic dysfunction.

Stark Effect and Nonlinear Impedance of the Asymmetric Ag-CO-Ag Junction: An Optical Rectenna

We present first-principles analysis of the Stark effect of CO adsorbed on an atomically sharp silver asperity, and current versus potential (I–V) characteristics of the Ag-CO-Ag junction. The analysis supports the suggestion that CO-bridged plasmonic junctions represent rectifying nanoantennas at optical frequencies and that the CO vibrational spectrum serves as a molecular voltmeter [M. Banik et al. ACS Nano 2012, 6, 10343]. The Stark effect is principally controlled by the field-induced charge redistribution between the antibonding 2π*-orbitals of CO and the s-electrons of Ag. The Stark tuning rate of the CO stretch, 1.5 × 10–6 cm–1/V cm–1, is ∼25% larger on atomically sharp asperities than on flat Ag, and remains constant over a large window of applied fields (±0.8 V/A). As such, both sign and strength of local electric field can be quantitatively determined by the vibrational shift of CO. The I–V curve of the Ag-CO-Ag junction is nonlinear, rendering it an effective rectifier with responsivity S = (∂...

1G41 衝撃引張ひずみを受ける培養神経細胞の耐性評価

Diffuse axonal injury (DAI), being the most common type of pathology in Traumatic Brain Injury (TBI), has two distinct types of axonal pathology; swellings that induced by the neurofilament accumulation as a result of the damaged neurofilament structure in the axonal cytoskeleton and focal compaction and/or impaired transport due to the mechanical insult along the axons fallowed by secondary axotomy, and the axonal bulbs which likely represent complete axonal disconnection. These cytoskeletal abnormalities which proceed to the formation of the swellings and secondary axotomy are the morphological indication of DAI. Although previous researches have provided some insight on understanding the cellular mechanism of neuronal injury, and suggested that the degree of electrophysiological impairment and morphological damage of neurons is directly related to the magnitude and rate of axonal stretch, the exact mechanisms that initiate secondary degeneration in DAI are yet to be fully characterized. Our previous studies suggested that the threshold of dysfunction and interruption of axonal transport is strains of 15-22 % at strain rates of 21-27 s^<-1> and both β-APP and Tau are promising candidates for injury analysis. However, quantitative relation between impulsive strain and axonal injury is yet to be discovered thoroughly. Therefore, in this study, axonal injury induced by uniaxial stretch on differentiated mouse neuronal stem cells in order to clarify the relation between the impulsive strain, strain rate and axonal injury. Herein, evaluation is performed by immunohistochemical labeling, with β-APP and tau protein accumulation as biochemical markers of choice.

A viscoplastic model for the active component in cardiac muscle.

The HMK model (Hunter et al. in Prog Biophys Mol Biol 69:289-331, 1998) proposes mechanobiological equations for the influence of intracellular calcium concentration [Formula: see text] on the evolution of bound calcium concentration [Formula: see text] and the tropomyosin kinetics parameter z, which model processes in the active component of the tension in cardiac muscle. The inelastic response due to actin-myosin crossbridge kinetics is modeled in the HMK model with a function Q that depends on the history of the rate of total stretch of the muscle fiber. Here, an alternative model is proposed which models the active component of the muscle fiber as a viscoplastic material. In particular, an evolution equation is proposed for the elastic stretch [Formula: see text] in the active component. Specific forms of the constitutive equations are proposed and used to match experimental data. The proposed viscoplastic formulation allows for separate modeling of three processes: the high rate deactivation of crossbridges causing rapid reduction in active tension; the high but lower rate reactivation of crossbridges causing recovery of active tension; and the low rate relaxation effects characterizing the Hill model of muscles.

PWE-390 Response of the anal canal to stretch and anal acoustic reflectometry

<h3>Introduction</h3> Anal acoustic reflectometry (AAR) is a new test that uses reflected sound waves to investigate patients with faecal incontinence (FI). AAR methodology and variables of opening pressure (OP), opening elastance (OE), closing pressure (CP), closing elastance (CE), hysteresis (HY), squeeze opening pressure (SOP) and squeeze opening elastance (SOE) have previously been described. The aim of this study was to establish the response to stretch of the anal canal. <h3>Method</h3> Prospective randomised cohort study in a tertiary pelvic floor unit. Patients were recruited and randomised into 2 groups of 25; the first group received normal rate AAR (5 cmH₂0/3secs) then manometry (maximum resting pressure MRP and maximum squeeze pressure MSP) followed by a 2 min rest and then fast rate AAR (5 cmH₂O/1secs) then manometry. The order was reversed for the second group. Clinical details and Vaizey score were recorded for all patients. <h3>Results</h3> 50 patients, 40 (80%) women, median age 62 (30–78), 27 (54%) mixed FI, 15 (30%) urge FI and 8 (16%) passive FI. The groups were matched for age (p = 0.6), sex (p = 0.27), type of FI (p = 0.06) and Vaziey score (p = 0.13). No difference was found between the normal and fast rate of AAR (values shown are means) for all AAR; OP 37.2 v 39.7 cmH₂O p = 0.08, OE 0.97 v 0.98 cmH₂O/mm²p = 0.87, CP 31.5 v 30.5 cmH₂O p = 0.44, CE 0.94 v 0.95 cmH₂O/mm²p = 0.67, HY 24.2 v 23.7% p = 0.73, SOP 66.1 v 62.2 cmH₂O p = 0.06, SOE 1.06 v 1.07 cmH₂O/mm²p = 0.82. Following AAR measurement no difference in manometry values were found; MRP 37.6 v 39.8 cmH₂O p = 0.34, MSP 65.9 v 66.6 cmH₂O p = 0.73. <h3>Conclusion</h3> Prior investigation with either fast or normal rate AAR does not influence manometry findings. Within the parameters of this study, the anal canal does not appear to respond differently to a faster rate of stretch, validating a faster method of performing AAR and suggesting that the response of the anal canal to stretch is already maximal at the lower rate of stretch. <h3>Disclosure of interest</h3> None Declared.

Mechanical, hormonal, and hypertrophic adaptations to 10 weeks of eccentric and stretch-shortening cycle exercise training in old males

The growth promoting effects of eccentric (ECC) contractions are well documented but it is unknown if the rate of stretch per se plays a role in such muscular responses in healthy aging human skeletal muscle. We tested the hypothesis that exercise training of the quadriceps muscle with low rate ECC and high rate ECC contractions in the form of stretch-shortening cycles (SSCs) but at equal total mechanical work would produce rate-specific adaptations in healthy old males age 60–70. Both training programs produced similar improvements in maximal voluntary isometric (6%) and ECC torque (23%) and stretch-shortening cycle function (reduced contraction duration [24%] and enhanced elastic energy storage [12%]) (p<0.05). The rate of torque development increased 30% only after SSC exercise (p<0.05). Resting testosterone and cortisol levels were unchanged but after each program the acute exercise-induced cortisol levels were 12–15% lower (p<0.05). Both programs increased quadriceps size 2.5% (p<0.05). It is concluded that both ECC and SSC exercise training produces favorable adaptations in healthy old males' quadriceps muscle. Although the rate of muscle tension during the SSC vs. ECC contractions was about 4-fold greater, the total mechanical work seems to regulate the hypetrophic, hormonal, and most of the mechanical adaptations. However, SSC exercise was uniquely effective in improving a key deficiency of aging muscle, i.e., its ability to produce force rapidly.

X-ROS signalling is enhanced and graded by cyclic cardiomyocyte stretch

A sustained, single stretch of a cardiomyocyte activates a transient production of reactive oxygen species by membrane-located NADPH oxidase 2 (Nox2). This NoX2-dependent ROS (X-ROS) tunes cardiac Ca(2+) signalling by reversibly sensitizing sarcoplasmic reticulum Ca(2+) release channels. In contrast to static length changes, working heart cells are cyclically stretched and shortened in the living animal. Additionally, this stretch cycle is constantly varied by changes in the pre-load and heart rate. Thus, the objective of this study was (i) to characterize X-ROS signalling during stretch-shortening cycles and (ii) to evaluate how the amplitude (pre-load) and frequency (heart rate) of cell stretch affects X-ROS and Ca(2+) signalling. Single adult rat cardiomyocytes were attached to MyoTak™-coated micro-rods and stretched, while ROS production and Ca(2+) signals were monitored optically. Although a sustained stretch led to only a transient burst of ROS, cyclic stretch-shortening cycles led to a steady-state elevation of ROS production. Importantly, this new redox state was graded by both the amplitude of stretch (3-15%) and cycle frequency (1-4 Hz). Elevated ROS production enhanced Ca(2+) signalling sensitivity as measured by the Ca(2+) spark rate. The steady-state level of ROS production in a cardiomyocyte is graded by the amplitude and frequency of cell stretch. Thus, mechanical changes that depend on the pre-load and heart rate regulate a dynamic redox balance that tunes cellular Ca(2+) signalling.

Effect of afferent feedback and central motor commands on soleus H-reflex suppression during arm cycling

Suppression of soleus H-reflex amplitude in stationary legs is seen during rhythmic arm cycling. We examined the influence of various arm-cycling parameters on this interlimb reflex modulation to determine the origin of the effect. We previously showed the suppression to be graded with the frequency of arm cycling but not largely influenced by changes in peripheral input associated with crank length. Here, we more explicitly explored the contribution of afferent feedback related to arm movement on the soleus H-reflex suppression. We explored the influence of load and rate of muscle stretch by manipulating crank-load and arm-muscle vibration during arm cycling. Furthermore, internally driven ("Active") and externally driven ("Passive") arm cycling was compared. Soleus H-reflexes were evoked with tibial nerve stimulation during stationary control and rhythmic arm-cycling conditions, including: 1) six different loads; 2) with and without vibration to arm muscles; and 3) Active and Passive conditions. No significant differences were seen in the level of suppression between the different crank loads or between conditions with and without arm-muscle vibration. Furthermore, in contrast to the clear effect seen during active cycling, passive arm cycling did not significantly suppress the soleus H-reflex amplitude. Current results, in conjunction with previous findings, suggest that the afferent feedback examined in these studies is not the primary source responsible for soleus H-reflex suppression. Instead, it appears that central motor commands (supraspinal or spinal in origin) associated with frequency of arm cycling are relatively more dominant sources.

Cardiac Myosin Binding Protein C Insufficiency Leads to Early Onset of Mechanical Dysfunction

Decreased expression of cardiac myosin binding protein C (cMyBPC) as a result of genetic mutations may contribute to the development of hypertrophic cardiomyopathy (HCM); however, the mechanisms that link cMyBPC expression and HCM development, especially contractile dysfunction, remain unclear. We evaluated cardiac mechanical function in vitro and in vivo in young mice (8-10 weeks of age) carrying no functional cMyBPC alleles (cMyBPC(-/-)) or 1 functional cMyBPC allele (cMyBPC(±)). Skinned myocardium isolated from cMyBPC(-/-) hearts displayed significant accelerations in stretch activation cross-bridge kinetics. Cardiac MRI studies revealed severely depressed in vivo left ventricular (LV) magnitude and rates of LV wall strain and torsion compared with wild-type (WT) mice. Heterozygous cMyBPC(±) hearts expressed 23±5% less cMyBPC than WT hearts but did not display overt hypertrophy. Skinned myocardium isolated from cMyBPC(±) hearts displayed small accelerations in the rate of stretch induced cross-bridge recruitment. MRI measurements revealed reductions in LV torsion and circumferential strain, as well reduced circumferential strain rates in early systole and diastole. Modest decreases in cMyBPC expression in the mouse heart result in early-onset subtle changes in cross-bridge kinetics and in vivo LV mechanical function, which could contribute to the development of HCM later in life.

Amplitude- and velocity-dependency of rigidity measured at the wrist in Parkinson’s disease

ObjectiveQuantify the effects of increased amplitude and rate of muscle stretch on parkinsonian rigidity. MethodsEighteen subjects with Parkinson’s disease participated in this study. Subjects’ tested hand was passively displaced through 60° and 90° ranges of wrist flexion and extension at velocities of 50°/s and 280°/s in both treated and untreated conditions. Joint angular position, resistance torque, and surface electromyography (EMG) of the wrist flexors and extensors were recorded. Rigidity was quantified by normalized work scores and normalized angular impulses for flexion and extension, separately. Reflex responses of stretched and shortened muscles were quantified by mean EMG and EMG ratio. A series of ANOVAs was performed to determine the effect of amplitude, velocity and medication on selected variables. ResultsBoth work scores and angular impulses revealed that the larger displacement amplitude and the higher velocity were associated with significantly greater rigidity, increased EMG ratio and mean EMG of stretched muscles. Dopaminergic medication was not associated with a reduction in rigidity. ConclusionsParkinsonian rigidity is modulated by the amplitude and rate of muscle stretch. SignificanceThese findings shed light on the biomechanical underpinnings and physiological characteristics of rigidity and may inform clinical rigidity assessment in Parkinson’s disease.

Pudendal afferent innervation of the guinea pig external anal sphincter

Sensory nerves to the external anal sphincter (EAS) contribute to mechanisms promoting continence and defecation, yet we know little about their function. We investigated the function of pudendal mechanoreceptors to the guinea pig EAS. Extracellular recordings from pudendal nerve branches to 14 EAS preparations, in vitro, were used to characterize extrinsic primary afferent nerve endings activated by circumferential distension. All 42 pudendal nerve afferents were silent under non-distended conditions. Thirty-three of 42 afferents had slowly adapting, low-threshold responses to circumferential stretch that correlated with stretch length (R(2) = 0.40, P<0.001). Twenty of 20 slowly adapting afferents reduced firing when stretch was maintained for 60 s (P<0.0001). They had low thresholds to von Frey hairs (0.1-0.5mN). Firing frequency correlated with degree of compression (R(2) =0.40, P<0.0001). Nine of 42 afferents had rapidly adapting responses at the onset/offset of isometric stretch. During ramp stretch, small vibrations from the stepper motor evoked rapid bursts of firing at frequencies up to 200Hz. Instantaneous frequency was unrelated to either the rate or degree of stretch. Rapidly adapting units had low thresholds (0.1-0.2mN) to von Frey hairs and small punctate mechanotransduction sites. Responses to von Frey hair compression were also rapidly adapting, and instantaneous frequency was unrelated to the degree of compression. The EAS has two functional classes of mechanoreceptors: slowly adapting low-threshold and rapidly adapting low-threshold mechanoreceptors. These two classes of afferents are likely to be involved in the maintenance of continence, and the process of defecation.

휴대용 심전도 기기와 직물형 전극을 이용한 생체정보 측정용 밀착 의복 개발

A Holter monitor is used for ECG monitoring of ambulatory daily life in hospital. However, the use of this apparatus causes skin allergies and discomfort in patients because of the attachment gel and tapes used to attach disposable electrodes to the skin. In this study, the development of tight-fitting clothing connected to a portable Holter monitor was proposed. In addition, the use of conductive fabrics as electrodes was proposed; this will enable the use of garments in u-health care for measuring ECG signals. The male subjects were university students in the ages of 20 to 24. Subjective wear sensations of the experimental garments were rated using seven Likert scales. A Likert type scale was used for the evaluation and a 7 point score indicates that it provided the best fit as a tight-fitting upper clothing. Clothing pressure was measured using an air-pack-type pressure sensor (model AMI 3037-2) at 4 locations (the conductive fabric electrode) As results, a male basic sloper for upper clothing was developed and that pattern was manipulated to the tight fit pattern by considering the reduction rate of the percentage stretch in the fabric. The developed tight-fitting garment was superior in terms of subjective sensation and 6t. The mean pressure of the garment with reduction rates of 40% in width and of 50% in length was 8.45gf/. A conductive fabric electrode was developed by considering the sewing method and the developed electrode was detected well. The ECG data were recorded for 13 hr 19 min 44 sec and the artifacts in the ECG signals were recorded for 9 hr 3 min 46 sec (total time: 22 hr 23 min 23 sec). The artifacts data were obtained during heavy activities.