Low daily MEWS scores as predictors of low-risk hospitalized patients

BACKGROUND

The Modified Early Warning System (MEWS) is a well-validated tool used by hospitals to identify patients at high risk for an adverse event to occur. However, there has been little evaluation into whether a low MEWS score can be predictive of patients with a low likelihood of an adverse event.

AIM

The present study aims to evaluate the MEWS score as a method of identifying patients at low risk for adverse events.

DESIGN

Retrospective cohort study of 5676 patient days and analysis of associated MEWS scores, medical comorbidities and adverse events. The primary outcome was the association of average daily MEWS scores in those who had an adverse event compared with those who did not.

RESULTS

Those with an average MEWS score of >2 were over 9 times more likely to have an adverse event compared with those with an average MEWS score of 1-2, and over 15 times more likely to have an adverse event compared to those with an average MEWS score of <1.

CONCLUSIONS

Our study shows that those with average daily MEWS scores <2 are at a significantly lower likelihood of having an adverse event compared with a score of >2, deeming them 'low-risk patients'. Formal recognition of such patients can have major implications in a hospital setting, including more efficient resource allocation in hospitals and better patient satisfaction and safety by adjusting patient monitoring according to their individual risk profile.

Benchmarking an 11-qubit quantum computer

The field of quantum computing has grown from concept to demonstration devices over the past 20 years. Universal quantum computing offers efficiency in approaching problems of scientific and commercial interest, such as factoring large numbers, searching databases, simulating intractable models from quantum physics, and optimizing complex cost functions. Here, we present an 11-qubit fully-connected, programmable quantum computer in a trapped ion system composed of 13 ¹⁷¹Yb⁺ ions. We demonstrate average single-qubit gate fidelities of 99.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document}%, average two-qubit-gate fidelities of 97.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document}%, and SPAM errors of 0.7\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document}%. To illustrate the capabilities of this universal platform and provide a basis for comparison with similarly-sized devices, we compile the Bernstein-Vazirani and Hidden Shift algorithms into our native gates and execute them on the hardware with average success rates of 78\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document}% and 35\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document}%, respectively. These algorithms serve as excellent benchmarks for any type of quantum hardware, and show that our system outperforms all other currently available hardware.

The growing complexity of quantum computing devices makes presents challenges for benchmarking their performance as previous, exhaustive approaches become infeasible. Here the authors characterise the quality of their 11-qubit device by successfully computing two quantum algorithms.

Ultrafast creation of large Schrödinger cat states of an atom

Mesoscopic quantum superpositions, or Schrödinger cat states, are widely studied for fundamental investigations of quantum measurement and decoherence as well as applications in sensing and quantum information science. The generation and maintenance of such states relies upon a balance between efficient external coherent control of the system and sufficient isolation from the environment. Here we create a variety of cat states of a single trapped atom’s motion in a harmonic oscillator using ultrafast laser pulses. These pulses produce high fidelity impulsive forces that separate the atom into widely separated positions, without restrictions that typically limit the speed of the interaction or the size and complexity of the resulting motional superposition. This allows us to quickly generate and measure cat states larger than previously achieved in a harmonic oscillator, and create complex multi-component superposition states in atoms.

Generation of mesoscopic quantum superpositions requires both reliable coherent control and isolation from the environment. Here, the authors succeed in creating a variety of cat states of a single trapped atom, mapping spin superpositions into spatial superpositions using ultrafast laser pulses.

Active stabilization of ion trap radiofrequency potentials

We actively stabilize the harmonic oscillation frequency of a laser-cooled atomic ion confined in a radiofrequency (rf) Paul trap by sampling and rectifying the high voltage rf applied to the trap electrodes. We are able to stabilize the 1 MHz atomic oscillation frequency to be better than 10 Hz or 10 ppm. This represents a suppression of ambient noise on the rf circuit by 34 dB. This technique could impact the sensitivity of ion trap mass spectrometry and the fidelity of quantum operations in ion trap quantum information applications.

Sensing Atomic Motion from the Zero Point to Room Temperature with Ultrafast Atom Interferometry

We sense the motion of a trapped atomic ion using a sequence of state-dependent ultrafast momentum kicks. We use this atom interferometer to characterize a nearly pure quantum state with n=1 phonon and accurately measure thermal states ranging from near the zero-point energy to n[over ¯]~10^{4}, with the possibility of extending at least 100 times higher in energy. The complete energy range of this method spans from the ground state to far outside of the Lamb-Dicke regime, where atomic motion is greater than the optical wavelength. Apart from thermometry, these interferometric techniques are useful for characterizing ultrafast entangling gates between multiple trapped ions.

Beat note stabilization of mode-locked lasers for quantum information processing

We stabilize a chosen radio frequency beat note between two optical fields derived from the same mode-locked laser pulse train in order to coherently manipulate quantum information. This scheme does not require access or active stabilization of the laser repetition rate. We implement and characterize this external lock, in the context of two-photon stimulated Raman transitions between the hyperfine ground states of trapped 171Yb(+) quantum bits.

Ultrafast spin-motion entanglement and interferometry with a single atom

We report entanglement of a single atom's hyperfine spin state with its motional state in a time scale of less than 3 ns. We engineer a short train of intense laser pulses to impart a spin-dependent momentum transfer of ± 2 ħk. Using pairs of momentum kicks, we create an atomic interferometer and demonstrate collapse and revival of spin coherence as the motional wave packet is split and recombined. The revival after a pair of kicks occurs only when the second kick is delayed by an integer multiple of the harmonic trap period, a signature of entanglement and disentanglement of the spin with the motion. Such quantum control opens a new regime of ultrafast entanglement in atomic qubits.

Effects of the dual PPAR-α/γ agonist aleglitazar on glycaemic control and organ protection in the Zucker diabetic fatty rat

AIMS

To evaluate the effects of aleglitazar, a dual peroxisome proliferator-activated receptor-α/γ agonist, on the development of diabetes-related organ dysfunction, in relation to glycaemic and lipid changes, in Zucker diabetic fatty (ZDF) rats.

METHODS

Six-week-old, male ZDF rats received aleglitazar 0.3 mg/kg/day or vehicle as food admix for 13 weeks (n = 10 per group). Age-matched male Zucker lean rats served as non-diabetic controls. Plasma and renal markers were measured at several time points. Histopathology and quantitative immunohistochemistry were performed at 13 weeks.

RESULTS

Glycated haemoglobin (5.4 vs. 9.2%) and blood glucose (8.3 ± 0.3 vs. 26.1 ± 1.0 mmol/l) were significantly reduced at 12 weeks with aleglitazar versus vehicle-treated ZDF rats (both p < 0.01), while aleglitazar preserved near-normal plasma insulin levels. Aleglitazar prevented the development of hypertriglyceridaemia (1.4 ± 0.1 vs. 8.5 ± 0.9 mmol/l) and reduced plasma non-esterified fatty acids (0.09 ± 0.02 vs. 0.26 ± 0.04 mmol/l) relative to vehicle-treated animals (both p < 0.01). Urinary glucose and protein concentrations were significantly reduced at 13 weeks with aleglitazar versus vehicle-treated rats (both p < 0.01). Consistent with its effect on glycaemic control, aleglitazar protected β-cell morphology, as evidenced by preservation of islet integrity, and reduction of β-cell apoptosis and islet fibrosis. Aleglitazar prevented renal glomerular hypertrophy, podocyte degeneration, glomerulosclerosis, tubulo-interstitial lesions and development of cataracts.

CONCLUSIONS

Aleglitazar strongly improved glycaemic and lipid parameters while protecting key tissues, including the pancreas, kidneys and eyes, against diabetes-associated structural and functional changes in the ZDF rat.

Ultrafast gates for single atomic qubits

We demonstrate single-qubit operations on a trapped atom hyperfine qubit using a single ultrafast pulse from a mode-locked laser. We shape the pulse from the laser and perform a π rotation of the qubit in less than 50 ps with a population transfer exceeding 99% and negligible effects from spontaneous emission or ac Stark shifts. The gate time is significantly shorter than the period of atomic motion in the trap (Ω(Rabi)/ν(trap)>10(4)), demonstrating that this interaction takes place deep within the strong excitation regime.

Entanglement of atomic qubits using an optical frequency comb

We demonstrate the use of an optical frequency comb to coherently control and entangle atomic qubits. A train of off-resonant ultrafast laser pulses is used to efficiently and coherently transfer population between electronic and vibrational states of trapped atomic ions and implement an entangling quantum logic gate with high fidelity. This technique can be extended to the high field regime where operations can be performed faster than the trap frequency. This general approach can be applied to more complex quantum systems, such as large collections of interacting atoms or molecules.

Reduced plaque formation induced by rosiglitazone in an STZ-diabetes mouse model of atherosclerosis is associated with downregulation of adhesion molecules

Adhesion molecules have been implicated in the development and progression of cardiovascular disease, which is highly prevalent in people with diabetes. Adhesion molecules can mediate adhesion of leukocytes to the endothelium. Furthermore, P-selectin expressed on platelets is able to mediate the adhesion of leukocytes to platelets. In this study, we examine the in-vivo and in-vitro effects of rosiglitazone with particular emphasis on three important adhesion molecules (VCAM-1, ICAM-1 and P-selectin). In the aorta of STZ-diabetic apolipoprotein E-deficient (apoE KO) mice, rosiglitazone significantly reduced both total and arch plaque area. The mechanism for this appeared to be reduced macrophage infiltration into the atherosclerotic plaque which was also associated with reduced mRNA levels for VCAM-1, ICAM-1, MCP-1 and P-selectin in the aorta. In-vitro studies revealed reduced cell adhesion of monocytic cells (THP-1) to fibrinogen and endothelial cells (HUVEC) after incubation with rosiglitazone. Furthermore, the reduction in leukocyte adhesion also correlated with significant reductions in mRNA levels for VCAM-1, ICAM-1 and P-selectin indicating that reduced macrophage infiltration in atherosclerotic plaques may occur as a result of a direct effect of rosiglitazone on adhesion molecules in both monocytes and endothelial cells. Thus, we have shown that rosiglitazone appears to have direct anti-atherosclerotic effects in an animal model of diabetes-associated atherosclerosis which are at least partly due to effects on VCAM-1, ICAM-1, MCP-1 and P-selectin expression which leads to decreased leukocyte adhesion and macrophage infiltration.

PPARs and diabetes-associated atherosclerosis

Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors affecting the regulation of various genes relevant to the pathogenesis of diabetic complications. A number of drugs have been developed to act as agonists of the three PPARs. To date, PPAR isoforms that have been identified are the alpha, beta/delta, and gamma isosforms. Fenofibrate and gemfibrozil are two drugs that act as PPARalpha agonists and are currently in use in the clinical setting. Rosiglitazone is a PPARgamma agonist also in clinical use. These drugs have proved very useful in regulation of either glucose or lipid metabolism and consequently are used in patients with type 2 diabetes. Here, we will review the anti-atherosclerotic potential of PPAR agonists with particular emphasis on recent studies in an animal model of diabetes-associated atherosclerosis, the streptozotocin diabetic apolipoprotein E deficient mouse. These studies have shown both PPARalpha agonists, gemfibrozil and fenofibrate, confer anti-atherosclerotic effects, partly independent of their metabolic effects. Similar positive findings have also been detected in a dose-dependent manner with the PPARgamma agonist, rosiglitazone. The potential clinical implications of these findings are also discussed in view of the recently reported results of the PROACTIVE and FIELD clinical trials with the PPAR agonists rosiglitazone and fenofibrate respectively.

Effect of selective fatiguing of the shank muscles on single-leg-standing sway

Control of standing requires the continuous activity of the leg muscles. In single leg standing the system is less redundant and muscular activity is more intensive. The objective of this study was to examine the effect of force imbalance of the shank muscles, evoked by their selective fatiguing, on postural control in single-leg standing. Five healthy subjects performed two single-leg standing trials, lasting as long as the subject could maintain steady balance, and separated by a 240s quasi-isotonic sustained effort to induce fatigue of the Tibialis Anterior and Peroneus muscles. The following were on-line monitored: sway-related parameters, e.g., ground reaction force and center of pressure in the standing trials; and electromyogram of the Tibialis Anterior, Peroneus and Gastrocnemius muscles in all experiments. Simple and multiple linear regressions served to study the fatigue effects on the relationship between muscle activity and postural sway. The results indicate that the evoked muscle imbalance leads to (a) increased postural sway; (b) increased correlation between muscle activity, and sway-related parameters. Thus, with the reduction of the level of redundancy the system becomes more synchronized. These results have potential relevance for cases of muscle impairment, in which electrical stimulation is required to augment muscle activity.

Transmission-line model for myelinated nerve fiber

Herein, the well-known cable equation for non-myelinated axon model is extended analytically for myelinated axon formulation. The classical cable equation is thereby modified into a linear second order ordinary differential equation with periodic coefficient, known as Hill's equation. Hill's equation exhibits periodic solutions, known as Floquet's modes. The Floquet's modes are recognized as the nerve fiber activation modes, which are conventionally associated with the nonlinear Hodgkin-Huxley formulation. They can also be incorporated in our linear model.

Muscle force augmentation by low-intensity electrical stimulation

In cases of muscle partial deficiency, force augmentation can be achieved by hybrid activation, i.e., by combining electrical stimulation (ES) with volitional activation. In the present study the volitional and electrically-induced torque components are resolved under visual-feedback activation. Isometric contraction of the tibialis anterior (TA) muscle was studied on 5 healthy subjects, using an activation protocol combining ES alone, volitional activation alone and hybrid activation. Ankle torque and TA EMG were measured. A computational algorithm was developed to dissociate the volitional from the overall torque, based on EMG filtering and on pre-measured calibration curves of volitional torque versus EMG. Based on a defined facilitation factor, the results indicate that within the range of stimulation intensities, there exist regions of increased facilitation of the volitional activation of the TA muscle, in which the torque contribution due to the induced activation is higher compared that of the recruitment curve.

Muscle enhancement using closed-loop electrical stimulation: volitional versus induced torque

In cases of partial deficiency of muscle activation capacity, force augmentation can be achieved by hybrid activation, i.e., by combining electrical stimulation (ES) with volitional activation. In this activation modality the shares of the volitional and induced torques within the overall hybrid torque are unknown. The purpose of this study was to suggest a computational approach to parcel out the volitional and stimulation induced components of joint torque generated during combined voluntary and electrical activation of the Tibialis Anterior muscle (TA). For this purpose, isometric contraction of the TA was studied on 5 healthy subjects, using an activation protocol involving ES alone, volitional activation alone and hybrid activation. Ankle torque and TA EMG were measured. A computational algorithm was developed to dissociate the volitional from the overall torque, based on EMG filtering and on pre-measured calibration curves of volitional torque versus EMG. The results indicated that for a certain hybrid torque there is a linear decaying relationship between the induced torque and the volitional torque shares. Moreover, based on a defined enhancement ratio, the results indicate that within the range of stimulation intensities, there exist regions of increased facilitation, in which the stimulation efficiency is higher under combined compared to isolated conditions.

Synthesis and biological evaluation of novel hexahydro-pyrido[3′,2′:4,5]pyrrolo[1,2-a]pyrazines as potent and selective 5-HT2C receptor agonists

Further lead optimization efforts on previously described 1,2,3,4,10,10a-hexahydro-1H-pyrazino[1,2-a]indoles led to the new class of 5,5a,6,7,8,9-hexahydro-pyrido[3',2':4,5]pyrrolo[1,2-a]pyrazines culminating in the discovery of (5aR,9R)-2-[(cyclopropylmethoxy)methyl]-5,5a,6,7,8,9-hexahydro-9-methyl-pyrido[3', 2':4,5]pyrrolo[1,2-a]pyrazine 18 as a potent, full 5-HT(2C) receptor agonist with an outstanding selectivity profile and excellent hERG and phospholipidosis properties.

Identification of 4-methyl-1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indoles as 5-HT2C receptor agonists

Synthesis and evaluation of the activity of new 4-methyl-1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indoles as 5-HT(2C) receptor agonists are described. Appropriately substituted, several analogs displayed selectivity against the other 5-HT(2) receptor subtypes of 1 order of magnitude or more. Selectivity was improved for several compounds versus the lead 1, increasing the therapeutic interest in this series of 5-HT(2C) receptor agonists.

Interaction of array of finite electrodes with layered biological tissue: effect of electrode size and configuration

A hybrid scheme, combining image series and moment method has been utilized for the calculation of the intramuscular three-dimensional (3-D) current density (CD) distribution and potential field transcutaneously excited by an electrode array. The model permits one to study the effect of tissue electrical properties and electrode placement on the CD distribution. The isometric recruitment curve (IRC) of the muscle was used for parameter estimation and model verification, by comparison with experimentally obtained IRCs of functional electrical stimulation (FES)-activated quadriceps muscle of paraplegic subjects. Sensitivity of the calculated IRC to parameters such as tissue conductivity, electrode size, and configuration was verified. The resulting model demonstrated characteristic features that were similar to those of experimentally obtained data. The model IRCs were insensitive to the electrode size; however, the inclusion of the bone-fascia layer significantly increased the intramuscular CD and, consequently, increased the IRC slope. Of the different configurations studied, a four-electrode array proved advantageous because, in this case, the CD between the electrodes was more evenly distributed, providing better resistance to fatigue. However, due to the steeper linear portion of the IRC, this configuration suffered from a somewhat reduced controllability of the muscle.

Effects of anorexinogen agents on cloned voltage-gated K(+) channel hKv1.5

Appetite suppressants have been associated with primary pulmonary hypertension (PPH), inhibition of voltage-gated potassium channels, membrane depolarization, and calcium entry in pulmonary artery smooth muscle cells. In cells taken from pulmonary arteries of primary pulmonary hypertensive patients, voltage-gated potassium channels appear to be dysfunctional and in particular, reduced hKv1.5 gene transcription and hKv1.5 mRNA instability have been shown. We have compared the effects of anorexinogen agents on hKv1.5 channels stably expressed in mammalian cell line. We found that aminorex, phentermine, dexfenfluramine, sibutramine, and fluoxetine cause a dose-dependent inhibition of hKv1.5 current. Aminorex, phentermine, and dexfenfluramine had a K(D) of inhibition greater than to 300 microM and are not potent inhibitors of hKv1.5. Sibutramine and fluoxetine inhibited hKv1.5 current with lower K(D) values of 41 and 21 microM, respectively. Block by both drugs increased rapidly between -20 and +10 mV, coincident with channel opening and suggested an open channel block mechanism. This was confirmed by a slower deactivation time course resulting in a "crossover" phenomenon when tail currents recorded under control conditions and in the presence of either drug were superimposed. Single channel experiments demonstrated that open probability and open duration of hKv1.5 were decreased by fluoxetine and sibutramine. These results indicate that among the anorexinogen agents tested, sibutramine and fluoxetine are the most potent toward hKv1.5 channel, which they preferentially block in the open state. Nevertheless, their inhibitory effects do not correlate with their ability to produce PPH neither with their previously reported therapeutic plasma concentrations.

Current distribution in skeletal muscle activated by functional electrical stimulation: image-series formulation and isometric recruitment curve

The present work develops an analytical model that allows one to estimate the current distribution within the whole muscle and the resulting isometric recruitment curve (IRC). The quasistatic current distribution, expressed as an image series, i.e., a collection of properly weighted and shifted point-source responses, outlines an extension for more than three layers of the classical image theory in conductive plane-stratified media. Evaluation of the current distribution via the image series expansions requires substantially less computational time than the standard integral representation. The expansions use a unique recursive representation for Green's function, that is a generic characteristic of the stratification. This approach permits one to verify which of the tissue electrical properties are responsible for the current density distribution within the muscle, and how significant their combinations are. In addition, the model permits one to study the effect of different electrode placement on the shape and the magnitude of the potential distribution. A simple IRC model was used for parameter estimation and model verification by comparison with experimentally obtained isometric recruitment curves. Sensitivity of the model to different parameters such as conductivity of the tissues and activation threshold was verified. The resulting model demonstrated characteristic features that were similar to those of experimentally obtained data. The model also quantitatively confirmed the differences existing between surface (transcutaneous) and implanted (percutaneous) electrode stimulation.

Fatigue-induced changes in decline running

OBJECTIVE

Study the relation between muscle fatigue during eccentric muscle contractions and kinematics of the legs in downhill running.

DESIGN

Decline running on a treadmill was used to acquire data on shock accelerations, muscle activity and kinematics, for comparison with level running.

BACKGROUND

In downhill running, local muscle fatigue is the cause of morphological muscle damage which leads to reduced attenuation of shock accelerations.

METHODS

Fourteen subjects ran on a treadmill above level-running anaerobic threshold speed for 30 min, in level and -4 degrees decline running. The following were monitored: metabolic fatigue by means of respiratory parameters; muscle fatigue of the quadriceps by means of elevation in myoelectric activity; and kinematic parameters including knee and ankle angles and hip vertical excursion by means of computerized videography. Data on shock transmission reported in previous studies were also used.

RESULTS

Quadriceps fatigue develops in parallel to an increasing vertical excursion of the hip in the stance phase of running, enabled by larger dorsi flexion of the ankle rather than by increased flexion of the knee.

CONCLUSIONS

The decrease in shock attenuation can be attributed to quadriceps muscle fatigue in parallel to increased vertical excursion of the hips.

The effect of gamma-interferon to inhibit macrophage-high density lipoprotein interactions is reversed by 15-deoxy-delta12,14-prostaglandin J2

Macrophage activation has been recognized as playing a central role in chronic inflammatory diseases in general and, more specifically, in the vascular wall during the progression of atherosclerotic lesions. Macrophage-activating factors present within the atherosclerotic lesion include the colony-stimulating factors and gamma interferon (IFNgamma). In the present study, the effects of IFNgamma on macrophage binding and uptake of fluorochrome-labeled high density lipoprotein (HDL) were investigated by flow cytometry and by measuring the amount of the type B scavenger receptors CD36 and scavenger receptor type B (SR-BI) by Northern blot analysis. IFNgamma-, but not granulocyte macrophage colony-stimulating factor (GM-CSF)-treated murine peritoneal macrophages displayed a two- to threefold decrease in Dil-labeled HDL uptake. This effect was observed in the absence of a comparable decrease in SR-BI message and protein or CD36 message. This decrease in both HDL binding and uptake was reversed by the peroxisome proliferator-activated receptor gamma (PPARgamma) agonist, 15-deoxy-delta12,4-prostaglandin J2 (15d-PGJ2), which also inhibited the IFNgamma induction of the beta2 integrin CD11a. Furthermore, 15d-PGJ2 increased the expression of SR-BI and CD36 message and SR-BI protein which was reflected in an increase in HDL binding and uptake. These results suggest a role for PPARgamma agonists in modulating the IFNgamma-mediated macrophage effector functions relevant to atherosclerotic disease progression.

The increased swelling and instantaneous deformation of osteoarthritic cartilage is highly correlated with collagen degradation

OBJECTIVE

To provide evidence for the hypothesis that the loss of tensile strength of osteoarthritic (OA) cartilage (resulting in swelling-the hallmark of OA) is due to an impaired collagen network and not to loss or degradation of proteoglycans.

METHODS

The amount of degraded collagen molecules, the fixed charge density (FCD) on a dry-weight basis, the degree of swelling in saline, and the instantaneous deformation (ID; a test reflecting the tensile stiffness of the collagen network) were measured in full-depth OA femoral condyle samples. In addition, levels of the crosslink hydroxylysylpyridinoline (HP), the amount of degraded collagen molecules, and the degree of swelling were determined in the 3 zones (surface, middle, and deep) of OA cartilage. We also compared the ID of normal and OA cartilage.

RESULTS

In full-depth OA cartilage, a close relationship was found between swelling and ID. Swelling and ID correlated strongly with the amount of degraded collagen molecules, and were not related to FCD. OA cartilage showed the same zonal pattern in HP levels as normal cartilage (i.e., an increase with depth). No relationship was found between collagen crosslinking and swelling of the surface, middle, and deep zones. In all 3 zones, swelling was proportional to the amount of degraded collagen molecules. Compared with that of normal cartilage, the change in ID of OA cartilage was most pronounced at the surface in a direction parallel to the direction of the collagen fibrils.

CONCLUSION

The decreased stiffness of the OA collagen network (as measured by swelling and ID) is strongly related to the amount of degraded collagen molecules. The anisotropy in ID parallel and perpendicular to the direction of the fibrils revealed that the impairment of strength resides mainly in, and not between, the fibrils. Proteoglycans play only a minor role in the degeneration of the tensile stiffness of OA cartilage.

Involvement of caspase 3- and 8-like proteases in ceramide-induced apoptosis of cardiomyocytes

Ceramides are the metabolic products of sphingolipids of the eukaryotic cell membranes and are believed to function as signaling molecules in a variety of biological processes. Ceramide induces apoptosis in cultured cardiomyocytes. However, the molecular pathway underlying ceramide-induced apoptosis is not clear. In this study, we investigated the role of the cysteinyl aspartate-specific proteases (caspases) in cardiomyocyte apoptosis induced by ceramide. Treatment of in vitro cultured rat neonatal cardiomyocytes with ceramide results in robust cell death, of which the majority is apoptotic, as shown by positive staining for terminal deoxyribonuclease transferase-mediated deoxyuridine triphosphate nick end-labeling and the appearance of pyknotic nuclei with Hoechst staining. Caspase 3- and 8-like protease activities are induced in cardiomyocytes by ceramide treatment. Addition of the tetrapeptide inhibitors for caspases attenuated ceramide-induced apoptosis. The nonselective caspase inhibitor (B-D-FMK) and the caspase 3 (Z-DEVD-FMK) and caspase 8 (Z-IETD-FMK) inhibitors reduced ceramide-induced cardiomyocyte death and significantly inhibited the activation of caspase 3. However, the inhibitors specific for caspases 1, 2, 4, 6, and 9 have no significant effects on cardiomyocyte survival under the same conditions. These data suggest that caspases 3- and 8-related proteases are involved in ceramide-induced cardiomyocyte apoptosis.

Biomechanical simulation of an amputated forearm with and without a prosthesis

In this study a computer simulation was developed for analysing the performance of a below-elbow amputated forearm, with and without a prosthesis. The upper extremity was represented in terms of two rigid bodies, the arm and the forearm. Five muscles, three elbow flexors and two elbow extensors, were included in the model. The muscle model used was the five-component model, including the contractile, parallel, series and viscous elements and the muscle mass. Dynamic and static simulations were conducted, with and without prosthesis, to study parametrically the effects of stump length, tendon distal transfer, tendon or muscle shortening and muscle physiological cross-sectional area. The performance measures which were the most affected included flexion moment of the forearm about the elbow, muscle moment, force in the joint, flexion rate and mechanical energy. The simulation presented an interesting case when the amputation site is more proximal than the anatomical insertion point of a muscle, necessitating shortening of the muscle to avoid the situation where it exerts no force. It was also found that, of the changeable parameters, the most beneficial changes in the forearm parameters for improved dynamic performance were: (a) tendon distal transfer and (b) increase of the muscle cross-sectional area, the latter achievable by means of physical training.

Fatigue-related loading imbalance on the shank in running: a possible factor in stress fractures

In previous reports we have shown that in long distance running the impact acceleration on the shank increases with progressing fatigue. The aim of the present study was to test whether, in parallel to this increase, an imbalance in the activities between the ankle plantar and dorsi flexor muscles develops. The tests were made on fourteen subjects during 30 min treadmill running above their anaerobic thresholds. Respiratory data were collected to determine the anaerobic threshold speed and to indicate the progressively developing metabolic fatigue. Surface electromyogram (EMG) was monitored to indicate the changing activity of the shank muscles. In the tibialis anterior the average integrated EMG (iEMG) and the mean power frequency (MPF) significantly decreased from the beginning to the end of running. In the gastrocnemius iEMG did not change, while MPF increased during the course of running. The impact acceleration, measured by means of an accelerometer attached to the tibial tuberosity, significantly increased during the course of running. It was concluded that, with developing fatigue, an imbalance in the contraction of the shank muscles develops in parallel to an increase in shank shock acceleration. The combination of these two changes may hamper the loading balance on the tibia since the bone becomes exposed to excessive bending stresses and to higher risk of stress injury.

Transcutaneous FES of the paralyzed quadriceps: is knee torque affected by unintended activation of the hamstrings?

This study addresses the question whether unintended response of the knee flexors (hamstrings) accompanies transcutaneous functional electrical stimulation (FES) of the quadriceps and whether the knee torque is hereby affected. Transcutaneous FES of the right quadriceps of two paraplegic subjects was applied and measurements were made of the net torque and of the myoelectric activities of the quadriceps and hamstrings muscles of the right leg. A low correlation was obtained between the peak-to-peak amplitudes of the M-waves of the two muscles. This correlation decreased further with the development of fatigue, which indicated that the electromyography (EMG) signals from the hamstrings were not the result of cross-talk between adjacent recording sites. The force profile of each muscle was determined from a developed model incorporating EMG-based activation, muscle anthropometry as obtained from in vivo magnetic resonance imaging of the thigh, and metabolic fatigue function, based on data acquired by 31P nuclear magnetic resonance spectroscopy. A sensitivity analysis revealed that the muscle specific tension and the muscle moment arms have a major influence on the resulting muscle forces and should therefore be accurately provided. The results show that during the unfatigued phase of contraction the estimated maximal force in the hamstrings was lower than 20% of that in the quadriceps and could be considered to be practically negligible. As fatigue progressed the hamstrings-to-quadriceps force ratio increased, reaching up to 45%, and the effect of co-activation on the torque partition between the two muscles was no longer negligible.

Shock accelerations and attenuation in downhill and level running

OBJECTIVE

A study was conducted to investigate the possible effects of fatigue on the heel strike-initiated shock accelerations and on attenuation of these shocks along the body during eccentric muscle contractions.

DESIGN

Level and decline running on a treadmill were used to acquire the experimental data on the foot strike-initiated shock accelerations.

BACKGROUND

Eccentric contractions of the lower limb muscles in combination with shock generation and propagation during downhill running and muscle fatigue may diminish their ability to dissipate and attenuate loading on the system.

METHODS

Fourteen young healthy males ran on a treadmill at a speed exceeding their anaerobic threshold by 5% for 30 min, as follows: (a) level running and (b) downhill running with a decline angle of -4 degrees. The foot strike-induced shock accelerations were recorded every five minutes on the tibial tuberosity and sacrum. Fatigue was monitored by means of the respiratory parameters.

RESULTS

The downhill running related with eccentric muscle contractions was associated with increased shock propagation from the tibial tuberosity to the sacrum levels, even though fatigue did not develop.

CONCLUSIONS

Shock propagation from the tibial tuberosity to the sacrum is augmented due to the eccentric action of the muscles, without metabolic fatigue development.

RELEVANCE

Eccentric muscle contraction in downhill running reduces the musculoskeletal ability to attenuate the heel strike-induced shock waves. Knowledge about the effect of fatigue on the shock propagation between the shank and the sacrum levels may help in understanding the mechanism of stress fractures and joint damage.

EMG and metabolite-based prediction of force in paralyzed quadriceps muscle under interrupted stimulation

A major issue associated with functional electrical stimulation (FES) of a paralyzed limb is the decay with time of the muscle force as a result of fatigue. A possible means to reduce fatigue during FES is by using interrupted stimulation, in which fatigue and recovery occur in sequence. In this study, we present a model which enables us to evaluate the temporal force generation capacity within the electrically activated muscle during first stimulation fatigue, i.e., when the muscle is activated from unfatigued initial conditions, and during postrest stimulation, i.e., after different given rest durations. The force history of the muscle is determined by the activation as derived from actually measured electromyogram (EMG) data, and by the metabolic fatigue function expressing the temporal changes of muscle metabolites, from existing data acquired by in vivo 31P MR spectroscopy in terms of the inorganic phosphorus variables, Pi or H2PO4-, and by the intracellular pH. The model was solved for supra-maximal stimulation in isometric contractions separated by rest periods, and compared to experimentally obtained measurements. EMG data were fundamental for prediction of the ascending force during its posttetanic response. On the other hand, prediction of the decaying phase of the force was possible only by means of the metabolite-based fatigue function. The prediction capability of the model was assessed by means of the error between predicted and measured force profiles. The predicted force obtained from the model in first stimulation fatigue fits well with the experimental one. In postrest stimulation fatigue, the different metabolites provided different prediction capabilities of the force, depending on the duration of the rest period. Following rest duration of 1 min, Pi provided the best prediction of force; H2PO4- extended the prediction capacity of the model to up to 6 min and pH provided a reliable prediction for rest durations longer than 12 min. The results presented shed light on the roles of EMG and of metabolites in prediction of the force history of a paralyzed muscle under conditions where fatigue and recovery occur in sequence.

Weight-bearing patterns on the knees of preterm infants

In this study we present a method of monitoring the forces under the knees of preterm infants lying in the prone position. Dual force sensing resistor transducers, connected to optically-isolated amplifiers, were used to monitor the forces. A thermistor airflow sensor was used for the parallel monitoring of the respiratory signal. The measurements were made on ten preterm infants. The average forces were 0.51 and 0.50 N for the left and right knees, respectively. In the frequency domain, the basic harmonic of the force traces was 1.27 Hz approximately, corresponding to the respiratory rhythm. Additional, smaller harmonics, were detected in the force traces at 2.54 and 3.81 Hz. A rather notable power signal could also be seen around 0.1 Hz. The results obtained indicate that the system developed is highly sensitive for providing data on the amplitudes, periods and sequences of oscillations and symmetry of load bearing in preterm infants. Knowledge of the normal and abnormal reaction force patterns may assist in the early diagnosis of abnormal neurodevelopment.

Standing sway: iterative estimation of the kinematics and dynamics of the lower extremities from force-plate measurements

In this study, a model for the estimation of the dynamics of the lower extremities in standing sway from force plate data only is presented. A three-dimensional, five-segment, four-joint model of the human body was used to describe postural standing sway dynamics. Force-plate data of the reactive forces and centers of pressure were measured bilaterally. By applying the equations of motion to these data, the transversal trajectory of the center of gravity (CG) of the body was resolved in the sagittal and coronal planes. An inverse kinematics algorithm was used to evaluate the kinematics of the body segments. The dynamics of the segments was then resolved by using the Newton-Euler equations, and the model's estimated dynamic quantities of the distal segments were compared with those actually measured. Differences between model and measured dynamics were calculated and minimized, using an iterative algorithm to re-estimate joint positioning and anthropometric properties. The above method was tested with a group of 11 able-bodied subjects, and the results indicated that the relative errors obtained in the final iteration were of the same order of magnitude as those reported for closed loop problems involved in direct kinematic measurements of human gait.

Intracolonic release of nitric oxide during trinitrobenzene sulfonic acid rat colitis

Nitric oxide is thought to play an important role in modulating the inflammatory process. Recently an increase in the inducible form of nitric oxide synthase (iNOS) has been found in the rat trinitrobenzene sulfonic acid model of experimental colitis, and inhibition of nitric oxide synthase activity resulted in an amelioration of tissue injury. The aim of our study was to evaluate in vivo intracolonic release of nitric oxide in this model of colitis. Experimental colitis was induced in male Sprague-Dawley rats by a single intracolonic administration of trinitrobenzene sulfonic acid. Nitrite levels were determined in rectal dialysates by HPLC. The tissue myeloperoxidase and iNOS and the luminal leukotriene B4 were also measured. Nitrite levels were significantly increased in rectal dialysates during colitis and correlated significantly with tissue myeloperoxidase and iNOS activity. The correlation between nitrite dialysate levels and wall iNOS activity confirms that nitrite in dialysates is produced by inflammatory cells and not by colonic bacterial flora. Determination of nitrite levels in rectal dialysates seems a valuable method to monitor colonic inflammation in rat trinitrobenzene sulfonic acid colitis.

Pharmacokinetics of isosorbide dinitrate in healthy volunteers after 24-hour intravenous infusion

No studies have examined the pharmacokinetics of isosorbide dinitrate (ISDN) after infusion of long duration, even though such infusions are used in patients. We therefore measured ISDN and its active metabolites, isosorbide-5-mononitrate (IS5MN) and isosorbide-2-mononitrate (IS2MN), in plasma of 9 healthy volunteers who received a continuous intravenous infusion of ISDN for 24 hours at a dose rate that lowered diastolic blood pressure by 10% during the first 30 minutes of infusion. All subjects tolerated the infusion except one who experienced intolerable headache. Five subjects received 1 microgram.min-1.kg-1, one 2 micrograms.min-1.kg-1, and two 4 micrograms.min-1.kg-1 ISDN, whereas the full rate of 6 micrograms.min-1.kg-1 was used continuously in one subject. At all infusion rates the plasma concentrations of ISDN were higher at 24 hours than at earlier times, suggesting that a steady-state condition had not been reached at that time. The same was true for the mononitrate metabolites, which reached higher plasma concentrations and were cleared more slowly than the parent compound after the end of the infusion. Apparent elimination half-lives of ISDN, IS2MN, and IS5MN were 67 +/- 10 minutes, 115 +/- 13 minutes, and 272 +/- 38 minutes, respectively. Comparison of low-rate infusions (1 and 2 micrograms.min-1.kg-1) with high-rate infusions (4 and 6 micrograms.min-1.kg-1) showed that the plasma concentration ratios at 24 hours of mononitrate metabolites to parent drug and apparent plasma clearance of ISDN were almost halved at the higher infusion rates.

The nitric oxide donor ITF 1129 augments subendocardial blood flow during exercise-induced myocardial ischemia

The effect of the nitric oxide donor ITF 1129 and nitroglycerin (NTG) on myocardial blood flow was examined in dogs with a Doppler velocity probe, hydraulic occluder, and indwelling microcatheter in the left anterior descending coronary artery (LAD). Studies were performed during treadmill exercise in the presence of a coronary artery stenosis. The effects of ITF 1129 in doses of 3 and 10 micrograms/kg/min i.v. were compared with NTG (2 micrograms/kg/min i.v.). Neither ITF 1129 nor NTG caused significant alteration of heart rate, arterial blood pressure, or left ventricular systolic pressure. During partial inflation of the occluder to decrease distal coronary pressure to 55 +/- 2 mm Hg, mean myocardial blood flow measured with microspheres was 0.72 +/- 0.14 ml/min/g in the region perfused by the stenotic coronary artery compared with 2.93 +/- 0.40 ml/min/g in a normally perfused control region. With no change in distal coronary pressure, ITF 1129 increased mean myocardial blood flow in the stenosis perfused region to 1.15 +/- 0.24 ml/min/g (3 micrograms/kg/min i.v.) and to 1.20 +/- 0.28 ml/ min/g (10 micrograms/kg/min i.v.), whereas NTG (2 micrograms/kg/min iv) increased blood flow to 1.16 +/- 0.22 ml/min/g (each p < 0.05). The increase in myocardial blood flow produced by ITF 1129 or NTG occurred principally in the deeper myocardial layers with no change in subepicardial flow. As a result, the subendocardial/subepicardial blood flow ratio (ENDO/EPI) increased from 0.44 +/- 0.09 during control stenosis to 0.85 +/- 0.13 after ITF 1129 (10 micrograms/kg/min i.v.) and to 0.81 +/- 0.12 after NTG. Neither ITF 1129 nor NTG significantly altered myocardial blood flow in the normally perfused control region. The effect of ITF 1129 and NTG on myocardial perfusion occurred without alterations of distal coronary pressure or left ventricular diastolic pressure, indicating a primary effect on the intramural coronary microvasculature.

Effect of ingested sodium bicarbonate on muscle force, fatigue, and recovery

The influence of acute ingestion of NaHCO3 on fatigue and recovery of teh quadriceps femoris muscle after exercise was studied in six healthy male subjects. A bicycle ergometer was used for exercising under three loading conditions: test A, load corresponding to maximal oxygen consumption; test B, load in test A + 17%; test C, load in test B but performed 1 h after acute ingestion of NaHCO3. Functional electrical stimulation (FES) was applied to provoke isometric contraction of the quadriceps femoris. The resulting knee torque was monitored during fatigue (2-min chronic FES) and recovery (10-s FES every 10 min, for 40 min). Quadriceps torques were higher in the presence of NaHCO3 (P < 0.05): with NaHCO3 the peak, residual, and recovery (after 40 min) normalized torques were, respectively, 0.68 +/- 0.05 (SD), 0.58 +/- 0.05, and 0.73 +/- 0.05; without NaHCO3 the values were 0.45 +/- 0.04, 0.30 +/- 0.06, and 0.63 +/- 0.06. The increased torques obtained after acute ingestion of NaHCO3 indicate the possible existence of improved nonoxidative glycolysis in isometric contraction, resulting in reduced fatigue and enhanced recovery.

Is balance impaired by recurrent sprained ankle?

OBJECTIVE

To evaluate uninjured and recurrent sprained ankles during single leg standing, both with and without visual input, and the contribution of related proprioceptive feedback in this event.

METHODS

A force measuring system was used for monitoring reaction forces in the anteroposterior and mediolateral directions during single leg standing. Differences between selected variables obtained in the uninjured and sprained ankles were analysed using two way analysis of variance.

RESULTS

Foot-ground reaction forces in both anteroposterior and mediolateral directions were the same in normal and sprained ankles of each subject while standing with either open or closed eyes. However, standing with closed eyes, irrespective of the ankle status, always produced significantly higher reaction forces than those obtained with open eyes (P < 0.05).

CONCLUSIONS

The amount of postural sway during single leg standing is similar in the chronically sprained and the uninjured ankle joint.

Predicted and measured muscle forces after recoveries of differing durations following fatigue in functional electrical stimulation

Using 31P nuclear magnetic resonance (NMR) spectroscopy, the bioenergetics of paralyzed muscles activated by functional electrical stimulation (FES) were studied in vivo during fatigue and recovery on paraplegic subjects. During the activation phase of the muscle, the muscle force was also monitored. The phosphorus metabolites were found to vary systemically during the fatigue and to recover slowly to their rest state values after cessation of FES. During fatigue, a good correlation was found between the decaying force and each of the profiles of phosphocreatine, inorganic phosphorus, and intracellular pH. A musculotendon 5 element model was proposed for the activated muscle to predict its force generation capacity. A fatigue recovery function, based on the metabolic profiles, was introduced into the model. This model allowed us to predict the force expected to be developed as a function of the time after recovery of given time durations. Validation experimental measurements of force were carried out and included recurrent fatigue tests, both in the initially unfatigued state and at various times in the postfatigue stage of the muscle. Comparison of the predicted and measured forces indicated satisfactory agreement of the results. The developed model of muscle dynamics should help to design a strategy for reducing muscle fatigue under FES.

A model of fatigue and recovery in paraplegic's quadriceps muscle subjected to intermittent FES

The objective of this paper was to propose a mathematical model for the fatigue and recovery phases of a paraplegic's quadriceps muscle subjected to intermittent functional electrical stimulation (FES). The model is based on in vivo, noninvasive, recording of fatigue related metabolic parameters recorded during stimulation and recovery. Records of the time variations of the muscle's phosphorus metabolites, particularly the phosphocreatine (PCr) and inorganic phosphorus (Pi), obtained from 31P magnetic resonance spectroscopy (MRS), were used to calculate the intracellular pH level in the muscle and this latter parameter was incorporated in a musculo-tendon model. The fatigue-recovery model allows the transition from the fatiguing phase to the recovery phase as soon as the stimulation terminates and vice versa. This model was incorporated into a Huxley type muscle model expressing the dynamics of the muscle. Two ordinary differential equations describing the musculo-tendon dynamics and the dynamics of the activation were solved simultaneously and records of the force trajectory during intermittent stimulations were obtained. Study cases ranging from 5 to 30 s for each of the stimulation and recovery alternating phases were stimulated. The force and the total impulse in the modeled quadriceps muscle were computed. It was found that the greatest impulse was produced in intermittent stimulation of 40-50 s duty cycle, with a 50 percent ratio between the stimulation and recovery intervals. An additional series of six runs, including two contractions, one of 3 min and one of 1 min, separated by rest periods of 3, 6, 9, 12, 15, and 30 min was performed. From the predicted force trajectories obtained, the maximal force values served for comparison with measured values made on one patient.

Nitrovasodilators ITF 296 and isosorbide dinitrate exert antiischemic activity by dilating coronary penetrating arteries

We examined the effect of the novel nitrovasodilator ITF 296 and isosorbide dinitrate (ISDN) on myocardial blood flow (BF) distal to a coronary artery stenosis. Eleven dogs with a Doppler velocity probe, hydraulic occluder, and indwelling microcatheter in the left anterior descending coronary artery (LAD) were studied during treadmill exercise in the presence of a coronary artery stenosis. On separate days, the effects of ITF 296 in doses of 4 and 20 micrograms/kg/min i.v. or ISDN 20 micrograms/kg/min i.v. were compared. Coronary pressure distal to the stenosis was maintained constant during the control period and after administration of either nitrovasodilator. Neither ITF 296 nor ISDN significantly altered heart rate (HR), arterial blood pressure (BP), or left ventricular end-diastolic pressure (LVEDP). In the presence of a stenosis that decreased distal coronary pressure to 58 +/- 4 mm Hg, mean myocardial BF measured with microspheres was 0.91 +/- 0.08 ml/min/g in the LAD-dependent region and 2.36 +/- 0.11 ml/min/g in the posterior control region, respectively. With no change in distal coronary pressure, ITF 296 increased mean BF in the LAD region to 1.25 +/- 0.05 ml/min/g (4 micrograms/kg/min i.v.) and 1.40 +/- 0.10 ml/min/g (20 micrograms/kg/min i.v.), whereas ISDN (20 micrograms/kg/min i.v.) increased flow to 1.28 +/- 0.18 ml/min/g (each p < 0.05). The increase in BF occurred exclusively in the deeper layers, with no change in subepicardial BF. Consequently, the endocardial/epicardial (endo/epi) BF ratio increased from 0.33 +/- 0.04 during control stenosis to 0.70 +/- 0.10 after ITF 296 (20 micrograms/kg/min), and to 0.56 +/- 0.08 after ISDN (each p < 0.05). Neither ITF 296 nor ISDN had an effect on myocardial BF in the normally perfused control region. Therefore, both ITF 296 and ISDN improved BF to the deeper myocardial layers distal to a coronary artery stenosis. This effect occurred without alterations in stenosis severity or diastolic intraventricular pressure, suggesting that these agents act by dilating the penetrating arteries which deliver BF to the subendocardium.

New antianginal nitro esters with reduced hypotensive activity. Synthesis and pharmacological evaluation of 3-[(nitrooxy)alkyl]-2H-1,3-benzoxazin-4(3H)-ones

New nitro ester 3-[(nitrooxy)alkyl]-2H-1,3-benzoxazin-4(3H)-ones show marked inhibitory activity against ischemia-induced electrocardiographic changes, with only limited systemic hemodynamic effects, and are reported in the present study. These new nitro vasodilators are potent inhibitors of the electrocardiographic T-wave and S-T segment elevation induced by intravenous or intracoronary administration of Arg-vasopressin or methacholine in the anesthetized rat. The most active compounds are up to 300- and 600-fold more potent than glyceryl trinitrate or Nicorandil, respectively. These nitro esters relax in a concentration-dependent manner the isolated rabbit aorta, at higher concentrations (2-40-fold) than glyceryl trinitrate, and reduce the mean arterial blood pressure at doses 7-300-fold higher than those required by glyceryl trinitrate to exert a similar hypotensive effect. Remarkably, these compounds retain their anti-ischemic and hemodynamic profile after oral (po) administration. These new nitro ester derivatives, endowed with a marked antianginal activity, which is not associated with concurrent and pronounced falls in systemic blood pressure, represent the leads of a new class of selective nitrovasodilators having a preferential action on large coronary vessels, which could be clinically relevant in the treatment of coronary artery diseases.

A biomechanical model of index finger dynamics

A dynamic model of the biomechanics of the index finger for flexion-extension and abduction-adduction motion is introduced. The model takes into account all the tendons in the finger and relates to their varying moment arms during motion. A new set of moment arm coefficients and elongation equations is derived based on experimental measurements of previous studies. Constraint equations using variable coefficients are introduced and an optimization approach used to obtain the tendon forces required for any given motion and external force. The model and optimization approach are tested with data from a rapid pinch experiment as well as a hypothetical disc rotation. Good correlation is obtained with respect to electromyographic data in the literature.

Simulation of distal tendon transfer of the biceps brachii and the brachialis muscles

Rupture of the distal tendons of the biceps brachii and the brachialis often consists of a clean avulsion of the end of the tendons from their tuberosities. In most of the reattachment procedures these tendons are reinserted to the same tuberosities. The purpose of this study was to examine the kinetic activity in the upper limb when the insertion locations of the two prime elbow flexors are altered. The right upper limb was modeled as a two-bar linkage moving in the vertical plane of the scapula. Our Hill-type musculo-tendon actuation system was modeled in terms of five muscles moving in three-dimensional space. The prime elbow flexors, i.e. the biceps brachii and the brachialis, were excited maximally, while the other muscles were left passive and were included as such in the analysis. The limb kinetics was studied in four different insertion locations of the biceps brachii and the brachialis. Data on the elbow kinematics, the muscle tensions histories, the muscle length-tension and velocity-tension relationships and the joint constraint forces were produced. The results indicate that when the new insertions of the biceps brachii and the brachialis are located further away from the elbow joint axis, the moments of these muscles about the joint axis increase. However, the shortening velocities of these muscles are increased as well, which results in a reduced tension. In addition, the magnitudes of the compressive force, the tangential forces and the torsional and bending moments are reduced. These results suggest that, whenever surgically possible, reinsertion of ruptured distal tendons of the biceps brachii and the brachialis more distally to the location of their tuberosities should be beneficial.