The effect of parameters of equilibrium-based 3-D biomechanical models on extracted muscle synergies during isometric lumbar exertion.

A hallmark of more advanced models is their higher details of trunk muscles represented by a larger number of muscles. The question is if in reality we control these muscles individually as independent agents or we control groups of them called "synergy". To address this, we employed a 3-D biomechanical model of the spine with 18 trunk muscles that satisfied equilibrium conditions at L4/5, with different cost functions. The solutions of several 2-D and 3-D tasks were arranged in a data matrix and the synergies were computed by using non-negative matrix factorization (NMF) algorithms. Variance accounted for (VAF) was used to evaluate the number of synergies that emerged by the analysis, which were used to reconstruct the original muscle activations. It was showed that four and six muscle synergies were adequate to reconstruct the input data of 2-D and 3-D torque space analysis. The synergies were different by choosing alternative cost functions as expected. The constraints affected the extracted muscle synergies, particularly muscles that participated in more than one functional tasks were influenced substantially. The compositions of extracted muscle synergies were in agreement with experimental studies on healthy participants. The following computational methods show that the synergies can reduce the complexity of load distributions and allow reduced dimensional space to be used in clinical settings.

Control of human spine in repetitive sagittal plane flexion and extension motion using a CPG based ANN approach.

The complexity associated with musculoskeletal modeling, simulation, and neural control of the human spine is a challenging problem in the field of biomechanics. This paper presents a novel method for simulation of a 3D trunk model under control of 48 muscle actuators. Central pattern generators (CPG) and artificial neural network (ANN) are used simultaneously to generate muscles activation patterns. The parameters of the ANN are updated based on a novel learning method used to address the kinetic redundancy due to presence of 48 muscles driving the trunk. We demonstrated the feasibility of the proposed method with numerical simulation of experiments involving rhythmic motion between upright standing and 55 degrees of flexion. The tracking performance of the model is accurate to within 2° while reciprocal muscle activation patterns were similar to the observed experimental coordination patterns in normal subjects. The suggested method can be used to map high-level control strategies to low-level control signals in complex biomechanical and biorobotic systems. This will also provide insight about underlying neural control mechanisms.

Determination of fentanyl in biological and water samples using single-drop liquid-liquid-liquid microextraction coupled with high-performance liquid chromatography.

A single-drop liquid-liquid-liquid microextraction (LLLME) method coupled with high-performance liquid chromatography (HPLC) was developed for the determination of fentanyl in biological (plasma and urine) and wastewater samples. Fentanyl is a potent synthetic narcotic analgesic administered in the form of a transdermal patch for the management of chronic pain. Fentanyl was extracted from 0.01 M NaOH solution (donor phase) into a thin layer of organic phase (100 muL), then back-extracted into 5 muL of the acidic acceptor microdrop (1 x 10(-3)M HClO(4)) immersed in the organic membrane from the tip of a 25-muL HPLC syringe. After the extraction, the microdrop was withdrawn into the syringe and injected directly into a HPLC system for analysis. The parameters influencing the extraction efficiency including the organic solvent and its volume, acceptor microdrop volume, composition of the donor and acceptor phases, stirring rate, temperature, salt addition and pre- and back-extraction times were investigated and optimized. At the most appropriate conditions (100 muL of n-octane, 3.6 mL of the donor phase maintained at 0.01 M NaOH, 5 muL of 1 x 10(-3)M HClO(4) as the acceptor microdrop, stirring rate of 1000 rpm for pre-extraction and 700 rpm for back-extraction, 30 degrees C, no salt addition, 30 min for pre-extraction and 20 min for back-extraction), an enrichment factor (EF) of 355 was obtained. The limit of detection (LOD) was 0.1 ngmL(-1) (based on S/N=3) and intra- and inter-day relative standard deviations less than 9% were obtained. The calibration graph was linear within the range of 0.5-1000 ngmL(-1) with the correlation coefficient (r) of 0.9999. Finally, the feasibility of the proposed method was evaluated by extraction and determination of fentanyl in plasma, urine and wastewater samples and satisfactory results were obtained.

Determination of tramadol in human plasma and urine samples using liquid phase microextraction with back extraction combined with high performance liquid chromatography.

Liquid phase microextraction by back extraction (LPME-BE) combined with high performance liquid chromatography (HPLC)-fluorescence detection was developed for the determination of tramadol in human plasma. Tramadol was extracted from 2 mL of basic sample solution (donor phase) with pH 11.5 through a micro liter-size organic solvent phase (100 microL n-octane) for 25 min and finally into a 3.5 microL acidic aqueous acceptor microdrop with pH 2.5 suspended in the organic phase from the tip of a HPLC microsyringe needle for 15 min with the stirring rate of 1250 rpm. After extraction for a period of time, the microdrop was taken back into the syringe and injected into HPLC. Effected the experimental parameters such as the nature of the extracting solvent and its volume, sample temperature, stirring rate, volume of the acceptor phase, pH and extraction time on LPME-BE efficiency was investigated. At the optimized condition, enrichment factor of 366 and detection limit (LOD) of 0.12 microg L(-1) were obtained. The calibration curve was linear (r=0.999) in the concentration range of 0.3-130 microg L(-1). Within-day relative standard deviation RSD (S/N=3) and between-day RSD were 3.16% and 6.29%, respectively. The method was successfully applied to determine the concentration of tramadol in the plasma and urine samples and satisfactory results were obtained.

Acute management of atrial fibrillation and atrial flutter in the critical care unit: should it be ibutilide?

BACKGROUND: Ibutilide is currently indicated for the rapid conversion of atrial fibrillation (Afb) or atrial flutter (Afl) of recent onset but limited to patients who are hemodynamically stable and without symptomatic cardiovascular conditions. HYPOTHESIS: The study was undertaken to assess the efficacy and safety of ibutilide in patients with Afb or Afl associated with acute cardiovascular-medical disorders and in patients receiving prior selective antiarrhythmic drug therapy. METHODS: The study included 34 patients, mean age 75 +/- 16.3 years, with Afb (n = 25) or Afl (n = 9) having a variety of disorders, for example, congestive heart failure, unstable angina, borderline hypotension, respiratory failure, and chronic renal failure. Prior antiarrhythmic drugs consisted of propafenone (n = 5) or amiodarone (n = 3). Eligibility for cardioversion was established with appropriate anticoagulation or transesophageal echocardiography findings. Ibutilide was given as up to two 10 min infusions of 1 mg separated by 10 min. RESULTS: The overall conversion rate after ibutilide was 79.4% (27/34 patients): 80% for Afb and 78% for Afl. More than 90% converted within 1 h of treatment. A high conversion rate of 92% resulted in those with an arrhythmia duration of < or = 1 week. All eight patients with prior antiarrhythmic therapy converted to sinus rhythm. The average baseline QTc interval for all patients increased 17.1% (397 +/- 63.3 to 465 +/- 60.2 ms) at 30 min. For eight patients (including four who received prior antiarrhythmic drugs), QTc interval prolongation > or = 500 ms was associated with nearly half the entire incidence of arrhythmic events. Proarrhythmia, the exclusive adverse effect, consisted of ventricular extrasystoles (n = 10) and nonsustained monomorphic ventricular tachycardia (VT) (n = 2) managed with intravenous MgSO4, and sustained polymorphic VT (n = 1) requiring electrical cardioversion. CONCLUSION: Ibutilide is an effective and well tolerated drug for the rapid termination of Afb or Afl of recent onset associated with symptomatic and/or hemodynamically unstable disorders, and it is most efficacious (> or = 90%) when the atrial arrhythmia is < or = 1 week in duration. Proarrhythmic events are readily manageable in a monitored unit with access to appropriate treatment.

Ibutilide for termination of atrial fibrillation in the Wolff-Parkinson-White syndrome.

Ibutilide promptly restored sinus rhythm on two occasions in an elderly patient with AF and rapid ventricular response associated with the WPW syndrome. As a selective Class III antiarrhythmic agent that prolongs cardiac refractoriness, ibutilide offers an alternative effective therapy for rapid termination of AF in WPW.

Acute myocardial infarction associated with anabolic steroids in a young HIV-infected patient.

The use and abuse of anabolic-androgenic steroids have increased over the past decade and pose a medical and public health problem. In addition to their use by athletes to increase muscle mass and improve performance, people with wasting and malignant diseases are finding that the agents improve both their physical appearance and strength. Unfortunately, anabolic steroids are associated with a number of adverse effects, not the least of which is acute myocardial infarction, which occurred in a 39-year-old man with human immunodeficiency virus infection. It is important for clinicians to be aware of the association and to counsel patients carefully about this and other untoward effects that may occur with the agents.