Myoelectric power spectrum dependence on muscular contraction level of elbow flexors

Summary The influence of the strength of contraction on surface recorded myoelectric power spectra was studied for three elbow flexors. Four subjects performed brief (3–5 s) isometric contraction levels (5–80% MVC). The experiment was repeated 23–26 times on different days. The surface myoelectric signal was recorded from the biceps brachii, the brachialis and the brachioradialis. By fast Fourier transform the myoelectric power spectrum was computed. The mean power frequency (MPF) was calculated and used as a single estimate of the myoelectric power spectrum. The MPF was found to increase with contraction strength with low level contractions. At levels in excess of 25–30% of MVC, the MPF became independent of contraction level. This dependence of the MPF on low level contractions is explained by tissue filtering effects and the recruitment order and distribution of motor units.This investigation was supported by grants from the Swedish Work Environment Fund and the Medical Faculty of Umeå University     

The dependence of cardiac contraction on depolarization and slow inward current

Summary The membrane potential of the guinea-pig's papillary muscle was controlled by a voltage clamp technique which employs one sucrose gap and one intracellular microelectrode. Both the membrane potential and the membrane current were recorded together with the contraction. The steady-state contractions were obtained after 6–8 contractions. The difference between the steady-state contractions and the succeeding test contractions was considered to be due to the difference in the trigger action between the conditioning and the test pulses. The following results were obtained: 1. when the test pulses were appropriately shortened so that a large tail of inward current flowed after the repolarization step, the contraction was augmented. This paradoxical increase of the contraction can be explained by assuming a direct action of the slow inward current on contraction. 2. The peak amplitude of the contraction increased with the size of the depolarizing step in the range of the membrane potential at which the calcium current should be small or zero. This suggests that in addition to the calcium current another effect of depolarization controls the contraction. 3. The rate of rise of contraction seemed to be determined by the calcium current which was maximum at a depolarization to +10 mV. At this level the slow inward current also reached the maximum. With further increase of the depolarization the rise of the contraction and the slow inward current were decreased. 4. During a series of the pulses the positive inotropic effect (staircase) was the more pronounced the larger the depolarization. This holds true for depolarization up to +70 mV. The potentiation occurred in spite of decrease of the slow inward current. It seems necessary to postulate a potentiating process which is dependent on the amplitude of the depolarization.This work was supported by the Deutsche Forschungsgemeinschaft.     

Active contraction of cardiac muscle: in vivo characterization of mechanical activation sequences in the beating heart

Progressive alterations in cardiac wall strains are a classic hallmark of chronic heart failure. Accordingly, the objectives of this study are to establish a baseline characterization of cardiac strains throughout the cardiac cycle, to quantify temporal, regional, and transmural variations of active fiber contraction, and to identify pathways of mechanical activation in the healthy beating heart. To this end, we insert two sets of twelve radiopaque beads into the heart muscle of nine sheep; one in the anterior-basal and one in the lateral-equatorial left ventricular wall. During three consecutive heartbeats, we record the bead coordinates via biplane videofluoroscopy. From the resulting four-dimensional data sets, we calculate the temporally and transmurally varying Green–Lagrange strains in the anterior and lateral wall. To quantify active contraction, we project the strains onto the local muscle fiber directions. We observe that mechanical activation is initiated at the endocardium slightly after end diastole and progresses transmurally outward, reaching the epicardium slightly before end systole. Accordingly, fibers near the outer wall are in contraction for approximately half of the cardiac cycle while fibers near the inner wall are in contraction almost throughout the entire cardiac cycle. In summary, cardiac wall strains display significant temporal, regional, and transmural variations. Quantifying wall strain profiles might be of particular clinical significance when characterizing stages of left ventricular remodeling, but also of engineering relevance when designing new biomaterials of similar structure and function.     

The distribution of activity among the muscles of a single group during isometric contraction

Summary The study of the relations between the electrical activity of a group of synergistic muscles and the biomechanical parameters characterizing the resultant movement is generally reduced to one of the muscles of this group, this muscle being considered as equivalent. This is in particular the case for the biceps brachii in the group of elbow flexor muscles. The validity of this concept in the case of isometric, isotonic contraction can be tested by the simultaneous utilization of surface-electrode and wire-electrode detection techniques.It has been shown 1. that the quadratic relation between the global integrated EMG of the biceps brachii and the external force resulting from the action of the group of flexors can be extended to each of the muscles of this group (brachialis, brachioradialis, pronator teres); 2. that the slope of the relation between the integrated EMG of the biceps brachii and the force differs according to whether the hand is supine or prone. An explanation of a mechanical nature has been proposed for this phenomenon; 3. that in a given situation the relations between the different integrated EMG's remain constant whatever the value of the force.It follows that 1. each value of the integrated EMG of a muscle equals a coefficient times the value of the force exerted by this muscle; 2. the notion of muscle equivalent is justified for a given situation.     

Intramuscular pressures during exercise: an evaluation of a fiber optic transducer-tipped catheter system

Summary The efficacy of a modified fibre optic transducer-tipped catheter system for measuring intramuscular pressures during exercise was determined. A microcapillary infusion technique using a catheter was employed as the standard of comparison due to its established dynamic properties. Pressures were measured in the tibialis anterior muscle of six healthy adults at rest before exercise, during isometric and concentric exercise, and at rest after exercise. The fibre optic system measured contraction pressures equal to the microcapillary infusion technique during all phases of the exercise protocols but recorded a lower relaxation pressure during isometric exercise and a lower rest pressure following 20 min of concentric exercise. Negative relaxation pressures were recorded by the fibre optic system for two subjects during continuous concentric exercise. It is hypothesized that a piston effect, due to the sliding of muscle fibres at the catheter tip following a contraction, rendered falsely low pressures during relaxation and that this artefact was reflected in the subsequent rest pressure following exercise. The larger volume (157 mm³) and area (3.49 mm²) of the fibre optic catheter in the muscle made it more prone to this effect than the conventional catheter (39 mm³ and 0.87 mm², respectively). The fibre optic system may be preferred when recording the musclecontraction pressures during complex limb movements but should not be used when assessing the relaxation pressures or the pressure at rest following exercise.This project was performed at the Division of Orthopaedics and Rehabilitation, Veterans Administration Medical Center and the University of California San Diego     

The effect of muscle vibration on human position sense during movements controlled by lengthening muscle contraction

Summary Muscle vibration studies suggest that during voluntary movement limb position is coded by muscle spindle information derived from the lengthening, antagonist muscle. However, these investigations have been limited to movements controlled by shortening contractions. This study further examined this property of kinesthesia during movements controlled by lengthening contraction. Subjects performed a horizontal flexion of the right forearm to a mechanical stop randomly positioned at 30, 50 and 70° from the starting position. The movement was performed against a flexor load (1 kg) requiring contraction of the triceps muscle. Vision was occluded and movements were performed under three conditions: no vibration, vibration of the right biceps and vibration of the right triceps. The perceived position of the right forearm was assessed by instructing subjects to simultaneously match the right limb position with the left limb. Vibration of the shortening biceps muscle had no effect on limb matching accuracy. However, triceps vibration resulted in significant overestimation of the vibrated limb position (10–13°). The variability in movement distance was uninfluenced by muscle vibration. During movements controlled by lengthening contraction, there is a concurrent gamma dynamic fusimotor input that would enhance primary afferent discharge. Despite this additional regulating input to the muscle spindle, it appears that muscle spindle information from the lengthening muscle is important for the accurate perception of limb movement and/or position.     

Ion-specific protein destabilization of the contractile proteins of cardiac muscle fibers

 We investigated the inhibitory effects of increased salt concentrations on maximal calcium-activated force (F _max) of rabbit cardiac papillary muscle bundles skinned with Triton X-100. While other studies have reported a lack of ion-specific effects on F _max of cardiac muscle, we clearly demonstrated the presence of such effects when a wider variety of salts was investigated. In addition, like skeletal muscle, cardiac muscle was found to be sensitive to ionic strength and not to ionic equivalence. In support of our hypothesis that the ion-specific effects are due to protein destabilization, we found that a protein stabilizer (trimethylamine N-oxide, TMAO) completely abolished the ion-specific effects on F _max. The ion-specific effect is probably due to binding of ions to the contractile proteins. The general ionic effect is most likely due to electrostatic shielding that remains in the presence of TMAO. Neither 300 mM sucrose nor TMAO significantly altered F _max at physiological ionic strength indicating that the ion-specific depression of F _max was not due to a colligative/osmotic effect. Furthermore, adding sucrose to solutions with a supraphysiological ionic strength caused a further decrease in F _max indicating that certain osmolytes can alter F _max if the contractile proteins are initially destabilized. Received: 9 May 1997 / Received after revision: 4 September 1997 / Accepted: 5 September 1997     

Influence of exercise on serum brain-derived neurotrophic factor concentrations in healthy human subjects

The effect of short-term exercise (15 min step-exercise) on serum brain-derived neurotrophic factor (BDNF) levels was evaluated in healthy human subjects. Results showed a short-term, significant increase in serum BDNF levels after exercise. Intra-individual differences in serum BDNF levels were remarkably small on the rest day and also when compared to rest values on the day of the exercise test. Inter-individual differences, on the other hand, were larger by comparison. The result of this study supports the need for larger sample size in studies on BDNF changes in psychiatric disorders or psychiatric drug effects.     

The effect of hypokinesia and hypodynamia on protein turnover and the growth of four skeletal muscles of the rat

An animal suspension model has been used to simulate the weightlessness experienced during space travel. This procedure results in a reduction in the normal shortening (i.e. hypokinesia) and force generation functions of hind limb muscles (i.e. hypodynamia). The ensuing muscle atrophy was studied over 12 days in different muscle types. Slow muscles (e.g. the soleus) underwent a more pronounced atrophy than intermediate (i.e. gastrocnemius) and fast phasic muscles (e.g. extensor digitorum longus). In all muscle types inactivity resulted in a smaller accumulation of DNA and losses of RNA and protein after 5 days. The latter arose from a decrease in the rate of protein synthesis (measured in vivo) and an increase in protein breakdown. Increased specific activities of cathepsins B and D also supported the view that there is an increased proteolysis after hypokinesia and hypodynamia.When the inactive soleus was simultaneously held in a lengthened (stretched) state the atrophy was prevented through a large increase in the fractional rate of protein synthesis. Protein degradation remained elevated with stretch, thereby slowing the growth of these muscles relative to those in pair-fed, ambulatory controls. The much smaller atrophy of the tibialis anterior and extensor digitorum longus muscles in suspended only limbs represented an underestimate of the true atrophic effects of hypokinesia and hypodynamia. In this model gravity pulls the suspended foot into a plantar flexed position, thereby permanently stretching and protecting such flexor muscles. When this influence of stretch was removed a greater atrophy ensued, mainly due to the loss of the stretch-induced stimulation of protein synthesis. Despite this, the inactive fast-twitch muscles still exhibited less atrophy than the gastrocnemius and soleus muscles.     

丹参、生脉注射液对中枢和神经肌接头兴奋传递及肌肉收缩疲劳的影响

目的 :研究复方丹参、生脉注射液对中枢、神经肌接头和肌肉疲劳的影响。方法 :记录蟾蜍坐骨神经干动作电位和腓肠肌收缩曲线 ,测定中枢、神经—肌接头、肌肉出现疲劳的时间。结果 :同对照组比较 ,丹参组和生脉组中枢、神经—肌接头、肌肉出现疲劳的时间都明显延长。差异具有显著性 (P <0 .0 1 )。结论 :复方丹参、生脉注射液具有抗中枢、神经—肌接头和肌疲劳的作用。     

无血清培养对人绒毛膜来源间充质干细胞免疫活性的影响

目的 评价人绒毛膜来源间充质干细胞(MSCs)在无血清培养体系中的免疫活性,探索干细胞安全的应用于临床的条件.方法 应用无血清与含10％胎牛血清培养基培养人绒毛膜来源MSCs,比较两种培养条件下培养细胞的形态、免疫表型、分化潜能及对混合淋巴细胞反应的抑制作用等生物学特性.结果 两种方法培养的细胞形态相似,表达CD73、CD90、CD105,不表达CD34、人类白细胞抗原(HLA)-DR;具有多向分化潜能,同样能明显抑制混合淋巴细胞反应体系中淋巴细胞的增殖,抑制率与加入的干细胞数量成正比,可以减少混合淋巴细胞反应中白细胞介素2、γ-干扰素的分泌.结论 人绒毛膜来源间充质干细胞经无血清培养后仍保持原有的细胞形态、免疫表型、多向分化等生物学特性,没有改变免疫学活性.无血清培养可取代有血清培养用于细胞培养,避免经有血清培养的干细胞移植等临床应用研究引起的免疫原性反应及人畜共患病.     

丝裂原活化蛋白激酶参与胰岛素对自发性高血压大鼠血管平滑肌细胞的增殖研究

目的:探讨高血压血管平滑肌细胞(VSMC)在胰岛素作用下胞内信号转导途径之一丝裂原活化蛋白激酶(MAPK)的影响,及其与VSMC增殖的关系。方法:选用6周龄自发性高血压大鼠(SHR)和WKY大鼠,无菌分离主动脉,体外纯化培养VSMC至6~8代,加胰岛素干预和蛋白激酶C(PKC)抑制剂,采用胶内髓磷脂碱性蛋白原位磷酸化法测定VSMC中MAPK活性,并用Western Blot检测VSMC中MAPK的含量, [³H]-TdR测定VSMC的DNA合成量。结果:胰岛素作用后,SHR组的DNA合成量显著增加,MAPK活性及蛋白含量也显著增加,PKC抑制剂可明显降低MAPK活性。结论:SHR体外培养的VSMC增殖与MAPK活性增加有关,胰岛素可影响其活性,并且可能存在胰岛素-PKC-MAPK轴。     

BAFF is elevated in serum of patients with Wegener's granulomatosis

BAFF (B-cell activating factor of the TNF family) plays a crucial role in B-cell survival. Elevated BAFF serum levels have been linked to several autoimmune diseases in humans, and therapies targeting BAFF were successful in animal models of rheumatoid arthritis and systemic lupus erythematosus. Wagener's granulomatosis (WG), a chronic systemic vasculitis, is characterized by circulating autoantibodies (cANCA) targeting neutrophils, which can produce BAFF. To investigate whether BAFF is involved in WG pathology, BAFF serum levels were measured by ELISA in 46 WG patients and 62 healthy donors. We report the novel finding that in WG patients serum levels of BAFF were significantly increased (median 3.95 ng/ml, p=0.009) compared to healthy controls (median 2.38 ng/ml). The difference was even more pronounced when comparing controls with untreated WG patients (median 4.61 ng/ml, p=0.001). Treatment of WG patients with glucocorticoids was associated with lower BAFF levels. The serum BAFF level in treated WG patients was about the same as in the control group. We propose that BAFF might be a pathogenic factor in WG and that targeting BAFF may represent a new therapeutic strategy in a subset of chronically relapsing WG patients with elevated BAFF levels.     

Age effect on fatigue-induced limb acceleration as a consequence of high-level sustained submaximal contraction

In reference to electromyographic measurement, the study was conducted to reassess differences in the behavior of fatigue-related neuromuscular function between young and elderly humans with limb acceleration (LA). Fourteen young and fourteen elderly subjects performed sustained index abduction at 75% of their maximal voluntary contractions (MVC) until task failure. Measures of neuromuscular function, including temporal/spectral features of muscle activity of the first dorsal interosseous (FDI) and LA of the index and hand, were monitored. The results showed a manifest fatigue-induced increase in LA of the index in the elderly group, but not in the young group. In contrast, only the young group developed a significant increase in amplitude of the electromyography (EMG) until task failure. Spectral analyses of LA in the index reflected marked age-dependent reorganization following muscle fatigue, with a greater reduction of relative spectral amplitude of LA in the range of 20–40 Hz, but a lesser reduction in coherence between EMG and LA in the elderly group. In line with fatigue-associated restructuring of LA, the mechanical coupling of the metacarpophalangeal joint was more severely undermined in the elderly group than in the young group. The present study manifested an age-related difference in the relative contributions of neural versus mechanical factors to muscle fatigue. Subsequent to a high-level sustained submaximal isometric contraction, a predominant mechanical failure of the musculotendon complex in the elderly was featured with LA, whereas EMG measurement characterized prevailing impairment of neuromuscular propagation in the young.     

人S100蛋白的表达及其抗血清的制备和脑脊液中S100含量测定方法的建立

目的：建立定量检测脑脊液（CSF）及血清中S100蛋白的方法，探讨S100蛋白的检测在辅助诊断克－雅病（CJD）中的应用。方法：利用脑cDNA文库，经PCR获得了S100基因并克隆至原核表达载体pGEX-2T上，在大肠埃希菌中表达了谷胱甘肽－S－转移酶（GST）－S100融合蛋白；融合蛋白经亲和纯化后，免疫家兔，制备抗体；抗体经纯化后，用生物素（BNHS）标记，建立了可定量检测S100蛋白的生物素－亲和素系统ELISA方法，并初步用于临床脑脊液的检测中。结果：所表达的GST－S100蛋白相对分子质量约为35000，以其为抗原制备的S100特异性抗血清具有良好的免疫反应性。建立了定量检测脑脊液中S100蛋白的双抗体夹心ELISA方法，对3例“可能性的CJD”患者（14－3－3蛋白阳性）和15例无痴呆症状患者脑脊液进行检测，结果显示，3例CJD患者脑脊液S100含量均超过2．900μg/L,而在无痴呆症状患者组中14例患者脑脊液S100含量都低于0．180μg/L。对正常人和CJD患者血清进行检测，显示S100蛋白含量个体间差异很大。结论：所建立的方法可用于脑脊液中S100蛋白的检测，进一步扩大标本量有助于明确脑脊液中S100蛋白的检测在辅助诊断CJD中的价值。     

Local anaesthetic-like effect of interleukin-2 on muscular Na+ channels: no evidence for involvement of the IL-2 receptor

The effects of interleukin-2 (IL-2) on muscular Na⁺ currents were studied in human myoballs. The transient Na⁺ inward currents, elicited by repetitive depolarizations at 1 Hz and recorded in the whole-cell mode, were inhibited by the cytokine, the half-maximum effect occurring at about 500 U/ml. The effects resembled those of local anaesthetics without use dependence, as the inactivation (h ) curve was shifted in a negative direction while the current/voltage curve was not affected. As with these local anaesthetics, depolarization at 1, 4 and 8 Hz in the presence of IL-2 did not produce any cumulative block. The interaction of IL-2 with the Na⁺ channels is very fast (within ms) and it is suggested that it occurs when the Na⁺ channels are in the state of fast inactivation. The recovery from inactivation was only slightly slowed by IL-2, in agreement with the absence of any use dependence. All effects were readily reversible on washout of the cytokine. The effects were seen both in tetrodotoxin-(TTX)-sensitive adult Na⁺ channels and in TTX-insensitive juvenile channels. In contrast to the whole-cell configuration, no inhibition was visible in the attached-patch configuration. Further, the preincubation with an anti-IL-2-receptor antibody did not prevent the inhibitory effect of IL-2 on the Na⁺ currents. It is concluded that the cytokine blocks the voltage-dependent muscular Na⁺ channels by keeping the channels in the state of fast inactivation. An IL-2 receptor and a second messenger system are not likely to be involved in this reaction.     

低氧对肺动脉平滑肌和内皮细胞蛋白激酶C α mRNA表达的影响

目的：探讨低氧对肺动脉平滑肌和内皮细胞蛋白激酶C(PKC)αmRNA表达的影响。方法：应用原位杂交技术了大鼠不同节段肺动脉平滑肌细胞和内皮细胞PKCαmRNA的分布及低氧对在体和离体肺动脉平滑肌细胞及内皮细胞PKCαmRNA表达的影响。结果：正常大鼠各级肺动脉平滑肌细胞和内皮细胞均有PKCαmRNA的表达,腺泡内肺动脉平滑肌细胞中的表达明显高于肌型肺动脉（P＜0．01）,低氧14d和28d肌型动脉和腺泡内肺动脉内皮细胞的表达均明显增高（P＜0．01）,腺泡内腺动脉平滑肌细胞的表达较对照组明显升高（P＜0．01）,低氧14d肌型肺动脉平滑肌细胞表达升高不明显,但低氧28d明显升高（P＜01）,正常条件下离体培养猪肺动脉平滑肌细胞和内皮细胞均有PKCαmRNA的表达,低氧1h对其表达无明显影响,48,72h表达明显升高,以72h升高最显著（P＜0．001）,结论：低氧可促进肺动脉平滑肌细胞和内皮细胞PKC amRNA 的表达,而以腺泡内肺动脉平滑肌细胞的变化最明显,PCKα在低氧性肺动脉高压的形成中可能起一定作用。     

Differential brain,but not serum VEGF levels in a genetic rat model of depression

Compared to the classical monoamine hypotheses focus on neuroplasticity is a major new approach in studies of depression and antidepressants. Recent studies have demonstrated that vascular endothelial growth factor (VEGF) is regulated by antidepressant treatment in rodents. However, in depressive patients no significant changes were found in the serum VEGF levels compared to control subjects. To our knowledge, brain and serum VEGF levels have never been reported in parallel for any psychiatric disease model. That prompted us to examine the levels of VEGF in serum, hippocampus, frontal cortex, corpus striatum, and hypothalamus in male Flinders Sensitive Line (FSL) and Flinders Resistant Line (FRL), a genetic rat model of depression. The VEGF levels were identical in the FSL and the FRL rats in serum, corpus striatum, and hypothalamus. In hippocampus and frontal cortex, the VEGF levels were significantly decreased in the FSL rats compared to the FRL rats. The results may add to the hypothesis that altered expression of growth factors/neurotrophic factors are related to the pathophysiology of depression.     

Effects of staphylococcal protein A-treated human leukemic serum on autologous leukemic blast growth and mitogenesis of lymphocytes

Sera and leukemic blasts of 14 patients with acute myelogenous leukemia were stored at –70°C. In eight patients in whom a remission was achieved, peripheral blood lymphocytes were cultured together with irradiated autologous leukemic cells in treated serum (serum adsorbed with protein A Sepharose) or control serum (Sepharose-treated). Lymphocyte activation was determined after 7 days in culture by [³H]thymidine incorporation. In the absence of stored leukemic blasts, significantly more [³H]thymidine incorporation occurred in six of the eight patients' lymphocytes cultured in treated serum compared to control. Enhanced activity was observed in all eight patients when irradiated leukemic blasts were cocultured with autologous lymphocytes in treated serum. In five patients, the addition of 10% or more of control serum to treated serum inhibited lymphocyte mitogenesis. Protein A immunoadsorption may allow increased stimulation of acute myelogenous leukemia remission peripheral blood lymphocytes, which is further enhanced in some patients by the presence of autologous leukemic cells. This change in lymphocyte activation may contribute to the antitumor effects of treating serum with protein A.     

Identification of a panel of serum protein markers in early stage of sepsis and its validation in a cohort of patients

Background

Sepsis is a life-threatening illness with a challenging diagnosis. Current serum biomarkers are not sensitive enough for diagnosis. With the aim of finding proteins associated with sepsis, serum protein profile was compared between patients and healthy donors and serum classical inflammatory proteins were analyzed in both groups.