[Feasibility study of expectant management of different degrees of vaginal fluid in pregnant women with premature rupture of membranes in the second trimester]

Objective: To investigate the feasibility of expectant management of different degrees of vaginal fluid in pregnant women with premature rupture of membranes in the second trimester. Methods: A retrospective cohort study was conducted to collect 103 pregnant women who were diagnosed with premature rupture of membranes in the second trimester of pregnancy and insisted on continuing the pregnancy in Shanxi Bethune Hospital from July 2012 to July 2022. According to the degree of vaginal fluid, pregnant women were divided into rupture group (with typical vaginal fluid, 48 cases) and leakage group (without typical vaginal fluid, 55 cases). The rupture latency (the time from rupture of membranes to termination of pregnancy), gestational weeks of termination, indications and methods of termination of pregnancy, maternal infection related indicators and perinatal outcomes were compared between the two groups. Univariate regression model was used to analyze the correlation between different degrees of vaginal fluid in pregnant women with premature rupture of membranes and maternal and neonatal outcomes. Results: (1) Obstetric indicators: there was no significant difference in the gestational age of rupture of membranes between the two groups (P>0.05). However, the proportion of rupture latency >28 days in the leakage group was significantly higher than that in the rupture group [42% (23/55) vs 13% (6/48); χ2=33.673, P<0.001], and the incidence of pregnancy termination ≥28 weeks was significantly higher [47% (26/55) vs 19% (9/48); χ2=9.295, P=0.002]. (2) Indications and methods of termination: the incidence of progressive reduction of amniotic fluid as the indication for termination in the leakage group was significantly lower than that in the rupture group [22% (12/55) vs 42% (20/48); χ2=4.715, P=0.030], and the incidence of full-term termination in the leakage group was significantly higher than that in the rupture group [31% (17/55) vs 12% (6/48); χ2=5.008, P=0.025], while there were no significant differences in the indications of termination of pregnancy, including amniotic cavity infection, uterine contraction failure and fetal distress between the two groups (all P>0.05). The incidence of induced labor or spontaneous contraction in the leakage group was significantly lower than that in the rupture group [53% (29/55) vs 81% (39/48); χ2=9.295, P=0.002], while the cesarean section rate and vaginal delivery rate were similar between the two groups (both P>0.05). (3) Infection related indicators: the incidence of amniotic cavity infection in the leakage group was significantly higher than that in the rupture group [31% (17/55) vs 13% (6/48); χ2=4.003, P=0.045]. However, there were no significant differences in the elevation of inflammatory indicators, the positive rate of cervical secretion bacterial culture and the incidence of tissue chorioamnionitis between the two groups (all P>0.05). (4) Perinatal outcomes: the live birth rate in the leakage group was significantly higher than that in the rupture group [51% (28/55) vs 27% (13/48); χ2=5.119, P=0.024]. The proportion of live births with 1-minute Apgar score >7 in the leakage group was significantly higher than that in the rupture group [38% (21/55) vs 17% (8/48); χ2=4.850, P=0.028]. However, there were no significant differences in the birth weight of live births and the incidence of neonatal complications between the two groups (all P>0.05). (5) Univariate regression analysis showed that compared with the rupture group, the leakage group had a higher risk of pregnancy termination at ≥28 gestational weeks (RR=2.521, 95%CI: 1.314-4.838; P=0.002), amniotic infection (RR=2.473, 95%CI: 1.061-5.764; P=0.025), perinatal survival (RR=1.880, 95%CI: 1.104-3.199; P=0.014). Conclusion: Compared with pregnant women with typical vaginal fluid in the second trimester of premature rupture of membranes, expectant treatment for pregnant women with atypical vaginal fluid is more feasible, which could effectively prolong the gestational weeks and improve the perinatal live birth rate.

Discovery of N-Phenylpropiolamide as a Novel Succinate Dehydrogenase Inhibitor Scaffold with Broad-Spectrum Antifungal Activity on Phytopathogenic Fungi

Based on the structural features of both succinate dehydrogenase inhibitors (SDHIs) and targeted covalent inhibitors, a series of N-phenylpropiolamides containing a Michael acceptor moiety were designed to find new antifungal compounds. Nineteen compounds showed potent inhibition activity in vitro on nine species of plant pathogenic fungi. Compounds 9 and 13 showed higher activity on most of the fungi than the standard drug azoxystrobin. Compound 13 could completely inhibit Physalospora piricola infection on apples at 200 μg/mL concentration over 7 days and showed high safety to seed germination and seedling growth of plants at ≤100 μg/mL concentration. The action mechanism showed that 13 is an SDH inhibitor with a median inhibitory concentration, IC₅₀, value of 0.55 μg/mL, comparable with that of the positive drug boscalid. Molecular docking studies revealed that 13 can bind well to the ubiquinone-binding region of SDH by hydrogen bonds and undergoes π-alkyl interaction and π-cation interaction. At the cellular level, 1 as the parent compound could destruct the mycelial structure of P. piricola and partly dissolve the cell wall and/or membrane. Structure-activity relationship analysis showed that the acetenyl group should be a structure determinant for the activity, and the substitution pattern of the phenyl ring can significantly impact the activity. Thus, N-phenylpropiolamide emerged as a novel and promising lead scaffold for the development of new SDHIs for plant protection.

[Construction of prediction model combined dual-energy CT quantitative parameters and conventional CT features for assessing the Ki-67 expression levels in invasive breast cancer]

Objective: To develop a model combined with dual-energy CT quantitative parameters and conventional CT features for evaluating the expression level of Ki-67 in invasive breast cancer. Methods: A total of 191 patients with histologically confirmed invasive breast cancer in Lishui Central Hospital from March 2019 to December 2020, were retrospectively enrolled, all of them were females, aged from 25 to 77 (53.2±11.3) years. All patients underwent preoperative non-contrast chest and contrast-enhanced Dual energy CT scans, and the normalized iodine concentration (NIC) of lesions on arterial and venous phase, spectral curve slope (λ_HU), and normalized effective atomic number (nZ_eff) were measured and calculated, and their conventional CT characteristics were assessed. According to the results of immunohistochemistry (IHC), the patients were divided into Ki-67 high expression group (n=129 patients) and low expression group (n=62 patients) level. The differences in clinical data, conventional CT characteristics and dual-energy CT quantitative parameters between the two groups were analyzed. The receiver operating characteristic curve (ROC) curve was conducted to assess the efficacy of each individual model and joint model in evaluating Ki-67 expression levels, and the area under the curve (AUC), sensitivity, specificity, and accuracy were calculated, respectively. Results: In the analysis of CT features, the longest diameter, shape and enhancement pattern of the tumor were significantly difference between the two groups (all P<0.05). The NIC, nZ_eff on the arterial phase and NIC, nZ_eff and λ_HU [M(Q₁,Q₃)] on the venous phase were higher in the high Ki-67 expression group compared to the low expression group [0.13 (0.12, 0.16) vs 0.11 (0.08, 0.14), 0.71 (0.70, 0.75) vs 0.70 (0.67, 0.72), 0.40 (0.32, 0.48) vs 0.23 (0.17, 0.32), 3.10 (2.58, 3.63) vs 2.86 (2.19, 3.48), 0.88 (0.85, 0.92) vs 0.85 (0.84, 0.86), all P<0.05]. The logistic regression model, which integrated significant conventional CT features and dual-energy CT quantitative parameters, demonstrated the highest diagnostic performance for assessing Ki-67 expression levels, with an AUC of 0.924, sensitivity of 88.37%, specificity of 83.87%, and accuracy of 86.91%; the AUC of the dual-energy CT parameter model was 0.908, sensitivity of 82.17%, specificity of 88.71%, and accuracy of 84.29%. Though the diagnostic efficacy was no significant difference (P=0.238), both models showed superior to the conventional CT feature model (all P<0.001). Conclusion: A dual-energy CT quantitative parameter combined with a conventional CT feature model was successfully constructed, which has a good evaluation performance on the expression level of Ki-67 in invasive breast cancer.

Simple Analogues of Quaternary Benzo[c]phenanthridine Alkaloids: Discovery of a Novel Antifungal 2-Phenylphthalazin-2-ium Scaffold with Excellent Potency against Phytopathogenic Fungi

Inspired by sanguinarine and chelerythrine, a novel antifungal 2-phenylphthalazin-2-ium scaffold as a simple analogue was designed. Most of the 30 compounds showed excellent inhibition activity against almost all eight phytopathogenic fungi, far superior to sanguinarine and chelerythrine. A third of the compounds were more active than azoxystrobin in most cases. Compounds 26 and 27 showed the highest total activity against all the fungi with EC₅₀ means of ca. 4.6 μg/mL. Fusarium solani showed the highest susceptibility with an EC₅₀ mean of 3.62 μg/mL to 19 compounds. A concentration of 25.0 μg/mL 27 can fully control the Colletotrichum gloeosporioides infection in apples over 9 days. Electron microscopic observations showed that 27 was able to damage the structures of the hypha and cell membrane. The structure-activity relationship showed that the presence of electron-withdrawing groups on the C-ring increases the activity against most of the fungi. Thus, 2-phenylphthalazin-2-ium compounds represent promising leads for the development of novel fungicides.

Metallic elements and Pb isotopes in PM2.5 in three Chinese typical megacities: spatial distribution and source apportionment

Heavy metal pollution in fine particulate matter (PM_2.5) is a serious environmental and health concern in China, particularly during winter. Here, we detected 40 elements in 24 h integrated daily PM_2.5 samples collected in January 2014 from three typical Chinese metropolises (Beijing, Changchun, and Chengdu) to reflect elemental spatial variations, local sources, and regional transport. The measured elemental concentrations in Changchun were 11.1% and 48.4% higher than those in Beijing and Chengdu, respectively. Thus, PM_2.5 from Changchun exhibited high levels and diversity in the elemental profile (characterized by high concentrations of industrial emission elemental markers). The results of elemental ratios and Pb isotopes proved that, except for a coal combustion source, vehicular emissions contributed more to PM_2.5 heavy metals in Beijing than in the other two cities; Changchun PM_2.5 elements received large contributions from industrial sources, including iron and steel manufacturing, and automobile industry. Moreover, crustal dust from long-range transport of regional air masses from the northwest regions of China played a crucial role in determining elemental levels in Beijing and Changchun, accounting for more than 50% of source intensity. However, a specific dominant source was not determined in Chengdu; the contribution of anthropogenic dust, mainly from construction activities, needs to be paid attention in Chengdu eastern area. This study contributed to enhancing our understanding of elemental spatial distribution characteristics and sources and to setting more judicious standards and strategies for PM_2.5 bound heavy metals in China.

Controllable valley filter in graphene topological line defect with magnetic field

The extended line defect of graphene is an extraordinary candidate in valleytronics while the high valley polarization can only occur for electrons with high incidence angles which brings about tremendous challenges to experimental realization. In this paper, we propose a novel quantum mechanism to filter one conical valley state in the line defect of graphene by applying a local magnetic field. It is found that due to the movement of the Dirac points, the transmission profiles of the two valleys are shifted along the injection-angle axis at the same pace, resulting in the peak transmission of one valley state being reduced drastically while remaining unaffected for the other valley state, which induces nearly perfect valley polarization. The valley polarization effect can occur for all the incident angle and plays a key role in graphene valleytronics.

[A comparative study of the calcaneal closing-wedge calcaneal osteotomy versus posterior-superior prominence removal in both sides with Haglund syndrome]

Objective: To compare the clinical outcome of removal of calcaneal posterior-superior prominence and that of calcaneal closing-wedge osteotomy for Haglund syndrome. Methods: From February 2009 to July 2014, 36 patients with Haglund syndrome were included.They were divided into two groups, and each group included 18 patients and underwent removal of calcaneal posterior-superior prominence and calcaneal closing-wedge osteotomy respectively.They were evaluated preoperatively and after 6 , 12 months and 24 months postoperatively by American Orthopedic Foot & Ankle Society (AOFAS) score, VAS score, VISA-A questionnaire and Maryland Foot Score.Fowler-Philip angle and calcaneal posterior slope of the two groups were compared preoperatively and after 6 months.All data were analysis utilizing SPSS 18.0. Results: At six months of follow-up, the weight-bearing lateral X-rays reveals that removal of calcaneal posterior-superior prominence did not change Fowler-Philip angle and calcaneal posterior slope and calcaneal closing-wedge osteotomy decreased Fowler-Philip angle and calcaneal posterior slope significantly[from preoperation (56.5±5.4)°, (120.0±1.3)°to postoperation (48.4±4.6)°, (109.0±5.3)°]. At six months of follow-up, the AOFAS score, VAS score, VISA-A questionnaire and Maryland Foot Score were worse in the wedge calcaneal osteotomy group.At twelve months of follow-up, no significant difference (P>0.05)was found between the two groups in terms of VAS score, and Maryland Foot Score, while the AOFAS score, and VISA-A questionnaire in the wedge calcaneal osteotomy group were better than those of posterior-superior prominence removal group.At twenty-four months of follow-up, the AOFAS score, VAS score, VISA-A questionnaire and Maryland Foot Score were better in the wedge calcaneal osteotomy group (P<0.05). Conclusions: Both the two surgical methods are effective for Haglund syndrome.Calcaneal closing-wedge osteotomy decreased Fowler-Philip angle and calcaneal posterior slope of calcaneus and its clinical outcome appears better than that removal of calcaneal posterior-superior prominence.

Effects of 2-aryl-1-cyano-1,2,3,4-tetrohydroisoquinolines on apoptosis induction mechanism in NB4 and MKN-45 cells

Our previous study found that 2-aryl-1-cyano-1,2,3,4-tetrahydroisoquinolines (CATHIQs) have excellent anti-cancer activity and obvious apoptosis induction phenomenon. As our continuing research, this study further explored their underlying molecular mechanism of apoptosis induction in cancer cells. Flow cytometry analysis showed that the NB4 cells treated by 1-cyano-2-(2-fluorophenyl)-1,2,3,4-tetrahydroisoquinoline or the MKN-45 cells treated by 1-cyano-2-(4-trifluoromethylphenyl)-1,2,3,4-tetrahydroisoquinoline for 48 h were at early stage of apoptosis, and the cell cycle arrest was only slightly affected. Apoptosis rates of the cells significantly increase with the treatment concentration of the compounds. The compounds could significantly decrease the activities of SOD, raise the MDA level and promote the LDH leakage, suggesting that the excessive formation of ROS should be involved in the cell apoptosis. Western blot analysis showed that the compounds improved both Bax/Bcl-2 ratio and cleavages of procaspase-3, promoted efflux of cytochrome c to cytosol and phosphorylation of p38 and JNK, and attenuated phosphorylations of Akt and ERK. Together, inhibitions of PI3K/Akt and ERK and activation of p38 mediated the compounds-induced apoptosis through modulating the mitochondrial pathway and/or ROS production.

Cytotoxic activity, apoptosis induction and structure-activity relationship of 8-OR-2-aryl-3,4-dihydroisoquinolin-2-ium salts as promising anticancer agents

As our continuing research, a series of 2-aryl-8-OR-3,4-dihydroisoquinolin-2-ium bromides were evaluated for cytotoxic activity on cancer cells and apoptosis induction in the present study. SAR was derived also. Among them, 23 compounds showed the higher cytotoxicity on MKN-45 cells with IC₅₀ values of 1.99-11.3μM than a standard anticancer drug cis-platinum (IC₅₀=11.4μM) or their natural model compound chelerythrine (IC₅₀=12.7μM); 16 compounds possessed the medium to high activity on NB4 cells with IC₅₀ values of 1.67-4.62μM. SAR analysis showed that both substitution patterns of the N-aromatic ring and the type of 8-OR significantly impact the activity. AO/EB staining and flow cytometry analysis with Annexin V/PI double staining showed that the compounds were able to induce apoptosis in a concentration-dependent manner. The results above suggested that the title compounds are a class of promising compounds for the development of new anti-cancer drugs.

Cycloheximide blocks TGF-beta1-induced apoptosis in murine hepatocytes

AIM

To study the mechanism of transforming growth factor beta1-induced apoptosis in cultured hepatocytes.

METHODS

DNA fragmentation and fluorescent microscopy were used to characterize cell apoptosis. Crystal violet staining was used to assess cell viability. Immunoblotting was used to detect Tak1, p53, and Bax. Dual luciferase assay was used to determine TGF-beta1-induced gene expression. Thin layer chromatography was used to examine ceramide level in AML12 cells.

RESULTS

In response to TGF-beta1 treatment, AML12 cells exhibited typical chang es, which was characteristic of apoptosis, such as condensation of chromatin, disintegration of nuclei, and DNA fragmentation. TGF-beta1-induced apoptosis in AML12 cells was completely blocked in the presence of cycloheximide. The inhibitory effect of cycloheximide was accompanied with down-regulation of Tak1 expression and TGF-beta1-induced PAI-1 expression. TGF-beta1 induced p53 expression but not Bax. No increase of ceramide was observed in TGF-beta1-induced apoptosis.

CONCLUSION

TGF-beta1-induced apoptosis requires TGF-beta1-induced gene expression.

Multifidus spasms elicited by prolonged lumbar flexion

STUDY DESIGN

The electromyogram of the L1-L7 multifidus muscles of the in vivo cat were recorded while applying a prolonged steady displacement to the lumbar spine through the L4-L5 supraspinous ligament, simulating a moderate anterior flexion.

OBJECTIVE

To demonstrate that tension-relaxation and laxity of the viscoelastic structures (ligaments, discs, and capsules) induced by prolonged static flexion of the spine results in loss of reflexive muscular stabilizing activity and in muscular disorders that may lead to or are associated with low back pain.

SUMMARY OF BACKGROUND

Epidemiologic data show that prolonged loading of the spine, such as in some occupational activities, can cause low back pain and muscle spasms. Direct experimental evidence linking prolonged loading to a decrease in spinal stability, low back pain, and muscle spasms was not found. It was hypothesized, however, that mechanoreceptors in the viscoelastic structures, when strained, reflexively activate the multifidus muscles to maintain intervertebral stability; that the reflexive muscular activity decreases with stress-relaxation and laxity in the viscoelastic structures; and that when severe strain and possible damage of the viscoelastic structures occurs with time, nociceptive receptors elicit spasms in the musculature and possible pain.

METHODS

The lumbar spine of seven in vivo cat preparations was displaced through the L4-L5 supraspinous ligament into moderate flexion that was steadily maintained for 50 minutes while intramuscular electromyograms were recorded from each of the multifidus muscles of L1-L2 through L6-L7. Load and electromyogram were continuously monitored and recorded. Five additional preparations were used as controls, in which dissection and recordings were identical, but the lumbar flexion was excluded.

RESULTS

Prolonged flexion of the lumbar spine resulted in initial reflexive electromyogram from the multifidus muscles that decreased to approximately 5% of its initial value as tension-relaxation began in the viscoelastic structures within the first 3 minutes, after which, random and unpredictable electromyogram discharges (i.e., spasms) of high amplitude were recorded from different levels. In some preparations the spasms were present in L1-L4, and in others in all the levels. In other preparations the spasms were recorded only at L5 and L6. The onset of the spasms was also unpredictable, because they were initiated in some cases within 2-3 minutes after the spine was loaded. In other cases, the spasms were observed anytime during the test period and up to 20 minutes after the load was removed. Spasms were also observed in the spinalis and longissimus muscles.

CONCLUSIONS

Prolonged flexion of the lumbar spine results in tension-relaxation and laxity of its viscoelastic structures, loss of reflexive muscular activity within 3 minutes and electromyogram spasms in the multifidus and other posterior muscles.

Closed-loop control of muscle length through motor unit recruitment in load-moving conditions

Neuroprostheses aimed at restoring lost movement in the limbs of spinal cord injured individuals are being developed in this laboratory. As part of this program, we have designed a digital proportional-integral-derivative controller integrated with a stimulation system which effects recruitment of motor units according to the size principle. This system is intended to control muscle length while shortening against fixed loads. Feline sciatic nerves were exposed and stimulated with ramp, triangular, sinusoidal, staircase and random signals as test inputs. Changes in muscle length and effective time delay under different conditions were measured and analyzed. Differences of tracking quality between open- and closed-loop conditions were examined through analysis of variance as well as the differences between small (250g) and large (1kg) loads. The results showed that parameters used to compare muscle length output to the input signals were dramatically improved in the closed-loop trials as compared to the open-loop condition. Mean squared correlation coefficients between input and output signals for ramp signals increased by 0.019, and for triangular signals by 0.12. Mean peak cross correlation between input and output signals for sinusoidal waveforms increased by 0.06, with decreases in time to peak cross correlation (effective time delay) from 195 to 38ms. In slow random signals (power up to 0.5Hz), peak cross correlation went from 0.74 to 0.89, and time-to-peak cross correlation decreased from 205 to 55ms. In fast random signals (power up to 1Hz), peak cross correlation went from 0.82 to 0.89, and time-to-peak cross correlation from 200 to 65ms. For staircase signals, both rise times and mean steady-state errors decreased. It was found that, once the length range was set, the load weight had no effect on tracking performance. Analysis of mean square error demonstrated that for all signals tested, the feedback decreased the tracking error significantly, whereas, again, load had no effect. The results suggest that tracking is vastly improved by using a closed-loop system to control muscle length, and that load does not affect the quality of signal tracking as measured by standard control system analysis methods.

Activation of phospholipase D activity in transforming growth factor-beta-induced cell growth inhibition

Cells regulate phospholipase D (PLD) activity in response to numerous extracellular signals. Here, we investigated the involvement of PLD activity in transforming growth factor-beta (TGF-beta1)-mediated growth inhibition of epithelial cells. TGF-beta1 inhibits the growth of MDCK, Mv1Lu, and A-549 cells. In the presence of 0.4% butanol, TGF-beta1 induces an increase in the formation of phosphatidylbutanol, a unique product catalyzed by PLD. TGF-beta1 also induces an increase in phosphatidic acid (PA) level in A-549 and MDCK cells. TGF-beta1 induces an increase in the levels of DAG labeled with [3H]-myristic acid in A-549 and MDCK cells but not in Mv1Lu cells. No increase of DAG was observed in cells prelabeled with [3H]-arachidonic acid. The data presented suggest that PLD activation is involved in the TGF-beta1-induced cell growth inhibition.

Force and surface mechanomyogram frequency responses in cat gastrocnemius

Muscle surface displacement is a mechanical event taking place simultaneously with the tension generation at the tendon. The two phenomena can be studied by the surface mechanomyogram signal (MMG) (produced by a laser distance sensor) and the force signal (from a load cell). The aim of this paper was to provide data on the reliability of the laser detected MMG in muscle mechanics research. To this purpose it was verified if the laser detected MMG was suitable to estimate a frequency response in the cat medial gastrocnemius and its frequency response was compared with the one retrieved by the force signal at the tendon level. The force and MMG from the exposed medial gastrocnemius of four cats were analysed. The frequency response was investigated by sinusoidally changing the number of orderly recruited motor units, in different trials, in the 0.4-6 Hz range. It resulted that it was possible to model the force and MMG frequency response by a critically damped second-order system with two real double poles and a pure time delay. On the average, the poles were at 1.83 Hz (with 22.6 ms delay) and at 2.75 Hz (with 38 ms delay) for force and MMG, respectively. It can be concluded that MMG appears to be a reliable tool to investigate the muscle frequency response during stimulated isometric contraction. Even though not statistically significant. the differences in the second-order system parameters suggest that different components of the muscle mechanical model may specifically affect the force or MMG.

Biomechanics of increased exposure to lumbar injury caused by cyclic loading: Part 1. Loss of reflexive muscular stabilization

STUDY DESIGN

The recording of electromyographic responses from the in vivo lumbar multifidus of the cat, obtained while cyclic loading was applied as in occupational bending/lifting motion over time.

OBJECTIVES

To determine whether the effectiveness of stabilizing reflexive muscular activity diminishes during prolonged cyclic activity; the recovery of lost muscle activity by a 10-minute rest; and whether such diminished muscular activity is caused by fatigue, neurologic habituation, or desensitization of mechanoreceptors in spinal viscoelastic tissues resulting from its laxity.

SUMMARY OF BACKGROUND DATA

The literature repeatedly confirms observation that cyclic occupational functions expose workers to a 10-fold increase in episodes of low back injury and pain. The biomechanical evidence indicates that creep in the viscoelastic tissues of the spine causes increased laxity in the intervertebral joints. The impact of cyclic activity on the function of the muscles, which are the major stabilizing structures of the spine, is not known.

METHODS

Electromyography was performed from the L1 to L7 in vivo multifidus muscles of the cat, while cyclic passive loading of 0.25 Hz was applied to L4-L5. Cyclic loading was applied for 50 minutes, followed by 10 minutes rest and a second 50-minute cyclic loading session. A third 50-minute cyclic loading period also was applied after the preload was reset to 0.5 N to offset the effect of laxity.

RESULTS

Reflexive muscular activity was recorded from the multifidus muscles of all lumbar levels at the initiation of the first 50 minutes of cyclic loading. Activity recorded on electromyography quickly diminished with each cycle during the first 8 minutes of loading to 15% of its initial value. A slower decrease in muscular activity was evident throughout the remaining period, settling at 5% to 10% of its initial level by the end of 50 minutes. A 10-minute rest provided a 20% to 25% recovery of the electromyographic activity, but that was lost within the first minute of cycling. Offsetting the laxity in the spine resulted in full restoration of the electromyographic activity at all lumbar levels.

CONCLUSIONS

The creep induced in the viscoelastic tissues of the spine as a result of cyclic loading desensitizes the mechanoreceptors within, which is manifest in dramatically diminished muscular activity, allowing full exposure to instability and injury, even before fatigue of the musculature sets in.

Biomechanics of increased exposure to lumbar injury caused by cyclic loading. Part 2. Recovery of reflexive muscular stability with rest

STUDY DESIGN

Electromyographic responses from the lumbar multifidus muscle of the cat were recorded in vivo during 50 minutes of cyclic loading followed by 2 hours of rest.

OBJECTIVE

To determine the rate of recovery of reflexive muscular stabilizing activity resulting from rest after viscoelastic laxity induced by 50 minutes of cyclic loading.

SUMMARY OF BACKGROUND DATA

Muscular forces from agonists and antagonists were repeatedly shown to be the most significant stabilizing structures of the lumbar spine. Reflexive muscular coactivation force from the multifidus muscle elicited by mechanoreceptors in the spinal viscoelastic structures were, however, shown to diminish drastically with the onset of laxity in the viscoelastic structures. Data describing the rate of recovery of reflexive muscular coactivation forces resulting from rest after cyclic loading were not found.

METHODS

Cyclic loading of the lumbar spine at 0.25 Hz was applied to L4-L5 for 50 minutes while electromyograms from the multifidus muscles of L1-L2 to L6-L7 were recorded. A rest period of up to 2 hours was given, during which electromyographic responses and load were measured every 10 minutes to sample recovery of laxity and reflexive muscular activity.

RESULTS

Load and electromyographic response demonstrated an exponential decrease during the 50 minutes of cyclic loading. The first 10 minutes of rest allowed a significant recovery in laxity and muscle activity, with additional slow recovery over the next 20 to 30 minutes. The electromyographic response and load were increasing at an extremely slow rate thereafter. Overall, 2 hours of rest yielded only a 20% to 30% recovery in electromyographic response. Full recovery was never observed. A biexponential model was developed to predict loss and recovery of reflexive muscular activity and viscoelastic tension with laxity.

CONCLUSIONS

Laxity in the viscoelastic structures of the lumbar spine desensitizes the mechanoreceptors within and causes loss of reflexive stabilizing forces from the multifidus muscles. The first 10 minutes of rest after cyclic loading results in fast partial recovery of muscular activity. However, full recovery is not possible even with rest periods twice as long as the loading period, placing the spine at an increased risk of instability, injury, and pain.

Comparison of effects of surfactant and inhaled nitric oxide in rabbits with surfactant-depleted respiratory failure

AIM

To compare effects of pulmonary surfactant and inhaled nitric oxide (iNO) in improvement of survival and blood oxygenation in ventilated rabbits with acute hypoxic respiratory failure induced by repeated bronchoalveolar lavage (BAL).

METHODS

After BAL all the rabbits had more than 50% reduction of dynamic lung compliance (Cdya), 50% increment of resistance of respiratory system (Rrs), and an increase of mean oxygenation index (OI) from 1 to 22. The rabbits were then randomly allocated to groups receiving (1) mechanical ventilation only (Control), (2) iNO 0.8 mumol.L-1 (20 ppm) (NO), (3) intratracheal bolus surfactant phospholipids at 100 mg.kg-1 (Surf), and (4) combined surfactant at 100 mg.kg-1 with inhaled NO at 0.8 mumol.L-1 (Surf + NO). All the rabbits were ventilated with standardized tidal volume (8-10 mL.kg-1) for another 8 h or until early death.

RESULTS

The rabbits in both control and NO groups had the lowest survival rate, deterioration of lung mechanics and OI, whereas those in the Surf and Surf + NO groups had modestly improved Cdyn, Rrs, and OI. Only rabbits in the Surf + NO group had significantly improved survival rate and alveolar expansion.

CONCLUSION

Surfactant with or without iNO is more effective compared to the control and iNO groups in rabbit, suggesting that iNO is not effective unless a method to recruit alveoli is applied.

Force and surface mechanomyogram relationship in cat gastrocnemius

The aim of this study was to compare the force (F) and the muscle transverse diameter changes during electrical stimulation of the motor nerve. In four cats the exposed motor nerves of the medial gastrocnemius were stimulated as follows: (a) eight separate trials at fixed firing rates (FR) from 5 to 50 Hz (9 s duration, supramaximal amplitude); (b) 5 to 50 Hz linear sweep in 2.5, 5, 7.5 and 10 s (supramaximal amplitude, separate trials); (c) four separate trials at 40 Hz, the motor units (MUs) being orderly recruited in 2.5, 5, 7.5 and 10 s. The muscle surface displacement was detected by a laser distance sensor pointed at the muscle surface. The resulting electrical signal was termed surface mechanomyogram (MMG). In stimulation patterns (a) and (b) the average F and MMG increased with FR. With respect to their values at 50 Hz the amplitude of the unfused signal oscillations at 5 Hz was much larger in MMG than in force. The signal rising phase was always earlier in MMG than in F. In (c) trials, F increased less in the first than in the second half of the recruiting time. MMG had an opposite behaviour. The results indicate that the force and the lateral displacement are not linearly related. The different behaviour of F and MMG, from low to high level of the MUs' pool activation, suggests that the force generation and the muscle dimensional change processes are influenced by different components of the muscle mechanical model.

The ligamento-muscular stabilizing system of the spine

STUDY DESIGN

Electrical and mechanical stimulation of the lumbar supraspinous ligament of three patients with L4-L5 spinal deficits and of the feline model, respectively, was applied while recording electromyography on the multifidus muscles.

OBJECTIVES

To determine if mechanoreceptors in the human spine can reflexively recruit muscle force to stabilize the lumbar spine, and to demonstrate, in the feline model, that such ligamento-muscular synergy is elicited by mechanical deformation of the lumbar supraspinous ligament (and possibly of other spinal ligaments), the facet joint capsule, and the disc.

SUMMARY OF BACKGROUND DATA

The literature repeatedly confirms that ligaments have only a minor mechanical role in maintaining spine stability, and that muscular co-contraction of anterior and posterior muscles is the major stabilizing mechanism of the spine. The literature also points out that various sensory receptors are present in spinal ligaments, and that the ligaments are innervated by spinal and autonomic nerves. Data that describe how ligaments and muscles interact to provide stability to the spine were not found.

METHODS

The supraspinous ligament at L2-L3 and L3-L4 was electrically stimulated in three patients undergoing surgery to correct deficits at L4-L5. Electromyography was performed from the multifidus muscles at L2-L3 and L3-L4, bilaterally. In 12 cats, the supraspinous ligaments from L1-L2 to L6-L7 were mechanically deformed, sequentially, while electromyography was performed from the multifidus muscles of the six levels. Loading of the ligament was applied before and after each of the two vertebrae were externally fixed to prevent motion.

RESULTS

Electromyograms were recorded from the multifidus muscles, bilaterally, in the two of the three patients, demonstrating a direct relationship to receptors in the supraspinous ligament. Electromyograms were recorded from the feline multifidus muscle with mechanical loading of the supraspinal ligament at each of the L1-L2 to L6-L7 motion segments. In the free-spine condition the largest electromyographic discharge was present in the level of ligament deformation, and lower electromyographic discharge was recorded in two rostral and caudal segments. After immobilizing any two vertebrae, loading of the ligament resulted in electromyographic discharge in the muscles of the same level and at least one level above and/or below.

CONCLUSIONS

Deformation or stress in the supraspinous ligament, and possibly in other spinal ligaments, recruits multifidus muscle force to stiffen one to three lumbar motion segments and prevent instability. Strong muscular activity is seen when loads that can cause permanent damage to the ligament are applied, indicating that spastic muscle activity and possibly pain can be caused by ligament overloading.

Methods to reduce the variability of EMG power spectrum estimates

Three methods that can significantly reduce the variability of the EMG power density spectrum (PDS) variable by eliminating artifactual components are described. Two methods, one that allows the subtraction of power line noise in the time domain and one which allows the subtraction of system noise in the frequency domain from the EMG, were shown to be effective in helping to accurately estimate the median frequency (MF) of the PDS, and especially during low level contractions (0-25% maximal voluntary contraction, MVC) when the signal-to-noise ratio is unfavorable. The techniques eliminate the artifactual effects of system and power line noises from the EMG recordings throughout the force range (0-100% MVC) while preserving the native EMG power at all frequencies. It was also shown that if a technique to train subjects to produce their true MVC is employed, the absolute force/torque produced could be as much as 30% higher than in untrained MVC. The effect of true MVC production was also shown to be significant when interpretation of PDS variables are correlated to the processes which produce contraction.

Force feedback control of motor unit recruitment in isometric muscle

The use of simple force feedback in an isometric muscle control system utilizing orderly recruitment of motor units is explored. Cat medial gastrocnemius motor units were stimulated with and without simple force feedback gain ranging from 0.7 to 0.9. Ramp, triangular, staircase, sinusoidal and bandwidth-limited pseudo-random input recruitment signals were used to study tracking accuracy through linear correlation in ramp and triangular signals, cross correlation in sinusoidal and random signals, and rise time and steady state error in staircase signals. Dramatic improvements were found in most tested tracking variables with the use of feedback; squared correlation coefficients increased from a mean of 0.93 to 0.99 for ramp signals and from 0.76 to 0.98 in triangular signals. Mean peak cross-correlations improved from 0.85 to 0.98 in random signals and from 0.93 to 0.98 for sinusoidal inputs, and mean time to peak cross-correlations decreased from 144 to 24 ms in random signals and from 156 to 25 ms in sine waves. Rise times in staircase signals decreased from a mean of 520 to 175 ms, and mean steady state error decreased from 12 to 3%. Significant effects of the triangle cycle time, sinusoidal frequency and staircase step were found on the performance of the muscle force control system. In addition, the possible effects of intrinsic feedback mechanisms on the control system were examined by repeating the closed loop part of the study but with the sciatic nerve cut proximally. The tracking results were essentially and statistically the same as in the closed loop condition. It was concluded that a simple feedback configuration provided superior tracking performance for a practical application in which orderly recruitment is used to control muscles; furthermore, it was concluded that this type of system would be virtually immune to external disturbances such as spasticity resulting from intact spinal neural feedback mechanisms found in paralyzed individuals.

Open-loop tracking performance of a limb joint controlled by random, periodic, and abrupt electrical stimulation inputs to the antagonist muscle pair

The ability of the cat's ankle joint to track various input signals when controlled by electrically elicited motor unit recruitment, firing rate and antagonist muscle coactivation was examined. Pseudo-random, sinusoidal and staircase signals were used to control the soleus and tibialis anterior muscles isometrically and with a 250-g pendulum. Tracking was evaluated through cross correlation for pseudo-random and sinusoidal signals, and by rise time and steady-state error in step signals. Better tracking was obtained in isometric conditions than in load-moving conditions. Pseudo-random signals resulted in 250-ms delay between input and isometric torque output. For load-moving conditions, 340-ms and 400-ms delay in torque and angle were obtained. For sinusoids, delays decreased from 240 ms at 0.5 Hz, to 140 ms at 2 Hz in isometric conditions. Time delays for angle were between 300 and 400 ms, decreasing as frequency increased. Poor cross correlation was found for torque in load-moving conditions, because of pendulum nonlinear dynamics. Step size was not uniform in staircase trials, with steady-state errors between 9% and 39%, and rise times between 200 and 1000 ms. It is concluded that open-loop joint control results in poor tracking, presumably because it is devoid of feedback mechanisms.

Frequency domain-based models of skeletal muscle

Models of skeletal muscle based on its response to sinusoidal stimulation have been in use since the late 1960s. In these methods, cyclic excitation at varying frequencies is used to determine force or muscle length amplitude and phase as functions of excitation frequency. These functions can then be approximated by models consisting of combinations of poles and zeros and pure time delays without the need to combine force-length or force-velocity relationships. The major findings of a series of frequency response studies undertaken in our laboratory revealed that: The frequency response models for isometric force including orderly recruitment of motor units were relatively invariant of the particular strategy or oscillation level employed. A critically damped second order model with corner frequency near 2 Hz and a pure time delay best described the relationship between input stimulation and output isometric force. The frequency response models for load-moving muscles consisted of an overall gain which is a function of mass, dependent mostly on the width of the length-force relation at a given load (force), and a frequency-dependent gain component independent of load mass. The phase lag between input and output was also independent of load. Muscle function and architecture are the primary determinants of its isometric force frequency response. Tendon viscoelasticity (excluding the aponeurosis) has no significant effect on isometric force dynamic response, but does have a minor effect on load-moving dynamic response. The effect of tendon in reducing or augmenting the load-moving muscle response bandwidth is muscle-dependent. The joint produces decreased high frequency gain and uniformly increased phase lags between input excitation and output force in isometric conditions. The joint acts as a lag network in load-moving conditions, increasing the phase lag without significant effect on the gain. Despite its inherent non-linear properties, the joint does not significantly deteriorate output signal quality in either isometric or load-moving conditions. Co-contraction strategy has a significant effect on the dynamic response of the joint. These frequency-based models have shown to be robust as long as the excitation type and mechanical conditions under which they are obtained are not varied. They are particularly useful for the design of neuroprostheses, where a dynamic description of muscle output as a function of stimulus input under given conditions is desirable.

Effects of recombinant human endothelial-derived interleukin-8 on hemorrhagic shock in rats

AIM

To study the effects of recombinant human endothelial-derived interleukin-8 (IL-8) on hemorrhagic shock.

METHODS

A profound hemorrhagic shock in rats was produced by exsanguination from femoral artery with mean arterial blood pressure (MABP) maintained at 5.32 kPa for 90 min. After transfusion, IL-8 250 micrograms.kg-1 was i.v. injected. Plasma endothelin-1 (ET-1) and 6 ketoprostaglandin F1 alpha (6-KPGF1 alpha) contents were determined with radioimmunoassay.

RESULTS

After i.v. IL-8, the MABP in IL-8 group was elevated obviously (P < 0.01), the rat survival 2 h after infusion was increased (P < 0.05). During profound shock the plasma ET-1 levels were higher (21 +/- 4 vs 8.2 +/- 1.8 ng.L-1, P < 0.01) and the plasma 6-KPGF1 alpha contents lower than those in normal rats (107 +/- 12 vs 157 +/- 11 ng.L-1, P < 0.01). IL-8 remarkably reduced the plasma ET-1 levels (10 +/- 4 ng.L-1, P < 0.01) and enhanced plasma 6-KPGF1 alpha contents (368 +/- 16 ng.L-1, P < 0.01).

CONCLUSION

IL-8 has beneficial antishock effects.

The influence of antagonist muscle control strategies on the isometric frequency response of the cat's ankle joint

This study investigated the effect of various strategies to control the interaction between agonist and antagonist muscles on the frequency response of the isometric cat ankle joint actuated by the tibialis anterior (TA) and soleus (SOL) muscles. Some strategies were based on the physiologic need for increasing joint stability during forceful contractions; with these strategies, the proportional rate of physiologic antagonist activity was termed antagonist gain. Other strategies were based on the electrical stimulation literature, which advocates co-contraction at low force levels. The range of crossover of antagonist activity to the agonist's domain was termed overlap. Strategies consisting of 0%, 10%, and 20% antagonist gain were combined with 0%, 50%, and 100% overlap for a total of nine strategies. These were applied to the TA and SOL using sinusoidal input signals varying in frequency from 0.4 to 6 Hz. Gain and phase Bode plots were constructed through the use of the fast Fourier transforms (FFT's); and analysis of variance determined the significance of differences in gain and phase across frequencies. Best-fit models consisting of four poles and two zeroes were used to fit the experimental data and compared against an analytical model of muscles acting independently across the joint. Harmonic distortion was calculated to evaluate signal quality. It was found that changing the overlap and the antagonist gain produces significant changes in the dynamic response of the two-muscle joint system. The analytical approach to modeling such a system tends to consistently overestimate gain. It is suggested that signal quality is optimal when a moderate amount of antagonist gain (10%) is engaged, with overlap of 50% to smooth transitions between opposing movements. It is expected that this type of strategy will achieve optimum signal quality while preserving the long-term integrity of the joint.

Evaluation of antagonist coactivation strategies elicited from electrically stimulated muscles under load-moving conditions

Muscle coactivation strategies that produce ankle dorsiflexion and plantar flexion were elicited by electrical stimulation of the tibialis anterior (TA) and soleus (SOL) muscles of the cat, and examined under several loading conditions. Four different load types were used: free-limb motion (no load), fly-wheel, and two pendulums, each with a different lever arm. Three types of coactivation strategies were considered. The first coactivation strategy consisted of antagonist activity that decreased as the agonist activity increased. The second strategy consisted of increasing antagonist activity with increasing agonist activity. And, in the third strategy, antagonist coactivation decreased at low force levels, then increased at high force levels. The three strategies were evaluated based on the joint angle's peak-to-peak movement and its ability to track a linear input command given by the correlation coefficient of the output signal versus linear input. Results showed that increasing antagonist activity resulted in decreasing peak-to-peak angle and a decreased signal tracking capability for each load condition. The latter, however, was not as obvious in the flywheel load (as compared with free-moving and pendulum conditions). A decreasing peak-to-peak torque for pendulum loads was also observed with increasing antagonist activity. In all loading conditions, maximal peak-to-peak angle and torque were present when a moderate degree of antagonist activity was engaged, and signal tracking capability improved with earlier engagement of the antagonist muscles. It is suggested that strategies using a combination of low-level coactivation, as described in the physiological literature and previous functional electrical stimulation (FES) studies, could satisfactorily address the issues of controllability and efficiency while maintaining long-term joint integrity.

Ligamentomuscular protective reflex in the elbow

A reflex are from the medial elbow ligaments to the forearm pronator muscles was shown to exist in the feline model. A single articular branch emerging from the median nerve and converging on the medial collateral ligament was identified and stimulated with supramaximal pulses of 100 microseconds duration at a rate of 10 pulses/s. Stimulation of the articular nerve elicited myoelectric activity in the flexor digitorum superficialis, flexor digitorum profundus, flexor carpi radialis, flexor carpi ulnaris, and pronator teres. Transection of the articular nerve between the electrodes and the median nerve resulted in the disappearance of any myoelectric activity in the muscles, thus confirming the afferent nature of the articular nerve. The mean time delay from the application of the stimulus to the corresponding myoelectric discharge ranged from 3.2 to 5.8 ms for the 5 muscles. The existence of a fast-acting reflex arc from the medial elbow ligaments to the forearm muscles both confirms the concept of ligamentomuscular protective synergy (shown to exist in the knee, shoulder, and ankle joints) and extends it to the elbow. This reflex arc has significant implications for both the planning of elbow surgery while preserving the neural supply of the ligaments and for the planning of postsurgical or conservative therapeutic rehabilitation modalities.

Evaluation of isometric antagonist coactivation strategies of electrically stimulated muscles

The performance of various coactivation strategies to control agonist-antagonist muscles in functional electrical stimulation (FES) applications was examined in a cat model using the tibialis anterior and soleus muscles to produce ankle isometric dorsiflexion and plantarflexion torques, respectively. Three types of coactivation strategies were implemented and tested. The first strategy was based on coactivation maps described in the literature as consisting of decreasing antagonistic activity as the input command to the agonist was increased. The second type of strategy was based on the physiologic coactivation data collected from normal subjects exhibiting joint stabilization during the full range of contractions. These strategies included scaled increasing antagonist activity and therefore joint stiffness with increasing agonist input command. A third strategy was devised which at low force levels mimicked the strategies described in the literature and at high force levels resembled strategies exhibited by normal subjects. The three strategies were evaluated based on their ability to track a linear or sinusoidal input command and their efficiency of torque transmission across the joint. Coactivation strategies using increasing antagonist activity resulted in decreased maximal joint torque and efficiency, decreased signal tracking capability for linear inputs, and increased harmonic distortion for sinusoidal inputs. Peak efficiency and tracking ability appeared when a moderate degree of antagonist activity was engaged near the neutral joint position. Signal tracking quality improved with earlier engagement of the antagonist muscles. Our results suggest that strategies combining low-level coactivation as described in the physiological literature and previous FES studies could satisfactorily address the issues of controllability, efficiency, and long-term joint integrity.

The glenohumeral-biceps reflex in the feline

The existence of a reflex arc from the anterior aspects of the glenohumeral capsule to the long head of the biceps was determined in a feline. A single articular branch of the musculocutaneous nerve terminating in the capsule was identified and stimulated with 100 microseconds supramaximal pulse train at 10 pulses per second. It was shown tht stimulation of the musculocutaneous articular nerve elicited myoelectric discharge in the biceps muscle. Transection of the articular nerve just distal to its emergence from the main trunk of the musculocutaneous nerve abolished the myoelectric discharge in the biceps, confirming the afferent nature of this articular nerve. The mean (+/- standard deviation) time delay from the application of the stimulus to the articular nerve to the recording of the corresponding myoelectric discharge in the biceps was 2.7 (+/- 0.3) milliseconds. The existence of a reflex arc from the capsule to the biceps confirms and extends the concept of passive (ligaments) and active (muscles) restraints of a joint and the synergy between them toward maintaining shoulder stability. If demonstrated in the human, such a reflex may have significant implications in modification of surgical procedures and the design of new rehabilitation modalities for treatment of shoulder defects.

The dynamic response of the cat ankle joint during load-moving contractions

The dynamic response of the cat's ankle joint during load-moving activation of the medial gastrocnemius was determined. Sinusoidal-input oscillations of ankle plantar flexion were performed by the muscle at frequencies ranging from 0.4 to 5 Hz against a 10-N load acting via a cable through a pulley with a 2 cm radius. This was followed by sinusoidal muscle length changes against the same load while excluding the joint. The frequency responses of the two conditions were compared and decomposed in terms of their relative phase and gain, and best-fit pole-zero models to yield the dynamic model of the joint isolated from the muscle properties. The muscle displacement transfer function M(j omega) was characterized as two sets of double poles at 2.1 and 3.2 Hz, with a pair of zeros at 0.92 and 20 Hz, and pure time delay of 8 mS. The joint model J(j omega) was obtained by adding a pole at 5 Hz and a zero at 13 Hz. It was concluded that the ankle joint acts as a lag system, introducing significant increase in the phase lag between stimulus input and mechanical output without affecting the frequency-dependent attenuation of gain. Average harmonic distortion was less than 5% in all cases. This particular finding reveals that, despite its inherently nonlinear mechanical characteristics, the joint introduces no degradation in the simplified linear behavior of the muscle-joint system. This model is useful in the design of systems employing electrical stimulation to restore movement to limbs paralyzed by spinal cord injury or stroke.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamic performance model of an isometric muscle-joint unit

The dynamic performance model of the medial gastrocnemius muscle of the cat was determined when generating isometric force at its tendon and when transmitting that force across the joint. The frequency response model of the muscle and of the muscle-joint was developed by fitting the experimentally obtained gain and phase Bode plots with a best fit linear second order system determined by recursive least squares. It was shown that the muscle could be represented with double poles at 2.3 Hz and a time delay of 16 ms whereas the muscle-joint was represented with an additional pole at 1.8 Hz, a zero at 3.8 Hz and 16 ms time delay. The harmonic distortion was less than 5% for sinusoidal force output in the frequency range of 0.4-4 Hz, and a force range of 20-80% of the maximal justifying a linear system model. The model is useful in the design of a neuromuscular prosthesis, using electrical stimulation of the muscle nerves, as a rehabilitation procedure for paralysed patients due to spinal cord injury.

[Effect of lithium applied iontophoretically on electrical activities of pain-related neurons in caudate-putamen nucleus of rat]

Multi-barrelled micro-electrode has been used to observe further the effect of Li+ applied iontophoretically on electrical activities of pain related neurons (PRN) of the rat caudate-putamen nucleus (CPN) and its mechanism of action was studied at the cellular level. It was found that PRN were homogeneously distributed throughout the head of CPN, but pain-excitation neurons (PEN) and pain-inhibition neurons (PIN) were heterogeneously distributed. The PIN were mainly distributed in the anterior part, while the PEN primarily in the central part of the head of CPN. The results may provide a clue to understand the complicacy in the pain regulation mechanism undergoing in the head of CPN. Li+ iontophoresis could inhibit the discharges of PEN, while the discharges of PIN were activated. The interference modes of pain discharge of PEN and PIN induced by Li+ iontophoresis were positively related to that induced by morphine. It was suggested that there existed some similarity in the mechanisms of analgesia induced by Li+ and morphine. This, in turn, appears to support the suggestion that endogenous opioid peptides and opioid receptors may be involved in the analgesic effect of Li+.

[Stability of liensinine injection]

The stability of liensinine injection was studied by accelarating test with classical isothermal method. Results of the study showed that the decomposition of the injection was found to be a first-order reaction. The activation energy was 75030 J.mol-1. The shelf life at 10 degrees C and 25 degrees C was predicted to be about 15 months and 3 months respectively. This experiment provides a reference for the storage of the injection.

[Analysis on the causes of maternal death with pregnancy induced hypertension in Shanghai from 1981 to 1990]

The total deliveries in Shanghai from 1981 to 1990 were 1,770,103 and there were 456 cases of maternal death. Among them, 42 cases were caused by pregnancy induced hypertension (PIH) which accounted for 9.21% and ranked fourth in the causes of maternal death in Shanghai. The maternal mortality of PIH was 2. 37/10(5). The cerebrovascular accident and heart failure were the leading causes which accounted for 66.67%. The study showed that strengthening prenatal care, supervising 3 main symptoms and signs of PIH, paying attention to mean arterial pressure (MAP), using antispasm drugs such as MgSO4 in proper way and timely termination of pregnancy are the key points of decreasing maternal death of PIH. The average MAP of 18 cases died of cerebrovascular accident was 17 kPa (1kPa = 7.5 mmHg). Among them, MAP > or = 18.7 kPa (140 mmHg) was found only in 4 cases which accounted for 22.22%. It suggested that the threshold value of cerebrovascular accident at the level of MAP > or = 18.7 kPa may be too high and need to be further studied.

[Quantitative determination of liensinine in the embryo Nelumbinis (Nelumbo nucifera Gaertn.) by TLC-scanning]

The content of liensinine in the green seed embryo of Nelumbo nucifera was determined by dual-wavelength TLC-scanning. The crude drug was extracted with two different method of impregnating and refluxing. The content of liensinine was determined to be 0.853% and 0.939% and the average recovery was 97.9% and 100.9% respectively.

The effect of joint velocity on the contribution of the antagonist musculature to knee stiffness and laxity

The electromyographic (EMG) coactivation patterns of the knee flexors and extensors when acting as antagonists were studied as a function of limb velocity to assess their contribution to joint stiffness and laxity. Normalized antagonist coactivation patterns developed from surface EMG recordings from the hamstrings and quadriceps during maximal effort isokinetic extension and flexion, respectively, demonstrated characteristic variations as the joint velocity increased from 15 deg/sec up to 240 deg/sec. The two-tailed t-test (P less than 0.01) was performed on the data obtained from eight normal knees. The results indicate that both hamstrings and quadriceps demonstrate a significant increase (greater than 100%) in their antagonist coactivation pattern during the final 40 degrees of fast extension and flexion movements, respectively, as limb velocity increases. A minor decrease in antagonist activity of the hamstrings (24%) and quadriceps (8%) was evident during the initial phase of the extension and flexion movements, respectively, as joint velocity increased. We concluded that as limb velocity is increased, there is a substantial reflexive (unintentional) increase in the contribution of the antagonist musculature to joint stiffness and reduction of laxity. The results also suggest that strength training of the hamstrings (rather than quadriceps) should be considered as a modality for conservative treatment of ACL deficiencies, as well as an adjunct to surgical reconstruction. Such training can also reduce the risk of high performance athletes in a reflexive manner by increasing joint stiffness.

Frequency response model of skeletal muscle: effect of perturbation level, and control strategy

The frequency response model of the soleus muscle of the cat was determined as a function of various firing rate and recruitment control strategies and at various force oscillation levels. We found that the basic frequency response models of the muscle during individual force oscillations at various control strategies in which the motor unit population of the muscle was fully recruited to obtain 50 per cent and up to 100 per cent of the maximum force, either concurrently with firing rate increase or at constant firing rate, were nearly identical. The model consisted of a second-order, linear low-pass filter with double poles at 1.85 Hz and a pure time delay of 16 ms. The model resulting from only firing rate increase from the frequency of fusion of the smallest motor unit to the maximum tetanic rate of the muscle while all the motor units were continuously active was nonlinear, and depended on the force's oscillation level. This nonlinear response of the rate coding process is also identified as the source of the increased harmonic distortion in the model where the initial 50 per cent of the force was generated by fully recruiting all the motor units, and the final 50 per cent of the force was generated by firing rate increase. We concluded that the basic frequency response model of a muscle under conditions similar to voluntary contraction consists of a linear, second-order system which is robust and independent of control strategy and force perturbation level.

Electromyogram coactivation patterns of the elbow antagonist muscles during slow isokinetic movement

Electromyograms from the flexor and extensor muscles of normal human elbows were simultaneously recorded during maximal-effort isokinetic movement at 15 degrees/s over the joint's full range of motion. The antagonist electromyogram was normalized with respect to its electromyogram when acting as agonist at maximal effort and plotted as a function of joint angle. The coactivation patterns were nearly inversely related to each muscle's moment arm variations with joint angle, suggesting that the antagonist may have generated constant opposing torque throughout the movement. Female subjects had a statistically significant higher coactivation level of the flexors and extensors compared with that of males, reflecting the increase in joint efficiency associated with daily muscular activity which is manifested by reduction in antagonist activity. The functional role of antagonist coactivation in augmenting ligament stabilizing functions, equalizing the pressure distribution over the articular surface, and regulating the joint's mechanical impedance are discussed. The source of such coactivation appears to be due to proprioceptive and joint kinesthetic afferent input in addition to possible direct common drive.

Muscular coactivation. The role of the antagonist musculature in maintaining knee stability

The objective of this study was to quantify the coactivation patterns of the knee flexor and extensor muscles as part of continued efforts to identify the role of the antagonist muscles in maintaining joint stability. The simultaneous EMG from the flexor and extensor muscles of the knee were recorded during maximal effort, slow isokinetic contractions (15 deg/sec) on the plane parallel to the ground to eliminate the effect of gravity. The processed EMG from the antagonist muscle was normalized with respect to its EMG as agonist at maximal effort for each joint angle. The plots of normalized antagonist EMG versus joint angle for each muscle group were shown to relate inversely to their moment arm variations over the joint range of motion. Additional calculations demonstrated that the antagonist exerts nearly constant opposing torque throughout joint range of motion. Comparison of data recorded from normal healthy subjects with that of high performance athletes with hypertrophied quadriceps demonstrated strong inhibitory effects on the hamstrings coactivations. Athletes who routinely exercise their hamstrings, however, had a coactivation response similar to that of normal subjects. We concluded that coactivation of the antagonist is necessary to aid the ligaments in maintaining joint stability, equalizing the articular surface pressure distribution, and regulating the joint's mechanical impedance. The reduced coactivation pattern of the unexercised antagonist to a hypertrophied muscle increases the risk of ligamentous damage, as well as demonstrates the adaptive properties of the antagonist muscle in response to exercise. It was also concluded that reduced risk of knee injuries in high performance athletes with muscular imbalance could result from complementary resistive exercise of the antagonist muscle.

The synergistic action of the anterior cruciate ligament and thigh muscles in maintaining joint stability

The synergistic action of the ACL and the thigh muscles in maintaining joint stability was studied experimentally. The EMG from the quadriceps and hamstring muscle groups was recorded and analyzed in three separate experimental procedures in which the knee was stressed. The test revealed that direct stress of the ACL has a moderate inhibitory effect on the quadriceps, but simultaneously it directly excites the hamstrings. Similar responses were also obtained in patients with ACL damage during loaded knee extension with tibia subluxation, indicating that an alternative reflex arc unrelated to ACL receptors was available to maintain joint integrity. The antagonist muscles (hamstrings) were clearly demonstrated to assume the role of joint stabilizers in the patient who has a deficient ACL. The importance of an appropriate muscle-conditioning rehabilitation program in such a patient is substantiated.

Historical update and new developments on the EMG-force relationships of skeletal muscles

The EMG-force relationships of skeletal muscles are of significant interest to the orthopedic-biomechanics researcher and have been a topic of interest and controversy for the last three decades. We present the developments reported in the literature, from the early 1950s, relevant to this topic, outlining the details of the controversy and providing additional new information resulting from recent studies. New data clearly illustrate that the EMG-force relationships are dependent on the firing rate and recruitment control strategy used by a muscle. Muscles that use motor unit recruitment to obtain the initial 50% of their maximal force, and use firing rate increase to complement the remaining 50%, have a nearly linear EMG-force relationship. Muscles that use recruitment to obtain 60% and up to 100% of their maximal force demonstrate progressive increase in non-linearity of their EMG-force curves. A clear warning is issued against the indiscriminate use of EMG as a representative of muscle force. The recruitment pattern of the muscle under consideration should first be obtained in such a way that the appropriate EMG-force curve is selected.