[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.

[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 (λHU), and normalized effective atomic number (nZeff) 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, nZeff on the arterial phase and NIC, nZeff and λHU [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.

[Clinical effect of metatarsal diaphysis Z-shaped rotating osteotomy in moderate and severe hallux valgus with metatarsophalangeal joint incongruency].

Objective: To evaluate the clinical effect of Z-shaped rotating osteotomy of metatarsal diaphysis in patients with moderate and severe hallux valgus with metatarsophalangeal joint incongruency. Methods: We selected 36 patients (38 feet) with moderate and severe hallux valgus with metatarsophalangeal joint incongruency who underwent Z-shaped rotating osteotomy of metatarsal diaphysis in the First Affiliated Hospital of Army Medical University of Chinese PLA from September 2010 to January 2019. There were 2 males and 34 females with an average age of (49±18) years (18-77 years). Hallux valgus angle (HVA), first-second intermetatarsal angle (IMA), distal metatarsal articular angle (DMAA), congruency index, length of first metatarsal, and functional scores were evaluated before and 6 weeks after surgery and at the last follow-up. The data were compared by one-way ANONA or t test. Results: The congruency index was significantly improved from 0.75±0.11 before surgery to 0.95±0.07 at the last follow-up (t=11.728, P<0.01). HVA and IMA improved significantly at 6 weeks after surgery, however, HVA at the last follow-up showed an increased trend compared with that at 6 weeks after the operation, while no significant improvement in IMA. Although DMAA increased slightly 6 weeks after surgery when compared with that before surgery, there was no significant difference in it between the last follow-up and the 6 weeks after surgery, and no significant difference in the length of the first metatarsal at different time points (F=0.991, P>0.05). In terms of functional scores, American Orthopaedic Foot & Ankle Society (AOFAS) score increased from 50±9 before surgery to 80±17 at the last follow-up, while visual analogue scale (VAS) decreased from 5.8±1.1 to 2.7±1.5, Manchester-Oxford Foot Questionnaire (MOXFQ) score decreased from 70±13 to 25±19 (t=12.024, 13.439, 16.880, all P<0.05). Conclusions: The treatment of moderate and severe hallux valgus with metatarsophalangeal joint incongruency by Z-shaped rotating osteotomy of metatarsal diaphysis can significantly increase the congruency index of metatarsophalangeal joint and improve the metatarsophalangeal joint matching relations. It will not significantly increase the DMAA. A certain degree of radiographic recurrence occurs during a longtime follow-up, but it doesn't influence the symptoms and function.

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 (PM2.5) is a serious environmental and health concern in China, particularly during winter. Here, we detected 40 elements in 24 h integrated daily PM2.5 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, PM2.5 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 PM2.5 heavy metals in Beijing than in the other two cities; Changchun PM2.5 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 PM2.5 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.

Pharmacokinetics of doxycycline in laying hens after intravenous and oral administration.

The pharmacokinetics of doxycycline in laying hens was investigated after a single intravenous (IV) or an oral (PO) dose at 20 mg/kg body weight. The concentrations of doxycycline in plasma samples were determined by high-performance liquid chromatography with an ultraviolet detector, and pharmacokinetic parameters were calculated using a compartmental model method. The disposition of doxycycline after one single IV injection was best described by a two-compartment open model and the main pharmacokinetic parameters were as follows: volume of distribution (Vd) was 865.15 ± 127.64 ml/kg, distribution rate constant (α) was (2.28 ± 0.38) 1/h, elimination rate constant (ß) was 0.08 ± 0.02 1/h and total body clearance (Cl) was104.11 ± 18.32 ml/h/kg, while after PO administration, the concentration versus time curve was best described by a one-compartment open model and absorption rate constant (Ka), peak concentration (Cmax), time to reach Cmax (tmax) and absolute bioavailability (F) were 2.55 ± 1.40 1/h, 5.88 ± 0.70 µg/ml, 1.73 ± 0.75 h and 52.33%, respectively. The profile of doxycycline exhibited favourable pharmacokinetic characteristics in laying hens, such as quick absorption and slow distribution and elimination, though oral bioavailability was relatively low. A multiple-dosing regimen (a dose of 20 mg/kg/d for 3 consecutive days) of doxycycline was recommended to treat infections in laying hens. But a further study should be conducted to determine the withdrawal time of doxycycline in eggs.

Biomechanics and electromyography of a cumulative lumbar disorder: response to static flexion.

OBJECTIVE: To assess the mechanical and neurological processes active in the development of a cumulative trauma disorder (CTD) associated with repetitive exposure to periods of static lumbar flexion. METHODS: The spine of the feline model was subjected to a series of three 10 min sessions of static lumbar flexion with each session followed by a 10 min rest. A 7 h rest period was implemented after the series of three flexion-rest sessions while monitoring viscoelastic (disks, ligaments, etc.) creep and multifidus EMG. A model was fitted to the experimental data from the flexion-rest period and the 7 h recovery period. RESULTS: The creep developed in each 10 min static flexion period did not fully recovery during the following 10 min rest, resulting in a large cumulative creep at the end of the flexion-rest period. The cumulative creep did not fully recover over the following 7 h rest period. A neuromuscular disorder consisting of reduced muscular activity superimposed by spasms during static flexion periods and hyperexcitability during the 7 h recovery was evident. Comparison of the data to previous tests of continuous static flexion for 20 min reveal that the neuromuscular disorder elicited by the series of three 10 min flexion-rest was substantially attenuated when compared to a single 20 min static flexion although the overall work time was 50% larger. CONCLUSIONS: Frequent rest periods are highly beneficial in attenuating the development of a CTD, yet not able to prevent it, as viscoelastic tissues residual creep accumulates and its recovery is of extremely long duration. RELEVANCE: The data provides direct biomechanical and physiological evidence that explain the development of a CTD due to prolonged exposure to static lumbar flexion as well as confirms the epidemiological data correlating such work conditions with substantial increase in symptoms of low back disorders. The benefit of frequent rest periods in attenuating the risk of such a disorder is validated as an effective intervention.

Muscular dysfunction elicited by creep of lumbar viscoelastic tissue.

The biomechanics, histology and electromyography of the lumbar viscoelastic tissues and multifidus muscles of the in vivo feline were investigated during 20 min of static as well as cyclic flexion under load control and during 7 h of rest following the flexion. It was shown that the creep developed in the viscoelastic tissues during the 20 min of static or cyclic flexion did not fully recover over the 7 h of following rest. It was further seen that a neuromuscular disorder with five distinct components developed during and after the static and cyclic flexion. The neuromuscular disorder consisted of a decreasing magnitude of reflexive EMG from the multifidus upon flexion as well as of superimposed spasms. The recovery period was characterized by an initial muscle hyperexcitability, a slowly increasing reflexive EMG and a delayed hyperexcitability. Histological data from the supraspinous ligament demonstrate significant increase (x 10) in neutrophil density in the ligament 2 h into the recovery and even larger increase (x 100) 6 h into the recovery from the 20 min flexion, indicating an acute soft tissue inflammation. It was concluded that sustained static or cyclic loading of lumbar viscoelastic tissues may cause micro-damage in the collagen structure, which in turn reflexively elicit spasms in the multifidus as well as hyperexcitability early in the recovery when the majority of the creep recovers. The micro-damage, however, results in the time dependent development of inflammation. In all cases, the spasms, initial and delayed hyperexcitabilities represent increased muscular forces applied across the intervertebral joints in an attempt to limit the range of motion and unload the viscoelastic tissues in order to prevent further damage and to promote healing. It is suggested that a significant insight is gained as to the development and implications of a common idiopathic low back disorder as well as to the development of cumulative trauma disorders.

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.

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.

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.

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.

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.

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.

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.