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PubMed2000

Estradiol exerts neuroprotective effects when administered after ischemic insult.

BACKGROUND AND PURPOSE: 17beta-Estradiol (E2) has been reported to exert neuroprotective effects when administered before an ischemic insult. This study was designed to determine whether E2 treatment after ischemia exerts the same effects and, if so, how long this therapeutic window remains open, and whether the effects are related to changes in cerebral blood flow (CBF). METHODS: Female Sprague-Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAO). In protocol 1, E2 was administered (100 microg/kg IV followed immediately by subcutaneous implantation of crystalline E2 in a silicone elastomer tube) to ovariectomized females (OVX+E2) at 0.5 (n=8), 1 (n=6), 2 (n=7), 3 (n=6), or 4 (n=9) hours after MCAO. Intact (INT; n=6) and ovariectomized females (OVX; n=12) were subjected to MCAO and received vehicle instead of E2. Two days after MCAO the animals were killed, and ischemic lesion volume was determined by 2,3,5-triphenyltetrazolium chloride staining. In protocol 2, CBF was monitored before and at 1, 24, and 48 hours in a group of animals receiving E2 or vehicle 0.5 hour after ischemia induction (INT, n=6; OVX, n=8; OVX+E2, n=6). RESULTS: Lesion volume was 20.9+/-2.2% and 21.8+/-1.2% in the INT and OVX groups, respectively. E2 was found to decrease lesion volume significantly when administered within 3 hours after MCAO. The lesion volumes were 6.3+/-0.5%, 10.3+/-2.1%, 11.8+/-1.8%, 13.5+/-1.6%, and 17.9+/-2.8% when E2 was administered at 0.5, 1, 2, 3, or 4 hours after MCAO, respectively. CBF decreased to 43.1+/-2.2% and 25.4+/-1.0% in the INT and OVX animals, respectively, at 5 minutes after MCAO. In comparison to OVX rats, CBF was not different at 1 hour after E2 administration but was increased significantly in the OVX+E2 group 1 and 2 days after E2 administration. CONCLUSIONS: E2 exerts neuroprotective effects when administered after ischemia, with a therapeutic window in a permanent focal cerebral ischemia model of approximately 3 hours. This effect of estradiol was associated with no immediate change in blood flow but with a delayed increase in CBF.

Animals↗
PubMedDate not supplied

Chronic exertional compartment syndrome: the controversial "fifth" compartment of the leg.

BACKGROUND: The existence of a "fifth" compartment in the leg capable of developing distinct chronic exertional compartment syndrome remains a subject of controversy. HYPOTHESIS: Specific pressure recordings and dissection will confirm or disprove the existence of a fifth compartment. STUDY DESIGN: Empirical anatomic study. METHODS: Radiopaque dye was injected directly into the tibialis posterior muscle of 25 embalmed cadaveric legs while intracompartmental pressure was monitored. Radiographs demonstrated dye distribution, and dissection-documented fascial and epimysial layers. RESULTS: Evidence was found that the fibular origin of the flexor digitorum longus muscle, when present, could create subcompartments within the deep posterior compartment. The nature of this attachment varied from being absent, to small (<8 cm), to extensive (>8 cm). The attachment partially covered the tibialis posterior muscle in the majority of the 14 legs that developed high pressures, and it was limited or absent in the 11 legs that did not. Radiographs demonstrated that the dye was confined to the tibialis posterior muscle in four legs. CONCLUSIONS: No consistent fifth compartment exists in the leg; however, subcompartments within the deep posterior compartment created by the fibular origin of the flexor digitorum longus muscle may develop pressures congruent with chronic exertional compartment syndrome. CLINICAL RELEVANCE: Potential deep posterior subcompartments demand accurate pressure investigation. A modified technique to decompress the entire deep posterior compartment, including the tibialis posterior muscle, is necessary for successful treatment of chronic exertional compartment syndrome.

Aged↗
PubMedDate not supplied

Fasciotomy for exertional anterior compartment syndrome: is lateral compartment release necessary?

The standard surgery for exertional anterior compartment syndrome is fasciotomy of the anterior and lateral compartments of the leg. We prospectively studied the necessity of lateral compartment release, which can add morbidity and extend recovery. We performed 30 anterior compartment releases in 20 patients (10 bilateral operations) with exertional anterior compartment syndrome but not lateral compartment involvement. We alternately performed only an anterior compartment release or both anterior and lateral compartment releases on 10 patients. The 10 patients who underwent bilateral surgery each had, during the same surgery, an anterior and lateral compartment release on one leg and only an anterior compartment release on the other. All were athletes involved in running sports. Overall, satisfactory outcomes were seen in 90% of the limbs--93% (14 of 15) that had anterior compartment release and 87% (13 of 15) that had release of both compartments (no statistically significant difference). For the patients who had unilateral surgery, the average time for full return to sports was 8.1 weeks after anterior release only and 11.4 weeks after release of both compartments, a statistically significant difference. The average time for full return to sports after bilateral surgery was 12.1 weeks. Among these patients, seven said that the leg with only anterior release seemed to recover faster. We concluded that when doing a fasciotomy for exertional anterior compartment syndrome alone, a lateral compartment release is not necessary.

Adolescent↗
PubMed2000

Effects of upper and lower limb static exertions on global synkineses in hemiparetic subjects.

OBJECTIVES: Global synkineses are nonpurposive pathological involuntary muscle activities or movements elicited at several or all of the joints of the affected limb or limbs during voluntary forceful resisted contractions. The purpose of this study was to assess the effect of upper and lower limb exertions on manifestations of upper limb global synkineses in hemiparetic subjects. DESIGN: Involuntary muscle activities on the affected upper limb of 11 hemiparetic subjects and on the left or right upper limb of 10 control subjects were recorded using surface electromyography during successive bilateral maximal ankle exertions and during contralateral grips. RESULTS: Significant differences in the level of involuntary electromyography (EMG) activities were observed between experimental conditions (ANOVAs, p < 0.05). EMG levels in hemiparetic subjects were significantly higher during contralateral grip tasks than during the ankle exertions. CONCLUSION: These results suggest that upper limb global synkinases are more prevalent in specific tasks and that this task specificity may reflect the neurophysiological mechanisms involved in the generation of global synkinases.

Adult↗
PubMed2004

Estrogen and selective estrogen receptor modulators exert neuroprotective effects and stimulate the expression of selective Alzheimer's disease indicator-1, a recently discovered antiapoptotic gene, in human neuroblast long-term cell cultures.

According to the fact that Alzheimer's disease (AD) is more common in postmenopausal women, estrogen treatment has been proposed. Experimental studies, still mostly performed using animal models, demonstrated that estrogen exerts neuroprotective effects. We previously established neuroblast long-term cell cultures from human fetal olfactory epithelium. In the present study, we addressed the role of estrogen in these unique human cells, which express both the estrogen receptor (ER)-alpha and ERbeta. We found that 17beta-estradiol (17betaE(2)) and the selective estrogen receptor modulators (SERMs) raloxifene and tamoxifen exerted neuroprotective effects, which were independent of cell proliferation, by increasing resistance against beta-amyloid-induced toxicity, with the exception of the highest concentrations of raloxifene (10 and 100 nm). In addition, 17betaE(2) exposure protected from oxidative stress, reduced apoptosis, and increased the expression of the catalytic subunit of telomerase. Furthermore, we evaluated by quantitative real-time RT-PCR whether estrogen/SERMs modulate the expression of the recently discovered seladin-1 (selective AD indicator-1) gene, which exerts neuroprotective effects and is down-regulated in AD-vulnerable brain regions. 17betaE(2) (100 pm to 100 nm) and SERMs (1 nm) significantly increased the amount of seladin-1 mRNA. Conversely, 10 and 100 nm raloxifene reduced the expression of seladin-1. The effect of estrogen appears mainly mediated by ERalpha because the selective ERalpha agonist propylpyrazole-triol determined a much greater increase of seladin-1 expression than the ERbeta agonist diarylpropionitrile. Our results add new evidence, using human neuronal cells, for a beneficial effect of estrogen in preventing neurodegenerative diseases and suggest for the first time that seladin-1 may mediate this effect.

Amyloid beta-Peptides↗
PubMed1985

The maximum forces exerted by animals.

This paper reviews the maximum forces exerted by animals in a wide range of activities including running, jumping, swimming and biting. Most of the data refer to vertebrates and arthropods, ranging in size from 0.5-mg fleas to 3-tonne elephants. Maximum forces exerted on the environment give values of (force/body weight) which lie, in most cases, between 0.5 body mass-1/3 (kg) and 20 body mass-1/3. Maximum forces exerted by major muscle groups give values of (force/body weight) in most cases between 10 body mass-1/3 and 50 body mass-1/3.

Animals↗
PubMed1996

Mechanisms of relief of exertional breathlessness following unilateral bullectomy and lung volume reduction surgery in emphysema.

STUDY OBJECTIVE: To explore mechanisms of relief of exertional breathlessness following surgery to reduce thoracic gas volume in patients with emphysema. MATERIALS AND METHODS: We studied 8 patients with emphysema (FEV1 = 39 +/- 3% predicted; residual volume [RV] = 234 +/- 12% predicted; mean +/- SEM) who were severely breathless despite optimal pharmacotherapy and who underwent unilateral bullectomy for giant bullae (greater than one third hemithorax); 4 of these also had ipsilateral lung reduction (pneumectomy). Pulmonary function and cycle exercise performance (n = 6) were evaluated before and 13 +/- 3 weeks after surgery. Chronic breathlessness was measured with the Baseline Dyspnea Index and the Medical Research Council dyspnea scale. Exertional breathlessness was measured using Borg ratings at a standardized work rate (BorgSTD). RESULTS: FEV1, FVC, and maximal inspiratory pressures increased postsurgery by 29 +/- 7% (p < 0.05), 24 +/- 10% (p = 0.06), and 39 +/- 12% (p < 0.01), respectively. Plethysmographic total lung capacity, RV, and functional residual capacity fell by 14 +/- 2%, 30 +/- 4%, and 18 +/- 3%, respectively (p < 0.001). All measures of chronic breathlessness improved significantly (p < 0.05). During exercise at a standardized work rate, BorgSTD fell 45% (p < 0.05), end-expiratory lung volume (EELV) fell 22% (p < 0.01), and breathing frequency (F) fell 25% (p = 0.08). By multiple stepwise regression analysis, 99% (p = 0.007) of the variance in symptom relief (delta BorgSTD) was explained by the combination of decreased ratio of the end-expiratory lung volume to total lung capacity, decreased F, and diminished mechanical constraints on tidal volume (tidal volume to vital capacity ratio). CONCLUSION: Reduced exertional breathlessness at a given workload after volume reduction surgery was attributed to a combination of reduced thoracic hyperinflation, reduced F, and reduced mechanical constraints on lung volume expansion.

Dyspnea↗
PubMed1999

Vocal cord dysfunction in patients with exertional dyspnea.

STUDY OBJECTIVES: To evaluate patients for vocal cord dysfunction (VCD) in a military population presenting with symptoms of exertional dyspnea. DESIGN: Cross-sectional, controlled study. SETTING: Pulmonary disease clinic at an army tertiary care center. PATIENTS: Forty military patients with complaints of exertional dyspnea and 12 military asymptomatic control subjects. INTERVENTION: Patients underwent direct visualization of vocal cords with flexible laryngoscopy before and after exercise to evaluate for presence of inspiratory vocal cord adduction. MEASUREMENTS AND RESULTS: Complete evaluation for all patients consisted of spirometry with flow-volume loops, lung volumes, diffusing capacity, and maximum voluntary ventilation at rest; chest radiograph; methacholine bronchoprovocation testing; and a maximal cardiopulmonary exercise test with expiratory gas analysis. Fifteen percent of patients studied prospectively were found to have VCD, whereas all control subjects were negative for VCD. There was minimal difference in pulmonary function testing between VCD-positive and VCD-negative patients, whereas control subjects had higher spirometric values. Twenty percent of VCD-positive patients had abnormal flow-volume loops compared with 14% of patients without VCD, but after methacholine, 60% of VCD-positive patients developed abnormal flow-volume loops. In the VCD-positive group, 60% had a positive methacholine response, but there was less decrease in FEV(1)/FVC ratio compared with either VCD-negative patients or control subjects. CONCLUSIONS: Paradoxical inspiratory vocal cord closure is a frequent occurrence in patients with symptoms of exertional dyspnea and should be strongly considered in their evaluation.

Adolescent↗
PubMed2002

Comparison of the peak exercise response measured by the ramp and 1-min step cycle exercise protocols in patients with exertional dyspnea.

STUDY OBJECTIVES: To compare the peak exercise response and determine the limits of agreement between the ramp and the 1-min step cycle protocols in a representative population of patients with exertional breathlessness attending a respiratory outpatient clinic. DESIGN: Crossover with the test order double blinded and randomized. SETTING: Outpatient exercise physiology laboratory. PATIENTS: Twenty-two patients (12 men; mean [SD] age, 59 [8] years; FEV(1), 71% [21%]) with lung disease and/or exertional breathlessness. INTERVENTION: Symptom-limited, maximum cycle exercise tests using a ramp and a 1-min step work rate (WR) protocols. The two protocols were assigned to subjects in a randomized manner. MEASUREMENTS AND RESULTS: Oxygen uptake (O(2)), minute ventilation (E), heart rate (HR), WR, exercise time, and Borg scores were compared at symptom-limited peak exercise. The mean (SD) peak values for the ramp and the step protocols, respectively, were as follows: peak O(2), 1.51 (0.44) L/min and 1.49 (0.43) L/min; peak E, 50.8 (12.9) L/min and 49.9 (14.5) L/min; and peak HR, 133 (24) beats/min and 131 (22) beats/min (p > 0.05). There were no significant differences between breathlessness and perceived exertion at peak exercise. Peak WR (WRpeak) and exercise time were significantly higher using the ramp protocol: 110.5 (37.1) W vs 105.6 (35.6) W, and 8.2 (2.0) min vs. 7.6 (1.9) min, respectively. CONCLUSIONS: The ramp protocol leads to a higher WRpeak, and this may have implications for exercise prescription. However, there were no significant differences between the two protocols for the peak physiologic responses. The choice of protocol for the measurement of maximal exercise capacity remains one of laboratory preference.

Aged↗
PubMed2004

Perceived exertion and rehabilitation with arm crank in elderly patients after total hip arthroplasty: a preliminary study.

This preliminary study examined, in a restricted randomized trial, the effects of a 6-week arm-crank rehabilitation training program in elderly osteoarthrosis patients after total hip arthroplasty, first on physiological and perceptual responses and second on physical function. Two groups of patients were studied: a training group (N = 7, mean age = 74.9 yr, standard deviation [SD] = 5.0 yr) who followed a training program in addition to traditional rehabilitation, and a control group who followed traditional rehabilitation only (N = 7 mean age = 75.4 yr, SD = 5.1 yr). At the beginning of the training program, the heart rate and the perceived exertion were not significantly correlated during the exercise session. However, at the end of the training program, five patients had a significant heart rate/perceived exertion relationship (p < 0.05). Furthermore, positive effects of the arm-crank rehabilitation training program were observed on cardioventilatory and functional responses in the training group compared with the control group. These results suggest that after an habituation period, most of our elderly osteoarthrosis patients experienced physical sensations that were connected to physiological responses. Therefore, perceived exertion could be useful in these patients to regulate exercise intensity, especially at the end of and after the rehabilitation period.

Aged↗
PubMed2002

Heart rate response and perceived exertion in college students during riding a scooter.

The purpose of this research is to examine the heart rate responses and the perceived exertion in college students during scootering, and to examine if scootering possibly makes heart rate increase up to the level that can contribute to maintaining or developing cardiorespiratory fitness. Five male students (20-23 yrs) participated in this research, mainly assigned to scooter on an official 400 m-tartan track. Each session of scootering was six minutes. Each subject did three sessions of scootering at different speeds, slow, ordinary, and very fast. During the scootering, heart rate was measured using a Polar Vantage XL. Immediately after each session, the subjects were questioned about their perceived exertion. To evaluate heart rate during scootering on the track, maximal heart rate was measured in advance with graded maximal tests. In each speed in the track trial, the mean heart rates and the standard deviations were 106 +/- 5.9, 129 +/- 4.2, and 179 +/- 13.7 beats/min respectively. They correspond to 54.0 +/- 4.2%, 65.8 +/- 4.2%, and 91.2 +/- 5.5% of the maximal heart rate respectively. The mean and standard deviation of perceived exertion based on Borg's scale in each scootering session were 7.2 +/- 0.45, 10.2 +/- 1.10, and 16.6 +/- 2.79 respectively. Conclusively, at ordinary speed, the heart rates of the college students on a tartan track were situated around the level of the lower boundary which the American College of Sports Medicine recommended to develop and maintain cardiorespiratory fitness for apparently healthy people. If people have places to ride a scooter briskly, their heart rate could rise above the minimum level.

Adult↗
PubMed2001

Perceived exertion scales attest to both intensity and exercise duration.

The present purpose was to study the relationships between perceived exertion (RPE, ETL) and exercise duration for all-out runs eliciting vVO2 max. 12 endurance-trained men performed three exhausting exercises on an indoor track. The first test was an incremental exercise to measure their maximal oxygen uptake (VO2 max), the velocity associated with VO2 max (vVO2 max), the velocity of the lacate concentration threshold (vLT) and the velocity delta 50 (vdelta50: the velocity halfway between vVO2 max and vLT). The second and third tests were a constant load all-out run at vVO2 max and vdelta50 to measure the time to exhaustion at these intensities (tlim vVO2 max and tlim vdelta50, respectively). vdelta50 corresponded to 90.1 +/- 2.5% vVO2 max; tlim vVO2 max and tlim vdelta50 were equal to 286 +/- 71 sec. and 547+/- 157 sec., respectively. For a same given relative time (%tlim), athletes perceived exercise as harder and felt that they could endure less for vVO2 max than vdelta50. When subjects began to perceive exercise as "hard" (RPE = 15), they had run for only 36.4 +/- 26.8%tlim at vVO2 max, whereas they had run for 46.1 +/- 15.7 %tlim at vdelta50. These results indicate that RPE and ETL scales were a combined subjective estimation of both intensity and exercise duration for all-out runs at 90 and 100% vVO2 max. Therefore, this scale could be used to assess duration as well as intensity of exercise for the practical application in sport. Moreover, it could be suggested that exercise duration can be prescribed as a function of perceived exertion for healthy normal people. Consequently, perceived exertion could be an important tool to individualize the prescription of a training program.

Adult↗
PubMed1992

Orally administered interferons exert their white blood cell suppressive effects via a novel mechanism.

Interferons (IFN) have been approved for a number of clinical uses. The accepted routes of administration are intramuscular, subcutaneous, and intravenous. Recently, interferons administered by the oral route have been shown to exert a systemic effect. Oral administrations of IFN-alpha, IFN-beta, and IFN-gamma have been shown to cause a suppression of the peripheral white blood cell (WBC) count in mice. This study investigates the mechanism by which this suppression occurs. The results show that, in contrast to their intraperitoneal administration, oral administration of rHuIFN-alpha A/D or rMuIFN-gamma does not result in the presence of detectable levels of interferons in the blood. In addition, although the presence of circulating specific antibody to interferon blocks the peripheral WBC suppressive effects of intraperitoneally administered MuIFN-beta or rMuIFN-gamma, the presence of those antibodies does not block the peripheral WBC suppressive effects of the orally administered interferons. The peripheral WBC suppressive effect of orally administered rHuIFN-alpha A/D and rMuIFN-gamma can be transferred by injection of blood from oral interferon-treated donor mice to recipient mice. Recipient mice receiving plasma from donor mice showed no peripheral WBC suppression. Recipient mice receiving blood cells from donor mice showed significant peripheral WBC suppression. No effect of orally administered rHuIFN-alpha A/D on the relative percentages of lymphocytes, neutrophils, and monocytes was noted. These results indicate that the mechanism by which orally administered interferons exert their WBC suppressive effect differs from that of intraperitoneally administered interferons. WBC suppression resulting from orally administered interferons may involve cell to cell transfer of the interferons' effects, rather than the systemic distribution of the interferons in the blood. These studies further suggest that there may be a role for oral administration as a new route of interferon administration and provide a glimpse into the mechanism by which the orally administered interferons exert their systemic effects.

Administration, Oral↗
PubMed1989

The significance of intracompartmental pressures in the diagnosis of chronic exertional compartment syndrome.

Chronic exertional compartment syndrome is one cause of pain in the lower extremity, a common disability in athletes. The significance of intracompartmental pressures in the diagnosis of chronic exertional compartment syndrome is somewhat controversial. The goal of this study was to review the compartment pressure tests in a group of patients that underwent fasciotomy for refractory exertional compartment syndrome and to compare these pressures with an asymptomatic control group. The results are presented and compared with those of previous studies.

Adolescent↗
PubMed1999

In vitro contractile responses and contracture testing of skeletal muscle from Quarter Horses with exertional rhabdomyolysis.

OBJECTIVE: To determine whether increased sensitivity to pharmacologic agents was a general property of equine exertional myopathies, including polysaccharide storage myopathy (PSSM) in Quarter Horses. ANIMALS: 5 adult Quarter Horses with exertional rhabdomyolysis and abnormal polysaccharide accumulation in skeletal muscle and 4 clinically normal adult Quarter or Quarter-type horses. PROCEDURES: Twitch time course measurements and contracture responses to various concentrations of caffeine and halothane for small bundles of intact external intercostal muscle fibers were measured in all horses. RESULTS: Caffeine contracture threshold of muscles from Quarter Horses with PSSM was not different from that of clinically normal horses (5 mM in both groups). Muscles from horses with PSSM and from clinically normal horses did not have contracture in response to up to 2% halothane. CONCLUSIONS AND CLINICAL RELEVANCE: Results were in contrast to the increased sensitivity to caffeine and halothane for muscles from Thoroughbreds with recurrent exertional rhabdomyolysis (RER). Although clinical signs of muscular stiffness after exercise are similar between Quarter Horses with PSSM and Thoroughbreds with RER, these breeds appear to have 2 distinct myopathies with different pathophysiologic bases. Unlike RER in Thoroughbreds, PSSM in Quarter Horses does not appear to be accompanied by a defect in regulation of muscle contraction.

Animals↗
PubMed1999

Pressures exerted against the cervical vertebrae by the standard and intubating laryngeal mask airways: a randomized, controlled, cross-over study in fresh cadavers.

UNLABELLED: In this randomized, controlled, cross-over study, we measured the pressures exerted by the standard laryngeal mask airway (LMA) and the intubating laryngeal mask airway (ILM) against the cervical vertebrae during insertion, intubation, and maneuvers commonly used to facilitate intubation. We also assessed the effect of these pressures on cervical spine (C-spine) movement. Twenty cadavers (6-24 h postmortem) without cervical abnormality were initially studied. Three microchip pressure sensors were implanted into the pharyngeal surface of C2-3. The size 5 ILM and LMA were inserted in random order into each cadaver with the head-neck in the neutral position. Maximal cervical pressures (CPmax) were recorded for both devices during cuff inflation from 0-40 mL and with the intracuff pressure (ICP) at 60 cm H2O, insertion, fiberscope-guided intubation, partial withdrawal/reinsertion (ILM only), elevation/depression of the handle with 20 N of force applied (ILM only). In five additional matched cadavers, the effect of pressure on posterior displacement of C3 was assessed, and CPmax was measured during laryngoscope- and fiberscope-guided oro/nasotracheal intubation (controls). CPmax was higher for the ILM than the LMA over the inflation range (96 vs 15 cm H2O; P < 0.0001) and with the ICP at 60 cm H2O (95 vs 10 cm H2O; P < 0.0001). During cuff inflation, CPmax was generally unchanged for the ILM but was always increased for the LMA. CPmax for the LMA and ILM was similar during insertion (224 vs 273 cm H2O) but higher for the ILM during fiberscope-guided intubation (96 vs 43 cm H2O; P < 0.0001). At 60 cm H2O ICP, CPmax increased during LMA (224 cm H2O; P < 0.0001) and ILM insertion (273 cm H2O; P < 0.0001) and increased for the LMA (43 cm H2O; P < 0.0001) but was unchanged for the ILM (96 cm H2O) during fiberscope-guided intubation. For the ILM, CP-max increased during handle depression (394 cm H2O; P < 0.0001) and partial withdrawal/reinsertion (265 cm H2O; P < 0.0001) but decreased during handle elevation (6 cm H2O; P < 0.00001). CPmax for the controls was usually zero and was always less than the LMA/ ILM (P < 0.0001). The mean (range) for posterior displacement of C3 was 0.8 (0-2) mm at 100 cm H2O and 2.8 (1-5) mm at 400 cm H2O. Laryngeal mask devices exert greater pressures against the cervical vertebrae than established intubation techniques and can produce posterior displacement of the C-spine. IMPLICATIONS: Laryngeal mask devices exert greater pressures against the cervical vertebrae than established intubation techniques and can produce posterior displacement of the cervical spine. We recommend that laryngeal mask devices only be used in the unstable cervical spine if difficulties are anticipated or encountered with established techniques, pending the results of studies demonstrating its relative safety.

Aged↗
PubMed1999

An electromyography-assisted model to estimate trunk muscle forces during fatiguing repetitive trunk exertions.

During submaximal shortening muscle contraction, fatigue characteristically results in an increase in measured surface electromyography, whereas the maximum force that can be produced by muscle is reduced. This finding compromises researchers' ability to estimate muscle stress in a joint system such as the spine, which is composed of more muscles than degrees of freedom of the joint. A three-dimensional, electromyography-assisted, dynamic biomechanical model of spinal loading was developed and validated for use during fatiguing repetitive trunk extension exertions. A time-varying maximum muscle stress was included to model the effect of a change in the maximum force-producing capacity of the erector spinae muscle. Sixteen men performed submaximal isokinetic trunk extension endurance tests at 15 degrees per second. The exertion level (35% and 70% of their maximum dynamic extension torque) and repetition rate (5 and 10 repetitions per minute) of the tests were varied during four testing sessions. Using trunk muscle electromyography and the measured torque as input, the model predicted significant linear reductions in the maximum muscle stress in 78% of the endurance tests, which resulted in an estimated decrease in erector spinae force in 75% of the tests. Conversely, if the maximum muscle stress was assumed to be constant, the erector spinae force would have been predicted to increase in 73% of the tests. The magnitude of the change in predicted erector spinae maximum muscle stress and force depended on the exertion level and repetition rate. This model will allow researchers to assess the effects of changes in recruitment patterns of trunk muscles during dynamic trunk extension on the estimated spinal loading of the lumbar spine.

Abdominal Muscles↗
PubMed1999

Epidemiologic analysis of factors influencing exertional rhabdomyolysis in Thoroughbreds.

OBJECTIVE: To determine incidence, effect on performance, and management practices associated with exertional rhabdomyolysis (ER) in Thoroughbreds. SAMPLE POPULATION: Medical records for 984 Thoroughbreds and a survey of trainers of horses with and without ER. PROCEDURES: Medical records for 984 Thoroughbreds stabled at a midwestern racetrack were examined to determine the incidence of ER during the 1995 racing season. A retrospective questionnaire was administered to trainers to determine management practices associated with ER in 59 Thoroughbreds with ER and 47 control Thoroughbreds in training. Multiple logistic regression was used to determine management factors associated with ER. RESULTS: ER affected 48 of 984 (4.9%) Thoroughbreds. Two-year-old females were most frequently affected, and 36 of 96 (37.5%) trainers had > or = 1 horse with ER. Horses with ER were more likely not to race during the racing season, compared with control horses. For horses that raced, differences were not found with respect to racing performance between ER and control horses. Exertional rhabdomyolysis developed frequently in susceptible horses that had > or = 1 day of rest prior to exercise and that galloped during exercise. Horses with ER were commonly fed > 4.5 kg of grain daily. Nervous and extremely nervous horses were 5.4 times more likely, and horses with some form of lameness were 4.2 times more likely, to have ER. CONCLUSIONS AND CLINICAL RELEVANCE: Exertional rhabdomyolysis is common in Thoroughbreds, and ER can be affected by temperament, sex, age, diet, exercise routines, and lameness. Management that minimizes excitability, particularly when tailored to each horse, may be most effective for controlling ER.

Age Factors↗