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At least 739 records · Page 41Linked to original sources
PubMed2003

Perceived exertion in fatiguing illness: Gulf War veterans with chronic fatigue syndrome.

PURPOSE: It has been reported that ratings of perceived exertion (RPE) are elevated in chronic fatigue syndrome (CFS). We have challenged this notion by examining perceived exertion in civilian females with CFS and expressing the data relative to exercise capacity (%[OV0312]O(2max)). The purpose of the present investigation was to further examine RPE during exercise in a unique population of CFS patients, Gulf veterans (GV). METHODS: Thirty-four GV (N = 15 CFS, 42 +/- 8 yr; N = 19 healthy, 43 +/- 5 yr) performed a maximal exercise test on a cycle ergometer. After a 3-min warm-up, exercise intensity increased by 30 W every minute until exhaustion. RPE were obtained during the last 15 s of each minute using Borg's CR-10 scale. RESULTS: With the exception of peak [OV0312]E, there were no significant differences in any peak exercise variables. Repeated measures ANOVA revealed significantly higher RPE at each power output examined (F(1,32) = 16.4, P < 0.001). Group differences in RPE remained significant when analyzed relative to peak [OV0312]O(2) (F(1,32) = 7.2, P = 0.01). Both group main effects and the interaction were eliminated when self-reported fatigue symptoms were controlled for in the analyses. Power functions for RPE as a function of relative oxygen consumption were not different between groups and were significantly greater than a linear value of 1.0 (1.6 +/- 0.3 for both groups, P < 0.02). CONCLUSIONS: Our results show that RPE are greater in GV with CFS regardless of whether the data were expressed in terms of absolute or relative exercise intensity. However, self-reported fatigue associated with CFS eliminated the group differences. These results suggest that GV with CFS were unique compared with their civilian counterparts. Future research aimed at determining the influence of preexisting fatigue on RPE during exercise is warranted.

Adult↗
PubMed2003

Two cases of exertional rhabdomyolysis precipitated by personal trainers.

INTRODUCTION: Numerous cases of exertional rhabdomyolysis have been reported in the literature, and these cases mostly involve individuals who were inexperienced exercisers, uneducated in fitness and health principles, dehydrated or heat stressed, taking drugs, or military recruits in basic training. PURPOSE: The purpose of this article is to review two cases of exertional rhabdomyolysis in healthy, experienced exercisers. METHODS/RESULTS: The cases reviewed are for a 22-yr-old female college student and a 37-yr-old male physician who presented with rhabdomyolysis secondary to exercise in a local health club that was part of a national chain. DISCUSSION: In these two cases individuals, both well educated and experienced in fitness, were encouraged by fitness instructors in a local health club to overexertion during their exercise routine leading to rhabdomyolysis.

Adult↗
PubMed2000

The Chinese herbal medicine Chai-Hu-Long-Ku-Mu-Li-Tan (TW-001) exerts anticonvulsant effects against different experimental models of seizure in rats.

We evaluated the anticonvulsant effect of Chai-Hu-Long-Ku-Mu-Li-Tan (TW-001), a Chinese herbal medicine, and its mechanisms in several standard rodent models of generalized seizure. TW-001 (4 g/kg, p.o.) significantly increased the threshold for tonic electroconvulsions and the threshold for tonic seizures in response to i.v. infusion of pentylenetetrazole (PTZ). In the s.c. PTZ seizure test, both the incidence and severity of seizures were decreased by TW-001. TW-001 (1-10 mg/ml) did not alter resting membrane potential or input resistance of the hippocampal CA1 neurons, but elicited a reversible suppression of stimulus-triggered epileptiform activity in area CA1 and spontaneously occuring epileptiform burst discharges in area CA3 elicited by picrotoxin. Both field excitatory postsynaptic potentials and population spikes were reversibly depressed by TW-001 (0.5-15 mg/ml) in a concentration-dependent manner. The sensitivity of postsynaptic neurons to a glutamate-receptor agonist, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid or N-methyl-D-aspartate, was not altered by TW-001 (10 mg/ml). However, TW-001 (5 mg/ml) clearly increased the magnitude of paired-pulse facilitation. TW-001 (5-10 mg/ml) reversibly limited the repetitive firing and reduced the maximal rate of rise of action potentials elicited by injection of depolarizing current pulses (0.4 nA, 200 ms) into the pyramidal cells. TW-001 (1-10 mg/ml) exerted a concentration-dependent reduction of the tetrodotoxin-sensitive sodium currents and high voltage-activated calcium currents. These results suggest that TW-001 is an interesting new anticonvulsant agent that exerts its anticonvulsant activity through inhibition of sodium and calcium channels, stabilizing neuronal membrane excitability and inhibiting glutamate release.

Action Potentials↗
PubMed2004

Polychlorinated biphenyls (PCBs) exert thyroid hormone-like effects in the fetal rat brain but do not bind to thyroid hormone receptors.

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants routinely found in human and animal tissues. Developmental exposure to PCBs is associated with neuropsychologic deficits, which may be related to effects on thyroid hormone (TH) signaling in the developing brain. However, PCBs may interfere with TH signaling solely by reducing circulating levels of TH, or they may exert direct effects on TH receptors (TRs). Therefore, we tested whether maternal exposure to a commercial PCB mixture, Aroclor 1254 (A1254), exerts effects in the fetal brain by one or both of these mechanisms. Dams were dosed daily with 0, 1, or 4 mg/kg A1254 from gestational day 6 (GD6) until they were sacrificed on GD16. A1254 significantly reduced circulating levels of triiodothyronine (T3) and thyroxine (T4) in pregnant rats but increased the expression of several TH-responsive genes in the fetal cortex, including neuroendocrine-specific protein A (NSP-A), RC3/neurogranin, and Oct-1. These findings are consistent with a direct action of PCBs on TRs. However, we did not identify parent PCB congeners or metabolites that bound to rat TRs isolated from hepatic nuclei. These findings indicate that PCBs can interfere with TH signaling in the fetal brain by direct actions on the fetus rather than by producing maternal hypothyroidism.

Animals↗
PubMed1998

Bone morphogenetic proteins and bFGF exert opposing regulatory effects on PTHrP expression and inorganic pyrophosphate elaboration in immortalized murine endochondral hypertrophic chondrocytes (MCT cells).

A fundamental question in endochondral development is why the expression of parathyroid hormone-related protein (PTHrP), which inhibits chondrocyte maturation and mineralization, becomes attenuated at the stage of chondrocyte hypertrophy. To address this question, we used clonal, phenotypically stable SV40-immortalized murine endochondral chondrocytes that express a growth-arrested hypertrophic phenotype in culture (MCT cells). Addition of individual cytokines to the medium of MCT cells revealed that bone morphogenetic protein (BMP)-6, which commits chondrocytes to hypertrophy, markedly inhibited PTHrP production. This activity was shared by three other osteogenic bone morphogenetic proteins (BMP-2, BMP-4, and BMP-7) and by transforming growth factor beta (TGF-beta), which all inhibited the level of PTHrP mRNA. In contrast, basic fibroblast growth factor (bFGF), an inhibitor of chondrocyte maturation to hypertrophy, induced PTHrP in MCT cells and antagonized the effects of BMP-2, BMP-4, BMP-6, and BMP-7 and TGF-beta on PTHrP expression. Opposing effects of bFGF and BMPs also were exerted on the elaboration of inorganic pyrophosphatase (PPi), which regulates the ability of hypertrophic chondrocytes to mineralize the matrix. Specifically, BMP-2 and BMP-4, but not BMP-6 and BMP-7, shared the ability of TGF-beta to induce PPi release, and this activity was inhibited by bFGF in MCT cells. Our results suggest that effects on PTHrP expression could contribute to the ability of BMP-6 to promote chondrocyte maturation. BMPs and bFGF exert opposing effects on more than one function in immortalized hypertrophic chondrocytes. Thus, the normal decrease in bFGF responsiveness that accompanies chondrocyte hypertrophy may function in part by removing the potential for bFGF to induce PTHrP expression and to oppose the effects of BMPs. MCT cells may be useful in further understanding the mechanisms regulating the differentiation and function of hypertrophic chondrocytes.

Animals↗
PubMed1994

Exertional hypotension in spinal cord injury.

STUDY OBJECTIVE: To assess blood pressure (BP) response to continuous maximal arm ergometry in patients with spinal cord injury (SCI). DESIGN: Cross-sectional analysis of data collected for a prospective study of functional electrical stimulation in patients with SCI. SETTING: Short-term rehabilitation hospital. PARTICIPANTS: Twenty individuals with SCI; 4 cervical (C6 to C8), 10 high thoracic (T1 to T6), and 6 low thoracic (T7 to T12). MEASUREMENTS AND RESULTS: Each subject performed continuous maximal arm ergometry with expired gas analysis. Blood pressure was measured using a technician-assisted protocol. The BP at maximal exercise was compared with the highest submaximal BP reached during the test (delta BP = final BP minus highest submaximal BP). All 20 subjects had a negative delta BP (mean +/- SD; -22.8 +/- 12.1 mm Hg) for mean BP and 19 of 20 had a negative delta BP (-25.8 +/- 14.4 mm Hg) for systolic BP. The delta BP was not significantly related to maximum exercise parameters, resting BP, or level of lesion. Four able-bodied subjects and six wheelchair-bound individuals without SCI showed no exertional hypotension. Repeated testing on the four able-bodied subjects showed excellent reproducibility for mean BP (coefficient of variation [CV] = 3.6 percent; r = 0.98; p < 0.01) and systolic BP (CV = 2.2 percent; r = 0.99; p < 0.01) using this protocol. CONCLUSIONS: These data describe, for the first time to our knowledge, that exertional hypotension is present in all individuals with SCI during continuous arm ergometry. Further studies are needed to clarify the mechanisms responsible for this phenomenon and to evaluate the long-term consequences for individuals with SCI.

Adult↗
PubMed1999

Ventilatory drive at rest and perception of exertional dyspnea in severe COPD.

BACKGROUND: The reasons for exertional dyspnea in severe COPD are not well established, but they are not solely related to the mechanical load. We tested the hypothesis that breathlessness may be determined, in part, by the response of an individual's central output. METHODS: In 26 patients with severe COPD (FEV1 < 50% predicted) and 22 matched control subjects, we assessed at rest the ventilatory and mouth occlusion pressure (P0.1) response to hyperoxic progressive hypercapnia. At rest and during a symptom-limited exercise test, routine cardiopulmonary variables were measured, and respiratory muscle function was evaluated using esophageal and gastric pressure. Dyspnea was assessed with a visual analog scale. RESULTS: Dyspnea with or without leg discomfort limited exercise in 73% of patients. Peak exercise dyspnea correlated only with dyspnea at rest (r = 0.5, p < 0.008) and P0.1 response to CO2 (deltaP0.1/delta[end-tidal PCO2]PETCO2) (r = 0.48, p = 0.02). Multiple regression analysis including resting and exercise data as independent variables revealed that 47% of the variance for dyspnea at peak exercise was explained by a model including dyspnea at rest and deltaP0.1/deltaPETCO2. Again, deltaP0.1/deltaPETCO2 was the only predictor for the change in dyspnea from rest to peak exercise (delta Dyspnea, r2 = 0.28, p = 0.005). There was no correlation between exercise dyspnea and any metabolic variable, pulmonary function, or respiratory muscle function test. CONCLUSION: In severe COPD, exertional dyspnea is not simply related to respiratory muscle load or mechanical impairment, but also to an individual's central motoneural output to the respiratory system.

Adult↗
PubMed2003

Estradiol exerts neuroprotective actions against ischemic brain injury: insights derived from animal models.

Over the last 100 yr, the life-span of women has increased from 50 yr to over 80 yr, but the age of the menopause has remained unchanged, at 51 yr. Menopause is one of the most permanent physiologic changes that a woman will experience and is marked by a dramatic decrease in circulating levels of ovarian estrogens. Because the timing of menopause has remained fixed in the face of an increasing life-span, more women will live a greater proportion of their lives in a hypoestrogenic state. We appreciate more and more that the actions of ovarian steroid hormones are complex, and possibly exert opposing actions in different contexts. I review here the results of my laboratory's recent studies that clearly establish that low physiologic levels of estradiol replacement can exert profound neuroprotective actions when administered prior to an ischemic strokelike injury.

Brain Ischemia↗
PubMed2002

Measurement of lateral loads exerted on the maxillofacial region by habitual postures.

Lateral loads exerted on the maxillofacial region by habitual postures and habits may cause lateral shift or deformity of the mandible. These loads were measured with a desktop dynamic-strain gauge (DPM-600, Kyowa Co.) connected to a small, highly sensitive pressure sensor (PSL-A type, Kyowa Co.), and recorded with an oscillographic recorder (RDM-100A, Kyowa Co.). Measurements were taken with a pressure sensor embedded in silicone impression material placed in a vinyl chloride resin bag, on which pressures were applied. A preliminary study was conducted to obtain a proportional constant and a conversion formula for load calculation. The subsequent main study included 20 healthy male volunteers for load measurement in 12 positions. The mean load exerted on the mandible was 43.7 N when the subjects lay face down and approximately 20 N when they sat resting the lateral part of the chin on the hand, indicating that these loads are greater than regular orthodontic forces.

Adult↗
PubMed2001

Calcium sensitivity of force production and myofibrillar ATPase activity in muscles from Thoroughbreds with recurrent exertional rhabdomyolysis.

OBJECTIVE: To determine whether the basis for recurrent exertional rhabdomyolysis (RER) in Thoroughbreds lies in an alteration in the activation and regulation of the myofibrillar contractile apparatus by ionized calcium. ANIMALS: 4 Thoroughbred mares with RER and 4 clinically normal (control) Thoroughbreds. PROCEDURES: Single chemically-skinned type-I (slow-twitch) and type-II (fast-twitch) muscle fibers were obtained from punch biopsy specimens, mounted to a force transducer, and the tensions that developed in response to a series of calcium concentrations were measured. In addition, myofibril preparations were isolated from muscle biopsy specimens and the maximal myofibrillar ATPase activity, as well as its sensitivity to ionized calcium, were measured. RESULTS: Equine type-I muscle fibers were more readily activated by calcium than were type-II muscle fibers. However, there was no difference between the type-II fibers of RER-affected and control horses in terms of calcium sensitivity of force production. There was also no difference between muscle myofibril preparations from RER-affected and control horses in calcium sensitivity of myofibrillar ATPase activity. CONCLUSIONS AND CLINICAL RELEVANCE: An alteration in myofibrillar calcium sensitivity is not a basis for pathologic contracture development in muscles from RER-affected horses. Recurrent exertional rhabdomyolysis in Thoroughbreds may represent a novel heritable defect in the regulation of muscle excitation-contraction coupling or myoplasmic calcium concentration.

Adenosine Triphosphatases↗
PubMed1996

Ratings of perceived exertion by a group of women: does Type A behavior act a modifier?

It has previously been suggested that individuals displaying the Type A behavior pattern underestimate their perceived exertion during physical exercise. Most research pertaining to these results has been performed with male participants. In the present study, 70 women (mean age 26.8 yr.) varying in scores on the Bortner scale participated in a standardized cycle ergometer test performed individually in a laboratory setting. Analysis showed small but nonsignificant differences in ratings by participants. This held over the whole range from light to heavy exercise intensity. Less than 1% of the explained variance in ratings of perceived exertion (RPE) could be traced back to the scores for behavior of the individuals. Thus, contrary to some prior reports of RPE suppression associated with the Type A behavior pattern, the results present instead a null finding. Possible causes for the equivocal results are the environment (laboratory vs field), the question whether a laboratory test performed individually is perceived as challenging enough to trigger the competitive urge, type of exercise, the individual's sex, the measure used for assessing Type A behavior pattern, and whether gender-based schematic/aschematic processing is involved.

Adult↗
PubMed2000

Influence of music on ratings of perceived exertion during 20 minutes of moderate intensity exercise.

The effects of different types of music on ratings of perceived exertion (RPE) during 20 min. of moderate intensity exercise were examined. 27 physically active subjects (age 18-30 yr.) performed a graded exercise test on a cycle ergometer to establish peak aerobic power (VO2peak). Four 20-min. exercise sessions were performed at a power output equal to 70% of VO2peak in a soundproof visually sterile room. The sessions were randomly assigned from the conditions of fast upbeat music, classical music, self-selected music, and no music. Heart rate, peripheral RPE, central RPE, and overall RPE were measured every 5 min. during exercise. No significant differences were found in heart rate among the four conditions indicating similar exercise intensity during each condition. Each type of music resulted in a reduced peripheral, central, and overall RPE when compared with the no-music condition. The data indicate that different types of music can act as an effective passive distractor during exercise and are associated with lower ratings of perceived exertion.

Adult↗
PubMed2001

Does perceived exertion depend on glycemic index of foods ingested throughout three hours before a one-hour high-intensity exercise?

The purpose of this study was to assess the relationships between perceived exertion (RPE) and plasma glucose concentrations or hunger feelings during a 1-hr. bicycle submaximal exercise after ingestion of pre-exercise test foods with a different glycemic index. Each of endurance-trained male triathletes ingested three different glycemic index (GI) foods (HighGI: glucose, LowGI: whole-wheat biscuit or water) throughout the 3 hr. before exercise at 80% maximal oxygen uptake (VO2 max). RPE values increased as a logarithmic function of time. This result is opposite to results obtained with longer exercise bouts up to 3 hr. duration. RPE and hunger ratings were not significantly different for the three test foods whatever the time. Moreover, RPE did not correlate with plasma glucose concentrations during exercise. Consequently, RPE did not depend on the GI of the pre-exercise test foods during a 1-hr. exercise at 80% VO2 max. Physiological and psychological factors other than glycemic index may have mediated the perceptual responses during a 1-hr. high-intensity exercise. It is possible that during endurance exercise of longer duration, the level of blood glucose mediates the intensity of peripheral exertional perceptions arising from active skeletal muscle during prolonged exercise.

Adult↗
PubMed1998

Stress, neuropsychiatric disorders and immunological effects exerted by benzodiazepines.

Psychoneuroimmunology is a growing scientific field which deals with the mutual interplay between nervous and immune systems. In this framework, many data have demonstrated that cytokines (CKs) derived from the periphery are able to cross the blood brain barrier and act upon the central nervous system (CNS) [e.g., the hypothalamic-pituitary-adrenal axis (HPAA)], thus regulating several physiological functions (thermoregulation, sleep, appetite) or damaging the nervous tissue, when released in exaggerated amounts. On the other hand, nervous cells, such as astrocytes and microglial cells also generate proinflammatory CKs which may be detrimental for the CNS. The neuromodulating CK network can be triggered by microorganisms and/or their products (i.e. bacterial endotoxins), but also stressful life events may activate the HPAA, thus affecting the immune system function. This review will place emphasis on some clinical conditions, such as phobia and migraine without aura (MWA), characterized by anxiety disorders. Patients affected by these neuropsychiatric alterations exhibit multiple functional deficits of phagocytes and T lymphocytes which allow penetration of various pathogens into the host. This is also supported by the detection of circulating bacterial endotoxins and the evidence of both spontaneous and induced exaggerated release of proinflammatory CKs in phobic and MWA patients. The possible iatrogenic effects of benzodiazepines (BDZ) on the immune system have been evaluated by in vitro and in vivo studies. In this respect, it emerges that diazepam exerts an inhibitory function on the immune system, while alprazolam behaves as an immunoenhancer. The presence of central and/or peripheral BDZ receptors on immune cells seems to be the key mechanism responsible for the immunomodulation exerted by these drugs.

Adjuvants, Immunologic↗
PubMed1990

Interaction of some limbic structures which exert inhibitory effect on corticosterone secretion.

The interaction between limbic structures which exert inhibitory influence on corticosterone secretion was investigated in the rat. The following experiments were performed: 1) electrical stimulation at mammillary medial nucleus (MMN) in rats with lesioned anterodrosal thalami nucleus (ADTN) or intermediate tegmental area; 2) electrical stimulation at ADTN in rats with lesioned retrosplenial cortex (RC). Bilateral stimulation at MMN in ADTN or RC-lesioned rats produces an increase in plasma corticosterone concentration. In animals with lesioned RC, values of plasma corticosterone after stimulation at ADTN were higher than before stimulation. Taking into consideration that electrical stimulation of MMN or ADTN in intact rats produces a decrease in plasma corticosterone concentration, these studies demonstrate that MMN and ADTN exert inhibitory influence on corticoadrenal activity only when their projection areas remain intact.

Animals↗
PubMed1999

[cDNA cloning of ju-myo protein (JP) and elucidation of the molecular mechanisms by which it exerts neurotrophic effects on neurons].

The adult life span in inbred strains of Drosophila melanogaster (Dm) has been found to be controlled by a few major genes (Hereditas 111:207, 1989; Hereditas 117: 251, 1992). A 77 kDa protein, which we named ju-myo (life-span) protein (JP) and is supposed to be the product of the gene on autosomal locus JmA on adult Dm was shown to have life-span prolonging effect when it was supplied in food. However, the knowledge of its structure and molecular mechanisms by which JP exerts its effects on cells is still unclear. Here we show that JP can exert neurotrophic activities on postmitotic fetal rat neurons isolated from cerebral cortical and dopaminergic neurons isolated from the midbrain: it enhanced survival of MAP2-positive cells and tyrosine hydroxylase immunoreactive neurons by approximately 2-fold over the control group. JP did not increase the density of astrocytes nor expression of glial fibrillary acidic protein (GFAP) in the mesencephalic neuron cultures. Amino acid analysis of JP protein showed that JP is identical to the larval serum protein 2, of which sequence and structure were determined in 1997. Our work provides basis for defining the physiological role of JP at the molecular level and for exploring its potential utility as an alternative approach to study mechanisms of aging.

Animals↗
PubMed2003

Psychological stress exerts an adjuvant effect on skin dendritic cell functions in vivo.

Psychological stress affects the pathophysiology of infectious, inflammatory, and autoimmune diseases. However, the mechanisms by which stress could modulate immune responses in vivo are poorly understood. In this study, we report that application of a psychological stress before immunization exerts an adjuvant effect on dendritic cell (DC), resulting in increased primary and memory Ag-specific T cell immune responses. Acute stress dramatically enhanced the skin delayed-type hypersensitivity reaction to haptens, which is mediated by CD8(+) CTLs. This effect was due to increased migration of skin DCs, resulting in augmented CD8(+) T cell priming in draining lymph nodes and enhanced recruitment of CD8(+) T cell effectors in the skin upon challenge. This adjuvant effect of stress was mediated by norepinephrine (NE), but not corticosteroids, as demonstrated by normalization of the skin delayed-type hypersensitivity reaction and DC migratory properties following selective depletion of NE. These results suggest that release of NE by sympathetic nerve termini during a psychological stress exerts an adjuvant effect on DC by promoting enhanced migration to lymph nodes, resulting in increased Ag-specific T cell responses. Our findings may open new ways in the treatment of inflammatory diseases, e.g., psoriasis, allergic contact dermatitis, and atopic dermatitis.

Animals↗
PubMedDate not supplied

Chronic exertional compartment syndrome.

Chronic exertional compartment syndrome is an often overlooked and uncommon cause of pain in the extremities of individuals who engage in repetitive physical activity. A thorough history, a careful physical examination, and compartment pressure testing are essential to establish the diagnosis. Catheter measurements can provide useful information on baseline resting compartment pressures as well as compartment pressures after exercise or trauma. Patients with chronic exertional compartment syndrome usually do not respond to nonsurgical therapy other than completely ceasing the activities that cause the symptoms. Surgical intervention entails fasciotomies of the involved compartments. Although obtaining accurate compartment pressure measurements can be difficult and fascial releases must be done carefully, patients typically have satisfactory functional results and are able to return to their usual physical activities after fasciotomy.

Angiography↗