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PubMedDate not supplied

Obtaining the shear stress versus shear rate relationship and yield stress of blood from capillary viscometry data by Tikhonov regularization.

This paper describes a procedure, based on Tikhonov regularization, for extracting the shear stress versus shear rate relationship and yield stress of blood from capillary viscometry data. The relevant equations and the mathematical nature of the problem are briefly described. The procedure is then applied to three sets of capillary viscometry data of blood taken from the literature. From each data set the procedure computes the complete shear stress versus shear rate relationship and the yield stress. Since the procedure does not rely on any assumed constitutive equation, the computed rheological properties are therefore model-independent. These properties are compared against one another and against independent measurements. They are found to be in good agreement for shear stress greater than 0.1 Pa but show significant deviations for shear stress below this level. A possible way of improving this situation is discussed.

Blood Viscosity↗
PubMed2005

Evidence for the Stepwise Stress Model: Gambusia holbrooki and Daphnia magna under acid mine drainage and acidified reference water stress.

The Stepwise Stress Model (SSM) states that a cascade of regulative behavioral responses with different intrinsic sensitivities and threshold values offers increased behavioral plasticity and thus a wider range of tolerance for environmental changes or pollutant exposures. We tested the SSM with a widely introduced fish Gambusia holbrooki (Girard) (Pisces, Poeciliidae) and the standard laboratory test species Daphnia magna Straus (Crustacea, Daphniidae). The stress was simulated by short-term exposure to acid mine drainage (AMD) and to acidified reference water (ACID). Recording of behavioral responses with the multispecies freshwater biomonitor (MFB) generated continuous time-dependent dose-response data that were modeled in three-dimensional (3D) surface plots. Both the pH-dependent mortalities and the strong linear correlations between pH and aqueous metals confirmed the toxicity of the AMD and ACID gradients, respectively, for fish and Daphnia, the latter being more sensitive. AMD stress at pH < or = 5.5 amplified circadian rhythmicity in both species, while ACID stress did so only in G. holbrooki. A behavioral stepwise stress response was found in both species: D. magna decreased locomotion and ventilation (first step) (AMD, ACID), followed by increased ventilation (second step) (AMD). G. holbrooki decreased locomotion (first step) (AMD, ACID) and increased ventilation at intermediate pH levels (second step) (AMD). Both species, although from different taxonomic groups and feeding habits, followed the SSM, which might be expanded to a general concept for describing the behavioral responses of aquatic organims to pollution. Stepwise stress responses might be applied in online biomonitors to provide more sensitive and graduated alarm settings, hence optimizing the "early warning" detection of pollution waves.

Acids↗
PubMed2003

Oxidative stress-induced apoptosis in dividing fibroblasts involves activation of p38 MAP kinase and over-expression of Bax: resistance of quiescent cells to oxidative stress.

Oxidative stress has been postulated to be involved in aging and age-related degenerative diseases. Cell death as a result of oxidative stress plays an important role in the age related diseases. Using human diploid fibroblasts (HDF) as model to study the mechanism of cell death induced by oxidative stress, a condition was standardized to induce apoptosis in the early passage sub-confluent HDFs by a brief exposure of cells to 250 microM hydrogen peroxide. It was observed that p38 MAP kinase (MAPK) was activated soon after the treatment followed by over-expression of Bax protein in cells undergoing apoptosis. An interesting finding of the present study is that the confluent, quiescent HDFs were resistant to cell death under identical condition of oxidative stress. The contact-inhibited quiescent HDFs exhibited increased glutathione level following H(2)O(2)-treatment, did not activate p38 MAP kinase, or over-express Bax, and were resistant to cell death. These findings indicated that there was a correlation between the cell cycle and sensitivity to oxidative stress. This is the first report to our knowledge that describes a relationship between the quiescence state and anti-oxidative defense. Furthermore, our results also suggest that the p38MAPK activation-Bax expression pathway might be involved in apoptosis induced by oxidative stress.

Antioxidants↗
PubMed1999

Lipid reactivity to stress: I. Comparison of chronic and acute stress responses in middle-aged airline pilots.

Lipids increase during psychological stress, but no studies have compared the effects of acute and chronic stressors on lipid responsivity in the same individuals. One hundred middle-aged men (n = 92) and women (n = 8) were examined during high chronic occupational stress, low chronic stress, and acute laboratory stressors. In addition to measures of perceived stress and affect, an extensive battery of lipid and lipoprotein measures was undertaken at each time point. Most lipid parameters were significantly increased during the chronic and acute stressors, although the responses to the different stressors were not consistently associated. For example, significant correlations among the chronic and acute stress responses were apparent for the apoproteins, but not for total, low density lipoprotein, or high density lipoprotein cholesterol. The factors and processes regulating these variables during stress may be different during acute and chronic stressors.

Acute Disease↗
PubMed2001

Postnatal maternal deprivation produces long-lasting modifications of the stress response, feeding and stress-related behaviour in the rat.

The hypothalamo-pituitary-adrenal (HPA) axis plays a central role both in the regulation of the stress response, and in the control of feeding behaviour. Sensitivity of the HPA axis to respond to stress varies both during ontogeny and between individuals, and can be altered by neonatal events. The aim of our experiments was to determine whether early events that affect the HPA axis could also induce persistent modifications in food intake (quantitatively and qualitatively), as well as alterations of anxiety-related behaviour. Twenty-four-hour maternal deprivation was introduced at two different periods of HPA maturation, on day 5 (DEP5) or day 14 (DEP14) after birth. Sequential measurements of plasma levels of adrenocorticotropin hormone (ACTH) and corticosterone showed that this deprivation altered the HPA axis of adults; the response to restraint stress was prolonged in DEP5 and a higher ACTH peak appeared in DEP14. The neonatal stress also produced long-lasting modifications of rat behaviour, as DEP14 adults became more anxious. Standard food intake decreased in both groups of deprived rats. Diet preferences also changed, as carbohydrate intake decreased in DEP5 rats. Corticosteroid receptor binding did not vary in the hippocampus of the deprived rats. The modifications of the stress response and the behaviour parameters could be due to the alteration of corticosteroid receptors in the hypothalamic paraventricular nucleus and/or corticotropin-releasing hormone or vasopressin function, but these parameters have yet to be determined. This early stress paradigm altering feeding behaviour could become an interesting model for research into human eating disorders.

Adrenocorticotropic Hormone↗
PubMed1999

Single stress induces long-lasting elevations in vasopressin mRNA levels in CRF hypophysiotrophic neurones, but repeated stress is required to modify AVP immunoreactivity.

Repeated stress is known to induce an increased vasopressin (AVP) expression in paraventricular corticotrophin-releasing factor (CRF) neurones which is supposed to enhance the ACTH-releasing capacity of these cells. To test the hypothesis that a single stress is sufficient to produce these changes, we used quantitative in-situ hybridization analysis to measure steady state CRF and AVP mRNA. Moreover the colocalized AVP and CRF immunoreactive sites were assessed in the dense core vesicle compartment of CRF axon terminals in the external zone of the median eminence with quantitative immunoelectron microscopy. Acute immobilization produced a significant increase in the average AVP and CRF mRNA levels (145% and 65%, respectively, above control values) in the medial parvocellular subdivisions of the paraventricular nucleus (PVN), and these changes persisted for over 4 days after stress. In contrast to these changes in AVP mRNA levels, there were no concomitant changes in AVP immunostaining in CRF terminals and axons during the 4-day period. However, when immobilization stress was repeated daily, the number of CRF terminals containing AVP increased progressively. Moreover, the ratio of AVP and CRF immunoreactivity in the dense core vesicle compartment was increased. Taken together, these results provide evidence that single stress experience can cause long-lasting changes in AVP and CRF mRNA steady state expression that is not apparently accompanied by changes in peptide levels. They also suggest that repeated stress is required for developing progressive shifts in the neurohormone storage pattern of these neurones.

Animals↗
PubMed2002

Stressful incidents, stress and coping strategies in the pre-registration house officer year.

CONTEXT: Previous studies have drawn attention to the stresses experienced by doctors in their first year. OBJECTIVES: To gain a deeper understanding of the causes of stress in newly qualified doctors, how they cope, and what interventions might make the year less traumatic. DESIGN: Postal questionnaire. This study focused on an open question asking about a stressful incident, the coping strategy used to deal with it, stressors in general and current levels of stress using the General Health Questionnaire. SETTING: 336 hospitals throughout the United Kingdom. SUBJECTS: A cohort of doctors followed from the time of their application to medical school, studied towards the end of their pre-registration year (n=2456). RESULTS: The response rate to the questionnaire was 58.4%. The incidents were categorised into the major groups Responsibility (33.6%), Interpersonal (29.7%), Overwork (17.0%), Death and disease (13.0%), and Self (6.7%). GHQ revealed psychological morbidity in 31% of respondents. Stress levels were highest in those reporting an incident about Responsibility or Self, lowest in those describing Death or disease. Stressors in general and preferred coping strategies differed between the groups. CONCLUSION: The incidents suggested the following interventions to reduce stress: better supervision in the first few weeks in post, at night, and for medical problems on surgical wards; more attention to avoiding sleep deprivation; more time for discussion with colleagues at work; more personal time with friends and family. The choice of incident described was influenced by the personal characteristics of the respondent.

Adaptation, Psychological↗
PubMed1998

Stress, headache, and physiological disregulation: a time-series analysis of stress in the laboratory.

This study examined the stress-headache relationship from a disregulation framework by monitoring both physiological responses (e.g., pulse, blood volume, skin resistance, and EMG) and self-reported responses to a stressful event in tension and migraine headache sufferers, as well as in headache-free controls. Responses were analyzed via time-series analyses to determine whether self-reports of stress were correlated with physiological measures of stress. It was hypothesized that tension and migraine headache sufferers would show fewer significant correlations than control participants between their self-reports of stress and physiological activity. Data analyses supported this hypothesis for tension headache sufferers, but generally not for migraine headache sufferers. The most compelling support for the hypothesis in tension headache sufferers came from the cross-correlations between self-reported stress and pulse rate.

Electromyography↗
PubMed1984

[Standardized psychological stress test for the provocation of tachycardial ventricular arrhythmias. Comparison with long-term ECG and stress ECG].

The effect of a standardized psychological stress test on frequency and severity of ventricular extrasystoles was compared in 42 patients with the results of 24-hour ECG monitoring and of an exercise ECG test. Frequent ventricular extrasystoles (greater than 1/min) occurred in the 24-hour-ECG in 22, in the psychological stress test in 24 and on physical exercise in 22 patients. 24-hour monitoring gave the only positive finding in ten, the psychological stress test in six, the exercise test in four. Complex arrhythmias (coupled or runs of ventricular extrasystoles) occurred in the 24-hour ECG in 30, with the psychological stress test in 16 and the exercise test in 12 patients. The 24-hour ECG was alone positive in 16, the psychological test in two, the exercise test in one. Thus in an individual patient the psychological stress test may provoke additional arrhythmias which are not recorded in either the 24-hour ECG or after exercise. The findings point to an independent significance of the psychological stress test in the diagnosis of simple and complex ventricular arrhythmias.

Adult↗
PubMed2002

Short day lengths augment stress-induced leukocyte trafficking and stress-induced enhancement of skin immune function.

Environmental conditions influence the onset and severity of infection and disease. Stressful conditions during winter may weaken immune function and further compromise survival by means of hypothermia, starvation, or shock. To test the hypothesis that animals may use photoperiod to anticipate the onset of seasonal stressors and adjust immune function, we evaluated glucocorticoids and the distribution of blood leukocytes in Siberian hamsters (Phodopus sungorus) exposed to long day lengths (i.e., summer) or short day (SD) lengths (i.e., winter) at baseline and during acute stress. We also investigated the influence of photoperiod and acute stress on a delayed-type hypersensitivity response in the skin. SDs increased glucocorticoid concentrations and the absolute number of circulating blood leukocytes, lymphocytes, T cells, and natural killer cells at baseline in hamsters. During stressful challenges, it appears beneficial for immune cells to exit the blood and move to primary immune defense areas such as the skin, in preparation for potential injury or infection. Acute (2 h) restraint stress induced trafficking of lymphocytes and monocytes out of the blood. This trafficking occurred more rapidly in SDs compared to long days. Baseline delayed-type hypersensitivity responses were enhanced during SDs; this effect was augmented by acute stress and likely reflected more rapid redistribution of leukocytes out of the blood and into the skin. These results suggest that photoperiod may provide a useful cue by which stressors in the environment may be anticipated to adjust the repertoire of available immune cells and increase survival likelihood.

Adaptation, Physiological↗
PubMed1997

Activation of the Ste20-like oxidant stress response kinase-1 during the initial stages of chemical anoxia-induced necrotic cell death. Requirement for dual inputs of oxidant stress and increased cytosolic [Ca2+].

Signal transduction mechanisms activated during the early stages of necrotic cell death are poorly characterized. We have recently identified the Sterile 20 (Ste20)-like oxidant stress response kinase-1, SOK-1, which is a member of the Ste20 kinase family. We report that SOK-1 is markedly activated as early as 20 min after chemical anoxia induced by exposure of Madin-Darby canine kidney or LLC-PK1 renal tubular epithelial cells to 2-deoxyglucose (2-DG) and any one of three inhibitors of the electron transport chain, cyanide (CN), rotenone, or antimycin A. Since oxidant stress activates SOK-1, we postulated that reactive oxygen species (ROS), which are produced by the electron transport chain during chemical anoxia, might be responsible for SOK-1 activation. The time course of CN/2-DG-induced SOK-1 activation and of production of ROS, measured in cells loaded with dichlorofluorescein, were compatible with a role for ROS in SOK-1 activation. Furthermore, preincubation of LLC-PK1 cells with three unrelated scavengers of ROS, pyrrolidine dithiocarbamate, pyruvate, or nordihydroguaiaretic acid, reduced both cellular oxidant stress and activation of SOK-1 by CN/2-DG. An increase in cytosolic free [Ca2+] ([Ca2+]i) was necessary but not sufficient for CN/2-DG-induced activation of SOK-1. Preincubation of cells with BAPTA-AM prevented activation of SOK-1. Incubation of cells with thapsigargin or the calcium ionophore, A23187, had no effect on SOK-1 activity, but preincubation of cells with either of these agents markedly enhanced CN/2-DG-induced activation of SOK-1 (20-fold versus 7-fold). In summary, chemical anoxia activates SOK-1 via an oxidant stress-dependent mechanism that is both critically dependent upon and markedly amplified by an increase in [Ca2+]i. This requirement for dual inputs of oxidant stress and an increase in [Ca2+]i may prevent inappropriate activation of the kinase by milder degrees of oxidant stress, which are insufficient to generate an increase in [Ca2+]i. The activation of SOK-1 may be one of the cell's earliest responses to inducers of necrotic cell death.

Animals↗
PubMed2001

Stress as a diagnostic challenge for postconcussive symptoms: sequelae of mild traumatic brain injury or physiological stress response.

There is considerable controversy regarding whether persistent postconcussive symptoms (PCS) are injury-specific, in a subgroup of individuals after mild traumatic brain injury (TBI). The following findings have contributed to this controversy: (1) The base rate of PCS in mild TBI is comparable to uninjured controls; and (2) The severity of PCS covary with daily stress levels (Gouvier, Cubic, Jones, Brantley, & Cutlip, 1992). We examined this relationship further by evaluating the effects of experimental conditions of stress or relaxation on individuals with TBI and uninjured control subjects, with low and high PCS endorsement. We evaluated psychophysiological parameters, neuropsychological performance, and changes in PCS and stress perception. In our study, subjects with TBI increased PCS after engaging in cognitively challenging tasks, and demonstrated significant autonomic changes in the stress condition. Symptomatic TBI subjects exposed to high stress had increases in PCS complaints, decreased speed of information processing, and subtle memory deficits. Our results suggest that PCS are injury-specific and that individuals with a history of TBI are susceptible to the effects of stress. Relaxation training including breathing retraining may be an effective means of decreasing PCS and cognitive complaints in subjects with mild TBI.

Adult↗
PubMedDate not supplied

"Stress knocks hard on your immune system": asthma and the discourse on stress.

Stress has been described by anthropologists and other scholars as a problematic concept, a discourse, a modern metaphor, a collective representation, and a cultural resource. The vast array of academic work in the arena of stress research belies the historical reality of stress as an object of inquiry; rather, stress is presented as new, the story of its emergence intermingled with processes of industrialization, individualism, and perceptions of modern life. This article traces the uses to which the concept of stress is put in the illness narratives of persons with asthma. It argues that multiple invocations of stress not only make visible the workings of personal responsibility and individualism regarding chronic illness management in the contemporary United States but also gesture toward the social relations of sickness that lie beyond individual control.

Adult↗
PubMed1998

Parenting stress among mothers of Malaysian children with cerebral palsy: predictors of child- and parent-related stress.

A hospital study was carried out to compare parenting stress among 87 Malaysian mothers of children with cerebral palsy and a control group (comprising 87 mothers of children without disability who attended the walk-in paediatric clinic), using the Parenting Stress Index (PSI) questionnaire. Multiple regression analysis was used to determine socio-demographic and medical factors associated with child-domain stress (CDS) and parent-domain stress (PDS). Mothers of children with cerebral palsy scored significantly higher than control subjects on all sub-scales of CDS and PDS (p < 0.01), except for the sub-scale of 'role restriction'. The presence of cerebral palsy (p < 0.001) and activities of daily living (ADL) scores (p < 0.001) were significantly associated with CDS. Factors predictive of PDS were ADL scores (p < 0.001), number of hospitalizations over the past year (p = 0.024), level of maternal education (p = 0.018) and Chinese mothers (p < 0.001). Although this study demonstrated that Malaysian mothers of children with cerebral palsy experienced higher levels of stress than controls, the impact of cerebral palsy per se on parenting stress was modified by other factors such as increased care-giving demands, low maternal education and ethnic background. Habilitation should be directed at easing the burden of daily care, minimizing hospital re-admissions and targeting appropriate psychosocial support at specific subgroups to change parental perception and expectations.

Adult↗
PubMed2004

Plasma catecholamines, blood pressure responses and perceived stress during mental arithmetic stress in young men.

We assessed plasma noradrenaline (NA) and adrenaline (A) at rest during a hyperinsulinaemic glucose clamp and responses to a mental arithmetic stress test (MST) in relation to blood pressure (BP) responses (Finapres) and distress in 20 men with high (> or =140/90 mmHg) and 21 men with normal (< or =115/75 mmHg) screening BP, 21-24 years of age. Perceived stress, effort and overall discomfort were scored 1-10. Catecholamines and BP increased in both groups, change in diastolic BP (DeltaDBP; 9.9 vs. 3.8 mmHg, p < 0.05) and DeltaDBP carryover (recovery period minus baseline) (7.2 vs. 2.2 mmHg, p < 0.01) being greater in men with high screening BP. Independently of BP status, change in systolic BP (DeltaSBP) and DeltaSBP carryover were related to A (both p < 0.001), and DeltaDBP and DeltaDBP carryover to DeltaNA (both p < 0.001). The subjective score sum correlated with maximal NA (rs = 0.40) and A (rs = 0.37) (both p < 0.05). Maximal NA was independently related to stress (p < 0.05) and the subjective score sum (p < 0.01). DeltaA% was greater in the high- (score > or =6) than in the low-stress category, independently of BP status (p < 0.05). High screening BP is associated with impaired BP recovery after mental stress. Plasma catecholamine responses are related to BP responses and carryover effects, and reflect perceived stress in young men.

Adult↗
PubMed2005

The cost of chronic stress: impacts of a nonhabituating stress response on metabolic variables and swimming performance in sturgeon.

Metabolic scope for activity (MSA) and critical swimming velocity (U(crit)) were measured in green sturgeon exposed to two stressors daily for 28 consecutive days. The results were compared with unstressed fish in an effort to measure the "cost" of chronic stress. Chronic stress was simulated by exposing fish to a randomized order of acute stressors: a 5-min chasing stressor, a 10-min water depth reduction stressor, or a 5-min confinement stressor. The acute cortisol response to each stressor was initially determined, and the maintenance of that response was verified in 7-d intervals during the chronic stress regime. Exposure to the chronic stress regime resulted in a 25% reduction of MSA caused by significantly increased maintenance metabolic rate (0.27+/-0.01 vs. 0.19+/-0.02 mg O(2) h(-1) g(-1), chronic and control fish, respectively) but did not affect the U(crit) of sturgeon. In addition, a 50% reduction in liver glycogen levels and a twofold increase of resting plasma glucose levels were measured in chronically stressed fish. We conclude that our chronic stress regime resulted in a significant maintenance cost to green sturgeon, possibly because of their inability to habituate to the stressors, but did not decrease their swimming performance.

Analysis of Variance↗
PubMed2001

Increased susceptibility to stress at a psychological assessment of stress tolerance is associated with impaired fetal growth.

BACKGROUND: This study aims to investigate the relationship between birthweight and psychological function, as evaluated by the results of a psychological conscript interview and assessment in young males, including an evaluation of stress susceptibility. METHODS: We performed a retrospective cohort study based on linked birth registry data and data from an assessment of psychological function during evaluation for military service. In all, 90 651 young males born 1973-1975, for whom birth record data were obtained from the Swedish Medical Birth Register, were investigated in addition to psychological stress susceptibility during their conscript evaluation in 1991-1994. The assessment of psychological functioning score, including the assessment of stress susceptibility, was used as the dependent variable in a multiple regression analysis in combination with the following independent variables: birthweight, adult weight, head circumference at birth, month of birth, gestational age, maternal parity, and maternal age. RESULTS: The mean value was 5.1 (SD 1.9) on the psychological assessment scale (range 1-9) of psychological level of functioning including evaluation of stress susceptibility, and 5.3 (1.6) on the general psychological performance (leadership) profile. A positive association was seen between birthweight and better assessment results up to a level of about 4000 g birthweight, but above that an inverse association was seen. Positive correlations (P < 0.001) were seen between psychological assessment score results and birthweight (r = 0.07), gestational age (0.03), head circumference (0.05), and maternal age (0.11), but inverse correlations with maternal parity (-0.11) and birth month of the offspring (-0.04). In multiple regression analyses, the strongest independent correlations were seen between increasing assessment scores and maternal age and birthweight (positive), as well as with maternal parity and offspring adult weight (negative). CONCLUSION: Young males at conscript testing show a better general psychological functioning score derived from psychological assessment, including evaluation of stress susceptibility, with increasing birthweight up to 4200 g. Above that birthweight an inverse association is noticed. Impaired fetal growth is predictive of suboptimal psychological functioning and increased stress susceptibility in males during early adult life.

Birth Weight↗
PubMed2003

Stress in police officers: a study of the origins, prevalence and severity of stress-related symptoms within a county police force.

BACKGROUND: High levels of stress-related illness are causing concern across industry. Against a background of impending legislative moves to try to improve this situation, there is a need to identify key work-related stressors. Police work tends to be regarded as inherently stressful because of the personal risk of exposure to confrontation and violence and the day-to-day involvement in a variety of traumatic incidents. As a result, high levels of stress-related symptoms might be expected in this population. OBJECTIVE: To examine the sources of stress-related symptoms within police officers and measure the prevalence of significant associated mental ill-health. METHOD: A cross-sectional questionnaire survey of a population of 1206 police officers was performed to assess levels of strain associated with a series of potential home and work related stressors. Participants were then split into low and high scoring groups on the basis of a General Health Questionnaire (GHQ) threshold score in order to identify those stressors most associated with mental ill-health effects. RESULTS: Occupational stressors ranking most highly within the population were not specific to policing, but to organizational issues such as the demands of work impinging upon home life, lack of consultation and communication, lack of control over workload, inadequate support and excess workload in general. The high scoring group constituted 41% of the population and differed significantly from those with low scores in perception of all stressors, ranking both personal and occupational stressors more highly, and from personality constraints appeared significantly more 'stress-prone'. A significant association between gender and mental ill-health was found, with females more likely to score more highly on the GHQ than males. CONCLUSION: This study confirms previous findings of organizational culture and workload as the key issues in officer stress. Given that the degree of symptomatology appears to be worsening, management action is required. Further research is indicated within the police population into a possible increased susceptibility in female officers.

Adult↗