Stein Knardahl

Open-field behavior of spontaneously hypertensive rats

The present experiment investigated the exploratory behavior of spontaneously hypertensive rats (SHR) of the Okamoto strain. A free-exploration open-field apparatus, permitting the animal to explore the novel environment from its home cage, was used for studying the open-field behavior of 10 prehypertensive spontaneously hypertensive rats and 10 normotensive control rats (NR) of the Wistar-Kyoto strain. In Experiment 1, each rat was run for one 15-min session on each of 10 consecutive days. The SHR gradually became much more active than the NR, showing shorter latency to leave the home cage, spending more time in the surrounding open field, and ambulating more. Experiment 2 involved introduction of a novel object. This resulted in a further increase in the activity of the SHR, developing gradually as in Experiment 1. The SHR explored the novel object more than the NR did, indicating that the hyperactivity observed in Experiments 1 and 2 was due to hyperexploration. Correlations between mean blood pressure as measured 2 months following the behavioral testing and mean total ambulatory activity showed that the SHR developing the most pronounced hypertension were the most active SHR. In contrast, the least active NR had higher blood pressures than the most active NR. The present behavioral results are interpreted as being due to increased effects of stimuli in SHR. It is suggested that increased neurohumoral load on the cardiovascular system due to increased effects of stimuli is important in the pathogenesis of hypertension in the SHR.

Work factors as predictors of sickness absence: a three month prospective study of nurses’ aides

Aims: To identify the work factors that predict sickness absence in nurses’ aides. Methods: The sample comprised 5563 Norwegian nurses’ aides, not on leave because of illness or pregnancy when they completed a mailed questionnaire in 1999. Of these, 4931 (88.6%) completed a second questionnaire three months later. The outcome measure was the three month incidence proportion of certified sickness absence (>3 days), as assessed by self reports at follow up. Results: Perceived lack of encouraging and supportive culture in the work unit (odds ratio (OR) 1.73; 95% confidence interval (CI) 1.28 to 2.34), working in psychiatric and paediatric wards, having injured the neck in an accident, and health complaints were associated with higher risk of sickness absence, after adjustments for a series of physical, psychological, and organisational work factors, personal engagement in the work unit, demographic characteristics, and daily consumption of cigarettes. Having untraditional jobs (for nurses’ aides) (OR 0.53; 95% CI 0.36 to 0.77), and engaging in aerobics or gym were associated with a lower risk of sickness absence. Conclusions: The study suggests that the three month effects of work factors on rates of certified sickness absence are modest in nurses’ aides. The most important work factor, in terms of predicting sickness absence, seems to be perceived lack of encouraging and supportive culture in the work unit.

Placebo-Induced Changes in Spinal Cord Pain Processing

Pain is an essential sensory modality, signaling injury or threat of injury. Pain perception depends on both biological and psychological factors. However, it is not known whether psychological factors modify spinal mechanisms or if its effect is limited to cortical processing. Here, we use a placebo analgesic model to show that psychological factors affect human spinal nociceptive processes. Mechanical hyperalgesia (hypersensitivity) after an injury is attributable to sensitized sensory neurons in the spinal cord. After a 5 min, 46°C heating of the skin, subjects developed areas of mechanical hyperalgesia. This area was smaller in a placebo condition compared with a baseline condition. This result suggests that placebo analgesia affects the spinal cord as well as supra-spinal pain mechanisms in humans and provides strong supporting evidence that placebo analgesia is not simply altered reporting behavior. Central sensitization is thought to mediate the exaggerated pain after innocuous sensory stimulation in several clinical pain conditions that follow trauma and nervous-system injury. These new data indicate that expectation about pain and analgesia is an important component of the cognitive control of central sensitization.

Workplace bullying and mental distress - a prospective study of Norwegian employees

OBJECTIVES Using a prospective design, the objective of this study was to determine the relationship between workplace bullying and mental distress. METHODS Altogether, 1971 Norwegian employees, recruited from 20 organizations, answered questions regarding workplace bullying and mental distress at both baseline and follow-up. Baseline data were gathered between 2004-2006, and follow-up data were gathered between 2006-2009. The time-lag between baseline and follow-up was approximately two years for all the respondents in all the organizations. The factors measured in the study were individual characteristics, mental distress measured with the Hopkins Symptom Checklist (HSCL-10), self-reported workplace bullying measured with a single item from the General Nordic Questionnaire for Psychological and Social Factors at Work (QPSNordic) and job demands and job control assessed by QPSNordic. RESULTS A multiple linear regression analysis adjusted for mental distress, sex, age, job demands and job control at baseline [β=0.05, 95% confidence interval (95% CI) 0.03-0.17] and a repeated measures ANOVA adjusted for sex and age [F(3,1965)=38.37; partial η (2)=0.06] showed that workplace bullying predicted mental distress. Furthermore, a multiple binary logistic regression analysis adjusted for bullying, sex, age, job demands and job control at baseline [odds ratio (OR) 2.30, 95% CI 1.43-3.69] showed that mental distress was a predictor of bullying. CONCLUSIONS We found support for the notion that self-reported workplace bullying is a predictor of mental distress two years later. Bullying had an independent effect on mental distress after adjusting for job demands and job control. Mental distress was also found to be a predictor of bullying, indicating that the reverse relationship is also important.

Work and neck pain: a prospective study of psychological, social, and mechanical risk factors.

&NA; To determine the impact of occupational psychological/social and mechanical factors on neck pain, a prospective cohort study with a follow‐up period of 2 years was conducted with a sample of Norwegian employees. The following designs were tested: (i) cross‐sectional analyses at baseline (n = 4569) and follow‐up (n = 4122), (ii) prospective analyses with baseline predictors, (iii) prospective analyses with average exposure over time [(T1 + T2)/2] as predictor, and (iv) prospective analyses with measures of change in exposure from T1 to T2 as predictors. A total of 2419 employees responded to both the baseline and follow‐up questionnaire. Data were analyzed using ordinal logistic regression. After adjustment for age, sex, neck pain at T1, and other exposure factors that had been estimated to be confounders, the most consistent risk factors were role conflict (highest OR 2.97, 99% CI: 1.29–6.74) and working with arms raised to or above shoulder level (highest OR 1.37, 99% CI: 1.05–1.78). The most consistent protective factors were empowering leadership (lowest OR 0.53, 99% CI: 0.35–0.81) and decision control (lowest OR 0.60, 99% CI: 0.36–1.00). Hence, psychological and social factors are important precursors of neck pain, along with mechanical factors. Although traditional factors such as quantitative demands and decision control play a part in the etiology of neck pain at work, in this study several new factors emerged as more important.

Work-induced pain, trapezius blood flux, and muscle activity in workers with chronic shoulder and neck pain

ABSTRACT Pain, trapezius microcirculation, and electromyography (EMG) were recorded during 90 min of simulated office work with time pressure and hand precision demands in 24 full‐time working subjects with chronic shoulder and neck pain. The responses were compared with those of a reference group of 28 healthy subjects without pain. Pain intensity was rated on a visual analogue scale. Intramuscular blood flux was measured by laser‐Doppler flowmetry (LDF) and muscle activity by surface EMG bilaterally in the upper trapezius. Pain increased during the work task, and the increase was larger in women than in men and in the reference group. Muscle activity was low: <4% of EMG during maximal voluntary contraction. LDF showed elevated intramuscular blood flux above baseline throughout the work task in both groups and during recovery in the pain group. Pain in the active side correlated positively with blood flux in the pain‐afflicted subjects and negatively in the reference group. In conclusion, office work induced pain, and trapezius vasodilation that did not return to resting values during recovery. These data show that pain is associated with trapezius vasodilation but not with muscle activity. Interaction between blood vessels and nociceptors may be important in the activation of muscle nociceptors in people with chronic shoulder and neck pain. Pain‐afflicted people may benefit from breaks spaced at shorter intervals than those needed by pain‐free subjects when working under time pressure.

Effects of localization and intensity of experimental muscle pain on ankle joint proprioception

Accurate proprioceptive input is a prerequisite for balance control and coordination of movement. The present study investigated whether experimental muscle pain induced in healthy human subjects disturbed movement sense (detection of movement) or position sense (recognition of a reference position). Muscle pain was produced by infusion of 6% hypertonic saline simultaneously in m. tibialis anterior (TA) and m. soleus (experiment 1), by infusion of 6% hypertonic saline in TA (experiment 2) and by infusion of 9% hypertonic saline in TA (experiment 3). Control measurements were done with infusions of 0.9% isotonic saline. All infusions of 6% and 9% saline produced pain intensities significantly higher than the corresponding control infusions. Only infusion of 6% saline in two muscles (visual analogue scale = 4–5) produced an elevation in movement detection thresholds which was significantly higher, compared with before infusion. No other significant changes in movement and position sense were found during the painful or control infusions. Pain of relatively high intensity in two antagonist muscles is necessary to disturb the movement detection threshold. The ability to recognize a reference position is not disturbed by experimentally induced muscle pain. Whether the disturbed movement sense is caused by sensitivity changes in muscle spindle afferents or altered processing of proprioceptive input cannot be answered. The present findings indicate that human ankle proprioception is rather robust to muscle pain.

Variation in reporting of pain and other subjective health complaints in a working population and limitations of single sample measurements.

&NA; Measuring health complaints by administrating a single report is common. Our aim was to assess variation in pain and other subjective complaints over an extended period, whether a single‐sample produces representative data, and determine associations between complaints. Health‐complaint reports were collected from postal workers at monthly intervals over a period of 32–34 consecutive months (1997–2000). We computed six compound complaint‐severity indices of 30 complaint‐severity scores (intensity score×duration score, scale 0–9). In 67% of the scores, the complaints exhibited larger deviation from a reference (12 consecutive reports in the last 24 months of the study period) when using one report from the respective reference period compared with the mean of two consecutive reports. Four consecutive samples were needed to obtain agreement for 95% of the data when the criterion of accepted deviation from the reference was set to ±1.0. Neither inspection of graphs nor statistical tests revealed any seasonal pattern or trend on either a group or individual level. The musculoskeletal and psychological complaint‐severity indices correlated strongly (rs>0.66). Correlations between the different somatic indices were generally weak or moderate (rs<0.55). The initial report produced higher complaint ratings than subsequent reports did. Due to large intra‐individual complaint variability and higher complaint‐severity level exhibited on the initial report compared to those that followed, measuring subjective health with a single‐sample approach does not produce data representativeness for average complaints over a period. More than two samples should be collected when the purpose is to reveal changes in health.

Short-term effects of exercise on plasma very low density lipoproteins (VLDL) and fatty acids.

PURPOSE In the fasted state the lipid fuels for muscle metabolism are free fatty acids (FFA) released either from intramuscular triglycerides (TG), plasma albumin, or TG in circulating very low density lipoproteins (VLDL). The purposes of this study were to determine the influence of acute exercise of moderate intensity on 1) plasma total concentration of TG and VLDL components, 2) the plasma concentration and distribution of individual albumin-bound long-chain FFA, and 3) lipid peroxidation as measured by thiobarbituric acid reactive substances (TBARS). METHODS Eight healthy male subjects each participated in one exercise (EX) and one rest (RE) experiment. In EX the subjects exercised for 90 min at 58+/-5% (mean +/- SD) of maximal O2 uptake on a cycle ergometer followed by 4.5 h bedrest. RE followed the same protocol, but without exercise. RESULTS In EX there was no immediate change in VLDL concentration during the exercise. After exercise there was a decrease in VLDL, VLDL-TG, -cholesterol, -protein and -phospholipids compared with those after RE. There was no change in percentage composition of VLDL as result of exercise. Total plasma FFA concentration increased appreciably during exercise and remained elevated for several hours postexercise. There was no correlation between the change in FFA concentration and VLDL-TG. There was a significant positive correlation between the exercise-related increments in the various long-chain FFA, but the effect varied so that the relative abundance of oleic acid increased and that of stearic and arachidonic acid decreased during exercise. Plasma TBARS concentration increased during the day in both experiments. CONCLUSION The results indicate that there is a delay in the effect of an exercise bout on plasma VLDL and confirm that exercise affects various FFA in plasma differentially.

Attenuated adrenergic responses to exercise in women with fibromyalgia--a controlled study.

The pathogenesis of widespread pain and fibromyalgia (FM) is unknown. Altered responses from the hypothalamus–pituitary–adrenal axis, sympathetic nervous system and muscular system have been suggested as being of importance. The present study was undertaken to determine: (i) whether the sympathoadrenal response to repetitive isometric contractions until exhaustion is altered in patients with FM, and (ii) whether sympathoadrenal responses are associated with muscle fatigue and pain during exercise.