Andrew Steptoe and Tessa M. Pollard
The acute physiological adjustments recorded during the performance of problem-solving or psychomotor tasks in the laboratory include: raised heart rate and blood pressure; alterations in cardiac output and peripheral vascular resistance; increased muscle tension and electrodermal (sweat gland) activity; disturbances in breathing pattern; and modifications in gastrointestinal activity and immune function. The best studied neurohormonal responses are those of the catecholamines (adrenaline and noradrenaline) and cortisol. Noradrenaline is the primary transmitter released by the nerves of the sympathetic branch of the autonomic nervous system. Adrenaline is released from the adrenal medulla following stimulation of the sympathetic nervous system, while activation of the pituitary gland by higher centres in the brain results in the release of cortisol from the adrenal cortex. These hormones support autonomic activation during stress and are responsible for other acute changes, such as stimulation of the processes that govern blood clotting, and the release of stored energy supplies from adipose tissue. It is likely that these kinds of response will also be seen during job stress, but studies in which work conditions are simulated, or in which people are tested in their normal jobs, are required to demonstrate such effects.
A variety of methods is available to monitor these responses. Conventional psychophysiological techniques are used to assess autonomic responses to demanding tasks (Cacioppo and Tassinary 1990). Levels of stress hormones can be measured in the blood or urine, or in the case of cortisol, in the saliva. The sympathetic activity associated with challenge has also been documented by measures of noradrenaline spillover from nerve terminals, and by direct recording of sympathetic nervous activity with miniature electrodes. The parasympathetic or vagal branch of the autonomic nervous system typically responds to task performance with reduced activity, and this can, under certain circumstances, be indexed through recording heart rate variability or sinus arrhythmia. In recent years, power spectrum analysis of heart rate and blood pressure signals has revealed wave bands that are characteristically associated with sympathetic and parasympathetic activity. Measures of the power in these wavebands can be used to index autonomic balance, and have shown a shift towards the sympathetic branch at the expense of the parasympathetic branch during task performance.
Few laboratory assessments of acute physiological responses have simulated work conditions directly. However, dimensions of task demand and performance that are relevant to work have been investigated. For example, as the demands of externally paced work increase (through faster pace or more complex problem solving), there is a rise in adrenaline level, heart rate and blood pressure, a reduction in heart rate variability and an increase in muscle tension. In comparison with self-paced tasks performed at the same rate, external pacing results in greater blood pressure and heart rate increases (Steptoe et al. 1993). In general, personal control over potentially stressful stimuli reduces autonomic and neuroendocrine activation in comparison with uncontrollable situations, although the effort of maintaining control over the situation itself has its own physiological costs.
Frankenhaeuser (1991) has suggested that adrenaline levels are raised when a person is mentally aroused or performing a demanding task, and that cortisol levels are raised when an individual is distressed or unhappy. Applying these ideas to job stress, Frankenhaeuser has proposed that job demand is likely to lead to increased effort and thus to raise levels of adrenaline, while lack of job control is one of the main causes of distress at work and is therefore likely to stimulate raised cortisol levels. Studies comparing levels of these hormones in people doing their normal work with levels in the same people at leisure have shown that adrenaline is normally raised when people are at work. Effects for noradrenaline are inconsistent and may depend on the amount of physical activity that people carry out during work and leisure time. It has also been shown that adrenaline levels at work correlate positively with levels of job demand. In contrast, cortisol levels have not been shown typically to be raised in people at work, and it is yet to be demonstrated that cortisol levels vary according to the degree of job control. In the “Air Traffic Controller Health Change Study”, only a small proportion of workers produced consistent increases in cortisol as the objective workload became greater (Rose and Fogg 1993).
Thus only adrenaline among the stress hormones has been shown conclusively to rise in people at work, and to do so according to the level of demand they experience. There is evidence that levels of prolactin increase in response to stress while levels of testosterone decrease. However, studies of these hormones in people at work are very limited. Acute changes in the concentration of cholesterol in the blood have also been observed with increased workload, but the results are not consistent (Niaura, Stoney and Herbst 1992).
As far as cardiovascular variables are concerned, it has repeatedly been found that blood pressure is higher in men and women during work than either after work or during equivalent times of day spent at leisure. These effects have been observed both with self-monitored blood pressure and with automated portable (or ambulatory) monitoring instruments. Blood pressure is especially high during periods of increased work demand (Rose and Fogg 1993). It has also been found that blood pressure rises with emotional demands, for example, in studies of paramedics attending the scenes of accidents. However, it is often difficult to determine whether blood pressure fluctuations at work are due to psychological demands or to associated physical activity and changes in posture. The raised blood pressure recorded at work is especially pronounced among people reporting high job strain according to the Demand-Control model (Schnall et al. 1990).
Heart rate has not been shown to be consistently raised during work. Acute elevations of heart rate may nevertheless be elicited by disruption of work, for example with breakdown of equipment. Emergency workers such as fire-fighters exhibit extremely fast heart rates in response to alarm signals at work. On the other hand, high levels of social support at work are associated with reduced heart rates. Abnormalities of cardiac rhythm may also be elicited by stressful working conditions, but the pathological significance of such responses has not been established.
Gastrointestinal problems are commonly reported in studies of job stress (see “Gastrointestinal problems” below). Unfortunately, it is difficult to assess the physiological systems underlying gastrointestinal symptoms in the work setting. Acute mental stress has variable effects on gastric acid secretion, stimulating large increases in some individuals and reduced output in others. Shift workers have a particularly high prevalence of gastrointestinal problems, and it has been suggested that these may arise when diurnal rhythms in the central nervous system’s control of gastric acid secretion are disrupted. Anomalies of small bowel motility have been recorded using radiotelemetry in patients diagnosed with irritable bowel syndrome while they go about their everyday lives. Health complaints, including gastrointestinal symptoms, have been shown to co-vary with perceived workload, but it is not clear whether this reflects objective changes in physiological function or patterns of symptom perception and reporting.