“Fear and Awe”: How important is stress after all?

Kati Thieme, PhD 
Institute of Medical Psychology, Philipps – University Marburg, Germany

The interaction of pain and fear as an etiological factor has been observed in patients with chronic pain, in psychosocial [1-5], psychophysiological [6, 7], psychophysical [8], endocrine [9, 10], genetic [11, 12] and central responses [13, 14], however inconsistent results suggest a heterogeneity in stress responses of chronic pain. Biopsychological mechanisms such as classical [15] and operant learning [16, 17] of different stress responses will be discussed.

The theoretical base of the stress influence on diseases was proposed by Lacey & Lacey “The principle of relative [stress] response specificity [is] formulated as follows: For a given set of autonomic functions (hence the term relative), subjects tend to respond with idiosyncratic pattern of autonomic activation in which maximal activation is shown by the same physiological function, whatever the stress.” ([18], p 50).

Our study with 120 female fibromyalgia patients examined the relationship of psychophysiological response patterns with psychological characteristics and comorbid mental disorders [7]. Surface electromyographic data, systolic and diastolic blood pressure (BP), heart rate (HR), and skin conductance levels were recorded continuously during baseline, stress, and relaxation tasks. Cluster analysis revealed 4 subgroups of patients who differed on pain intensity, cognitive, affective, and behavioural responses to pain and stress (Table 1):

FM patients with hyperreactive BP (I) and increased electrodermal stress response (III) displayed the highest number of pain behaviours as expression of fear, in contrast to patients with hyporeactive BP (II). The results suggest that the stress response in patients with high BP and high sudomotor response may be related to operant learning that reinforces pain behaviour expression[7]. Several studies show that baroreceptor response operantly modified by phasic BP changes [19, 20]. It is assumed that a long-term stress associated with adrenergic dysregulation [10] increases both systolic and diastolic BP and a reduction of BP and pressure variability in the carotid sinus. Since baroreceptors are activated only by changes of pressure intensities, reduced BP variability leads to a diminished baroreflex sensitivity that provokes a reduced regulatory activity of the dorsal medial nucleus tractus solitarii (dmNTS) reflex arcs (Fig. 1) that regulate pain, blood pressure and fear [21, 22]. The diminished solitary pathway and the disruption of emotion and emotional modulation of pain and nociception may contribute to chronic pain [14].
These findings contrast with those from patients with a hypotensive stress response that show reduced sympathetically mediated profiles at rest and in response to stress. This pattern is consistent with a relative enhancement in baroreceptor buffering capacity, which mediates a reduction in pain perception and diminished psychological and functional distress [7]. Patients with hypotensive stress responses display an overlap of thermoregulation and pain modification with lower body temperatures, lower metabolic rates, and lower circulating cortisol/corticosterone in response to stress [23].
The identification of the mechanisms that contribute to these group differences will further our understanding of the mechanisms involved in the development and maintenance of chronic pain and suggest differential treatment strategies [16, 24-26].

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Figure 1: NTS reflex arcs

Figure 1: NTS reflex arcs