Rupert Hölzl

Heart rate changes as an autonomic component of the pain response

Autonomic variables have been recommended as measures of the affective-motivational component of the pain response in objective algesimetry. In the present study components of heart rate responses to painful heat stimuli and their relation to stimulus and sensation variables were analyzed. Twelve healthy subjects served. Sixty phasic stimuli of varying temperatures above and below pain threshold were delivered through a Marstock thermode in 1 session. Heart rate, respiration, and subjective stimulus ratings were recorded simultaneously. Phasic heat stimulation above and below pain threshold induced a tonic increase of the heart rate lasting up to more than 20 sec. High intensity stimulation generated steeper rises and greater mean increase than low intensity stimulation. In general, heart rate responses were more closely related to subjective sensation than to stimulus intensity. However, differential temporal analysis demonstrates that, until about 3 sec after stimulation, the autonomic response is determined solely by stimulus temperature, whereas, after approximately 6 sec, it is related only to subjective judgement. Accordingly, the heart rate responses reflect both a brief nocifensive reflex induced by the sensory component and, subsequently, a longer-lasting response which seems to be related to affective and/or cognitive evaluation. This separation of different stages of pain-processing by an autonomic indicator may be useful in clinical algesimetry.

Diurnal variations in pain perception and thermal sensitivity

&NA; Pain and thermal sensitivity thresholds in healthy volunteers were examined for diurnal variations. The subjects were 11 men aged between 22 and 27 years (x = 23.5, S.D. = 1.5). Data were collected for 2 days, with 7 measurements per day. To ensure the pain specificity of the results the subliminal modality i.e., thermal sensitivity thresholds to warm and cold stimuli, was investigated in addition to the threshold for perception of heat pain. Assessments were made on the right hand and foot, the stimuli being presented with a thermoelectric contact‐thermode. Despite the influence of variables other than time of day (45–56% of the total variance), diurnal variations were found for some subjects on the pain threshold measure (significant correlation between days and relatively high frequency of 24 h component in Fourier analysis spectra). However, they could not be demonstrated for the thermal sensitivity measures. The diurnal variations in pain perception thresholds did not have a consistent pattern over all subjects (Friedman test). The small diurnal variations with interindividual differences in the pattern are therefore not sufficient to explain the variations seen in clinical pain, but they may be useful in detecting pain modulators by investigating correlations.

ANXIETY INDUCED BY CARDIAC PERCEPTIONS IN PATIENTS WITH PANIC ATTACKS: A FIELD STUDY

In panic disorder bodily sensations appear to play an important role as a trigger for anxiety. In our psychophysiological model of panic attacks we postulate the following vicious circle: individuals with panic attacks perceive even quite small increases in heart rate and interpret these changes as being catastrophic. This elicits anxiety and a further increase in heart rate. To evaluate this model we conducted a field study of 28 subjects with panic attacks and 20 healthy controls. A 24 hr ambulatory ECG was recorded and the subjects were instructed to report any cardiac perceptions during this period and to rate the anxiety elicited by these perceptions. The incidence of cardiac perceptions was about the same in both groups, but only subjects with panic attacks reported anxiety associated with such perceptions. Analysis of the ECGs revealed that in both groups heart rate accelerations preceded cardiac perceptions. Following cardiac perceptions, the healthy controls showed a heart rate deceleration, whereas the subjects with panic attacks had a further acceleration. This heart rate increase after cardiac perceptions was positively related to the level of anxiety elicited by the perceptions. These results provide clear evidence in support of the vicious circle model of panic attacks.

SDT Analysis of Experimental Thermal Pain, with “Signal” and “No-Signal” Being Determined Psychophysically

In a signal-detection experiment, the effects of repeated pain stimulation and the induction of fear on pain thresholds and SDT parameters were studied. “Signal” and “no-signal” were not defined physically, but by means of an independent criterion as the primary sensations “pain” and “no-pain.” First, the relationship between sensation levels for “phasic” (short stimulus, used in the SDT procedure) and “tonic” (longer stimulus, used in the criterion measurement) heat stimuli was determined in 14 subjects. It was quadratic (polynomial regression) and sufficient to define the distinction between “signal/pain” and “no-signal/no-pain.” In the signal-detection experiment, a significant upward trend (adaptation) in threshold parameters, but no systematic change in the SDT parameters (discrimination ability and response bias) was found. Manipulation of anxiety by instructions caused unsystematic changes in discrimination ability. The procedure employed determines both the absolute strength of pain sensation and the ability to discriminate pain from no pain. These variables proved to be independent.

Surface Gastrograms as Measures of Gastric Motility

Since the early observations by Beaumont (1833), a number of studies have been reported on the psychophysiology of stomach secretory and electromotor activity. The latter, which serves as the necessary mixing and transport functions of the stomach for digestion, has been evaluated by various techniques. Beaumont used direct observation of a part of the stomach wall in a patient with a large fistula and found marked changes in secretory and contractile activity of the stomach under psychological influences including strong emotions and anticipation of meals. A century later Wolf and Wolff (1943) used this method in a more systematic study of their famous patient, Tom, to show that the motor activity of the fistulated stomach section changed with different emotional states. Whether hyper- or hypomotility was observed depended on the kind of emotion elicited (cf. Stern, Chapter 9, this volume).

Threshold Tracking for Assessment of Long-Term Adaptation and Sensitization in Pain Perception:

To assess temporal variations in the perception of “phasic” heat pain stimuli a psychophysical tracking procedure was developed that enables repeated assessment of the pain threshold at short intervals. This “double-tracking” procedure produces two tracking curves simultaneously, one that approaches the pain threshold gradually from above, the other from below. The threshold for phasic heat pain was measured in 80 tracking trials with stimuli at temperatures near the pain threshold. Concurrently, the threshold for “tonic” heat pain was determined after every 20 tracking trials with a stimulus adjustment procedure. Eleven healthy subjects (age: 26.4 yr. ± 6.0) participated in 2 sessions each. Phasic stimulation near the pain threshold did not produce any trends in either of the two threshold measures. Hence there was no long-term adaptation or sensitization. However, there were random variations (random walks) in the tracking curves, which we interpret as resulting from a stochastic relationship between stimulus and sensation. In agreement with other reports, discrimination seemed to be better at painful than at nonpainful temperatures.

Psychophysiological Indices of the Feeding Response in Anorexia Nervosa Patients

The question as to whether and how afferent signals from the gastrointestinal tract (GIT), and from the stomach in particular, regulate food intake has been a classic issue at least since Cannon and Washburn (1912). Despite later refutations of their concept of “hunger contractions” as the direct stimulus to eat, and some controversy between “centralists” and “peripheralists” in the animal literature, the role of feedback from the GIT in food intake regulation is now generally accepted (Konturek and Rosch 1976; Booth 1978). Neglecting effects of “conditioned hunger” and “appetites” for the moment, it seems that initiation of eating is governed mainly by hypothalamic centers according to humoral factors. Termination of meals, however, is under the control of a “fast feedback loop”, in which afferent information from the GIT about gastric filling and nutritional composition of food ingested serves as control variable in conjunction with olfactory and gustatory stimuli arising during oral stages of ingestion. Contents absorbed from the intestines and blood concentrations of nutritional substances provide second- and third-stage feedback signals with longer time constants. They mainly determine the length of interdigestive intervals and not termination of intake.

Concurrent changes in discrimination performance and criterion stability in thermal pain perception

FR Interpretation of sensory decision theory (SlYI!) data depends strongly on the assumption that discrimination and decision bias are influenced by separate psychological variables. This claim has recently been challenged. Using a new approach to define the individual cutoff between innocuous and noxious thermal stimuli, changes of discrimination performance and criterion stability during a two-hour experiment were studied. 14 volunteers were asked to rate 60 thermal cutaneous stimuli on a 9point rating scale. An anxiety inducing (N=7) vs a neutral instruction was applied before the last block of 20 trials. The Method of Subjective Sensitization (PAIN 1985,pp.369-378) was used to calculate a corrected estimate of the cutoff temperature between painful and nonpainful stimuli. This was based on data of a previous experiment deriving the psychometric function between tonic and phasic pain. The estimation was repeated every 20 trials. Analysis was performed separately for nonpainful (NP) and painful (P) stimuli. In the P condition discrimination quality and criterion stability both decreased over the session. In the NP condition an improvement of discrimination and a curvilinear pattern of criterion stability were found. Anxiety also had different effects depending on stimulus intensity (P:reduction, NP:improvement of discrimination). Standard SIYT-assumptions such as independence of discrimination and decision bias appear invalid in the context of pain experiments. Conflicting reports concerning the effects of psychological variables (eg anxiety) on these measures may be explained by ccsmon processes (eg attention, activation) determining both discrimination performance and the stability of the decision criterion.