Attentional and physiological characteristics of patients with dental anxiety

Abstract

Twenty patients with dental anxiety were investigated while seated in a dental chair in a dental clinic. Heart rate (HR), heart rate variability (HRV), and skin conductance level (SCL) were recorded while the patients were exposed to scenes of dental treatment as well as a Stroop attentional task. Results showed an attentional bias with longer manual reaction times (RT’s) to the incongruent compared to the congruent color words as well as the threat compared to the neutral words. Longer RT’s to the incongruent and the threat words were found in the low HRV patients compared to the high HRV patients. Furthermore, all patients showed an increase in HR during exposure and the Stroop task compared to baseline. The HRV showed a decrease during the exposure and the Stroop task compared to baseline. HR and HRV did not differ between exposure and the Stroop task. Moreover, HR and HRV did not return to baseline levels during the recovery period. The SCL showed an increase from baseline to exposure, from exposure to the Stroop task and a decrease in the recovery phase. Results showed the importance of vagal cardiac control in attentional, emotional, and physiological processes in patients suffering from dental fear.

Introduction

Dental anxiety is a common disorder in Western societies. In a randomly selected sample of 1420 Canadian subjects 16.4% suffered from dental anxiety (Locker, Liddell, & Shapiro, 1999). In a Norwegian study using the same questionnaire 19% of 18-year-olds reported high levels of dental anxiety (Skaret, Raadal, Berg, & Kvale, 1998). These individuals have been reported to have greater avoidance of dental treatment, greater tendency to somatization, and greater sensitivity to dental stimuli compared to an average dental population (Kaufman, Bauman, Lichtenstein, Adi, et al., 1991). These individuals are also at higher risk for poor oral health including tooth decay and poorer oral function (Hagglin, Berggren, Hakeberg, & Ahlqwist, 1996). Moreover, patients with dental anxiety even report elevated scores on a wide range of psychological complaints as measured by the Symptom Checklist 90-Revised (Aartman, de Jongh, & van der Meulen, 1997). Thus dental phobia is an anxiety disorder that has important health implications.

Understanding of the complex mix of cognitive, emotional, and physiological factors associated with anxiety disorders is aided by a comprehensive approach. A model linking vagal regulation of heart rate (HR) to organism adaptability has recently been suggested by Thayer and Lane (2000). These researchers propose that vagally-mediated HRV is an index of the central-peripheral feedback capacity of the organism. This capacity will affect the subject’s ability to allocate psychophysiological resources to meet environmental demands (see also Thayer & Lane, in press). Vagally-mediated HRV has been associated with information processing (Porges, 1992), affective processing (Thayer & Lane, 2000), and physiological regulation (Levy, 1990). Thus, vagal activity might be of importance in the excessive fear associated with dental anxiety.

The most common way of interpreting the physiological symptoms described by patients has been as activation of the sympathetic branch of the autonomic nervous system (ANS). For example, increased HR has often been interpreted as an indication of sympathetic activation. However, recent studies have put more emphasis on parasympathetic processes, and this is especially true for cardiovascular responses. Increased HR associated with stress and anxiety has been shown to be related to decreased parasympathetic tone in numerous situations (Friedman & Thayer, 1998). Importantly, persons with persistent anxiety have been found to have low tonic HRV (Friedman & Thayer, 1998; Thayer, Friedman, & Borkovec, 1996). Moreover, decreased HRV has been associated with attentional dysregulation and increased symptoms in some populations (Friedman et al., 1993, Thayer et al., 2000).

The cardiovascular system can also be used to index information processing of stimuli that differ in emotional content. It has been shown that presenting nonthreat and threat words to patients suffering from generalized anxiety disorder (GAD) resulted in different phasic HR responses compared to nonanxious controls (Thayer et al., 2000). An attentional deficit occurred in GAD in that such individuals were not able to habituate to nonthreat words. That is, they showed a phasic HR-deceleration to both the first and last presentation of a neutral word. HR deceleration is associated with the orienting response and has been related to tuning of sensory organs and information uptake from the environment (Lacey, 1967). In addition, GAD patients showed a change from an HR deceleration (orienting response; OR) to the first threat word to an HR acceleration to the last threat word whereas the nonanxious controls showed an OR throughout. HR-acceleration is associated with the defense reaction because it is related to increased sensory thresholds and in that sense rejection of information from the environment (Lacey, 1967). Furthermore, less tonic HRV was found in GAD patients compared to normal controls. Importantly, tonic HRV was correlated with the attention-related phasic HR responses in that study.

Thayer et al. (2000) concluded that the cardiovascular system was sensitive to information processing of threat and nonthreat stimuli and that GAD patients showed an attentional deficiency manifested in their inability to ignore neutral stimuli. Attentional bias has also been found for threat stimuli in other clinical samples (Cooper, Anastasiades, & Fairburn, 1992; Mathews & MacLeod, 1986). Johnsen, Laberg, Cox, Vaksdal, and Hugdahl (1994), using a modified version of the Stroop (1935) test, found that alcoholics had longer verbal reaction time (RT) in color naming alcohol related words than neutral words of equal length. This was interpreted as an attentional bias for alcoholics to automatically and involuntarily draw their attention to alcohol related stimuli. The same effect occurred in smokers for smoking related words (Johnsen, Thayer, Laberg, & Asbjørnsen, 1997). Active smokers performed more poorly on the color naming task than abstinent smokers and nonsmokers. Since smoking is associated with decreased HRV (Hayano et al., 1990; Nabors–Oberg, Thayer, Niaura, & Sollers, 2002) it was speculated that the effect could be caused by lowered vagal tone in the active smokers compared to the other groups. Low HRV represents a low degree of neurovisceral integration in the organism and decreased ability to organize resources to meet demands such as in an attentional task (Porges, 1992, Thayer & Lane, 2000). Importantly, such attentional bias may serve to perpetuate the fear associated with the threat stimuli and lead to the disorder being resistant to treatment as well as to an increased risk of relapse (Johnsen et al., 1997). Thus, decreased attentional regulation and decreased HRV may be linked to maladaptive behavior.

Therefore, it was hypothesized that if patients with dental anxiety have an attentional bias towards threatening stimuli in their surroundings, we would not only expect longer RT’s to incongruent color words compared to congruent color words, but also longer RT’s to threat words compared to neutral words. If vagal tone is related to attentional processes, patients with low HRV would show longer RT’s in the attentional task compared to patients with high HRV.

Ecological validity remains a concern in anxiety research. One problem with most clinical studies is the use of artificial laboratory settings. It would be advantageous to conduct well-controlled experiments in the natural setting where the phenomena of interest occur. The present study aimed to further investigate the relationship between attentional, emotional and physiological aspects of maladaptive behavior in subjects with dental anxiety during in vitro exposure to dental treatment as well as during an attentional task while seated in a dental chair in a dental clinic. Measuring reactions in a natural setting may give us more valid information and lead to greater generalizability of the findings than laboratory settings or mere self-report of reactions.

Since previous research has shown that HR increases and HRV decreases in anxious persons exposed to threat stimuli and these responses do not recover to baseline levels after the stimuli are removed (Lyonfields, Borkovec, & Thayer, 1995), the same pattern was expected in the present study. Thus the following predictions were made:

• Longer manual RT to Stroop and threat words compared to neutral words.

• Longer manual RT on Stroop and threat words in the low HRV compared to the high HRV group.

• An increase in HR from baseline to exposure and attentional task.

• If vagal influences caused the change in observed HR, it was hypothesized that HRV would decrease during both exposure and the attentional task compared to baseline and not return to baseline levels during recovery.

• If sympathetic arousal caused the HR changes, then a corresponding pattern to HR changes would be observed in specific sympathetic measures like skin conductance level (SCL).