Stephan Devriese

Media warnings about environmental pollution facilitate the acquisition of symptoms in response to chemical substances.

Objective Previous studies showed that somatic symptoms can be acquired in response to chemical substances using an associative learning paradigm, but only when the substance was foul smelling and not when it smelled pleasant. In this study, we investigated whether warnings about environmental pollution would facilitate acquiring symptoms, regardless of the pleasantness of the smell. Method One group received prior information framing the study in the context of the rapidly increasing chemical pollution of our environment. Another group received no prior information. Conditional odor stimuli (CS) were diluted ammonia (foul-smelling) and niaouli (neutral-positive smelling); the unconditional stimulus (UCS) was 10% CO2-enriched air. Each subject breathed one odor mixed with CO2 and a control odor mixed with air in 80-sec breathing trials. The type of odor mixed with CO2 was counterbalanced across participants. Next, the same breathing trials were administered without CO2. Breathing behavior was measured during each trial; subjective symptoms were assessed after each trial. Results Only participants who had been given warnings about environmental pollution reported more symptoms to the odor that had previously been associated with CO2, compared with the control odor. This was so for both the foul- and the pleasant-smelling odor. Symptom learning did not occur in the group that did not receive warnings. The elevated symptom level could not be accounted for by altered respiratory behavior, nor by experimental demand effects. Conclusions Raising environmental awareness through warnings about chemical pollution facilitates learning of subjective health symptoms in response to chemical substances.

Generalization of acquired somatic symptoms in response to odors: a pavlovian perspective on multiple chemical sensitivity.

Objective Somatic symptoms that occur in response to odors can be acquired in a pavlovian conditioning paradigm. The present study investigated 1) whether learned symptoms can generalize to new odors, 2) whether the generalization gradient is linked to the affective or irritant quality of the new odors, and 3) whether the delay between acquisition and testing modulates generalization. Methods Conditional odor stimuli (CS) were (diluted) ammonia and niaouli. One odor was mixed with 7.4% CO2-enriched air (unconditional stimulus) during 2-minute breathing trials (CS+ trial), and the other odor was presented with air (CS− trial). Three CS+ and three CS− trials were conducted in a semirandomized order (acquisition phase). The test phase involved one CS+-only (CS+ without CO2) and one CS− test trial, followed by three trials using new odors (butyric acid, acetic acid, and citric aroma). Half of the subjects (N = 28) were tested immediately, and the other half were tested after 1 week. Ventilatory responses were measured during and somatic symptoms were measured after each trial. Results Participants had more symptoms in response to CS+-only exposures, but only when ammonia was used as the CS+. Also, generalization occurred: More symptoms were reported in response to butyric and acetic acid than to citric aroma and only in participants who had been conditioned. Both the selective conditioning and the generalization effect were mediated by negative affectivity of the participants. The delay between the acquisition and test phases had no effect. Conclusions Symptoms that occur in response to odorous substances can be learned and generalize to new substances, especially in persons with high negative affectivity. The findings further support the plausibility of a pavlovian perspective of multiple chemical sensitivity.

Hyperventilation beyond fight/flight: respiratory responses during emotional imagery

Hyperventilation (HV) is often considered part of a defense response, implying an unpleasant emotion (negative valence) combined with a strong action tendency (high arousal). In this study, we investigated the importance of arousal and valence as triggers for HV responses. Forty women imagined eight different scripts varying along the arousal and valence dimensions. The scripts depicted relaxation, fear, depressive, action, and desire situations. After each trial, the imagery was rated for valence, arousal, and vividness. FetCO2, inspiratory and expiratory time, tidal volume, and pulse rate were measured in a nonintrusive way. FetCO2 drops and decreases in inspiratory and expiratory time occurred in all but the depressive and the relaxation scripts, suggesting that a defense conceptualization of hyperventilation is not always appropriate.

Acquiring Symptoms in Response to Odors: A Learning Perspective on Multiple Chemical Sensitivity

Abstract: In this chapter, a learning account is discussed as a potential explanation for the symptoms in multiple chemical sensitivity. Clinical evidence is scarce and anecdotal. A laboratory model provides more convincing results. After a few breathing trials containing CO2‐enriched air as an unconditioned stimulus in a compound with harmless odor substances as conditioned stimuli, subjective symptoms are elicited and respiratory behavior is altered by the odors only. Also, mental images can become conditioned stimuli to trigger subjective symptoms. The learning effects cannot be explained by a response bias or by conditioned arousal, and they appear to involve basic associative processes that do not overlap with aware cognition of the relationship between the odors and the CO2 inhalation. Learned symptoms generalize to new odors and they can be eliminated in a Pavlovian extinction procedure. In accordance with clinical findings, neurotic subjects and psychiatric cases are more vulnerable to learning subjective symptoms in response to odors. Consistent with a learning account, cognitive‐behavioral treatment techniques appear to produce beneficial results in clinical cases. Several criticisms and unresolved questions regarding the potential role of learning mechanisms are discussed.

Accuracy of respiratory symptom perception in persons with high and low negative affectivity

Accuracy of respiratory symptom perception was investigated in different contexts in participants (N = 56) scoring high or low for negative affectivity (NA). Within subject-correlations were calculated between minute ventilation (frequency per minute × tidal volume) and the subjective symptom ‘faster and/or deeper breathing’ across 10 subsequent breathing trials of 2 min with varying air mixtures, containing fresh or foul smelling odours and/or 5.5% CO2. Half the participants were given a positive information frame for the sensations (‘some air mixtures may induce a pleasantly arousing feeling, like when being in love’), whereas the other half was given a negative frame (‘some air mixtures may induce feelings of being anxious and distressed’). Interoceptive accuracy was overall fairly high (r = 0.56–0.74), but it dropped considerably (r = 0.27), when bodily sensations were induced in high NA persons in a negative information frame (interaction, p < 0.005). Interoceptive accuracy appears low when persons with high NA are in situations characterised by negative affective cues.

Imagined risk of suffocation as a trigger for hyperventilation.

Objective: Although hyperventilation has been hypothesized to play a role in many pathologies, its critical triggers remain poorly understood. The present experiment aimed to test whether stronger hyperventilation responses occur in response to suggested risk of suffocation compared with other fearful situations in high- and low-trait anxious women. Methods: Fractional end-tidal CO2-concentration (FetCO2), respiratory frequency, and inspiratory volume were measured nonintrusively in high- (n = 24) and low- (n = 24) trait anxious women during imagery of 3 fear, 1 tension, 1 depressive, and 3 relaxation scripts. The fear scripts were equal in ratings of unpleasantness and arousal but differed regarding the inclusion of suggested risk of suffocation and entrapment. After each imagery trial, participants rated the emotional dimensions of pleasantness, arousal, and dominance and the vividness of their imagery. Results: Decreases in FetCO2 occurred in all fear scripts. High-trait anxious women showed a stronger reduction in FetCO2 compared with low-trait anxious women during the fear script suggesting risk of suffocation but not during the other fear scripts. This effect was unrelated to any of the self-reported fear ratings. Self-reported fear of entrapment was associated with an overall lower FetCO2 but not with enhanced reactivity to imagined entrapment. Conclusion: High-trait anxiety is associated with stronger respiratory responsivity to imagined risk of suffocation and may constitute a specific vulnerability factor for the development of panic disorder and claustrophobia. FetCO2 = fractional concentration of end-tidal carbon dioxide; fr = respiratory frequency; Vi = inspiratory volume; CPS = checklist for psychosomatic symptoms; STAI-T = trait version of the state-trait anxiety inventory; FS = fear of suffocation; FR = fear of restriction.

Critical conditions for hyperventilation responses. The role of autonomic response propositions during emotional imagery.

Hyperventilation is often conceived of as part of a fight-or-flight response, triggered by situations with high arousal and negative valence. However, a previous study using emotional imagery found hyperventilation responses during imagery of high-arousal scenes regardless of their valence. Those imagery scripts contained suggestions of autonomic activity, which may have partly induced or enhanced the hyperventilatory responsivity. The present study used four emotional scripts—depicting relaxing, fearful, depressive, and pleasant situations—without suggestions of autonomic or respiratory responses. After each imagery trial, participants rated their imagery for valence, arousal, and vividness. Fractional end-tidal carbon dioxide (FetCO2), inspiratory and expiratory time, tidal volume, and pulse rate were measured in a non-intrusive way. Results showed significant FetCO2 drops during the fearful and pleasant scripts. However, this effect was much smaller compared to imagery scripts with autonomic response propositions. Participants imagining scripts without autonomic response information found it harder to imagine the scripts vividly and reported lower levels of subjective arousal.

Acquired lightheadedness in response to odors after hyperventilation.

Objective: This study aimed to investigate whether lightheadedness in response to odors could be acquired through previous associations with hyperventilation-induced hypocapnia. Methods: Diluted ammonia and acetic acid served as conditional odor cues (CSs) in a differential associative learning paradigm. Hyperventilation-induced hypocapnia (unconditional stimulus [US]) was used to induce lightheadedness. In a training phase, participants (n = 28) performed three hypocapnic and three normocapnic overbreathing trials of 60 seconds each. One odor was consistently paired with the hypocapnic overbreathing (CS+); the other (control) odor was paired with normocapnic overbreathing (CS−). In the test phase, each odor was presented once during spontaneous breathing and once during normocapnic overventilation. Lightheadedness was assessed online during each breathing trial, which was followed by an extensive hyperventilation symptom checklist. Fractional end-tidal CO2, breathing frequency, and inspiratory volume were measured throughout the experiment. Results: In the test phase, participants experienced lightheadedness more quickly in response to the odor that had been paired with hypocapnic overbreathing compared with the control odor. They also scored higher on the symptom “feeling unreal.” Conclusion: Lightheadedness in response to odors can be acquired easily. The present results may help to elucidate the paradox that both avoidance and exposure to chemicals seem to be effective in reducing symptoms in idiopathic environmental illness. IEI = idiopathic environmental illness; NPC = neuropsychological complaints; CS = conditional stimulus; US = unconditional stimulus; Ti = inspiratory time; Te = expiratory time; Vi = inspiratory volume; Ve = expiratory volume; FETCO2 = fractional end-tidal CO2; CBF = cerebral blood flow.

Symptom Learning in Response to Odors in a Single Odor Respiratory Learning Paradigm

Among the many different explanations given for multiple chemical sensitivity (MCS), classical conditioning has often been suggested and experimental evidence consistent with such an explanation is accumulating.1 Most of this experimental evidence was acquired using a differential respiratory conditioning paradigm with odors as conditioned stimuli (CS) and CO2-enriched air (e.g., 7.5%) as the unconditioned stimulus (US). This operationalization may mimic the effects of a toxic exposure or occasional (stress-induced) hyperventilation (US) in an odorous context (CS). The differential paradigm uses two distinct innocuous odors, implying two types of breathing trials for each subject: one containing an odor mixed with CO2enriched air and the other mixed with room air (the combination of the specific odor with CO2 or air is counterbalanced between subjects). In the test phase, breathing trials are administered without CO2 and symptoms to the odors alone are registered. This paradigm typically showed elevated symptoms to the odor that was previously mixed with CO2. However, the effect only occurred when the conditioned odor was unpleasant (ammonia or butyric acid) and not when it was neutral/pleasant (niaouli).2–4 Since a differential paradigm induces a form of discrimination learning, we wanted to extend our findings to a standard conditioning paradigm, pairing one single odor with the aversive event (CO2 inhalation) during the acquisition phase. Subsequently, the odor was presented alone and symptoms were measured. The conditioning effect was tested between subjects using different control conditions.5

Contingency awareness in a symptom learning paradigm: Necessary but not sufficient?

In previous studies, we found that bodily symptoms can be learned in a differential conditioning paradigm, using odors as conditioned stimuli (CSs) and CO2-enriched air as unconditioned stimulus (US). However, this only occurred when the odor CS had a negative valence (a selective conditioning effect), and tended to be more pronounced in persons scoring high for Negative Affectivity (NA). This paper considers the necessity and/or sufficiency of awareness of the CS-US contingency in three studies using this paradigm. The relation between contingency awareness and the selective conditioning effect, and between contingency awareness and NA was also considered. Both self reported symptoms and respiratory physiology served as dependent variables. A learning effect on symptoms was found only for participants aware of the CS-US contingency, but not all participants reporting contingency awareness showed a learning effect. No conditioning effects appeared on the physiological measures. Also contingency awareness did not account for the selective conditioning effect, and did not interact with NA. Overall, the necessity but insufficiency hypotheses can only be withhold for group data and not for individual data.