Johan Bresseleers

Distorted Symptom Perception in Patients With Medically Unexplained Symptoms

The present study investigated differences in symptom perception between a clinical sample with medically unexplained symptoms (MUS) and a matched healthy control group. Participants (N = 58, 29 patients) were told that they would inhale different gas mixtures that might induce symptoms. Next, they went through 2 subsequent rebreathing trials consisting of a baseline (60 s room air breathing), a rebreathing phase (150 s, which gradually increased ventilation, PCO2 in the blood, and perceived dyspnea), and a recovery phase (150 s, returning to room air breathing). Breathing behavior was continuously monitored, and dyspnea was rated every 10 s. The within-subject correlations between dyspnea on the one hand and end-tidal CO2 and minute ventilation on the other were used to index the degree to which perceived dyspnea was related to specific relevant respiratory changes. The results showed that perceived symptoms were less strongly related to relevant physiological parameters in MUS patients than in healthy persons, specifically when afferent physiological input was relatively weak. This suggests a stronger role for top-down psychological processes in the symptom perception of patients with MUS.

Why do you sigh? Sigh rate during induced stress and relief

Whereas sighing appears to function as a physiological resetter, the psychological function of sighing is largely unknown. Sighing has been suggested to occur both during stress and negative emotions, such as panic and pain, and during positive emotions, such as relaxation and relief. In three experiments, sigh rate was investigated during short imposed states of stress and relief. Stress was induced by exposure to a loud noise stressor or by anticipation of it. Relief was induced by the end of the stressor or the anticipation that no stressor would follow. Breathing parameters were recorded continuously by means of the LifeShirt System. Results consistently showed that more sighing occurred during conditions of relief compared to conditions of stress.

Defense reactions to interoceptive threats: A comparison between loaded breathing and aversive picture viewing

Human fear research has mostly applied exteroceptive stimuli to induce fear. Interoceptive sensations however can also be very threatening and play a major role in a number of anxiety disorders. In this study, we compared affective responses to inspiratory resistive loads with those to aversive pictures. During repeated administrations of two loads, a light and a moderate one, and five aversive pictures we measured electrodermal activity, startle blink responses, subjective fear and ratings on valence, arousal and dominance. Results indicate that loads evoke affective reactions comparable or stronger than those evoked by the pictures. Startle data did not follow this pattern with an absence of startle potentiation during the moderate load, suggesting that fear potentiated startle does not occur when the background aversive stimulus is of an interoceptive nature.

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.

Feeling lightheaded: the role of cerebral blood flow.

Objective: The main aims of this study were a) to investigate the relationship between lightheadedness and cerebral blood flow velocity (CBFv) during hyperventilation-induced hypocapnia, and b) to investigate whether and why the relationship between lightheadedness and CBFv may change after several episodes of this sensation. Methods: Three hypocapnic and three normocapnic overbreathing trials were administered in a semirandomized order to healthy participants (N = 33). Each type of breathing trial was consistently paired with one odor. Afterward, participants were presented each odor once in two spontaneous breathing and in two normocapnic overbreathing trials. CBFv in the right middle cerebral artery was measured by transcranial Doppler ultrasonography (TCD). Also breathing behavior and self-reported lightheadedness were measured continuously. Each trial was followed by a symptom checklist. Results: Self-reported lightheadedness was closely related to changes in CBFv in the hypocapnic overbreathing trials. During the subsequent normocapnic trials, however, participants experienced more lightheadedness and “feeling unreal” to the odor that had previously been paired with hyperventilation-induced hypocapnia. These complaints were not accompanied by changes in end-tidal CO2 nor in CBFv. Conclusions: The results show that lightheadedness is associated with changes in CBFv but that after a few episodes, the underlying mechanism for this symptom may shift to perceptual-cognitive processes. These findings may help to understand why lightheadedness occurs during emotional distress and panic. In addition, altered cerebral blood flow is unlikely to play a primary precipitating role in recurrent symptoms of lightheadedness. Abbreviations: PNC = pseudoneurological complaints; IEI = idiopathic environmental illness; CBF = cerebral blood flow; CBFv = cerebral blood flow velocity; CS = conditioned stimulus; US = unconditional stimulus; TCD = Transcranial Doppler ultrasonography; MCA = middle cerebral artery; VAS = Visual Analogue Scale; Vi = inspiratory volume; FetCO2 = fractional end-tidal CO2; Vm = intensity weighted mean blood flow velocity in the right middle cerebral artery.

Anxiety, pCO2 and cerebral blood flow.

This study examined the effect of anxiety on cerebral blood flow at different levels of pCO2 in healthy participants (N=29). Three types of breathing were used to manipulate pCO2 in a within-subject threat-of-shock paradigm: spontaneous breathing, CO2-inhalation and hyperventilation resulting in normo-, hyper- and hypocapnia. Transcranial Doppler ultrasonography was used to measure CBF velocity (CBFv) in the right middle cerebral artery, while breathing behavior and end-tidal pCO2 were monitored. During normocapnia, elevated anxiety was clearly associated with increased CBFv. Consistent with the cerebral vasoconstrictive and vasodilating effects of, respectively, hypo- and hypercapnia, we observed a positive linear association between CBFv and pCO2. The slope of this association became steeper with increasing anxiety, indicating that anxiety enhances the sensitivity of CBFv to changes in pCO2. The findings may elucidate conflicting findings in the literature and are relevant for brain imaging relying on regional cerebral blood flow.