The Effects of Repeated Dyspnea Exposure on Response Inhibition

Repeated exposure to aversive sensations differentially affects neural gating and bodily perception

Habituation to bodily sensations is highly relevant for the experience of chronic bodily symptoms, but the neural mechanisms behind diminished habituation are currently unclear. One potentially relevant mechanism is neural gating (NG), reflected as the short-term suppression of cortical responses to redundant stimuli. We investigated the effects of repeated exposure to aversive sensations on NG and subjective perception in 91 healthy adults, by measuring their NG of respiratory and electrocutaneous stimuli using electroencephalography during two sessions separated by one week, in addition to their self-report of intensity and unpleasantness of the sensations. To test for intra- and cross-modal effects, 1/2 participants returned three times in the intervening week to experience additional aversive respiratory stimulation, while the other 1/2 received aversive electrocutaneous stimulation. Participants reported lower unpleasantness of all sensations in the final session (intra- and cross-modal habituation). NG was improved for respiratory sensations only in the group receiving additional respiratory stimulation (intra-modal habituation). We found no relationships between NG and perceptual habituation, adding to the mixed results on the relevance of NG to perceptual changes in healthy adults. Future research with clinical populations and different methods is encouraged to further clarify the mechanisms behind neural gating and diminished symptom habituation.

The effects of age on dyspnea and respiratory mechanical and neural responses to exercise in healthy men

The respiratory muscle pressure generation and inspiratory and expiratory neuromuscular recruitment patterns in younger and older men were compared during exercise, alongside descriptors of dyspnea. Healthy younger (n = 8, 28 ± 5 years) and older (n = 8, 68 ± 4 years) men completed a maximal incremental cycling test. Esophageal, gastric (Pga ) and transdiaphragmatic pressures, and electromyography (EMG) of the crural diaphragm were measured using a micro-transducer and EMG catheter. EMG of the parasternal intercostals, sternocleidomastoids, and rectus abdominis were measured using skin surface electrodes. After the exercise test, participants completed a questionnaire to evaluate descriptors of dyspnea. Pga at end-expiration, Pga expiratory tidal swings, and the gastric pressure-time product (PTPga ) at absolute and relative minute ventilation were higher (p < 0.05) for older compared to younger men. There were no differences in EMG responses between older and younger men. Younger men were more likely to report shallow breathing (p = 0.005) than older men. Our findings showed younger and older men had similar respiratory neuromuscular activation patterns and reported different dyspnea descriptors, and that older men had greater expiratory muscle pressure generation during exercise. Greater expiratory muscle pressures in older men may be due to compensatory mechanisms designed to offset increasing airway resistance due to aging. These results may have implications for exercise-induced expiratory muscle fatigue in older men.

Impact of inspiratory threshold loading on brain activity and cognitive performances in healthy humans

In healthy humans, inspiratory threshold loading deteriorates cognitive performances. This can result from motor-cognitive interference (activation of motor respiratory-related cortical networks vs. executive resources allocation), sensory-cognitive interference (dyspnea vs. shift in attentional focus), or both. We hypothesized that inspiratory loading would concomitantly induce dyspnea, activate motor respiratory-related cortical networks, and deteriorate cognitive performance. We reasoned that a concomitant activation of cortical networks and cognitive deterioration would be compatible with motor-cognitive interference, particularly in case of a predominant alteration of executive cognitive performances. Symmetrically, we reasoned that a predominant alteration of attention-depending performances would suggest sensory-cognitive interference. Twenty-five volunteers (12 men; 19.5-51.5 years) performed the Paced Auditory Serial Addition test (PASAT-A and B; calculation capacity, working memory, attention), the Trail Making Test (TMT-A, visuospatial exploration capacity; TMT-B, visuospatial exploration capacity and attention), and the Corsi block-tapping test (visuospatial memory, short-term and working memory) during unloaded breathing and inspiratory threshold loading in random order. Loading consistently induced dyspnea and respiratory-related brain activation. It was associated with deteriorations inPASAT A (52 [45.5;55.5] (median [interquartile range]) to 48 [41;54.5], p=0.01), PASAT B (55 [47.5;58] to 51 [44.5;57.5], p=0.01), and TMT B (44s [36;54.5] to 53s [42;64], p=0.01), but did not affect TMT-A and Corsi. The concomitance of cortical activation and cognitive performance deterioration is compatible with competition for cortical resources (motor-cognitive interference), while the profile of cognitive impairment (PASAT and TMT-B but not TMT-A and Corsi) is compatible with a contribution of attentional distraction (sensory-cognitive interference). Both mechanisms are therefore likely at play.

Targeting excessive avoidance behavior to reduce anxiety related to asthma: A feasibility study of an exposure-based treatment delivered online

There is an established relationship between anxiety and asthma, which is associated with poor health outcomes. Most previous cognitive behavior therapies (CBT) have focused on comorbid panic disorder whereas anxiety related to asthma may rather be illness-specific. The feasibility of an online CBT targeting avoidance behavior in anxiety related to asthma was evaluated, using a pretest-posttest design. Thirty participants with self-reported anxiety related to asthma were offered an eight-week treatment with therapist support. Mean adherence was good (80% of content), and most participants (89%) reported adequate relief after treatment. Catastrophizing about asthma (CAS), assessed at 2 months after treatment, improved significantly with a large effect size (Cohen's d = 1.52). All secondary outcomes, including asthma control, avoidance behavior, fear of asthma symptoms and quality of life, improved significantly with moderate to large effect sizes (d: 0.40-1.44). All improvements were stable at 4 months follow up. Weekly ratings showed that a decrease in avoidance behavior predicted a decrease in CAS the following week throughout the treatment period. We conclude that CBT targeting avoidance behavior is a feasible treatment for anxiety related to asthma. The results justify investigation of efficacy and mechanisms of change in a randomized controlled trial. ClinicalTrials.gov, ID: NCT03486756.

The test-retest reliability of the respiratory-related evoked potential

The respiratory-related evoked potential (RREP) is an established technique to study the neural processing of respiratory sensations. We examined the test-retest reliability of the RREP during an unloaded baseline condition (no dyspnea) and an inspiratory resistive loaded breathing condition (dyspnea) over a one-week period. RREPs were evoked by short inspiratory occlusions (150 ms) while EEG was continuously measured. The mean amplitudes of the RREP components Nf, P1, N1, P2, and P3 were studied. For the no dyspnea condition, moderate test-retest reliability for Nf (intraclass correlation coefficient ICC: 0.73) and P1 (ICC: 0.74), good test-retest reliability for N1 (ICC: 0.89) and P3 (ICC: 0.76), and excellent test-retest reliability for P2 (ICC: 0.92) was demonstrated. For the dyspnea condition, moderate test-retest reliability was found for Nf (ICC: 0.69) and P1 (ICC: 0.57) and good test-retest reliability for N1 (ICC: 0.77), P2 (ICC: 0.84), and P3 (ICC: 0.77). This indicates that the RREP components Nf, P1, N1, P2, and P3, elicited by inspiratory occlusions, show adequate reliability in a test-retest study design with or without parallel sustained resistive load-induced dyspnea.

Experimental dyspnoea interferes with locomotion and cognition: a randomised trial

BACKGROUND

Chronic respiratory diseases are associated with cognitive dysfunction, but whether dyspnoea by itself negatively impacts on cognition has not been demonstrated. Cortical networks engaged in subjects experiencing dyspnoea are also activated during other tasks that require cognitive input and this may provoke a negative impact through interference with each other.

METHODS

This randomised, crossover trial investigated whether experimentally-induced dyspnoea would negatively impact on locomotion and cognitive function among 40 healthy adults. Crossover conditions were unloaded breathing or loaded breathing using an inspiratory threshold load. To evaluate locomotion, participants were assessed by the Timed Up and Go (TUG) test. Cognitive function was assessed by categorical and phonemic verbal fluency tests, the Trail Making Tests (TMTs) A and B (executive function), the CODE test from the Wechsler Adult Intelligence Scale (WAIS)-IV (processing speed) and by direct and indirect digit span (working memory).

RESULTS

The mean time difference to perform the TUG test between unloaded and loaded breathing was -0.752 s (95% CI -1.012 to -0.492 s) (p<0.001). Executive function, processing speed and working memory performed better during unloaded breathing, particularly for subjects starting first with the loaded breathing condition.

CONCLUSION

Our data suggest that respiratory threshold loading to elicit dyspnoea had a major impact on locomotion and cognitive function in healthy adults.