Interactions Between Dyspnea and the Brain Processing of Nociceptive Stimuli: Experimental Air Hunger Attenuates Laser-Evoked Brain Potentials in Humans

Just Breathe: Improving LEP Outcomes through Long Interval Breathing

Background: Laser-evoked potentials (LEPs) constitute an objective clinical diagnostic method used to investigate the functioning of the nociceptor system, including signaling in thin peripheral nerve fibers: Aδ and C fibers. There is preliminary evidence that phase locking LEPs with the breathing cycle can improve the parameters used to evaluate LEPs. Methods: We tested a simple breathing protocol as a low-cost improvement to LEP testing of the hands. Twenty healthy participants all underwent three variants of LEP protocols: following a video-guided twelve-second breathing instruction, watching a nature video, or using the classic LEP method of focusing on the hand being stimulated. Results: The breath protocol produced significantly shorter latencies as compared with the nature or classic protocol. It was also the least prone to artifacts and was deemed most acceptable by the subjects. There was no difference between the protocols regarding LEP amplitudes. Conclusions: Using a breathing video can be a simple, low-cost improvement for LEP testing in research and clinical diagnostics.

Dyspnoea-12 and Multidimensional Dyspnea Profile: Systematic Review of Use and Properties

CONTEXT

The Dyspnoea-12 (D-12) and Multidimensional Dyspnea Profile (MDP) were specifically developed for assessment of multiple sensations of breathlessness.

OBJECTIVES

This systematic review aimed to identify the use and measurement properties of the D-12 and MDP across populations, settings and languages.

METHODS

Electronic databases were searched for primary studies (2008-2020) reporting use of the D-12 or MDP in adults. Two independent reviewers completed screening and data extraction. Study and participant characteristics, instrument use, reported scores and minimal clinical important differences (MCID) were evaluated. Data on internal consistency (Cronbach's α) and test-retest reliability (intraclass correlation coefficient, ICC) were pooled using random effects models between settings and languages.

RESULTS

A total 75 publications reported use of D-12 (n = 35), MDP (n = 37) or both (n = 3), reflecting 16 chronic conditions. Synthesis confirmed two factor structure, internal consistency (Cronbach's α mean, 95% CI: D-12 Total = 0.93, 0.91-0.94; MDP Immediate Perception [IP] = 0.88, 0.85-0.90; MDP Emotional Response [ER] = 0.86, 0.82-0.89) and 14 day test-rest reliability (ICC: D-12 Total = 0.91, 0.88-0.94; MDP IP = 0.85, 0.70-0.93; MDP ER = 0.84, 0.73-0.90) across settings and languages. MCID estimates for clinical interventions ranged between -3 and -6 points (D-12 Total) with small variability in scores over 2 weeks (D-12 Total 2.8 (95% CI: 2.0 to 3.7), MDP-A1 0.8 (0.6 to 1.1) and six months (D-12 Total 2.9 (2.0 to 3.7), MDP-A1 0.8 (0.6 to 1.1)).

CONCLUSION

D-12 and MDP are widely used, reliable, valid and responsive across various chronic conditions, settings and languages, and could be considered standard instruments for measuring dimensions of breathlessness in international trials.

Air Hunger: A Primal Sensation and a Primary Element of Dyspnea

The sensation that develops as a long breath hold continues is what this article is about. We term this sensation of an urge to breathe "air hunger." Air hunger, a primal sensation, alerts us to a failure to meet an urgent homeostatic need maintaining gas exchange. Anxiety, frustration, and fear evoked by air hunger motivate behavioral actions to address the failure. The unpleasantness and emotional consequences of air hunger make it the most debilitating component of clinical dyspnea, a symptom associated with respiratory, cardiovascular, and metabolic diseases. In most clinical populations studied, air hunger is the predominant form of dyspnea (colloquially, shortness of breath). Most experimental subjects can reliably quantify air hunger using rating scales, that is, there is a consistent relationship between stimulus and rating. Stimuli that increase air hunger include hypercapnia, hypoxia, exercise, and acidosis; tidal expansion of the lungs reduces air hunger. Thus, the defining experimental paradigm to evoke air hunger is to elevate the drive to breathe while mechanically restricting ventilation. Functional brain imaging studies have shown that air hunger activates the insular cortex (an integration center for perceptions related to homeostasis, including pain, food hunger, and thirst), as well as limbic structures involved with anxiety and fear. Although much has been learned about air hunger in the past few decades, much remains to be discovered, such as an accepted method to quantify air hunger in nonhuman animals, fundamental questions about neural mechanisms, and adequate and safe methods to mitigate air hunger in clinical situations. © 2021 American Physiological Society. Compr Physiol 11:1449-1483, 2021.

Neuroergonomic and psychometric evaluation of full-face crew oxygen masks respiratory tolerance: a proof-of-concept study

INTRODUCTION

Preventing in-flight hypoxia in pilots is typically achieved by wearing oxygen masks. These masks must be as comfortable as possible to allow prolonged and repeated use. The consequences of mask-induced facial contact pressure have been extensively studied, but little is known about mask-induced breathing discomfort. Because breathlessness is a strong distractor and engages cerebral resources, it could negatively impact flying performances.

METHODS

Seventeen volunteers (age 20-32) rated respiratory discomfort while breathing with no mask and with two models of quick-donning full-face crew oxygen masks with regulators (mask A, mask B). Electroencephalographic recordings were performed to detect a putative respiratory-related cortical activation in response to inspiratory constraint (experiment 1, n=10). Oxygen consumption was measured using indirect calorimetry (experiment 2, n=10).

RESULTS

With mask B, mild respiratory discomfort was reported significantly more frequently than with no mask or mask A (experiment 1: median respiratory discomfort on visual analogue scale 0.9 cm (0.5-1.4), experiment 1; experiment 2: 2 cm (1.7-2.9)). Respiratory-related cortical activation was present in 1/10 subjects with no mask, 1/10 with mask A and 6/10 with mask B (significantly more frequently with mask B). Breathing pattern, sigh frequency and oxygen consumption were not different.

CONCLUSIONS

In a laboratory setting, breathing through high-end aeronautical full-face crew oxygen masks can induce mild breathing discomfort and activate respiratory-related cortical networks. Whether or not this can occur in real-life conditions and have operational consequences remains to be investigated. Meanwhile, respiratory psychometric and neuroergonomic approaches could be worth integrating to masks development and evaluation processes.

Dyspnoea in patients receiving noninvasive ventilation for acute respiratory failure: prevalence, risk factors and prognostic impact: A prospective observational study

Dyspnoea is a frequent and intense symptom in intubated patients, but little attention has been paid to dyspnoea during noninvasive mechanical ventilation in the intensive care unit (ICU).The objectives of this study were to quantify the prevalence, intensity and prognostic impact of dyspnoea in patients receiving noninvasive ventilation (NIV) for acute respiratory failure (ARF) based on secondary analysis of a prospective observational cohort study in patients who received ventilatory support for ARF in 54 ICUs in France and Belgium. Dyspnoea was measured by a modified Borg scale.Among the 426 patients included, the median (interquartile range) dyspnoea score was 4 (3-5) on admission and 3 (2-4) after the first NIV session (p=0.001). Dyspnoea intensity ≥4 after the first NIV session was associated with the Sequential Organ Failure Assessment Score (odds ratio (OR) 1.12, p=0.001), respiratory rate (OR 1.03, p=0.032), anxiety (OR 1.92, p=0.006), leaks (OR 2.5, p=0.002) and arterial carbon dioxide tension (OR 0.98, p=0.025). Dyspnoea intensity ≥4 was independently associated with NIV failure (OR 2.41, p=0.001) and mortality (OR 2.11, p=0.009), but not with higher post-ICU burden and altered quality of life.Dyspnoea is frequent and intense in patients receiving NIV for ARF and is associated with a higher risk of NIV failure and poorer outcome.

Interferences between breathing, experimental dyspnoea and bodily self-consciousness

Dyspnoea, a subjective experience of breathing discomfort, is a most distressing symptom. It implicates complex cortical networks that partially overlap with those underlying bodily self-consciousness, the experience that the body is one's own within a given location (self-identification and self-location, respectively). Breathing as an interoceptive signal contributes to bodily self-consciousness: we predicted that inducing experimental dyspnoea would modify or disrupt this contribution. We also predicted that manipulating bodily self-consciousness with respiratory-visual stimulation would possibly attenuate dyspnoea. Twenty-five healthy volunteers were exposed to synchronous and asynchronous respiratory-visual illumination of an avatar during normal breathing and mechanically loaded breathing that elicited dyspnoea. During normal breathing, synchronous respiratory-visual stimulation induced illusory self-identification with the avatar and an illusory location of the subjects' breathing towards the avatar. This did not occur when respiratory-visual stimulation was performed during dyspnoea-inducing loaded breathing. In this condition, the affective impact of dyspnoea was attenuated by respiratory-visual stimulation, particularly when asynchronous. This study replicates and reinforces previous studies about the integration of interoceptive and exteroceptive signals in the construction of bodily self-consciousness. It confirms the existence of interferences between experimental dyspnoea and cognitive functions. It suggests that respiratory-visual stimulation should be tested as a non-pharmacological approach of dyspnoea treatment.

The effect of light level, CO2 flow rate, and anesthesia on the stress response of mice during CO2 euthanasia

Euthanasia protocols are designed to mitigate the stress experienced by animals, and an environment that induces minimal stress helps achieve that goal. A protocol that is efficient and practical in a typical animal research facility is also important. Light intensity, isoflurane, and CO2 flow rate were studied for their impact on the stress response of mice during CO2 euthanasia. Behavior was observed and scored during euthanasia and serum corticosterone was measured immediately after death. Unsurprisingly, animals euthanized with a high-flow rate of CO2 became unconscious in the least amount of time, while animals euthanized with a low-flow rate required the most time to reach unconsciousness. There was a significant increase in anxious behaviors in animals in the isoflurane group (F1,12 = 6.67, P = 0.024), the high-flow rate CO2 group (F1,12 = 10.24, P = 0.007), and bright chamber group (F1,12 = 7.27, P = 0.019). Serum corticosterone was highest in the isoflurane group (124.72 ± 83.98 ng/ml), however there was no significant difference in corticosterone levels observed for the other study variables of light and flow-rate. A darkened chamber and low CO2 flow rates help to decrease stress experienced during CO2 euthanasia, while the use of isoflurane was observed to increase the stress response during euthanasia.

Relieving dyspnoea by non-invasive ventilation decreases pain thresholds in amyotrophic lateral sclerosis

BACKGROUND

Dyspnoea is a threatening sensation of respiratory discomfort that presents many similarities with pain. Experimental dyspnoea in healthy subjects induces analgesia. This 'dyspnoea-pain counter-irritation' could, in reverse, imply that relieving dyspnoea in patients with chronic respiratory diseases would lower their pain thresholds.

METHODS

We first determined pressure pain thresholds in 25 healthy volunteers (22-31 years; 13 men; handheld algometer), during unloaded breathing (BASELINE) and during inspiratory threshold loading (ITL). Two levels of loading were used, adjusted to induce dyspnoea self-rated at 60% or 80% of a 10 cm visual analogue scale (ITL6 and ITL8). 18 patients with chronic respiratory failure due to amyotrophic lateral sclerosis (ALS) were then studied during unassisted breathing and after 30 and 60 min of non-invasive ventilation-NIV30 and NIV60-(same dyspnoea evaluation).

RESULTS

In healthy volunteers, pressure pain thresholds increased significantly in the deltoid during ITL6 (p<0.05) and ITL8 (p<0.05) and in the trapezius during ITL8 (p<0.05), validating the use of pressure pain thresholds to study dyspnoea-pain counter-irritation. In patients with ALS, the pressure pain thresholds measured in the deltoid during unassisted breathing decreased by a median of 24.5%-33.0% of baseline during NIV30 and NIV60 (p<0.05).

CONCLUSION

Relieving dyspnoea by NIV in patients with ALS having respiratory failure is associated with decreased pressure pain thresholds. Clinical implications have yet to be determined, but this observation suggests that patients with ALS could become more susceptible to pain after the institution of NIV, hence the need for reinforced attention towards potentially painful diagnostic and therapeutic interventions.