The effect of trait self-control on dyspnoea and tolerance to a CO2 rebreathing challenge in healthy males and females

Biological sex differences in the perception of CO2-induced air hunger

INTRODUCTION

Biological sex may mediate 'dyspnoea' during submaximal exercise, but whether it mediates air hunger (AH), a highly unpleasant form of dyspnoea, remains unclear.

METHOD

Forty healthy adults (twenty females) completed 6-min of quiet breathing (rest) followed by a hyperoxic CO2 rebreathing task to evoke AH. AH intensity (AH-I) and unpleasantness (AH-U) were measured every 30-s. The Multidimensional Dyspnoea Profile (MDP) was administered after CO2 rebreathing.

RESULTS

Compared to males, AH-I and AH-U thresholds occurred at lower PETCO2 in females (AH-I: 44.15 ± 2.81 vs 48.90 ± 4.47 mmHg, P < 0.001; AH-U: 43.86 ± 2.57 vs 47.59 ± 2.75 mmHg, P < 0.001) and after a smaller increase in PETCO2 above resting PETCO2 (AH-I: 7.04 ± 2.63 vs 10.08 ± 5.28 mmHg, P = 0.027; AH-U: 6.75 ± 2.22 vs 8.77 ± 2.99 mmHg, P = 0.020). AH-I and AH-U were higher in females than males at standardised absolute V̇E of 25, 30 and 35 L/min (P < 0.05). AH-U, but not AH-I, remained higher (main effect of sex, P = 0.026) in females than males at standardised relative V̇E of 20, 25, and 30 % MVV. More females (n = 9) than males (n= 4) terminated CO2 rebreathing due to maximal AH perception (P = 0.001). Compared to males, females reported greater intensities of 'mental effort/concentration' (7 ± 3 vs 4 ± 3), 'tight/constricted lungs' (6 ± 3 vs 2 ± 2), and 'breathing work/effort' (6 ± 2 vs 4 ± 3) (all P < 0.05) on the MDP.

CONCLUSION

Our findings suggest that sex differences exist in the perception of AH, which are not entirely accounted for by sex differences in ventilatory capacity.

Prior self-control exertion decreases pre-frontal cortex oxygenation during a CO2 rebreathing challenge but does not affect perceptions of dyspnoea or tolerance time

INTRODUCTION

Dyspnoea perception is influenced by a complex interplay of physiological, psychological, and environmental factors. Recently, we showed that males with high trait self-control experience less dyspnoea and persist for longer in a carbon dioxide (CO2) rebreathing challenge than males with low trait self-control. As self-control can also vary within individuals (state self-control), the primary aim of the present study was to investigate whether prior self-control exertion influenced perceptions of dyspnoea and tolerance of a CO2 rebreathing challenge in healthy young males. We also used functional near-infrared spectroscopy (fNIRS) to assess haemodynamic activity of the pre-frontal cortex (PFC) which is a region of interest (ROI) in dyspnoea research, and the primary brain region associated with exertion of self-control.

METHODS

In a within-subjects design, fifteen healthy young males completed an easy (congruent) Stroop task (control condition) and a difficult (incongruent) Stroop task (prior self-control exertion, experimental condition) followed by a CO2 rebreathing challenge until the limit of tolerance. Changes in oxyhaemoglobin (ΔO2Hb) and deoxyhaemoglobin (ΔHHb) were assessed continuously in the Stroop task and CO2 rebreathing challenge. During the CO2 rebreathing challenge, dyspnoea intensity and unpleasantness were rated every 30 s.

RESULTS

Prior self-control exertion did not affect perceptions of dyspnoea or tolerance time in the CO2 rebreathing challenge (all P > 0.05). ΔO2Hb from baseline was higher in the left (+38 %) and right (+44 %) pre-frontal cortices during the difficult Stroop task than the easy Stroop task (both P < 0.05). During the subsequent CO2 rebreathing challenge, ΔO2Hb was attenuated following prior self-control exertion in the left PFC.

CONCLUSIONS

Although prior self-control exertion decreased pre-frontal cortex oxygenation during a subsequent CO2 rebreathing challenge, there was no change in tolerance time or perceptions of dyspnoea.

Multidimensional assessment of exertional dyspnea in young healthy males and females who select unsatisfied inspiration at peak exercise

Historically, it was thought that healthy humans predominantly described their breathing as a sense of increased work or effort (W/E) during maximal exercise. However, emerging data show that many healthy adults select unpleasant dyspnea descriptors such as "unsatisfied inspiration" (UI), with relatively more females selecting UI than males. We hypothesized that males and females who select UI would report higher dyspnea intensity ratings during exercise, select more distressing dyspnea qualities post exercise, and have greater inspiratory constraints than those who do not. Sixty-four healthy, nonsmokers (32 males:32 females; 23 ± 5 yr) completed questionnaires, pulmonary function tests, and maximal incremental cycling with detailed dyspnea evaluation. Males in UI and non-UI subgroups reported similar Borg 0-10 dyspnea intensity ratings of W/E, UI, and unsatisfied expiration (UE) (all P > 0.05). Females in the UI subgroup reported significantly higher UI and UE ratings than females in the non-UI subgroup (both P < 0.01). Both UI subgroups reported greater air hunger, chest tightness, and mental breathing effort than non-UI participants (all P < 0.05). In males only, masculine gender was negatively correlated (ρ = -0.402, P = 0.02) and anxiety positively correlated (ρ = 0.363, P = 0.04) with submaximal UI ratings. Females with UI had smaller peak tidal volume (Vt) [1.74 (0.32) vs. 2.06 (0.33) L, P = 0.03] than non-UI females; and Vt was negatively correlated with submaximal (ρ = -0.496, P = 0.004) and peak (ρ = -0.495, P = 0.004) UI ratings in all females. There were no differences in Vt or correlations between Vt and dyspnea in male subgroups. Absolute lung volumes and psychosocial factors appear important in understanding sex differences in the perception of UI during exercise.NEW & NOTEWORTHY The mechanisms of sex-based differences in the sensation of unsatisfied inspiration (UI) in healthy humans during exercise are poorly understood. We found that females who selected UI at peak exercise had worse dyspnea intensity ratings throughout exercise. Both sexes who selected UI at peak exercise also reported more distressing dyspnea qualities post exercise. Psychosocial factors appeared to influence male dyspnea perception, whereas smaller absolute lung volumes correlated with worse UI ratings in females.

The effect of unpredictability on the perception of breathlessness: a narrative review

Breathlessness is an aversive bodily sensation impacting millions of people worldwide. It is often highly detrimental for patients and can lead to profound distress and suffering. Notably, unpredictable breathlessness episodes are often reported as being more severe and unpleasant than predictable episodes, but the underlying reasons have not yet been firmly established in experimental studies. This review aimed to summarize the available empirical evidence about the perception of unpredictable breathlessness in the adult population. Specifically, we examined: (1) effects of unpredictable relative to predictable episodes of breathlessness on their perceived intensity and unpleasantness, (2) potentially associated neural and psychophysiological correlates, (3) potentially related factors such as state and trait negative affectivity. Nine studies were identified and integrated in this review, all of them conducted in healthy adult participants. The main finding across studies suggested that unpredictable compared to predictable, breathlessness elicits more frequently states of high fear and distress, which may contribute to amplify the perception of unpredictable breathlessness, especially its unpleasantness. Trait negative affectivity did not seem to directly affect the perception of unpredictable breathlessness. However, it seemed to reinforce state fear and anxiety, hence possible indirect modulatory pathways through these affective states. Studies investigating neural correlates of breathlessness perception and psychophysiological measures did not show clear associations with unpredictability. We discuss the implication of these results for future research and clinical applications, which necessitate further investigations, especially in clinical samples suffering from breathlessness.

Prevalence of dyspnea in general adult populations: A systematic review and meta-analysis

INTRODUCTION

Dyspnea is a commonly described symptom in various chronic and acute conditions. Despite its frequency, relatively little is known about the prevalence and assessment of dyspnea in general populations. The aims of this review were: 1) to estimate the prevalence of dyspnea in general adult populations; 2) to identify associated factors; and 3) to identify used methods for dyspnea assessment.

METHODS

A systematic literature search was conducted using MEDLINE/PubMed, Embase, CINAHL and JAMA network. Records were screened by two independent reviewers and quality was assessed by using the Joanna Briggs Institute checklist for risk of bias in prevalence studies. Multi-level meta-analysis was performed to estimate pooled prevalence. The protocol was registered on PROSPERO (CRD42021275499).

RESULTS

Twenty original articles, all from studies in high-income countries, met the criteria for inclusion. Overall, their quality was good. Pooled prevalence of dyspnea in general adult populations based on 11 studies was 10% (95% CI 7, 15), but heterogeneity across studies was high. The most frequently reported risk factors were increasing age, female sex, higher BMI and respiratory or cardiac disease. The MRC or the modified MRC scale was the most used tool to assess dyspnea in general populations.

CONCLUSIONS

Dyspnea is a common symptom in adults in high-income countries. However, the high heterogeneity across studies and the lack of data from low- and middle-income countries limit the generalizability of our findings. Therefore, more research is needed to unveil the prevalence of dyspnea and its main risk factors in general populations around the world.