Experimental dyspnea as a stressor: differential cardiovegetative responses to inspiratory threshold loading in healthy men and women

Multimodal physiological correlates of dyspnea ratings during breath-holding in healthy humans

INTRODUCTION AND OBJECTIVES

Dyspnea is associated with fear and intense suffering and is often assessed using visual analog scales (VAS) or numerical rating scales (NRS). However, the physiological correlates of such ratings are not well known. Using the voluntary breath-holding model of induced dyspnea, we studied healthy volunteers to investigate the temporal relationship between dyspnea, the neural drive to breathe assessed in terms of involuntary thoracoabdominal movements (ITMs) and neurovegetative responses.

PARTICIPANTS AND METHODS

Twenty-three participants (10 men; median [interquartile range] age 21 [20-21]) performed three consecutive breath-holds with the continuous assessment of dyspnea (urge-to-breathe) using a 10 cm VAS, thoracic and abdominal circumferences measured with piezoelectric belt-mounted transducers, heart rate and heart rate variability (HRV), and galvanic skin response (GSR). Urge-to-breathe VAS at the onset of ITMs (gasping point) was identified visually or algorithmically.

RESULTS

Urge-to-breathe VAS at the end of the breath-hold was 9.7 [8.6-10] cm. Total breath-hold duration was 93 [69-130] s. Urge-to-breathe VAS, ITM, heart rate, HRV, and GSR significantly increased during breath-hold. Urge-to-breathe VAS correlated with the magnitude of the thoracic and abdominal movements (rho = 0.51 and rho = 0.59, respectively, p < 0.001). The urge-to-breathe ratings corresponding with ITM onset were 3.0 [2.0-4.7] cm and 3.0 [1.0-4.0] cm for visual and algorithmic detection, respectively (p = 0.782).

CONCLUSION

An urge-to-breathe VAS of 3 cm (30% of full scale on a 10 cm VAS) corresponds to a physiological turning point during the physiological response to voluntary breath-holding in healthy humans.

Does wearing a facemask decrease arterial blood oxygenation and impair exercise tolerance?

INTRODUCTION

Concerns have been raised that COVID-19 face coverings compromise lung function and pulmonary gas exchange to the extent that they produce arterial hypoxemia and hypercapnia during high intensity exercise resulting in exercise intolerance in recreational exercisers. This study therefore aimed to investigate the effects of a surgical, flannel or vertical-fold N95 masks on cardiorespiratory responses to incremental exercise.

METHODS

This investigation studied 11 adult males and females at rest and while performing progressive cycle exercise to exhaustion. We tested the hypotheses that wearing a surgical (S), flannel (F) or horizontal-fold N95 mask compared to no mask (control) would not promote arterial deoxygenation or exercise intolerance nor alter primary cardiovascular variables during submaximal or maximal exercise.

RESULTS

Despite the masks significantly increasing end-expired peri-oral %CO₂ and reducing %O_2, each ∼0.8-2% during exercise (P < 0.05), our results supported the hypotheses. Specifically, none of these masks reduced sub-maximal or maximal exercise arterial O₂ saturation (P = 0.744), but ratings of dyspnea were significantly increased (P = 0.007). Moreover, maximal exercise capacity was not compromised nor were there any significant alterations of primary cardiovascular responses (mean arterial pressure, stroke volume, cardiac output) found during sub-maximal exercise.

CONCLUSION

Whereas these results are for young healthy recreational male and female exercisers and cannot be applied directly to elite athletes, older or patient populations, they do support that arterial hypoxemia and exercise intolerance are not the obligatory consequences of COVID-19-indicated mask-wearing at least for cycling exercise.

Sleep deprivation reduces vagal tone during an inspiratory endurance task in humans

STUDY OBJECTIVES

Sleep deprivation alters inspiratory endurance by reducing inspiratory motor output. Vagal tone is involved in exercise endurance. This study aimed to investigate the effect of sleep deprivation on vagal tone adaptation in healthy subjects performing an inspiratory effort.

METHODS

Vagal tone was assessed using Heart Rate Variability normalized units of frequency domain component HF (high frequency) before, at the start, and the end of an inspiratory loading trial performed until exhaustion by 16 volunteers after one night of sleep deprivation and one night of normal sleep, where sleep deprivation reduced the inspiratory endurance by half compared to the normal sleep condition (30 min vs 60 min).

RESULTS

At rest, heart rate was similar in sleep deprivation and normal sleep conditions. In normal sleep condition, heart rate increased during inspiratory loading task; this increase was greater in sleep deprivation condition. In normal sleep condition, vagal tone increased at the beginning of the trial. This vagal tone increase was absent in sleep deprivation condition.

CONCLUSIONS

Sleep deprivation abolished vagal tone response to inspiratory load, possibly contributing to a higher heart rate during the trial and to a reduced inspiratory endurance.

CLINICAL TRIAL REGISTRATION

NCT02725190.

Rostral cuneiform nucleus and the defence reaction: Direct and indirect midbrain-medullary 5-HT mechanisms in baroreflex inhibition

BACKGROUND AND PURPOSE

Activation of the defence reaction inhibits the baroreflex response via the intermediate rostro-ventromedial medulla (B3 raphé) and nucleus tractus solitarius (NTS). Our aim was to determine whether and how baroreflex inhibition, induced by the disinhibition of the rostral cuneiform nucleus (part of the defence pathway), involves 5-HT neurons in B3 and 5-HT₃ receptors in the NTS.

EXPERIMENTAL APPROACH

We performed immunohistochemistry and anatomical experiments to determine whether raphé 5-HT cells expressing Fos were directly targeted by the rostral cuneiform nucleus. The effect of blocking raphé 5-HT neurotransmission and NTS 5-HT₃ receptors on cuneiform-induced inhibition of the baroreflex cardiac response were also analysed.

KEY RESULTS

Bicuculline, microinjected into the rostral cuneiform nucleus, induced an increase of double-labelled Fos-5-HT-IR cells in both the lateral paragigantocellular nucleus (LPGi) and raphé magnus. The anterograde tracer Phaseolus vulgaris leucoaggutinin injected into the rostral cuneiform nucleus revealed a dense projection to the LPGi but not raphé magnus. Cuneiform-induced baroreflex inhibition was prevented by B3 injection of 8-OH-DPAT, a selective 5-HT_1A receptor agonist. Cuneiform disinhibition also failed to inhibit the baroreflex bradycardia after NTS microinjection of the 5-HT₃ receptor antagonist granisetron and in 5-HT₃ receptor knockout mice.

CONCLUSION AND IMPLICATIONS

The rostral cuneiform nucleus participates in the defence inhibition of the baroreflex bradycardia via direct activation of the LPGi and via a projection to the raphé magnus to activate NTS 5-HT₃ receptors and inhibit second-order baroreflex neurons. These data bring new insights in primary and secondary mechanisms involved in vital baroreflex prevention during stress.

Suicidal ideation in patients with coronary heart disease and hypertension: Baseline results from the DEPSCREEN-INFO clinical trial

BACKGROUND

A high proportion of cardiac patients suffers from depression, which is an antecedent for suicidal ideation. This study identifies clinical vulnerabilities for suicidal ideation in cardiac patients.

METHODS

The primary outcome of the study was severity of suicidal ideation as measured with the Patient Health Questionnaire (PHQ-9) item No. 9. Covariates were demographics, cardiac characteristics (i.e., Canadian Cardiovascular Society angina rating of chest pain and New York Heart Association rating of shortness of breath), depression (PHQ-8,i.e., PHQ-9 minus item No. 9), anxiety (Generalized Anxiety Disorder-7, GAD-7), somatic symptoms (PHQ-15), illness perception (Brief-Illness Perception Questionnaire), and health-related quality of life (EuroQol-5D, EQ 5D).

RESULTS

Data from 1,976 patients were analysed. At least 14% (95% CI [12%, 16%]) of patients indicated suicidal ideations within the last 2 weeks. Bivariate analyses yielded associations between suicidal ideation and higher levels of depression severity, anxiety severity, somatic symptom burden, chest pain, shortness of breath, negative illness perceptions, reduced health-related quality of life, and a higher probability of living alone (all p < 0.001). A multivariable ordinal regression revealed depression severity and anxiety severity to show the highest associations with suicidal ideation (OR_PHQ-8  = 1.22, p < 0.001; OR_GAD-7  = 1.09, p < 0.001). Having a defibrillator implant was associated with a lower probability of suicidal ideation (OR = 0.27, p = 0.017).

CONCLUSIONS

This study identified several clinical vulnerabilities of suicidal ideation. The results stress the importance of screening for suicidal ideation in clinical practice.