Chemosensitivity and perception of dyspnea in patients with a history of near-fatal asthma

Blunted perception of breathlessness in three cases of low grade insular-glioma

Better understanding of breathlessness perception addresses an unmet clinical need for more effective treatments for intractable dyspnoea, a prevalent symptom of multiple medical conditions. The insular-cortex is predominantly activated in brain-imaging studies of dyspnoea, but its precise role remains unclear. We measured experimentally-induced hypercapnic air-hunger in three insular-glioma patients before and after surgical resection. Tests involved one-minute increments in inspired CO2, raising end-tidal PCO2 to 7.5 mmHg above baseline (38.5 ± 5.7 mmHg), whilst ventilation was constrained (10.7 ± 2.3 L/min). Patients rated air-hunger on a visual analogue scale (VAS). Patients had lower stimulus-response (2.8 ± 2 vs. 11 ± 4 %VAS/mmHg; p = 0.004), but similar threshold (40.5 ± 3.9 vs. 43.2 ± 5.1 mmHg), compared to healthy individuals. Volunteered comments implicated diminished affective valence. After surgical resection; sensitivity increased in one patient, decreased in another, and other was unable to tolerate the ventilatory limit before any increase in inspired CO2.We suggest that functional insular-cortex is essential to register breathlessness unpleasantness and could be targeted with neuromodulation in chronically-breathless patients. Neurological patients with insula involvement should be monitored for blunted breathlessness to inform clinical management.

Brittle Asthma: Still on Board?

(1) Background: "Brittle Asthma" was considered an asthma clinical phenotype and deemed to be life-threatening in the early 2000s; then, this definition disappeared. The purpose of this review is to examine what has historically been referred to as this term and see whether it may be applied to modern clinical practice, thus acquiring fresh relevance and meaning. (2) Methods: A non-systematic search of the literature was conducted using both MeSH and free-text phrases. No limitations on the research design or type of publication were applied. (3) Results: Reliable data regarding "Brittle Asthma" are lacking due to the paucity of current data and the few studies available. After a few years of reworking, it was divided into two sub-classes: one characterized by a wide PEF variability despite high-dose therapy and the other by sudden acute attacks in otherwise apparently normal airway functions or well-controlled asthma. Their characteristics were hardly defined because of their low prevalence. Data regarding risk factors, atopy, mechanisms, and treatments were analyzed. (4) Conclusions: Over time, different terminology has been introduced to define asthma severity and control. It would be worth investigating whether the term "Brittle Asthma" previously used may be helpful to find new hints to stratify patients and improve disease management.

The normal distribution of the hypoxic ventilatory response and methodological impacts: a meta-analysis and computational investigation

The hypoxic ventilatory response (HVR) is the increase in breathing in response to reduced arterial oxygen pressure. Over several decades, studies have revealed substantial population-level differences in the magnitude of the HVR as well as significant inter-individual variation. In particular, low HVRs occur frequently in Andean high-altitude native populations. However, our group conducted hundreds of HVR measures over several years and commonly observed low responses in sea-level populations as well. As a result, we aimed to determine the normal HVR distribution, whether low responses were common, and to what extent variation in study protocols influence these findings. We conducted a comprehensive search of the literature and examined the distributions of HVR values across 78 studies that utilized step-down/steady-state or progressive hypoxia methods in untreated, healthy human subjects. Several studies included multiple datasets across different populations or experimental conditions. In the final analysis, 72 datasets reported mean HVR values and 60 datasets provided raw HVR datasets. Of the 60 datasets reporting raw HVR values, 35 (58.3%) were at least moderately positively skewed (skew > 0.5), and 21 (35%) were significantly positively skewed (skew > 1), indicating that lower HVR values are common. The skewness of HVR distributions does not appear to be an artifact of methodology or the unit with which the HVR is reported. Further analysis demonstrated that the use of step-down hypoxia versus progressive hypoxia methods did not have a significant impact on average HVR values, but that isocapnic protocols produced higher HVRs than poikilocapnic protocols. This work provides a reference for expected HVR values and illustrates substantial inter-individual variation in this key reflex. Finally, the prevalence of low HVRs in the general population provides insight into our understanding of blunted HVRs in high-altitude adapted groups. KEY POINTS: The hypoxic ventilatory response (HVR) plays a crucial role in determining an individual's predisposition to hypoxia-related pathologies. There is notable variability in HVR sensitivity across individuals as well as significant population-level differences. We report that the normal distribution of the HVR is positively skewed, with a significant prevalence of low HVR values amongst the general healthy population. We also find no significant impact of the experimental protocol used to induce hypoxia, although HVR is greater with isocapnic versus poikilocapnic methods. These results provide insight into the normal distribution of the HVR, which could be useful in clinical decisions of diseases related to hypoxaemia. Additionally, the low HVR values found within the general population provide insight into the genetic adaptations found in populations residing in high altitudes.

Under-perception of airflow limitation, self-efficacy, and beliefs in older adults with asthma

OBJECTIVE

Under-perception of airflow limitation is more common in older adults with asthma and may lead to under-reporting of asthma symptoms. Asthma management self-efficacy is linked with better asthma control and quality of life (QoL). We sought to examine asthma and medication beliefs as a mediator in the relationship between both under-perception and self-efficacy with asthma outcomes.

METHODS

This cross-sectional study recruited participants with asthma ≥60 years from hospital-affiliated practices in East Harlem and the Bronx, New York. Perception of airflow limitation was measured for 6 weeks by having participants enter peak expiratory flow (PEF) estimates into an electronic peak flow meter followed by PEF blows. We used validated instruments to assess asthma and medication beliefs, asthma management self-efficacy, asthma control, and QoL. Asthma self-management behaviors (SMB) were quantified by electronic and self-report measures of inhaled corticosteroid (ICS) adherence and observation of inhaler technique.

RESULTS

The sample comprised 331 participants (51% Hispanic, 27% Black, 84% female). Beliefs mediated the relationship between greater under-perception and better self-reported asthma control (β = -0.08, p = .02) and better asthma QoL (β =0.12, p = .02). Higher self-efficacy was also associated with better reported asthma control (β = -0.10, p = .006) and better asthma QoL (β =0.13, p = .01) in this indirect effect through beliefs. Accurate perception of airflow limitation was associated with higher adherence to SMB (β = 0.29, p = .003).

CONCLUSIONS

Less threatening asthma beliefs may be maladaptive in under-perception of airflow limitation by contributing to under-reporting of asthma symptoms, but adaptive in the context of higher self-efficacy and better asthma control.

Inappropriate Ventilatory Homeostatic Responses in Hospitalized COVID-19 Patients

Background

The clinical presentation of COVID-19 suggests altered breathing control - tachypnoea, relative lack of dyspnoea, and often a discrepancy between severity of clinical and radiological findings. Few studies characterize and analyse the contribution of breathing drivers and their ventilatory and perceptual responses.

Aim

To establish the prevalence of inappropriate ventilatory and perceptual response in COVID-19, by characterizing the relationships between respiratory rate (RR), dyspnoea and arterial blood gas (ABG) in a cohort of COVID-19 patients at presentation to hospital, and their post-Covid respiratory sequelae at follow-up.

Methods

We conducted a retrospective cohort study including consecutive adult patients admitted to hospital with confirmed COVID-19 between 1st March 2020 and 30th April 2020. In those with concurrent ABG, RR and documented dyspnoea status on presentation, we documented patient characteristics, disease severity, and outcomes at hospital and 6-week post-discharge.

Results

Of 492 admissions, 194 patients met the inclusion criteria. Tachypnoea was present in 75% pronounced (RR>30) in 36%, and persisted during sleep. RR correlated with heart rate (HR) (r = 0.2674), temperature (r = 0.2824), CRP (r = 0.2561), Alveolar-arterial (A-a) gradient (r = 0.4189), and lower PaO₂/FiO₂ (PF) ratio (r = −0.3636). RR was not correlated with any neurological symptoms. Dyspnoea was correlated with RR (r = 0.2932), A-a gradient (r = 0.1723), and lower PF ratio (r = −0.1914), but not correlated with PaO₂ (r = −0.1095), PaCO₂ (r = −0.0598) or any recorded neurological symptom except for altered consciousness. Impaired ventilatory homeostatic control of pH/PaCO₂ [tachypnoea (RR>20), hypocapnia (PaCO₂ <4.6 kPa), and alkalosis (pH>7.45)] was observed in 29%. This group, of which 37% reported no dyspnoea, had more severe respiratory disease (A-a gradient 38.9 vs. 12.4 mmHg; PF ratio 120 vs. 238), and higher prevalence of anosmia (21 vs. 15%), dysgeusia (25 vs. 12%), headache (33 vs. 23%) and nausea (33 vs. 14%) with similar rates of new anxiety/depression (26 vs. 23%), but lower incidence of past neurological or psychiatric diagnoses (5 vs. 21%) compared to appropriate responders. Only 5% had hypoxia sufficiently severe to drive breathing (i.e. PaO₂ <6.6 kPa). At 6 weeks post-discharge, 24% (8/34) showed a new breathing pattern disorder with no other neurological findings, nor previous respiratory, neurological, or psychiatric disorder diagnoses.

Conclusions

Impaired homeostatic control of ventilation i.e., tachypnoea, despite hypocapnia to the point of alkalosis appears prevalent in patients admitted to hospital with COVID-19, a finding typically accompanying more severe disease. Tachypnoea prevalence was between 12 and 29%. Data suggest that excessive tachypnoea is driven by both peripheral and central mechanisms, but not hypoxia. Over a third of patients with impaired homeostatic ventilatory control did not experience dyspnoea despite tachypnoea. A subset of followed-up patients developed post-covid breathing pattern disorder.

Cognition, symptom perception, and medication non-adherence in older adults with asthma

BACKGROUND

Cognitive impairment (CI) is highly prevalent in elderly asthmatics and is associated with worse asthma self-management (SM) and outcomes. CI may also explain why older adults may under-perceive asthma symptoms. We hypothesized that CI would be associated with low medication adherence and asthma symptom under-perception (ASP). We also hypothesized that ASP would mediate the relationship between CI and medication adherence.

METHODS

Participants of this longitudinal cohort study were asthmatics (N = 334) ≥60 years (51% Hispanic, 25% Black). Cognitive measures assessed general cognition, attention, processing speed, executive functioning, memory, and language. Measures of SM were self-reported and electronically measured adherence to controller medications. ASP was assessed for 6 weeks by participants entering estimates of peak expiratory flow (PEF) into a programmable peak flow meter, followed by PEF blows. Participants were blinded to actual PEF values. Percentage of time that participants were in the over-perception zone was calculated as an average.

RESULTS

In regression analyses, those with impairments in memory and general cognition had lower odds ratios (OR) for self-reported non-adherence (OR: 0.96, 95% CI 0.93 - 0.98 & OR: 0.90, 95% CI 0.83 - 0.96, respectively). CI was not associated with electronically measured non-adherence or ASP. In structural equation modeling, while CI was associated with adherence (β = 0.04, SE = 0.021, p = 0.04), ASP did not mediate this relationship.

CONCLUSIONS

While results confirmed the importance of cognition in asthma SM, these findings were not linked to ASP. Future analyses are needed to understand the role of confounding factors.

Ventilatory efficiency in athletes, asthma and obesity

During submaximal exercise, minute ventilation (V' _E) increases in proportion to metabolic rate (i.e. carbon dioxide production (V' _CO2 )) to maintain arterial blood gas homeostasis. The ratio V' _E/V' _CO2 , commonly termed ventilatory efficiency, is a useful tool to evaluate exercise responses in healthy individuals and patients with chronic disease. Emerging research has shown abnormal ventilatory responses to exercise (either elevated or blunted V' _E/V' _CO2 ) in some chronic respiratory and cardiovascular conditions. This review will briefly provide an overview of the physiology of ventilatory efficiency, before describing the ventilatory responses to exercise in healthy trained endurance athletes, patients with asthma, and patients with obesity. During submaximal exercise, the V' _E/V' _CO2 response is generally normal in endurance-trained individuals, patients with asthma and patients with obesity. However, in endurance-trained individuals, asthmatics who demonstrate exercise induced-bronchoconstriction, and morbidly obese individuals, the V' _E/V' _CO2 can be blunted at maximal exercise, likely because of mechanical ventilatory constraint.

Breath-holding as a novel approach to risk stratification in COVID-19

BACKGROUND

Despite considerable progress, it remains unclear why some patients admitted for COVID-19 develop adverse outcomes while others recover spontaneously. Clues may lie with the predisposition to hypoxemia or unexpected absence of dyspnea ('silent hypoxemia') in some patients who later develop respiratory failure. Using a recently-validated breath-holding technique, we sought to test the hypothesis that gas exchange and ventilatory control deficits observed at admission are associated with subsequent adverse COVID-19 outcomes (composite primary outcome: non-invasive ventilatory support, intensive care admission, or death).

METHODS

Patients with COVID-19 (N = 50) performed breath-holds to obtain measurements reflecting the predisposition to oxygen desaturation (mean desaturation after 20-s) and reduced chemosensitivity to hypoxic-hypercapnia (including maximal breath-hold duration). Associations with the primary composite outcome were modeled adjusting for baseline oxygen saturation, obesity, sex, age, and prior cardiovascular disease. Healthy controls (N = 23) provided a normative comparison.

RESULTS

The adverse composite outcome (observed in N = 11/50) was associated with breath-holding measures at admission (likelihood ratio test, p = 0.020); specifically, greater mean desaturation (12-fold greater odds of adverse composite outcome with 4% compared with 2% desaturation, p = 0.002) and greater maximal breath-holding duration (2.7-fold greater odds per 10-s increase, p = 0.036). COVID-19 patients who did not develop the adverse composite outcome had similar mean desaturation to healthy controls.

CONCLUSIONS

Breath-holding offers a novel method to identify patients with high risk of respiratory failure in COVID-19. Greater breath-hold induced desaturation (gas exchange deficit) and greater breath-holding tolerance (ventilatory control deficit) may be independent harbingers of progression to severe disease.

Functional pathophysiology of SARS-CoV-2-induced acute lung injury and clinical implications

The worldwide pandemic caused by the SARS-CoV-2 virus has resulted in over 84,407,000 cases, with over 1,800,000 deaths when this paper was submitted, with comorbidities such as gender, race, age, body mass, diabetes, and hypertension greatly exacerbating mortality. This review will analyze the rapidly increasing knowledge of COVID-19-induced lung pathophysiology. Although controversial, the acute respiratory distress syndrome (ARDS) associated with COVID-19 (CARDS) seems to present as two distinct phenotypes: type L and type H. The "L" refers to low elastance, ventilation/perfusion ratio, lung weight, and recruitability, and the "H" refers to high pulmonary elastance, shunt, edema, and recruitability. However, the LUNG-SAFE (Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure) and ESICM (European Society of Intensive Care Medicine) Trials Groups have shown that ∼13% of the mechanically ventilated non-COVID-19 ARDS patients have the type-L phenotype. Other studies have shown that CARDS and ARDS respiratory mechanics overlap and that standard ventilation strategies apply to these patients. The mechanisms causing alterations in pulmonary perfusion could be caused by some combination of 1) renin-angiotensin system dysregulation, 2) thrombosis caused by loss of endothelial barrier, 3) endothelial dysfunction causing loss of hypoxic pulmonary vasoconstriction perfusion control, and 4) hyperperfusion of collapsed lung tissue that has been directly measured and supported by a computational model. A flowchart has been constructed highlighting the need for personalized and adaptive ventilation strategies, such as the time-controlled adaptive ventilation method, to set and adjust the airway pressure release ventilation mode, which recently was shown to be effective at improving oxygenation and reducing inspiratory fraction of oxygen, vasopressors, and sedation in patients with COVID-19.

Acute severe asthma: management and treatment

Patients with acute asthma attack usually access the emergency room with severe functional impairment, despite low perception of symptoms. In this scenario, early functional assessment is essential focusing on vital parameters and respiratory function, alongside perceived dyspnea. Impairment of ventilatory mechanics due to progressive dynamic pulmonary hyperinflation should be promptly treated with medical inhalation and/or intravenous therapy, reserving intensive treatment in case of non-response and/or worsening of the clinical conditions. Therapeutic planning at patient's discharge is no less important than treatment management during emergency room access as educating the patient about therapeutic adherence significantly impact long-term outcomes of asthma. With this review we aim at exploring current evidence on acute asthma attack management, focusing of pharmacological and ventilatory strategies of care and highlighting the importance of patient education once clinical stability allows discharge from the emergency department.

Factors associated with discrepancies between poor dyspnea perception and abnormal lung function in 65 asthmatic patients

Background

Dyspnea is a subjective symptom of asthma whose perception is characterized by an interindividual variability. Poor dyspnea perception is usually associated with increased risk of exacerbation and may lead to inappropriate asthma management and under-treatment. We sought to identify factors associated with discrepancies between poor dyspnea perception and abnormal lung function in patients with moderate persistent asthma.

Methodology

65 patients, who attended their scheduled follow-up pulmonology consultation at Ibn Sina Hospital (Rabat - Morocco), underwent interrogation including modified Medical Research Council (mMRC) scale for dyspnea, physical examination and spirometry. Two groups, those with mMRC < 2 (poor dyspnea perceivers) and those with mMRC scale ≥ 2 were compared.

Results

Poor dyspnea perception was found in 21 patients (32.3%). Associated factors were male sex (p : 0.03), low socio-economic income (p : 0.01), an onset of symptoms greater than 10 years (p : 0.01), BMI ≥ 25 Kg/m2 (p : 0.04) and depression (p : 0.04).

Conclusion

The results revealed factors significantly associated with poor dyspnea perception despite an obstructive ventilatory disorder. These factors could usefully be considered to successfully manage asthma as well as the regular prescription of an objective test like spirometry.

Dyspnea perception and neurological symptoms in non-severe COVID-19 patients

Introduction

The relationship between dyspnea and COVID-19 is unknown. In COVID-19 patients, the higher prevalence of neurological symptoms and the lack of dyspnea may suggest common underlying pathogenetic mechanisms. The aim of this preliminary study is to address whether there is a lack of dyspnea in COVID-19 patients and if there is a relationship between neurological symptoms and the perception of dyspnea.

Methods

A structured interview regarding the occurrence of subjective neurological symptoms was performed and coupled with a questionnaire about the intensity and qualities of dyspnea. Respiratory rate (RR) and an arterial blood gas on room air were concurrently evaluated.

Results

Twenty-two patients (age 68.4 ± 13.9 years, 13 males and 9 females) were included and divided into two groups according to the Borg dyspnea scale: dyspneic patients BU ≥ 1(DYSP) and non-dyspneic patients BU < 1 (NDYSP). The prevalence of dyspnea overall was 31.8%. The prevalence of neurological symptoms, dyspnea descriptors, RR, pH, PaCO₂, PaO₂, or lactate was similar between groups.

Conclusion

This study confirms that the prevalence of dyspnea is low in non-severe COVID-19 patients, but contrary to our hypothesis of a relationship between shortness of breath and neurological symptoms, we have not been able to find any evidence of an impairment in dyspnea perception, either in the DYSP or NDYSP group.

Dyspnea perception during the inspiratory resistive loads test in obese subjects waiting bariatric surgery

Identification of low dyspnea perception is relevant, since this condition is significantly associated with worse outcomes. We investigated dyspnea perception during the inspiratory resistive loads test on obese subjects waiting bariatric surgery in comparison with normal subjects. Secondarily, we analysed the proportion of obese subjects with low, moderate and high dyspnea perception. This observational study included subjects with body mass index (BMI) ≥ 35 kg/m², compared to healthy subjects with BMI ≥ 18 and <25 kg/m². Subject underwent clinical evaluation, inspiratory test with progressive resistive loads and spirometry. We studied 23 obese subjects (mean BMI = 51.9 ± 9.3 kg/m²) and 25 normal subjects (mean BMI = 24.3 ± 2.3 kg/m²). With the increase magnitude of resistive loads there was a significant increase in dyspnea score (p < 0.001) and progressive increase of the generated inspiratory pressure (p < 0.001), but there was no difference between the groups in terms of dyspnea score (p = 0.191) and no interaction effect (p = 0.372). Among the obese subjects, 4 individuals were classified as low perception, 11 as moderate and 8 as high. In conclusion, the degree of dyspnea perception during the inspiratory progressive resistive loads test did not differ between obese and normal subjects. Among obese subjects, only 17% were classified as low dyspnea perception.

Health Services Utilization Is Increased in Poor Perceivers of Bronchoconstriction and Hyperinflation in Asthma

BACKGROUND

Impaired symptom perception is often listed as a risk factor for life-threatening asthma, but there is limited evidence to support this.

OBJECTIVE

We aimed to determine whether impaired perception of bronchoconstriction (BC) and/or dynamic hyperinflation (DH) are risk factors for severe asthma exacerbations.

METHODS

In this prospective cohort study, individuals with asthma underwent high-dose methacholine challenge testing. Changes in forced expiratory volume in 1 second (FEV₁) (% predicted) and inspiratory capacity (IC) (% predicted) were measured to assess the degree of BC and DH, respectively, during high-dose methacholine bronchoprovocation. Participants rated dyspnea intensity during testing and were categorized as poor, normal, and over perceivers of BC and DH based on perception scores at standardized changes (20%, 30%, and 40%) in FEV₁ (% predicted) and IC (% predicted). We compared the rates of severe asthma exacerbations (defined as one of emergency department [ED] visit or hospitalization) between groups, using Ontario's administrative health databases.

RESULTS

Poor perceivers had higher rates of ED visits and hospitalizations as compared with normal perceivers at 4 of 6 threshold decreases in FEV₁ and IC studied. Poor perceivers of severe DH had a 6-fold increase in asthma exacerbations (odds ratio, 5.7; 95% confidence interval, 1.31-25.03).

CONCLUSIONS

Health services utilization is increased in individuals with asthma who have poor perception of BC and DH. Poor perceivers of severe DH appear to be at the highest risk of exacerbations.

Evaluation and management of the critically ill adult asthmatic in the emergency department setting

INTRODUCTION

Asthma is a common reason for presentation to the Emergency Department and is associated with significant morbidity and mortality. While patients may have a relatively benign course, there is a subset of patients who present in a critical state and require emergent management.

OBJECTIVE

This narrative review provides evidence-based recommendations for the assessment and management of patients with severe asthma.

DISCUSSION

It is important to consider a broad differential diagnosis for the cause and potential mimics of asthma exacerbation. Once the diagnosis is determined, the majority of the assessment is based upon the clinical examination. First line therapies for severe exacerbations include inhaled short-acting beta agonists, inhaled anticholinergics, intravenous steroids, and magnesium. Additional therapies for refractory cases include parenteral epinephrine or terbutaline, helium‑oxygen mixture, and consideration of ketamine. Intravenous fluids should be administered, as many of these patients are dehydrated and at risk for hypotension if they receive positive pressure ventilatory support. Noninvasive positive pressure ventilation may prevent the need for endotracheal intubation. If mechanical ventilation is required, it is important to avoid breath stacking by setting a low respiratory rate and allowing permissive hypercapnia. Patients with severe asthma exacerbations will require intensive care unit admission.

CONCLUSIONS

This review provides evidence-based recommendations for the assessment and management of severe asthma with a focus on the emergency clinician.

Blockade of astrocytic activation delays the occurrence of severe hypoxia-induced seizure and respiratory arrest in mice

Seizures are induced when subjects are exposed to severe hypoxia. It is followed by ventilatory fall-off and eventual respiratory arrest, which may underlie the pathophysiology of death in patients with epilepsy and severe respiratory disorders. However, the mechanisms of hypoxia-induced seizures have not been fully understood. Because astrocytes are involved in various neurological disorders, we aimed to investigate whether astrocytes are operational in seizure generation and respiratory arrest in a severe hypoxic condition. We examined the effects of astrocytic activation blockade on responses of EEG and ventilation to severe hypoxia. Adult mice were divided into two groups; in one group (n = 24) only vehicle was injected, and in the other group (n = 24) arundic acid, an inhibitory modulator of astrocytic activation, was administered before initiation of recording. After recording EEG and ventilation by whole body plethysmography in room air, the gas in the recording chamber was switched to 5% oxygen (nitrogen balanced) until a seizure and ventilatory depression occurred, followed by prompt switch back to room air. Severe hypoxia initially increased ventilation, followed by a seizure and ventilatory suppression in all mice examined. Fourteen mice without arundic acid showed respiratory arrest during loading of hypoxia. However, 22 mice pretreated with arundic acid did not suffer from respiratory arrest. Time from the onset of hypoxia to the occurrence of seizures was significantly longer in the group with arundic acid than that in the group without arundic acid. We suggest that blockade of astrocytic activation delays the occurrence of seizures and prevents respiratory arrest.

Symptoms and perception of airway obstruction in asthmatic patients: Clinical implications for use of reliever medications

BACKGROUND

Asthma causes the unpleasant sensation of breathlessness (dyspnea) caused by airway obstruction. Patients with poor perception of airway obstruction are at risk of delay in seeking medical attention and undertreatment, which can lead to avoidable deaths. Conversely, those with heightened perception are at risk of overtreatment and iatrogenic adverse effects with reliever medications, anxiety, and unnecessary use of health care resources.

OBJECTIVE

We sought to review evidence about symptom misperception in asthmatic patients and how to identify and manage affected patients, particularly with regard to reliever medications.

METHODS

We conducted a systematic literature search for studies of perception of airway function in asthmatic patients. We searched the OVID (Medline and Medline [R] in process [PubMed]), Embase, and Adisearch/Odyssey databases, restricting our search to human studies published in English from 1990-2018, with no restrictions on age, sex, or racial origin.

RESULTS

We found that both underperception and overperception assessed during induced bronchoconstriction or bronchodilation or during changes in airway resistance were common across all age groups and that aging, disease severity, smoking, sex, ethnicity, psychologic factors, and medication are all associated with differences in perception. Importantly, airway inflammation was associated with impaired perception and a history of severe or near-fatal asthma. We also identified knowledge gaps, such as whether an individual patient's perception varies over time and the influence perception has on patients' use of reliever medication.

CONCLUSION

We found that abnormal perception of airway obstruction has important clinical implications for the management of patients with asthma.

Mandibular advancement reveals long-term suppression of breathing discomfort in patients with obstructive sleep apnea syndrome

Obstructive sleep apnoea syndrome (OSAS) patients do not report breathing discomfort in spite of abnormal upper airway mechanics. We studied respiratory sensations in OSAS patients without and with mandibular advancement device (MAD). Fifty-seven moderate to severe non obese OSAS patients were asked about breathing discomfort using visual analogue scales (VAS) in the sitting position (VAS-1), after lying down (VAS-2), then with MAD (VAS-3). Awake critical closing pressure (awake Pcrit) was measured in 15 patients without then with MAD. None of the patients reported breathing discomfort when sitting but 19 patients (33%) did when lying (VAS-2: -20% or less). A feeling of "easier breathing" with MAD was observed and was more marked in patients reporting breathing discomfort when supine (VAS-3: +66.0% [49.0; 89.0]) than in those not doing so (VAS-3: +28.5% [1.0; 56.5], p = 0.007). MAD-induced change in awake Pcrit was correlated to VAS-3. In conclusion, MAD revealed "latent dyspnea" related to the severity of upper airways mechanics abnormalities in OSAS patients.

Clinical and experimental aspects of breathing modulation by inflammation

Neuroinflammation is produced by local or systemic alterations and mediated mainly by glia, affecting the activity of various neural circuits including those involved in breathing rhythm generation and control. Several pathological conditions, such as sudden infant death syndrome, obstructive sleep apnea and asthma exert an inflammatory influence on breathing-related circuits. Consequently breathing (both resting and ventilatory responses to physiological challenges), is affected; e.g., responses to hypoxia and hypercapnia are compromised. Moreover, inflammation can induce long-lasting changes in breathing and affect adaptive plasticity; e.g., hypoxic acclimatization or long-term facilitation. Mediators of the influences of inflammation on breathing are most likely proinflammatory molecules such as cytokines and prostaglandins. The focus of this review is to summarize the available information concerning the modulation of the breathing function by inflammation and the cellular and molecular aspects of this process. I will consider: 1) some clinical and experimental conditions in which inflammation influences breathing; 2) the variety of experimental approaches used to understand this inflammatory modulation; 3) the likely cellular and molecular mechanisms.

Evidence against a subcortical gate preventing conscious detection of respiratory load stimuli

Respiratory related evoked potentials (RREP) were used to examine respiratory stimulus gating. RREPs produced by consciously detected vs. undetected loads, near the detection threshold, were compared. Participants (n = 17) were instrumented with EEG and a nasal mask connected to a loading manifold, which presented a range of mid-inspiratory resistive loads, plus a control, in a random block design. Participants were cued prior to the stimulus and signalled detection by a button press. There were statistically significant differences in peak-to-peak amplitude of the P1 RREP peak for detected (mean ± SD; 3.86 ± 1.45 μV; P =  0.020) and undetected loads (3.67 ± 1.27 μV; P =  0.002) vs. control (2.36 ± 0.81 μV), although baseline-to-peak differences were not significantly different. In contrast peak-to-peak P3 amplitude was significantly greater for detected (5.91 ± 1.54 μV; P <  0.001) but not undetected loads (3.33 ± 0.98 μV; P = 0.189) vs. control (3.69 ± 1.46 μV), with the same pattern observed for baseline-to-peak measurements. The P1 peak, thought to reflect arrival of somatosensory information, appeared to be present in response to both detected and undetected loads, but the later P3 peak, was present for detected loads only. This suggests that for sub-threshold loads sensory information may reach the cortex, arguing against a sub-cortical gating process.

Passive Nocturnal Physiologic Monitoring Enables Early Detection of Exacerbations in Children with Asthma. A Proof-of-Concept Study

RATIONALE

Asthma management depends on prompt identification of symptoms, which challenges both patients and providers. In asthma, a misapprehension of health between exacerbations can compromise compliance. Thus, there is a need for a tool that permits objective longitudinal monitoring without increasing the burden of patient compliance.

OBJECTIVES

We sought to determine whether changes in nocturnal physiology are associated with asthma symptoms in pediatric patients.

METHODS

Using a contactless bed sensor, nocturnal heart rate (HR), respiratory rate, relative stroke volume, and movement in children with asthma 5-18 years of age (n = 16) were recorded. Asthma symptoms and asthma control test (ACT) score were reported every 2 weeks. Random forest model was used to identify physiologic parameters associated with asthma symptoms. Elastic net regression was used to identify variables associated with ACT score.

MEASUREMENTS AND MAIN RESULTS

The model on the full cohort performed with sensitivity of 47.2%, specificity of 96.3%, and accuracy of 87.4%; HR and respiratory parameters were the most important variables in this model. The model predicted asthma symptoms 35% of the time on the day before perception of symptoms, and 100% of the time for a select subject for which the model performed with greater sensitivity. Multivariable and bivariable analyses demonstrated significant association between HR and respiratory rate parameters and ACT score.

CONCLUSIONS

Nocturnal physiologic changes correlate with asthma symptoms, supporting the notion that nocturnal physiologic monitoring represents an objective diagnostic tool capable of longitudinally assessing disease control and predicting asthma exacerbations in children with asthma at home.

Effect of adjusting the combination of budesonide/formoterol on the alleviation of asthma symptoms

Background

The combination of budesonide + formoterol (BFC) offers the advantages of dose adjustment in a single inhaler according to asthma symptoms. We analyzed the relationship between asthma symptoms in terms of peak expiratory flow (PEF) and dose adjustment by the patient.

Methods

Twenty-eight patients with asthma who used BFC for alleviation of their symptoms (12 men, 16 women; 60 years old) were instructed that the inhaled BFC dose could be increased to a maximum of 8 inhalations per day according to symptom severity. Patients measured and recorded PEF every morning and evening in their asthma diary along with their symptoms and the dose of drugs taken.

Results

Sixteen of the 28 patients increased their dose for asthma symptoms. The time to recovery from the asthma symptoms was significantly shorter when cough was the only symptom present compared with dyspnea or wheeze (1.4 vs. 5.3 or 6.6 days, p < 0.05) and when they had only one symptom compared with two or three symptoms (1.3 vs. 5.7 or 10.5, p < 0.01). The relationship between PEF (% of personal best) when the dose was increased (Y) and the days for the increased dose to achieve a PEF greater than PEF in the symptom-free state (X) was determined to be Y = - 0.591X + 89.2 (r² = 0.299, p < 0.001).

Conclusion

As a guide for increasing the BFC dose when patients with mild asthma have asthma symptoms, the dose should be increased when cough is present or PEF is decreased to 88.9% (i.e., X = 0.5).

Dyspnea in pregnancy

Dyspnea in pregnancy is common. It can result from adaption to body changes in pregnancy and also from complications therein. Understanding the mechanisms of change in the respiratory system during pregnancy helps with the differential diagnosis of dyspnea in normal pregnancy as opposed to pathological dyspnea.

Identification of patterns of factors preceding severe or life-threatening asthma exacerbations in a nationwide study

BACKGROUND

Reducing near-fatal asthma exacerbations is a critical problem in asthma management.

OBJECTIVES

To determine patterns of factors preceding asthma exacerbations in a real-world setting.

METHODS

In a nationwide prospective study of 190 patients who had experienced near-fatal asthma exacerbation, cluster analysis was performed using asthma symptoms over the 2-week period before admission.

RESULTS

Three distinct clusters of symptoms were defined employing the self-reporting of a visual analogue scale. Cluster A (42.1%): rapid worsening within 7.4 hours from moderate attack to admission, young to middle-aged patients with low Body mass index and tendency to depression who had stopped anti-asthma medications, smoked, and hypersensitive to environmental triggers and furred pets. Cluster B (40.0%): fairly rapid worsening within 48 hours, mostly middle-aged and older, relatively good inhaled corticosteroid (ICS) or ICS/long-acting beta-agonist (LABA) compliance, and low perception of dyspnea. Cluster C (17.9%): slow worsening over 10 days before admission, high perception of dyspnea, smokers, and chronic daily mild-moderate symptoms. There were no differences in overuse of short-acting beta-agonists, baseline asthma severity, or outcomes after admission for patients in these 3 clusters.

CONCLUSION

To reduce severe or life-threatening asthma exacerbation, personalized asthma management plans should be considered for each cluster. Improvement of ICS and ICS/LABA compliance and cessation of smoking are important in cluster A. To compensate for low perception of dyspnea, asthma monitoring of peak expiratory flow rate and/or exhaled nitric oxide would be useful for patients in cluster B. Avoidance of environmental triggers, increase usual therapy, or new anti-type 2 response-targeted therapies should be considered for cluster C.

Near-fatal asthma: a heterogeneous clinical entity

PURPOSE OF REVIEW

The aims of the present review were to describe the heterogeneous nature of near-fatal asthma (NFA) and to summarize the distinctive phenotypes identified in this subtype of asthma.

RECENT FINDINGS

Clinical, physiological, and histological studies have shown a large number of triggers, pathological mechanisms, and risk factors associated with NFA. Based on the demographic and clinical characteristics of the patients, the circumstances surrounding the asthma exacerbation and some distinctive features of the disease, several clinical profiles of asthma patients with NFA have been described. Recent data show new associations between some gene expression patterns and fatal asthma, as well as with some biological markers related to inflammatory or immunologic mechanisms in the airways. Also, the use of statistical methods, such as cluster analysis, allowed identifying and confirming different phenotypes of life-threatening asthma patients.

SUMMARY

NFA is a heterogeneous clinical entity, in which different patients' clinical profiles may coexist [e.g. rapid-onset NFA, NFA in patients with dyspnea hypoperception or sensitized to certain pneumoallergens (Alternaria alternata, soybean), NFA related to the menstrual cycle, brittle asthma]. Knowledge of these phenotypes as well as adequate and specific management strategies can reduce morbidity and mortality in patients suffering from NFA.

Mechanisms, measurement and management of exertional dyspnoea in asthma: Number 5 in the Series "Exertional dyspnoea" Edited by Pierantonio Laveneziana and Piergiuseppe Agostoni

Asthma is a heterogeneous condition, with dyspnoea during exercise affecting individuals to a variable degree. This narrative review explores the mechanisms and measurement of exertional dyspnoea in asthma and summarises the available evidence for the efficacy of various interventions on exertional dyspnoea. Studies on the mechanisms of dyspnoea in asthma have largely utilised direct bronchoprovocation challenges, rather than exercise, which may invoke different physiological mechanisms. Thus, the description of dyspnoea during methacholine challenge can differ from what is experienced during daily activities, including exercise. Dyspnoea perception during exercise is influenced by many interacting variables, such as asthma severity and phenotype, bronchoconstriction, dynamic hyperinflation, respiratory drive and psychological factors. In addition to the intensity of dyspnoea, the qualitative description of dyspnoea may give important clues as to the underlying mechanism and may be an important endpoint for future interventional studies. There is currently little evidence demonstrating whether pharmacological or non-pharmacological interventions specifically improve exertional dyspnoea, which is an important area for future research.

Assessment of asthma severity and control

BACKGROUND

Asthma is a disease of great variability. Untreated asthma can have lifelong implications in terms of lung growth as well as residual lung function throughout life. Close attention to establishing severity of the disease and level of control established in each patient through treatment are important to achieving the best results.

METHODS

Available English-language literature was reviewed. Citations were included based on the quality of the original paper and relevance to the specific aims of this primer.

RESULTS

Assessing intrinsic severity of the patient's disease at the first encounter using impairment measures of short-acting beta agonist use, nighttime awakenings, interference of disease with normal activity, and pulmonary function testing, as well as measures of patient risk of acute exacerbations is vitally important. At subsequent patient encounters, adjusting therapy based on both impairment and risk components of control will improve long-term outcomes.

CONCLUSION

Any practitioner undertaking to care for asthma patients should be conversant with the degrees of disease severity and levels of disease control on therapy. Application of these principles will maximize patient benefit from asthma care.

Epidemiology and Pulmonary Physiology of Severe Asthma

The epidemiology and physiology of severe asthma are inherently linked because of varying phenotypes and expressions of asthma throughout the population. To understand how to better treat severe asthma, we must use both population data and physiologic principles to individualize therapies among groups with similar expressions of this disease.

Severe or life-threatening asthma exacerbation: patient heterogeneity identified by cluster analysis

BACKGROUND

Severe or life-threatening asthma exacerbation is one of the worst outcomes of asthma because of the risk of death. To date, few studies have explored the potential heterogeneity of this condition.

OBJECTIVES

To examine the clinical characteristics and heterogeneity of patients with severe or life-threatening asthma exacerbation.

METHODS

This was a multicentre, prospective study of patients with severe or life-threatening asthma exacerbation and pulse oxygen saturation < 90% who were admitted to 17 institutions across Japan. Cluster analysis was performed using variables from patient- and physician-orientated structured questionnaires.

RESULTS

Analysis of data from 175 patients with severe or life-threatening asthma exacerbation revealed five distinct clusters. Cluster 1 (n = 27) was younger-onset asthma with severe symptoms at baseline, including limitation of activities, a higher frequency of treatment with oral corticosteroids and short-acting beta-agonists, and a higher frequency of asthma hospitalizations in the past year. Cluster 2 (n = 35) was predominantly composed of elderly females, with the highest frequency of comorbid, chronic hyperplastic rhinosinusitis/nasal polyposis, and a long disease duration. Cluster 3 (n = 40) was allergic asthma without inhaled corticosteroid use at baseline. Patients in this cluster had a higher frequency of atopy, including allergic rhinitis and furred pet hypersensitivity, and a better prognosis during hospitalization compared with the other clusters. Cluster 4 (n = 34) was characterized by elderly males with concomitant chronic obstructive pulmonary disease (COPD). Although cluster 5 (n = 39) had very mild symptoms at baseline according to the patient questionnaires, 41% had previously been hospitalized for asthma.

CONCLUSIONS & CLINICAL RELEVANCE

This study demonstrated that significant heterogeneity exists among patients with severe or life-threatening asthma exacerbation. Differences were observed in the severity of asthma symptoms and use of inhaled corticosteroids at baseline, and the presence of comorbid COPD. These findings may contribute to a deeper understanding and better management of this patient population.

Identification and characterization of near-fatal asthma phenotypes by cluster analysis

BACKGROUND

Near-fatal asthma (NFA) is a heterogeneous clinical entity and several profiles of patients have been described according to different clinical, pathophysiological and histological features. However, there are no previous studies that identify in a unbiased way--using statistical methods such as clusters analysis--different phenotypes of NFA. Therefore, the aim of the present study was to identify and to characterize phenotypes of near fatal asthma using a cluster analysis.

METHODS

Over a period of 2 years, 33 Spanish hospitals enrolled 179 asthmatics admitted for an episode of NFA. A cluster analysis using two-steps algorithm was performed from data of 84 of these cases.

RESULTS

The analysis defined three clusters of patients with NFA: cluster 1, the largest, including older patients with clinical and therapeutic criteria of severe asthma; cluster 2, with an high proportion of respiratory arrest (68%), impaired consciousness level (82%) and mechanical ventilation (93%); and cluster 3, which included younger patients, characterized by an insufficient anti-inflammatory treatment and frequent sensitization to Alternaria alternata and soybean.

CONCLUSIONS

These results identify specific asthma phenotypes involved in NFA, confirming in part previous findings observed in studies with a clinical approach. The identification of patients with a specific NFA phenotype could suggest interventions to prevent future severe asthma exacerbations.

Assessing the risks and benefits of step-down asthma care: a case-based approach

Guidelines have called for pharmacologic stepped care to improve asthma treatment. Therapeutic options which have been approved provide physicians and their patients alternatives for stepping up asthma treatment to achieve control. However, few studies have been performed to identify and characterize procedures for optimal stepping-down treatment in patients with asthma. The resulting uncertainty as well as a lack of prioritization for asthma reassessment once control has been maintained has led to a lack of well-defined procedures for stepping down asthma treatment. However, recent studies provide guidance regarding the risks of stepping down asthma medications. This review uses case-based examples to demonstrate how health care providers may engage patients in discussions regarding guideline recommendations to promote individualized asthma care.

What long-term changes in lung function can tell us about asthma control

Asthma severity is typically classified according to lung function, but asthma control in relation to lung function is often harder to define. In this paper, we will review how lung function measured at rest, as well as over time, relates to asthma control. We will explore not only conventional lung function as measured by spirometry, such as peak expiratory flow and forced expiratory volume in 1 s, but also more sophisticated measurements of peripheral airway function related to respiratory system impedance and ventilation heterogeneity. In particular, we will review the emerging area of assessing the fluctuation of lung function over time and how it may correlate to both past and future asthma control.

Variability of the perception of dyspnea in healthy subjects assessed through inspiratory resistive loading

Objective:

Few studies have evaluated the variability of the perception of dyspnea in healthy subjects. The objective of this study was to evaluate the variability of the perception of dyspnea in healthy subjects during breathing against increasing inspiratory resistive loads, as well as to assess the association between the level of perception of dyspnea and the level of physical activity.

Methods:

This was a cross-sectional study involving healthy individuals 16 years of age or older. Subjects underwent inspiratory resistive loading testing, in which the level of perception of dyspnea was quantified with the modified Borg scale. We also determined body mass indices (BMIs), assessed maximal respiratory pressures, performed pulmonary function tests, applied the international physical activity questionnaire (IPAQ)-long form, and conducted six-minute walk tests (6MWTs). The level of perception of dyspnea was classified as low (Borg score < 2), intermediate (Borg score, 2-5), or high (Borg score > 5).

Results:

We included 48 healthy subjects in the study. Forty-two subjects completed the test up to a load of 46.7 cmH₂O/L/s. The level of perception of dyspnea was classified as low, intermediate, and high in 13, 19, and 10 subjects, respectively. The level of perception of dyspnea was not significantly associated with age, gender, BMI, IPAQ-long form score, maximal respiratory pressures, or pulmonary function test results.

Conclusions:

The scores for perceived dyspnea induced by inspiratory resistive loading in healthy subjects presented wide variability. The perception of dyspnea was classified as low in 31% of the subjects, intermediate in 45%, and high in 24%. There was no association between the level of perception of dyspnea and the level of physical activity (IPAQ or six-minute walk distance).

Reliability and predictors of resistive load detection in children with persistent asthma: a multivariate approach

OBJECTIVE

Resistive load detection tasks enable analysis of individual differences in psychophysical outcomes. The purpose of this study was to determine both the reliability and predictors of resistive load detection in children with persistent asthma who completed multiple testing sessions.

METHODS

Both University of North Carolina (UNC) Charlotte and Ohio University institutional review boards approved the research protocol. The detection of inspiratory resistive loads was evaluated in 75 children with asthma between 8 and 15 years of age. Each child participated in four experimental sessions that occurred approximately once every 2 weeks. Multivariate analyses were used to delineate predictors of task performance.

RESULTS

Reliability of resistive load detection was determined for each child, and predictors of load detection outcomes were investigated in two groups of children: those who performed reliably in all four sessions (n = 31) and those who performed reliably in three or fewer sessions (n = 44). Three factors (development, symptoms, and compliance) accounted for 66.3% of the variance among variables that predicted 38.7% of the variance in load detection outcomes (Multiple R = 0.62, p = 0.004) and correctly classified performance as reliable or less reliable in 80.6% of the children, χ(2)(12) = 28.88, p = 0.004.

CONCLUSIONS

Cognitive and physical development, appraisal of symptom experiences, and adherence-related behaviors (1) account for a significant proportion of the interrelationships among variables that affect perception of airflow obstruction in children with asthma and (2) differentiate between children who perform more or less reliably in a resistive load detection task.

Repeatability of the evaluation of perception of dyspnea in normal subjects assessed through inspiratory resistive loads

Purpose:

Study the repeatability of the evaluation of the perception of dyspnea using an inspiratory resistive loading system in healthy subjects.

Methods:

We designed a cross sectional study conducted in individuals aged 18 years and older. Perception of dyspnea was assessed using an inspiratory resistive load system. Dyspnea was assessed during ventilation at rest and at increasing resistive loads (0.6, 6.7, 15, 25, 46.7, 67, 78 and returning to 0.6 cm H2O/L/s). After breathing in at each level of resistive load for two minutes, the subject rated the dyspnea using the Borg scale. Subjects were tested twice (intervals from 2 to 7 days).

Results:

Testing included 16 Caucasian individuals (8 male and 8 female, mean age: 36 years). The median scores for dyspnea rating in the first test were 0 at resting ventilation and 0, 2, 3, 4, 5, 7, 7 and 1 point, respectively, with increasing loads. The median scores in the second test were 0 at resting and 0, 0, 2, 2, 3, 4, 4 and 0.5 points, respectively. The intra-class correlation coefficient was 0.57, 0.80, 0.74, 0.80, 0.83, 0.86, 0.91, and 0.92 for each resistive load, respectively. In a generalized linear model analysis, there was a statistically significant difference between the levels of resistive loads (p<0.001) and between tests (p=0.003). Dyspnea scores were significantly lower in the second test.

Conclusion:

The agreement between the two tests of the perception of dyspnea was only moderate and dyspnea scores were lower in the second test. These findings suggest a learning effect or an effect that could be at least partly attributed to desensitization of dyspnea sensation in the brain.

Inspiratory Muscle Training and the Perception of Dyspnea in Parkinson's Disease

Background:

Pulmonary and respiratory muscle function impairment are common in patients with Parkinson's disease (PD). Inspiratory muscle training may improve strength, dyspnea and functional capacity in healthy subjects and in those with chronic obstructive pulmonary disease. This study investigated the effect of specific inspiratory muscle training (SIMT) on pulmonary functions, inspiratory muscle performance, dyspnea and quality of life, in patients with PD.

Patients and Methods:

Twenty patients with PD (stage II and III Hoehn and Yahr scale) were recruited for the study and were divided into two groups: a) ten patients who received SIMT and b) ten patients who received sham training, for three months. Pulmonary functions, the respiratory muscle strength and endurance, the perception of dyspnea (POD) and the quality of life were studied before and within one week after the training period. All subjects trained daily, six times a week, each session consisting of 1/2 hour, for 12 weeks.

Results:

Following the training period, there was a significant improvement, in the training group but not in the control group, in the following parameters: inspiratory muscle strength, (PImax, increased from 62.0±8.2 to 78.0±7.5 cm of H2O (p<0.05), inspiratory muscle endurance (increased from 20.0±2.8 to 29.0±3.0 cm of H2O (p<0.05), and the POD (decreased from 17.9±3.2 to 14.0±2.4 units (p<0.05). There was a close correlation between the increase in the inspiratory muscle performance and the decrease in the POD.

Conclusions:

The inspiratory muscle performance may be improved by SIMT in patients with PD. This improvement is associated with a significant decrease in their POD.

Regional quantification of cerebral venous oxygenation from MRI susceptibility during hypercapnia

There is an unmet medical need for noninvasive imaging of regional brain oxygenation to manage stroke, tumor, and neurodegenerative diseases. Oxygenation imaging from magnetic susceptibility in MRI is a promising new technique to measure local venous oxygen extraction fraction (OEF) along the cerebral venous vasculature. However, this approach has not been tested in vivo at different levels of oxygenation. The primary goal of this study was to test whether susceptibility imaging of oxygenation can detect OEF changes induced by hypercapnia, via CO2 inhalation, within selected a priori brain regions. Ten healthy subjects were scanned at 3T with a 32-channel head coil. The end-tidal CO2 (ETCO2) was monitored continuously and inspired gases were adjusted to achieve steady-state conditions of eucapnia (41±3mmHg) and hypercapnia (50±4mmHg). Gradient echo phase images and pseudo-continuous arterial spin labeling (pcASL) images were acquired to measure regional OEF and CBF respectively during eucapnia and hypercapnia. By assuming constant cerebral oxygen consumption throughout both gas states, regional CBF values were computed to predict the local change in OEF in each brain region. Hypercapnia induced a relative decrease in OEF of -42.3% in the straight sinus, -39.9% in the internal cerebral veins, and approximately -50% in pial vessels draining each of the occipital, parietal, and frontal cortical areas. Across volunteers, regional changes in OEF correlated with changes in ETCO2. The reductions in regional OEF (via phase images) were significantly correlated (P<0.05) with predicted reductions in OEF derived from CBF data (via pcASL images). These findings suggest that susceptibility imaging is a promising technique for OEF measurements, and may serve as a clinical biomarker for brain conditions with aberrant regional oxygenation.

Gender differences in the effect of urge-to-cough and dyspnea on perception of pain in healthy adults

Previous studies have reported that respiratory sensations, such as urge‐to‐cough and dyspnea, have an inhibitory effect on pain. Considering the existence of gender differences in both urge‐to‐cough and pain, it is conceivable that a gender difference also exists in the analgesia induced by urge‐to‐cough. In this study, we evaluated gender differences in the pain perception response to urge‐to‐cough, as well as to dyspnea. Twenty‐seven male and 26 female healthy nonsmokers were originally enrolled. Citric acid challenge was used to induce the urge‐to‐cough sensation, and dyspnea was elicited by inspiratory loaded breathing. Before and during inductions of these two respiratory sensations, perception of pain was assessed by the thermal pain threshold, and differences between men and women were compared. The thermal pain threshold in women (43.83 ± 0.17°C) was significantly lower than that in men (44.75 ± 0.28°C; P < 0.05) during the baseline period. Accompanying increases in both citric acid concentration and inspiratory resistive load, thermal pain threshold values significantly increased in both men and women. The average thermal pain threshold changes for comparable increases in the urge‐to‐cough Borg score were parallel between men and women. Furthermore, the mean value of the thermal pain threshold plotted against the dyspnea Borg score also showed no significant gender difference. These results demonstrate that although gender differences exist in respiratory sensations, that is, urge‐to‐cough and dyspnea, the inhibitory effects of these respiratory sensations on the perception of pain are not significantly different between the sexes.

The relationships between citric acid dose and urge‐to‐cough rating or thermal pain threshold in each subject grouped by sex.

Perception of bronchoconstriction following methacholine and eucapnic voluntary hyperpnea challenges in elite athletes

OBJECTIVE

Self-reported respiratory symptoms are poor predictors of exercise-induced bronchoconstriction (EIB) in athletes. The objective of this study was to determine whether athletes have an inadequate perception of bronchoconstriction.

METHODS

One hundred thirty athletes and 32 nonathletes completed a standardized questionnaire and underwent eucapnic voluntary hyperpnea (EVH) and methacholine inhalation test. Perception scores were quoted on a modified Borg scale before each spirometry measurement for cough, breathlessness, chest tightness, and wheezing. Perception slope values were also obtained by plotting the variation of perception scores before and after the challenges against the fall in FEV1 expressed as a percentage of the initial value [(perception scores after - before)/FEV1].

RESULTS

Up to 76% of athletes and 68% of nonathletes had a perception score of ≤0.5 at 20% fall in FEV1 following methacholine. Athletes with EIB/airway hyperresponsiveness (AHR) had lower perception slopes to methacholine than nonathletes with asthma for breathlessness only (P=.02). Among athletes, those with EIB/AHR had a greater perception slope to EVH for breathlessness and wheezing (P=.02). Female athletes had a higher perception slope for breathlessness after EVH and cough after methacholine compared with men (P<.05). The age of athletes correlated significantly with the perception slope to EVH for each symptom (P<.05).

CONCLUSIONS

Minimal differences in perception of bronchoconstriction-related symptoms between athletes and nonathletes were observed. Among athletes, the presence of EIB/AHR, older age, and female sex were associated with slightly higher perception scores.

Historical perspectives on the control of breathing

Among the several topics included in respiratory studies investigators have focused on the control of breathing for a relatively few number of years, perhaps only the last 75 to 80. For a very long time, the phenomenon of respiration presented a great mystery. The Chinese had suggestions for proper breathing, and later the Egyptians sought to understand its purpose. But in the western world, the early Greeks made the more significant observations. Centuries passed before the anatomical structures pertinent to respiration were properly visualized and located. There followed efforts to understand if lung movement was necessary for life and what happened in the lung. The rise of chemistry in the 18th century eventually clarified the roles of the gases significant in respiratory behavior. More time was needed to understand what gases provoked increases in breathing and where those gases worked. At this point, control of breathing became a significant focus of respiratory investigators. Studies included identifying the structures and functions of central and peripheral chemoreceptors, and airway receptors, sources of respiratory rhythm and pattern generation, the impact of the organism's status on its breathing including environment and disease/trauma. At this same time, mid- to late-20th century, efforts to mathematicize the variables in the control of breathing appeared. So though wonderment about the mysterious phenomenon of respiration began over two millennia ago, serious physiological investigation into its control is by comparison very young.

Effects of feedback on the perception of inspiratory resistance in children with persistent asthma: a signal detection approach

OBJECTIVE

Accurate perception of asthma episodes increases the likelihood that they will be managed effectively. The purpose of the study was to examine the effect of feedback in a signal detection task on perception of increased airflow obstruction in children with persistent asthma.

METHODS

The effect of feedback training on the perception of resistive loads was evaluated in 155 children with persistent asthma between 8 and 15 years of age. Each child participated in four experimental sessions that occurred approximately once every 2 weeks, an initial session followed by three training sessions. During the initial session, the threshold resistance to breathing was determined for each child. Subsequently, each child was randomly assigned to one of two resistive load training conditions in a signal detection paradigm: training with immediate performance feedback or training with no performance feedback.

RESULTS

The threshold resistance to breathing, determined in the initial session, was equivalent between groups. Children in the feedback condition discriminated more accurately between both the presence and the absence of increases in the resistance to breathing (206 [48] versus 180 [39] correct responses, p < .001), and differences over time between groups increased reliably as a function of training (165 [40] versus 145 [32] correct responses, p < .001). Response times and confidence ratings were equivalent between groups, and no differences in breathing patterns were observed between conditions.

CONCLUSIONS

Feedback training results in improved perception of respiratory sensations in children with asthma, a finding with implications for strategies of asthma self-management.

Dyspnea perception in cystic fibrosis patients

We evaluated dyspnea perception in cystic fibrosis patients compared with normal subjects, during an inspiratory resistive loading test and 6-min walk test. We also evaluated the correlation between dyspnea scores induced by resistive loads and by the 6-min walk test. In this prospective, cross-sectional study, 31 patients with cystic fibrosis (≥15 years of age) and 31 age-, gender-, and ethnicity-matched healthy volunteers (20 females and 11 males per group) underwent inspiratory resistive loading, spirometry, and the 6-min walk test. As the magnitude of the inspiratory loads increased, dyspnea scores increased (P<0.001), but there was no difference between groups in dyspnea score (P=0.654). Twenty-six (84%) normal subjects completed all the resistive loads, compared with only 12 (39%) cystic fibrosis patients (P<0.001). Dyspnea scores were higher after the 6-min walk test than at rest (P<0.001), but did not differ between groups (P=0.080). Post-6-min walk test dyspnea scores correlated significantly with dyspnea scores induced by resistive loads. We conclude that dyspnea perception induced in cystic fibrosis patients by inspiratory resistive loading and by 6-min walk test did not differ from that induced in normal subjects. However, cystic fibrosis patients discontinued inspiratory resistive loading more frequently. There were significant correlations between dyspnea perception scores induced by inspiratory resistance loading and by the 6-min walk test. This study should alert clinicians to the fact that some cystic fibrosis patients fail to discriminate dyspnea perception and could be at risk for delay in seeking medical care.

A review of psychological dysfunction in asthma: affective, behavioral and cognitive factors

BACKGROUND

The research on psychological dysfunction in asthma is extensive but heterogeneous. We undertook a narrative review about the effects of psychological dysfunction on asthma.

METHODS

Electronic searches of MEDLINE, EMBASE, CINAHL and the Cochrane Library were conducted, supplemented by hand-searching bibliographies and seeking expert opinion.

RESULTS

The impact of psychological factors on asthma can be classified according to dysfunction in the domains of affect, behavior and cognition. Affective or emotional disturbance may lead to poor asthma control by directly modulating disease activity. Maladaptive behaviors may occur in asthma patients. These include maladaptive breathing behaviors, such as impaired voluntary drive to breathe and dysfunctional breathing, as well as impaired asthma health behaviors, that is, a coordinated range of activities performed to maintain good disease control. Dysfunctional cognitions (thoughts and beliefs) about asthma and impaired cognitive processing of the perception of dyspnea are associated with poorly controlled disease and asthma deaths, respectively. The three domains of psychological dysfunction are often closely intertwined, leading to vicious circles.

CONCLUSIONS

We have conceptualized psychological dysfunction in asthma using a framework consisting of affect, behavior and cognition. Their influences are intertwined and complex. Future research should focus on the formulation of a psychological assessment tool based on this framework and evaluating its efficacy in improving asthma outcomes.