Sex differences in exertional dyspnea in patients with mild COPD: physiological mechanisms

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.

Sex Differences in Chronic Obstructive Pulmonary Disease: Implications for Pathogenesis, Diagnosis, and Treatment

Chronic obstructive pulmonary disease (COPD) is a leading chronic disease worldwide, with significant healthcare utilization, morbidity, and mortality. Irreversible airflow obstruction identified on spirometry establishes the diagnosis of COPD, but the disease entity encompasses a heterogeneous collection of lung diseases, including chronic bronchitis and emphysema. Despite the enormous burden of COPD, there are no pharmacological therapies that slow its progression or reduce mortality, indicating the need for a deeper understanding. There are sex differences concerning COPD prevalence, pathology, and symptoms. Historically thought to primarily affect males, its effect on females has increased significantly over time due to a rising prevalence of smoking and exposure to harmful pollutants among females. Over the past decade, the age-adjusted prevalence of COPD has been consistently higher in females than in males. Despite this, the impacts of biological sex continue to be confusing and poorly defined. The primary goal of this review is to organize and collate sex-dependent factors that may contribute to disease differences in males and females, thereby identifying future research questions in this area.

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.

Unravelling the complex interplay of factors behind exercise limitations and physical inactivity in COPD

Exercise limitation and physical inactivity are known treatable traits for people with COPD. Maximising exercise capacity and keeping people physically active improves health status and survival rates among people with COPD. However, managing these two treatable traits can be extremely challenging for clinicians due to the complex intersectionality of factors influencing an individual's capacity, opportunity and motivation to engage in physical activity. This review presents the complex factors influencing exercise capacity ("can do"), levels of physical activity ("do do") and sedentary behaviours amongst people with COPD and provides practical recommendations on how clinicians can address some of these factors in practice. Most importantly, it highlights the importance of referring to pulmonary rehabilitation as a way to improve exercise capacity among people with COPD.

Physiological Characterization of Preserved Ratio Impaired Spirometry in the CanCOLD Study: Implications for Exertional Dyspnea and Exercise Intolerance

Rationale: It is increasingly recognized that adults with preserved ratio impaired spirometry (PRISm) are prone to increased morbidity. However, the underlying pathophysiological mechanisms are unknown. Objectives: Evaluate the mechanisms of increased dyspnea and reduced exercise capacity in PRISm. Methods: We completed a cross-sectional analysis of the CanCOLD (Canadian Cohort Obstructive Lung Disease) population-based study. We compared physiological responses in 59 participants meeting PRISm spirometric criteria (post-bronchodilator FEV1 < 80% predicted and FEV1/FVC ⩾ 0.7), 264 control participants, and 170 ever-smokers with chronic obstructive pulmonary disease (COPD), at rest and during cardiopulmonary exercise testing. Measurements and Main Results: Individuals with PRISm had lower total lung, vital, and inspiratory capacities than healthy controls (all P < 0.05) and minimal small airway, pulmonary gas exchange, and radiographic parenchymal lung abnormalities. Compared with healthy controls, individuals with PRISm had higher dyspnea/[Formula: see text]o2 ratio at peak exercise (4.0 ± 2.2 vs. 2.9 ± 1.9 Borg units/L/min; P < 0.001) and lower [Formula: see text]o2peak (74 ± 22% predicted vs. 96 ± 25% predicted; P < 0.001). At standardized submaximal work rates, individuals with PRISm had greater Vt/inspiratory capacity (Vt%IC; P < 0.001), reflecting inspiratory mechanical constraint. In contrast to participants with PRISm, those with COPD had characteristic small airways dysfunction, dynamic hyperinflation, and pulmonary gas exchange abnormalities. Despite these physiological differences among the three groups, the relationship between increasing dyspnea and Vt%IC during cardiopulmonary exercise testing was similar. Resting IC significantly correlated with [Formula: see text]o2peak (r = 0.65; P < 0.001) in the entire sample, even after adjusting for airflow limitation, gas trapping, and diffusing capacity. Conclusions: In individuals with PRISm, lower exercise capacity and higher exertional dyspnea than healthy controls were mainly explained by lower resting lung volumes and earlier onset of dynamic inspiratory mechanical constraints at relatively low work rates. Clinical trial registered with www.clinicaltrials.gov (NCT00920348).

Sex-differences in COPD: from biological mechanisms to therapeutic considerations

Chronic obstructive pulmonary disease (COPD) is a heterogeneous respiratory condition characterized by symptoms of dyspnea, cough, and sputum production. We review sex-differences in disease mechanisms, structure-function-symptom relationships, responses to therapies, and clinical outcomes in COPD with a specific focus on dyspnea. Females with COPD experience greater dyspnea and higher morbidity compared to males. Imaging studies using chest computed tomography scans have demonstrated that females with COPD tend to have smaller airways than males as well as a lower burden of emphysema. Sex-differences in lung and airway structure lead to critical respiratory mechanical constraints during exercise at a lower absolute ventilation in females compared to males, which is largely explained by sex differences in maximum ventilatory capacity. Females experience similar benefit with respect to inhaled COPD therapies, pulmonary rehabilitation, and smoking cessation compared to males. Ongoing re-assessment of potential sex-differences in COPD may offer insights into the evolution of patterns of care and clinical outcomes in COPD patients over time.

Breathlessness limiting exertion in very old adults: findings from the Newcastle 85+ study

INTRODUCTION

Long-term breathlessness is more common with age. However, in the oldest old (>85 years), little is known about the prevalence, or impact of breathlessness. We estimated breathlessness limiting exertion prevalence and explored (i) associated characteristics; and (ii) whether breathlessness limiting exertion explains clinical and social/functional outcomes.

METHODS

Health and socio-demographic characteristics were extracted from the Newcastle 85+ Study cohort. Phase 1 (baseline) and follow-up data (18 months, Phase 2; 36 months, Phase 3; 60 months, Phase 4 after baseline) were examined using descriptive statistics and cross-sectional regression models.

RESULTS

Eight hundred seventeen participants provided baseline breathlessness data (38.2% men; mean 84.5 years; SD 0.4). The proportions with any limitation of exertion, or severe limitation by breathlessness were 23% (95% confidence intervals (CIs) 20-25%) and 9% (95%CIs 7-11%) at baseline; 20% (16-25%) and 5% (3-8%) at Phase 4. Having more co-morbidities (odds ratio (OR) 1.34, 1.18-1.54; P < 0.001), or self-reported respiratory (OR 1.88, 1.25-2.82; P = 0.003) or cardiovascular disease (OR 2.38, 1.58-3.58; P < 0.001) were associated with breathlessness limiting exertion. Breathlessness severely limiting exertion was associated with poorer self-rated health (OR 0.50, 029-0.86; P = 0.012), depression (beta-coefficient 0.11, P = 0.001), increased primary care contacts (beta-co-efficient 0.13, P = 0.001) and number of nights in hospital (OR 1.81; 1.02-3.20; P = 0.042).

CONCLUSIONS

Breathlessness limiting exertion appears to become less prevalent over time due to death or withdrawal of participants with cardio-respiratory illness. Breathlessness severely limiting exertion had a wide range of service utilisation and wellbeing impacts.

Exertional ventilation/carbon dioxide output relationship in COPD: from physiological mechanisms to clinical applications

There is well established evidence that the minute ventilation (V′_E)/carbon dioxide output (V′_CO2) relationship is relevant to a number of patient-related outcomes in COPD. In most circumstances, an increased V′_E/V′_CO2 reflects an enlarged physiological dead space (“wasted” ventilation), although alveolar hyperventilation (largely due to increased chemosensitivity) may play an adjunct role, particularly in patients with coexistent cardiovascular disease. The V′_E/V′_CO2 nadir, in particular, has been found to be an important predictor of dyspnoea and poor exercise tolerance, even in patients with largely preserved forced expiratory volume in 1 s. As the disease progresses, a high nadir might help to unravel the cause of disproportionate breathlessness. When analysed in association with measurements of dynamic inspiratory constraints, a high V′_E/V′_CO2 is valuable to ascertain a role for the “lungs” in limiting dyspnoeic patients. Regardless of disease severity, cardiocirculatory (heart failure and pulmonary hypertension) and respiratory (lung fibrosis) comorbidities can further increase V′_E/V′_CO2. A high V′_E/V′_CO2 is a predictor of poor outcome in lung resection surgery, adding value to resting lung hyperinflation in predicting all-cause and respiratory mortality across the spectrum of disease severity. Considering its potential usefulness, the V′_E/V′_CO2 should be valued in the clinical management of patients with COPD.

The minute ventilation/carbon dioxide production relationship is relevant to a number of patient-related outcomes in COPD. Minute ventilation/carbon dioxide production, therefore, should be valued in the clinical management of these patients.https://bit.ly/3df2upH

An integrative approach to the pulmonary physiology of exercise: when does biological sex matter?

Historically, many studies investigating the pulmonary physiology of exercise (and biomedical research in general) were performed exclusively or predominantly with male research participants. This has led to an incomplete understanding of the pulmonary response to exercise. More recently, important sex-based differences with respect to the human respiratory system have been identified. The purpose of this review is to summarize current findings related to sex-based differences in the pulmonary physiology of exercise. To that end, we will discuss how morphological sex-based differences of the respiratory system affect the respiratory response to exercise. Moreover, we will discuss sex-based differences of the physiological integrative responses to exercise, and how all these differences can influence the regulation of breathing. We end with a brief discussion of pregnancy and menopause and the accompanying ventilatory changes observed during exercise.

Recent Advances in the Physiological Assessment of Dyspneic Patients with Mild COPD

There is growing recognition that a sizable fraction of COPD patients with forced expiratory volume in one second (FEV₁)/forced vital capacity ratio below the lower limit of normal but preserved FEV₁ reports out-of-proportion dyspnea relative to the severity of airflow limitation. Most physicians, however, assume that patients' breathlessness is unlikely to reflect the negative physiological consequences of COPD vis-à-vis FEV₁ normalcy. This concise review integrates the findings of recent studies which uncovered the key pathophysiological features shared by these patients: poor pulmonary gas exchange efficiency (increased "wasted" ventilation) and gas trapping. These abnormalities are associated with two well-known causes of exertional dyspnea: heightened ventilation relative to metabolic demand and critically low inspiratory reserves, respectively. From a clinical standpoint, a low diffusion capacity associated with increased residual volume (RV) and/or RV/total lung capacity ratio might uncover these disturbances, identifying the subset of patients in whom exertional dyspnea is causally related to "mild" COPD.

Dyspnoea and symptom burden in mild-moderate COPD: the Canadian Cohort Obstructive Lung Disease Study

Studies assessing dyspnoea and health-related quality of life (HRQoL) in chronic obstructive pulmonary disease (COPD) have focussed on patients in clinical settings, not the general population. The aim of this analysis was to compare the prevalence and severity of dyspnoea and impaired HRQoL in individuals with and without COPD from the general population, focussing on mild-moderate COPD. Analysis of the 3-year Canadian Cohort Obstructive Lung Disease (CanCOLD) study included four subgroups: mild COPD (Global Initiative for Chronic Obstructive Lung Disease (GOLD) 1); moderate COPD (GOLD 2); non-COPD smokers; and non-COPD never-smokers. The primary outcome was dyspnoea (Medical Research Council (MRC) scale), and the secondary outcome was HRQoL (COPD Assessment Test (CAT) score; Saint George's Respiratory Questionnaire (SGRQ) score). Subgroups were analysed by sex, physician-diagnosed COPD status and exacerbations. 1443 participants (mild COPD (n=397); moderate COPD (n=262(; smokers (n=449) and never-smokers (n=335)) were studied. People with mild COPD were more likely to report more severe dyspnoea (MRC 2 versus 1) than those without COPD (OR (95% CI) 1.42 (1.05-1.91)), and non-COPD never-smokers (OR (95%CI) 1.64 (1.07-2.52)). Among people with mild COPD, more severe dyspnoea was reported in women versus men (MRC2 versus 1; OR (95% CI) 3.70 (2.23-6.14)); people with, versus without, physician-diagnosed COPD (MRC2 versus 1; OR (95% CI) 3.27 (1.71-6.23)), and people with versus without recent exacerbations (MRC2 versus 1; ≥2 versus 0 exacerbations: OR (95% CI) 3.62 (1.02-12.86); MRC ≥3 versus 1; 1 versus 0 exacerbation: OR (95% CI): 9.24 (2.01-42.42)). Similar between-group differences were obtained for CAT and SGRQ scores. Careful assessment of dyspnoea and HRQoL could help identify individuals for earlier diagnosis and treatment.

Use of the COPD Assessment Test (CAT) to screen for COPD in dairy farmers: AIRBAg study

OBJECTIVES

People at risk of chronic obstructive pulmonary disease (COPD) can benefit from appropriate medical management before severe symptoms appear. This study assesses the value of the COPD Assessment Test (CAT) questionnaire for screening dairy farmers, who tend to be slow or reluctant to seek health care.

METHODS

During the time period 2012-2017, 2089 randomly selected dairy farmers in Brittany (France) were invited to complete self-administered questionnaires (including the CAT) and to undergo an occupational health check-up using an electronic mini-spirometer and conventional spirometry. Those showing symptoms suggestive of COPD and/or a ratio FEV₁ /FEV₆ < 80% were sent to a pulmonologist for a further check-up, including spirometry with a reversibility test. Multivariate logistic models based on CAT scores and socio-demographic or work-related factors were developed to predict COPD.

RESULTS

The 1231 farmers who underwent the occupational health check-up included 1203 who met the inclusion/exclusion criteria. Pulmonologist identified 16 (1.3%) cases of COPD. A multivariate logistic regression model (covariates: CAT sum score, on-farm time, BMI, smoking status, free-stall mulching) provided an area under the receiver-operating characteristic curve (AUC) of 0.87 (95% CI: 0.75-0.98). Using a cut-off of 0.007 gave a sensitivity of 93.8% and a specificity of 62.4%. Another model that included CAT breathlessness and the same covariates performed marginally better (AUC = 0.88, 95% CI: 0.77-0.98).

CONCLUSION

Our predictive models can both benefit dairy farmers by providing early diagnosis and management of their COPD and avoid unnecessary, costly spirometry during the screening process.

Chronic Obstructive Pulmonary Disease in Women: A Biologically Focused Review with a Systematic Search Strategy

Purpose

Evidence suggests that chronic obstructive pulmonary disease (COPD) symptoms and progression may differ between men and women. However, limited information is currently available on the pathophysiological and biological factors that may underlie these sex-related differences. The objective of this review is to systematically evaluate reports of potential sex-related differences, including genetic, pathophysiological, structural, and other biological factors, that may influence COPD development, manifestation, and progression in women.

Patients and Methods

A PubMed literature search was conducted from inception until January 2020. Original reports of genetic, hormonal, and physiological differences, and biological influences that could contribute to COPD development, manifestation, and progression in women were included.

Results

Overall, 491 articles were screened; 29 articles met the inclusion criteria. Results from this analysis demonstrated between-sex differences in inflammatory, immune, genetic, structural, and physiological factors in patients with COPD.

Conclusion

Various biological differences are observed between men and women with COPD including differences in inflammatory and metabolic pathways related to obesity and fat distribution, immune cell function and autophagy, extent and distribution of emphysema and airway wall remodeling. An enhanced understanding of these differences has the potential to broaden our understanding of how COPD develops and progresses, thereby providing an opportunity to ultimately improve diagnosis, treatment, and monitoring of COPD in both men and women.

The effect of carotid chemoreceptor inhibition on exercise tolerance in chronic obstructive pulmonary disease: A randomized-controlled crossover trial

BACKGROUND

Patients with chronic obstructive pulmonary disease (COPD) have an exaggerated ventilatory response to exercise, contributing to exertional dyspnea and exercise intolerance. We recently demonstrated enhanced activity and sensitivity of the carotid chemoreceptor (CC) in COPD which may alter ventilatory and cardiovascular regulation and negatively affect exercise tolerance. We sought to determine whether CC inhibition improves ventilatory and cardiovascular regulation, dyspnea and exercise tolerance in COPD.

METHODS

Twelve mild-moderate COPD patients (FEV₁ 83 ± 15 %predicted) and twelve age- and sex-matched healthy controls completed two time-to-symptom limitation (T_LIM) constant load exercise tests at 75% peak power output with either intravenous saline or low-dose dopamine (2 μg·kg^-1·min^-1, order randomized) to inhibit the CC. Ventilatory responses were evaluated using expired gas data and dyspnea was evaluated using a modified Borg scale. Inspiratory capacity maneuvers were performed to determine operating lung volumes. Cardiac output was estimated using impedance cardiography and vascular conductance was calculated as cardiac output/mean arterial pressure (MAP).

RESULTS

At a standardized exercise time of 4-min and at T_LIM; ventilation, operating volumes and dyspnea were unaffected by dopamine in COPD patients and controls. In COPD, dopamine decreased MAP and increased vascular conductance at all time points. In controls, dopamine increased vascular conductance at T_LIM, while MAP was unaffected.

CONCLUSION

There was no change in time to exhaustion in either group with dopamine. These data suggest that the CC plays a role in cardiovascular regulation during exercise in COPD; however, ventilation, dyspnea and exercise tolerance were unaffected by CC inhibition in COPD patients.

New insights into early intervention of chronic obstructive pulmonary disease with mild airflow limitation

Chronic obstructive pulmonary disease (COPD) has become one of the major public health problems worldwide due to its high morbidity and mortality. Up until now, COPD is still under-diagnosed and under-treated, especially for mild or moderate patients. It is widely accepted that the majority of patients with COPD are in the early stages, yet this subpopulation is underestimated. In recent years, growing evidence indicates that substantial physiological and clinical abnormalities exist in patients with mild COPD compared with healthy controls. Furthermore, recent studies suggest that pharmacologic intervention in early COPD has the potential to alter clinical outcomes. The main objective of this review is to summarize recent research regarding the heterogeneous pathophysiology, clinical features, and treatment of mild and moderate COPD. We also discuss promising markers of disease progression, which may contribute to the development of precision medicine in early COPD.

Functional Status of Patients with COPD Assessed by London Chest Activity of Daily Living Scale: Gender Association and Validity of a Cutoff Point

PURPOSE

Whether the difference in the impact of chronic obstructive pulmonary disease (COPD) on the functional status of men and women stems from clinical distinctions or to the measuring instrument used is unclear. Like most instruments for assessing functional limitation in COPD, the interpretation of the results of the London Chest Activity of Daily Living (LCADL) scale is limited because a lack of a valid cutoff point to this scale. For that, this study sought to compare the functional status between men and women with COPD; and propose a cutoff point for LCADL capable of discriminating the prognosis of these individuals.

METHODS

A sample of 138 subjects with moderate-severe COPD was evaluated by the LCADL. The percentage of the individual maximum score was used to obtain a cutoff point capable of discriminating patients with the worse prognosis according to the BODE Index. The cutoff point was also tested in an independent sample (n = 70).

RESULTS

Regarding the total score, domestic and leisure domains of the LCADL, men had better scores than women (P ≤ 0.01). The cutoff point found was 37% (area under the curve = 0.70, 95% confidence interval = 0.60-0.80, sensitivity = 0.55 and specificity = 0.74). Individuals who scored ≥ 37% had a worse prognosis and level of physical activities of daily living than those who scored below (P ≤ 0.02).

CONCLUSION

When evaluated by the LCADL, men and women with COPD present difference in the functional status. The established cutoff point (37%) adequately discriminates individuals regarding the prognosis, contributing to improve the interpretation capacity of the LCADL.

The six-minute stepper test is related to muscle strength but cannot substitute for the one repetition maximum to prescribe strength training in patients with COPD

Purpose

There are many barriers to pulmonary rehabilitation, including a limited access to evaluation centers. To cope with these difficulties, field tests are often used to prescribe endurance training. As field tests are related to muscle strength, they could also be used to prescribe strength training and increase the access to pulmonary rehabilitation in rural area. However, their validity for this purpose has never been studied.

Patients and methods

The relationship between the 6-minute stepper test (6MST), 6-minute walk test, maximal workload achieved during cardiopulmonary exercise testing (Wpeak), and one repetition maximum (1RM) was assessed in 35 patients with COPD through a retrospective chart review to derive predictive equation of the 1RM from these tests. The effectiveness of these equations to prescribe strength training at 70% of the 1RM was assessed in an independent cross-validation group of 34 patients with COPD.

Results

There was a moderate relationship between the 6MST, Wpeak and the 1RM (r=0.44 and r=0.41, respectively, both P≤0.01). Whatever the test, the prescription of strength training using the estimated 1RM compared with the measured 1RM resulted in a mean absolute difference and a mean bias of about 30 kg.

Conclusion

The use of the 6MST and Wpeak for the prescription of strength training would result in a clinically not acceptable error. Therefore, they should not be used as a substitute for the 1RM to prescribe strength training.

Manipulation of mechanical ventilatory constraint during moderate intensity exercise does not influence dyspnoea in healthy older men and women

KEY POINTS

The perceived intensity of exertional breathlessness (i.e. dyspnoea) is higher in older women than in older men, possibly as a result of sex-differences in respiratory system morphology. During exercise at a given absolute intensity or minute ventilation, older women have a greater degree of mechanical ventilatory constraint (i.e. work of breathing and expiratory flow limitation) than their male counterparts, which may lead to a greater perceived intensity of dyspnoea. Using a single-blind randomized study design, we experimentally manipulated the magnitude of mechanical ventilatory constraint during moderate-intensity exercise at ventilatory threshold in healthy older men and women. We found that changes in the magnitude of mechanical ventilatory constraint within the physiological range had no effect on dyspnoea in healthy older adults. When older men and women perform moderate intensity exercise, mechanical ventilatory constraint does not contribute significantly to the sensation of dyspnoea.

ABSTRACT

We aimed to determine the effect of manipulating mechanical ventilatory constraint during submaximal exercise on dyspnoea in older men and women. Eighteen healthy subjects (aged 60-80 years; nine men and nine women) completed two days of testing. On day 1, subjects were assessed for pulmonary function and performed a maximal incremental cycle exercise test. On day 2, subjects performed three 6-min bouts of cycling at ventilatory threshold, in a single-blind randomized manner, while breathing: (i) normoxic helium-oxygen (HEL) to reduce the work of breathing (W_b ) and alleviate expiratory flow limitation (EFL); (ii) through an inspiratory resistance (RES) of ∼5 cmH₂ O L^-1  s^-1 to increase W_b ; and (iii) ambient air as a control (CON). Oesophageal pressure, diaphragm electromyography, and sensory responses (category-ratio 10 Borg scale) were monitored throughout exercise. During the HEL condition, there was a significant decrease in W_b (men: -21 ± 6%, women: -17 ± 10%) relative to CON (both P < 0.01). Moreover, if EFL was present during CON (four men and five women), it was alleviated during HEL. Conversely, during the RES condition, W_b (men: 42 ± 19%, women: 50 ± 16%) significantly increased relative to CON (both P < 0.01). There was no main effect of sex on W_b (P = 0.59). Across conditions, women reported significantly higher dyspnoea intensity than men (2.9 ± 0.9 vs. 1.9 ± 0.8 Borg scale units, P < 0.05). Despite significant differences in the degree of mechanical ventilatory constraint between conditions, the intensity of dyspnoea was unaffected, independent of sex (P = 0.46). When older men and women perform moderate intensity exercise, mechanical ventilatory constraint does not contribute significantly to the sensation of dyspnoea.

Impact of pulmonary emphysema on exercise capacity and its physiological determinants in chronic obstructive pulmonary disease

Exercise limitation is common in chronic obstructive pulmonary disease (COPD). We determined the impact of pulmonary emphysema on the physiological response to exercise independent of contemporary measures of COPD severity. Smokers 40–79 years old with COPD underwent computed tomography, pulmonary function tesing, and symptom-limited incremental exercise testing. COPD severity was quantified according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) by spirometry (GOLD 1–4); and symptom burden and exacerbation risk (GOLD A-D). Emphysema severity was quantified as the percent lung volume <−950 Hounsfield units. Regression models adjusted for age, gender, body size, smoking status, airflow limitation, symptom burden and exacerbation risk. Among 67 COPD subjects (age 67 ± 8 years; 75% male; GOLD 1–4: 11%, 43%, 30%, 16%), median percent emphysema was 11%, and peak power output (PPO) was 61 ± 32 W. Higher percent emphysema independently predicted lower PPO (−24 W per 10% increment in emphysema; 95%CI −41 to −7 W). Throughout exercise, higher percent emphysema predicted 1) higher minute ventilation, ventilatory equivalent for CO₂, and heart rate; and 2) lower oxy-hemoglobin saturation, and end-tidal PCO₂. Independent of contemporary measures of COPD severity, the extent of pulmonary emphysema predicts lower exercise capacity, ventilatory inefficiency, impaired gas-exchange and increased heart rate response to exercise.

Effects of pulmonary rehabilitation in patients with mild-to-moderate chronic obstructive pulmonary disease: Bottom of an iceberg

OBJECTIVES

This study aims to compare the effects of pulmonary rehabilitation (PR) in patients with mild-to-moderate and severe-to-very severe chronic obstructive pulmonary disease (COPD).

PATIENTS AND METHODS

Between January 2005 and December 2010, a total of 76 patients with mild-to-moderate (Global Initiative for Chronic Obstructive Lung Disease [GOLD] Stages I+II, n=33, mean age 66.0±8.6 years) and severe-to-very severe (GOLD Stages III+IV, n=43, mean age 63.5±8.8 years) COPD completed an eight-week outpatient PR program. Incremental and endurance shuttle walk tests (ISWT, ESWT), St. George's Respiratory Questionnaire (SGRQ), Chronic Respiratory Questionnaire (CRQ), and Hospital Anxiety and Depression Scale were assessed before and after PR. Changes after the intervention were compared between two groups.

RESULTS

There were significant improvements in the ISWT and median 60 m [(-150)-(400)] in mild-to-moderate group and 70 m [(0)-(270)] in severe-to-very severe group (both, p<0.001). The ESWT time improved in both groups, 122s [(-279)-(665)] (p=0.002) and 61s [(-180)- (878)] (p<0.001), respectively. Significant effects were observed in all domains of the SGRQ except the impact score in mild-to-moderate patients. There were significant improvements in all domains except the symptoms score in severe-to-very severe patients. Using the CRQ, a significant improvement was shown in all domains of CRQ except the dyspnea score of mild-to-moderate patients. Anxiety and depression scores decreased after PR in both groups (p<0.05). According to changes in outcomes, there was no difference in any parameters between two groups.

CONCLUSION

This study demonstrates that patients with mild-to-moderate COPD benefit from PR comparably to patients with severe-to- very-severe COPD. Although patients with mild-to-moderate COPD are not usually symptomatic, our findings suggest that they should be included in PR.

Clinical impact of the lower limit of normal of FEV1/FVC on detecting chronic obstructive pulmonary disease: A follow-up study based on cross-sectional data

BACKGROUND

Criteria of obstruction that establish a diagnosis of COPD have been debated in recent years. We carried out a follow-up study to assess the impact of the new LLN reference equation for Chinese on detecting COPD compared with the traditional 0.7fixed criteria.

METHODS

We examined the prevalence and characteristics of airflow limitation for a non-child population using post-bronchodilator airflow with both age-dependent predicted lower limit of the normal value and fixed-ratio spirometric criterion. Questionnaires and spirometry were completed for all eligible subjects during the baseline examination. Participants with inconsistent diagnosis according to the two criteria, normal participants (controls) and COPD patients in stages I or II, were invited to take a cardiopulmonary exercise testing (CPET) examination and follow up for 2-4 years.

RESULTS

A total of 5448 (mean age 50.51 ± 13.2 yr) study subjects with acceptable spirometry and complete questionnaire data were included in our final analyses. COPD detection based on LLN was consistent with the GOLD 0.7 fixed-ratio in general, as 51 subjects (0.9%) were underdiagnosed, and 61 subjects (1.1%) were overdiagnosed when using LLN as the reference diagnostic criterion. The underdiagnosed subjects were younger, had more symptoms, more exposure to biofuels and worse FEV₁ than the normal group; they also demonstrated a damaged cardiopulmonary reserve capacity and significant FEV₁ decline. Except for being older, the overdiagnosed subjects differed little from the normal group.

CONCLUSIONS

Individual-dependent LLN appears to better reveal impacts on detecting airflow limitation. Participants underdiagnosed by GOLD criterion should be paid more attention.

CLINICAL TRIAL REGISTRATION

ChiCTR-ECS-13004110.

Neurophysiological mechanisms of exertional dyspnoea in fibrotic interstitial lung disease

Our understanding of the mechanisms of dyspnoea in fibrotic interstitial lung disease (ILD) is incomplete. The aims of this study were two-fold: 1) to determine whether dyspnoea intensity is better predicted by neural respiratory drive (NRD) or neuromechanical uncoupling (NMU) of the respiratory system in fibrotic ILD, and 2) to examine the effect of breathing 60% oxygen on NRD, NMU and dyspnoea ratings.Fourteen patients with fibrotic ILD were included. Visit 1 comprised a familiarisation incremental cycle exercise test, Visit 2 comprised a normoxic incremental cycling test to address Aim 1, and Visits 3 and 4 consisted of constant-load cycling while breathing room air or 60% oxygen to address Aim 2. Diaphragmatic electromyography (EMGdi) was used as a surrogate of NRD. NMU was calculated as the ratio between EMGdi (%max) and tidal volume (%vital capacity).On adjusted analysis, NMU and its constituents were all significantly associated with dyspnoea ratings during incremental cycling, with EMGdi having the strongest correlation. The between-treatment change in dyspnoea ratings during constant load cycling was only correlated with change in exercise endurance time and NMU.Dyspnoea more strongly reflected the level of EMGdi than NMU in fibrotic ILD. However, the improvement in dyspnoea with 60% oxygen was better predicted by improvements in NMU.

Absolute lung size and the sex difference in breathlessness in the general population

Background

Breathlessness is associated with major adverse health outcomes and is twice as common in women as men in the general population. We evaluated whether this is related to their lower absolute lung volumes.

Methods

Cross-sectional analysis of the population-based Swedish CardioPulmonarybioImage Study (SCAPIS) Pilot, including static spirometry and diffusing capacity (n = 1,013; 49% women). Breathlessness was measured using the modified Medical Research Council (mMRC) scale and analyzed using ordinal logistic regression adjusting for age, pack-years of smoking, body mass index, chronic airway limitation, asthma, chronic bronchitis, depression and anxiety in all models.

Results

Breathlessness was twice as common in women as in men; adjusted odds ratio (OR) 2.20 (95% confidence interval, 1.32−3.66). Lower absolute lung volumes were associated with increased breathlessness prevalence in both men and women. The sex difference in breathlessness was unchanged when adjusting for lung function in %predicted, but disappeared when controlling for absolute values of total lung capacity (OR 1.12; 0.59−2.15), inspiratory capacity (OR 1.26; 0.68−2.35), forced vital capacity (OR 0.84; 0.42−1.66), forced expiratory volume in one second (OR 0.70; 0.36−1.35) or lung diffusing capacity (OR 1.07; 0.58−1.97).

Conclusion

In the general population, the markedly higher prevalence of breathlessness in women is related to their smaller absolute lung volumes.

Systemic effects of chronic obstructive pulmonary disease in young-old adults' life-space mobility

PURPOSE

The objective was to assess whether dyspnea, peripheral muscle strength and the level of physical activity are correlated with life-space mobility of older adults with COPD.

PATIENTS AND METHODS

Sixty patients over 60 years of age (40 in the COPD group and 20 in the control group) were included. All patients were evaluated for lung function (spirometry), life-space mobility (University of Alabama at Birmingham Study of Aging Life-Space Assessment), dyspnea severity (Modified Dyspnea Index), peripheral muscle strength (handgrip dynamometer), level of physical activity and number of daily steps (accelerometry). Groups were compared using unpaired t-test. Pearson's correlation was used to test the association between variables.

RESULTS

Life-space mobility (60.41±16.93 vs 71.07±16.28 points), dyspnea (8 [7-9] vs 11 [10-11] points), peripheral muscle strength (75.16±14.89 vs 75.50±15.13 mmHg), number of daily steps (4,865.4±2,193.3 vs 6,146.8±2,376.4 steps), and time spent in moderate to vigorous activity (197.27±146.47 vs 280.05±168.95 minutes) were lower among COPD group compared to control group (p<0.05). The difference was associated with the lower mobility of COPD group in the neighborhood.

CONCLUSION

Life-space mobility is decreased in young-old adults with COPD, especially at the neighborhood level. This impairment is associated to higher dyspnea, peripheral muscle weakness and the reduced level of physical activity.

Absolute values of lung function explain the sex difference in breathlessness in the general population

Activity-related breathlessness is twice as common among females as males in the general population and is associated with adverse health outcomes. We tested whether this sex difference is explained by the lower absolute forced expiratory volume in 1 s (FEV1) or forced vital capacity (FVC) in females.

This was a cross-sectional analysis of 3250 subjects (51% female) aged 38−67 years across 13 countries in the population-based third European Community Respiratory Health Survey. Activity-related breathlessness was measured using the modified Medical Research Council (mMRC) scale. Associations with mMRC were analysed using ordered logistic regression clustering on centre, adjusting for post-bronchodilator spirometry, body mass index, pack-years smoking, cardiopulmonary diseases, depression and level of exercise.

Activity-related breathlessness (mMRC ≥1) was twice as common in females (27%) as in males (14%) (odds ratio (OR) 2.21, 95% CI 1.79−2.72). The sex difference was not reduced when controlling for FEV1 % predicted (OR 2.33), but disappeared when controlling for absolute FEV1 (OR 0.89, 95% CI 0.69−1.14). Absolute FEV1 explained 98−100% of the sex difference adjusting for confounders. The effect was similar within males and females, when using FVC instead of FEV1 and in healthy never-smokers.

The markedly more severe activity-related breathlessness among females in the general population is explained by their smaller spirometric lung volumes.

Physiological and clinical relevance of exercise ventilatory efficiency in COPD

Exercise ventilation (V'_E) relative to carbon dioxide output (V'_CO2 ) is particularly relevant to patients limited by the respiratory system, e.g. those with chronic obstructive pulmonary disease (COPD). High V'_E-V'_CO2 (poor ventilatory efficiency) has been found to be a key physiological abnormality in symptomatic patients with largely preserved forced expiratory volume in 1 s (FEV₁). Establishing an association between high V'_E-V'_CO2 and exertional dyspnoea in mild COPD provides evidence that exercise intolerance is not a mere consequence of detraining. As the disease evolves, poor ventilatory efficiency might help explaining "out-of-proportion" breathlessness (to FEV₁ impairment). Regardless, disease severity, cardiocirculatory co-morbidities such as heart failure and pulmonary hypertension have been found to increase V'_E-V'_CO2 In fact, a high V'_E-V'_CO2 has been found to be a powerful predictor of poor outcome in lung resection surgery. Moreover, a high V'_E-V'_CO2 has added value to resting lung hyperinflation in predicting all-cause and respiratory mortality across the spectrum of COPD severity. Documenting improved ventilatory efficiency after lung transplantation and lung volume reduction surgery provides objective evidence of treatment efficacy. Considering the usefulness of exercise ventilatory efficiency in different clinical scenarios, the V'_E-V'_CO2 relationship should be valued in the interpretation of cardiopulmonary exercise tests in patients with mild-to-end-stage COPD.

Respiratory constraints during activities in daily life and the impact on health status in patients with early-stage COPD: a cross-sectional study

In patients with chronic obstructive pulmonary disease (COPD), exercise capacity is reduced, resulting over time in physical inactivity and worsened health status. It is unknown whether ventilatory constraints occur during activities of daily life (ADL) in early stages of COPD. The aim of this study was to assess respiratory mechanics during ADL and to study its consequences on dyspnoea, physical activity and health status in early-stage COPD compared with healthy controls. In this cross-sectional study, 39 early-stage COPD patients (mean FEV₁ 88±s.d. 12% predicted) and 20 controls performed 3 ADL: climbing stairs, vacuum cleaning and displacing groceries in a cupboard. Respiratory mechanics were measured during ADL. Physical activity was measured with accelerometry. Health status was assessed by the Nijmegen Clinical Screening Instrument. Compared with controls, COPD patients had greater ventilatory inefficiency and higher ventilatory requirements during ADL (P<0.05). Dyspnoea scores were increased in COPD compared with controls (P<0.001). During ADL, >50% of the patients developed dynamic hyperinflation in contrast to 10–35% of the controls. Higher dyspnoea was scored by patients with dynamic hyperinflation. Physical activity was low but comparable between both groups. From the patients, 55–84% experienced mild-to-severe problems in health status compared with 5–25% of the controls. Significant ventilatory constraints already occur in early-stage COPD patients during common ADL and result in increased dyspnoea. Physical activity level is not yet reduced, but many patients already experience limitations in health status. These findings reinforce the importance of early diagnosis of COPD and assessment of more than just spirometry.

Heart-lung interaction in a model of COPD: importance of lung volume and direct ventricular interaction

Chronic obstructive pulmonary disease (COPD) is associated with dynamic lung hyperinflation (DH), increased pulmonary vascular resistance (PVR), and large increases in negative intrathoracic pressure (nITP). The individual and interactive effect of these stressors on left ventricular (LV) filling, emptying, and geometry and the role of direct ventricular interaction (DVI) in mediating these interactions have not been fully elucidated. Twenty healthy subjects were exposed to the following stressors alone and in combination: 1) inspiratory resistive loading of -20 cmH₂O (nITP), 2) expiratory resistive loading to cause dynamic hyperinflation (DH), and 3) normobaric-hypoxia to increase PVR (hPVR). LV volumes and geometry were assessed using triplane echocardiography. LV stroke volume (LVSV) was reduced during nITP by 7 ± 7% (mean ± SD; P < 0.001) through a 4 ± 5% reduction in LV end-diastolic volume (LVEDV) (P = 0.002), while DH reduced LVSV by 12 ± 13% (P = 0.001) due to a 9 ± 10% reduction in LVEDV (P < 0.001). The combination of nITP and DH (nITP+DH) caused larger reductions in LVSV (16 ± 16%, P < 0.001) and LVEDV (12 ± 10%, P < 0.001) than nITP alone (P < 0.05). The addition of hPVR to nITP+DH did not further reduce LV volumes. Significant septal flattening (indicating DVI) occurred in all conditions, with a significantly greater leftward septal shift occurring with nITP+DH than either condition alone (P < 0.05). In summary, the interaction of nITP and DH reduces LV filling through DVI. However, DH may be more detrimental to LV hemodynamics than nITP, likely due to mediastinal constraint of the heart amplifying DVI.

Prevalence and Outcomes of Breathlessness in Older Adults: A National Population Study

OBJECTIVES

To determine the prevalence and outcomes of breathlessness in older Americans.

SETTING

Community-dwelling older adults.

PARTICIPANTS

Individuals aged 70 and older in the nationally representative Health and Retirement Study (2008, follow-up through 2012) (N = 3,671; mean age 78).

MEASUREMENTS

Breathlessness was assessed by asking the question, "How often do you become short of breath while awake?" Responses of often or sometimes were considered to represent a level of breathlessness sufficient to warrant clinical attention. The prevalence of breathlessness is described overall and in subpopulations, then rates of associated symptoms, well-being, and health services use of participants who were breathless are compared with rates of those who were not. The risk of decline in activities of daily living (ADLs) and death through 2012 was estimated by creating a multivariable Cox proportional hazards model, adjusting for age, sex, race and ethnicity, and education.

RESULTS

Twenty-five percent of participants reported breathlessness. The prevalence of breathlessness was higher in certain subpopulations: chronic lung disease (63%), multimorbidity (≥2 chronic conditions) (45%), current smokers (38%), heart disease (36%), obesity (body mass index ≥30.0 kg/m² ) (33%), and education less than high school (32%). Breathlessness was associated with higher rates of depression, anxiety, and severe fatigue; lower ratings of well-being; and higher rates of clinic and emergency department visits and hospitalizations (all P < .001). Breathlessness predicted ADL decline over 5 years (adjusted hazard ratio (aHR) = 1.43, 95% confidence interval (CI) = 1.22-1.68) and death (aHR 1.62, 95% CI = 1.32-2.02).

CONCLUSION

One in four adults aged 70 and older in the United States experiences breathlessness, which is associated with lack of well-being, greater health services use, and a 40% greater risk of worsened function and 60% greater risk of death over the next 5 years.

Qualitative dimensions of exertional dyspnea in adults with cystic fibrosis

No studies of cystic fibrosis (CF) have systematically characterized the evolution of the qualitative dimensions of exertional dyspnea. Adults with CF (n = 25) and control individuals matched for sex, age, and body mass index (n = 25) underwent cardiopulmonary cycle exercise testing with a detailed evaluation of ventilatory and dyspnea responses. The qualitative dimensions of dyspnea were examined during each exercise stage by having subjects select phrases that best described their breathing (i.e., "work/effort," "unsatisfied inspiration," and "unsatisfied expiration"). Subjects also selected phrases that described the quality of their breathing at peak exercise using an established 15-item questionnaire, which was then clustered into different categories. Subjects with CF had greater ventilatory requirements, higher end-inspiratory and end-expiratory lung volumes (% total lung capacity), and an earlier inflection/plateau in tidal volume during exercise compared with control subjects. Increased work/effort was the dominant qualitative descriptor in both groups throughout exercise. Unsatisfied inspiration was selected by 48% of subjects with CF and 40% of controls at some point during exercise. The onset of unsatisfied inspiration in these subjects occurred at a significantly lower relative exercise intensity in subjects with CF vs. controls (72 ± 21 vs. 94 ± 11% Wmax, P < 0.01). Chest tightness was the only qualitative descriptor cluster that was selected more frequently by subjects with CF vs. controls (36 vs. 0%, respectively, P < 0.05) at peak exercise. Therapeutic interventions that reduce ventilatory requirements and improve lung volumes may delay the onset of distressing sensations such as unsatisfied inspiration and chest tightness in adults with CF.

Breathlessness in Elderly Adults During the Last Year of Life Sufficient to Restrict Activity: Prevalence, Pattern, and Associated Factors

OBJECTIVES

To investigate relationships between age, clinical characteristics, and breathlessness sufficient to have people spend at least half a day a month in bed or to cut down on their usual activities (restricting breathlessness) during the last year of life.

DESIGN

Secondary data analysis.

SETTING

General community.

PARTICIPANTS

Nondisabled persons aged 70 and older (N=754).

MEASUREMENTS

Monthly telephone interviews were conducted to determine the occurrence of restricting breathlessness. The primary outcome was percentage of months with restricting breathlessness reported during the last year of life.

RESULTS

Data regarding breathlessness were available for 548 of 589 (93.0%) participants who died (mean age 86.7, range 71-106; 38.8% male) between enrollment (March 1998 to October 1999) and June 2013; 311 of these (56.8%) reported restricting breathlessness at some point during the last year of life, but none reported it every month. Frequency increased in the months closer to death, irrespective of cause. Restricting breathlessness was associated with anxiety (0.25 percentage points greater in months with breathlessness per percentage point months reported anxiety, 95% confidence interval (CI)=0.16-0.34, P<.001), depression (0.14, 95% CI=0.05-0.24, P=.003), and mobility problems (0.07, 0.03-0.1, P<.001). Percentage months of restricting breathlessness was greater if chronic lung disease was noted at the most-recent comprehensive assessment (6.62 percentage points, 95% CI=4.31-8.94, P<.001), heart failure (3.34 percentage points, 95% CI=0.71-5.97, P=.01), and ex-smoker status (3.01 percentage points, 95% CI=0.94-5.07, P=.004) but decreased with older age (-0.19 percentage points, 95% CI=-0.37 to -0.02, P=.03).

CONCLUSION

Restricting breathlessness increased in this elderly population in the months preceding death from any cause. Breathlessness should be assessed and managed in the context of poor prognosis.

The Interpretation of Dyspnea in the Patient with Asthma

Physicians have noted dyspnea in severely ill asthmatic patients to be associated with fright or panic; in more stable patients dyspnea may reflect characteristics including lung function, personality and behavioral traits. This study evaluates the symptom of dyspnea in 32 asthmatic patients twice: first when acutely ill and again after an initial response to therapy. Spirometry was performed, dyspnea quantified (Borg scale), and panic assessed with a specialized measure of acute panic (the acute panic inventory (API)) in the 32 patients before and again after treatment. After treatment, questionnaires to evaluate somatization and panic disorder were also administered. When acutely ill, both the API and all spirometric measures (PEFR; FEV1; IC) correlated with dyspnea. Multiple linear regression showed that measures of the API, the peak expiratory flow rate, and female sex taken together accounted for 41% of dyspnea in acute asthma. After treatment, the API again predicted dyspnea while spirometric data did not. Those subjects who described themselves as having chronic panic disorder reported high grades of dyspnea after treatment also. We conclude that interpretations of the self-report of asthma differ between acutely ill and stable asthmatic patients.

Cardiorespiratory and sensory responses to exercise in adults with mild cystic fibrosis

The purpose of this study was to evaluate cardiorespiratory fitness and reasons for exercise curtailment in a contemporary adult cystic fibrosis (CF) cohort with mild lung disease. Adults with mild CF (n = 19, forced expiratory volume in 1 s = 95 ± 17% predicted) were age-, sex-, ethnicity-, and body mass index-matched to healthy controls (n = 19) and underwent a detailed cardiopulmonary cycle exercise test. While CF subjects had a reduced peak oxygen uptake compared with controls, the values were normal when expressed as %predicted in 14/19 (74%) of subjects. Both groups demonstrated a normal cardiovascular limitation to exercise and stopped exercise primarily because of leg fatigue. Despite not being exercise-limited by respiratory factors, there was some evidence of ventilatory abnormalities as patients with mild CF had increased end-inspiratory lung volumes and reached an inflection/plateau in tidal volume relative to minute ventilation at lower exercise intensities compared with controls. Subjects with CF were not more likely to demonstrate expiratory flow limitation compared with controls and did not have evidence of dynamic hyperinflation during exercise. Despite increased end-inspiratory lung volumes and an earlier tidal volume inflection/plateau, CF subjects did not experience higher levels of dyspnea. In an exploratory analysis, a significant inverse correlation was observed between sweat chloride and peak work rate. Adult CF subjects with relatively well preserved spirometry have normal exercise performance relative to reference values and are primarily limited by nonrespiratory factors. However, ventilatory abnormalities were detected even in this mild CF cohort and should be evaluated in future therapeutic trials focused on disease-modifying therapies in mild CF.

Pulmonary Gas Exchange Abnormalities in Mild Chronic Obstructive Pulmonary Disease. Implications for Dyspnea and Exercise Intolerance

RATIONALE

Several studies in mild chronic obstructive pulmonary disease (COPD) have shown a higher than normal ventilatory equivalent for carbon dioxide ([Formula: see text]e/[Formula: see text]co2) during exercise. Our objective was to examine pulmonary gas exchange abnormalities and the mechanisms of high [Formula: see text]e/[Formula: see text]co2 in mild COPD and its impact on dyspnea and exercise intolerance.

METHODS

Twenty-two subjects (11 patients with GOLD [Global Initiative for Chronic Obstructive Lung Disease] grade 1B COPD, 11 age-matched healthy control subjects) undertook physiological testing and a symptom-limited incremental cycle exercise test with arterial blood gas collection.

MEASUREMENTS AND MAIN RESULTS

Patients (post-bronchodilator FEV1: 94 ± 10% predicted; mean ± SD) had evidence of peripheral airway dysfunction and reduced peak oxygen uptake compared with control subjects (80 ± 18 vs. 113 ± 24% predicted; P<0.05). Arterial blood gases were within the normal range and effective alveolar ventilation was not significantly different from control subjects throughout exercise. The alveolar-arterial O2 tension gradient was elevated at rest and throughout exercise in COPD (P<0.05). [Formula: see text]e/[Formula: see text]co2, dead space to tidal volume ratio (Vd/Vt), and arterial to end-tidal CO2 difference were all higher (P<0.05) in patients with COPD than in control subjects during exercise. In patients with COPD versus control subjects, there was significant dynamic hyperinflation and greater tidal volume constraints (P<0.05). Standardized dyspnea intensity ratings were also higher (P<0.05) in patients with COPD versus control subjects in association with higher ventilatory requirements. Within all subjects, Vd/Vt correlated with the [Formula: see text]e/[Formula: see text]co2 ratio during submaximal exercise (r=0.780, P<0.001).

CONCLUSIONS

High Vd/Vt was the most consistent gas exchange abnormality in smokers with only mild spirometric abnormalities. Compensatory increases in minute ventilation during exercise maintained alveolar ventilation and arterial blood gas homeostasis but at the expense of earlier dynamic mechanical constraints, greater dyspnea, and exercise intolerance in mild COPD.

Sex differences in the intensity and qualitative dimensions of exertional dyspnea in physically active young adults

Understanding sex differences in the qualitative dimensions of exertional dyspnea may provide insight into why women are more affected by this symptom than men. This study explored the evolution of the qualitative dimensions of dyspnea in 70 healthy, young, physically active adults (35 M and 35 F). Participants rated the intensity of their breathing discomfort (Borg 0-10 scale) and selected phrases that best described their breathing from a standardized list (work/effort, unsatisfied inspiration, and unsatisfied expiration) throughout each stage of a symptom-limited incremental-cycle exercise test. Following exercise, participants selected phrases that described their breathing at maximal exercise from a list of 15 standardized phrases. Intensity of breathing discomfort was significantly higher in women for a given ventilation, but differences disappeared when ventilation was expressed as a percentage of maximum voluntary ventilation. The dominant qualitative descriptor in both sexes throughout exercise was increased work/effort of breathing. At peak exercise, women were significantly more likely to select the following phrases: "my breathing feels shallow," "I cannot get enough air in," "I cannot take a deep breath in," and "my breath does not go in all the way." Women adopted a more rapid and shallow breathing pattern and had significantly higher end-inspiratory lung volumes relative to total lung capacity throughout exercise relative to men. These findings suggest that men and women do not differ in their perceived quality of dyspnea during submaximal exercise, but subjective differences appear at maximal exercise and may be related, at least in part, to underlying sex differences in breathing patterns and operating lung volumes during exercise.

Physiological impairment in mild COPD

Chronic obstructive pulmonary disease (COPD) is a common and often progressive inflammatory disease of the airways, alveoli and microvasculature that is both preventable and treatable. It is well established that smokers with mild airway obstruction, as spirometrically defined, represent the vast majority of patients with COPD, yet this population has not been extensively studied. An insidious preclinical course means that mild COPD is both underdiagnosed and undertreated. In this context, recent studies have confirmed that even patients with mild COPD can have extensive physiological impairment, which contributes to poor perceived health status compared with non-smoking healthy controls. This review describes the heterogeneous pathophysiology that can exist in COPD patients with only mild airway obstruction on spirometry. It exposes the compensatory adaptations that develop in such patients to ensure that the respiratory system fulfils its primary task of maintaining adequate pulmonary gas exchange for the prevailing metabolic demand. It demonstrates that adaptations such as increased inspiratory neural drive to the diaphragm due to combined effects of increased mechanical loading and chemostimulation underscore the increased dyspnoea and exercise intolerance in this population. Finally, based on available evidence, we present what we believe is a sound physiological rationale for earlier diagnosis in this population.

Physiologic characterization of the chronic bronchitis phenotype in GOLD grade IB COPD

BACKGROUND

Smokers with persistent cough and sputum production (chronic bronchitis [CB]) represent a distinct clinical phenotype, consistently linked to negative clinical outcomes. However, the mechanistic link between physiologic impairment, dyspnea, and exercise intolerance in CB has not been studied, particularly in those with mild airway obstruction. We, therefore, compared physiologic abnormalities during rest and exercise in CB to those in patients without symptoms of mucus hypersecretion (non-CB) but with similar mild airway obstruction.

METHODS

Twenty patients with CB (≥ 3 months cough/sputum in 2 successive years), 20 patients without CB but with GOLD (Global Initiative for Chronic Obstructive Lung Disease) grade IB COPD, and 20 age- and sex-matched healthy control subjects underwent detailed physiologic testing, including tests of small airway function and a symptom-limited incremental cycle exercise test.

RESULTS

Patients with CB (mean ± SD postbronchodilator FEV1, 93% ± 12% predicted) had greater chronic activity-related dyspnea, poorer health-related quality of life, and reduced habitual physical activity compared with patients without CB and control subjects (all P < .05). The degree of peripheral airway dysfunction and pulmonary gas trapping was comparable in both patient groups. Peak oxygen uptake was similarly reduced in patients with CB and those without compared with control subjects (% predicted ± SD, 70 ± 26, 71 ± 29 and 106 ± 43, respectively), but those with CB had higher exertional dyspnea ratings and greater respiratory mechanical constraints at a standardized work rate than patients without CB (P < .05).

CONCLUSIONS

Patients with CB reported greater chronic dyspnea and activity restriction than patients without CB and with similar mild airway obstruction. The CB group had greater dynamic respiratory mechanical impairment and dyspnea during exercise than patients without CB, which may help explain some differences in important patient-centered outcomes between the groups.

Significant predictors of poor quality of life in older asthmatics

BACKGROUND

Morbidity and mortality from asthma are high in older adults and quality of life (QOL) might be lower, although standardized measurements of QOL have not been validated in this population.

OBJECTIVE

To determine predictors of asthma-related QOL in older adults.

METHODS

Allergy and pulmonary outpatients (n = 164) at least 65 years old with an objective diagnosis of asthma completed the Mini-Asthma Quality of Life Questionnaire (mAQLQ). Demographics, medical history, and mean value for daily elemental carbon attributable to traffic, a surrogate for diesel exposure, were obtained. Regression analysis was used to determine predictors of mAQLQ scores.

RESULTS

Total mAQLQ (mean ± SD 5.4 ± 1.1) and symptom, emotional, and activity domain scores were similar to those of younger populations, whereas environmental domain scores (4.4 ± 1.7) appeared lower. Poorer mAQLQ scores were significantly associated with emergency department visits (adjusted β [aβ] = -1.3, where β values indicate the strength and direction of association, P < .0001) and with poorer scores on the Asthma Control Questionnaire (aβ = -0.7, P < .0001). Greater ECAT exposure (aβ = -1.6, P < .02), female sex (aβ = -0.4, P < .006), body mass index of at least 30 kg/m(2) (aβ = -0.4, P < .01), gastroesophageal reflux (aβ = -0.4, P < .01), nonatopic status (aβ = -0.5, P < .002), and asthma onset before 40 years of age (aβ = -0.5, P < .004) were significantly associated with poorer mAQLQ scores.

CONCLUSION

The mAQLQ scores in older adults with stable asthma were similar to those in younger populations and were predictive of other measurements of asthma control, verifying that the mAQLQ is an appropriate tool in older adults with asthma. Traffic pollution exposure was the strongest predictor of poorer asthma-related QOL in older adults with asthma.

Cluster Analysis in Patients with GOLD 1 Chronic Obstructive Pulmonary Disease

Background

We hypothesized that heterogeneity exists within the Global Initiative for Chronic Obstructive Lung Disease (GOLD) 1 spirometric category and that different subgroups could be identified within this GOLD category.

Methods

Pre-randomization study participants from two clinical trials were symptomatic/asymptomatic GOLD 1 chronic obstructive pulmonary disease (COPD) patients and healthy controls. A hierarchical cluster analysis used pre-randomization demographics, symptom scores, lung function, peak exercise response and daily physical activity levels to derive population subgroups.

Results

Considerable heterogeneity existed for clinical variables among patients with GOLD 1 COPD. All parameters, except forced expiratory volume in 1 second (FEV₁)/forced vital capacity (FVC), had considerable overlap between GOLD 1 COPD and controls. Three-clusters were identified: cluster I (18 [15%] COPD patients; 105 [85%] controls); cluster II (45 [80%] COPD patients; 11 [20%] controls); and cluster III (22 [92%] COPD patients; 2 [8%] controls). Apart from reduced diffusion capacity and lower baseline dyspnea index versus controls, cluster I COPD patients had otherwise preserved lung volumes, exercise capacity and physical activity levels. Cluster II COPD patients had a higher smoking history and greater hyperinflation versus cluster I COPD patients. Cluster III COPD patients had reduced physical activity versus controls and clusters I and II COPD patients, and lower FEV₁/FVC versus clusters I and II COPD patients.

Conclusions

The results emphasize heterogeneity within GOLD 1 COPD, supporting an individualized therapeutic approach to patients.

Trial registration

www.clinicaltrials.gov. NCT01360788 and NCT01072396.

New insights into the pathophysiology of mild chronic obstructive pulmonary disease

The classification of mild chronic obstructive pulmonary disease (COPD) requires a postbronchodilator forced expiratory volume in 1 s (FEV1) to forced vital capacity ratio <0.7 and an FEV1 ≥80% predicted. Given their relatively well-preserved spirometry, some have argued that respiratory symptoms in patients with mild COPD are unlikely to be related to pulmonary function abnormalities and that early detection of COPD is a 'waste of resources'. Despite this viewpoint, there is emerging clinical and physiological evidence of peripheral airway dysfunction, diminished quality of life and reduced physical activity levels, and increased mortality, hospitalizations, dyspnea and exercise intolerance in patients with mild COPD compared with healthy controls. The purpose of the present focused review was to summarize recent research regarding the pathophysiology and treatment of mild COPD.

Lung hyperinflation in chronic obstructive pulmonary disease: mechanisms, clinical implications and treatment

Lung hyperinflation is highly prevalent in patients with chronic obstructive pulmonary disease and occurs across the continuum of the disease. A growing body of evidence suggests that lung hyperinflation contributes to dyspnea and activity limitation in chronic obstructive pulmonary disease and is an important independent risk factor for mortality. In this review, we will summarize the recent literature on pathogenesis and clinical implications of lung hyperinflation. We will outline the contribution of lung hyperinflation to exercise limitation and discuss its impact on symptoms and physical activity. Finally, we will examine the physiological rationale and efficacy of selected pharmacological and non-pharmacological 'lung deflating' interventions aimed at improving symptoms and physical functioning.

Mechanisms of exercise intolerance in global initiative for chronic obstructive lung disease grade 1 COPD

The purpose of this study was to determine if a dissociation existed between respiratory drive, as estimated by diaphragmatic electromyography (EMGdi), and its pressure-generating capacity during exercise in mild chronic obstructive pulmonary disease (COPD) and whether this, if present, had negative sensory consequences. Subjects meeting spirometric criteria for mild COPD (n=16) and age and sex-matched controls (n=16) underwent detailed pulmonary function testing and a symptom limited cycle test while detailed ventilatory, sensory and respiratory mechanical responses were measured. Compared with controls, subjects with mild COPD had greater ventilatory requirements throughout submaximal exercise. At the highest equivalent work rate of 60 W, they had a significantly higher: total work of breathing (32±17 versus 16±7 J·min(-1); p<0.01); EMGdi (37.3±17.3 versus 17.9±11.7% of maximum; p<0.001); and EMGdi to transdiaphragmatic pressure ratio (0.87±0.38 versus 0.52±0.27; p<0.01). Dyspnoea-ventilation slopes were significantly higher in mild COPD than controls (0.17±0.12 versus 0.10±0.05; p<0.05). However, absolute dyspnoea ratings reached significant levels only at high levels of ventilation. Increased respiratory effort and work of breathing, and a wider dissociation between diaphragmatic activation and pressure-generating capacity were found at standardised work rates in subjects with mild COPD compared with controls. Despite these mechanical and neuromuscular abnormalities, significant dyspnoea was only experienced at higher work rates.

Should mild COPD be treated? Evidence for early pharmacological intervention

Chronic obstructive pulmonary disease (COPD) is a common and often progressive inflammatory disease of the airways that is both preventable and treatable. It is well established that those with mild-to-moderate disease severity represent the majority of patients with COPD, yet this subpopulation is relatively under-studied. Because of an insidious pre-clinical phase, COPD is both under-diagnosed and under-treated. Recent studies have confirmed that even patients with mild, grade 1 COPD [i.e. those with a reduced forced expiratory volume in one second (FEV1)/forced vital capacity ratio but normal FEV1], have measurable physiological impairment with increased morbidity and a higher risk of mortality compared with non-smoking healthy controls. Beyond the imperative of smoking cessation-the pivotal intervention in all COPD stages-the role of pharmacotherapy for prevention of disease progression has yet to be established. The main objective of this review is to provide a concise overview of the heterogeneous pathophysiology of COPD with only mild airway obstruction on spirometry and obstacles for early diagnosis. We emphasize that the absence of sufficiently powered trials involving a large number of patients precludes definitive recommendations in support of (or against) long-term pharmacological treatment in mild COPD. Despite these limitations, we present a rationale for earlier pharmacological intervention derived from recent physiological studies performed in symptomatic patients with mild COPD.

Activity restriction in mild COPD: a challenging clinical problem

Dyspnea, exercise intolerance, and activity restriction are already apparent in mild chronic obstructive pulmonary disease (COPD). However, patients may not seek medical help until their symptoms become troublesome and persistent and significant respiratory impairment is already present; as a consequence, further sustained physical inactivity may contribute to disease progression. Ventilatory and gas exchange impairment, cardiac dysfunction, and skeletal muscle dysfunction are present to a variable degree in patients with mild COPD, and collectively may contribute to exercise intolerance. As such, there is increasing interest in evaluating exercise tolerance and physical activity in symptomatic patients with COPD who have mild airway obstruction, as defined by spirometry. Simple questionnaires, eg, the modified British Medical Research Council dyspnea scale and the COPD Assessment Test, or exercise tests, eg, the 6-minute or incremental and endurance exercise tests can be used to assess exercise performance and functional status. Pedometers and accelerometers are used to evaluate physical activity, and endurance tests (cycle or treadmill) using constant work rate protocols are used to assess the effects of interventions such as pulmonary rehabilitation. In addition, alternative outcome measurements, such as tests of small airway dysfunction and laboratory-based exercise tests, are used to measure the extent of physiological impairment in individuals with persistent dyspnea. This review describes the mechanisms of exercise limitation in patients with mild COPD and the interventions that can potentially improve exercise tolerance. Also discussed are the benefits of pulmonary rehabilitation and the potential role of pharmacologic treatment in symptomatic patients with mild COPD.