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.

Systemic Determinants of Exercise Intolerance in Patients With Fibrotic Interstitial Lung Disease and Severely Impaired DLCO.

BACKGROUND: The precise mechanisms driving poor exercise tolerance in patients with fibrotic interstitial lung diseases (fibrotic ILDs) showing a severe impairment in single-breath lung diffusing capacity for carbon monoxide (DLCO < 40% predicted) are not fully understood. Rather than only reflecting impaired O2 transfer, a severely impaired DLCO may signal deranged integrative physiologic adjustments to exercise that jointly increase the burden of exertional symptoms in fibrotic ILD. METHODS: Sixty-seven subjects (46 with idiopathic pulmonary fibrosis, 24 showing DLCO < 40%) and 22 controls underwent pulmonary function tests and an incremental cardiopulmonary exercise test with serial measurements of operating lung volumes and 0-10 Borg dyspnea and leg discomfort scores. RESULTS: Subjects from the DLCO < 40% group showed lower spirometric values, more severe restriction, and lower alveolar volume and transfer coefficient compared to controls and participants with less impaired DLCO (P < .05). Peak work rate was ∼45% (vs controls) and ∼20% (vs DLCO > 40%) lower in the former group, being associated with lower (and flatter) O2 pulse, an earlier lactate (anaerobic) threshold, heightened submaximal ventilation, and lower SpO2 . Moreover, critically high inspiratory constrains were reached at lower exercise intensities in the DLCO < 40% group (P < .05). In association with the greatest leg discomfort scores, they reported the highest dyspnea scores at a given work rate. Between-group differences lessened or disappeared when dyspnea intensity was related to indexes of increased demand-capacity imbalance, that is, decreasing submaximal, dynamic ventilatory reserve, and inspiratory reserve volume/total lung capacity (P > .05). CONCLUSIONS: A severely reduced DLCO in fibrotic ILD signals multiple interconnected derangements (cardiovascular impairment, an early shift to anaerobic metabolism, excess ventilation, inspiratory constraints, and hypoxemia) that ultimately lead to limiting respiratory (dyspnea) and peripheral (leg discomfort) symptoms. DLCO < 40%, therefore, might help in clinical decision-making to indicate the patient with fibrotic ILD who might derive particular benefit from pharmacologic and non-pharmacologic interventions aimed at lessening these systemic abnormalities.

Inflammation associated with lung function abnormalities in COVID-19 survivors.

BACKGROUND: Activation of inflammatory pathways promotes organ dysfunction in COVID-19. Currently, there are reports describing lung function abnormalities in COVID-19 survivors; however, the biological mechanisms remain unknown. The aim of this study was to analyze the association between serum biomarkers collected during and following hospitalization and pulmonary function in COVID-19 survivors. METHODS: Patients recovering from severe COVID-19 were prospectively evaluated. Serum biomarkers were analyzed from admission to hospital, peak during hospitalization, and at the time of discharge. Pulmonary function was measured approximately 6 weeks after discharge. RESULTS: 100 patients (63% male) were included (age 48 years, SD ± 14) with 85% having at least one comorbidity. Patients with a restrictive spirometry pattern (n = 46) had greater inflammatory biomarkers compared to those with normal spirometry (n = 54) including peak Neutrophil-to-Lymphocyte ratio (NLR) value [9.3 (10.1) vs. 6.5 (6.6), median (IQR), p = 0.027] and NLR at hospital discharge [4.6 (2.9) vs. 3.2 (2.9) p = 0.005] and baseline C-reactive protein value [164.0 (147.0) vs. 106.5 (139.0) mg/dL, p = 0.083). Patients with an abnormal diffusing capacity (n = 35) had increased peak NLR [8.9 (5.9) vs. 5.6 (5.7) mg/L, p = 0.029]; baseline NLR [10.0 (19.0) vs. 4.0 (3.0) pg/ml, p = 0.002] and peak Troponin-T [10.0 (20.0) vs. 5.0 (5.0) pg/ml, p = 0.011] compared to patients with normal diffusing capacity (n = 42). Multivariable linear regression analysis identified predictors of restrictive spirometry and low diffusing capacity, but only accounted for a low degree of variance in pulmonary function outcome. CONCLUSION: Overexpression of inflammatory biomarkers is associated with subsequent lung function abnormalities in patients recovered from severe COVID-19.

Exercise responses and mental health symptoms in COVID-19 survivors with dyspnoea.

Objectives: Dyspnoea is a common persistent symptom post-coronavirus disease 2019 (COVID-19) illness. However, the mechanisms underlying dyspnoea in the post-COVID-19 syndrome remain unclear. The aim of our study was to examine dyspnoea quality and intensity, burden of mental health symptoms, and differences in exercise responses in people with and without persistent dyspnoea following COVID-19. Methods: 49 participants with mild-to-critical COVID-19 were included in this cross-sectional study 4 months after acute illness. Between-group comparisons were made in those with and without persistent dyspnoea (defined as modified Medical Research Council dyspnoea score ≥1). Participants completed standardised dyspnoea and mental health symptom questionnaires, pulmonary function tests, and incremental cardiopulmonary exercise testing. Results: Exertional dyspnoea intensity and unpleasantness were increased in the dyspnoea group. The dyspnoea group described dyspnoea qualities of suffocating and tightness at peak exercise (p<0.05). Ventilatory equivalent for carbon dioxide (V'E/V'CO2) nadir was higher (32±5 versus 28±3, p<0.001) and anaerobic threshold was lower (41±12 versus 49±11% predicted maximum oxygen uptake, p=0.04) in the dyspnoea group, indicating ventilatory inefficiency and deconditioning in this group. The dyspnoea group experienced greater symptoms of anxiety, depression and post-traumatic stress (all p<0.05). A subset of participants demonstrated gas-exchange and breathing pattern abnormalities suggestive of dysfunctional breathing. Conclusions: People with persistent dyspnoea following COVID-19 experience a specific dyspnoea quality phenotype. Dyspnoea post-COVID-19 is related to abnormal pulmonary gas exchange and deconditioning and is linked to increased symptoms of anxiety, depression and post-traumatic stress.

Physiological underpinnings of exertional dyspnoea in mild fibrosing interstitial lung disease.

The functional disturbances driving "out-of-proportion" dyspnoea in patients with fibrosing interstitial lung disease (f-ILD) showing only mild restrictive abnormalities remain poorly understood. Eighteen patients (10 with idiopathic pulmonary fibrosis) showing preserved spirometry and mildly reduced total lung capacity (≥70% predicted) and 18 controls underwent an incremental cardiopulmonary exercise test with measurements of operating lung volumes and Borg dyspnoea scores. Patients' lower exercise tolerance was associated with higher ventilation (V̇E)/carbon dioxide (V̇CO2) compared with controls (V̇E/V̇CO2 nadir=35 ± 3 versus 29 ± 2; p < 0.001). Patients showed higher tidal volume/inspiratory capacity and lower inspiratory reserve volume at a given exercise intensity, reporting higher dyspnoea scores as a function of both work rate and V̇E. Steeper dyspnoea-work rate slopes were associated with lower lung diffusing capacity, higher V̇E/V̇CO2, and lower peak O2 uptake (p < 0.05). Heightened ventilatory demands in the setting of progressively lower capacity for tidal volume expansion on exertion largely explain higher-than-expected dyspnoea in f-ILD patients with largely preserved dynamic and "static" lung volumes at rest.

Neurophysiological mechanisms of exertional dyspnea in post-pulmonary embolism syndrome.

Following pulmonary embolism (PE), a third of patients develop persistent dyspnea, which is commonly termed the post-PE syndrome. The neurophysiological underpinnings of exertional dyspnea in patients with post-PE syndrome without pulmonary hypertension (PH) are unclear. Thus, the current study determined if abnormally high inspiratory neural drive (IND) due, in part, to residual pulmonary gas-exchange abnormalities, was linked to heightened exertional dyspnea and exercise limitation, in such patients. Fourteen participants with post-PE syndrome (without resting PH) and 14 age-, sex-, and body mass index-matched healthy controls undertook pulmonary function testing and a symptom-limited cycle cardiopulmonary exercise test with measurements of IND (diaphragmatic electromyography), ventilatory requirements for CO2 (V̇e/V̇co2), and perceived dyspnea intensity (modified Borg 0-10 scale). Post-PE (vs. control) had a reduced resting transfer coefficient for carbon monoxide (KCO: 84 ± 15 vs. 104 ± 14%pred, P < 0.001) and peak oxygen uptake (V̇o2peak) (76 ± 14 vs. 124 ± 28%pred, P < 0.001). IND and V̇e/V̇co2 were higher in post-PE than controls at standardized submaximal work rates (P < 0.05). Dyspnea increased similarly in both groups as a function of increasing IND but was higher in post-PE at standardized submaximal work rates (P < 0.05). High IND was associated with low KCO (r = -0.484, P < 0.001), high V̇e/V̇co2 nadir (r = 0.453, P < 0.001), and low V̇o2peak (r = -0.523, P < 0.001). In patients with post-PE syndrome, exercise IND was higher than controls and was associated with greater dyspnea intensity. The heightened IND and dyspnea in post-PE, in turn, were strongly associated with low resting KCO and high exercise V̇e/V̇co2, which suggest important pulmonary gas-exchange abnormalities in this patient population.NEW & NOTEWORTHY This study is the first to show that increased exertional dyspnea in patients with post-pulmonary embolism (PE) syndrome, without overt pulmonary hypertension, was strongly associated with elevated inspiratory neural drive (IND) to the diaphragm during exercise, compared with healthy controls. The greater IND was associated with impairments in pulmonary gas exchange and significant deconditioning. Our results help to explain why many patients with post-PE syndrome report significant dyspnea at relatively low levels of physical activity.

Voluntary activation of the diaphragm after inspiratory pressure threshold loading.

After a bout of isolated inspiratory work, such as inspiratory pressure threshold loading (IPTL), the human diaphragm can exhibit a reversible loss in contractile function, as evidenced by a decrease in transdiaphragmatic twitch pressure (PDI,TW ). Whether or not diaphragm fatigability after IPTL is affected by neural mechanisms, measured through voluntary activation of the diaphragm (D-VA) in addition to contractile mechanisms, is unknown. It is also unknown if changes in D-VA are similar between sexes given observed differences in diaphragm fatigability between males and females. We sought to determine whether D-VA decreases after IPTL and whether this was different between sexes. Healthy females (n = 11) and males (n = 10) completed an IPTL task with an inspired duty cycle of 0.7 and targeting an intensity of 60% maximal transdiaphragmatic pressure until task failure. PDI,TW and D-VA were measured using cervical magnetic stimulation of the phrenic nerves in combination with maximal inspiratory pressure maneuvers. At task failure, PDI,TW decreased to a lesser degree in females vs. males (87 ± 15 vs. 73 ± 12% baseline, respectively, p = 0.016). D-VA decreased after IPTL but was not different between females and males (91 ± 8 vs. 88 ± 10% baseline, respectively, p = 0.432). When all participants were pooled together, the decrease in PDI,TW correlated with both the total cumulative diaphragm pressure generation (R2  = 0.43; p = 0.021) and the time to task failure (TTF, R2 = 0.40; p = 0.30) whereas the decrease in D-VA correlated only with TTF (R2  = 0.24; p = 0.041). Our results suggest that neural mechanisms can contribute to diaphragm fatigability, and this contribution is similar between females and males following IPTL.

Cardiorespiratory physiology, exertional symptoms, and psychological burden in post-COVID-19 fatigue.

Fatigue is a common, debilitating, and poorly understood symptom post-COVID-19. We sought to better characterize differences in those with and without post-COVID-19 fatigue using cardiopulmonary exercise testing. Despite elevated dyspnoea intensity ratings, V̇O2peak (ml/kg/min) was the only significant difference in the physiological responses to exercise (19.9 ± 7.1 fatigue vs. 24.4 ± 6.7 ml/kg/min non-fatigue, p = 0.04). Consistent with previous findings, we also observed a higher psychological burden in those with fatigue in the context of similar resting cardiopulmonary function. Our findings suggest that lower cardiorespiratory fitness and/or psychological factors may contribute to post-COVID-19 fatigue symptomology. Further research is needed for rehabilitation and symptom management following SARS-CoV-2 infection.

Impaired Ventilatory Efficiency, Dyspnea, and Exercise Intolerance in Chronic Obstructive Pulmonary Disease: Results from the CanCOLD Study.

Rationale: Impaired exercise ventilatory efficiency (high ventilatory requirements for CO2 [[Formula: see text]e/[Formula: see text]co2]) provides an indication of pulmonary gas exchange abnormalities in chronic obstructive pulmonary disease (COPD). Objectives: To determine 1) the association between high [Formula: see text]e/[Formula: see text]co2 and clinical outcomes (dyspnea and exercise capacity) and its relationship to lung function and structural radiographic abnormalities; and 2) its prevalence in a large population-based cohort. Methods: Participants were recruited randomly from the population and underwent clinical evaluation, pulmonary function, cardiopulmonary exercise testing, and chest computed tomography. Impaired exercise ventilatory efficiency was defined by a nadir [Formula: see text]e/[Formula: see text]co2 above the upper limit of normal (ULN), using population-based normative values. Measurements and Main Results: Participants included 445 never-smokers, 381 ever-smokers without airflow obstruction, 224 with Global Initiative for Chronic Obstructive Lung Disease (GOLD) 1 COPD, and 200 with GOLD 2-4 COPD. Participants with [Formula: see text]e/[Formula: see text]co2 above the ULN were more likely to have activity-related dyspnea (Medical Research Council dyspnea scale ⩾ 2; odds ratio [5-95% confidence intervals], 1.77 [1.31 to 2.39]) and abnormally low peak [Formula: see text]o2 ([Formula: see text]o2peak below the lower limit of normal; odds ratio, 4.58 [3.06 to 6.86]). The Kco had a stronger correlation with nadir [Formula: see text]e/[Formula: see text]co2 (r = -0.38; P < 0.001) than other relevant lung function and computed tomography metrics. The prevalence of [Formula: see text]e/[Formula: see text]co2 above the ULN was 24% in COPD (similar in GOLD 1 and 2 through 4), which was greater than in never-smokers (13%) and ever-smokers (12%). Conclusions: [Formula: see text]e/[Formula: see text]co2 above the ULN was associated with greater dyspnea and low [Formula: see text]o2peak and was present in 24% of all participants with COPD, regardless of GOLD stage. The results show the importance of recognizing impaired exercise ventilatory efficiency as a potential contributor to dyspnea and exercise limitation, even in mild COPD.

Sex Differences in Diaphragm Voluntary Activation after Exercise.

INTRODUCTION: The female diaphragm develops less fatigue after high-intensity exercise compared with males. Diaphragm fatigability is typically defined as a decrease in transdiaphragmatic twitch pressure (Pdi,TW) and represents the contractile function of the muscle. However, it is unclear whether this sex difference persists when examining changes in voluntary activation, which represents a neural mechanism contributing to fatigability. PURPOSE: This study aimed to determine if high-intensity cycling results in a decrease in diaphragm voluntary activation (D-VA) and to explore if the decrease in D-VA is different between sexes. METHODS: Twenty-five participants (15 females) completed a single bout of high-intensity constant load cycling. D-VA and Pdi,TW were measured before and after exercise using cervical magnetic stimulation of the phrenic nerves to assess diaphragm fatigability. RESULTS: Participants were of similar aerobic fitness when expressed relative to predicted values (females: 114% ± 25% predicted, males: 111% ± 11% predicted; P = 0.769). Pdi,TW decreased relative to baseline to 85.2% ± 16.7% and 70.3% ± 12.4% baseline (P = 0.012) in females and males, respectively, immediately after exercise. D-VA also decreased in both females and males immediately after exercise. The decrease in D-VA was less in females compared with males (95.4% ± 4.9% baseline vs 87.4% ± 10.8% baseline, respectively; P = 0.018). CONCLUSIONS: D-VA decreases after whole-body exercise in both females and males, although the magnitude of the decrease is not as large in females compared with males. The findings of this study suggest that the female diaphragm is more resistant to both contractile and neural mechanisms of fatigability after whole-body exercise.

Compensatory responses to increased mechanical abnormalities in COPD during sleep.

PURPOSE: To assess whether night-time increases in mechanical loading negatively impact respiratory muscle function in COPD and whether compensatory increases in inspiratory neural drive (IND) are adequate to stabilize ventilatory output and arterial oxygen saturation, especially during sleep when wakefulness drive is withdrawn. METHODS: 21 patients with moderate-to-severe COPD and 20 age-/sex-matched healthy controls (CTRL) participated in a prospective, cross-sectional, one-night study to assess the impact of COPD on serial awake, supine inspiratory capacity (IC) measurements and continuous dynamic respiratory muscle function (esophageal manometry) and IND (diaphragm electromyography, EMGdi) in supine sleep. RESULTS: Supine inspiratory effort and EMGdi were consistently twice as high in COPD versus CTRL (p < 0.05). Despite overnight increases in awake total airways resistance and dynamic lung hyperinflation in COPD (p < 0.05; not in CTRL), elevated awake EMGdi and respiratory effort were unaltered in COPD overnight. At sleep onset (non-rapid eye movement sleep, N2), EMGdi was decreased versus wakefulness in COPD (- 43 ± 36%; p < 0.05) while unaffected in CTRL (p = 0.11); however, respiratory effort and arterial oxygen saturation (SpO2) were unchanged. Similarly, in rapid eye movement (stage R), sleep EMGdi was decreased (- 38 ± 32%, p < 0.05) versus wakefulness in COPD, with preserved respiratory effort and minor (2%) reduction in SpO2. CONCLUSIONS: Despite progressive mechanical loading overnight and marked decreases in wakefulness drive, inspiratory effort and SpO2 were well maintained during sleep in COPD. Preserved high inspiratory effort during sleep, despite reduced EMGdi, suggests continued (or increased) efferent activation of extra-diaphragmatic muscles, even in stage R sleep. CLINICAL TRIAL INFORMATION: The COPD data reported herein were secondary data (Placebo arm only) obtained through the following Clinical Trial: "Effect of Aclidinium/Formoterol on Nighttime Lung Function and Morning Symptoms in Chronic Obstructive Pulmonary Disease" ( https://clinicaltrials.gov/ct2/show/NCT02429765 ; NCT02429765).

Qualitative Components of Dyspnea during Incremental Exercise across the COPD Continuum.

INTRODUCTION: Evaluation of the intensity and quality of activity-related dyspnea is potentially useful in people with chronic obstructive pulmonary disease (COPD). The present study sought to examine associations between qualitative dyspnea descriptors, dyspnea intensity ratings, dynamic respiratory mechanics, and exercise capacity during cardiopulmonary exercise testing (CPET) in COPD and healthy controls. METHODS: In this cross-sectional study, 261 patients with mild-to-very severe COPD (forced expiratory volume in 1 s, 62 ± 25%pred) and 94 age-matched controls (forced expiratory volume in 1 s, 114 ± 14%pred) completed an incremental cycle CPET to determine peak oxygen uptake (V˙O2peak). Throughout exercise, expired gases, operating lung volumes, and dyspnea intensity were assessed. At peak exercise, dyspnea quality was assessed using a modified 15-item questionnaire. RESULTS: Logistic regression analysis revealed that among 15 dyspnea descriptors, only those alluding to the cluster "unsatisfied inspiration" were consistently associated with an increased likelihood for both critical inspiratory mechanical constraint (end-inspiratory lung volume/total lung capacity ratio ≥0.9) during exercise and reduced exercise capacity (V˙O2peak < lower limit of normal) in COPD (odds ratio (95% confidence interval), 3.26 (1.40-7.60) and 3.04 (1.24-7.45), respectively; both, P < 0.05). Thus, patients reporting "unsatisfied inspiration" (n = 177 (68%)) had an increased relative frequency of critical inspiratory mechanical constraint and low exercise capacity compared with those who did not select this descriptor, regardless of COPD severity or peak dyspnea intensity scores. CONCLUSIONS: In patients with COPD, regardless of disease severity, reporting descriptors in the unsatisfied inspiration cluster complemented traditional assessments of dyspnea during CPET and helped identify patients with critical mechanical abnormalities germane to exercise intolerance.

Case Studies in Physiology: Cardiopulmonary exercise testing and inspiratory muscle training in a 59-year-old, 4 years after an extrapleural pneumonectomy.

This case report characterizes the physiological responses to incremental cycling and determines the effects of 12 wk of inspiratory muscle training (IMT) on respiratory muscle strength, exercise capacity, and dyspnea in a physically active 59-yr-old female, 4 years after a left-sided extrapleural pneumonectomy (EPP). On separate days, a symptom-limited incremental exercise test and a constant work rate (CWR) test at 75% of peak work rate (WR) were completed, followed by 12 wk of IMT and another CWR test. IMT consisted of two sessions of 30 repetitions twice daily for 5 days per week. Physiological and perceptual variables were measured throughout each exercise test. The participant had a total lung capacity that was 43% predicted post-EPP. A rapid and shallow breathing pattern was adopted throughout exercise, and the ratio of minute ventilation to carbon dioxide output was elevated for a given work rate. Oxygen uptake was 71% predicted and WR was 88% predicted. Following IMT, maximal inspiratory pressure improved by 36% (-27.1 cmH2O) and endurance time by 31 s, with no observable changes in any submaximal or peak cardiorespiratory variables during exercise. The intensity and unpleasantness of dyspnea increased by 2 and 3 Borg 0-10 units, respectively, at the highest equivalent submaximal exercise time achieved on both tests. Despite having undergone a significant reduction in lung volume post-EPP, the participant achieved a relatively normal peak incremental WR, which may reflect a high level of physical conditioning. This case report also demonstrates that IMT can effectively increase respiratory muscle strength several years following EPP.NEW & NOTEWORTHY Constraints on tidal volume expansion and the adoption of a rapid and shallow breathing pattern result in a ventilatory limitation and increased ventilatory inefficiency during exercise in a patient several years after extrapleural pneumonectomy (EPP). Inspiratory muscle training can effectively increase respiratory muscle strength after EPP.

Mechanisms of Exertional Dyspnea in Patients with Mild COPD and a Low Resting DLCO.

Patients with mild chronic obstructive pulmonary disease (COPD) and lower resting diffusing capacity for carbon monoxide (DLCO) often report troublesome dyspnea during exercise although the mechanisms are not clear. We postulated that in such individuals, exertional dyspnea is linked to relatively high inspiratory neural drive (IND) due, in part, to the effects of reduced ventilatory efficiency. This cross-sectional study included 28 patients with GOLD I COPD stratified into two groups with (n = 15) and without (n = 13) DLCO less than the lower limit of normal (

Reduced exercise tolerance in mild chronic obstructive pulmonary disease: The contribution of combined abnormalities of diffusing capacity for carbon monoxide and ventilatory efficiency.

BACKGROUND AND OBJECTIVE: The combination of both reduced resting diffusing capacity of the lung for carbon monoxide (DLCO ) and ventilatory efficiency (increased ventilatory requirement for CO2 clearance [V˙E /V˙CO2 ]) has been linked to exertional dyspnoea and exercise intolerance in chronic obstructive pulmonary disease (COPD) but the underlying mechanisms are poorly understood. The current study examined if low resting DLCO and higher exercise ventilatory requirements were associated with earlier critical dynamic mechanical constraints, dyspnoea and exercise limitation in patients with mild COPD. METHODS: In this retrospective analysis, we compared V˙E /V˙CO2 , dynamic inspiratory reserve volume (IRV), dyspnoea and exercise capacity in groups of patients with Global Initiative for Chronic Obstructive Lung Disease stage 1 COPD with (1) a resting DLCO at or greater than the lower limit of normal (≥LLN; Global Lung Function Initiative reference equations [n = 44]) or (2) below the

Pulmonary function and functional capacity in COVID-19 survivors with persistent dyspnoea.

The purpose of this study was to examine the physiological mechanisms of persistent dyspnoea in COVID-19 survivors. Non-critical patients (n = 186) with varying degrees of COVID-19 severity reported persistent symptoms using a standardized questionnaire and underwent pulmonary function and 6-minute walk testing between 30 and 90 days following the onset of acute COVID-19 symptoms. Patients were divided into those with (n = 70) and without (n = 116) persistent dyspnoea. Patients with persistent dyspnoea had significantly lower FVC (p = 0.03), FEV1 (p = 0.04), DLCO (p = 0.01), 6-minute walk distance (% predicted, p = 0.03), and end-exercise oxygen saturation (p < 0.001), and higher Borg 0-10 ratings of dyspnoea and fatigue (both p < 0.001) compared to patients without persistent dyspnoea. We have shown that dyspnoea is a common persistent symptom across varying degrees of initial COVID-19 severity. Patients with persistent dyspnoea had greater restriction on spirometry, lower DLCO, reduced functional capacity, and increased exertional desaturation and symptoms. This suggests that there is a true physiological mechanism that may explain persistent dyspnoea after COVID-19.

Elevated exercise ventilation in mild COPD is not linked to enhanced central chemosensitivity.

BACKGROUND: The purpose of this study was to determine if altered central chemoreceptor characteristics contributed to the elevated ventilation relative to carbon dioxide production (V̇E/V̇CO2) response during exercise in mild chronic obstructive pulmonary disease (COPD). METHODS: Twenty-nine mild COPD and 19 healthy age-matched control participants undertook lung function testing followed by symptom-limited incremental cardiopulmonary exercise testing . On a separate day, basal (non-chemoreflex) ventilation (V̇EB), the central chemoreflex ventilatory recruitment threshold for CO2 (VRTCO2), and central chemoreflex sensitivity (V̇ES) were assessed using the modified Duffin's CO2 rebreathing method. Resting arterialized blood gas data were also obtained. RESULTS: At standardized exercise intensities, absolute V̇E and V̇E/V̇CO2 were consistently elevated and the end-tidal partial pressure of CO2 was relatively decreased in mild COPD versus controls (all p < 0.05). There were no between-group differences in resting arterialized blood gas parameters, basal V̇E, VRTCO2, or V̇ES (all p > 0.05). CONCLUSION: These data have established that excessive exercise ventilation in mild COPD is not explained by altered central chemosensitivity.

Mechanisms of orthopnoea in patients with advanced COPD.

Many patients with severe chronic obstructive pulmonary disease (COPD) report an unpleasant respiratory sensation at rest, which is further amplified by adoption of a supine position (orthopnoea). The mechanisms of this acute symptomatic deterioration are poorly understood.Sixteen patients with advanced COPD and a history of orthopnoea and 16 age- and sex-matched healthy controls underwent pulmonary function tests (PFTs) and detailed sensory-mechanical measurements including inspiratory neural drive (IND) assessed by diaphragm electromyography (EMGdi), oesophageal pressure (P es) and gastric pressure (P ga), in both sitting and supine positions.Patients had severe airflow obstruction (forced expiratory volume in 1 s (FEV1): 40±18% pred) and lung hyperinflation. Regardless of the position, patients had lower inspiratory capacity (IC) and higher IND for a given tidal volume (V T) (i.e. greater neuromechanical dissociation (NMD)), higher intensity of breathing discomfort, higher minute ventilation (V'E) and higher breathing frequency (f B) compared with controls (all p<0.05). For controls in a supine position, IC increased by 0.48 L versus sitting erect, with a small drop in V'E, mainly due to reduced f B (all p<0.05). By contrast, IC remained unaltered in patients with COPD, but dynamic lung compliance (C Ldyn) decreased (p<0.05) in the supine position. Breathing discomfort, inspiratory work of breathing (WOB), inspiratory effort, IND, NMD and neuroventilatory uncoupling all increased in COPD patients in the supine position (p<0.05), but not in the healthy controls. Orthopnoea was associated with acute changes in IND (r=0.65, p=0.01), neuroventilatory uncoupling (r=0.76, p=0.001) and NMD (r=0.73, p=0.002).In COPD, onset of orthopnoea coincided with an abrupt increase in elastic loading of the inspiratory muscles in recumbency, in association with increased IND and greater NMD of the respiratory system.

Deterioration of Nighttime Respiratory Mechanics in COPD: Impact of Bronchodilator Therapy.

BACKGROUND: COPD is associated with nighttime respiratory symptoms, poor sleep quality, and increased risk of nocturnal death. Overnight deterioration of inspiratory capacity (IC) and FEV1 have been documented previously. However, the precise nature of this deterioration and mechanisms by which evening bronchodilation may mitigate this occurrence have not been studied. RESEARCH QUESTION: What is the effect of evening dosing of dual, long-acting bronchodilation on detailed nocturnal respiratory mechanics and inspiratory neural drive (IND)? STUDY DESIGN AND METHODS: A double-blind, randomized, placebo-controlled crossover study assessed the effects of evening long-acting bronchodilation (aclidinium bromide/formoterol fumarate dihydrate: 400/12 µg) or placebo on morning trough IC (12 h after the dose; primary outcome) and serial overnight measurements of spirometry, dynamic respiratory mechanics, and IND (secondary outcomes). Twenty participants with COPD (moderate/severe airway obstruction and lung hyperinflation) underwent serial measurements of IC, spirometry, breathing pattern, esophageal and transdiaphragmatic pressures, and diaphragm electromyography (diaphragmatic electromyography as a percentage of maximum; IND) at 6 time points from 0 to 12 h after the dose and compared with sleeping IND. RESULTS: Compared with placebo, evening bronchodilation was not associated with increased morning trough IC 12 h after the dose (P = .48); however, nadir IC (lowest IC, independent of time), peak IC, area under the curve for 12 h after the dose, and IC for 10 h after the dose were improved (P < .05). During placebo, total airways resistance, lung hyperinflation, IND, and tidal esophageal and transdiaphragmatic pressure swings all increased significantly overnight compared with baseline evening values; however, each of these parameters improved with bronchodilator treatment (P < .05) with no change in ventilation or breathing pattern. INTERPRETATION: Respiratory mechanics significantly deteriorated at night during placebo. Although the morning trough IC was unchanged, evening bronchodilator treatment was associated consistently with sustained overnight improvements in dynamic respiratory mechanics and inspiratory neural drive compared with placebo CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT02429765.