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

Circadian clock-based therapeutics in chronic pulmonary diseases

The circadian clock is the biochemical oscillator that orchestrates the observable circadian rhythms in physiology and behavior. Disruption of the circadian clock in the lungs during chronic pulmonary diseases is considered one of the key etiological risk factors that drive pathobiology. Preclinical studies support that pharmacological manipulation of the circadian clock is a conceivable approach for the development of novel clock-based therapeutics. Despite recent advances, no effort has been undertaken to integrate novel findings for the treatment and management of chronic lung diseases. We, therefore, recognize the need to discuss the candidate clock genes that can be potentially targeted for therapeutic intervention. Here, we aim to create the first roadmap that will advance the development of circadian- clock-based therapeutics that may provide better outcomes in treating chronic pulmonary diseases.

Ventilatory neural drive in chronically hypercapnic patients with COPD: effects of sleep and nocturnal noninvasive ventilation

Sleep brings major challenges for the control of ventilation in humans, particularly the regulation of arterial carbon dioxide pressure (P _aCO2 ). In patients with COPD, chronic hypercapnia is associated with increased mortality. Therefore, nocturnal high-level noninvasive positive-pressure ventilation (NIV) is recommended with the intention to reduce P _aCO2 down to normocapnia. However, the long-term physiological consequences of P _aCO2 "correction" on the mechanics of breathing, gas exchange efficiency and resulting symptoms (i.e. dyspnoea) remain poorly understood. Investigating the influence of sleep on the neural drive to breathe and its translation to the mechanical act of breathing is of foremost relevance to create a solid rationale for the use of nocturnal NIV. In this review, we critically discuss the mechanisms by which sleep influences ventilatory neural drive and mechanical consequences in healthy subjects and hypercapnic patients with advanced COPD. We then discuss the available literature on the effects of nocturnal NIV on ventilatory neural drive and respiratory mechanics, highlighting open avenues for further investigation.

Pre-operative screening for sleep disordered breathing: obstructive sleep apnoea and beyond

Sleep disordered breathing describes an important group of conditions that causes abnormal nocturnal gas exchange, with important implications in the peri-operative management plan. An understanding of the pathophysiology behind obstructive sleep apnoea and other disorders that may lead to hypoventilation can help to prevent complications. Patients with these disorders may be minimally symptomatic and it requires careful screening in the pre-operative assessment process for a diagnosis to be made. Decisions regarding initiation of therapy, such as positive airway pressure, and delay of the operation need to be carefully weighed up against the urgency of the surgical intervention. Planning of the peri-operative care, including the use of positive airway pressure therapy and appropriate post-operative monitoring, can help to avoid respiratory and cardiovascular morbidities and improve clinical outcomes.

Educational aims

To review different types of sleep disordered breathing and available screening methods in pre-operative assessment.To understand the pathophysiology behind sleep disordered breathing and how it can lead to complications in the peri-operative setting.To review the planning and treatment strategies that should be considered as part of peri-operative management.

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).

The physiology and pathophysiology of exercise hyperpnea

In health, the near-eucapnic, highly efficient hyperpnea during mild-to-moderate intensity exercise is driven by three obligatory contributions, namely, feedforward central command from supra-medullary locomotor centers, feedback from limb muscle afferents, and respiratory CO₂ exchange (V̇CO₂). Inhibiting each of these stimuli during exercise elicits a reduction in hyperpnea even in the continuing presence of the other major stimuli. However, the relative contribution of each stimulus to the hyperpnea remains unknown as does the means by which V̇CO2 is sensed. Mediation of the hyperventilatory response to exercise in health is attributed to the multiple feedback and feedforward stimuli resulting from muscle fatigue. In patients with COPD, diaphragm EMG amplitude and its relation to ventilatory output are used to decipher mechanisms underlying the patients' abnormal ventilatory responses, dynamic lung hyperinflation and dyspnea during exercise. Key contributions to these exercise-limiting responses across the spectrum of COPD severity include high dead space ventilation, an excessive neural drive to breathe and highly fatigable limb muscles, together with mechanical constraints on ventilation. Major controversies concerning control of exercise hyperpnea are discussed along with the need for innovative research to uncover the link of metabolism to breathing in health and disease.

Sleep quality and architecture in COPD: the relationship with lung function abnormalities

OBJECTIVE

Impaired respiratory mechanics and gas exchange may contribute to sleep disturbance in patients with COPD. We aimed to assess putative associations of different domains of lung function (airflow limitation, lung volumes, and gas exchange efficiency) with polysomnography (PSG)-derived parameters of sleep quality and architecture in COPD.

METHODS

We retrospectively assessed data from COPD 181 patients ≥ 40 years of age who underwent spirometry, plethysmography, and overnight PSG. Univariate and multivariate linear regression models predicted sleep efficiency (total sleep time/total recording time) and other PSG-derived parameters that reflect sleep quality.

RESULTS

The severity of COPD was widely distributed in the sample (post-bronchodilator FEV1 ranging from 25% to 128% of predicted): mild COPD (40.3%), moderate COPD (43.1%), and severe-very severe COPD (16.6%). PSG unveiled a high proportion of obstructive sleep apnea (64.1%) and significant nocturnal desaturation (mean pulse oximetry nadir = 82.2% ± 6.9%). After controlling for age, sex, BMI, apnea-hypopnea index, nocturnal desaturation, comorbidities, and psychotropic drug prescription, FEV1/FVC was associated with sleep efficiency (β = 25.366; R2 = 14%; p < 0.001), whereas DLCO predicted sleep onset latency (β = -0.314; R2 = 13%; p < 0.001) and rapid eye movement sleep time/total sleep time in % (β = 0.085; R2 = 15%; p = 0.001).

CONCLUSIONS

Pulmonary function variables reflecting severity of airflow and gas exchange impairment, adjusted for some potential confounders, were weakly related to PSG outcomes in COPD patients. The direct contribution of the pathophysiological hallmarks of COPD to objectively measured parameters of sleep quality seems to be less important than it was previously assumed.

Aclidinium bromide/formoterol fumarate as a treatment for COPD: an update

Introduction: Aclidinium/formoterol is a long-acting muscarinic antagonist (LAMA) and long-acting β₂-agonist (LABA) dual bronchodilator used as a maintenance treatment for patients with chronic obstructive pulmonary disease (COPD). The efficacy of aclidinium/formoterol has been demonstrated consistently in patients with moderate-to-severe COPD versus placebo and monocomponents, with a comparable safety profile.Areas covered: This review examines recent research findings that expand our understanding of the impact of aclidinium/formoterol on the burden of COPD. Reviewed outcomes include improvements in lung function, respiratory symptoms, health-related quality of life, exercise tolerance, exacerbation rates, and clinically important deteriorations. In addition, the reported cardiovascular safety of aclidinium and current LAMA/LABA treatment recommendations are discussed.Expert opinion: Aclidinium/formoterol reduces disease burden in patients with COPD, including those that are treatment-naïve, without a significant increase in safety risk compared with monotherapies. Furthermore, evidence supports an improvement in lung function over a 24-hour period with aclidinium/formoterol treatment versus monotherapy and placebo, which may offer an advantage over some once-daily LAMA/LABA combinations. In summary, the recent evidence discussed in this review adds weight to the use of LAMA/LABA combinations as an initial therapy for certain patients newly diagnosed with COPD.

European Respiratory Society International Congress 2020: highlights from best-abstract awardees

#ERSCongress 2020 best-abstract awardees summarise their virtual European Respiratory Society International Congress experience and views on the evolving field of research for their respective assembly https://bit.ly/3kJ9JrJ.

Clinical Utility of Measuring Inspiratory Neural Drive During Cardiopulmonary Exercise Testing (CPET)

Cardiopulmonary exercise testing (CPET) has traditionally included ventilatory and metabolic measurements alongside electrocardiographic characterization; however, research increasingly acknowledges the utility of also measuring inspiratory neural drive (IND) through its surrogate measure of diaphragmatic electromyography (EMGdi). While true IND also encompasses the activation of non-diaphragmatic respiratory muscles, the current review focuses on diaphragmatic measurements, providing information about additional inspiratory muscle groups for context where appropriate. Evaluation of IND provides mechanistic insight into the origins of dyspnea and exercise limitation across pathologies; yields valuable information reflecting the integration of diverse mechanical, chemical, locomotor, and metabolic afferent signals; and can help assess the efficacy of therapeutic interventions. Further, IND measurement during the physiologic stress of exercise is uniquely poised to reveal the underpinnings of physiologic limitations masked during resting and unloaded breathing, with important information provided not only at peak exercise, but throughout exercise protocols. As our understanding of IND presentation across varying conditions continues to grow and methods for its measurement become more accessible, the translation of these principles into clinical settings is a logical next step in facilitating appropriate and nuanced management tailored to each individual's unique physiology. This review provides an overview of the current state of understanding of IND measurement during CPET: its origins, known patterns of behavior and links with dyspnea in health and major respiratory diseases, and the possibility of expanding this approach to applications beyond exercise.

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 (EMG_di), 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.