Comparison of normal and asthmatic circadian rhythms in peak expiratory flow rate

Circadian rhythm and variability of large and small airway spirometric variables in healthy individuals

Objective

To assess the diurnal rhythm and variability of lung function in healthy individuals, encompassing both large and small airways.

Methods

A prospective study enrolled 35 healthy adults without a history of smoking. Initial spirometry and a bronchodilation test were performed using the Jaeger spirometer, followed by a seven-day continuous home monitoring using the GOSPT2000. We evaluated repeatability using the intraclass correlation coefficient and agreement through linear regression and Bland-Altman analyses. Circadian rhythm and variability in spirometric measurements were analyzed using the coefficient of variation (CV) and daily variation rate.

Results

The GOSPT2000 demonstrated strong repeatability and high agreement with the Jaeger spirometer. Notable findings included a decrease in nocturnal forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), and FEV3 by 44, 59, and 53 mL, respectively. In contrast, peak expiratory flow at noon showed an increase of 0.143L/min. Small-airway variables, including forced expiratory flow at 50% and 75% of the FVC and maximum midexpiratory flow, showed no significant diurnal variation. The nocturnal CV for large-airway variables was ≤ 4%, while for small-airway variables, it was ≤ 11.89%.

Conclusion

This study has established a spectrum of variability for both large and small airways in healthy populations. The variability of small-airway variables is higher than that of large-airway variables. The investigation into the diurnal rhythms and variability characteristics of both large and small airway variables in the healthy population can serve as a foundation for diagnosing asthma or assessing the efficacy of asthma treatments.

Cough and cough hypersensitivity as treatable traits of asthma

Cough is a common and troublesome symptom in people with asthma and is often associated with poorer asthma control and exacerbations. Apart from asthma, other causes or comorbidities might underlie cough in asthma, such as rhinosinusitis and bronchiectasis. Eosinophilic inflammation and bronchoconstriction can lead to an acute episode of cough or worsen chronic cough. Cough hypersensitivity with laryngeal paraesthesia, allotussia, and hypertussia might underlie the cough of asthma through augmented sensory nerve excitability of upper-airway vagal sensory nerves. Cough associated with bronchoconstriction and type 2 inflammation should respond to inhaled corticosteroids and long-acting β-adrenoceptor agonist therapy. For cough hypersensitivity in adults, speech and language therapy and neuromodulators (eg, gabapentin) could be considered. In children, there is no consistent association of asthma with cough sensitivity or between cough and asthma severity. Further research is needed to realise the potential of cough as a measure of asthma control, to understand the mechanisms of cough in asthma, and to develop safe, effective treatments and a precision-medicine approach to the management of cough in asthma in children and adults.

Clinical Potential of Eosinophil-Derived Neurotoxin in Asthma Management

The assessment and management of patients with asthma is challenging because of the complexity of the underlying inflammatory mechanisms and heterogeneity of their clinical presentation. Optimizing disease management requires therapy individualization that should rely on reliable biomarkers to unravel the phenotypes and endotypes of asthma. The secretory activity and turnover of eosinophils, as assessed by measuring eosinophil-derived proteins, may provide an accurate and complementary tool that mirrors the eosinophil activation status. Emerging evidence suggests that eosinophil-derived neurotoxin has considerable potential as a precision medicine biomarker. In this review, we explore the suitability of eosinophil-derived neurotoxin as a biomarker in asthma management, with particular emphasis on its clinical significance in the management of both pediatric and adult populations.

Epidemiology of Asthma: Prevalence and Burden of Disease

Asthma, a common airway disease, results in a significant burden to both patients and society worldwide. Yet, despite global political commitment backed by the United Nations, progress to reduce the burden of asthma remains inadequate. This is particularly true in low-income countries. To date, progress has been delayed by the lack of uniform data collection, imperfect surveillance methods, inadequate resources, poor access to effective therapies, substandard asthma education, ineffective governmental policies, rapid urbanization, progressive increase in asthma prevalence, increased life expectancy and obesity rates worldwide, asthma heterogeneity and disease complexity, smoking, and environmental exposures to allergens and pollution. A thorough understanding of the challenges facing the international community is essential to define future strategies to improve the burden of asthma.

Age-related circadian rhythm and variability of large- and small-airway function in healthy non-smoking adults: Data from 7-day diurnal and nocturnal home monitoring using an electronic portable spirometer

Background

The aim of the study was to investigate the possible influencing factors of the large- and small-airway function variation in healthy non-smoking adults.

Methods

Healthy non-medical non-smoking adults were enrolled in this prospective cohort study. Each participant took the portable spirometer test relying only on video teaching. Then conventional spirometry and bronchodilation test were conducted using a Jaeger spirometer, followed by 7-day diurnal and nocturnal home monitoring using a portable spirometer.

Results

A drop in both large- and small-airway function began at about 25 years of age, and a rapidly decline at about 50 years. The CV of FEV₁ (r = 0.47, P = 0.0082) and small-airway function variables correlated with age (r ≥ 0.37, P < 0.05 for both MEFs and MEFs/FVC), especially for evening small-airway function variables. The CV of large (4.666 ± 1.946, P = 0.002 for FEV₁; 4.565 ± 2.478, P = 0.017 for FEV₃) and small airways (10.38 ± 3.196, P = 0.031 for MEF50 and 11.21 ± 4.178, P = 0.023 for MMEF) was higher in the 45- to 60-year subgroup than in the 30- to 45-year and 18- to 30-year subgroups.

Interpretation

Age was the main influencing factor of both central and peripheral airway function variability, especially for the small-airway function in the evening. The LLN of small-airway variables varies depending on the age and circadian rhythm. People older than 45 years should pay more attention to monitoring small-airway function in the evening, which will be helpful for early clinical detection of those at high risk for asthma.

Trial registration number

ChiCTR2100050355.

Static lung volumes and diffusion capacity in adults 30 years after being diagnosed with asthma

Background

Long-term follow-up studies of adults with well-characterized asthma are sparse. We aimed to explore static lung volumes and diffusion capacity after 30 + years with asthma.

Methods

A total of 125 adults with an objectively verified diagnosis of asthma between 1974–1990 at a Danish respiratory outpatient clinic completed a follow-up visit 2017–19. All participants (age range 44–88 years) completed a comprehensive workup and were, based on these assessments, classified as having either active asthma or being in complete remission. The examination program included measurements of static lung volumes and diffusion capacity.

Results

Participants with active asthma were hyperinflated (residual volume/total lung capacity ratio 0.43, 95% CI 0.41—0.45) (RV/TLC ratio) compared with those in remission (RV/TLC ratio 0.38, 95% CI 0.36—0.41) (p < 0.03). A tendency towards higher diffusion capacity per liter lung volume was seen in participants with active asthma (KCO 100% predicted, 95% CI 97—104) compared with those in remission (KCO 94% pred., 95% CI 89—99) (P = 0.10). Longer asthma duration was associated with a higher KCO 0.47% pred./year (95% CI 0.14—0.80), adjusted for age and smoking. Patients on GINA step 4 and 5 treatment were more hyperinflated (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta$$\end{document}Δ RV 14% pred., 95% CI 3—27) and had higher airway resistance (mean 53% pred., 95% CI 9—97) than participants on lower GINA steps. Patients with uncontrolled disease had substantially higher airway resistance (72% pred. 95% CI 20—124) than well-controlled patients.

Conclusion

Thirty years after a confirmed diagnosis of asthma, those continuing to have active asthma and those having severe asthma, have higher diffusion capacity and more hyperinflation than patients in remission.

Work Around the Clock: How Work Hours Induce Social Jetlag and Sleep Deficiency

A growing body of evidence has placed an increasing emphasis on how sleep affects health. Not only does insufficient sleep make one subjectively feel worse, but is associated with chronic diseases that are considered epidemics in industrialized nations. This is partly caused by the growing need for prolonged work and social schedules, exemplified by shift work, late-night weekends, and early morning work/school start times (social jetlag). Here, we consider fundamental relationships between the circadian clock and biologic processes and discuss how common practices, such as shift work and social jetlag, contribute to sleep disruption, circadian misalignment, and adverse health outcomes.

Sleep Deficiency, Sleep Apnea, and Chronic Lung Disease

With sleep occupying up to one-third of every adult's life, addressing sleep is essential to overall health. Sleep disturbance and deficiency are common in patients with chronic lung diseases and associated with worse clinical outcomes and poor quality of life. A detailed history incorporating nocturnal respiratory symptoms, symptoms of obstructive sleep apnea (OSA) and restless legs syndrome, symptoms of anxiety and depression, and medications is the first step in identifying and addressing the multiple factors often contributing to sleep deficiency in chronic lung disease. Additional research is needed to better understand the relationship between sleep deficiency and the spectrum of chronic lung diseases.

Adaptive immunity, chronic inflammation and the clock

The adaptive arm of the immune system facilitates recognition of specific foreign pathogens and, via the action of T and B lymphocytes, induces a fine-tuned response to target the pathogen and develop immunological memory. The functionality of the adaptive immune system exhibits daily 24-h variation both in homeostatic processes (such as lymphocyte trafficking and development of T lymphocyte subsets) and in responses to challenge. Here, we discuss how the circadian clock exerts influence over the function of the adaptive immune system, considering the roles of cell intrinsic clockwork machinery and cell extrinsic rhythmic signals. Inappropriate or misguided actions of the adaptive immune system can lead to development of autoimmune diseases such as rheumatoid arthritis, ulcerative colitis and multiple sclerosis. Growing evidence indicates that disturbance of the circadian clock has negative impact on development and progression of these chronic inflammatory diseases and we examine current understanding of clock-immune interactions in the setting of these inflammatory conditions. A greater appreciation of circadian control of adaptive immunity will facilitate further understanding of mechanisms driving daily variation in disease states and drive improvements in the diagnosis and treatment of chronic inflammatory diseases.

The endogenous circadian system worsens asthma at night independent of sleep and other daily behavioral or environmental cycles

Asthma often worsens at night. To determine if the endogenous circadian system contributes to the nocturnal worsening of asthma, independent of sleep and other behavioral and environmental day/night cycles, we studied patients with asthma (without steroid use) over 3 wk in an ambulatory setting (with combined circadian, environmental, and behavioral effects) and across the circadian cycle in two complementary laboratory protocols performed in dim light, which separated circadian from environmental and behavioral effects: 1) a 38-h "constant routine," with continuous wakefulness, constant posture, 2-hourly isocaloric snacks, and 2) a 196-h "forced desynchrony" incorporating seven identical recurring 28-h sleep/wake cycles with all behaviors evenly scheduled across the circadian cycle. Indices of pulmonary function varied across the day in the ambulatory setting, and both laboratory protocols revealed significant circadian rhythms, with lowest function during the biological night, around 4:00 AM, uncovering a nocturnal exacerbation of asthma usually unnoticed or hidden by the presence of sleep. We also discovered a circadian rhythm in symptom-based rescue bronchodilator use (β2-adrenergic agonist inhaler) whereby inhaler use was four times more likely during the circadian night than day. There were additive influences on asthma from the circadian system plus sleep and other behavioral or environmental effects. Individuals with the lowest average pulmonary function tended to have the largest daily circadian variations and the largest behavioral cycle effects on asthma. When sleep was modeled to occur at night, the summed circadian, behavioral/environmental cycle effects almost perfectly matched the ambulatory data. Thus, the circadian system contributes to the common nocturnal worsening of asthma, implying that internal biological time should be considered for optimal therapy.

Aerosol deposition and airflow dynamics in healthy and asthmatic human airways during inhalation

Inhalation of aerosols such as pharmaceutical aerosols or virus aerosol uptake is of great concern to the human population. To elucidate the underlying aerosol dynamics, the deposition fractions (DFs) of aerosols in healthy and asthmatic human airways of generations 13-15 are predicted. The Navier-stokes equations governing the gaseous phase and the discrete phase model for particles' motion are solved using numerical methods. The main forces responsible for deposition are inertial impaction forces and complex secondary flow velocities. The curvatures and sinusoidal folds in the asthmatic geometry lead to the formation of complex secondary flows and hence higher DFs. The intensities of complex secondary flows are strongest at the generations affected by asthma. The DF in the healthy airways is 0%, and it ranges from 1.69% to 52.93% in the asthmatic ones. From this study, the effects of the pharmaceutical aerosol particle diameters in the treatment of asthma patients can be established, which is conducive to inhibiting the inflammation of asthma airways. Furthermore, with the recent development of COVID-19 which causes pneumonia, the predicted physics and effective simulation methods of bioaerosols delivery to asthma patients are vital to prevent the exacerbation of the chronic ailment and the epidemic.

The Relevance of Small Airway Dysfunction in Asthma with Nocturnal Symptoms

Rationale

Small airway dysfunction (SAD) is a frequent feature of asthma that has been linked to disease severity and poor symptom control. However, little is known about the role of SAD in nocturnal asthma.

Objective

To study the association between the severity of SAD and frequency of nocturnal symptoms compared to conventional lung function testing.

Methods

We assessed the frequency of self-reported nocturnal symptoms through the asthma control test. We studied the impact of nocturnal asthma using the Asthma Quality of Life Questionnaire (AQLQ) and the Multidimensional Fatigue Inventory (MFI-20). We assessed the lung function using spirometry, body plethysmography, impulse oscillometry, single and multiple inert gas washout and measured markers of T2-inflammation (blood and sputum eosinophils; fractional exhaled nitric oxide (FeNo)). We stratified the patients according to the presence and frequency of nocturnal asthma.

Results

A total of 166 asthma patients were enrolled in the analysis. Eighty-seven patients (52%) reported to have nocturnal symptoms at least once in the last four weeks. The odds ratio of nocturnal asthma correlated with the severity of all non-spirometric measures of SAD, yet neither with airflow obstruction (FEV1 and FEV/FVC) nor with large airway resistance (R20). Patients with frequent nocturnal asthma (n = 29) had a numerical increase of T2 markers and more severe SAD, as indicated by all non-spirometric measures of SAD (all p-values < 0.05), worse overall asthma control, increased fatigue and reduced quality of life (all p-values < 0.01) compared to patients with infrequent nocturnal asthma (n = 58) or patients without nocturnal asthma (n = 79). We identified 63 patients without airflow obstruction, nearly 43% of them (n = 27) had nocturnal asthma. In this subgroup, only markers of air trapping and ventilation heterogeneity were significantly elevated and correlated with the frequency of nocturnal symptoms: LCI (Spearman’s coefficient = −0.42, p < 0.001), RV% (−0.32, p = 0.02).

Conclusion

SAD is closely associated to asthma with nocturnal symptoms. Spirometry might underestimate the broad spectrum of distal lung function impairments in this population of patients.

Asthma diagnosis: into the fourth dimension

Asthma is the most common chronic respiratory disease in the UK; however, the misdiagnosis rate is substantial. The lack of consistency in national guidelines and the paucity of data on the performance of diagnostic algorithms compound the challenges in asthma diagnosis. Asthma is a highly rhythmic disease, characterised by diurnal variability in clinical symptoms and pathogenesis. Asthma also varies day to day, seasonally and from year to year. As much as it is a hallmark for asthma, this variability also poses significant challenges to asthma diagnosis. Almost all established asthma diagnostic tools demonstrate diurnal variation, yet few are performed with standardised timing of measurements. The dichotomous interpretation of diagnostic outcomes using fixed cut-off values may further limit the accuracy of the tests, particularly when diurnal variability straddles cut-off values within a day, and careful interpretation beyond the 'positive' and 'negative' outcome is needed. The day-to-day and more long-term variations are less predictable and it is unclear whether performing asthma diagnostic tests during asymptomatic periods may influence diagnostic sensitivities. With the evolution of asthma diagnostic tools, home monitoring and digital apps, novel strategies are needed to bridge these gaps in knowledge, and circadian variability should be considered during the standardisation process. This review summarises the biological mechanisms of circadian rhythms in asthma and highlights novel data on the significance of time (the fourth dimension) in asthma diagnosis.

Cellular clocks in hyperoxia effects on [Ca2+]i regulation in developing human airway smooth muscle

Supplemental O2 (hyperoxia) is necessary for preterm infant survival but is associated with development of bronchial airway hyperreactivity and childhood asthma. Understanding early mechanisms that link hyperoxia to altered airway structure and function are key to developing advanced therapies. We previously showed that even moderate hyperoxia (50% O2) enhances intracellular calcium ([Ca2+]i) and proliferation of human fetal airway smooth muscle (fASM), thereby facilitating bronchoconstriction and remodeling. Here, we introduce cellular clock biology as a novel mechanism linking early oxygen exposure to airway biology. Peripheral, intracellular clocks are a network of transcription-translation feedback loops that produce circadian oscillations with downstream targets highly relevant to airway function and asthma. Premature infants suffer circadian disruption whereas entrainment strategies improve outcomes, highlighting the need to understand relationships between clocks and developing airways. We hypothesized that hyperoxia impacts clock function in fASM and that the clock can be leveraged to attenuate deleterious effects of O2 on the developing airway. We report that human fASM express core clock machinery (PER1, PER2, CRY1, ARNTL/BMAL1, CLOCK) that is responsive to dexamethasone (Dex) and altered by O2. Disruption of the clock via siRNA-mediated PER1 or ARNTL knockdown alters store-operated calcium entry (SOCE) and [Ca2+]i response to histamine in hyperoxia. Effects of O2 on [Ca2+]i are rescued by driving expression of clock proteins, via effects on the Ca2+ channels IP3R and Orai1. These data reveal a functional fASM clock that modulates [Ca2+]i regulation, particularly in hyperoxia. Harnessing clock biology may be a novel therapeutic consideration for neonatal airway diseases following prematurity.

Remission and Changes in Severity Over 30 Years in an Adult Asthma Cohort

BACKGROUND

Long-term follow-up studies of adults with well-characterized asthma are sparse.

OBJECTIVE

We aimed to examine long-term remission and change in disease severity over 30 years in adults with asthma.

METHODS

A total of 125 individuals diagnosed with asthma between 1974 and 1990 at a Danish respiratory and allergy clinic, based on history and objective assessments, were included. At follow-up (2017-2019), participants completed questionnaires and had spirometry, bronchodilator reversibility, airway responsiveness, and blood biomarkers measured. Based on these assessments, participants were classified as having either active asthma, clinical remission (no symptoms or prescribed asthma medication within the last year), or complete remission (fractional exhaled nitric oxide <50 parts per billion, no bronchodilator reversibility, no airway hyperresponsiveness, and no airflow limitation). Changes in severity were determined according to Global Initiative for Asthma guidelines based on symptom control and currently prescribed medication.

RESULTS

At follow-up, 25% (n = 31) and 15% (n = 19), respectively, had clinical and complete remission. Our analyses showed that a longer duration of symptoms before the initial assessment (odds ratio, 0.86; 95% confidence interval, 0.75-0.98) was associated with a lower chance of asthma remission. At follow-up, 30% had well-controlled asthma compared with none at baseline. Female sex, previous severe exacerbation(s), and older age at baseline were associated with uncontrolled asthma at follow-up. Blood-eosinophil count (≥0.3 × 10⁹/L) and prescribed inhaled corticosteroid (ICS) at baseline were associated with being prescribed medium/high-dose ICS at follow-up.

CONCLUSION

Despite 30 years of follow-up, asthma rarely remits in adults, especially in individuals with longer duration and presumably more severe disease. Initial signs of pronounced disease activity were associated with uncontrolled asthma at follow-up.

Circadian Rhythms in Environmental Health Sciences

PURPOSE OF REVIEW

This review aims to explore how circadian rhythms influence disease susceptibility and potentially modify the effect of environmental exposures. We aimed to identify biomarkers commonly used in environmental health research that have also been the subject of chronobiology studies, in order to review circadian rhythms of relevance to environmental health and determine if time-of-day is an important factor to consider in environmental health studies. Moreover, we discuss opportunities for studying how environmental exposures may interact with circadian rhythms to structure disease pathology and etiology.

RECENT FINDINGS

In recent years, the study of circadian rhythms in mammals has flourished. Animal models revealed that all body tissues have circadian rhythms. In humans, circadian rhythms were also shown to exist at multiple levels of organization: molecular, cellular, and physiological processes, including responding to oxidative stress, cell trafficking, and sex hormone production, respectively. Together, these rhythms are an essential component of human physiology and can shape an individual's susceptibility and response to disease. Circadian rhythms are relatively unexplored in environmental health research. However, circadian clocks control many physiological and behavioral processes that impact exposure pathways and disease systems. We believe this review will motivate new studies of (i) the impact of exposures on circadian rhythms, (ii) how circadian rhythms modify the effect of environmental exposures, and (iii) how time-of-day impacts our ability to observe the body's response to exposure.

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.

Circadian rhythm of exhaled biomarkers in health and asthma

Circadian rhythms regulate and reflect many biological processes. Investigating circadian variability in biomarkers is important since the diurnal variability of any potential biomarker must be quantified and controlled in research and clinical practice. Time of day is particularly important in inflammatory diseases such as asthma, which are linked to exaggerated circadian rhythms. Airway narrowing in asthma is greatest at around 04:00 h and coincides with an increase in symptoms; asthma deaths are also more likely to occur at this time [1, 2]. Likewise eosinophilic airway inflammation peaks in the morning, with clinical implications for biomarker-guided steroid therapy [3].

Exhaled volatile chemicals and fractional exhaled nitric oxide oscillate over 24 h, highlighting the importance of time of day in diagnostic sampling and suggesting potential applications for chronotyping. http://bit.ly/2YZGXbH

Circadian variability in airways characteristics: A spirometric study

Background: Chronic obstructive pulmonary disease (COPD) and Asthma patients exhibit exacerbation of symptoms in night hours and early morning. Temporal variability in airway caliber have been reported in past using peak expiratory flow rate which represents large airways caliber, while in COPD and Asthma, smaller airways are particularly affected. We studied circadian variability of airway caliber using Forced Expiratory Volume in the First Second (FEV1) and Mid Expiratory Flow rate. Methods: Male volunteers (18-26 years), having similar daily routine were recruited. Spirometry was performed at 5: 00, 8:00, 11:00, 14:00, 17:00, 20:00 and 23:00 h. Data from 104 subjects was analyzed for diurnal variability parameters viz., amplitude percent mean and standard deviation percent of mean. For circadian rhythm Cosinor curve was fitted and rhythm characteristics in terms of MESOR, Amplitude and Acrophase were determined. Results: Repeated measures ANOVA revealed significant differences in spirometric parameters measured at different time points during the day. In general, spirometric parameters follow a sinusoidal pattern and exhibit minimum values during night hours and maximum values during day time. FEV1 Cosinor rhythm was significant in 31% of subjects (Zero amplitude test). The distribution of acrophase revealed interindividual differences in chronophenotypes. Variability was minimum for FEV1% and maximum for FEF75 suggesting dynamic interplay of airway geometry and neuro-chemical influences. Conclusion: The presence of different chronophenotypes in normal subjects suggests that the nocturnal asthma may also be a different phenotype. Availability of portable spirometers and home monitoring thus may be required for ascertaining chronophenotype and tailoring chronotherapeutic interventions.

Sleep and asthma

PURPOSE OF REVIEW

There is a longstanding recognition of the detrimental effect of poorly controlled asthma on sleep, but recent years have seen a growing interest in how asthma and sleep may interact. This review examines the current evidence of relationships between asthma, sleep and sleep disorders.

RECENT FINDINGS

Poor quality sleep and sleep disturbance is highly prevalent in asthmatic patients, and particularly in those with severe asthma. Impaired sleep quality correlates with worse asthma control and quality of life. Sleep disturbance in asthma may be related to due circadian variation in airway inflammation, but may also be related to specific sleep disorders. Obstructive sleep apnoea (OSA) appears to be significantly more common in asthmatic patients than nonasthmatic patients, and treatment of OSA with continuous positive airway pressure (CPAP) may lead to improved asthma-specific quality of life. Nocturnal CPAP may also be of benefit to asthmatic patients without OSA, potentially because of stretching of airway smooth muscle. Insomnia is also highly prevalent in severe asthma patients, and is associated with a history of poor asthma control and increased healthcare utilization.

SUMMARY

Asthma, sleep and sleep disorders appear to have complex, but significant relationships. Prospective observational and controlled interventional studies are needed to quantify how addressing sleep difficulties may benefit asthma patients.

Do laboratory challenge tests for occupational asthma represent what happens in the workplace?

Specific inhalation challenge (SIC) is the diagnostic reference standard for occupational asthma; however, a positive test cannot be considered truly significant unless it can be reproduced by usual work exposures. We have compared the timing and responses during SIC in hospital to Oasys analysis of serial peak expiratory flow (PEF) during usual work exposures.All workers with a positive SIC to occupational agents between 2006 and 2015 were asked to measure PEF every 2 h from waking to sleeping for 4 weeks during usual occupational exposures. Responses were compared between the laboratory challenge and the real-world exposures at work.All 53 workers with positive SIC were included. 49 out of 53 had records suitable for Oasys analysis, 14 required more than one attempt and all confirmed occupational work-related changes in PEF. Immediate SIC reactors and deterioration within the first 2 h of starting work were significantly correlated with early recovery, and late SIC reactors and a delayed start to workplace deterioration were significantly correlated with delayed recovery. Dual SIC reactions had features of immediate or late SIC reactions at work rather than dual reactions.The concordance of timings of reactions during SIC and at work provides further validation for the clinical significance of each test.

Timing Matters: Circadian Rhythm in Sepsis, Obstructive Lung Disease, Obstructive Sleep Apnea, and Cancer

Physiological and cellular functions operate in a 24-hour cyclical pattern orchestrated by an endogenous process known as the circadian rhythm. Circadian rhythms represent intrinsic oscillations of biological functions that allow for adaptation to cyclic environmental changes. Key clock genes that affect the persistence and periodicity of circadian rhythms include BMAL1/CLOCK, Period 1, Period 2, and Cryptochrome. Remarkable progress has been made in our understanding of circadian rhythms and their role in common medical conditions. A critical review of the literature supports the association between circadian misalignment and adverse health consequences in sepsis, obstructive lung disease, obstructive sleep apnea, and malignancy. Circadian misalignment plays an important role in these disease processes and can affect disease severity, treatment response, and survivorship. Normal inflammatory response to acute infections, airway resistance, upper airway collapsibility, and mitosis regulation follows a robust circadian pattern. Disruption of normal circadian rhythm at the molecular level affects severity of inflammation in sepsis, contributes to inflammatory responses in obstructive lung diseases, affects apnea length in obstructive sleep apnea, and increases risk for cancer. Chronotherapy is an underused practice of delivering therapy at optimal times to maximize efficacy and minimize toxicity. This approach has been shown to be advantageous in asthma and cancer management. In asthma, appropriate timing of medication administration improves treatment effectiveness. Properly timed chemotherapy may reduce treatment toxicities and maximize efficacy. Future research should focus on circadian rhythm disorders, role of circadian rhythm in other diseases, and modalities to restore and prevent circadian disruption.

BMAL1 links the circadian clock to viral airway pathology and asthma phenotypes

Patients with asthma experience circadian variations in their symptoms. However it remains unclear how specific aspects of this common airway disease relate to clock genes, which are critical to the generation of circadian rhythms in mammals. Here, we used a viral model of acute and chronic airway disease to examine how circadian clock disruption affects asthmatic lung phenotypes. Deletion of the core clock gene bmal1 or environmental disruption of circadian function by jet lag exacerbated acute viral bronchiolitis caused by Sendai virus (SeV) and influenza A virus in mice. Post-natal deletion of bmal1 was sufficient to trigger increased SeV susceptibility and correlated with impaired control of viral replication. Importantly, bmal1-/- mice developed much more extensive asthma-like airway changes post infection, including mucus production and increased airway resistance. In human airway samples from two asthma cohorts, we observed altered expression patterns of multiple clock genes. Our results suggest a role for bmal1 in the development of asthmatic airway disease via the regulation of lung antiviral responses to common viral triggers of asthma.

Role of Small Airways in Asthma

Asthma is an inflammatory condition of both the small and large airways. Recently the small airways have gained attention as studies have shown significant inflammation in the small airways in all severities of asthma. This inflammation has correlated with peripheral airway resistance and as a result, noninvasive methods to reliably measure small airways have been pursued. In addition, recent changes in asthma inhalers have led to alterations in drug formulations and the development of extrafine particle inhalers that improve delivery to the distal airways.

Pulmonary function and high-resolution computed tomography examinations among offshore drill floor workers

Purpose

The aim of this study was to assess short-term changes in pulmonary function in drill floor workers currently exposed to airborne contaminants generated as a result of drilling offshore. We also aimed to study the prevalence of pulmonary fibrosis using high-resolution computed tomography (HRCT) scans of another group of previously exposed drill floor workers.

Methods

Pulmonary function was measured before and after a 14-day work period in a follow-up study of 65 drill floor workers and 65 referents. Additionally, 57 other drill floor workers exposed to drilling fluids during the 1980s were examined with HRCT of the lungs in a cross-sectional study.

Results

The drill floor workers had a statistically significant decline in forced expiratory volume in 1 s (FEV₁) across the 14-day work period after adjustment for diurnal variations in pulmonary function (mean 90 mL, range 30–140 mL), while the small decline among the referents (mean 20 mL, range − 30 to 70 mL) was not of statistical significance. Larger declines in FEV₁ among drill workers were associated with the fewer number of days of active drilling. There were no signs of pulmonary fibrosis related to oil mist exposure among the other previously exposed drill floor workers.

Conclusion

After 14 days offshore, a statistically significant decline in FEV₁ was observed in the drill floor workers, which may not be related to oil mist exposure. No pulmonary fibrosis related to oil mist exposure was observed.

Perception of circadian variation of symptoms in Chinese patients with chronic obstructive pulmonary disease

BACKGROUND

Although, the variable pattern of asthmatic symptoms is well recognized, little is known about the respiratory symptoms variability in patients of chronic obstructive pulmonary disease (COPD). The present study evaluated the variability of the respiratory symptoms in a day and their influence on the daily activities in a cohort of Chinese COPD patients.

METHODS

An observational cross-sectional study was conducted in 11 medical centers of China. Participants were outpatient ≥40 years old with stable COPD, post-bronchodilator forced expiratory volume in 1 second (FEV1) <80% predicted. Overall, data of 1,032 eligible patients were valid for final analysis.

RESULTS

Mean post bronchodilator FEV1 (predicted %) was 46.5%. Cough, expectoration and dyspnea were the most commonly observed symptoms (73.6%, 68.8% and 61.4%, respectively). Daily symptom variability was experienced by 50.2% of symptomatic patients. The wake up time in the morning was the worst and the most troublesome time during the day (39.3%), followed by the nighttime (21.3%). The morning activities were most affected by COPD symptoms. Multivariate analyses revealed that COPD assessment test (CAT) scores was the only factor correlated with patients' symptom variability [odds ratio (OR) =0.463, P<0.0001].

CONCLUSIONS

Patient-perceived symptoms vary during the day in Chinese COPD patients. They experience the greatest increase in respiratory symptoms early in the morning. This variation should be considered as a potential new target in the long-term COPD management.

COMPARATIVE ANALYSIS OF THE EFFECTIVENESS OF CHRONOTHERAPY AND TRADITIONAL METHOD OF ALOPECIA AREATA TREATMENT

Alopecia areata – is the one of widespread baldness forms, difficultly subjected to treatment. The method of chronotherapy that gains an essential circulation in Ukraine and throughout the world may play the important role in its solution. Aim: to study the clinical effectiveness of chronotherapy for alopecia areata treatment. Materials and methods. For attaining the set aim 108 persons with the diagnosis alopecia areata were examined and treated. Patients were divided in two groups. The main group included 45 persons – treated using the method of chronotherapy. The control group consisted of 67 persons, who received the traditional treatment of alopecia areata. The series of clinical, biochemical and immunological studies, directed on the assessment of the treatment effectiveness, were realized. Results. The treatment of patients with alopecia areata by the method of chronotherapy is statistically reliably more effective than the traditional treatment of this pathology and provides the renewal of hair growth in 53,3 % of patients that is accompanied by normalization of alexin, sulfhydryl groups content, acid phosphatase activity, serine, asparagine acid, valine, threonine, alanine, cystine, leucine, isoleucine concentrations. The offered chronotherapy method has the expressed anabolic effect on patients’ organism. The menstrual cycle is normalized, pre-menstrual syndrome symptoms and aldodysmenorrhea disappear, patients’ working ability and state of health improve. Conclusions. The obtained data deepen knowledge about the pathogenesis of alopecia areata at the biochemical and immunological levels and favor the rise of the effectiveness of diagnostics and treatment of this pathology. At the study the high chronotherapy effectiveness at treating alopecia areata was revealed and the possibility of its use for the effective treatment of a series of other pathologies was proved.

Randomized Trial of Interventions to Improve Childhood Asthma in Homes with Wood-burning Stoves

BACKGROUND

Household air pollution due to biomass combustion for residential heating adversely affects vulnerable populations. Randomized controlled trials to improve indoor air quality in homes of children with asthma are limited, and no such studies have been conducted in homes using wood for heating.

OBJECTIVES

Our aims were to test the hypothesis that household-level interventions, specifically improved-technology wood-burning appliances or air-filtration devices, would improve health measures, in particular Pediatric Asthma Quality of Life Questionnaire (PAQLQ) scores, relative to placebo, among children living with asthma in homes with wood-burning stoves.

METHODS

A three-arm placebo-controlled randomized trial was conducted in homes with wood-burning stoves among children with asthma. Multiple preintervention and postintervention data included PAQLQ (primary outcome), peak expiratory flow (PEF) monitoring, diurnal peak flow variability (dPFV, an indicator of airway hyperreactivity) and indoor particulate matter (PM) PM2.5.

RESULTS

Relative to placebo, neither the air filter nor the woodstove intervention showed improvement in quality-of-life measures. Among the secondary outcomes, dPFV showed a 4.1 percentage point decrease in variability [95% confidence interval (CI)=-7.8 to -0.4] for air-filtration use in comparison with placebo. The air-filter intervention showed a 67% (95% CI: 50% to 77%) reduction in indoor PM2.5, but no change was observed with the improved-technology woodstove intervention.

CONCLUSIONS

Among children with asthma and chronic exposure to woodsmoke, an air-filter intervention that improved indoor air quality did not affect quality-of-life measures. Intent-to-treat analysis did show an improvement in the secondary measure of dPFV.

TRIAL REGISTRATION

ClincialTrials.gov NCT00807183. https://doi.org/10.1289/EHP849.

CYCLOPS reveals human transcriptional rhythms in health and disease

Circadian rhythms modulate many aspects of physiology. Knowledge of the molecular basis of these rhythms has exploded in the last 20 years. However, most of these data are from model organisms, and translation to clinical practice has been limited. Here, we present an approach to identify molecular rhythms in humans from thousands of unordered expression measurements. Our algorithm, cyclic ordering by periodic structure (CYCLOPS), uses evolutionary conservation and machine learning to identify elliptical structure in high-dimensional data. From this structure, CYCLOPS estimates the phase of each sample. We validated CYCLOPS using temporally ordered mouse and human data and demonstrated its consistency on human data from two independent research sites. We used this approach to identify rhythmic transcripts in human liver and lung, including hundreds of drug targets and disease genes. Importantly, for many genes, the circadian variation in expression exceeded variation from genetic and other environmental factors. We also analyzed hepatocellular carcinoma samples and show these solid tumors maintain circadian function but with aberrant output. Finally, to show how this method can catalyze medical translation, we show that dosage time can temporally segregate efficacy from dose-limiting toxicity of streptozocin, a chemotherapeutic drug. In sum, these data show the power of CYCLOPS and temporal reconstruction in bridging basic circadian research and clinical medicine.

Electrodermal Screening of Asthmatics with AcuGraph 4

Traditional Chinese Medicine holds that acupuncture meridian activity is correlated with quality of function of specific organs. This study sets out to determine acupuncture meridian characteristics of subjects with moderate asthma distinguishing them from healthy subjects. Fifty asthma patients (age 35.36 ± 8.68 years) and fifty similarly aged (34.11 ± 7.29 years) healthy volunteers were enrolled in the study. Electrodermal conductances at Jing Well points were measured with Acugraph 4 and also Peak Expiratory Flow Rate (PEFR) for the asthma group. All mean meridian conductances were lower for the asthma group, significance differences were in Lung and right Bladder meridians. In contrast, all but two of the standard deviations of group meridian conductances for the Asthma group were higher than those for the Healthy group. Difference in mean PEFR values between Asthma and Healthy groups was significant. These suggest that group measures of electrical conductance at Jing Well points can distinguish asthma from healthy individuals. The study provides support for the usefulness of meridian energy measurements to assess organ related dysfunction and for the idea that pathology groups exhibit higher standard deviations i.e. lower quality of regulation.

Overnight Changes in Lung Function of Obese Patients with Obstructive Sleep Apnoea

PURPOSE

Obstructive sleep apnoea (OSA) is a prevalent disorder, characterised by collapse of the upper airways during sleep. The impact of sleep-disordered breathing on pulmonary function indices is however currently not well described. The aim of the study was to evaluate diurnal change in lung function indices in a cohort of patients with OSA and relate pulmonary function changes to disease severity.

METHODS

42 patients with OSA and 73 healthy control subjects participated in the study. Asthma and COPD were excluded in all volunteers following a clinical and spirometric assessment. Spirometry was then performed in all subjects in the evening and the morning following a polysomnography study.

RESULTS

There was no difference in evening or morning FEV₁ or FVC between patients and control subjects (p > 0.05). Neither FEV₁ nor FVC changed in control subjects overnight (p > 0.05). In contrast, FEV₁ significantly increased from evening (2.18/1.54-4.46/L) to morning measurement (2.26/1.42-4.63/L) in OSA without any change in FVC. The FEV₁ increase in OSA was related to male gender, obesity and the lack of treatment with statins or β-blockers (all p < 0.05). A tendency for a direct correlation was apparent between overnight FEV₁ change and RDI (p = 0.05, r = 0.30).

CONCLUSIONS

Diurnal variations in spirometric indices occur in patients with OSA and FEV₁ appears to increase in subjects with OSA overnight. These changes occur in the absence of change in FVC and are directly related to the severity of OSA. These findings dictate a need to consider time of lung function measurement.

Sleep complaints and sleep breathing disorders in upper and lower obstructive lung diseases

Upper and lower obstructive lung diseases can induce sleep complaints and can be part of the pathogenesis of sleep breathing disorders. In fact, the physiological changes of the pattern of respiration during sleep, added to the airways disease can lead to symptomatic worsening of rhinitis, asthma and chronic obstructive pulmonary diseases (COPD); moreover, their functional and anatomical features can lead to sleep breathing disorders such as obstructive sleep apnea syndrome (OSAS). This review highlights the above-mentioned relationships and the effect of disease management on its comorbidities and the patient's quality of life. Rhinitis, asthma and COPD represent causes of sleep complaints that may be reduced with optimal management of these obstructive airways diseases. Continuous positive airway pressure (CPAP) treatment of sleep apnea needs to be tailored after optimization of the therapy of concomitant diseases, but it can often ameliorate comorbid disease.

Montelukast medicines of today and tomorrow: from molecular pharmaceutics to technological formulations

Montelukast sodium is a leukotriene antagonist of growing interest as an alternative therapy for asthma across different age groups due to its bronchoprotective, anti-inflammatory and anti-allergic properties. Currently, montelukast is commercialized only in oral solid dosage forms, which are the favorite of adult patients but may pose challenges in administration to children of young age or patients suffering from dysphagia. This review presents a comprehensive revision of scientific reports and patents on emerging strategies for the delivery of montelukast. A common ground to these reports is the pursue of an enhanced montelukast performance, by increasing its bioavailability and physico-chemical stability. A wide variety of strategies can be found, from the formation of supramolecular adducts with cyclodextrins to encapsulation in nanoparticles and liposomes. The new dosage forms for montelukast are designed for non-enteric absorption, some for absorption in the oral cavity and another two being for local action in the nasal mucosa or in the pulmonary epithelium. The review describes the emerging delivery strategies to circumvent the current limitations to the use of montelukast that are expected to ultimately lead to the development of more patient-compliant dosage forms.

Population intervention models to estimate ambient NO2 health effects in children with asthma

Health effects of ambient air pollution are most frequently expressed in individual studies as responses to a standardized unit of air pollution changes (e.g., an interquartile interval), which is thought to enable comparison of findings across studies. However, this approach does not necessarily convey health effects in terms of a real-world air pollution scenario. In the present study, we use population intervention modeling to estimate the effect of an air pollution intervention that makes explicit reference to the observed exposure data and is identifiable in those data. We calculate the association between ambient summertime nitrogen dioxide (NO2) and forced expiratory flow between 25% and 75% of forced vital capacity (FEF25-75) in a cohort of children with asthma in Fresno, California. We scale the effect size to reflect NO2 abatement on a majority of summer days. The effect estimates were small, imprecise, and consistently indicated improved pulmonary function with decreased NO2. The effects ranged from -0.8% of mean FEF25-75 (95% confidence interval (CI): -3.4, 1.7) to -3.3% (95% CI: -7.5, 0.9). We conclude by discussing the nature and feasibility of the exposure change analyzed here given the observed air pollution profile, and we propose additional applications of population intervention models in environmental epidemiology.

Quantitative characterization of circadian rhythm of pulmonary function in asthmatic patients treated with inhaled corticosteroids

The aim of this study was to characterize the circadian rhythm observed for forced expiratory volume in 1 s (FEV1) in patients with persistent asthma being treated with inhaled corticosteroids. The database included 3379 FEV1 measurements from 189 patients with mild to moderate asthma. A model using the sum of two Sine functions with periods of 12 and 24 h and a constant component of mean circadian rhythm adequately described the circadian rhythm in FEV1 measurements over time. The model adequateness was evaluated by various approaches including visual predictive check (VPC), prediction-corrected VPC, standardized VPC and normalized prediction distribution error. Covariates tested included age, body weight, height, body mass index, baseline FEV1, and sex. Age and height were found to have significant effects on the mean FEV1 level and no covariate was found to have an effect on the magnitude and timing of circadian rhythm. The model predicted that a minimum FEV1 occurred in the early morning and maximum FEV1 occurred in the early afternoon, with a population mean fluctuation of 170 mL, which is consistent with the finding that asthma symptoms usually exacerbate in the early morning for patients with persistent asthma. This developed model provides the first quantitative approach to describing FEV1 circadian rhythm with ICS background treatment and provided insight in designing future registration trials for asthma drug development.

A randomized, three-period crossover study of umeclidinium as monotherapy in adult patients with asthma

BACKGROUND

To our knowledge, no studies in patients with asthma have assessed a long-acting muscarinic antagonist in the absence of inhaled corticosteroids (ICS).

OBJECTIVE

Evaluate the dose-response, efficacy, and safety of umeclidinium (UMEC) in patients with asthma not receiving ICS.

METHODS

In this double-blind, three-period crossover study, 350 subjects were randomized to a sequence of three of eight inhaled treatments: UMEC 15.6, 31.25, 62.5, 125, or 250 mcg once daily (OD), UMEC 15.6 or 31.25 mcg twice daily (BID), or placebo, administered for 14 days (12-14-day washout). Trough forced expiratory volume in one second (FEV1), 0-24-h weighted mean (WM) FEV1, and safety were assessed. Serial spirometry and pharmacokinetic assessments were performed in a subgroup.

RESULTS

Subjects had a mean baseline pre- and post-bronchodilator FEV1 of 71% and 88% predicted, respectively. Significant improvements in change from baseline trough FEV1 were observed for UMEC 15.6 OD (0.066 L; p = 0.036) and UMEC 125 OD (0.088 L; p = 0.005) versus placebo, but not other OD or BID doses. UMEC increased 0-24-h WM FEV1 versus placebo (0.068-0.121 L [p ≤ 0.017] with no clear dose-response). Treatment differences were similar for corresponding OD and BID doses in serial assessments. UMEC was rapidly absorbed, with evidence of some accumulation. The incidence of on-treatment adverse events was 9-21% for UMEC and 12% for placebo. There were no treatment-related effects on laboratory parameters.

CONCLUSION

The modest trough FEV1 improvements did not conclusively support a therapeutic benefit of UMEC in non-ICS treated patients with asthma.

CLINICALTRIALSGOV

NCT01641692.

The effect of fluticasone furoate/umeclidinium in adult patients with asthma: a randomized, dose-ranging study

BACKGROUND

We evaluated the dose-response of umeclidinium (UMEC; a long-acting muscarinic antagonist) combined with fluticasone furoate (FF; an inhaled corticosteroid [ICS]) in patients with asthma.

METHODS

In a double-blind, three-period crossover study, 421 subjects (symptomatic on ICS), were randomized to a sequence of three of seven treatments: FF 100 mcg alone, FF 100 mcg combined with UMEC (15.6, 31.25, 62.5, 125, or 250 mcg), or vilanterol 25 mcg (a long-acting β-agonist), inhaled once-daily for 14 days (12-14-day washout). Trough forced expiratory volume in one second (FEV1), peak expiratory flow (PEF), and safety were assessed.

RESULTS

Period baseline was a significant covariate, indicating a potential carryover effect between treatment periods. Across all treatment periods, trough FEV1 improved with FF/UMEC 125 and 250 versus FF (treatment difference 0.055 L [both doses]; p = 0.018). FF/UMEC increased morning (15.9-22.9 L/min) and evening (16.2-28.8 L/min) PEF versus FF. As intended assessments were confounded, post hoc Period 1 data analyses were performed, demonstrating significant increases in trough FEV1 with FF/UMEC 31.25, 62.5, and 250 versus FF. Trough FEV1 improvements with FF/UMEC were greater in subjects with fixed (0.095-0.304 L) versus non-fixed (-0.084 to 0.041 L) obstruction. The incidence of on-treatment adverse events was 13-25% across groups. No treatment-related effects on laboratory parameters were reported.

CONCLUSION

FF/UMEC may be a viable treatment for patients with asthma symptomatic on ICS; benefit may be most prominent in those with fixed obstruction. The carryover effect suggests future UMEC studies should use an alternative design. ClinicalTrials.gov: NCT01573624.

Sleep in asthma

Many patients with asthma experience worsening of symptoms at night. Understanding the mechanism of nocturnal asthma and the factors that exacerbate asthma during sleep would lead to better management of the condition.

Update on obstructive sleep apnea and its relation to COPD

Chronic obstructive pulmonary disease (COPD) is a common and preventable lung disease that affects millions of people in the United States. Sleep disorders including obstructive sleep apnea (OSA) are also common. It is not surprising that many people with COPD also suffer from OSA. This relationship, however, puts people at risk for more nocturnal desaturations and potential complications related to this, including pulmonary hypertension and heart rhythm disturbances. This update focuses on the physiology of sleep disturbances in COPD as well as the clinical implications of OSA in COPD.

Timing, sleep, and respiration in health and disease

Breathing is perhaps the physiological function that is most vital to human survival. Without breathing and adequate oxygenation of tissues, life ceases. As would be expected for such a vital function, breathing occurs automatically, without the requirement of conscious input. Breathing is subject to regulation by a variety of factors including circadian rhythms and vigilance state. Given the need for breathing to occur continuously with little tolerance for interruption, it is not surprising that breathing is subject to both circadian phase-dependent and vigilance-state-dependent regulation. Similarly, the information regarding respiratory state, including blood-gas concentrations, can affect circadian timing and sleep-wake state. The exact nature of the interactions between breathing, circadian phase, and vigilance state can vary depending upon the species studied and the methodologies employed. These interactions between breathing, circadian phase, and vigilance state may have important implications for a variety of human diseases, including sleep apnea, asthma, sudden unexpected death in epilepsy, and sudden infant death syndrome.