Does sleep cause nocturnal asthma?

Association of delayed chronotype with allergic diseases in primary school children

To investigate the associations of sleep midpoint for both weekdays and weekends, and chronotype, with allergic diseases, specifically asthma, allergic rhinitis, and eczema in primary school children. In this cross-sectional study, we evaluated 10409 children between 7 and 12 years of age (mean 9.21 ± 1.51 years; male 52.2%). Each allergic disease was defined as children with both diagnosed disease and current symptoms, and the reference group was described as children without any allergic symptoms. Sleep durations and mid-sleep times were calculated by reported sleep timing. Chronotype was determined by mid-sleep time on free days corrected for oversleeping. Children with allergies have shorter sleep duration and later sleep preferences. Late weekly sleep midpoints were associated with higher odds of allergies, and the odds were even higher for later weekday midpoints than their weekend counterparts. Regarding chronotype, the more evening chronotype, the higher the odds of allergic rhinitis and eczema. Additionally, effect of weekday late sleep midpoint on allergies was stronger as the participants who slept less (asthma: aOR,1.62, 95 CI%,1.25-2.10, p < .001; allergic rhinitis: aOR,2.12, 95 CI%,1.68-2.67, p < .001; eczema: aOR, 1.94, 95 CI%,1.52-2.48, p < .001). Further, the associations of chronotype with allergic rhinitis were confounded by second-hand smoking exposure. Our study, which finds an association between chronotype and the odds of three allergic diseases, hopes to improve sleep health awareness, especially in the particular population with allergic diseases, and describes the importance of evaluating modifiable behavioral factors, such as sleep habits, as a plausible factor for the prevention and treatment of allergic 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.

Impact of sleep opportunity on asthma outcomes in adolescents

RATIONALE

Insufficient sleep is associated with a number of negative health outcomes; as most adolescents obtain <7 h of sleep per night, it is important to understand how sleep impacts asthma among adolescents.

OBJECTIVES

To examine the impact of sleep opportunity on asthma in adolescents.

METHODS

In this study, 54 adolescents with asthma (12-17 years, 69% female, 65% Caucasian) participated in a randomized, cross-over sleep manipulation trial, including a sleep stabilization week, five nights of a "Short" sleep opportunity (time in bed: 6.5 h/night), and five nights of a "Long" sleep opportunity (time in bed: 9.5 h/night). Wake times were consistent across all three study weeks. Primary outcomes were lung function (daily peak expiratory flow rate, weekly spirometry) and functional asthma outcomes (daily asthma symptoms, Asthma Control Questionnaire, PROMIS Asthma Impact Scale). Markers of inflammation were also explored.

MEASUREMENTS AND MAIN RESULTS

Compared to the Long sleep week, during the Short sleep week, morning FEV1 was lower (p = 0.006), while asthma symptoms and albuterol use was higher (p < 0.05), and asthma showed a trend towards greater negative impact on daily life (p = 0.07). No differences were found for weekly measures of lung function or inflammation.

CONCLUSIONS

An insufficient sleep opportunity negatively impacts objective and subjective daily symptoms of asthma in adolescents, as well as health related quality of life. As most adolescents are significantly sleep deprived, it is important to target sleep health in the treatment of asthma.

An unidentified monster in the bed--assessing nocturnal asthma in children

Nocturnal asthma (NA) is increasing in prevalence, affecting millions of people worldwide. In addition to being associated with increased mortality, NA is associated with a decreased quality of life. NA associated sleep disturbances and increased daytime sleepiness are especially important in children due to the accompanying behavioral and developmental difficulties. As diurnal spirometry is not a practical tool for the diagnosis and monitoring of NA, self or parental reports are used. Children underreport and underestimate their NA symptoms and parents are not fully aware of their child's NA indicators. In addition, there is the lack of physician familiarity regarding the assessment and treatment of NA. Therefore, NA is chronically underreported. The development of a non-invasive, objective, home-based diagnostic tool is crucial in diagnosing and monitoring children with NA. The presence of wheeze during sleep has been successfully employed as a tool to measure NA in children. This review discusses the increasing prevalence of NA, current diagnostic tools and the consequences of undiagnosed NA in children. In conclusion, this paper suggests that an automated wheeze detective device is an objective and practical tool to aid the diagnosis and monitoring of NA.

Sleep and medical disorders

Extensive evidence links cardiovascular disease and sleep disordered breathing. OSA has adverse effects on blood pressure, cardiovascular status,and mortality. Effective CPAP therapy can improve blood pressure and cardiac function in patients who have OSA. Patients who have congestive heart failure have a high prevalence of sleep-disordered breathing, with OSA occurring in 30% of such patients and Cheyne-Stokes respiration in 40%.CPAP is the preferred mode of therapy for both types of sleep-disordered breathing in patients who have coexistent congestive heart failure. Nocturnal worsening of asthma is a common manifestation of this disease that indicates increased disease severity. Therapy focuses on judicious use of long-acting bronchodilators, and the presence of OSA should also be considered. COPD is frequently associated with impaired sleep, likely because of chronic dyspnea and sleep-associated hypoxemia. Appropriate therapy again includes long-acting bronchodilators and possibly nocturnal supplemental oxygen. Gastroesophageal reflux during sleep may lead to prolonged episodes of esophageal acid exposure and may be a common sequela of OSA, perhaps triggering nocturnal worsening of asthma. Endstage renal disease and chronic dialysis are commonly associated with a host of troublesome sleep problems,including OSA, RLS, PLMD, and daytime sleepiness.

Circadian patterns of breathing

In the rat, a mostly nocturnal animal, activity, body temperature and metabolic rate increase during the dark hours of the day. Since all these variables are known to influence breathing, it is expected that also pulmonary ventilation (VE) will present a circadian pattern. In rats chronically instrumented for measurements of body temperature and activity by telemetry, carbon dioxide production and oxygen consumption (V(O(2))) were measured continuously for several days by an open-circuit method, while VE was monitored by a modification of the barometric technique. Tidal volume, frequency, and VE increased in the dark (D) compared to the light (L) hours, with minor L-D differences in VE/V(O(2)). L-D differences in activity were not responsible for the circadian pattern of VE. Both in hypoxia and in hypercapnia the degree of hyperventilation (percent increase in VE/V(O(2))) was essentially independent of the time of the day, despite the fact that in hypoxia, differently from hypercapnia, the amplitude of the circadian pattern of all variables decreased, activity being the least affected, and body temperature the most. These effects of hypoxia, which occurred before and after sino-aortic denervation and did not compromise the period of the biological clock, may be mediated by the hypothalamic thermoregulatory centers. The data of these experiments and of others reviewed in this article indicate that (1) breathing and its control mechanisms accompany the daily oscillations of numerous physiological variables, and (2) the advantages of a biological clock do not compromise the adequacy of the hyperventilatory responses to chemical challenges.

Endogenous circadian rhythm of pulmonary function in healthy humans

Numerous studies have demonstrated a diurnal rhythm in indices of pulmonary function in both healthy subjects and subjects with asthma, with minima occurring during the night. To determine whether such diurnal changes are caused by an endogenous circadian rhythm or by diurnal alterations in behavior or the environment, we measured indices of pulmonary function throughout a "constant routine" protocol designed to unmask underlying circadian rhythms. After two acclimation days in the laboratory, 10 healthy adults maintained relaxed wakefulness in a semirecumbent posture in a constant environment with low light (10 lux) for 41 h. Measurements of FEV(1), FEVC, PEF, blood cortisol, and core body temperature (CBT) were performed every 2 h. Results of cosinor analysis of group data aligned to CBT circadian minimum revealed significant circadian variations in FEV(1) and FEV(1)/FEVC, cortisol, and CBT, and lack of significant circadian variations in FEVC and PEF. The ranges (peak to trough) of mean circadian changes in spirometric variables were 2. 0-3.2% of the mesor. The circadian minima of all variables occurred within the usual sleep period (although subjects remained awake). Because of differences in phase relationships between CBT and pulmonary function among subjects, the circadian rhythms within subjects were generally larger than the group average circadian changes, being significant for FEV(1)/FEVC in 5 of 10 subjects and for PEF in 6 of 10 subjects. Sleep deprivation (24 h) failed to cause a significant change in any pulmonary function variable (when controlled for circadian phase). Thus, endogenous circadian rhythms contribute to diurnal changes in pulmonary function in healthy subjects.

Sleep, respiratory physiology, and nocturnal asthma

The nocturnal worsening of asthma is a common feature of this disease that recently has received extensive investigation. Most recent efforts have focused on the role of circadian biorhythms that could promote a nocturnal increase in airway inflammation, leading to a subsequent increase in airflow obstruction and asthma symptoms. However, definitive studies remain lacking. As discussed in this review, there is also substantial evidence that sleep itself may play a direct role in the nocturnal worsening of asthma. Potential mechanisms for such a sleep-related effect could include the supine posture, alterations in sympathetic and parasympathetic "balance," sleep-associated reductions in lung volume, intrapulmonary pooling of blood, and sleep-associated upper airway narrowing, both with and without snoring and obstructive sleep apnea (OSA). These potential contributors to this troublesome phenomenon deserve further consideration when investigating mechanisms of nocturnal asthma.

Chronobiology and chronotherapy in medicine

There is a fascinating and exceedingly important area of medicine that most of us have not been exposed to at any level of our medical training. This relatively new area is termed chronobiology; that is, how time-related events shape our daily biologic responses and apply to any aspect of medicine with regard to altering pathophysiology and treatment response. For example, normally occurring circadian (daily cycles, approximately 24 hours) events, such as nadirs in epinephrine and cortisol levels that occur in the body around 10 PM to 4 AM and elevated histamine and other mediator levels that occur between midnight and 4 AM, play a major role in the worsening of asthma during the night. In fact, this nocturnal exacerbation occurs in the majority of asthmatic patients. Because all biologic functions, including those of cells, organs, and the entire body, have circadian, ultradian (less than 22 hours), or infradian (greater than 26 hours) rhythms, understanding the pathophysiology and treatment of disease needs to be viewed with these changes in mind. Biologic rhythms are ingrained, and although they can be changed over time by changing the wake-sleep cycle, these alterations occur over days. However, sleep itself can adversely affect the pathophysiology of disease. The non-light/dark influence of biologic rhythms was first described in 1729 by the French astronomer Jean-Jacques de Mairan. Previously, it was presumed that the small red flowers of the plant Kalanchoe bloss feldiuna opened in the day because of the sunlight and closed at night because of the darkness. When de Mairan placed the plant in total darkness, the opening and closing of the flowers still occurred on its intrinsic circadian basis. It is intriguing to think about how the time of day governs the pathophysiology of disease. On awakening in the morning, heart rate and blood pressure briskly increase, as do platelet aggregability and other clotting factors. This can be linked to the acrophase (peak event) of heart attacks. During the afternoon we hit our best mental and physical performance, which explains why most of us state that "I am not a morning person." Even the tolerance for alcohol varies over the 24-hour cycle, with best tolerance around 5 pm (i.e. "Doctor, I only have a couple of highballs before dinner"). Thus, all biologic functions, from those of the cell, the tissue, the organs, and the entire body, run on a cycle of altering activity and function.(ABSTRACT TRUNCATED AT 400 WORDS)

Nocturnal airflow obstruction, histamine, and the autonomic central nervous system in children with allergic asthma

A study was carried out to investigate whether an imbalance in the autonomic nervous system or release of histamine, or both, is responsible for the nocturnal increase in airflow obstruction in asthmatic children. The study comprised 18 children with allergic asthma, nine with (group 1) and nine without (group 2) nocturnal airflow obstruction, and an age matched control group. All drugs were withheld for three days before and during the study. On day 4 each child was admitted to hospital and a series of measurements was made every four hours for 24 hours. These included measurements of the forced expiratory volume in one second (FEV1), heart rate and sinus arrhythmia gap from an electrocardiogram (an indirect measure of parasympathetic activity) and urine sampling for determination of catecholamine and N'-methylhistamine concentrations (measures of sympathetic activity and histamine release respectively). Urinary N'-methylhistamine excretion was significantly higher over the 24 hours in children in group 1 than in children in group 2, and overnight values were also significantly higher in children in group 1 than those in group 2. Mean (SEM) values (mumol/mol creatinine) were 154.6 (11.2) in group 1 and 110 (11.2) in group 2 for 2400-0400 hours samples and 139.2 (13.1) and 101.2 (10.6) 0400-0800 hours samples. There was no evidence of decreased sympathetic or increased parasympathetic activity in association with the nocturnal airflow obstruction; noradrenaline concentrations were increased in group 1. These observations indicate that nocturnal airflow obstruction is associated with increased release of histamine overnight.

Relation between nocturnal symptoms and changes in lung function on lying down in asthmatic children

Nocturnal symptoms are common in young asthmatic children. Such symptoms may be caused by increased impairment of lung function when they adopt the supine posture. Thirty one children aged 2.8-8.3 years were studied, of whom 20 had asthma (10 with frequent nocturnal symptoms) and 11 had no respiratory problems (control subjects). Peak expiratory flow (PEF) was measured with a Wright's peak flow meter and functional residual capacity (FRC) by a helium gas dilution technique after 30 minutes of lying supine; the values were compared with FRC measured sitting and PEF standing. Peak flow fell significantly on adoption of the supine posture in the asthmatic children, but there was no difference in this fall between the asthmatic children with and without nocturnal symptoms. FRC also fell on adoption of the supine posture, but the decrease in FRC was significant only in the control children and the asthmatic children without nocturnal symptoms. The failure to find a greater fall in PEF or a greater change in FRC on adoption of the supine posture among asthmatic children with nocturnal symptoms suggests that mechanisms other than increased impairment of lung function are responsible for nocturnal asthma.

Twenty-four hour lung function in adult patients with asthma. Chronoptimized theophylline therapy once-daily dosing in the evening versus conventional twice-daily dosing

Many patients with asthma experience a worsening of symptoms at night and in the early morning, resulting in sleep disruption and possibly altered daily performance. A bronchodilator agent that exerts its maximal effect overnight to control nocturnal symptoms, without a worsening of the disease during the daytime, should improve the treatment of asthma. This investigation examined the efficacy and kinetics of a new chronotherapeutically optimized, sustained-release theophylline formulation administered once daily (OD) in the evening at 8:00 P.M. in comparison with a conventional sustained-release theophylline administered twice daily (TD) at 8:00 A.M. and at 8:00 P.M. in the same dose. After a theophylline clearance study to substantiate normal or slow metabolism of the drug, a dose-titration period, and a 24-h baseline spirometric study of patients not receiving any medication, participants were randomized to 7-day treatment phases with either OD or TD. Each outpatient segment of 6 days of OD and TD was followed by a 24-h inpatient study on Day 7 when serum drug level and spirometric (PEF, FEV1, and FEF25-75) parameters were obtained every 2 h. The conventional TD treatment was associated with a constant serum theophylline level over the 24 h. In contrast, the OD treatment was associated with larger peak-to-trough drug level fluctuation, with higher levels produced overnight and lower ones in the evening at the end of the dosing interval. Compared with the baseline references, both OD and TD significantly improved airflow over the entire 24 h and to a comparable extent. However, between 2:00 and 6:00 A.M., PEF and FEV1 were significantly greater with OD than with TD. The improvement in PEF and FEV1 at this time, because of OD, was correlated with the serum theophylline level. This was not the case for TD. The improvement in airflow over baseline values between 2:00 and 6:00 P.M. was not correlated with theophylline level with either treatment regime. Overall, the chronotherapeutically conceptualized OD treatment administered in the evening resulted in better airflow levels overnight than did the TD regime without loss of airflow in the afternoon.

Diurnal variation of lung reactivity in normal and myopathic hamsters

In this study we measured the diurnal variation in lung reactivity in normal and myopathic hamsters. Lung reactivity to an intravenous bolus of 0.7 mg/kg acetylcholine (ACh) was measured as the change in peak airway pressure of anesthetized ventilated animals. In the normal hamsters, lung reactivity was 57% higher during the day (8 A.M., 12 P.M., and 4 P.M.) than during the night (p = 0.01). This increased reactivity was not associated with any changes in baseline pressures. The lung reactivity was correlated to body activity as measured on an electronic activity monitor over seven consecutive days. The hamster, being a nocturnal forager, gradually increased activity at about 6 P.M. and maintained intermittent activity until about 6 A.M. Sleep occurred between 6 A.M. and 6 P.M., and this was when the lung reactivity was greatest. In the myopathic hamsters, although the magnitude of the response to ACh was about 40% lower than that in normal animals, the lung reactivity during the daytime was still about 46% greater than that during the night (p = 0.007). The body activity records from the myopathic animals showed that these animals do not have a normal sleep pattern during the daytime; sleep is not continuous, showing intermittent periods of physical activity. Our results in the normal animals are consistent with observations in man, which show greater problems with airway obstruction and asthmatic attacks during the night.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis and pathophysiology of nocturnal asthma

Nocturnal wheezing is a major component of asthma. This article reviews the many factors (allergen exposure, sleep, airway cooling, diminished clearance of mucous secretions) that have been identified as contributing to nocturnal asthma. Also discussed are recent data suggesting that diurnal variations in hormone concentrations and in autonomic nervous system control are possible mechanisms of nocturnal asthma. Decreased epinephrine secretion and increased vagal tone during sleep not only cause airway obstruction but may also enhance bronchial reactivity. These changes in the modulation of airway smooth muscle tone produce bronchial obstruction, which, in turn, accentuates ventilation-perfusion mismatch and increases hypoxia.

Parasympathetic nervous system in nocturnal asthma

To investigate the effect of vagal blockade with atropine on nocturnal fall in peak expiratory flow rate 10 patients with asthma who had a diurnal variation in peak expiratory flow rate of greater than 20% were given 30 micrograms/kg of intravenous atropine or a placebo at 4 am and 4 pm. Vagal blockade caused significant bronchodilatation at 4 am and 4 pm (peak expiratory flow rate rose from 260 to 390 l/min at 4 am and 400 to 440 l/min at 4 pm) and significantly increased the pulse rate from 60 to 121 beats/minute at 4 am and from 76 to 122 beats/minute at 4 pm. Nocturnal asthma was almost totally reversed, implying that vagal mechanisms are fundamental in its pathophysiology. Other mechanisms--diurnal changes in plasma adrenaline concentration, the activity of non-adrenergic non-cholinergic nerves, and circadian rhythms of inflammatory mediator activity--may also be implicated.

Breathing patterns during sleep in patients with nocturnal asthma

Breathing patterns early and late in the night, at the same sleep stage, were compared in six healthy subjects and 15 adults with nocturnal asthma, to try to identify changes of overnight bronchoconstriction, and breathing patterns at different sleep stages, to see whether there were changes related to sleep stages that were indicative of bronchoconstriction. Despite an average 31% fall in FEV1 overnight in the patients with asthma, neither breathing frequency nor expiratory time, which might be expected to change during bronchoconstriction, was different early in the night from late in the night, nor did they differ between sleep stages. There was no evidence of asynchronous movement of the chest and abdomen in any patient. This study did not identify any abnormality of breathing pattern that would indicate the development of nocturnal asthma without the need to awaken the patient.

Diurnal rhythm of asthma

A diurnal rhythm in the occurrence and severity of asthma symptoms is almost universal with disturbed sleep due to enhanced symptoms at night paralleled by a change in lung function. The mechanisms involved are not completely understood. However, it appears to be related to an exaggerated response to a circadian rhythm in lung function observed in healthy individuals. The circadian nature of asthma must be considered in diagnosis and evaluating the adequacy of therapy. Inhaled therapy with additional suppressive and anti-inflammatory treatment as required should be effective in treating most patients with nocturnal asthma.

Day-night patterns in bronchial patency and dyspnea: basis for once-daily and unequally divided twice-daily theophylline dosing schedules

Asthma typically worsens overnight. Although 24-hr variation in environmental conditions may contribute to the worsening of dyspnea at night, this does not fully explain day-night patterns of this disease. Circadian (about 24-hr) rhythms in bioprocesses which influence airways patency constitute major contributory factors. The nighttime exacerbation of asthma may represent the influence of circadian bioperiodicities in bronchial patency, airways hyperreactivity to acetylcholine, histamine and house dust, and altered levels of several plasma constituents such as cortisol, epinephrine, histamine and cyclic AMP.

Treatment of nocturnal asthma: the role of sustained-release theophylline and oral beta-2-mimetics

In two double-blind, multiple-dose cross-over studies the therapeutic effects of SR theophylline preparations given once each night (mean 11.2 mg/kg per day) versus twice daily in equal doses (mean 10.3 mg/kg per day) (study I) and SR-terbutaline in equal doses (mean 0.25 mg/kg per day) versus SR theophylline in unequally divided daily doses (mean 5.3 mg/kg morning dose, 10.6 mg/kg evening dose) study II) were compared in 19 patients with nocturnal asthma. At the end of each treatment period drug serum concentrations and PEFR were measured every 2 hr over a 24-hr period. With the twice-daily, equally divided regimen, serum theophylline concentrations were lower at night than during the day (mean 9.4 +/- 0.9 versus 11.3 +/- 1.0 mg/l). With the single evening administration, serum theophylline concentrations were considerably higher at night (Cmax 16.3 +/- 1.4 mg/l) and the circadian variation of PEFR was significantly reduced. PEFR was higher during night and early morning (283 +/- 14 versus 217 +/- 11 l/min, P less than 0.005). During daytime in study II, PEFR values were slightly higher with theophylline than terbutaline. There was no significant difference in peak flow between either treatment during the night and early morning. However, additional use of inhaled beta-2-mimetics because of asthmatic attacks occurred more often during terbutaline (79 times in 8/10 patients) than theophylline treatment (29 times in 5/10 patients). Symptom scores, number of attacks and side-effects clearly favor the theophylline regimen. We conclude that for patients with nocturnal asthma a once-nightly dose of SR theophylline can be sufficient for stabilization of the airways.

Effect of sleep deprivation on overnight bronchoconstriction in nocturnal asthma

Nocturnal cough and wheeze are common in asthma. The cause of nocturnal asthma is unknown and there is conflicting evidence on whether sleep is a factor. Twelve adult asthmatic subjects with nocturnal wheeze were studied on two occasions: on one night subjects were allowed to sleep and on the other they were kept awake all night, wakefulness being confirmed by electroencephalogram. Every patient developed bronchoconstriction overnight both on the asleep night, when peak expiratory flow (PEF) fell from a mean (SE) of 418 (40) 1 min-1 at 10 pm to 270 (46) 1 min-1 in the morning, and on the awake night (PEF 10 pm 465 (43), morning 371 (43) 1 min-1). The morning values of PEF were, however, higher (p less than 0.1) after the awake night and both the absolute and the percentage overnight falls in PEF were greater when the patients slept (asleep night 38% (6%), awake night 20% (4%); p less than 0.01). This study suggests that sleep is an important factor in determining overnight bronchoconstriction in patients with nocturnal asthma.

Do asthmatics suffer bronchoconstriction during rapid eye movement sleep?

Many patients with asthma are troubled by nocturnal wheeze. The cause of this symptom is unknown, but sleep is an important factor. A study was carried out to determine whether nocturnal bronchoconstriction is related to any specific stage of sleep. Eight asthmatics with nocturnal wheeze and eight control subjects performed forced expiratory manoeuvres immediately after being woken from rapid eye movement (REM) or non-REM sleep, wakings being timed to differentiate temporal effects from those related to the stage of sleep. The control subjects showed no significant temporal bronchoconstriction or bronchoconstriction related to the stage of sleep. All patients showed bronchoconstriction overnight, the mean peak expiratory flow rate falling from 410 (SEM 50) 1/min before sleep to 186 (49)1/min after sleep. After the patients had been woken from REM sleep the forced expiratory volume in one second was on average 300 ml lower (p less than 0.02) and peak expiratory flow rate 45 1/min lower (p less than 0.03) than after they had been woken from non-REM sleep. As wakenings from REM sleep were 21(8) minutes later in the night than those from non-REM sleep multivariate analysis was performed to differentiate temporal effects from those related to the stage of sleep. This showed that the overnight decreases in forced expiratory volume in one second and peak expiratory flow rate were significantly related both to time and to REM sleep. This study suggests that asthmatics may suffer bronchoconstriction during REM sleep.

Chronobiology and asthma. I. Day-night differences in bronchial patency and dyspnea and circadian rhythm dependencies

The symptoms of allergic asthmatic patients typically worsen during the night, especially during the early morning hours. Although 24-hour variations in the environment contribute to the intensification of the asthmatic condition nocturnally, environmental changes themselves do not fully explain the temporal aspects of this disease. Circadian (about 24-hour) rhythms in critical bioprocesses constitute significant contributory factors. The exacerbation of asthma during the night represents the changing status of biological functioning due to circadian rhythms in bronchial patency; airways hyperreactivity to acetylcholine, histamine, and house dust; and plasma cortisol, epinephrine, histamine, and cyclic AMP, among others.

Comparison of morning and evening dosing with a 24-hour sustained-release theophylline, Uniphyl, for nocturnal asthma

Sixteen adults who had chronic asthma with nocturnal symptoms were selected to evaluate and compare the effectiveness of 7 A.M. versus 7 P.M. single daily dosing with the 24-hour sustained-release theophylline Uniphyl. The study was a randomized, double-blind, placebo-controlled trial in which the patients were given 800 mg of Uniphyl at either 7 A.M. or 7 P.M. for one week each. Serum theophylline levels showed significantly higher peak (18.1 +/- 1.8 micrograms/ml versus 12.7 +/- 1.2 microgram/ml) and trough (12.4 +/- 1.3 microgram/ml versus 7.6 +/- 1.0 microgram/ml) concentrations during evening dosing. Furthermore, daily peak flow values were higher in the morning when Uniphyl was given at 7 P.M. Thus, nocturnal dosing with Uniphyl gives higher serum theophylline concentrations and, with this, better control of nocturnal asthma.

Circadian variation in airway function

Nocturnal asthma is a common and troublesome problem. Many possible mechanisms have been proposed, including exposure to allergens, sleep itself, the supine posture, withdrawal of bronchodilator drugs, gastric reflux, mucus plugging, and airway cooling. Although these may be contributory factors in individual patients, they cannot provide a universal explanation for the phenomenon of nocturnal and early morning wheezing. It now seems that nocturnal asthma may best be understood in terms of circadian rhythms. A circadian variation in airway caliber has been demonstrated in normal subjects; in asthmatic subjects, the same rhythm is present but with greater amplitude. The amplitude is magnified by bronchial hyper-responsiveness, a cardinal feature of asthma. Evidence now suggests that the fall in circulating epinephrine level at night removes an important defense against bronchoconstriction in asthmatic subjects, and this itself may be magnified by removal of the braking effect of epinephrine on mast cell mediator release. In addition, increased vagal reflex bronchoconstriction and the delayed effects of the fall in plasma cortisol level may also contribute to nocturnal wheezing. Thus, nocturnal asthma may be explained by a complex interaction of several coincident circadian rhythms, which produce only small changes in airway caliber in normal subjects; however, in asthmatic patients, these constrictor effects are magnified to produce bronchospasm severe enough to wake the patient.

Nocturnal asthma and timing of treatment

Nocturnal deterioration of pulmonary function in asthmatic patients is a well-recognized and well-documented phenomenon. The mechanism of this "morning dip," however, remains uncertain. Although the circadian rhythms of body temperature, corticosteroid, catecholamine, histamine, and opiate peptide levels, and even sleep itself have been shown to be in phase with the diurnal variation in asthma, a causal relationship has yet to be established. Increased nighttime bronchial reactivity to histamine, acetylcholine, and house dust allergen have been demonstrated. In general, continuous treatment with theophylline, beta-adrenergic agonists, or corticosteroids attenuates the degree of morning dip but does not completely eliminate the circadian rhythm of asthma. The significance of nocturnal asthma is emphasized by the observation that asthma deaths occur more frequently during nighttime hours and are often preceded by large daily swings in peak expiratory flow. Further studies examining the etiology and treatment of nocturnal asthma are needed.

Characteristics and prognostic value of morning dipping of peak expiratory flow rate in stable asthmatic subjects

Characteristics and prognostic relevance of morning dip of peak expiratory flow rate (PEFR) were evaluated in stable asthmatic subjects. Among 246 outpatients monitored four times daily for two weeks, 38 (group A) showed a significant difference between morning reading of PEFR and each of the others; they were compared to 38 randomly selected patients (group B) not showing morning dip in PEFR. Less frequent seasonal course, extrinsic pathogenesis, and sensitization to mites characterized group A; starting airflow limitation was more severe in those with morning dip, but no significant difference between mean PEFR measured throughout two weeks was found. At 6 to 12 weeks, morning dip was not found in 19 of 38 subjects in group A and appeared in seven of 38 subjects in group B, with no clearcut relationship to treatment being evident. At 25 to 104 weeks, no significant difference between therapeutic requirements and the forced expiratory volume in one second was detected; therefore, unlike the short-term, morning dip is not a risk factor for worse long-term prognosis.

Sleep-associated airway problems in children

Several of the most common and most important sleep-associated airway problems are discussed, including obstructive sleep apnea syndrome, gastroesophageal reflux and nocturnal aspiration, spasmodic croup, nocturnal asthma, and sleep hypoxemia in chronic lung disease, and guidelines are offered for the often difficult diagnosis and for treatment.

Effect of naloxone on circadian rhythms in lung function

To determine whether the endogenous opioid peptides play a part in the pathogenesis of asthmatic morning dipping, six patients with chronic asthma with a reproducible peak flow pattern of morning dipping were investigated in a double blind, randomised, crossover study of naloxone versus placebo. Naloxone was given as a loading dose of 8 mg followed by a continuous infusion of 5.6 mg/h from midnight until 10 am on two consecutive nights. Naloxone had no significant effect on PEFR, FEV1, or FVC at 6 am. There was, however, an improvement over placebo values in all these indices between the hours of 8 am and 8 pm on the day after the first naloxone infusion in all six patients. This effect was not observed after the second naloxone infusion.

Airway cooling and nocturnal asthma

It has long been recognized that asthma often worsens at night. The nature of nocturnal asthma is unclear. Previously we have demonstrated that acute asthma attacks can be induced by exposing the body to cold, and that such attacks can be prevented by breathing warm, humidified air (WHA). Since body temperature begins to decrease late at night and continues through the early morning hours, we suspected that part if not all of nocturnal asthma may be triggered by the same mechanism as asthma induced by body cooling. To test this hypothesis, eight asthmatic patients were studied on four occasions. The subjects breathed either ambient room air (RA; 23 degrees C, 20 percent relative humidity) or WHA (37 degrees C, 100 percent relative humidity) for eight hours during the night with or without taking their regular evening medication. Each night, oral temperature and pulmonary function were measured at 9:45 PM (baseline measurement) and again at 6:15 AM (morning measurement). Results showed that when RA was used, morning pulmonary function and oral temperature decreased significantly from baseline. Using WHA in conjunction with regular evening medication completely prevented both nocturnal asthma and changes in oral temperature. Using WHA without regular evening medication did not prevent but substantially reduced bronchoconstriction compared with RA. These results suggest that airway cooling, which occurs as a consequence of body cooling, plays a significant role in triggering nocturnal asthma.

Irregular breathing and hypoxaemia during sleep in chronic stable asthma

Breathing patterns, ear oxygen saturation (SaO2), and EEG sleep-stage throughout an undisturbed night's sleep were compared in ten adult stable asthmatics and ten age-matched healthy subjects. The two groups slept equally long (5.0-7.2, mean 6.2 h), but the asthmatics slept less well; they had more periods of wakefulness and drowsiness and irregular breathing than did the healthy subjects. They also had greater and more frequent falls in SaO2. Most hypoxaemic episodes occurred in the rapid-eye movement phase of sleep and were associated with hypopnoea or apnoea, but no patient had a classical sleep-apnoea syndrome. The severity of nocturnal hypoxaemia was related to the level of SaO2 when the subjects were awake, but did not correlate with the fall in forced expiratory volume recorded in eight out of ten asthmatics after sleep.

Diurnal variation in airflow obstruction in chronic bronchitis

Twelve patients fulfilling strict criteria for chronic obstructive bronchitis recorded serial peak expiratory flow rates (PEFR) five times daily for a two-week period. Despite a 9.2% improvement in forced expiratory volume in one second (FEV1) with ipratropium bromide, and an 11.3% improvement with ipratropium bromide plus salbutamol, the inherent diurnal variation in PEFR while on no medication was greater than the improvement caused by either bronchodilator. In the group as a whole, the difference between the highest and the lowest daily PEFR over the two weeks was 24% of the mean daily value. Using cosinor analysis, 10 of the 12 patients showed a significant rhythm in PEFR with a computed mean amplitude between highest and lowest readings of 8.6% of the mean daily value. This is no greater than that found in normal subjects, but is considerably less than the variation in PEFR in patients with bronchial asthma.

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

A computer technique (cosinor analysis) has been used to evaluate circadian rhythms in airway calibre in normals and asthmatics. Two hundred and twenty-one normal subjects recorded peak expiratory flow rate (PEFR) at home four times a day for seven days. Rhythm detection was statistically significant in 145 of them (65.6%) who showed a mean amplitude of 8.3% of individual mean PEFR (+/- SD 5.2%). Amplitude was independent of age, sex, atopy, family history of asthma, and smoking habit. Fifteen of them were also studied three times a day for five days in the laboratory with flow-volume loops. Eleven showed significant PEFR rhythms at home. No single measurement from the flow-volume loop showed periodicity in as many of them but rhythms were now also detected in the other four normal subjects in some components of the loop. Fifty-six asthma patients were studied with a similar protocol of PEFR measurement and compared with the 145 rhythmic normal subjects. Mean phases of the normal and asthmatic rhythms were not significantly different with acrophases (peak of rhythm cycle) at 1557 and 1526 respectively. The mean asthmatic amplitude was, however, significantly greater at 50.9%. Nocturnal asthma, therefore, probably represents an exaggeration of a normal circadian rhythm in airway calibre. The amplitude of the PEFR rhythm is an index of bronchial lability and is thus valuable in monitoring asthma patients. An amplitude of greater than 20% should be a useful screening test for asthma.