During nocturnal asthma, your FEV1 decreases by at least 15% from bedtime to getting up in the morning in patients with asthma. For some people, the decline in lung function can be significantly more -- and this is all associated with increased symptoms, such as cough, wheezing and shortness of breath that disrupt sleep. Patients with large nighttime changes in their FEV1 may also have more daytime symptoms.
Diagnosing Asthma at Night or Nocturnal Asthma?
The easiest way to diagnose nocturnal asthma is to check a bedtime peak flow and a peak flow on awakening. If there is more than a 15% difference in your peak flow, you have significant variability that may be the cause of your symptoms. However, peak flow meters are not very sensitive to detect FEV1 changes. Thus, you and your healthcare provider may need to consider this and start a therapeutic trial.
How Common Is Nocturnal Asthma?
Studies of asthma have revealed that as may as 74% of asthmatics have nighttime awakenings at least once per week, while as many as 64% may have asthma at night 3 or more times per week. Importantly, as many as 40% asthmatics experience symptoms nightly.
Asthmatics may ignore nighttime symptoms as a sign of poor asthma control. In another study, 26% of patients who rated their asthma as "mild" reported experiencing asthma symptoms like cough, wheezing, and shortness of breath nightly.
It is important to recognize these nighttime symptoms as poor control, because a significant proportion of fatal asthma in adults and children from respiratory arrest and sudden death occurs between midnight and 8 a.m.
What Is the Physiology Behind Nocturnal Asthma?
While no one knows for sure, asthma at night has been associated with:
- Decreased nitric oxide levels: Because nitric oxide is a potent bronchodilator, decreased levels could possibly explain the increased nighttime symptoms.
- Decreased Beta 2-receptors: Both the number and function of Beta 2 receptors -- the receptors that are responsible for the bronchodilitation that opens up your airways -- decrease between 4 p.m. and 4 a.m.
- Decreased steroid receptors: Similar to Beta 2 receptors, both the numbers and function of steroid receptors, responsible for decreasing inflammation, decline at night. This decline may be responsible for increased inflammation due to a lack of response to your bodies naturally produced steroids or steroids prescribed by your doctor.
- Abnormal pituitary function: Cortisol, a hormone produced by the pituitary gland, production declines overnight and these reductions are associated with declines in FEV1. Among patients with low cortisol levels, treating patients with hydrocortisone, a therapeutic steroid given to patients when cortisol levels are low, is associated with improvements in FEV1.
- Melatonin: Patients with nocturnal asthma have been noted to have low melatonin levels compared to patients without nocturnal asthma.
How Is Nocturnal Asthma Treated?
Most patients with asthma at night meet criteria as moderate or severe persistent asthma according to the NHLBI guidelines. You should be being treated according to these guidelines, but you and your provider may want to consider some of the following points if you think you have nocturnal asthma:
- Inhaled glucocorticoids: In a study comparing 800 μg (4 puffs of an Azmacort inhaler) at 3 p.m. each day to the traditional dose of 1 puff 4 times per day, the 3 p.m. dosing worked as well as the 4 times per day. When the dosing was changed to either 8:30 a.m. or 5 p.m. for convenience, the once daily 5:30 p.m. dosing still did better than the 4 times per day dosing, but the early morning dosing did worse.
- Inhaled β2 adrenergic agonists: Long acting β2 agonists, similar to your rescue inhaler but lasts 6 or more hours, like salmeterol have been shown to improve lung function overnight, improve sleep quality and overall quality of life in nocturnal asthma.
- Oral β2 adrenergic agonists: Oral forms of albuterol given as a slow release pill increase morning peak expiratory flow rates and decrease wheezing and shortness of breath.
- Theophylline: Different types of theophylline have different properties. One that may particularly help nocturnal asthma is a preparation designed to have higher levels at night, like Uniphyl, when you are experiencing more symptoms. With this regimen the theophylline levels decrease during the day and patients experience fewer side effects than with traditional dosing.
- Treatment of other conditions that worsen asthma: A number of other medical conditions like gastric reflux, sinus problems and obesity may worsen your asthma. If you are having nocturnal asthma symptoms make sure that you are not at risk for these conditions.
Sutherland ER. Nocturnal asthma. J Allergy Clin Immunol. 2005 Dec;116(6):1179-86.
Martin RJ. UpToDate. Nocturnal asthma. Accessed April 5, 2009.