Nocturnal asthma is characterized by worsening symptoms like coughing, wheezing, and shortness of breath, typically occurring between midnight and 8 a.m. This increase in airway sensitivity and obstruction during sleep is a common issue affecting a large percentage of people with asthma. The supine, or lying flat, position creates physiological changes that contribute to this nighttime distress.
How Lying Down Changes Airway Mechanics
Adopting a horizontal body position alters the distribution of blood and the mechanics of the chest cavity, immediately affecting lung function. When lying down, the weight of the abdomen and chest cavity presses against the diaphragm. This pressure slightly reduces the functional residual capacity (FRC), the volume of air remaining in the lungs after exhaling. This reduction in lung volume can cause small airways to narrow or collapse, increasing airflow resistance.
The shift in gravity also causes a temporary increase in blood pooling in the chest and pulmonary circulation. This engorgement of lung blood vessels further constricts sensitive airways, contributing to chest tightness. Lying flat also makes it challenging for the cilia, the tiny hairs lining the airways, to move mucus and secretions upward. As mucus accumulates, it blocks smaller air passages, potentially triggering coughing and wheezing episodes.
Acid Reflux as a Major Contributor
The supine position significantly increases the likelihood of gastroesophageal reflux (GER) becoming a trigger for nocturnal asthma. When lying flat, stomach acid easily travels up the esophagus since gravity no longer helps contain it. This condition, often referred to as GERD, is highly prevalent in people with asthma. It sometimes occurs without typical heartburn symptoms, a phenomenon known as silent reflux.
The acid irritates the lining of the esophagus, triggering the vagally mediated esophago-bronchial reflex. This reflex involves the vagus nerve connecting the esophagus to the lungs. When stimulated by acid, the nerve signals the airways to constrict, resulting in bronchospasm. Additionally, tiny droplets of stomach acid can be inhaled into the airways, a process called microaspiration. This microaspiration directly inflames the bronchial tubes and intensifies asthma symptoms.
Hidden Triggers in the Sleep Environment
The bedroom environment introduces external factors that can exacerbate asthma during sleep. Bedding is a prime habitat for allergens, especially dust mites, which thrive in warm, humid conditions. Exposure to dust mite droppings and pet dander trapped in mattresses and pillows can cause an allergic reaction. This reaction leads to airway inflammation and tightening overnight.
Postnasal drip, where mucus drains down the back of the throat, is another factor. When lying flat, this fluid collects and irritates sensitive airways, leading to a cough. Furthermore, the temperature of inhaled air can act as a trigger. Breathing in cold air causes the airways to cool and dry out. This moisture loss can trigger a reaction similar to exercise-induced bronchoconstriction, narrowing air passages and worsening symptoms.
Strategies for Managing Nocturnal Symptoms
Several practical strategies can address the primary causes of nighttime asthma. To counteract the effects of gravity and reflux, physically elevate the head of the bed by six to nine inches. Use blocks under the bedposts or a wedge pillow, rather than just stacking pillows. This incline uses gravity to reduce the chance of stomach acid flowing up the esophagus.
Addressing environmental triggers involves strict control of bedroom allergens. This includes:
- Washing all bedding weekly in hot water.
- Using allergen-proof encasings on mattresses and pillows.
- Using an air purifier with a HEPA filter to remove airborne particulates.
- Regulating the bedroom temperature to prevent cold air from triggering airway constriction.
From a behavioral standpoint, avoiding large meals or snacks within three hours of bedtime limits the potential for reflux.
It is beneficial to discuss medication timing with a physician, as the body’s natural anti-inflammatory hormones, like cortisol, are lowest overnight. Adjusting the schedule of long-acting controller medications to be taken closer to bedtime ensures peak drug concentration when lung function naturally decreases. Keeping a quick-relief inhaler at the bedside is a necessary safety measure for any breakthrough symptoms.