An expiratory wheeze is a high-pitched, musical sound produced when air is forced through narrowed airways during breathing out. The specific occurrence of this sound when lying down is known as positional wheezing. This positional trigger suggests a strong dependency on gravity, body fluid dynamics, or the mechanical effects of the supine position, helping distinguish between general respiratory issues and those exacerbated by being flat.
The Mechanics of Expiratory Wheezing
The characteristic sound of a wheeze is produced by the turbulent flow of air vibrating the walls of a constricted airway. This narrowing results from factors like bronchospasm, mucosal swelling, or thick secretions. The high velocity of air moving through the reduced diameter creates the whistling effect.
Wheezing is more pronounced during expiration because the airways naturally narrow during this phase of the breathing cycle. As the chest cavity volume decreases during exhalation, the intrathoracic pressure increases. This pressure compresses the smaller airways, raising resistance and making any underlying obstruction more audible. A purely expiratory wheeze generally indicates a mild to moderate obstruction.
Airway Conditions Worsened by Position
Respiratory conditions are significantly worsened when a person lies flat, primarily due to gravity’s effect on secretions and internal pressure. Nocturnal asthma is a common example, partially attributed to changes in the body’s circadian rhythm that increase inflammation and reduce airway function overnight.
Lying supine causes mucus and secretions to pool within the lower airways rather than draining effectively, further obstructing inflamed bronchial tubes. In asthma, this poor mucus clearance combined with inflammation can trigger bronchospasm, narrowing the airways and leading to wheezing. The supine position also increases the amount of fluid shifted from the lower body into the chest cavity, which contributes to airway narrowing and increased respiratory resistance.
For conditions like Chronic Obstructive Pulmonary Disease (COPD) or bronchitis, lying down impairs the clearance of excess phlegm and mucus. The flattened diaphragm in severe COPD patients is mechanically disadvantaged when supine, increasing the work of breathing and exacerbating airflow limitation. Additionally, post-nasal drip, where nasal mucus drains down the throat, can irritate the upper airway. This irritation may trigger a reflex cough or reactive bronchospasm, contributing to wheezing.
Non-Pulmonary Systemic Causes
Causes of wheezing when lying down often originate outside the respiratory system, specifically in the digestive and cardiovascular systems. Gastroesophageal Reflux Disease (GERD) is a frequent trigger because the supine position removes gravity’s assistance in keeping stomach acid contained, allowing it to easily reflux up the esophagus.
Reflux triggers wheezing through two mechanisms. First, micro-aspiration involves tiny droplets of acid entering the upper airways, causing direct irritation and inflammation. Second, acid in the esophagus stimulates a nerve-mediated reflex that causes the bronchial tubes to constrict. This irritation and constriction often lead to nocturnal wheezing that is worse when lying down and may be accompanied by heartburn or a sour taste.
Cardiovascular issues, particularly Congestive Heart Failure (CHF), are another significant systemic cause of positional wheezing, often referred to as “cardiac asthma.” When the heart cannot pump blood efficiently, fluid backs up in the body’s circulation. The supine position causes a fluid shift, moving blood and interstitial fluid from the lower extremities into the central circulation and subsequently into the lungs.
This sudden increase in central fluid volume raises pressure in the lung’s capillaries, leading to fluid leakage into the lung tissue, a condition called pulmonary edema. The fluid in the lungs decreases lung compliance and compresses the smaller airways, causing the characteristic wheezing sound. This fluid-driven wheezing is typically worse at night or immediately upon lying down, often forcing the person to sit up or stand to relieve shortness of breath (orthopnea).
Understanding Symptoms and When to Seek Care
Identifying associated symptoms helps distinguish the cause of positional wheezing. Wheezing due to GERD is often accompanied by a burning sensation in the chest, a sour taste, or a chronic cough, especially after meals. Wheezing caused by heart failure may include symptoms of fluid retention, such as unexplained weight gain and swollen legs or ankles, or waking up gasping for air. Wheezing from asthma or COPD is more likely associated with a prior respiratory infection or exposure to an allergen, along with a cough that produces mucus.
Any recurrent wheezing that interrupts sleep or worsens over time warrants a medical evaluation. A doctor will perform a physical examination and may order diagnostic tests to determine the root cause, such as:
- Spirometry to assess lung function.
- A chest X-ray to look for fluid in the lungs.
- An electrocardiogram (EKG).
- An echocardiogram to evaluate heart function.
It is important to seek immediate emergency care if the wheezing is accompanied by signs of critically low oxygen levels or severe airway obstruction, including:
- Severe difficulty breathing.
- An inability to speak in full sentences.
- Confusion.
- A bluish tint to the lips or skin.
For less severe, chronic symptoms, simple measures like elevating the head of the bed by six to nine inches can often provide relief by using gravity to reduce reflux or decrease the fluid shift into the lungs.