It is possible to lose consciousness from coughing too hard. This phenomenon occurs when a severe, forceful bout of coughing temporarily disrupts the normal flow of blood to the brain. This sudden loss of consciousness (syncope or fainting) is usually brief, lasting only a few seconds. The body quickly recovers as the cough subsides and circulation returns to normal.
What Is Tussive Syncope
The medical term for passing out specifically due to a cough is tussive syncope, a form of situational syncope. This type of fainting is triggered by specific bodily functions that involve straining, such as urination, defecation, or swallowing. The loss of consciousness occurs immediately following a severe or prolonged fit of coughing.
Situational syncope is a neurally mediated reflex involving an inappropriate response in the nervous system. The episode typically has a rapid onset, a very short duration, and is followed by a complete recovery of awareness. While the event is generally not a sign of a primary heart or brain problem, the sudden collapse can lead to serious injury. The underlying cause must be addressed to eliminate the fainting episodes.
The Mechanics of Fainting
The core mechanism behind tussive syncope involves a sudden drop in the amount of blood reaching the brain, a condition called cerebral hypoperfusion. A forceful, sustained cough acts like a powerful Valsalva maneuver, causing an immediate and extreme increase in pressure inside the chest cavity, known as intrathoracic pressure.
The increased pressure compresses the large veins that return blood to the heart, particularly the vena cava. Compression of these vessels severely restricts the flow of blood back to the heart. With less blood returning, the heart’s output of oxygenated blood to the rest of the body, including the brain, rapidly decreases.
This cascade of events leads to a sharp, temporary drop in systemic blood pressure. Blood flow to the brain is highly sensitive to pressure changes, and this sudden hypotension causes the brain to be starved of its constant supply of oxygen and glucose. The resulting lack of sufficient cerebral blood flow triggers the brief loss of consciousness.
The rapid development of cerebral hypoperfusion often explains why many people do not have the typical warning signs, or prodrome, like lightheadedness or blurred vision. Other factors may also contribute, including a reflex-mediated response that causes blood vessels to widen and the heart rate to slow down.
Common Causes and Vulnerability
Tussive syncope is the result of a chronic, severe, and paroxysmal cough that is intense enough to trigger the necessary pressure changes. The most common underlying medical conditions associated with this severe coughing include chronic obstructive pulmonary disease (COPD), chronic bronchitis, and severe asthma. Post-infectious coughs, such as those that linger after an infection like pertussis (whooping cough), can also produce the necessary force and duration to cause fainting.
Gastroesophageal reflux disease (GERD) is another frequent cause, as stomach acid irritating the throat and airways can trigger a persistent and violent cough reflex. Individuals with pre-existing cardiovascular issues or those taking certain medications, such as anti-hypertensives or diuretics, may be more susceptible to the sudden drop in blood pressure. These medications can worsen the hypotension that occurs during the cough.
The condition is most frequently observed in middle-aged, overweight men who are current or former smokers and may have a history of heavy alcohol use. This demographic is more prone to chronic lung conditions like COPD. Additionally, a larger body build may allow for the generation of the high intrathoracic pressures needed to trigger the syncope.
Diagnosis and Management
Anyone experiencing fainting, especially if it is recurrent or causes an injury, should seek medical attention to determine the underlying cause. A doctor will take a detailed medical history, focusing on the circumstances of the fainting episode and the nature of the cough. Tussive syncope is a diagnosis of exclusion, meaning serious, life-threatening causes of fainting, particularly cardiac and neurological issues, must be ruled out.
Initial diagnostic tests typically include an electrocardiogram (ECG) to check for abnormal heart rhythms and a chest X-ray to assess the lungs. Further evaluation may involve cardiac event monitoring for arrhythmias or pulmonary function studies to diagnose underlying obstructive lung disease. In some cases, a tilt-table test may be used to reproduce the vasodepressor response associated with situational syncope.
The primary management strategy for tussive syncope is to treat the underlying condition causing the severe cough. If COPD is the cause, bronchodilators may be prescribed to reduce the frequency and intensity of the coughing fits. If GERD is identified, medications to reduce stomach acid production are used. Treatment also includes patient education on practical measures, such as avoiding known cough triggers and sitting or lying down when a severe bout of coughing is anticipated to prevent falls.