When a forceful, hacking cough causes a temporary blacking out, the event is medically known as cough syncope, or tussive syncope. Syncope describes a sudden, brief loss of consciousness followed by a spontaneous, complete recovery. This phenomenon occurs when a violent cough briefly starves the brain of sufficient blood flow. Understanding the mechanism behind this blackout, identifying the factors that increase its likelihood, and knowing when to seek medical help are important steps for anyone who experiences this condition.
The Sudden Drop in Blood Flow
The primary mechanism behind cough syncope involves an acute spike in pressure within the chest cavity. A forceful, deep cough is essentially a modified Valsalva maneuver, requiring the closure of the vocal cords and the forceful contraction of the chest and abdominal muscles. This action can temporarily raise the pressure inside the chest, known as intrathoracic pressure.
This pressure increase immediately affects the large veins, specifically the vena cava, which return deoxygenated blood to the heart. The high pressure compresses these veins, momentarily blocking blood return to the right side of the heart. The heart’s filling drops sharply, which leads directly to a significant reduction in the amount of blood the heart pumps out, known as the cardiac output.
Since the brain requires a steady supply of oxygenated blood to maintain consciousness, this transient fall in cardiac output results in a momentary reduction in blood flow to the brain, a state called cerebral hypoperfusion. The brain temporarily shuts down, leading to the brief loss of consciousness that lasts only a few seconds, usually until the coughing fit subsides. The rapid pressure changes can also stimulate baroreceptors, triggering a reflex that causes peripheral blood vessels to dilate and blood pressure to drop further, compounding the effect.
Conditions That Increase Susceptibility
Cough syncope typically occurs in individuals who have predisposing factors, most commonly those with a chronic cough. Patients who experience this are often middle-aged, overweight men who have a history of smoking, though it can affect anyone with persistent, forceful coughing. The presence of chronic obstructive lung diseases, such as chronic bronchitis or emphysema, increases the likelihood of experiencing these episodes. These conditions often lead to prolonged, severe coughing fits that generate the high intrathoracic pressures necessary to trigger the syncope.
Other factors can make an individual more susceptible by affecting the body’s ability to maintain blood pressure. Dehydration reduces overall blood volume, making the circulatory system less resilient to the sudden drop in venous return caused by the cough. Certain medications that lower blood pressure, such as antihypertensives or diuretics, can also worsen the hypotensive response during a coughing fit. Underlying issues like gastroesophageal reflux disease (GERD) or the use of ACE inhibitors, which cause a persistent, dry cough, must be identified and addressed.
Recognizing Serious Warning Signs
While cough syncope is tied directly to the mechanical act of coughing, any loss of consciousness warrants a medical evaluation to rule out more dangerous causes. It is important to distinguish this situational syncope from other conditions, such as cardiac or neurological issues, that may mimic the symptom. A warning sign is any episode of syncope that occurs without an immediate, preceding cough.
The duration of the unconsciousness is also a clue; cough syncope is typically brief, lasting only a few seconds, with a rapid and complete return to normal awareness. If consciousness is lost for a prolonged period, or if the individual experiences chest pain, heart palpitations, or significant confusion upon waking, immediate medical attention is necessary. Neurological symptoms accompanying the blackout, such as weakness, paralysis, or persistent headache, could suggest a problem within the brain or its blood vessels, requiring urgent imaging studies. Fainting episodes that become frequent or occur during activities like driving are also concerning.
Clinical Diagnosis and Treatment Approaches
The medical assessment for cough syncope begins with a detailed patient history to confirm the link between the violent cough and the loss of consciousness. A physician will perform a physical examination and often order a 12-lead electrocardiogram (ECG) to check for underlying heart rhythm problems. Further cardiac testing may be warranted, such as Holter monitoring to capture abnormal heart rhythms or an echocardiogram to check for structural heart defects.
To investigate the underlying cause of the chronic cough, a physician may recommend pulmonary function tests to assess for lung diseases or specialty evaluations for conditions like GERD. The definitive treatment focuses on eliminating or controlling the underlying trigger, not on treating the blackout itself. This may involve using bronchodilators to manage obstructive lung disease, starting proton pump inhibitors for GERD, or adjusting medications known to cause chronic cough. Patients are also advised on lifestyle changes, such as avoiding known cough triggers and employing physical counter-pressure maneuvers, like sitting or squatting, to help maintain blood pressure and prevent the syncopal episode.