🤧 Post-Nasal Drip Cough Mechanism Simulator

Sinus & Nasal Mucosa Overproduction

Allergic or infected nasal lining floods the sinuses with watery mucus.

• ~1 L/day: Normal mucus turnover (swallowed unnoticed)
• 2–4×: Rhinitis mucus increase (baseline output)
• 2: Common triggers (allergic + infectious)
• Minutes: Onset after exposure (histamine-driven)

Allergic rhinitis pathway

Allergen binds IgE on mast cells, releasing histamine fast.

Histamine dilates vessels, mucosa swells and weeps fluid.

Sinusitis pathway

Infected sinus lining secretes thicker, sometimes purulent mucus.

Turbinate mucosa response

Goblet cells and glands ramp up secretion within the nose.

Mucus Drips Down the Posterior Pharynx

Gravity and cilia move excess mucus backward, not forward, out the nose.

• Nasopharynx: Drip pathway (to oropharynx)
• ~1 cm/min: Mucociliary flow (posterior direction)
• Throat clearing: Sensation reported (classic symptom)
• Lying down: Worsens when (nighttime cough)

Posterior pharyngeal wall

Excess volume overwhelms anterior drainage, mucus falls backward.

Cilia and gravity

Mucociliary escalator normally clears forward; overload reverses flow.

Supine position lets gravity pool mucus deep in the throat.

Symptom correlation

Patients feel a persistent drip and frequent throat clearing.

Mucus Contacts Cough Receptors

Pooled mucus touches sensory nerve endings lining the larynx and throat.

• Rapid-adapting: Receptor type (mechano/chemo)
• Vagus nerve: Innervation (CN X afferents)
• Mechanical + chemical: Stimulus type (mucus contact)
• Highest: Density (larynx, carina)

Cough receptor anatomy

Sensory nerve endings sit just under the laryngeal mucosa.

Mucus as an irritant

Thick or acidic mucus mechanically and chemically triggers firing.

Receptor stimulation builds until a firing threshold is crossed.

Threshold behavior

Below threshold, only tickling or urge-to-clear sensation occurs.

Cough Reflex Arc Fires

An afferent signal to the brainstem returns as a motor cough command.

• Vagus (CN X): Afferent nerve (sensory limb)
• Brainstem: Integration site (nucleus tractus solitarius)
• Phrenic + spinal: Efferent nerves (motor limb)
• <1 second: Reflex latency (signal to cough)

Afferent limb

Vagal fibers carry the irritation signal up to the brainstem.

Brainstem integration

Cough center processes input and commands a motor response.

One reflex arc: sensory in, motor out, cough produced.

Efferent limb

Diaphragm and laryngeal muscles contract to expel air forcefully.

Chronic Cough Until Rhinitis Is Treated

The cycle repeats hourly until the underlying mucus source is controlled.

• #1: Cause of chronic cough (post-nasal drip)
• Antihistamine: First-line therapy (or nasal steroid)
• Days: Symptom relief onset (with treatment)
• Persistent: Untreated course (weeks to months)

Why the cough persists

Mucus keeps forming, so receptors keep firing, cough repeats.

Treatment breaks the loop

Antihistamines or nasal steroids shrink mucosa and cut mucus.

Less mucus reaching the pharynx means fewer cough episodes.

Resolution

As inflammation subsides, drip and cough frequency taper off.