Is the glottis open or closed during a cough?

Glottis Status During Cough

The glottis is closed during the compression phase of cough and then rapidly opens during the expulsive phase to generate high-velocity airflow for effective airway clearance. 1

Phases of Cough and Glottic Movement

The cough mechanism involves distinct phases with specific glottic positioning:

Compression Phase (Glottis Closed)

• After inspiration, the glottis closes completely for approximately 0.2 seconds while expiratory muscles contract against this closed valve 2
• This glottic closure maintains lung volume while intrathoracic and intra-abdominal pressures build rapidly, potentially reaching as high as 300 mm Hg 2
• The tightness of glottic closure, along with expiratory muscle contraction magnitude and compression phase duration, determines peak subglottic pressure 1
• Glottic closure minimizes expiratory muscle shortening, promoting an "isometric" contraction that allows generation of greater positive pressures 2

Expulsive Phase (Glottis Opens)

• The glottis rapidly opens once subglottic pressure reaches a threshold, initiating the high-velocity expiratory airflow 1
• This opening produces an initial peak expiratory flow lasting 30-50 ms that can reach flow rates as great as 12 L/s 2
• The classical cough flow pattern shows "cessation of flow during glottis closure and then rapid expiration followed by plateau and termination" 1

Multiple Cough Reaccelerations

• During cough bouts with multiple expulsive events, the glottis transiently recloses between each expulsive effort 1
• This reclosure allows subglottic pressure to increase again, generating renewed shear forces when reopened 1
• Each compression phase has similar duration (~0.30 seconds in healthy individuals) and is terminated by rapid glottic opening 1

Clinical Implications

Glottic Closure Enhances But Is Not Essential

• While glottic closure substantially improves cough effectiveness, productive cough can occur without it 2, 3
• Patients with tracheostomy or endotracheal tubes can produce effective cough through "huffing maneuvers" performed with an open glottis 2
• However, transient glottic closure is necessary to render cough effective in patients with respiratory muscle weakness, as it enables transmission of abdominal pressure to the thorax while impeding dissipation of intrathoracic pressure 4

Endotracheal Intubation Effects

• Tracheal intubation prevents glottic closure but does not impair ability to develop normal cough pressures 5
• With intubation, airflow begins earlier (before peak pressure) and does not cease fully between cough bursts, disrupting normal timing 5
• Tracheostomy need not be performed for the express purpose of improving cough efficiency in intubated patients 2

Pathophysiology Considerations

• The glottis is the most constricted area during the compression phase, followed by laryngeal vestibule, nasopharynx, hypopharynx, oropharynx, and cervical trachea 6
• Stronger coughs result in more constriction across all upper airway areas compared to weaker coughs 6
• Failure to close the glottis contributes to ineffective cough in weak tracheostomized patients and those with bulbar disorders 4