Expansion
Inspiration, glottic closure, compression, then explosive expiration
Expansion
Four phases:
- Inspiration - a deep breath, to about 50 per cent of vital capacity
- Glottic closure with contraction of expiratory muscles
- Compression - intrathoracic pressure rises to over 100 cmH2O
- Expulsion - the glottis opens and air is expelled at up to 500 miles per hour, with dynamic compression narrowing the airways and further raising velocity
Afferents: irritant receptors in the larynx, trachea and large bronchi, travelling in the vagus (and the superior laryngeal nerve from the larynx).
Centre: medulla. Efferents: phrenic, intercostal and laryngeal nerves.
Cough fails when any component fails: weak inspiration in neuromuscular disease, inability to close the glottis in bulbar palsy or with a tracheostomy, or weak expiration in spinal cord injury and myopathy. Each leads to retained secretions and pneumonia, and each has different management, from cough assist devices to physiotherapy.