Chest
Volume 129, Issue 1, Supplement, January 2006, Pages 48S-53S
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Supplement
Diagnosis and Management of Cough: ACCP Evidence-Based Clinical Practice Guidelines
Global Physiology and Pathophysiology of Cough: ACCP Evidence-Based Clinical Practice Guidelines

https://doi.org/10.1378/chest.129.1_suppl.48SGet rights and content

Objective:

The anatomy and neurophysiology of cough has been reviewed in the preceding section. The objective of this section is to describe how the varied anatomic components of the respiratory system work in concert to produce an effective cough.

Methods:

This was accomplished by reviewing (1) the factors needed to produce effective cough pressures and gas velocity in the airways, and (2) the salient features of the interaction between the airflow generated during a cough and the mucus that lines the tracheobronchial tree. The MEDLINE database was searched for this review, and the search consisted of studies published in English between 1960 and April 2004. Search terms were “cough mechanics” and “cough physiology.”

Results:

Inhaling to high lung volumes and glottic closure prior to the expiratory phase of cough facilitate the generation of high intrathoracic pressures. These high intrathoracic pressures (1) provide the driving force for airstream flow during cough and (2) dynamically compress the central airways, which further enhances the cough airstream velocity.

Conclusions:

High intrathoracic pressures are needed to generate the requisite cough expiratory flows and airstream velocities. However, cough may be effective in individuals with mild-to-moderate degrees of respiratory muscle weakness, as only modest increases in intrathoracic pressure are needed to dynamically compress the large intrathoracic airways and increase cough flow velocity.

Section snippets

Cough Mechanics

Cough mechanics can be evaluated by considering the timing of the varied events that constitute cough. The sequence of events that lead to an effective cough has been previously described, and the phases have been classified as inspiratory, compressive, and expiratory (Fig 1).1, 2, 3, 4, 5, 6, 7 The initial phase of cough is characterized by the inhalation of gas. The volume of gas that is inhaled may be as little as 50% of tidal volume or as great as 50% of vital capacity.8, 9 During

RECOMMENDATION

1. In patients with endotracheal tubes, tracheostomy need not be performed to improve cough effectiveness. Level of evidence, expert opinion; net benefit, substantial; grade of recommendation, E/A

Following the initial blast of air, there is a more prolonged period characterized by lower expiratory flows. This stage lasts 200 to 500 ms with sustained flows in the range of 3 to 4 L/s.5 During this timeframe, lung volume falls, transpulmonary pressure decreases, and cough expiratory flows fall. As

Altered Cough Mechanics

Several factors may interfere with the capacity of the respiratory system to produce the requisite pressures and gas velocities needed for effective cough. The initial phase of cough is accompanied by inhaling a volume to near total lung capacity. Inhaling to high lung volumes will optimize expiratory pressures, and will enhance expiratory airflow and velocity. At high lung volumes, the expiratory muscles are near their optimal length and respiratory system elastic recoil is increased; both

RECOMMENDATION

2. Individuals with neuromuscular weakness and no concomitant airway obstruction may benefit from mechanical aids to improve cough. Level of evidence, low; net benefit, intermediate; grade of recommendation, C

Expiratory muscle weakness also contributes to cough inefficiency by limiting dynamic airway compression, a condition that augments expiratory gas velocity. Dynamic compression is needed to increase gas velocity for a given flow rate and thereby enhance the kinetic energy available to

CONCLUSIONS

An effective cough constitutes an important host-defense mechanism. High intrathoracic pressures promote dynamic airway compression and are needed to generate the requisite expiratory flows and airstream velocities. However, only modest increases in intrathoracic pressure are needed to narrow the large intrathoracic airways and increase cough flow velocity. Thus, cough may be effective in individuals with mild-to-moderate degrees of respiratory muscle weakness. Cough ineffectiveness may occur

RECOMMENDATION

3. In patients with ineffective cough, the clinician should be aware of and monitor for possible complications, such as pneumonia, atelectasis, and/or respiratory failure. Level of evidence, low; net benefit, substantial; grade of recommendation, B

SUMMARY OF RECOMMENDATIONS

  • 1.

    In patients with endotracheal tubes, tracheostomy need not be performed to improve cough effectiveness. Level of evidence, expert opinion; net benefit, substantial; grade of recommendation, E/A

  • 2.

    Individuals with

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