Mini-Symposium: Cardio-Respiratory considerations in CNMDAirway clearance modalities in neuromuscular disease
Introduction
Airway clearance, also referred to as secretion clearance or mucus clearance, is a critical aspect of respiratory care and when impaired represents a life-threatening aspect of many diseases. Airway clearance consists of two related processes: mucociliary clearance and cough clearance. The mucociliary “escalator” requires functioning cilia on the airway epithelium as well as a normal periciliary fluid layer. Diseases in which there is impairment of mucociliary clearance include cystic fibrosis [CF], primary ciliary dyskinesia [PCD], bronchiectasis and chronic obstructive pulmonary disease [COPD]. In patients with neuromuscular disease there can be impairment of cough clearance, despite the presence of normal mucociliary clearance (Table 1). As a result, there is a disproportionately high degree of respiratory disease in neuromuscular patients who have involvement of the respiratory musculature. This article will review modalities of therapy available to assist airway clearance in the patient with neuromuscular weakness.
Section snippets
Phases of cough
Coughing is a complex process.1 It has been described as having 4 phases, although it can be argued that the process has 5 steps. The phases of coughing are as follows (Fig. 1):
- 1.
Irritation: The cough is triggered by a chemical or physical irritant in the tracheobronchial tree. There are many irritant sensors in the airway (nasopharynx and tracheobronchial tree).
- 2.
Inspiratory phase: irritation triggers inspiration through a widely opened glottis (inhalation volume varies). Length-tension
Improving mucociliary clearance
It should be first stated that most patients with neuromuscular disease have normal mucociliary clearance at baseline. Occasional patients with neuromuscular disease (NMD) will have chronic aspiration, which can lead to a chronic mucopurulent bronchitis state with impaired cilia. Chronic retention of secretions can also damage cilia secondary to the inflammatory cascade induced by white blood cell products. It is for these reasons that aiding mucociliary clearance can at times be helpful in the
Improving cough clearance
It can be said that without an effective cough, secretion mobilization will not result in secretion clearance. In other words, one needs both mucociliary clearance and cough clearance for successful airway clearance. Assisting cough clearance can be achieved in two ways – manual cough assistance and mechanical cough assistance.
Manually assisted cough (MAC) has been demonstrated to improve peak cough flows.9, 10, 11 The manoeuvre involves first insufflating the patient to a maximal capacity and
Conclusion
Impaired cough clearance, previously an insurmountable problem leading to death in the neuromuscular patient, is now readily treatable. Aiding airway clearance in the patient with neuromuscular weakness can be readily achieved using a combination of manual and mechanical techniques. Training of caregivers in these techniques and in the use of newer technologies is critical to the success of any programme designed to prevent pulmonary morbidity in this population.
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