Airway clearance techniques in neuromuscular disorders
In healthy individuals, mucociliary clearance and cough mechanisms are effective and efficient in defending against secretion encumbrance, but these mechanisms may become ineffective if the systems malfunction and/or in the presence of excessive bronchial secretions.
Individuals with weak or impaired inspiratory and/or expiratory muscles, with or without glottis closure issues (bulbar insufficiency, tracheostomy), will have decreased peak cough flow (PCF). Weakness of the inspiratory muscles leads to a progressive decrease in vital capacity (VC). Reduced ability to cough leads to secretion retention, predisposing to progessive respiratory morbity. Severe bulbar dysfunction and glottic dysfunction most commonly occurs in patients with amyotrophic lateral sclerosis (ALS), spinal muscle atrophy (SMA) type 1, and other rarer neuromuscular disorders (NMD).
Inability to close the glottis and vocal cords results in complete loss of the ability to cough and swallow. Difficulty swallowing liquids may result in pooling of saliva and mucus in the pharynx. Alterations in alveolar ventilation, atelectasis, mucus plugging, and recurrent respiratory tract infections (RTI's), as a consequence of an ineffective cough; together with severe bulbar dysfunction, are the main causes of morbility and mortality in patients with NMD.
Respiratory physiotherapy is an essential part of the multidisciplinary management of these individuals, but owing to the inherent heterogeneity of the condition, the growing number of available airway clearance techniques (ACTs) and associated technological developments, it is challenging for physiotherapists to understand what assessments are required and what treatment options are available and appropriate for people with NMD.
In this article you'll find an extensive overview of evidence of:
- Proximal ACT's: diagnostic tools (PCF, PEF) and airway clearance techniques that aim to augment the cough by assisting inspiration, expiration or both (manually assisted cough (MAC), exsufflation, assisted or stacked inspiration (bag, GPB ("frog breathing") or IPPB device), mechanical insufflation-exsufflation (MI-E) or a combination of techniques);
- Peripheral ACT's: aim to improve ventilation, loosen secretions and enhance mucus transport from peripheral airways to the central airways with higher expiratory than inspiratory airflows. These include: manual techniques (MT), high frequency chest wall oscillations (HFCWO), or compression (HFCWC), intrapulmonary percussive ventilation (IPV) and chest wall strapping (CWS).
In this state of the art review it is recommended that PCF is routinely measured in patients with NMD.
For proximal ACTs it is recommended to use MAC and assisted inspirations, as single breaths, AS and GPB, in patients with higher PCF. MI-E appears to be very effective in patients with lower PCF's (< 160 L/min).
Peripheral ACTs: all discussed techniques may be effective in patients with NMD and should be considered according to availability and local expertise in patients to mobilise the secretions prior to proximal ACTs.
> From: Chatwin et al., Respiratory Medicine 136 (2018-01-22 22:18:24) 98-110. All rights reserved to The Author(s). Click here for the online summary.