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Loss of motor neurons in the cortex, brainstem and spinal cord is the hallmark of motor neuron disease/amyotrophic lateral sclerosis (MND/ALS), resulting in weakness of limbs, respiratory and bulbar muscles and eventually death from respiratory failure in the majority of patients. Around 20%–30% have bulbar symptoms at onset—this is less common in younger patients, but affects more than 40% of those over 70 years.1 Virtually all patients will develop bulbar symptoms with disease progression. Symptoms consist of dysarthria, dysphagia, difficulties clearing oropharyngeal secretions, impaired cough, choking, laryngospasm and aspiration. Each symptom is attributable to lower motor neuron weakness (true bulbar palsy), upper motor neuron weakness (pseudobulbar palsy) or a combination of both.
Safe swallowing requires adequate strength and coordination of orofacial and lingual muscles. With increasing weakness, difficulties in mastication, bolus preparation and oral food transport develop resulting in oral, pharyngeal and laryngeal residues of food. Lip closure and problems swallowing saliva lead to drooling. Failure of the larynx to move superiorly and anteriorly on swallowing and incomplete closure leads to laryngeal penetration or overt aspiration into the lungs.
The clearance of aspirated food, saliva or bronchial secretions depends on a forceful cough. An effective cough requires the inspiratory muscles to generate a deep inspiration of around 2–4 L, followed by closure of the glottis and the generation of a peak cough flow (PCF) of 360 to 1000 L/min in adults—depending on age, size and gender. This level of expiratory flow after glottal opening is required to shear secretions and debris from the airway and lift these to the upper airway/mouth. It is assumed that a minimum PCF of 160 L/min is required in adults and is estimated that those with values of 270 L/min or less may be prone to secretion retention at the time of chest infections, as these are associated with …
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