Why is it important to monitor cough strength in people who have DMD?
The muscles required for coughing may weaken over time, and this can result in difficulty clearing the chest in addition to more frequent chest infections. The strength of the cough when well can predict the ability to clear the chest when unwell, for example, with a chest infection.
How does reduced cough strength impact airway clearance?
If the muscles involved in coughing become weaker, this can result in a reduced ability to generate the force to clear secretions from the chest. This increases the risk of chest infections and in turn may increase antibiotic use and/or hospital admissions, which is often the experience of those with DMD. There are numerous groups of muscles involved in coughing including accessory muscles of the shoulder girdle complex and abdominals and also the main respiratory muscles.
How does cough strength when well help predict cough strength when unwell?
It is common when unwell for cough strength to reduce. Previous experience in home ventilation services and research has suggested that a peak cough flow of 270 litres/minute or more when well predicts the ability to clear the chest during chest infections (and other respiratory deterioration) and to recover more rapidly after a respiratory deterioration.
What other things should be considered when prescribing cough augmentation?
The cause of the excess secretions should be considered and treated. These can be secretions due to excess saliva or secretions from the chest. Treatment of excess saliva is often important as it may make cough augmentation easier to tolerate. Sometimes, mucolytics or prophylactic antibiotics for the treatment of chest secretions are suggested, which may also facilitate chest clearance.
It is important to consider extra-thoracic factors such as posture and positioning when completing cough augmentation and the impact that altered posture, such as scoliosis, may have on this. In advanced DMD, it is important to consider other factors such as dysphagia, which may affect the risks of MI-E, and gastrostomy feeding, which may impact the ability to tolerate manual techniques such as a manually assisted cough.
For more information on DMD and respiratory read the Development of respiratory care guidelines for Duchenne muscular dystrophy in the UK: key recommendations for clinical practice published in Thorax, December 2023.