The utility of using peak expiratory flow and forced vital capacity to predict poor expiratory cough flow in children with neuromuscular disorders.
Brenda M Morrow, Lauren Angelil, Juliet Forsyth and 3 others
PMID 31309167WHAT IT FOUND
In 41 South African children with neuromuscular disorders, peak expiratory flow and forced vital capacity tracked peak cough flow.
Values below 160 L.min −1 peak flow or 1.2 L vital capacity pointed to likely ineffective cough, but confirmation is needed before replacing cough tests.
Key findings
01In 41 children with neuromuscular disorders, peak cough flow was strongly correlated with peak expiratory flow (r = 0.81; p < 0.0001) and forced vital capacity (r = 0.67; p < 0.0001).
02Peak expiratory flow below 160 L.min −1 and forced vital capacity below 1.2 L corresponded to peak cough flow below 160 L.min −1 and were excellent predictors of that threshold.
03Peak expiratory flow below 250 L.min −1 predicted peak cough flow below 270 L.min −1, but forced vital capacity below 1.8 L did not reach a significant relationship with that threshold.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study was a single-centre retrospective folder review, so data quality and selection were subject to bias. Only 41 of 242 patients assessed for eligibility were included, and exclusion was based on acceptable-quality spirometry, which may have removed children with fatigue or marked respiratory muscle weakness. The sample was small and heterogeneous, and sub-analyses by neuromuscular disorder type, ventilated status, obesity, or chest deformity type were not possible. Duchenne muscular dystrophy accounted for 43.9% of participants, so the results may be skewed toward that condition. The peak cough flow thresholds of 160 L.min −1 and 270 L.min −1 were largely derived from adult or older adolescent evidence, not from children under 12 years. The agreement between peak cough flow and peak expiratory flow was too wide to allow the tests to be used interchangeably. Chest wall deformity severity was not recorded objectively or systematically. The study did not follow patients over time, so it did not show whether using these cut-offs reduces respiratory complications or hospitalisations.
The easy way to misread this
Do not read peak expiratory flow or forced vital capacity as proven replacements for peak cough flow. The study was small and retrospective, the peak cough flow thresholds were adult-derived, and the agreement between peak cough flow and peak expiratory flow was wide.