A decline of 25 percent each year in cough peak flow, a test of cough strength and airway clearance, is a predictor of poor survival in people with amyotrophic lateral sclerosis (ALS), a small study from Japan reports.
The study “Cough peak flow decline rate predicts survival in patients with amyotrophic lateral sclerosis” was published in the journal Muscle Nerve.
The respiratory muscles are invariably affected in ALS patients, and respiratory failure is a leading cause of death among patients.
Weakness in the breathing muscles is often accompanied by respiratory infections — a recent study reported that 32% of ALS patients who died from respiratory failure were also positive for aspiration pneumonia, a lung infection that develops after food particles, liquid, or vomit enters the lungs. Failure to cough was shown to have a large influence on survival.
Neuromuscular diseases like ALS can impair muscle strength, affecting the ability to cough. The cough peak flow is a simple measure of assess respiratory and bulbar muscle function, the latter related to the activity of muscles used in speech and swallowing.
Researchers investigated the predictive power of the cough peak flow to assess decline in 34 ALS patients (32 with sporadic disease and two with familial), all being treated at an outpatient clinic in Tokyo between July 2009 and June 2017.
The study also included five cases of progressive muscular atrophy, which shares symptoms with ALS.
Researchers analyzed patients’ cough peak flow and forced vital capacity (FVC), a parameter for measuring lung’s function. Additionally, they measured body mass index (BMI) and assessed patients’ functional status using the revised ALS Functional Rating Scale (ALSFRS-R), a self-reported measure of physical abilities, from speech to breathing to walking.
Participants were followed until their breathing declined to the point they needed a tracheostomy (inserting a tube into the trachea to ease breathing), were placed on a ventilator, or died.
Results showed that the drop in cough peak flow was significantly linked to progression of bulbar and respiratory muscle dysfunction, as shown by lower ALSFRS-R scores and FVC. Moreover, a decline of 25% or more each year in the cough peak flow “was a strong predictor of shorter survival,” the study said.
Estimated median survival from disease onset was 6.1 years in patients with a cough peak flow of 220 L/min or higher, and 2.9 years in those with a cough peak flow lower than 220 L/min.
“From this study, we suggest a cutoff value for CPF [cough peak flow] as 220 L/min for the prediction of survival,” they researchers wrote.
“A rapid decline in CPF in the early stage of ALS reflects the early progression of bulbar and respiratory dysfunction and predicts shorter survival,” they added, and suggested that cough peak flow be included in assessments of ALS patients — along with ALSFRS-R, FVC, and BMI — to help clinicians predict likely outcomes.