Single Breath Count Can Replace Spirometry to Screen for Muscle Weakness in Myasthenia Gravis

Single breath count can be used as an alternative to spirometry to screen for respiratory muscle weakness in people with myasthenia gravis, according to research results presented at the North American Neuro-Ophthalmology Society (NANOS) 2021 Annual Conference, held virtually February 20 to 23, 2021.

Because single breath count can be measured without the use of any specialized equipment, researchers sought to determine whether any correlation existed between single breath count and spirometry results, and further, whether single breath count could be used in place of spirometry in patients with myasthenia gravis. 

The cohort included 196 patients (183 with ocular myasthenia gravis, 13 with generalized myasthenia gravis); 135 of these patients had both spirometry and single breath count measurements recorded. At each clinic visit, both spirometry results — including forced expiratory volume in 1 second (FEV1) and standing and supine forced vital capacity (FVC) — and single breath count were measured. Data were also collected indicating whether patients developed respiratory symptoms at any point. 

 Investigators found a modest correlation between single breath count and FVC (r=0.505; P =.00001). Paired Student t tests were performed for individual patients, the results of which indicated a decrease in single breath count before the onset of respiratory symptoms. According to researchers, single breath counts in these instances were 24 counts lower on average (P =.0003). 

“[Single breath count] is a useful tool for assessment of respiratory function in patients with [myasthenia gravis],” the researchers concluded. “Trends in [single breath count] over time can be valuable in screening for respiratory muscle weakness.”

Disclosure: One study author declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures. 

Reference

Ramsewak S, Wong SH. Single breath count as a measure of respiratory function in patients with myasthenia gravis. Presented at: North American Neuro-Ophthalmology Society 2021 Annual Meeting; February 20-23; Poster 81.