Single breath counting as a respiratory muscle function assessment test

Abstract

<b>Background:</b> Spirometry may be used as a surrogate marker of respiratory muscle strength in patients with neuromuscular disorders. However, it is an aerosol-generating procedure, not readily conducted during remote consultation, and its use has been limited by infection control guidance during the COVID-19 pandemic. Single breath counting (SBC) has been reported to predict vital capacity (VC). We aimed to evaluate the utility of SBC in our clinic. <b>Methods:</b> We conducted an evaluation to compare SBC and VC measurements in healthy volunteers and patients with respiratory muscle weakness. To perform SBC, individuals were asked to maximally inhale and then count every second in time with a metronome from 1 to the highest number they could manage in a single breath. SBC was repeated 3 times and the mean and maximum results were recorded. Individuals performed spirometry for slow VC in accordance with ERS guidelines. Results were compared using Spearman’s rank correlation coefficient. <b>Results:</b> 31 healthy controls and 18 cases were included. The correlation between VC and SBC were rho=0.697 (p&lt;0.001) and rho=0.694 (p&lt;0.001) for mean and maximal efforts respectively (Figure). <b>Conclusion:</b> Primary findings highlight the potential usefulness of SBC for respiratory muscle function assessment. This promising technique is simple and feasible with current infection control guidelines and may be useful in remotely conducted appointments.