Respiratory muscle strength and small airway function in long COVID-19 syndrome patients

<bold>Background:</bold> Respiratory muscle and small airways function may be affected following hospitalisation due to SARS-COV-2 infection. <bold>Aim:</bold> To investigate the association between small airway function and respiratory muscle strength in individuals with long COVID-19 syndrome. <bold>Methods:</bold> Thirty-three patients [age (mean±SD): 53±11years and BMI: 28±5.5 Kg·m-2] were included in the analysis 149±90 days following hospital discharge. Routine lung function testing was performed. Respiratory muscle function was assessed by measuring maximum static inspiratory (PImax) and expiratory (PEmax) mouth pressure using a semi-rigid flanged mouthpiece fitted to a metallic stem incorporating a 3-way tap. Small airway function was evaluated by the single breath nitrogen washout test. <bold>Results:</bold> FEV₁ %pred was 100±19, TLC %pred was 94±27, and DLco %pred was 78±23%. None of the patients presented with obstructive ventilatory defect. PImax (68±32%) and PEmax (73±33%) were reduced in 19 and 22 patients respectively. Eight patients had tidal airway closure as their open capacity (OC) was less than their inspiratory capacity (IC) (OC-IC= -0.140±0.090 L). The slope of phase III (71±52%) was abnormal in 3 patients. Closing capacity (CC) (115±28%) was abnormal in 14 patients. PImax correlated with OC (r=0.532, p=0.002) and OC-IC (r=0.482, p=0.005), whilst PEmax correlated with OC (r=0.614, p=0.001) and CC/TLC (r=0.411, p=0.019). OC-IC was associated with Pimax %pred and Pemax %pred, (r=0.470, p=0.007) and (r=0.352, p=0.05), respectively. <bold>Conclusions:</bold> Respiratory muscle and small airway function are affected in a subgroup of patients with long covid-19 syndrome. Respiratory muscle strength is associated with small airways function.