Dysfunctional breathing diagnosed by cardiopulmonary exercise testing in 'long COVID' patients with persistent dyspnoea

Background 'Long COVID'-associated dyspnoea may persist for months after SARS-CoV-2 infection. Among the causes of persistent dyspnoea, dysfunctional breathing (DB), defined as an erratic or inappropriate ventilation at rest or exercise, has been observed, but little is known about its occurrence and pathophysiology among individuals with 'long COVID'. We aimed to describe the occurrence and identify clinical predictors of DB among patients following SARS-CoV-2 infection. Methods Cardiopulmonary exercise testing (CPET) was performed in 51 SARS-CoV-2 patients (median age, 64 years (IQR, 15)); male, 66.7%) living with 'long COVID' and persistent dyspnoea. CPET was classified into three dominant patterns: respiratory limitation with gas exchange abnormalities (RL); normal CPET or O-2 delivery/utilisation impairment (D); and DB. Non-parametric and chi(2) tests were applied to analyse the association between CPET dominant patterns and demographics, pulmonary function tests and SARS-CoV-2 severity. Results Among 51 patients, DB mostly without hyperventilation was found in 29.4% (n=15), RL in 54.9% (n=28) and D in 15.7% (n=8). When compared with RL individuals, patients with DB were younger, had significantly less severe initial infection, a better transfer capacity for carbon monoxide (median 85% (IQR, 28)), higher oxygen consumption (22.9 mL/min/kg (IQR, 5.5)), a better ventilatory efficiency slope (31.6 (IQR, 12.8)), and a higher SpO(2) (95% (IQR, 3)). Conclusions Our findings suggest that DB without hyperventilation could be an important pathophysiological mechanism of disabling dyspnoea in younger outpatients following SARS-CoV-2 infection, which appears to be a feature of COVID-19 not described in other viral diseases.

Automated summary

Among 51 patients living with 'long COVID' and persistent dyspnoea, cardiopulmonary exercise testing revealed that nearly one-third of patients had dysfunctional breathing (DB), a larger proportion had respiratory limitation (RL), and only a small number had O2 delivery/utilisation impairment (D). Patients with DB were typically younger, had milder initial infections, better transfer capacity for carbon monoxide, higher oxygen consumption, better ventilatory efficiency slope, and higher oxygen saturation compared to those with RL.