Two-day cardiopulmonary exercise testing in long COVID post-exertional malaise diagnosis

Background: Long COVID patients present with a myriad of symptoms that can include fatigue, exercise intolerance and post exertional malaise (PEM). Long COVID has been compared to other post viral syndromes, including myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), where a reduction in day 2 cardiopulmonary exercise test (CPET) performance of a two-day CPET protocol is suggested to be a result of PEM. We investigated cardiopulmonary and perceptual responses to a two-day CPET protocol in Long COVID patients.

Methods: 15 Long COVID patients [n=7 females; mean (SD) age: 53(11) yr; BMI = 32.2(8.5) kg/m²] performed a pulmonary function test and two ramp-incremental CPETs separated by 24 hr. CPET variables included gas exchange threshold (GET), peak oxygen uptake (V̇O_2peak) and peak work rate (WR_peak). Ratings of perceived dyspnoea and leg effort were recorded at peak exercise using the modified 0-10 Borg Scale. PEM (past six months) was assessed using the modified DePaul Symptom Questionnaire (mDSQ). One-sample t-tests were used to test significance of mean difference between days (p<0.05).

Results: mDSQ revealed PEM in 80 % of patients. Lung function was normal. Responses to day 1 CPET were consistent with the presence of aerobic deconditioning in 40 % of patients (V̇O_2peak <80 % predicted, in the absence of evidence of cardiovascular and pulmonary limitations). There were no differences between day-1 and day-2 CPET responses (all p>0.05).

Conclusion: PEM symptoms in Long COVID patients, in the absence of differences in two-day CPET responses separated by 24 hours, suggests that PEM is not due to impaired recovery of exercise capacity between days.