Performance of Commonly-Used Modified Exercise Tests in Patients with COVID-19 Infection

Introduction: Although hypoxaemia is an important prognostic factor in COVID-19, its absence is not always reassuring, as some patients with initially mild symptoms can rapidly progress into severe or critical diseases. The aim was to compare the performance of modified exercise tests against a 6-minute walk test and investigate if modified exercise tests can be used as an early severity prediction tool.
Methods: This prospective cross-sectional study included all patients aged 12 and above admitted to the University Medical Unit of Teaching Hospital Anuradhapura with COVID-19 infection and normal resting oxygen saturation (94–100%). Patients with acute and chronic cardiorespiratory diseases were excluded. Each participant was randomly allocated to perform one of the three selected modified exercise tests, a 1-minute sit-to-stand test, a 30-second sit-to-stand test, and a 40-step walk test. All underwent a 6-minute walk test after 15 minutes of rest, as the latter is validated in some respiratory diseases. Saturation before and after each test and patient outcomes were recorded. Desaturation by 3% or more was considered a positive test.
Results: Males were the majority (56.5%, n=62), and the mean age was 45.8(SD+16.3) years. Proportions for positive tests were 5/22(22.7%) for 1-minute sit-to-stand test, 4/23(17.3%) for 30-second sit-to-stand test, 5/17(29.4%) for 40-step walk test and 9/62(14.5%) for 6-minute walk test. None developed severe disease in this sample. Only two patients (3%) developed moderate disease needing oxygen; one had both negative 30-second sit-to-stand test and 6-minute walk test, while the other was positive for the 40-step walk test and the 6-minute walk test. Eleven (17.7%) had a negative 6-minute walk test despite a positive modified exercise test.
Conclusions: Modified exercise tests and the 6-minute walk test are not comparable. We recommend adequately powered large-scale studies to test the validity of these tests in clinical practice.