Prevalence of orthostatic intolerance in long covid clinic patients and healthy volunteers: A multicenter study by Lee, C, Greenwood, DC, Master, H, Balasundaram, K, Williams, P, Scott, JT, Wood, C, Cooper, R, Darbyshire, JL, Gonzalez, AE, Davies, HE, Osborne, T, Corrado, J, Iftekhar, N, Rogers, N, Delaney, B, Greenhalgh, T, Sivan, M