Long COVID Patients with Orthostatic Intolerance Have Reduced Heart Variability and Preserved Physiological Response to Active StandingBy J Antonio Gonzalez Hermosillo, Claudia Lerma, Dulce Andrea Celestino Montelongo, Maria Del Carmen Alba Lorenzo, Emiliana Salas Santos, Atziri Gun Cuninghame Ballesteros, Esteban Jorge Galarza and Maria del Rocio Martinez Alvarado