Heart rate fragmentation as a marker of autonomic function in healthy young individuals: insights from graded head-up tilt test and controlled breathing. - da Silva TM; Carandina A; Scatà C; Salafia G; Magna F; Giobbi LS; Rodrigues GD; Tobaldini E; Silva LEV; Salgado HC; Fazan R Jr; Montano N (Frontiers in physiology, 2026)