“…HR does change only minimally in the early stages, and when finally becoming beyond the “normal” range, the hypovolemic shock has already developed (Secher and Van Lieshout, 2010 ; Schiller et al, 2017 ; Suresh et al, 2018 ). Because of these limitations, several approaches, such as wearable sensors and advanced machine-learning techniques, have been suggested in an attempt to promote more sensitive metrics for the prediction of outcomes in civil patients and on the battlefield (Secher and Van Lieshout, 2005 , 2010 , 2013 , 2016 ; Rickards et al, 2007 , 2008 ; Convertino et al, 2011 , 2020a , b ; Ryan et al, 2011 ; Nadler et al, 2014 ; Schlotman et al, 2019 ; Rashedi et al, 2021 ).…”