GROŠPIC, Antonín, et al. “Method of Checking the Function of Implanted Artificial Valve by Pulsed Doppler Echocardiography – in Vitro Study”. Archives of Acoustics, vol. 9, no. 1-2, July 2015, pp. 223-32, https://acoustics3.ippt.pan.pl/index.php/aa/article/view/3218.