1. Robert WM Frater Cardiovascular Research Centre, Department of Cardiothoracic Surgery, Faculty of Health Sciences, University of the Free State, Bloemfontein, South Africa
2. Department of Mechanical and Mechatronic Engineering, Faculty of Engineering, Stellenbosch University, Stellenbosch, South Africa
3. Department of Health Sciences, Central University of Technology, Bloemfontein, South Africa