After anaesthesia stabilisation, we used the unique control system, called the 'tidal volume divider'. This device was placed between the anaesthetic machine and the double lumen tube of the patient. This control system enables conventional ventilation (without any intervention from the control system, as the settings are defined on the ventilator), as well as independent ventilation with division of the tidal volume between the lungs in proportions of 1:1, 2:1, 3:1, and 5:1. It also enables PEEP (selective positive end-expiratory pressure) application to each lung. With independent ventilation, settings such as frequency, tidal volume and inspiration time are defined by ventilator, and this system only controls the direction of tidal volume to each lung (as the control system is a flow divider) by using a differential pneumatic resistor. It also enables dependent and non-dependent lung ventilation in the lateral decubitus positions. Furthermore, the system monitors the expired volume, airway pressure and dynamic compliance of each lung. This device was described and tested on mechanical lung models with a variety of lung model mechanics (compliance, resistance) and ventilation parameters (frequency, tidal volume). It was also tested clinically for its safety during our previous study. The system was invented, developed and patented by a group of Polish engineers from the Nałęcz Institute of Biocybernetics and Biomedical Engineering, the Polish Academy of Sciences, Poland.