Sensors are used to measure gas flows for various purposes in modern medical ventilation technology. A variety of measuring principles are used, depending on the manufacturer and the intended use. Many different sensor products are now available on the market. Medical ventilation technology has made rapid progress since the invention of the "iron long" about 80 years ago – the first device used for patient ventilation. Along with pressure sensors, flow sensing technology and gas flow sensors play a significant role today. The original iron lung used negative pressure to achieve patient ventilation, but modern devices use positive pressure in the patient's lungs for this purpose. Along with air, other gases – primarily oxygen – are also used for ventilation. The quantity and mixture of the various gases are precisely controlled and monitored using sensor systems. The requirements on sensor systems vary greatly, depending on where and how the ventilation device is used.