A window on the lungs

Weinheim, November 12, 2014. Every year, almost 50 million people throughout the world are mechanically ventilated, whether in the operating theatre or in intensive care. The lungs are among people's most sensitive organs; 15  percent of artificially ventilated patients suffer acute respiratory failure and 39 percent of these patients then die. An innovative system combining electrical impedance tomography (EIT) with an electrode belt for the real-time monitoring of the human lungs offers a remedy. The SensorBelt is positioned around the patient's chest and provides something that was never possible before – a window on the lungs. Freudenberg developed this innovative system together with the Swiss company Swisstom AG. Freudenberg Business Groups enmech and Freudenberg Non-Wovens contributed their expertise in the fields of flexible circuit boards and skin-friendly nonwovens. Medical technology solutions have a long tradition and enjoy high priority at Freudenberg. "A world population that is both ageing and growing will have considerable impact on the health market," says Dr. Mohsen Sohi, Speaker of the Board of Management of the Freudenberg Group. "We can play a key contribution in this field with our materials competence and our product solutions."

Optimum respiratory therapy saves lives. It is important to monitor the local effects of ventilation on the fragile tissue of the lungs. This is where the EIT system with the SensorBelt comes into its own. The sensors use the principle of electrical impedance tomography without x-rays. Alternating current flows through the patient's body, creating voltages on the surface of the body which change rhythmically as the patient breathes. The sensors in the SensorBelt pick up these very small changes in voltage and a computer uses the measurements to create real-time images of the lungs as they breathe.

This is a considerable benefit to intensive medicine, as Dr. Christian Karagiannidis, senior pneumologist at the Cologne-Merheim Lung Hospital, explains. He has already tested the product in practice. In contrast to the large, inflexible units used to date, the EIT system with the SensorBelt allows continuous analysis of the function of the lungs during each breath directly at the patient's bedside without any need for radiation. "Especially for seriously ill patients, this allows us to optimize mechanical ventilation and to recognize any pathological changes very rapidly," Karagiannidis reports.

Close-fitting and safe

To ensure contact between the electronic systems and the patient's skin at all times even under the difficult conditions of intensive care units, the electrode belt must fit the patient like a second skin. A tight fit is ensured by the flexible circuit boards from enmech on which the 32 sensors are installed. The skin-friendly outer fabric is provided by Freudenberg Non-Wovens. It protects both the body and the electronic systems against environmental effects.

The non-woven that is used consists of very fine polyurethane threads, a backing material that is also used for wound dressings. These threads can be spun to form a very tight fabric that still remains breathable and elastic. "We had to find a material that was flexible and would adapt well to the patient's body at the same time as remaining stable and retaining its shape after the belt had been opened and closed several times," Katja Herbrand, Area Sales Manager Medical Europe at Freudenberg Non-Wovens, reports. 

A flexible health system

The circuit boards for the SensorBelt are supplied by enmech. This Freudenberg company was selected because it is "in a position to produce flexible circuit boards with a length of over one meter and to equip them with electronic components such as our EIT Chip at the same time as complying with the highest possible quality standards," explains Stephan Böhm, Medical Director of Swisstom AG. Different-sized circuit boards are required for different body girths. enmech produces these circuit boards and also equips them with the electronic components required. "This reduces electrical interfaces and complex electrode cabling is not required," Christophe Luciani, Managing Director of enmech responsible for sales, purchasing and quality, explains.

Quality is the top priority in the production process for the SensorBelt. The quality of brazed joints is ensured by 100% automatic optical inspection (AOI). An individually adapted electric end-of-line (EOL) test ensures that the electronic systems function properly. The most stringent hygiene requirements apply to the integration of the flexible circuit board with the electrodes into the non-woven fabric.

The EIT system with the SensorBelt may prove to be a life-saver for many patients. "The system has already been tested at various hospitals throughout the world and the feedback has been extremely positive," says Böhm. The Swisstom system provides measured data and images of unprecedented quality, without any side effects or detrimental impact on the patient.