The sensor technology inside cosinuss° devices works with an optical measuring method. This works similarly to the finger clip sensors that are used in hospitals for example. With the help of optical measurement technology, the photo plethysmographic signal, or PPG signal for short, is derived. Important vital parameters such as heart rate or blood pressure can be derived from these generated individual pulse waves.
Simplified, the PPG signal correlates with the blood volume in the auditory canal and this in turn correlates with the blood pressure. So, the more blood volume there is, the higher the blood pressure.

Although pulse waves are very individual, there are some relevant key points for determining blood pressure, which are illustrated in the graph below:

Fig.3: Schematic amplitude of the pulse curve from a photoplethysmogram and its essential features for determining blood pressure.

Starting at the systolic foot, the cardiac cycle begins. The blood volume at the measurement point ear then increases continuously until the systolic peak is reached. Another important point for determining blood pressure is located between the two values: the maximum slope of the rapid systolic upstroke. Once the systolic peak is reached, the PPG signal drops and so does the blood volume up to the point of the dicrotic notch. Due to the closure of the aortic valve ( = dicrotic notch) the blood volume drops briefly and leads graphically to a local minimum. When the heart valves open again, the blood volume (and thus the PPG signal) rises again to the diastolic peak. It then drops again and a new cardiac cycle begins.If there are changes in the characteristics shown graphically above, the blood pressure of the person taking the measurement will also change with them.

As PPG waveforms are very person-specific, cosinuss° uses a calibration approach in the measurement. This minimizes uncertainties and increases blood pressure measurement accuracy. The complex task of blood pressure determination is solved by a neural network developed inside cosinuss°. Important dependencies and calculations for blood pressure take place in the respective layers (planes). The generated information is then translated into blood pressure values.

Those parameters shown above represent a selection of many parameters that cosinuss° uses to algorithmically evaluate the heartbeats for blood pressure calculation. Based on this technology, cosinuss° is able to continuously measure blood pressure inside the ear.