Photoplethysmography (PPG) inside the ear canal as a basis for calculating blood pressure is an innovative method based on the direct relationship between the blood volume in the vessels of the ear canal and blood pressure. Put it simply, you can say that when the blood volume in the vessels increases, blood pressure also increases. These changes are also reflected in the PPG pulse shape, so that changes in blood pressure can be seen directly in the PPG curve.
The cosinuss° approach
The basis for blood pressure calculations is PPG data. Using the c-med° alpha in-ear sensor, cosinuss° records high-quality green, red and infrared PPG signals that are generated by the blood flow in the vessels that run close to the external auditory canal. The quality of this PPG data is of crucial importance because the characteristics of the resulting PPG curves must be analyzed very precisely in order to derive the blood pressure. The reason for this lies in the individual variability of vascular stiffness from person to person and the associated individuality of the PPG waveforms.
To meet this challenge, cosinuss° developed a neural network which applies different layers to break down each pulse wave into its individual parts and characterizes them based on numerous characteristics. The information generated is then processed in further steps and finally translated into blood pressure values.
If the PPG curves are disturbed or not of high quality due to lack of blood flow or excessive movement during measurement, decomposition and analysis of the features becomes very difficult and blood pressure determination becomes a major challenge. The quality of the PPG data is therefore very important.
Advantages of photoplethysmography in the ear
The optical measurement of PPG signals in the external auditory canal offers decisive advantages over optical measurements on the wrist or fingers. The reason for this is the constant blood flow to this region of the body, which is not present in the extremities for a variety of reasons, such as cold, shock or when using tourniquets. However, if the measurement site is not supplied with blood, no usable PPG signals can be recorded and no vital parameters can be derived. Due to the location of the external auditory canal in the core of the body and the proximity to the brain, blood circulation is always ensured and vital parameters can be calculated here.
Another advantage of measuring in the ear is that the patient does not have to be undressed in cold environments. Access to the monitoring place is quick and easy over the ear. This is particularly relevant in mountain or offshore rescue, where the decision often has to be made whether, for example, blood pressure should be measured, which carries the risk of hypothermia, or whether to forgo this important data.
In addition, measuring in the ear canal is less susceptible to motion artifacts that can occur when measuring on the wrist or fingers. The dark environment in the ear canal also minimizes external light influences, which further improves the signal quality.
Blood pressure algorithm in the approval phase
In recent years, cosinuss° has collected and comprehensively analyzed high-quality data in numerous studies – both internally and in collaboration with clinical partners. So today there is a valuable data treasure with information from more than 500 people, over five million heartbeats and a total of almost 86,400 minutes of recording.
This database has made it possible to expand the neural network and to continuously train and optimize the machine learning models in order to finalize a blood pressure algorithm that meets certification standards. In the next step, cosinuss° will validate this algorithm in a clinical study and finalize approval in order to be able to offer blood pressure as an additional medical certified vital parameter.
