Motivation

Measurement of blood pressure is the most frequently applied medical examination worldwide. Present measurement devices can be divided in invasive (very precise and continuous) and non-invasive systems. Non-invasive devices are generally based on oscillometric respectively auscultation methods and do require an inflatable cuff. They are simple to use but, due to the squeezing cuff, inconvenient for the patient. Furthermore they do not allow continuous monitoring and are very imprecise. For those devices the average blood pressure correlation with an invasive reference measurement is 0.80 systolic and is 0.70 diastolic. The average standard deviation for the systolic pressure is about 12 mmHg and about 10 mmHg for the diastolic pressure.

Method

To overcome the mentioned problems, there is a need for an innovative method, measuring blood pressure continuously and stressless without a squeezing cuff. By measuring different cardiovascular parameters, like blood flow and pulse wave velocity, it is possible to calculate blood pressure.

Several bio-signals are recorded and a specific number of signal characteristics are extracted. Those characteristics are used to determine the systolic and diastolic blood pressure for each pulse. The calculation of blood pressure can be performed with the use of various patient specific sensors which ensure a high flexibility and comfort of the patient.

Field of application

With the here presented method it is possible to replace the invasive blood pressure measurement which is often applied in intensive care. Hence the surgery which comes along with the invasive measurement and accompanies a certain risk can be avoided. Furthermore, this method can be applied to monitor the blood pressure in a home care environment. Therefore, a mobile and comfortably wearable sensor unit is being developed.

Realization

The continuously and non-invasive measuring blood pressure monitor consists of a medical panel PC performing the calculation and visualization of the measured values. The monitoring device is controlled by the means of a build in touch-panel. The sensors of the cardiovascular signals are connected to an analog signal conditioning unit. In the realization shown below the sensors are a 1-channel ECG and a laser-doppler flow-sensor for the application at the finger. This system allows an online calculation of blood pressure pulse per pulse.

Clinical trial

The presented method has been tested in a clinical trial. The average correlation of the there acquired and calcu-lated blood pressure and invasive blood pressure are 0,90 (systolic) respectively 0,81 (diastolic). The average standard deviations of 5.8 mmHg for the systolic pressure and 2.3 mmHg for the diastolic pressure are clearly better than the standard deviations of the conventional devices. In the diagram shown below, the continuously calculated (light) and invasively measured (dark) blood pressure are given for an example measurement. Here the red line represents the systolic and the blue line the diastolic pressure.

Integration

Due to the mostly given medical necessity of blood pressure measurements, the blood pressure monitor is a vital component of the Personal Health Monitoring System. The gathered data is transmitted via Bluetooth to the patient related mobile base station. From there it is possible to store the data in a central electronic patient file. Furthermore, the miniaturization of the blood pressure monitor will allow a continuous measurement under normal conditions without an excitement of the patient for the first time.