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 and 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 for systolic and 0.70, for diastolic. The average standard deviation for the systolic pressure is about 12 mmHg and about 10 mmHg, for the diastolic pressure.
To overcome the problems mentioned, 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 the 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 for the patient.
The continuously and non-invasive measuring blood pressure monitor consists basically of the sensor units for the acquisition of the necessary bio-signals and a computing unit which determines and displays the actual blood pressure. The stand-alone sensors are optionally connected to the computing unit by means of a Bluetooth™ connection. Thus blood pressure can be monitored in the natural patient environment and no psychological effects, such as “White Coat Hypertension”, altering the measurement. Furthermore the patient does not notice the measurement itself and is not restricted in his movements.
The processing and visualization of the measured signals are performed on a medical panel PC with a build in touch-screen - this could also be done by a mobile PDA. From there it is possible to store the data in a central electronic patient file via a flexible data connection.
The method has been tested in a clinical trial. The average correlation of the blood pressure acquired and calculated is 0,90 (systolic) and 0,81 (diastolic). The average standard deviations of 5.8 mmHg for the systolic pressure and 2.3 mmHg for the diastolic pressure are a substantial improvement compared to 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, the red line representing the systolic and the blue line the diastolic pressure.
Fields of Application & Miniaturization
Using the method presented above it is possible to replace the invasive blood pressure measurement which is often used in intensive care. Hence, the surgery which comes along with the invasive measurement and are accompanied by a certain risk can be avoided. Furthermore, this method can be applied to monitor the blood pressure in a home care environment. Such a sensor enables completely new possibilities for future diagnosis and therapy, e.g., for cardiovascular diseases. For this application a mobile and comfortably wearable sensor unit is being developed.
Personal Health Monitor (PHMon)