Non-invasive monitoring of important cardiovascular parameters

Non-invasive monitoring of important cardiovascular parameters

Martin Jahn; Hans-Georg Ortlepp; Martin Schädel; Olaf Brodersen; Michael Scherf

In the field of mobile patient monitoring, in addition to the development of novel, increasingly miniaturized and more comfortable sensor solutions, there is a trend towards the parallel collection of various vital parameters. The combination of these data allows the creation of an increasingly complete image of the health situation of individual patients and thus the creation of more precise diagnoses. In order to enable a comprehensive recording of the cardiovascular condition, the digilog research project therefore aimed at the parallel use of the mobile ECG recorder CM 100 (GETEMED Medizin- und Informationstechnik AG, Germany) and the in-ear sensor system (CiS Forschungsinstitut für Mikrosensorik GmbH, Germany). In this way, the results of the long-term ECG can be enriched by the course of blood pressure and oxygen saturation. Parameters such as heart rate and pulse rate are also recorded redundantly by both systems. This information can be used to synchronize and monitor the quality of both measurements.


For the test measurements carried out, a proven procedure for the controlled influence of blood pressure was used, the so-called tilting table examination. This method is usually used to examine the body's ability to regulate blood pressure. For this purpose, the test subject, who is initially lying, is tilted in an upright position, causing the blood to sink into the lower extremities. The body then compensates for the drop in blood pressure. In the present case, the subject (male, 32 years old, no hypertension diagnosed) initially lay for seven minutes, was then tilted upright (70° to horizontal) and monitored for seven minutes in a standing position. He was then placed in a diagonal position (45° to the horizontal) for three minutes and observed lying down again for another five minutes. Throughout the procedure, the ECG recorder and ear sensor measured in parallel, with the ECG being started a few minutes earlier for practical reasons.


Selected results of these measurements are shown in Figure 1. For Figure 1a, the time course of the pulse rate resulting from the PPG data of the ear sensor was shifted so that the curve is superimposed with that of the ECG recorder data. The high correspondence of both curves can be seen in the magnification in Figure 1b. The resulting time shift was then used to synchronize the parameters determined by the ear sensor, such as the blood pressure curve (see Figure 1a), and the ECG data. The drop in blood pressure after approximately 470 s is characteristic for the process of controlled tilting into an upright position. At the same time, the heart rate suddenly increases, which is an indicator of the body's own countermeasures to compensate for the drop in blood pressure. In addition, the ECG data from a 5-minute interval at which the test person lay still (highlighted in color in Figure 2a) were spectrally analyzed. Further medically relevant parameters can be extracted from the resulting power density spectrum, which is shown in Figure 1c.

With the help of the tilting table tests, it was shown that the combination of the mobile ECG recorder CM 100 with the ear sensor can provide valid data for future test series. In particular, the redundant information of heart and pulse rate helps greatly to improve data quality by identifying and differentiating areas of interference in the raw signals (see Figure 2). Furthermore, the redundant information can be used for the synchronization of the signals from the different data sources (see Figure 3). This makes it possible to correlate rhythm events or other parameters derived from the ECG with the synchronously measured blood pressure and oxygen saturation processes in order to gain new insights and make more differentiated diagnoses.

The very positive results from the tilting table examination and further measurements within the digilog research project form the basis for more extensive validation measurements, which are necessary for the acceptance and introduction of in-ear blood pressure measurement for diagnosis and therapy support.
Abbildungen:

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Abbildung 1 (a) Blood pressure curve determined by the ear sensor (green line) and the change in heart rate over time derived from data of the ear sensor (red line) and the Getemed ECG recorder CM100 (grey line). The colored area marks the range of the 5-minute interval used to calculate the power density spectrum from the heart rate progression. (b) Magnification of the color-coded 5-minute interval. (c) Representation of the power density spectrum determined from the ECG recorder data. The medically relevant frequency bands are separated by the yellow lines and additionally marked in color.

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Abbildung 2 Example of the use of deviations in redundant information to improve results.

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Abbildung 3 Example of linking different vital parameters measured with the aid of (a) the ear sensor (oxygen saturation and blood pressure) and (b) the mobile ECG CM100 (heart rate, respiratory rate and further HRV parameters).

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