Abstract:
The invention relates to a method of operating a long-term blood pressure measurement device having a measurement sensor for detecting a pulse wave signal, having a measurement sensor for body current signals, having a pressure cuff for a non-invasive determination of the blood pressure, having a control and evaluation unit for determining blood pressure values, on the one hand from signals acquired by means of the pressure cuff (pressure cuff signals), and, on the other hand from a pulse wave transit time that is derived from body current signals and pulse wave signals, and having a memory for storing blood pressure values.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Patent Application No. 102016105684.7, filed Mar. 29, 2016, which is incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a method of operating a long-term blood pressure measurement device having a measurement sensor for detecting a pulse wave signal, having a measurement sensor for body current signals, having a pressure cuff fora non-invasive determination of the blood pressure, having a control and evaluation unit for determining blood pressure values, on the one hand from signals acquired by means of the pressure cuff (pressure cuff signals), and, on the other hand from a pulse wave transit time that is derived from body current signals and pulse wave signals, and having a memory for storing blood pressure values. 
         [0003]    Such devices have been known for some time and are used e.g. in mobile form to be worn on the body of persons over comparatively long time periods of several hours or several days. In known devices, blood pressure measurements as a rule take place periodically at fixedly predefined time intervals, e.g. every 15 or 30 minutes. This has the result in a disadvantageous manner that significant blood pressure changes remain unrecognized when they occur in the time intervals between two measurements. Furthermore, with regularly occurring measurements, unnecessary measurements are also carried out with unchanged blood pressure values, with these measurements then putting unnecessary stress on or unnecessarily irritating the persons wearing the device. 
         [0004]    With known devices of the named kind that are equipped with a measurement sensor for detecting a pulse wave signal, a blood pressure measurement can advantageously be triggered via the pressure cuff not only at regular time intervals, but also in dependence on the progression of the pulse wave signal. A blood pressure measurement can therefore always be triggered via the pressure cuff, for example, when there is an indication of a noticeable blood pressure value due to the progression of the pulse wave signal. Such a long-term blood pressure measurement device is described, for example, in the German patent application DE 10 2007 050 598.3. For example, the fact that the pulse wave signal is detected via a measurement sensor that has to be fixed to the finger or to the earlobe of a person, which is often irritating for the person, in particular in daily life, and which also frequently results in artifacts in the pulse wave signal due to movements of the person, is a disadvantage of this long-term blood pressure measurement device. 
         [0005]    It is furthermore a disadvantage in the mentioned long-term blood pressure measurement device that the actual measurement of the blood pressure takes place via the pressure cuff, which for persons is associated with a high pressure on the upper arm, on the one hand, and with a comparatively loud noise of the compressed air source acting on the pressure cuff, on the other hand. This has an irritating effect in everyday life and can also have the result that blood pressure values are falsified since some people are agitated by the blood pressure measurement they can clearly perceive, which then results in increased values and ultimately in values unrealistic for a normal everyday situation. 
         [0006]    It is furthermore known to use devices of the initially named kind such that blood pressure values are determined in long-term operation only from the pulse wave transit time by means of different calculation methods, with a blood pressure measurement by means of the pressure cuff only being used for an initial calibration or for a later recalibration. The calculation and calibration methods used here, however, disadvantageously frequently result in falsified blood pressure values. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    It is an object of the invention to further develop the known long-term blood pressure measurement devices such that persons are disturbed as little as possible by the carrying out of the blood pressure measurements in long-term operation and such that simultaneously a high accuracy can be achieved in the determined blood pressure values. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0008]    In accordance with the invention, this object is satisfied by the features of claim  1  and in particular in that, for calibration with an initially named long-term blood pressure measurement device, first
       a) a blood pressure value is determined from pressure cuff signals and in parallel therewith a pulse wave transit time is determined;   b) a correlation between the blood pressure value and the pulse wave transit time corresponding thereto takes place in the form of a value pair in the memory; and   c) in that the steps a) and b) are repeated for different blood pressure values at time intervals, whereby a correlation table is produced in the memory with a plurality of value pairs of a respective blood pressure value and a pulse wave transit time; and   in that then, in long-term operation,   d) pulse wave transit times are determined at consecutive points in time whose corresponding blood pressure values are each determined by means of the correlation table or by means of an approximation function acquired therefrom and are stored together with the associated points in time.       
 
         [0014]    In accordance with the invention, different blood pressure values are therefore first determined by means of pressure cuff signals as part of a calibration, with the pulse wave transit time then current at the respective point in time also being determined simultaneously with the determination of the respective blood pressure values. A plurality of value pairs of blood pressure and pulse wave transit time can thus be formed, whereby ultimately the correlation table in accordance with the invention is produced. When only the pulse wave transit time is then determined without the use of the pressure cuff in the subsequent long-term operation, the associated blood pressure value can be taken from the correlation table provided that the pulse wave transit time determined in long-term operation is included in the correlation table. An extrapolation of the determined value pairs can be carried out, for example as part of the calibration, for the pulse wave transit times not included in the correlation table such that ultimately all the possible pulse wave transit times with the associated blood pressure values are included in the correlation table. It is alternatively possible to determine an approximation function via the determined value pairs as part of the calibration that comprises the value pairs in the best possible manner such that then ultimately all the blood pressure values can be determined via this approximation function from the pulse wave transit times determined in long-term operation. 
         [0015]    The respective blood pressure value that occurs can be determined very accurately and in an non-falsified manner from the pulse wave transit times in long-term operation by these methods in accordance with the invention. The blood pressure values determined in accordance with the invention in this respect correspond to the systolic blood pressure. 
         [0016]    A further substantial advantage of the device in accordance with the invention comprises the blood pressure generally being measured during long-term operation without a pressure cuff only by a suitable evaluation of the body current signals and pulse wave signals. In this respect, the pulse wave transit time that ultimately indicates how long it takes until a pulse wave triggered by a heartbeat reaches the location of the measurement sensor for the pulse wave signal is determined from the time relationship between the body current signals, preferably recorded close to the heart, and the pulse wave signals. The start of the pulse wave transit time interval results from the body current signal and the end of this time interval results from the pulse wave signal. The blood pressure can then be determined after the previous calibration in accordance with the invention in the already explained manner from the pulse wave transit time. It is thus possible without problem not only to carry out a blood pressure measurement in accordance with the invention in long-term operation every 15 or 30 minutes, but considerably more frequently, if not even continuously, without the wearing of the long-term blood measurement device thereby becoming less pleasant for the person. A monitoring of the blood pressure of the person that has a lot fewer gaps thus becomes possible without any additional strain caused by an activation of the pressure cuff. 
         [0017]    The blood pressure measurement in long-term operation is thus comparatively pleasant for the person since the person anyway always wears the measurement sensor for body current signals and pulse wave signals at the body, with the person not being able to perceive either in a tactile or acoustic manner whether these measurement sensors are active or not. This means that the person ultimately does not notice at all when a blood pressure measurement is taking place via body current signals and pulse wave signals such that the person is not impaired in any way in his everyday life here and also no measurement values can be falsified due to the imperceptible measurement. 
         [0018]    The long-term blood pressure measurement in accordance with the invention thus provides the possibility of carrying out blood pressure measurements in a manner pleasant for the person without using the pressure cuff and of only carrying out the blood pressure measurement via the pressure cuff for calibration purposes or only from time to time in order, for example, to verify the blood pressure values determined without a pressure cuff. 
         [0019]    The calibration in accordance with the invention takes place by a plurality of measurements at different points in time. At these points in time, the pressure cuff can be respectively applied again; it is alternatively also possible to leave the pressure cuff applied permanently over a time period of several hours. 
         [0020]    The calibration preferably takes place over a time period of 24 hours, with the individual measurements being distributed over this time period. 
         [0021]    The individual measurements during the calibration can be triggered in an automated manner, for example, and can take place at regular time intervals. Alternatively or additionally, measurements can also be triggered individually by the patient during the calibration, in particular whenever the patient suspects a change of his blood pressure values. Such changers can, for example, be triggered by agitation, physical activity or by a change in the measurement conditions (walking, standing, sitting, lying). 
         [0022]    It is additionally or alternatively possible that the pulse wave transit time is determined continuously during the calibration and that a blood pressure measurement by means of pressure cuff signals is triggered when a change of the pulse wave transit time disposed above a predefined threshold is detected. A blood pressure measurement can be triggered in an automated manner in this manner whenever a change of the blood pressure value is very likely present. 
         [0023]    It has already been explained that the blood pressure values are determined from the correlation table in accordance with the invention or via the approximation function determined in accordance with the invention in long-term operation. It is preferred in this respect if an individual correlation table or approximation function is determined for every patient to be examined as part of the calibration. 
         [0024]    It is particularly preferred if a respective individual calibration takes place under different measurement conditions (walking, standing, sitting, lying) such that a respective separate correlation table or approximation function is present for the different measurement conditions. The correlation table or approximation function used in long-term operation is then always selected or changed in dependence on the measurement conditions respectively present in long-term operation. 
         [0025]    If different correlation tables or approximation functions should be used for different measurement conditions, it is particularly advantageous if the measurement condition respectively present is determined continuously during the calibration and a blood pressure measurement by means of pressure cuff signals is at least triggered when a change of the measurement condition is detected. 
         [0026]    In order then to be able to activate the correlation table or approximation function belonging to the respectively valid measurement condition in long-term operation, it is sensible if the measurement condition respectively present is determined with reference to motion sensors and/or positional sensors during long-term operation. These sensors are then preferably elements of the measurement device used in accordance with the invention. 
         [0027]    It is particularly advantageous if the measurement sensor for detecting the pulse wave signal is adapted for fastening in or at the ear, at the finger or at the wrist of a person. A fastening in the ear is particularly preferred in this respect since the measurement sensor is in this case located in the auditory canal of the person like an ITE hearing aid and not, for instance, at the earlobe or behind the ear as with BTE hearing aids. This is not only of substantial advantage with respect to the comfort in wear, but also under esthetic aspects since the measurement sensor can only be perceived by third parties when looking intensely. In addition, much fewer artifacts that falsify the pulse wave signal occur with the measurement sensor in accordance with the invention than with measurement sensors that are attached to the finger or to the earlobe. In addition, it is of advantage here in the determination of the pulse wave transit time that the distance between the heart and the ear is comparatively short such that only very small errors can occur in the pulse wave transit time determination here. 
         [0028]    Individual or all the measurement sensors can be coupled to the control and evaluation unit via a wireless connection. The ANT+ standard or Bluetooth are suitable for such a coupling. 
         [0029]    The measurement sensor for body current signals can comprise at least two electrodes, but preferably also three or more electrodes, and can be fastened to a chest strap that is comfortable to wear. A transmitter can then likewise be located at the chest strap and transmits the recorded body current signals to the control and evaluation unit. 
         [0030]    In a corresponding manner, the measurement sensor can have a transmitter for the pulse wave signal in its housing and the pulse wave signals can be transmitted via said transmitter to the control and evaluation unit. 
         [0031]    The control and evaluation unit is preferably accommodated in a housing that can be fastened to the wrist of a person or to a strap respectively a belt. This allows a particularly comfortable wearing of the long-term blood pressure measurement device. On the accommodation of the control and evaluation unit in a housing at the wrist of a person, it is of advantage that measured values delivered from the measurement sensors or signals derived therefrom can be read out without problem by the person at a display of the housing. 
         [0032]    If the control and evaluation unit is accommodated in a housing that can be fastened to the strap, the compressed air source for the pressure cuff can additionally also be accommodated in this housing. In this case, only a single housing is required for the compressed air source and the control and evaluation unit. On an arrangement of the control and evaluation unit at the wrist, in contrast, a housing has to be provided at the wrist and a housing for the compressed air source has to be provided at the strap of the person. 
         [0033]    The long-term blood pressure measurement device in accordance with the invention can alternatively or additionally also be used as a mobile long-term ECG device, with it being preferred in this case if the device has one or more of the features that are disclosed in the German patent application DE 10 2007 050 601.7. 
         [0034]    The long-term blood pressure measurement device in accordance with the invention can furthermore also have one or more of the features that are disclosed in the German patent application DE 10 2007 050 598.3. 
         [0035]    Further preferred embodiments of the invention are explained in the dependent claims, in the description of the Figures and in the drawing. 
         [0036]    The components of a possible embodiment of the long-term blood pressure measurement device in accordance with the invention will be explained in the following with reference to the only drawing: 
       BRIEF DESCRIPTION OF THE DRAWING 
       [0037]    The person shown in the Figure wears a strap  10  to which a housing  12  is fastened. A control and evaluation unit, a compressed air source for a pressure cuff  14  and a signal memory at least for the storage of pulse wave transit times and blood pressure values are accommodated in this housing  12 . The pressure cuff  14  that the person wears at the upper arm is connected to the compressed air source arranged in the housing  12  and to the control and evaluation unit likewise arranged there via a compressed air and signal line  16 . 
         [0038]    A reception unit is furthermore provided in the housing  12  that is suitable to receive body current signals and pulse wave signals. 
         [0039]    The person shown furthermore wears a chest strap  18  at whose inner side two or three electrodes are arranged that are electrically coupled to a transmission unit  20  likewise fastened to the chest. The transmission unit  20  transmits the body current signals recorded by the electrodes in the chest strap  18  to the reception unit accommodated in the housing  12 . 
         [0040]    A measurement sensor  22  for pulse wave signals is located in the ear of the person shown. The housing of this measurement sensor  22  furthermore comprises a transmission unit that is suitable to transmit recorded pulse wave signals to the reception unit accommodated in the housing  12 . values.