Abstract:
An extracorporeal physiological measurement device is disclosed, having fastening means for attaching to the body of a person or animal, measurement means for detection of values of a physiological measured variable on the body, and movement-detecting means and measured-value-influencing means connected thereto at the input for influencing the detected measured values before processing or storage as a function of a position or movement status of the body or the measurement device detected by the detection means such that the measured-value-influencing means have a unit for detection of a shift in position between the measurement device and the body.

Description:
RELATED APPLICATION 
     This patent application claims the benefit of U.S. Provisional Patent Application No. 61/258,623, filed on Nov. 7, 2009, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a physiological measurement device which is to be worn on the body of a person. 
     BACKGROUND 
     Physiological measurement devices to be worn on the body are known, e.g., in the form of wrist watches with a pulse-measuring function or blood pressure meters also worn on the wrist or recently also measurement devices worn in a similar way for determining blood oxygen saturation. To some extent, these measurement devices are already in practical use on a wide scale. Measured-value-influencing means are not necessary and are not provided with all such measurement devices. Wrist watches with a pulse-measuring function in particular may also achieve a relatively high precision, which is at any rate completely adequate for the leisure sports area even without such correction means. 
     In the case of other mobile devices that are worn on the body and have, e.g., optical sensors for determination of oxygen saturation, determination of movement artifacts, and a corresponding correction of the primary measurement result play an important role and constitute a special challenge. It is known that movement sensors (e.g., acceleration meters) may be used to solve this problem. If a significant movement of the device is detected during a certain measurement phase, then the measured values obtained in that phase are discarded. 
     However, it has been found that these devices still do not operate completely satisfactorily and the wearing habits of the user are also important for their functionality. In particular, errors may occur due to a relatively loose mechanical connection between the body and the measurement device and may lead to deviations in the movement sequences between the two. An attempt to solve these problems by providing fastening means, which are supposed to ensure a tight and constant connection between the body and the measurement device, e.g., through a tight elastic wristband, substantially impair user acceptance (patient compliance) and thus have a negative effect on the market chances of the corresponding devices. 
     It is also conceivable for movements of a certain body area to be detected directly by a movement sensor (e.g., an acceleration meter) implanted in the body area where the measurement devices are usually worn and to use these movement signals detected either directly or in combination with movement signals detected in a comparable manner on the measurement device to eliminate or discard movement artifacts from primary measurement signals. An implanted movement sensor would be constantly available and could be placed in the body in such a way that it is not detectable from outside the body. 
     However, many potential users are frightened off from implantation and especially explantation as surgical procedures as well as by the mere idea of having an implant, so that even with this approach, user acceptance, on average, is not satisfactory. Furthermore, the medical cost to implement this approach is relatively high. 
     However, although analysis of other parameters, e.g., electromyogram (EMG) measurements sensed by surface leads for conduction of muscle activity, can provide information about whether the measurement device is in contact with the proper body area (EMG visible) or not (EMG invisible), such an analysis does not provide information about the amplitude or direction of movement of the measurement device with respect to the body area. 
     SUMMARY 
     The present disclosure relates to a physiological measurement device which is to be worn on the body of a human subject (person) or an animal subject, and has corresponding fastening means, such as a fastener, for attaching it to the body and measurement means, such as a detector, for detecting values of a physiological measured variable on the body as well as movement-detecting means, such as a motion detector, and measured-value-influencing means connected thereto at the input end for influencing the detected measured values before they are processed or stored as a function of a position or movement state of the body or the measurement device as detected by the detection means. 
     A feature of the present disclosure is therefore to provide an improved measurement device of the aforementioned type, which will permit more accurate and more reliable measurements in everyday use in particular and will nevertheless enjoy a high user acceptance. 
     This feature is achieved by a measurement device having the features of claim  1 . Expedient further embodiments of the inventive idea are the subject of the dependent claims. 
     The disclosure is directed to a measurement device attached as tightly as possible and in a defined manner to the body of the user, preferably having a fastening means that allows a shift in position (relative movement) between the measurement device and the user&#39;s body within certain limits with a high user acceptance. It also takes into account the fact that with a corresponding possibility of adjusting the fastening means, different users will select different degrees of connection and thus a shift in position of varying degrees is allowed. 
     Instead of mechanically affixing the measurement system or detecting movements of the measurement device and the body separately, the movement (shift in position) of the measurement devices on the body is to be detected and the information thereby obtained is to be used to influence, or to control, the physiological measured values thereby detected. Accordingly, the measured-value-influencing means therefore have a device for detecting a shift in position between the measurement device and the body. 
     The present invention offers the following advantages, particularly in preferred embodiments: 
     An unpleasant tight mechanical connection of the measurement system to the subject&#39;s arm is no longer necessary, so it is possible to respond better to the wishes and habits of the user and patient compliance can thereby be increased. 
     Furthermore, measurement accuracy and also availability of the measured value over time are increased because measurement interruptions caused by movement may fail to occur entirely or may at least be greatly reduced. 
     In measurement of oxygen saturation by an optical method, for example, movement artifacts have greater dynamics than the actual measured value, so appropriate elimination thereof, which is ensured by the present embodiments, is especially important for the device function. 
     One embodiment has optical position-detecting means, e.g., a position detector in the manner of an optical mouse in particular for time-dependent determination of the position of a section of the measurement device on a section of a person&#39;s body. In particular, this provides for the position-detecting means to have a light or infrared (IR) emitter, a light or IR signal receiving unit for a light or IR pattern reflected by the skin of the person or animal and an evaluation unit connected downstream from the receiving unit for analyzing the light pattern or IR pattern and deriving a position signal therefrom. This embodiment may rely mostly on inexpensive components such as mass produced computer accessories and therefore can be implemented less expensively and more easily. 
     According to another embodiment, the movement detection means have an acceleration sensor system, and the measured-value-influencing means have an acceleration signal-evaluating unit, and the device for detecting a shift in position is connected to a correction stage downstream from the acceleration-signal-evaluating unit. Physiological measurement instruments with appropriate sensor systems have long been known, so these device components are also available inexpensively as mass-produced products of a well-engineered technology. 
     In another embodiment, the measured-value-influencing means are for use in deletion or suppression of further processing or transmission of values of the physiological measured variable from a measurement period of time during which a movement of the body or measurement device, or a shift in position between the measurement device and the body in excess of a predetermined amount has been detected. Alternatively, the handling of movement artifacts detected, having been revised with the results of detection of the shift in position between the measurement device and the body, may be such that the measured-value-influencing means perform a calculated correction of values of the physiological measured variable from a measurement period of time during which a movement of the body or the measurement device or a shift in position between the measurement device and the body in excess of a predetermined amount was detected. 
     In one aspect of these embodiments, the measured-value-influencing means have an influencing program memory for storing control programs or correction programs to be applied to the measured values of the physiological measured variable to be detected, said means for addressing various programs by detection results of the movement detection means, corrected by detection results of the device for detecting a shift in position. In the simplest case, the aforementioned control programs or correction programs may involve conditional deletion commands but also complicated correction methods for calculating movement effects from detected values of the physiological measured variable(s) determined in measurement series in advance. The addressing and application of a corresponding program to the physiological measured variable(s) may be independent of the type (e.g., direction or speed) or absolute value of movements detected. Detection results of the device for detecting a shift in position are taken into account as (additional) correction variables for this purpose. 
     In another embodiment, which is especially important for practical reasons, the fastening means include a wristband, and the measurement device may be worn as a wristband device. In another embodiment, the measurement device may be integrated into a garment such as a shirt, a vest or a jacket or the like, which at the same time serves as the fastening means. In another embodiment, which may be used for the purposes of sports medicine in particular, the measurement device is integrated into an accessory such as glove or a shoe or the like, which at the same time serves as the fastening means. 
     EXEMPLARY EMBODIMENT 1 
     General 
     The goal is to determine the acceleration of a body extremity, for example. 
     A measurement unit attached to a wristband is available. 
     The measurement unit has an acceleration sensor and an optical movement sensor. 
     Because the measurement unit moves with respect to the body extremity, the signal of the acceleration sensor is subject to error, i.e., it measures movement of the measurement unit and NOT movement of the body extremity. 
     The optical movement sensor is used for the correction. 
     The movement sensor detects movement of the measurement unit on the body extremity. 
     More specifically: 
     The light source, e.g., a light emitting diode (LED) or laser, illuminates a skin surface. 
     Light is reflected by the skin surface and captured by an image sensor (e.g., a complimentary metal oxide semiconductor (CMOS) sensor), e.g., as an image line or image area. 
     The captured image is forwarded to a digital signal processor (DSP) for analysis. 
     The DSP prepares image data and compares the image with one or more previous images. 
     From differences in the images, e.g., edges, shifting of patterns, the direction of the movement, and the speed and acceleration of the movement (shown below in  FIG. 5A , curve d, signal of the correction unit) of the measurement unit on the body extremity are calculated. The acceleration sensor of the correction unit is calculated with the signal determined by the acceleration sensor. This minimizes (see curve  5 A e) measurement error (see curve  5 A c) and yields actual acceleration values of the movement of the extremity (see curve  5 A a). 
     In a further embodiment commercially available optical mouse sensors (OMS) are used to measure displacement of the watch over the wrist of the person wearing it to demonstrate feasibility of the concept. 
     These OMS sensors measure their movement (displacement) over a surface extending in the X and Y directions. The orientation of the displacements can be seen in  FIG. 1 . 
     A value for surface quality is available in common OMS enabling to detect the presence or absence of a surface. This value can be used here to detect that the watch is moving in the Z direction, i.e. that it is too far away to perform a measurement. Furthermore, an OMS feature, Automatic Gain Control (AGC), enables them to be used with a wide variety of surfaces from white paper to printed media. X and Y values and a sampling frequency are then used to derive acceleration values, which are then combined with an acceleration measured in the device to give a corrected acceleration value.
 
The following parameters and their typical values are needed for the acceleration correction.
 
                                             Preset Parameters   Preset Value   Dimension   Comment               Acc_Watch_Max_X, Y, Z   ±5 g typical   [m/s 2 ]   For X, Y, Z; range given by acc sensor in                    device       Acc_Watch_Threshold_X, Y, Z    0.5-20 typical   [m/s 2 ]   Acc_Watch_Measured &lt; Acc_Watch       f_sample   100 typical   [Hz]   Sampling rate for X, Y, Z       OMS_v_max_X, Y   1   [m/s]   Max. speed “over ground” for OMS to work                    correctly [2, p. 1]       OMS_fps_max   9000   —   Max frames per second = max measurements                    per second [2, p. 1]       OMS_cpm_X, Y   126000   [n/m]   Counts per meter = resolution [2, p. 1] derived                   from 3200 cpi [counts per inch]               Measured &amp; Derived Parameters       Dimension   Comment               Acc_Watch_X, Y, Z   Measured   [m/s 2 ]   For X, Y, Z; given by acc sensor in device       OMS_Displacement   Measured   [m]   For X, Y, distance moved since last measurement       OMS_Speed   Derived   [m/s]   Derived from OMS_Displacement via                   integration       OMS_Acc   Derived   [m/s 2 ]   Derived from OMS_Speed via integration       Surface_quality   Measured   —   = 0 if OMS is too far away from surface       Acc_Corrected   Derived   [m/s 2 ]   = Acc_Watch + Acc_OMS                    
The following program excerpt demonstrates a possible workflow for the correction of the acceleration.
 
Workflow:
         At a frequency of F sample  per second, perform measurement of
           ACC_Watch and   OMS_Displacement simultaneously   
           If (Acc_Watch&gt;Acc_Watch_Threshold) and (Surface_Quality=0) then discard, else   Get OMS_Displacement for X,Y   Integrate X, Y values TWICE over time to get from distance via speed to acceleration “over ground” from OMS   Add Acc_Watch and Acc_OMS to get Acc_Corrected   Acc_Corrected is then to be used for further analysis/data storage as desired
 
To give a numerical example the following is assumed:
   A patient having a tremor of typically about 5 Hz   Acceleration of wrist watch Acc_Watch_X,Y,Z≦±2 g   Maximum. movement of the watch ±3 cm around patients wrist ( 50 ), induced by the tremor   As an approximation this movement is here regarded to be linear, i.e. in the X-Y plane.   Some points of the movement are assumed faster, so a maximum speed of 0.5 m/s is assumed   A sampling rate F sample  of 100 Hz for all channels (Acc_Watch_X,Y,Z; OMS_Displacement X,Y)   For simplicity the sampling rates of acceleration sensors and OMS are assumed to be the same here:   F sample =100 Hz yields a measurement every 10 ms   Tremor of 5 Hz yields a rate of 200 ms per cycle   Consequently, there are 20 measurements per cycle   Maximum speed of 0.5 m/s=0.005 m/10 ms=5 mm/10 ms   Thus, maximum OMS_displacement=5 mm per sample       

     From these values the acceleration can be calculated via an integration operation, allowing the correction of acceleration values measured by the acceleration sensor of the extracorporeal physiological measurement device. 
     Advantages and expediencies of the present invention are also derived from the following description of exemplary embodiments on the basis of the figures, in which: 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a pictorial perspective view of a physiological measurement device worn on the wrist, with a display of the degrees of freedom of the movement, 
         FIG. 2  shows a diagram of an embodiment of the measurement device based on  FIG. 1 , 
         FIG. 3  shows a schematic diagram of essential function components of the measurement device according to  FIG. 2 , 
         FIG. 4  shows a schematic functional block diagram of another embodiment of the measurement device, 
         FIGS. 5A and 5B  show graphic plots to illustrate the effects of the measurement device, and 
         FIGS. 6A and 6B  show pictorial views of other embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a pictorial perspective view of a wristband measurement device  1 , which is attached to the wrist of the hand H of a person by means of a wristband  3 . Arrows A and B illustrate typical degrees of freedom of movement of such a wristband device with respect to the patient&#39;s body, namely a rotational movement (arrow A) and a longitudinal displacement (arrow B) with respect to the arm. An acceleration sensor system  5  of the measurement device  1  detects movement (more precisely, the second lead of the shifts in position in space) of the measurement device, and its output signal may be used for influencing the measured value of physiological measured values of a patient detected by the measurement device  1 . 
       FIG. 2  shows a wristband measurement device  1 ′ containing an acceleration sensor system  5  and optical position-detecting means  7  having a detection range or “angle of view” C for additional detection of shifts in position of the measurement device  1 ′ with respect to the body, specifically the user&#39;s hand H, as an embodiment that has been modified in comparison with the measurement device  1  according to  FIG. 1 . The position-detecting means  7  function in the manner of an optical mouse, such as those which have long been known as a computer accessory item. 
       FIG. 3  shows in somewhat greater detail the wristband measurement device  1 ′ with regard to its essential parts if this figure is to be understood as a schematic diagram corresponding to  FIG. 1  and  FIG. 3 . This figure shows that the optical position-detecting means  7  have a light emitter unit  7   a , which emits measurement light L 1  in the direction of the user&#39;s wrist H′, and also a light signal-receiving unit  7   b , receiving reflected light L 2 , reflected by the wrist, and evaluating light L 2  with regard to its distribution in space and time to derive a shift-in-position signal, characteristic of a shift in position between the measurement device  1 ′ and the wrist. The light signal-receiving unit  7   b  comprises a multipart light receiver, e.g., a charge coupled device (CCD) or a CMOS array that is essentially known in its design and function and is not the subject of the present disclosure. 
     In addition,  FIG. 3  shows that the measurement signals of the acceleration sensor system  5  are combined as movement detection means, and the signals of the optical position-detecting means  7  are combined as signals characterizing the shift in position of the measurement device with respect to the user&#39;s body in an evaluation unit  9 . The evaluation unit  9  supplies a control signal or a calculated correction variable for influencing the physiological measured values using predetermined methods coordinated with the functioning of the actual physiological measurement means of the measurement device  1 ′. 
       FIG. 4  shows the evaluation unit  9  in greater detail in a partial view of the measurement device  1 ′ in the embodiment described above. In addition to the optical position-determining means  7 , evaluation unit  9  forms the measured-value-influencing means of the measurement device  1 ′. The evaluation unit  9  comprises an acceleration signal-processing unit  9   a  connected, at its input, to the acceleration sensor system  5  and a position signal-processing unit  9   b  connected at the input to the optical position-detecting means  7 , a time control and synchronization stage  9   d  connected to a real-time clock  9   c  and an influencing signal-output stage  9   e  as interface components on the input or output ends. The principal item of the evaluation unit  9  is an influencing program-selector unit  9   f , which is connected at the input to the outputs of the acceleration signal-processing unit  9   a  and the position signal-processing unit,  9   b  for use in addressing an influence program memory  9   g . At the output end, the influencing signal-output stage  9   e  is connected to a measurement signal reprocessing stage  11   b , which, in the embodiment shown here, is situated between a measurement signal sensor system  11   a  and the measurement signal transmission stage  11   c  which together form a physiological measurement component  11  of the measurement device F. 
     With control by the time-control-and-synchronization stage  9   d , the influencing program selector unit  9   f  combines detected acceleration values and shift-in-position values of the measurement device  1 ′ according to an internally stored evaluation program, which may also include, for example, threshold-value discrimination on the basis of pre-stored threshold values. With the result of this evaluation, it generates an address signal for addressing a memory area of the influencing program memory  9   g , in which an influencing program for the physiological measured variable to be monitored by the measurement device  1 ′ is stored, said measurement device  1 ′ or program ensuring a suitable influence (e.g., deletion or suppression of a transmission, or processing, or computer-assisted processing) of the values of the measured variable detected in a relevant period of time during which a significant movement of the measurement device  1 ′ was detected. 
       FIGS. 5A and 5B  show the operation of one embodiment in graphic plots for two different types of a hand or wrist action, namely for a gripping movement with a rapid start and subsequent deceleration and approach of the hand to a target ( FIG. 5A ), or a tremor ( FIG. 5B ). Time is plotted on the abscissa and an acceleration value is plotted on the ordinate. In  FIG. 5A , P 1  denotes the start of the gripping movement and P 2  denotes its deceleration and the approach of the hand to the target. 
     The top curve shows a chronological characteristic of the acceleration signal in the actual movement of the wrist, the second curve shows the signal measured by the acceleration sensor system  5  on the measurement device  1 ′, the third curve shows an uncorrected measurement error (i.e., difference between the top curve and the second curve), the fourth curve shows a signal of the optical position-detecting means  7 , i.e., a signal characterizing the shift in position between the measurement device  1 ′ and the wrist, and finally the last curve shows a corrected measurement error, i.e., the difference between the third curve and the fourth curve. These graphs illustrate that the fully corrected movement-induced measurement error is much smaller than would be expected according to the evaluation of the signal of the acceleration sensor system  5  on the measurement device F. It is self-evident that this is of great importance in the handling of detected measured values of physiological variables potentially subject to a substantial influence due to movement artifacts. This device thus allows a quantitative and possibly also qualitative change in the method of taking into account movement artifacts in such measured values. 
     As an additional embodiment,  FIG. 6A  shows a diagram of a measurement device  15  incorporated into a garment such as a vest  13  and optionally containing a suitable acoustic sensor system (not shown) for detection of pulmonary sounds in a patient. Accordingly, it may also be used to suppress or minimize movement artifacts as a result of movements of a patient or test subject wearing the vest. Instead of incorporating the measurement device into a vest, a comparable configuration of the measurement device might also be one in which it is incorporated into a shirt or a jacket or the like, for example. 
     As an additional embodiment,  FIG. 6B  shows a glove  17  having a measurement device  19 , for use in detecting the blood oxygen saturation, incorporated in the area of an index finger. Glove  17  may also have inventive means for elimination or minimization of movement artifacts in a measurement signal of the oxygen saturation sensor system (not shown). 
     Embodiments of the present invention are not limited to the examples described above and the aspects emphasized above, but instead a variety of modifications which fall within the scope of technical expertise would also be possible. 
     It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teaching. The disclosed examples and embodiments are presented for purposes of illustration only. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention.