Abstract:
Graphical layouts, algorithms, and methods are introduced herein to implement user interfaces for mobile and/or wearable medical devices. In one aspect of the present invention, new graphical layouts are introduced for simplified presentation of time-dependent patient data. In another aspect of the invention, methods and algorithms are introduced to acquire, extract and present relevant features of patient data in real-time in order to simplify the graphical presentation and interpretation. In another aspect of the invention, elements of a multi-modal user interface are introduced in order to simplify and minimize the user&#39;s interaction with the medical wearable device. In yet another aspect of the invention, further methods are introduced for real-time interaction between a user or several users and a wearable or several wearable medical devices. In one embodiment of the present invention, a smartphone, a smart watch, a head-mounted device or similar devices can be used to acquire and display in real-time patient data, e.g., electrocardiogram and relevant features, e.g., heart rate, etc. In another embodiment of the present invention, smartphones, smart watches, head-mounted devices or similar devices can be used to share in real-time the patient data.

Description:
[0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 62/027,801 filed on Jul. 23, 2014, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates in general to simplified user interfaces for medical devices and in particular to simplified user interfaces which can be used for mobile and/or wearable medical devices. In the context of the present invention, mobile medical devices are medical devices which make use of mobile platforms, e.g., smartphones or tablets. In the context of the present invention, wearable medical devices are medical devices which make use of wearable platforms, e.g., smart watches, head-mounted devices, contact lenses, and other wearable objects integrating medical technology functions, etc. The invention introduces algorithms and methods which allow for the real-time data acquisition and extraction of relevant features of the clinical data for simplified presentation and interpretation. The invention further introduces graphical layouts optimized for the real-time display of clinical data on mobile platforms, e.g., smartphones, smart watches, head-mounted devices, and similar wearable devices. The invention further introduces methods of real-time interaction between users and wearable medical devices in order to allow for simplified interaction and easy sharing of clinical data. 
       BACKGROUND OF THE INVENTION 
       [0003]    Currently there exists a growing tendency to use mobile platforms and wearable devices for medical applications. With such devices, the user interface paradigm is changing in several ways when compared to traditional medical devices. For example, the display/screen becomes smaller with mobile platforms and wearable devices, if a display exists at all. With mobile platforms and wearable devices, a range of different and/or new user interaction methods become more frequent compared with traditional medical devices, e.g., touch screens, voice control, gesture control. With mobile platforms and wearable devices, the ability to access information at remote locations and to share information in real-time increases when compared to traditional medical devices. For all the above mentioned reasons, new user interfaces for wearable and mobile medical devices are needed in order to optimize the real-time interaction, acquisition, presentation and interpretation of medical information using the new paradigm of mobile and wearable technology. 
         [0004]    Several U.S. patents and patent applications describe aspects of using portable, mobile and wearable devices for medical applications. For example, in U.S. Pat. No. 7,261,691 “Personalized Emergency Medical Monitoring and Transmission System”, a portable medical system for real-time applications is described without any emphasis on its user interface. In U.S. Pat. No. 8,326,651 a user interface is described for managing medical data focused on off-line use, i.e., not in real-time. In U.S. Pat. No. 8,521,122 a user interface for mobile devices is introduced for displaying emergency information. However, this invention does not address any aspects regarding the real-time acquisition of patient data nor does it address aspects related to extracting relevant information in order to simplify the user interface. U.S. 2011/0015496 describes the use of a mobile communication device for real-time patient data acquisition. No emphasis is placed on optimizing the user interface of the mobile device for its intended use. In U.S. 2011/0306859 a multipurpose, modular platform for mobile medical instrumentation is described including the use of a cell phone or tablet computer for real-time patient data acquisition. Once again, no emphasis is placed on optimizing the user interface of the mobile device for its intended use. 
       SUMMARY OF THE INVENTION 
       [0005]    Graphical layouts, algorithms, and methods are introduced herein to implement new user interfaces for mobile and/or wearable medical devices. In one aspect of the present invention, graphical layouts are introduced for simplified presentation of time-dependent patient data. In another aspect of the invention, methods and algorithms are introduced to acquire, extract and present relevant features of patient data real-time in order to simplify the graphical presentation and interpretation. In another aspect of the invention, elements of a multi-modal user interface are introduced in order to simplify and minimize the user&#39;s interaction with the medical wearable device. In yet another aspect of the invention, further methods are introduced for real-time interaction between a user or several users and a wearable or several wearable medical devices. In one embodiment of the present invention, a smartphone, a smart watch, a head-mounted device or similar devices can be used to acquire and display in real-time patient data, e.g., electrocardiogram and relevant features, e.g., heart rate, etc. In another embodiment of the present invention, smartphones, smart watches, head-mounted devices or similar devices can be used to share in real-time the patient data. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1 : Methods of extracting relevant features from patient data in real-time according to the present invention. 
           [0007]      FIG. 2 : Displaying time-dependent patient data using a simplified time coordinate according to the present invention. 
           [0008]      FIG. 3 : One simplified display of relevant features of patient data according to the present invention. 
           [0009]      FIG. 4 : Another simplified display of relevant features of patient data according to the present invention. 
           [0010]      FIG. 5 : Some algorithms used to support relevant feature extraction from patient data according to the present invention. 
           [0011]      FIG. 6 : Simplified user interface showing changes in relevant patient data features and tracking history of such changes according to the present invention. 
           [0012]      FIG. 7 : Using the user interface according to the present invention for catheter guidance. 
           [0013]      FIG. 8 : Simplified user interface showing both time-dependent patient data and relevant features according to the present invention. 
           [0014]      FIG. 9 : Simplified user interface showing time-dependent patient data in real time and frozen as reference according to the present invention. 
           [0015]      FIG. 10 : Elements of a user interface and methods for user interaction according to the present invention. 
           [0016]      FIG. 11 : Simplified user interface for a head-mounted device according to the present invention. 
           [0017]      FIG. 12 : Head-mounted device and methods for user interaction according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]      FIG. 1  illustrates a method for the extraction of relevant features from patient data in real-time according to the present invention. In one embodiment of the present invention, the graph  100  illustrates a sequence of 5 periods (t 0  through t 4 ) of a biological signal represented in the coordinate system Amplitude-Time (A-t). Such a signal can represent, for example, electrocardiogram (ECG), plethysmogram, pulse oximetry, blood pressure, etc. One of the characteristics of such signal is that it has a certain periodicity corresponding to the periodicity of body functions. 
         [0019]    In one embodiment of the present invention, periodical signals are considered for feature extraction. In another embodiment of the present invention, signals are considered which are not periodical and happen at irregular time intervals. Traditionally, the variations in the amplitude of a signal are displayed on a time axis as illustrated by graph  100 . For example, in Graph  100 , a signal or waveform period  101  is illustrated starting at the moment t 0  and ending at moment t 1 , followed by signal period  102  starting at t 1  and ending at t 2 , period  103  starting at t 2  and ending at t 3 , period  104  starting at t 3  and ending at t 4 , and period  105  starting at t 4  and ending at t S . One of the benefits of such a display ( 100 ) is that it allows for trend analysis, i.e., the user can follow the history of amplitude changes. One disadvantage of such display on a time axis is that it requires a relatively large real estate to be used for the display, e.g., a large screen or long print-outs in order to display a large enough number of signal periods. The amount of signal data increases even more in the case of patient monitoring, when such signals must be monitored and potentially recorded over long periods of time, i.e., days and weeks. 
         [0020]    By observing the sequence of waveforms in Graph  100 , one can notice that each period can be analyzed and certain relevant features extracted for each such period. In one embodiment of the present invention,  FIG. 1 ,  130  illustrates certain relevant features which can be extracted from the signal sequence in Graph  100 . It should be obvious for somebody skilled in the art that the illustrations in  FIG. 1 ,  130  are not limitations of the present inventions and that other relevant features can be extracted from the signal in both time and frequency domains based on the same principles and with the same goals as described by the present inventions. It should further be obvious for somebody skilled in the art that a signal period can be divided into any number of relevant segments as well as any number of signal periods can be grouped into one segment of interest. 
         [0021]      FIG. 1 ,  130  illustrates several relevant features of the periodic biological signal from Graph  100 : a) the segments of interest  142 ,  145 , and  146 ; b) the amplitude of interests  135  in segment  145 , i.e., the maximum value of the signal in segment  145 ; the amplitudes of interest  137  and  140  in segment  142 , i.e., the maximum and respectively the minimum values of the signal in segment  142 ; the average value of the signal  148  in segment  146 . 
         [0022]    The amplitudes of interest  135 ,  137 , and  140  and the average value of the signal  148  can be determined in a number of ways as illustrated in the present invention. It should be obvious to somebody skilled in the art that such ways are not limitations of the present invention and that other ways to determine the amplitude of interest can be easily determined. In one embodiment of the present invention, the amplitude  135  is determined as the largest amplitude within a signal period. 
         [0023]    In another embodiment of the present invention, the amplitude  135  is determined as the largest amplitude within a certain period of time after a steep increase in the signal as determined by computing the signal&#39;s first derivative or slope. In one embodiment of the present invention, amplitude  137  is calculate as the largest amplitude of the signal segment  142  and amplitude  140  is calculated as the smallest amplitude of the signal segment  142 . 
         [0024]    In another embodiment of the present invention, an average value  148  of the segment  146  is calculated and subtracted from the signal values in segments  142  and  145 . In such an embodiment, the amplitude  135  is calculated as the largest positive value of segment  145 , the amplitude  137  is calculated as the largest positive amplitude of segment  142  and the amplitude  140  is calculated as the largest negative amplitude of segment  142 . 
         [0025]    In one embodiment of the present invention, the average value  148  of segment  146  is calculated using equation  540  in  FIG. 5 . 
         [0026]    The segments of interest  142 ,  145 , and  146  can be determined in a number of ways as illustrated in the present invention. It should be obvious to somebody skilled in the art that such ways are not limitations of the present invention and that other ways to determine the segments of interest can be easily described. In one embodiment of the present invention, segment  145  is determined as being of a certain time length around the maximum amplitude  135  determined as described above herein. In one embodiment of the present invention, the determination of the start, end, and duration of segment  145  is made based on known physiological behavior generating the patient data/signal. For example, in the case of the signal being an ECG signal and the maximum amplitude  135  being an R-peak, the typical start, end and duration of segment  145  are determined by the activity of the atrio-ventricular node and are documented in the literature. 
         [0027]    In one embodiment of the present invention, segment  146  is identified as the period of time with no or little activity of the signal, i.e., the period of time in which the amplitude of the signal is constant or quasi-constant. In one embodiment of the present invention, equation  510  in  FIG. 5  is used to compute the signal variance and to determine the presence or lack of activity if the variance goes above or stays below a certain threshold, respectively. 
         [0028]    In another embodiment of the present invention, the lack of activity in segment  146  is determined if the differences between the largest and the smallest of the amplitudes of consecutive or quasi-consecutive samples remain below a certain threshold. 
         [0029]    In one embodiment of the present invention, the determination of the start, end, and duration of segment  142  is determined from known physiological behavior generating the patient data/signal. For example, in the case of the signal being an ECG signal and the maximum amplitude  135  being an R-peak, the typical start, end and duration of segment  142  are determined by the activity of the sino-atrial node and are documented in the literature as the P-segment and the P-wave. In another embodiment of the present invention, segment  142  and  145  are adjacent. Segment  142  ends and segment  145  starts at or at a certain time interval before the signal reaches its minimum amplitude value between the moment when it reaches amplitude  137  and the moment when it reaches amplitude  135 . 
         [0030]    A signal period, e.g. periods  101  through  105  can be identified in number of ways as illustrated in the present invention. It should be obvious to somebody skilled in the art that such ways are not limitations of the present invention and that other ways to determine the signal period can be easily determined. 
         [0031]    In one embodiment of the present invention, a signal period is considered to start when the slope of the signal curve calculated as the signal&#39;s first derivative surpasses a certain threshold. The signal period is considered to stop when the subsequent signal period starts. In another embodiment of the present invention, a signal period is considered to start when the amplitude  135  is detected and last until the next (subsequent) amplitude  135  is detected. The duration of the signal period is measured in seconds and is computed by dividing the number of signal samples of the signal period by the sampling rate. 
         [0032]    The method of extraction of relevant features from patient data as illustrated herein is not a limitation of the present invention. It should be obvious to somebody skilled in the art that other methods for feature extraction can be applied with a twofold purpose: a) to minimize the amount of information needed to be presented to the user and b) to minimize and/or simplify the presentation of time-dependent data. Such feature extraction methods can be morphological, statistical, and computational and other artificial intelligence methods, including adaptive and auto-adaptive methods, obvious to somebody skilled in the art. They can be applied in the time domain, in the frequency domain (using the Fourier Transform), or in another domain obtained by data transformation, e.g. principal component analysis (using the Karhunen-Loeve Transform). The relevant feature extraction according to the present invention does act as a practical data compression and principal components analysis algorithm, i.e., instead of having to interpret the entire sequence of patient data, one can interpret only the relevant features extracted. Thus, the system display and the user/system interaction can be simplified as described herein. 
         [0033]    In one embodiment of the present invention, morphological or descriptive methods are used for feature extraction including: maximum and minimum signal amplitudes, signal slopes, presence or lack of signal changes, sequence of certain signal elements like amplitudes, segments, and slopes, identification of signal segments based of specific segment characteristics. In another embodiment of the present invention, statistical features are extracted from the signal including statistical moments of first and second order, e.g.,: a) average signal values over a signal segment, over a signal period or over multiple signal segments and periods, e.g., computed according to  FIG. 5 ,  540 ; b) signal variance over a signal period or over multiple signal segments and periods, e.g., computed according to  FIG. 5 ,  510 ; c) signal correlation over a signal period or over multiple signal segments and periods, e.g., computed according to  FIG. 5 ,  520 . 
         [0034]    In another embodiment of the present invention, new features are calculated based on extracted features from the data, as for example, illustrated in  FIG. 5  by  530 , whereby AM may correspond to amplitude  135 , P M+  may correspond to amplitude  137 , P M−  may correspond to amplitude  140 , and T M  may correspond to amplitude  148  or to another amplitude of interest of another segment of interest in the signal period. The changes in relevant features extracted from the signal from period to signal period and over longer periods of time can be displayed in a simplified manner according to the present invention as shown further herein. 
         [0035]    For example, in one embodiment of the present invention, the values of the signal variance in segment  142  can be displayed and certain changes in the signal variance can be interpreted to reflect medical conditions or specific data acquisition locations in the body. In another embodiment of the present invention, the computed feature according to  530  in  FIG. 5  may be displayed in a simplified manner as illustrated in  FIG. 8 . 
         [0036]    Correspondingly, Graph  100  can be redrawn as illustrated by Graphs  150  through  154 , signal period by signal period by taking into account the relevant features illustrated by Graph  130 . Graph  150  corresponds to the signal period starting at t 0  with its two relevant segments  166  and  168  and its relevant amplitude  167  for segment  166  and amplitude  169  for segment  168 . Similarly, Graph  151  corresponds to the signal period starting at t 1  with its two relevant segments  171  and  173  and its relevant amplitude  172  for segment  171  and amplitude  174  for segment  173 . Graph  152  corresponds to the signal period starting at t 2  with its two relevant segments  176  and  180  and its relevant amplitude  178  and  177  for segment  176  and amplitude  179  for segment  180 . Graph  153  corresponds to the signal period starting at t 3  with its two relevant segments  181  and  183  and its relevant amplitude  182  for segment  181  and amplitude  184  for segment  183 . And Graph  154 , which corresponds to the signal period starting at t 4  with its two relevant segments  185  and  189  and its relevant amplitude  186  and  187  for segment  185  and amplitudes  188  and  190  for segment  189 . 
         [0037]    According to the present invention, graphs  150  through  154  do not need to be displayed at the same time on the same screen but can be displayed one after another on the screen. Tus, a smaller screen can be used to display the data from sequence of Graphs  150 - 154  instead of using Graph  100 . Second, by extracting the relevant features from the patient data in Graph  100  as illustrated by Graph  130 , according to the present invention, only the relevant segments and amplitudes need to be displayed and not all the patient data in Graph  100 . Thus, according to the present invention, a smaller screen can be used to display the data by displaying only the relevant features instead of all the data. As a result, according to the present invention, a) the original sequence of patient data (signal) was compressed, i.e. reduced to a lesser number of relevant elements and b) the time-dependency of the patient data can be displayed in a simplified way in order to allow for the use of a smaller layout and screen real estate. 
         [0038]      FIG. 2  illustrates displaying time-dependent patient data using a simplified time coordinate according to the present invention. The Graphs  150  through  154  from  FIG. 1  are superimposed on the same Graph  200 . In one embodiment of the present invention, graphs  150  through  154  are aligned at a fix point on the display. In one embodiment of the invention, the maximum amplitude  135  in  FIG. 1  is used to align these graphs by always displaying the time of the amplitude  135  at the same location (abscissa) on the screen. 
         [0039]    In one embodiment of the present invention, superimposing graphs on the same screen as illustrated by  FIG. 2  also corresponds to the history of the signal periods, i.e., the graphs corresponding to each signal period are superimposed one behind the other in the order of their temporal moments with the most recent signal period in front. Any number of signal periods from Graph  100  in  FIG. 1  can be transformed into individual graphs as illustrated by Graphs  150  through  154  in  FIG. 1  and then superimposed on the same graph as illustrated by Graph  200  in  FIG. 2 . The Graph  200  illustrates two relevant signal segments  220  and  210  as they have been identified in Graphs  150  ( 166  and  168 ) through  154  ( 185  and  189 ). The corresponding signals and relevant features illustrated in Graphs  150  through  154  from  FIG. 1  are superimposed on Graph  200 . The signal at time moments t 0  through t 4  are represented by  225  in segment  220  and by  215  in segment  210 . The relevant amplitudes are represented by  227  and  228  in segment  220  and by  217  in segment  210 . 
         [0040]    In one embodiment of the present invention, the most recent signal corresponding to signal period at moment t 4  is represented by a full line while the waveforms corresponding to signal periods at prior moments t 0  through t 3  are represented by dotted lines ( 222  in segment  220  and  212  in segment  210 ). Any number of signal periods at any number of moments can be superimposed on the same Graph illustrated by  200 . 
         [0041]    In another embodiment of the present invention, the waveforms corresponding to different signal periods at different moments in time are represented by different colors. In another embodiment of the present invention, the waveforms at more recent moments are presented in brighter (higher intensity) colors while the waveforms at past moments are represented with fading colors such that the most recent waveform has the brightest color. In another embodiment of the present invention, the different waveforms at different moments are represented using different shades of gray. The purpose of this display layout is to emphasize the display on the same display area of the relevant features at the current moment in time, e.g., relevant amplitudes while showing at the same time some history of the waveforms at some previous moments in time. 
         [0042]    In one embodiment of the present invention, the Graph displayed in  FIG. 2  is updated with every new signal period showing the most recent and several past most recent relevant features and waveforms. 
         [0043]      FIG. 3  illustrates one simplified display of patient data according to the present invention. In display  300  only the relevant features extracted from patient data are displayed. In one embodiment of the present invention, relevant amplitudes are displayed for two segments of interest  302  and  304 . In one embodiment of the present invention, the amplitudes at the current moment in time are displayed as full dots,  340  and  345  for segment  304  and  350  for segment  302  respectively. In one embodiment of the present invention, the amplitudes at two previous moments in time are displayed as dotted circles  370  for segment  304  and  375  for segment  302 . 
         [0044]    In one embodiment of the present invention, the dotted line  310  identifies the amplitude of interest  217  from  FIG. 2  or amplitude  135  from  FIG. 1 . In one embodiment of the present invention, the dotted line  320  identifies the amplitude of interest  227  in  FIG. 2  or  137  in  FIG. 1  and the dotted line  330  identifies the amplitude of interest  228  in  FIG. 2  or  140  in  FIG. 1 . In one embodiment of the present invention, the graph displayed in  FIG. 3  is updated with every new signal period and shows the most recent and several past most recent relevant features. 
         [0045]    In one embodiment of the present invention, the levels  355  and  360  represent the average value  148  from  FIG. 1 . In another embodiment of the present invention, the levels  355  and  360  represent another reference value, e.g., the value zero. 
         [0046]      FIG. 4  illustrates another simplified display of relevant features of patient data according to the present invention. The Graph  400  in  FIG. 4  does not show any more the relevant data segments identified by  130  in  FIG. 1 . 
         [0047]    In one embodiment of the present invention, Graph  400  displays only the relevant features as intensity bars. In one embodiment of the present invention, intensity bar  410  represents the amplitude of interest  217  from  FIG. 2 , intensity bar  420  represents the amplitude of interest  227  from  FIG. 2  and intensity bar  430  represents the amplitude of interest  228  from  FIG. 2 . 
         [0048]    In another embodiment of the present invention, an intensity bar represents the value computed according to equation  530  in  FIG. 5 . 
         [0049]    In another embodiment of the present invention, intensity bars represent the value computed according to equations  510  and or  520  in  FIG. 5 . In one embodiment of the present invention, the level of the intensity bar corresponds to the most current value of the relevant feature, value  450  for feature represented by the bar  410 , value  445  for the feature represented by the bar  420  and value  440  for the feature represented by the bar  430 . 
         [0050]    In one embodiment of the present invention, the level  460  represents the average value  148  from  FIG. 1 . In another embodiment of the present invention, the level  460  represents another reference value, e.g., the value zero. In one embodiment of the present invention, markers are used to indicate the maximum maximorum value attained by relevant features in time, e.g., marker  470  for feature  410 , marker  475  for feature  420 . In one embodiment of the present invention, marker  465  indicates the minimum minimorum value attained by feature  430 . 
         [0051]    In one embodiment of the present invention, the intensity bars and the maximum maximorum and minimum minimorum values displayed in  FIG. 4  are updated with every new signal period. 
         [0052]      FIG. 5  illustrates algorithms used to support relevant feature extraction from patient data according to the present invention. In one embodiment of the present Invention, the standard deviation of the signal Sxj is computed according to  510 , whereby n represents the number n of data samples x i  for the j-th signal period, i=1,n. The value  − x represents the average value of the data samples over the j-th signal period  540 . The standard deviation computed according to  510  is a measure of the variations of the signal values around its average value during a signal period. 
         [0053]    In one embodiment of the present invention, the auto-correlation coefficient Cx j,j-1  is computed according to  520  for the signal x at the j-th signal period and at the previous j−1 signal period, whereby n represents the number of data samples x i  for the j-th signal period, i=1,n. The value  −x   j  represents the average value of the data samples over the j-th signal period computed according to  540 . The value −x j−1  represents the average value of the data samples computed according to  540  over the j-1-th signal period, i.e., of the one signal period before the j-th heart cycle. Sx j  is the standard deviation of the signal computed according to  510  for the j-th signal period. Sx j−1  is the standard deviation of the signal computed according to  510  for the j-1-th signal period. In general, the number of samples n for the j-th signal period is different than the number of samples for the j-1-th signal period. 
         [0054]    According to the present invention, n samples are considered for the calculation of both Sx j  and Sx j−1 , whereby n is the number of samples of the j-th signal period. In another embodiment of the invention, the auto-correlation coefficient can be calculated using  520  as Cx j,k , whereby j and k are any two signal periods. This includes the situation in which j=k and the coefficient is calculated for the same signal period. 
         [0055]    In one embodiment of the present invention, the auto-correlation coefficient  520  is used to filter out signal periods very different from one another. It is assumed that, under normal conditions, the signal periods have a certain degree of similarity to each other. In the presence of noise or other artifacts or in case of malfunctions, the signal periods may be very different from one another. The auto-correlation coefficient  520  is used to estimate the degree of similarity between signal periods. A higher auto-correlation coefficient indicates a higher degree of similarity between two signal periods than a lower auto-correlation coefficient. Thus, if the auto-correlation coefficient of two signal periods is below a certain threshold, it can be considered that the two signal periods are weakly correlated or uncorrelated. In such a case, which may occur, for example, due to electromagnetic interference, the two signal periods are excluded from the computation of relevant features. With other words, according to the present invention, only signal periods which have a reasonable degree of similarity are considered for the extraction of relevant features. 
         [0056]    In one embodiment of the present invention, one relevant feature computed from the signal is the sum Σ M  of maximum relevant amplitudes of the signal for each signal period. In one embodiment of the present invention, the sum Σ M  is calculated according to equation  530  in  FIG. 5 , whereby A M  is the maximum amplitude of the signal in the segment of interest  145  in  FIG. 1 , P M+  is the maximum positive amplitude of the signal aligned with the segment of interest  142  in  FIG. 1 , P M−  is the maximum negative amplitude of the signal aligned with the segment of interest  142  in  FIG. 1 , and T M  is the maximum amplitude of the signal aligned to another segment of interest of the signal period, for example with the segment  146  in  FIG. 1 . 
         [0057]    In another embodiment of the present Invention, the sum Σ M  is calculated as: Σ M =A M +P M+ +P M− . 
         [0058]    In another embodiment of the present invention, T M  is the average value of the signal in segment  146  in  FIG. 1  and the value Σ M  is calculated as: Σ M =A M +P M+ +P M− −T M . 
         [0059]    In one embodiment of the present invention, the parameters in  FIG. 5 , i.e., the standard deviation  510 , the auto-correlation  520 , the sum of relevant amplitudes  530 , and the average value  540  are computed for a signal period. In another embodiment of the present invention, the parameters in  FIG. 5  are computed for several consecutive signal periods. In another embodiment of the present invention, the parameters in  FIG. 5  are computed for a fraction of a signal period, e.g., only for an interval/segment of interest within a signal period. 
         [0060]      FIG. 6  illustrates a simplified user interface showing changes in relevant features and tracking history of such changes according to the present invention. Values of a relevant feature are represented on the axis  620 . Such a relevant feature can be any of the relevant features extracted from the patient data as described herein. 
         [0061]    In one embodiment of the present invention, a relevant feature may be an amplitude of interest. 
         [0062]    In another embodiment, a relevant feature may be the sum computed according to  530  in  FIG. 5 . 
         [0063]    In one embodiment of the present invention only one relevant feature is displayed as illustrated by display  600 . 
         [0064]    In another embodiment of the present invention, several relevant features are displayed at the same time on a same screen using one display  600  for each of the relevant features. The level  630  illustrates the reference level of the values of the relevant feature. The icon  605  representing a warning sign is displayed whenever an issue is detected regarding the computation of the value of the relevant feature. In one embodiment of the present invention, a warning sign may be displayed if the auto-correlation coefficient calculated according to  520  in  FIG. 5  decreases below a certain threshold. The warning sign can be displayed in different ways in different embodiments of the present invention. 
         [0065]    In one embodiment of the present invention, an audible warning signal is also generated when a warning signal is displayed. The marker  610  represents the lower acceptable limit of the value range for the values of the relevant feature and the marker  615  represents the upper acceptable limit of the value range. In one embodiment of the present invention, the corresponding marker changes appearance whenever the value of the relevant feature is less than the lower limit or larger than the upper limit, in order to indicate that the value of the relevant feature is outside the acceptable range. 
         [0066]    In one embodiment of the present invention markers  610  and  615  turn yellow whenever the value of the relevant feature is less than the lower limit  610  or larger than the upper limit  615 . A graphical warning signal may be displayed and/or an audible warning signal may be generated according to the present invention whenever the value of the relevant feature is outside the acceptable range. The markers  640  and  650  are history markers. Marker  640  represents the minimum value within the acceptable range, i.e., within the limits  610  to  615 , which the relevant feature has attained during a certain period of time, i.e., the minimum minimorum value. Correspondingly, marker  650  represents the maximum value within the acceptable range, i.e., within the limits  610  to  615 , which the relevant feature has attained during a certain period of time, i.e., the maximum maximorum value. 
         [0067]    In one embodiment of the present invention, the purpose of the markers  660  and  670  is twofold. On one hand, a marker  660  or  670  shows the current value of the relevant feature on the axis  620 . On the other hand, a marker  660  or  670  shows the direction/trend of the change of the value since the last display. 
         [0068]    In one embodiment of the present invention, if the current value of the relevant feature is larger than the previous value, then the marker  660  pointing upwards is displayed at the level of the current value on axis  620 . If the current value of the relevant feature is smaller than the previous value then the marker  670  pointing downwards is displayed at the level of the current value on axis  620 . In another embodiment of the present invention, only the current value of the relevant feature is displayed on the axis  620  without the display of the change/trend. 
         [0069]    In another embodiment of the present invention, the trend analysis of the values of the relevant features takes into account filtering and averaging to allow for a more accurate determination of the trend than by only considering the difference between the current and the previous values of the relevant feature. 
         [0070]      FIG. 7  illustrates one embodiment of the present invention applied to catheter guidance using the electrical conduction system of the heart and one control electrode placed over the manubrium of the sternum. 
         [0071]    In the embodiment of the present invention illustrated in  FIG. 7 , the signal illustrated in  FIG. 1  is a navigation signal computed from the intravascular ECG signal at the tip of the catheter and the skin ECG signal at the control electrode. 
         [0072]    In this embodiment, the segment of interest  142  identified in  FIG. 1  is aligned with the P-segment of the patient&#39;s ECG waveform, the segment  145  identified in  FIG. 1  is aligned with the QRS complex of the patient&#39;s ECG waveform, and the segment  146  identified in  FIG. 1  is aligned with the baseline segment of the patient&#39;s ECG waveform between the T and P segments. The relevant feature displayed on axis  730  of display  700  is the sum Σ M  calculated as Σ M =A M +P M+ +P M− , whereby A M  is the maximum amplitude of the navigation signal in the segment of interest aligned with the QRS complex of the ECG waveform, P M+  is the maximum positive amplitude of the navigation signal aligned with the P-segment of the ECG waveform, and P M−  is the maximum negative amplitude of the navigation signal aligned with the P-segment of the ECG waveform. 
         [0073]    In one embodiment of the present invention, the reference level  720  represents the value of Σ M  when the tip of the catheter is closest to the control electrode. 
         [0074]    In another embodiment of the present invention, the reference level  720  represents the average value  148  of segment  146  in  FIG. 1 , i.e., the average value of the ECG baseline. 
         [0075]    In yet another embodiment of the present invention, the reference level  720  has the value zero, which means that values below the reference level  720  are negative and values above the reference level  720  are positive. The display  715  displays the heart rate in beats per minute computed from the ECG signal period determined from the ECG signal at the control electrode with one of the methods described in  FIG. 1 . The signal period is measured in seconds and the heart rate in beats per minute is computed as one over the signal period and divided by 60. 
         [0076]    In one embodiment of the present invention, the heart rate is calculated for each new signal period. 
         [0077]    In another embodiment of the present invention, the heart rate is calculated as an average value over several signal periods and after exclusion of the uncorrelated signal periods based on the auto-correlation criterion described in  FIG. 5 . 
         [0078]    In one embodiment of the present invention, the icon  710  represents a warning sign displayed whenever an issue is detected regarding the computation of Σ M . 
         [0079]    In one embodiment of the present invention, the warning sign is displayed if the auto-correlation coefficient calculated according to  520  in  FIG. 5  decreases below a certain threshold. The warning sign can be displayed in different ways in different embodiments of the present invention. In one embodiment of the present invention, an audible warning signal is also generated when a warning signal  710  is displayed. 
         [0080]    In one embodiment of the present invention, the icon  705  illustrates a heart on which the cavo-atrial junction is visibly marked. The location of icon  705  on the display  700  at the top of the axis  730  signifies the fact that, the closer the value displayed on the axis is to the icon, the closer the catheter tip is to the cavo-atrial junction. 
         [0081]    In one embodiment of the present invention, icon  725  illustrates the relative location on the axis  730  of values of the navigation signal corresponding to the tip of the catheter in the proximity of the control electrode. With other words, whenever the value Σ M  shown on axis  730  is close to icon  725 , then the tip of the catheter is close to the control electrode. 
         [0082]    In one embodiment of the present invention, the marker  725  turns blue whenever the value Σ M  shown on axis  730  is close to the reference level  720 . In one embodiment of the present invention, a symbol is represented in the color blue indicating the reference level  720 . The marker  735  indicates the lowest acceptable value Σ M  which can be displayed without distortions and the marker  740  indicates the highest acceptable value Σ M  which can be displayed without distortions. All values of Σ M  higher than the marker  740  are represented at the level of marker  740  and all values of Σ M  lower than the marker  735  are represented at the level of marker  735  on the axis  730 . Such situations can happen, for example in the case of inappropriate selection of signal scale and in case of electromagnetic interferences. In such situations, a warning signal  710  is displayed and the user can correct the situation by selecting an appropriate signal scale or eliminating the cause of electromagnetic interference. 
         [0083]    In one embodiment of the present invention, a warning signal  710  is also displayed if the auto-correlation coefficient  520  in  FIG. 5  is below a certain threshold. The marker  745  represents the minimum minimorum value of Σ M  recorded during the course of a catheter placement procedure and the marker  750  represents the maximum maximorum value of Σ M  recorded during the course of a catheter placement procedure. 
         [0084]    In one embodiment of the present invention, initially, i.e., in the beginning of the catheter placement procedure, the values represented by  745  and  750  are zero. For each signal period, a current positive value of Σ M  is compared with the value represented by  750 . If the current value of Σ M  is larger than the value represented by  750  then the value represented by  750  is updated with the current value of Σ M . Thus the value  750  always represents the largest attained value of Σ M . Similarly, for each signal period, a current negative value of Σ M  is compared with the value represented by  745 . If the current value of Σ M  is smaller than the value represented by  745  then the value represented by  745  is updated with the current value of Σ M . Thus,  745  always represents the smallest (or the largest negative) attained value of Σ M . 
         [0085]    In one embodiment of the present invention, the value of Σ M  is represented on the axis  730  as either an upwards pointing arrow as illustrated by  755  or a downwards pointing arrow as illustrated by  760 . The horizontal line of the icons  755  and  760  represent the current value of Σ M  on the axis  730 . The arrow of icons  755  and  760  represent the trend in the change of the value, either from the last update or during a certain period of time. If the arrow points upwards as illustrated by icon  755 , then the current value of Σ M  represents an increase in value compared to a previous value or average value or trend of value change. If the arrow points downwards as illustrated by icon  760 , then the current value Σ M  represents a decrease in value compared to a previous value or average value or trend of value change. 
         [0086]    In one embodiment of the present invention, the markers  755  and  750  are displayed in green in order to indicate a desired trend in the values displayed on axis  730 . In one embodiment of the present invention, the markers  760  and  745  are displayed in red in order to indicate an undesired trend in the values displayed on axis  730 . 
         [0087]    In one embodiment of the present invention markers  740  and  735  turn to yellow whenever the value of the relevant feature is less than the lower limit  735  or larger than the upper limit  740  in order to indicate a warning condition. 
         [0088]    In one embodiment of the present invention, audible signals or sequences of audible signals of different frequencies and intensities are generated when any of the markers  725 ,  735 ,  740 ,  745 ,  750 ,  755  or  760  changes colors. 
         [0089]      FIG. 8  illustrates a simplified user interface showing both time-dependent patient data and the display of relevant features according to the present invention. 
         [0090]    In one embodiment of the present invention, the display  800  contains the following elements: a) a display  810  of a relevant feature using intensity bars as illustrated in  FIG. 4 ; b) a display  820  of patient signals in the simplified format illustrated in  FIG. 2 ; c) a display  830  of a relevant feature showing value tracking and display history as illustrated in  FIG. 6 ; d) a numerical display of patient information  840  as illustrated in  FIG. 7 ; and a warning signal  850  as illustrated in  FIGS. 6 and 7 . 
         [0091]    In one embodiment of the present invention, the elements  810 ,  820 , and  830  of the display  800  represent the same relevant feature. 
         [0092]    In another embodiment of the present invention, the elements  810 ,  820 , and  830  of the display  800  represent different relevant features, e.g., the display  820  represents the patient&#39;s ECG waveforms and their relevant amplitudes, display  830  represents the relevant feature Σ M  as described in 
         [0093]      FIG. 7 , the intensity bar  810  displays the patient&#39;s oxygen saturation, the field  840  displays the heart rate and the warning signal  850  relates to thresholds of the patient&#39;s blood pressure. The display  800  is not a limitation of the present invention and it should be obvious to somebody skilled in the art that other display configurations are possible showing one or several or additional display elements as illustrated in  FIG. 8 . It should be further obvious to somebody skilled in the art that the display elements of the display  800  can refer to different types of patient information than those described herein. 
         [0094]      FIG. 9  illustrates a simplified user interface showing time-dependent patient data in real time and frozen patient data for reference according to the present invention. In certain clinical situations it is needed that the user can compare the currently displayed patient data with patient data displayed at a previous moment in time. 
         [0095]    In one embodiment of the present invention, on display  900  in  FIG. 9 , real time data  910  is displayed in a similar manner as in  FIG. 2 . Frozen data at a previous moment in time is displayed by  920 . 
         [0096]    In one embodiment of the present invention, only the most recent signal period represented by a full line in display  910  is frozen for display by the display  920 . In one embodiment of the present invention, the icon  930  has a twofold purpose. On a touch screen, the icon  930  serves as a Freeze button. Whenever the user taps on the icon  930 , the current data displayed by  910  is copied to the display  920 . The display  920  remains unchanged until the next time the user touches the icon  930  and new data is copied from display  910  to display  920 . Icon  930  serves also to indicate to the user that the data in display  920  is frozen, i.e., it has been acquired at a previous moment in time. 
         [0097]    In one embodiment of the present invention, double tapping on the icon  930  clears the display  920 . In one embodiment of the present invention, the Freeze function illustrated in  FIG. 9  can be achieved by voice control. By pronouncing the word “Freeze”, the user performs the same action as tapping on icon  930 . By pronouncing the word ‘Clear”, the user clears the display  920 . In another embodiment of the present invention, the Freeze function illustrated in  FIG. 9  can be implemented with any display or combination of displays and data as, for example, those illustrated in  FIG. 8 . The illustrations in  FIG. 9  are not limitations of the current invention. It should be obvious to somebody skilled in the art that other types of data and patient information can be presented as a duality of real-time and frozen displays, whereas other icons and voice commands can be used to freeze data and clear the display. 
         [0098]      FIG. 10  illustrates elements of a user interface and methods for user interaction according to the present invention. 
         [0099]    In one embodiment of the present invention, the display  1000  illustrates several display and control elements. 
         [0100]    In one embodiment of the present invention the display  1000  is also a touch screen. In one embodiment of the present invention, relevant features of patient data  1070  are displayed as illustrated in  FIG. 7 . 
         [0101]    In another embodiment of the present invention, relevant features of patient data are displayed as illustrated in  FIG. 8 . Relevant patient information may also be displayed as an alphanumeric field  1025 . Icons, illustrated by  1060 , may be displayed indicating the significance of the relevant features of interest displayed by  1070 . A warning signal  1030  may be displayed as illustrated in  FIGS. 6 and 7 . 
         [0102]    By using the touchscreen function of the display  1000 , in one embodiment of the present invention, a method to scroll the reference level of  1070  up and down on the screen, for example swiping using one finger, is illustrated by  1050 . 
         [0103]    By using the touchscreen function of the display  1000 , in one embodiment of the present invention, a method to increase and decrease the scale for the display  1070 , for example using two fingers, is illustrated by  1052 . 
         [0104]    By using the touchscreen function of the display  1000 , in one embodiment of the present invention, a method to increase and decrease the display update speed (or scroll speed) of display  1070 , for example using two fingers, is illustrated by  1054 . 
         [0105]    In one embodiment of the present invention, by using the reset touchscreen button  1048 , the user can reset to zero the values of the minimum minimorum and maximum maximorum markers of the display  1070 . 
         [0106]    In one embodiment of the present invention, several touchscreen icons are used to navigate different menus and screens of the user interface. Touching or tapping on icon  1046  navigates to the home screen, which in one embodiment of the invention is the display  1000 . Touching or tapping on icon  1044  goes back one step in the navigation path. Touching or tapping on icon  1042  leads to a menu for settings. Touching or tapping on icon  1040  leads to a list of available menus, including a patient information menu. 
         [0107]    In one embodiment of the present invention, touch icon  1005  allows the user to make a phone call while looking at the display  1000 . In one embodiment of the present invention, when the user makes a phone call while displaying display  1000 , the entire display or only the relevant feature display  1070  are duplicated on the screen of the receiving phone. 
         [0108]    In one embodiment of the present invention, the user can receive and pick up a phone call while displaying display  1000  and the entire display or only the relevant feature  1070  are duplicated on the screen of the calling phone. 
         [0109]    In one embodiment of the present invention, button  1020  provides additional methods for the interaction of the user with the device. 
         [0110]    In one embodiment of the present invention, by rotating the button  1020  clockwise or counterclockwise, the user can increase or respectively decrease the scale of the display  1070 . By pulling the button  1020  and then rotating it, the user can scroll up and down the reference level of display  1070 . By pressing the button  1020 , the user can reset to zero the minimum minimorum and the maximum maximorum values of display  1070 . It should be obvious to somebody skilled in the art that other methods and relevant functionality can be implemented using one or several buttons like  1020 . 
         [0111]    In one embodiment of the present invention, icon  1007  illustrates a headphone and is displayed on display  1000  when a headphone is available for user interaction, for example by connecting an external headphone to the jack  1017 . 
         [0112]    In one embodiment of the present invention, the icon  1010  illustrates a microphone and is displayed on display  1000  when a microphone is available for user interaction, for example by connecting an external microphone to jack  1015 . 
         [0113]    In one embodiment of the present invention, if a microphone is available for interaction, a method for the user to interact with the display  1000  is by voice control. In one embodiment of the present invention, the word “Up” increases the scale of display  1070 , the word “Down” decreases the scale of the display  1070 , and the word “Reset” resets to zero the minimum minimorum and maximum maximorum values of display  1070 . 
         [0114]    In one embodiment of the present invention, touch icon  1008  allows the user to take a picture and or make a short movie while displaying display  1000 . 
         [0115]    In one embodiment of the present invention, such a picture or movie are transmitted to a receiving or calling phone if a phone call initiated using icon  1005  is in progress. 
         [0116]    In one embodiment of the present invention, icon  1008  indicates when a camera is available for use with the display  1000 . In the situation in which a camera is available for use, the user can use gestures as a method to interact with the display  1000 . 
         [0117]    In one embodiment of the present invention, waving the hand in front of the camera resets to zero the minimum minimorum and maximum maximorum values of display  1070 . In one embodiment of the present invention, holding two fingers in front of the camera increases the scale of display  1070  while holding one finger in front of the camera decreases the scale of display  1070 . In one embodiment of the present invention, holding the hand in front of the camera sends the relevant display data to a printer, if a printer is connected, for example by Bluetooth. 
         [0118]    In one embodiment of the present invention the display, the interaction elements, and the interaction methods illustrated in  FIG. 10  can be implemented using a cellphone. 
         [0119]    In another embodiment of the present invention the display, the interaction elements, and the interaction methods illustrated in  FIG. 10  can be implemented using a smart watch. In another embodiment of the present invention the display, the interaction elements, and the interaction methods illustrated in  FIG. 10  can be implemented using a head-mounted display. 
         [0120]    In another embodiment of the present invention the display, the interaction elements, and the interaction methods illustrated in  FIG. 10  can be implemented using a Google glass. 
         [0121]    In another embodiment of the present invention the display, the interaction elements, and the interaction methods illustrated in  FIG. 10  can be implemented using other types of mobile and/or wearable devices. 
         [0122]    The illustrations in  FIG. 10  are not a limitation of the present invention. It should be obvious for somebody skilled in the art that other interaction elements, other functions, and other interaction methods can be implemented using the elements illustrated in  FIG. 10 . 
         [0123]      FIG. 11  illustrates a simplified user interface for a head-mounted device according to the present invention. 
         [0124]    In one embodiment of the present invention, the display  1100  is a color 640×360 pixel display. In one embodiment of the present invention, the main display layout  1100  is divided into a left image or column for live information  1110 , a field  1120  for static information, e.g., for frozen data or images, footer for supplementary information  1130 , a menu bar  1140 , and a status bar  1150 . 
         [0125]    In one embodiment of the present invention, the live information field  1110  displays relevant features of patient data as illustrated in  FIG. 10 ,  1070 . 
         [0126]    In another embodiment of the present invention, the live information field  1110  displays relevant features of patient data are displayed as illustrated in  FIG. 8 . 
         [0127]    In one embodiment of the present invention, the static field  1120  displays frozen images and patient data as illustrated in  FIG. 9 ,  920 . 
         [0128]    In one embodiment of the present invention, the footer  1130  for additional information displays warning signs, time stamps, and other relevant information, e.g., the patient&#39;s heart rate as described in  FIGS. 6 and 7 . 
         [0129]    In one embodiment of the present invention, the menu bar  1140  displays items as those described in  FIG. 10 , e.g.,  1040 ,  1042 ,  1044  and  1048  and in  FIG. 9 ,  930 . 
         [0130]    In one embodiment of the present invention, the status bar  1150  shows the current set of data being displayed, progress information for different user interactions, or other information related to system status, e.g., Bluetooth communication. The illustrations in  FIG. 11  are not a limitation of the present invention. It should be obvious for somebody skilled in the art that other screen layouts and the display of other information and control elements are possible. 
         [0131]      FIG. 12  illustrates a head-mounted device and methods for user interaction according to the present invention. In one embodiment of the present invention, a head-mounted device  1200  contains a display or screen  1210 , a front video camera  1220 , a microphone  1230 , a headphone  1240 , a lateral video camera  1270 , battery, processing unit, and other sensors  1250 , and a touchpad  1260 . 
         [0132]    In one embodiment of the present invention the unit  1250  includes a  3  axis gyroscope, a  3  axis accelerometer, an ambient light sensor, and a proximity sensor. In one embodiment of the present invention, the head-mounted device in  FIG. 12  is a Google glass. 
         [0133]    In one embodiment of the present invention, other wireless devices are connected to the head-mounted device, e.g., a Bluetooth printer, a smartphone, or a tablet. 
         [0134]    In one embodiment of the present invention, the method of interaction between an operator and the head-mounted device is optimized for the use by a sterile operator, i.e., for an operator with sterile gloves operating in a sterile filed who cannot touch the head-mounted device. 
         [0135]    In such an embodiment all interaction between the operator and the head-mounted device is based on voice, hand gestures, and head movements. 
         [0136]    In one embodiment of the present invention, the touchpad  1260  allows the user to tap, to slide forward, backward, up, and down, and to swipe up and down. The user can scroll through items displayed on the screen by sliding one finger over the touchpad and select one item and by tapping on the desired item. If the user selects an item like the reference level of the display  1110 , sliding up and down on the touchpad will move the reference level up and down on the display. Swiping down on the touchpad will go back to a previous screen. This action is similar to a back button as illustrated in  FIG. 10 ,  1044 . 
         [0137]    In one embodiment of the present invention, tilting the head down will exit the application. Shaking the head left and right will move through a list of options displayed on the screen, e.g., like the one illustrated in  FIG. 11 ,  1140  and holding the hand in front of a camera will select an item from that list. 
         [0138]    In one embodiment of the present invention, waving the hand in front of the front or lateral camera will freeze an image as in  FIG. 9  or will reset markers as in  FIG. 10  depending on the display mode. Holding two fingers in front of the camera will increase the scale of the signal displayed by  1110  in  FIG. 11  and holding one finger in front of the camera will decrease the signal scale. If in data display mode, holding the hand in front of a camera will send the current data displayed on the display to a connected device, e.g., to a printer, to a smartphone or to a tablet. 
         [0139]    In one embodiment of the present invention, the head-mounted device in  FIG. 12  can be controlled by voice. The word “Up” increases the scale of display illustrated by  1110  in  FIG. 11 , the word “Down” decreases the scale of the display  10110 , and the word “Reset” resets to zero the minimum minimorum and maximum maximorum values of display  1110 . The word “Patient” changes the static display  1120  to a patient information display and the word “Data” changes it back to displaying relevant data. The word “Back” has similar effects like the back button  1044  in  FIG. 10 . In one embodiment of the present invention, the head-mounted device can be taught new voice commands by initiating actions and associating words to them. 
         [0140]    In one embodiment of the present invention, the headphone  1240  is used for audible warning signals generated as described herein, for example in  FIG. 10 . 
         [0141]    The illustrations in  FIG. 12  are not a limitation of the present invention. It should be obvious for somebody skilled in the art that other methods of interaction can be implemented using voice control, hand gestures, head movements and tapping and swiping on the touchpad.