WO2007025341A1

WO2007025341A1 - Visual display for blood pressure

Info

Publication number: WO2007025341A1
Application number: PCT/AU2006/001267
Authority: WO
Inventors: Marcus Watson
Original assignee: The University Of Queensland
Priority date: 2005-08-31
Filing date: 2006-08-31
Publication date: 2007-03-08

Abstract

Blood pressure measurements, including systolic and diastolic blood pressure readings (11, 10), are obtained at successive instances in time, and displayed on a visual display. The systolic and diastolic blood pressure readings are displayed. in respective upper and lower portions (5, 6) of the display, and associated systolic and diastolic blood pressure readings are joined by a vertical line (12) on the display. The current reading is displayed graphically relative to at least the previous measurement. Typically, the most current systolic and diastolic blood pressure readings are joined, respectively, to the next previous systolic and diastolic blood pressure readings by lines on the display. Historical measurements (9) may also be displayed. The display preferably includes a temporal indicator indicating how long ago the most current readings of systolic and diastolic blood pressures were taken.

Description

VISUAL DISPLAY FOR BLOOD PRESSURE

FIELD OF THE INVENTION

This invention relates to a method and apparatus for monitoring blood pressure. In particular, but not exclusively, it relates to an improved method of displaying blood pressure readings for both medical professional and lay persons.

BACKGROUND OF THE INVENTION Systolic and diastolic blood pressures are fundamental cardiovascular measurements that can be used to interpret the force driving the perfusion of the body and in part reflects the workload of the heart [I]. There are many different methods for measuring blood pressure, with most measuring devices providing measurements or readings for systolic and diastolic blood pressure in millimetres of mercury (or mniHg). Blood pressure rises and falls with each heartbeat. Systolic blood pressure represents the pressure in the arteries as the heart contracts and sends blood into the circulation, while diastolic pressure represents the lowest pressure to which the arteries are exposed between heartbeats.

There are difficulties in obtaining and interpreting reading of blood pressures as different techniques produce significantly different readings and blood pressure readings can be influenced by environmental or emotional changes. To use systolic and diastolic blood pressure information effectively to interpret patient states, medical practitioners require blood pressure trend information preferably combined with other relevant physiological measures of the patient.

In the operating theatre and other clinical settings, interpreting blood pressure in relation to other physiological parameters can be difficult, especially when using automatic intermittent ^"non-invasive blood pressure (NIBP) measurements. When NIBP measures are used the time elapsed since the last measurement might be unknown, and it is not immediately apparent whether a loss of information is due to failure within the machine or the patient [I].

Blood pressure is most commonly represented using numerical and/or graphical visual displays. There are various proposed integrated data displays that include blood pressure information in a way that shows higher order properties of the patient's state [2]- [7]. These displays may provide complex higher information as well as information about the rates of change of many parameters. They require considerable training and expertise to be able to interpret and require a large number of measured and derived physiological variables.

For example, Blike et al. [5] developed a configural display for hemodynamic monitoring that included five measured variables (HR, BP, CVP, PAP and CO), two derived variables (SVR and SV), and four relationships (MAP-CVP=CO* SVR, CO=HR*SV, LVEDV-PAD, RVEDV-CVP). The cardiovascular (CV) display of Agutter et al. [6] incorporated CVP, PVR, HR, MAP, ST-segment, SV, PAP, LAP, SVR, SaO₂ and CO in a pipe-like image. These configurable displays do not define the relationship between the measured variables, and the derived variables within the shape of the display. Therefore, changes in the shape of the display only indicate abnormality, relying on the anaesthetist to interpret the graphical elements of the display. None of these displays incorporates the relationship between systolic and diastolic blood pressure. Rather they seek to incorporate a range of measured parameters (including invasive parameters such as CVP) that would normally only be available under ICU or operating theatre monitoring conditions. Without information from the full range of measured parameters, these displays cannot work.

It is an aim of the present invention to provide an improved method and apparatus for displaying blood pressure, which overcome or alleviate the limitations and disadvantages of prior art blood pressure visual displays inside and outside medical facilities, or which at least provide the public with a useful choice.

STATEMENT OF THE INVENTION

In one broad form, the invention provides a method of representing or displaying blood pressure of a subject visually, comprising the steps of obtaining information relating to blood pressure readings or measurements at successive instances in time, and displaying the information in two dimensions on a visual display, such that the current measurement is displayed graphically relative to at least the previous measurement. In another broad form, the invention provides an apparatus for representing or displaying blood pressure of a subject visually, comprising display means adapted to receive information relating to blood pressure readings taken at successive instances in time, and to display the information such that the current reading is displayed graphically relative to at least the previous reading. The blood pressure information may comprise arterial or pulmonary arterial systolic, diastolic and/or mean blood pressure measurements, obtained by invasive or noninvasive means. This information, if not already in digital form, is suitably converted to digital form by the signal processing means. Preferably, the current and previous measurements are each displayed or represented as vertical lines, the top point of a vertical line being dependent upon a measurement of systolic blood pressure for a reading and the bottom point of the vertical line being dependent upon a measurement of diastolic blood pressure at the associated reading. In a preferred embodiment, the top and bottom points of the vertical line representing the current reading are joined respectively to the top and bottom points of the vertical line representing the previous reading by straight lines, to thereby form a quadrilateral graphical display. This quadrilateral graphical display will be of rhomboid or trapezoid shape, i.e. a quadrilateral shape with at least two parallel sides. The vertical and straight "lines" mentioned above may be actual or virtual lines.

The term "virtual line" as used herein includes a discontinuous line, an edge or boundary of a shape or coloured portion, or an imaginable line extending between two points.

Preferably, a plurality of historical readings are displayed in addition to the current and next previous readings.

In use, changes in the systolic, diastolic and/or mean blood pressure of the subject are readily conveyed by the quadrilateral display and the historical display. In particular, the current readings of systolic and diastolic blood pressure and most recent historical blood pressure readings comprise the two vertical sides of the quadrilateral to facilitate the detection of changes in blood pressure and the identification of blood pressure related events. The use of lines linking the previous measures of systolic and diastolic blood pressure and the current measure of systolic and diastolic blood pressure allows for blood pressure gestalts to be easily recognised. For example, a large decrease in both systolic and diastolic pressure may indicate rapid blood loss . The use of a temporal indicator to indicate how long ago the most current readings of systolic and diastolic blood pressures were taken is preferably provided to allow the operator to decide how meaningful the information is in relation to other monitors and possible interventions conducted over the elapsed time. Advantageously, the display includes a background comprising coloured or shaded partitioning to indicate nominal blood pressure ranges. ^'

A linear or non-linear scale may be used to identify low, high and normal blood pressure. In one embodiment, systolic and diastolic blood pressure values of the output J signal are mapped to a nine step scale with three steps in the low, normal and high ranges.

Alternative scales for systolic and diastolic blood pressure measurements using a different number of points can also be selected by the operator.

Preferably, the apparatus also includes a user interface means which allows the operator to change the mapping of the systolic and diastolic blood pressure scales, a 0 selection control to select the type of blood pressure represented, for example NIBP or

ART, a selection control to select the length of signal interval, a selection control to select foreground and background colours of the display, and/or a selection control to select the historical information.

The user interface means may be an electronic or electromechanical control means. 5 In order that the invention may be better understood and put into practice, a . preferred embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS 0 Figure 1 illustrates the different visual components of a BP display according to one embodiment of the invention.

Figure 2 shows a modified version of the display of Fig. 1. Figure 3 illustrates the use of a nine point scale on the display. Figures 4 to 8 show some variants on the display of Fig. 1. 5 Figures 9 and 10 illustrate how the display can be implemented for continuous measurements of BP.

Figures 1 1 and 12 show some variants on how the display can be implemented for continuous measurements of BP.

Figure 13 illustrates how the BP display can be positioned on a patient monitor. 0

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Figure 1 illustrates the different visual components of the blood pressure display, including the current values for systolic and diastolic blood pressures, the next most recent readings and historical information. The upper portion 5 of the display represents the

Substitute Sheet (Rule 26) RO/AU systolic measurements while the middle section 6 represents the diastolic measurements.

The associated systolic and diastolic blood pressure readings are joined by vertical lines on the display. The current systolic blood pressure reading is also joined by a line to the next most recent systolic blood pressure reading. Similarly, the current diastolic blood pressure

J reading is joined by a line to the next most recent diastolic blood pressure reading. The current and next most recent systolic and diastolic blood pressure readings are therefore located at the corners of a quadrilateral as shown in Fig. 1.

The background can be divided into strips of contrasting shades or colours representing ranges, to facilitate visual recognition of foreground value. In this example a 0 light background 1 indicates the normal ranges for systolic (top) and diastolic (bottom) blood pressure. The range is consistent for the current and historical measures of systolic and diastolic blood pressure. A dark background 2 indicates the abnormal high and low regions for systolic and diastolic blood pressure; although these could be further differentiated with other shadings or colours. 5 The foreground colour 3, i.e. the colour of the lines, can be set to support visual recognition of foreground position. Blood pressure measurements in abnormal ranges can be reinforced with either a change in the colour of the line link between two corners or the whole foreground shape.

The history information 4 about previous measurements can be represented by a 0 variety of means. The history can include colour coding for measurements taken in abnormal ranges. Column charts should be able to specify width and distance between columns.

The lowest part of the display indicates the time between blood pressure readings and can be distinguished by a different background shading or colour. A temporal display 8 5 indicates the proportion of time elapsed between samples, indicated by either a slider or preset time indicators. In this example, three minutes have elapsed since the last measures of blood pressure were taken, and there is a further two minutes until the next measurements of blood pressure will be calculated.

Figure 2 further illustrates the functionality of the visual components of the blood 0 pressure display. This figure shows an alternative version of the historical information 9 suitable for display with low pixel definition. The lines can be used to compare historical readings with the two most recent readings 11,10 represented in a quadrilateral display, described in more detail below. This display helps the viewer interpret the importance of the current blood pressure measurements. For example a systolic blood pressure changing from the top of the normal range to the bottom of the high range will be interpreted differently depending upon whether the history for the systolic blood pressure was constant in the normal range or fluctuated between the normal and the high range.

As described above in relation to Fig. 1, the systolic and diastolic values for the current (n) measurement of blood pressure are represented by the ends of the vertical line 11. The top of the vertical line 11 indicates the current measurement of systolic blood pressure; in this case the value is towards the top of the normal range for systolic blood pressure. The bottom of the vertical line 11 indicates the previous diastolic blood pressure; in this case the value is in the middle of the low range for diastolic blood pressure. The systolic and diastolic values for the previous (n-1) measurement of blood pressure are represented by the vertical line 10. The top of the vertical line 10 indicates the previous measurement of systolic blood pressure; in this case the value is just below the normal range for systolic blood pressure. The bottom of the vertical line 10 indicates the previous diastolic blood pressure; in this case the value is just above the normal range for diastolic blood pressure.

The top and bottom of line 10 are joined to the top and bottom of line 11, respectively, by lines 12, to form a quadrilateral display. This quadrilateral may be filled in with a different shading or colour.

The slope of the lines 12 connecting the previous blood pressure and the current blood pressure measurements indicate the magnitude and direction of change. In this case the systolic blood pressure has risen substantially, while the diastolic blood pressure has fallen dramatically. The shape and the location of the quadrilateral graphical display against the background colour indicators can be used to identify changes in the patient's blood pressure. Unlike numerical displays, the quadrilateral graphical display allows for the recognition of gestalts such as blood loss.

Figure 3 further illustrates how a nine point scale can be used to indicate blood pressure. The use of a nine point scale allows for significant variations in blood pressures to be identified. Other more or less sensitive scales could be used instead of a nine point scale, for example, a 7 or a 25 point scale could be used. The scales should be provided with a set range and the ability for the operator to define their own range. The use of a different or operator defined range should be clearly indicated, for example by a change in either the foreground or background colour. This prevents other viewers from misinterpreting the blood pressure readings. In Fig 3, a nine point scale 13 is used for the display of systolic and diastolic blood pressure measurements. The top three points 14 indicate abnormally high values for the current systolic blood pressure. The middle three points 15 indicate normal values for the current systolic blood pressure. The lower three points 16 indicate abnormally low values for the current systolic blood pressure. Similar comments apply to the diastolic blood pressure display. The use of three points within the normal range allows for the detection of blood pressure fluctuations.

Figures 4 to 8 show five examples of the blood pressure quadrilateral graphical display, historical information, and time between blood pressure readings layouts. The quadrilateral graphical display may use a solid or in-filled form rather than the quadrilateral outline to indicate that the scale has been altered or in low definition displays where the pixel number is to small to clearly represent the quadrilateral line. Historical information may again use a solid area or a line on low definition displays, or an outline.

Figures 9 and 10 illustrate how continuous measurements of blood pressure can be implemented with a quadrilateral display. The quadrilateral will change every time a measurement of systolic and/or diastolic blood pressure changes from the current range. As these changes may be frequent or infrequent, depending upon the patient and situation, the rate of change is indicated by the temporal display. The temporal display may use a slider 17 to indicate the amount of elapsed time since the last change. The dashed lines, not Used on the actual display, show the amount of the time elapsed on the historical graph indicated by the light shaded slider on the temporal display. If this time exceeds the maximum time, nominally but not limited to five minutes, then the slider stops at the maximum (18), indicating that both systolic and diastolic blood pressure have been constant for a substantial amount of time. Figures 1 1 & 12 show alternative displays that do not use the quadrilateral graphical display, relying on a combination of the current values for systolic and diastolic blood pressure, the historical systolic and diastolic blood pressure and the temporal display 19.

Figure 13 illustrates how the quadrilateral display can be incorporated into a display on a patient monitor (second from top in the column on right). The foregoing describes only some embodiments of the invention and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention.

For example, in the quadrilateral display, the current and next previous readings can be represented only by the endpoints of the lines 1 1,10 so that the display effectively

Substitute Sheet (Rule 26) RO/AU δ consists of the lines 12. Further, the lines need not be solid or continuous, but may be dotted or dashed lines.

REFERENCES

1. Miller, R. (1994). Anesthesia, 4th ed. Churchill Livingstone Inc.

2. Sharp, T.D, Helmicki, A. J., "Application of the Ecological Interface Design Approach to Neonatal Intensive Care", Human Factors and Ergonomics Society, 42nd Annual Meeting, October, 1998.

3. Jungk A, Thull B, Hoeft A, Rau G. (2000). Evaluation of two new ecological interface approaches for the anesthesia workplace. J Clin Monitor Comput. 16(4):243-258. Refs: 45 / Code: ANE; HMI

4. Zhang Y, Drews F, Westenskow D₃ Foresti S, Agutter J, Bermudez J, Blike G, Loeb R. (2002). Effects of integrated graphical displays in situation awareness in anesthesiology. Cognition, Technology, and Work. Berlin: Springer.

5. Blike GT, Surgenor SD, Whalen K, Jensen J. Specific elements of a new hemodynamics display improves the performance of anesthesiologists. Journal of Clinical Monitoring and Computing 2000;16:485-91.

6. Agutter J, Drews F, Syroid N et al. Evaluation of graphic cardiovascular display in a high-fidelity simulator. Anesthesia and Analgesia 2003;97: 1403-13.

7. Syroid ND, Agutter J, Drews FA et al. Development and evaluation of a graphical anesthesia drug display. Anesthesiology 2002,96:565-75.

Claims

1. A method of displaying blood pressure of a subject visually, comprising the steps of obtaining information relating to blood pressure measurements at successive instances in time, and displaying the information in two dimensions on a visual display, such that the current measurement is displayed graphically relative to at least the previous measurement.

2. A method as claimed in claim 1, wherein the blood pressure measurements include associated systolic and diastolic blood pressure.

3. A method as claimed in claim 2, wherein the associated systolic and diastolic blood pressure measurements are displayed in respective upper and lower portions of the display, and wherein the associated systolic and diastolic blood pressure measurements are joined by a line on the display.

4. A method as claimed in claim 3, wherein the upper and lower portions of the display are divided into portions of contrasting shades or colours representing predetermined ranges of measurements.

5. A method as claimed in claim 3, wherein the top and bottom points of a vertical line representing current systolic and diastolic blood pressure measurements reading are joined respectively to the top and bottom points of a vertical line representing the next previous systolic and diastolic blood pressure measurements by straight lines, to thereby form a quadrilateral graphical display.

6. A method as claimed in claim 1, including the step of displaying a plurality of historical measurements in addition to the current and next previous measurements.

7. A method as claimed in claim 1, including the step of displaying a temporal indicator on the visual display to indicate how long ago the most current measurements of systolic and diastolic blood pressures were taken.

8. A method as claimed in claim 1, wherein the blood pressure measurements are mapped to a stepped scale on the display.

9. A method as claimed in claim 8, wherein the scale is a non-linear scale.

10. A method of displaying blood pressure visually, comprising the steps of obtaining readings of both systolic and diastolic blood pressure at successive instances in time, and displaying the information on a visual display, wherein

(i) the systolic and diastolic blood pressure readings are displayed in respective upper and lower portions of the display,

(ii) associated systolic and diastolic blood pressure readings are joined by a line on the display,

(iii) the most current systolic and diastolic blood pressure readings are joined, respectively, to the next previous systolic and diastolic blood pressure readings by lines on the display, and

(iv) a plurality of historical readings are displayed in addition to the current and next previous readings.

11. A method as claimed in claim 10, including the step of displaying a temporal indicator on the visual display to indicate how long ago the most current readings of systolic and diastolic blood pressures were taken.

12. Apparatus for displaying blood pressure of a subject visually, comprising display means adapted to receive information relating to blood pressure readings taken at successive instances in time, and to display the information such that the current reading is displayed graphically relative to at least the previous reading.

13. Apparatus as claimed in claim 12, wherein the blood pressure readings include associated systolic and diastolic blood pressure readings, and the display means includes a screen display divided into upper and lower portions, the associated systolic and diastolic blood pressure readings being displayed in respective upper and lower portions of the screen display, joined by a line.

14. Apparatus as claimed in claim 13 wherein the blood pressure measurements are mapped to a stepped scale on the display, the apparatus including at least one of the following:

(i) a user interface means to vary the mapping of the systolic and diastolic blood pressure to the scale,

(ii) a selection control to select the type of blood pressure represented on the display,

(iii) a selection control to select the displayed length of the interval between readings, and

(iv) a selection control to select foreground and background colours of the display.