Patent GB-1438694-A (GB)
Title: Method and apparatus for producing a visible contour plot
IPC: G06F3/153
Filed: 1973-09-25
Abstract: 1438694 Electrical measurements GENERAL ELECTRIC CO 25 Sept 1973 [27 Sept 1972] 44918/73 Heading G1N [Also in Division H4] A cathode ray tube oscilloscope (or other display device) displays a plurality of physiological parameters as a contour plot. Each parameter is represented by one of a plurality of equiangularly spaced vectors which radiate from the centre of the display the ends of the vectors being connected by a trace which, when the parameters are normalized, (all vectors of equal length) forms a circle so that a change in one or more of the parameters results in a readily observable change in the contour. Alternatively, the contour, initially, may be other than circular (e.g. indicative of the ideal parameters for a patient in a particular condition) so that parameter changes are manifest by a change towards circularity. Upper and lower limits for each parameter are also displayed. In the described embodiment, which is concerned with the display of eight parameters (measured by known means in association with a patient) on a cathode ray tube oscilloscope (21) Fig. 1 reference (fiducial) lines 1-8, which may be inscribed on the face of the tube or on a transparent mask in front of the face or may be generated electronically by the beam, divide the contour into eight sectors (octants) and associated with each line upper and lower limit, adjustable markers 23, 24 are generated electronically by the tube beam. The beam is also employed to generate the parameter identifying legends which, as shown, comprise: HR = Heart Rate; MABP = Mean Arterial Blood Pressure; MVBP = Mean Vanous Blood Pressure; CO = Cardiac Output; pO 2  = Blood Oxygen Partial Pressure; pCO 2  = Carbon Dioxide Partial Pressure; RR = Respiratory Rate and PVC = Premature Ventricular Contractions per min. When one or more of the parameters change from their normalized value(s) the display may take the form shown in Fig. 3 and where any of the parameters exceed the pre-set limits the relevant octant, limit markers and parameter identifying legend is "blinked". When some parameters are not being monitored the octant portion of the contour for such parameter(s) is produced in dashed line form as shown in Fig. 5. The display may be renormalized (to produce a circular contour) with existing parameter values so that changes in the latter are more readily discerned, the time of such renormalization being indicated on a panel 25 and elapsed time since renormalization indicated on a panel 26. In the general operation of the arrangement circuitry Figs. 2, 4 and 6 to 15, (none shown), acts to subtract initially selected digital parameter values PN, i.e. normal (standard) physiological values, from the measured values P(t). Thus, in respect of each parameter the quantity [P(t)-PN] is formed and in order to improve the contour "distortion sensitivity" of the display, i.e. to ensure that a significant vector length change occurs in response to a given change in parameter value, the above quantity is multiplied by a factor K, unique to each parameter. Thus the expression K[P(t)-PN] is formed for each parameter and to this a constant value RN equal to a predetermined vector (radius) length for a normalized circular contour trace is added to produce a beam deflection control signal K[P(t)-PN] + RN. The limit values are processed in a similar manner to produce a composite beam deflection control signal which is then integrated and modulated by sine and cosine waveforms to provide the actual beam deflection signals for application to X and Y beam deflection control elements. Alternatively, high-speed printers, chart recorders &c. may be employed. In an alternative arrangement the various parameter and limit values are computed as "video" signals and employed for intensity control of a line scanned raster Figs. 16 and 17 (neither shown).