Patent GB-1068828-A (GB)
Title: Perspective vectorcardioscope
IPC: A61B5/04
Filed: 1963-11-08
Abstract: 1,068,828. Cathode-ray tube displays. STANDARD TELEPHONES & CABLES Ltd. Nov. 8, 1963 [Nov. 13, 1962], No. 44170/63. Heading H4T. A perspective view of the trace of a threeco-ordinate vector is produced on the screen of a cathode-ray tube by deflecting the beam in mutually perpendicular directions under the control of signals representative respectively of two of the co-ordinates to trace a continuous line curve whilst employing signals representative of the third co-ordinate to vary the real or apparent thickness of the line curve. This variation is effected either by controlling the tube focusing means to vary the spot size or by the application of spot-wobble of controlled amplitude. The brightness of the trace is controlled to compensate for variations arising from variations in the speed of the beam and is further controlled as a function of the third co-ordinate representative signal to enhance the depth impression created. Additionally, depth reference marks are produced by producing momentary brightness fluctuations. The invention is described as applied to the display of electrocardiographic signals such as those picked up by three pairs of electrodes (1, 2 &c., Fig. 4) placed along mutually orthogonal line position which defines three co-ordinate axes through the heart muscle of a subject under observation. These signals are fed to a connecting unit (8, Figs. 1 and 2) comprising a manually operated switch (Fig. 3) by means of which selective combinations can be effected between the input signals and the ground terminal (7) to provide three-co-ordinate output signals (X<SP>1</SP>, Y<SP>1</SP>, Z<SP>1</SP>) which, in accordance with the switch setting produce a display " looking towards " either the sagittal, frontal or horizontal planes and from either the top or bottom or left or right of such planes. The (X<SP>1</SP> and Y<SP>1</SP>) signals are fed via computing circuits (13), (14) to the X and Y co-ordinate deflection means of the cathode-ray display device (25), the circuits (13), (14) including summing amplifiers (30), (37) having, as additional inputs, quadrature phase carrier oscillations derived from oscillator (64) and amplitude modulated by the signal (Z<SP>1</SP>). The curve is thus traced out as a spiral of varying diameter which varies as the signal (Z<SP>1</SP>) so that the effective width of the trace varies according to the latter (depth) co-ordinate, a typical trace being shown in Fig. 5 (not reproduced). In order to compensate for brightness variations due to the varying speed of movement of the beam the (xl) and (y<SP>1</SP>) co-ordinate signals are differentiated in circuits (55) and (56) and fed via summing amplifier (44) to the brightness control (27) of the display tube. To enhance the depth perspective impressions the brightness is also controlled in accordance with the signal (z<SP>1</SP>) fed to amplifier (44) over line (12a) and additionally, and selectively by a portion of switch (57), by means of short duration pulses (contacts 87, 88) produced respectively on the zero-crossings of the difference between the voltage on conductor (12b) and a manually adjustable voltage on conductor (82) representative of a hypothetical z = o reference plane to produce short duration brightness fluctuations or (contacts 93, 94) by means of signals derived from a flip-flop (92) which produces discrete brightness increases in either the near or distal field. Further perspective impression enhancement is provided by controlling the brightness in accordance with pulses (103) or (104) selected by switch (61) and produced under the control of an oscillator (101) of adjustable frequency such that a " comet-tail " effect during marked intervals results. An embodiment in which the trace thickness variation is produced by varying the focus of the electron beam by means of the z<SP>1</SP> co-ordinate representative signal is described with reference to Fig. 6 (not shown).