Patent GB-1528197-A (GB)
Title: Cardiac monitor
IPC: A61B5/0452
Filed: 1975-10-08
Abstract: 1528197 Cardiac monitoring HYCEL Inc 8 Oct 1975 [15 Oct 1974] 41212/75 Heading G1N(E) In a system controlled by a digital computer 20 having a memory, for simultaneously monitoring the E.C.G. signals of a plurality of patients PN1-PN8, an averaged cycle taken from over a plurality of initial cycles is stored for each patient. Subsequently, during patient monitoring, each E.C.G. signal cycle is compared with the stored cycle. If any selected charges exceeding pre-set limits are detected an error message is given. The system is also capable of detecting and reporting ectopic beats (e.g. wrongly timed beats &c.) Initially the computer determines the heart beat rate and will only "work" with the patient if the rate is within specified limits. The previously recorded E.C.G. wave of each patient is divided into four sub-intervals Fig. 2 (not shown) in order to note changes in the shape of the wave and uses an auto correlation mask to detect any changes in the wave form. The memory organization of the computer 20 is divided into areas containing an executive program, a plurality of application programs, the working memory and the "patient parameter files". Facility is provided for a "printout" of a histogram of the occurance of ectopic beats during the last 24 hours. The signals from each patient PN1....PN8 are passed via amplifiers 12 on lines 14 to a multi-plexer, sample, and analogue-to-digital converter circuit 16. The circuit 16 samples the analogue values of each of the signals one at a time, 120 times a second and converts each sampled value to a digital value. The digital values are stored until requested by the computer 20 over line 18 where upon the value is delivered via line 22. The output of each amplifier 12 is also applied over lines 24 to a relay control circuit 26 which is controlled by the computer 20 via line 28. The relays are arranged to transmit the same or a different selected signal from the amplifiers 12 to a E.C.G. strip chart recorder 30, or an electro cardioscope 32. The computer can also activate an alarm 34 via the relay control 26. A keyboard 38 is used to enter information and control instructions to the amplifier and a printer 36 provides the data output. Every 3 seconds the computer looks for the presence of any E.C.G. signal absence due to say heart failure or electrode detachment. If this occurs an alarm is sounded. In the event of a "premature" or "late" beat the alarm is just sounded three times then switched off. Also connected to the computer 20 is a unit 44, which includes: a fail safe unit 46 (that actuates an alarm) - a "lights unit" 48 comprising a series of lights that are activated when a patient's heart beat is detected by the computer 20; and a delay memory 50. The delay memory is a series of shift registers responsive to, say, the six most significant bits of the eight bit digit sample values, from a respective one of the eight E.C.G. signals provided over line 54 from the circuit 16. Delay memory 50 is responsive to an internal clock so that each 1/120th of a second the six bit word is shifted a place in the register. Thus when an error is detected the computer routes the contents of the delay memory 50 via the relay control 26 so that the event preceding the error detection can be displayed. The description refers to a series of "words" that when entered on the keyboard will invoke a print out of a particular patient parameter. The description explains at great length the associated flow diagrams Figs. 4-24 (not shown). The reader is directed to the description of the Figures which provides further abridged information of the various functions or measurements facilities performed by the program with its associated flow diagram.