The present invention relates generally to visual display systems. More particularly, the present invention relates to visual displays for physiological waveforms. Even more particularly the present invention relates to enhanced displays for physiological waveforms.
Visual display systems using cathode ray tubes are well known in the electronics art. Additionally, cathode ray tube (CRT) display systems are known for the visual display of various vital sign signals of patients, and particularly for the display of physiological waveforms. In such displays of physiological waveforms it may be desirable to indicate or mark the occurrence of some event relative to the displayed waveform. For instance, in cardioresuscitation systems having a defibrillator capable of operation in a synchronized mode and an accompanying CRT for display of a patient's ECG waveform, it may be desirable to visually indicate to the operator exactly when in the cardiac cycle the discharge of defibrillating energy will occur. Such visual evidence of the sync pulse which times the defibrillator's discharge is reassuring to the operator and permits verification of the correctness of its timing in the cardiac cycle, particularly as related to the so-called vulnerable period of the cycle.
Because of the importance of such event markers which are of usually short duration in the cardiac cycle, it is important that they be highly visible and distinctly displayed on the CRT monitor. Although deflection of the CRT's electron beam, either vertically or horizontally, from the normal trace of the displayed physiological waveform is one possible means of visually marking the occurrence of the particular event relative to the waveform, a marker provided by such technique may be limited in intensity and clarity due to writing speed limitations caused by slew-rate limitations of the circuitry and/or speed limitations of the CRT's phosphor. This problem is particularly evident in "refreshed" or "non-fade" displays in which the data to be displayed is recirculated at a fast rate within a recirculating memory. Such displays may either be stationary or may precess and permit one or more full cardiac cycles of the ECG waveform to continuously appear on the CRT, thereby facilitating the observer's correlation of the event marker with the remainder of the cardiac cycle. In either event, the sweep frequencies of the CRT beam are sufficiently high and the normal circuitry associated therewith sufficiently slew-rate limited that it becomes difficult to rapidly deflect the electron beam from the trace of the waveform with sufficient amplitude to comprise the marker and yet also with the speed needed to prevent significant distortion to the basic waveform. Further, the relatively high writing speed required of such a marker deflection inherently results in a diminished display intensity.
Distortion of the basic waveform may be particularly noticeable in those situations in which the marker occurs on the relatively steep slope of certain types of physiological waveforms, as for instance the R-wave of the cardiac cycle.
Although many of these problems are overcome by changing (increasing) the intensity of the electron beam each time the event marker occurs in the sweep, there may be random increase in intensity at other portions of the waveform trace which prove confusing. For instance, the base line and other portions of the waveform which do not vary rapidly in the vertical direction may normally appear brighter than portions which vary rapidly in the vertical direction.
The aforementioned problems regarding certain types of event markers may be further complicated if markers for different types of events are to be included and must be separately recognizable on the display.
Accordingly, it is a principal object of the invention to provide a system for enhancing the display of physiological waveforms. Included within this object is the provision of means for clearly distinctly, and unambiguously marking events on the displayed physiological waveform.
It is a further object of the invention to provide enhanced display of event markers on physiological waveforms visually displayed by non-fade or refreshed displays employing a cathode ray tube. Included in this object is the provision of an event marker which minimizes distortion of the basic physiological waveform. Still further included within this object is the provision of a clear and distinct event marker occurring during an interval of steep slope in the displayed physiological waveform.
It is a still further object of the present invention to provided enhanced and non-ambiguous display of the event markers associated with different types of events associated with a particular physiological waveform.