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This invention relates to pacemaker programmers, and more particularly to a pacemaker programmer which can be operated by a patient.
A typical present-day programmable cardiac pacemaker can be programmed by a physician to assume any one of a number of states. Toward this end, the physician utilizes a pacemaker programmer which transmits electromagnetic energy in the form of coded pulses through the patient's body, pacemaker detecting circuitry responding to these pulses and setting the pacemaker state in accordance with the transmitted code. Several different functions usually can be controlled.
For example, a typical pacemaker marketed by the assignee of this application can be programmed to pace at any one of eight different rates (60, 65, 70, 75, 80, 85, 90, 100 and 110 pulses per minute). The pacemaker can also be set to generate pulses at either a high or a low level (5.2 or 2.6 volts). Lastly, the pacemaker can be set to operate in any one of three modes. In the ventricularinhibited mode (also known as "demand" operation), a pacemaker pulse is generated only when the heart fails to beat spontaneously within a predetermined time interval subsequent to the last beat. In the synchronous mode, the pacemaker operates in the same way to generate a stimulating pulse whenever the heart fails to beat, but a pulse is also generated whenever the heart does beat spontaneously, the pacemaker pulse thus "reinforcing" the spontaneous beat. In the asynchronous mode, the pacemaker beats at a fixed rate independent of spontaneous heart activity.
With eight possible rates, two possible pulse levels and three possible modes, it is apparent that theoretically the pacemaker can be operated in any one of fortyeight different states. The physician programmer is capable of controlling any one of these states. (As will become apparent below, some combinations of mode and rate are not allowed, so there are actually fewer than forty-eight states). Over extended periods of time, it may be necessary for the physician to change the value of one, two or even all three of the rate, mode and level parameters which characterize pacemaker operation. (As used herein, even mode is considered a pacemaker "parameter" and the mode setting is considered a "value".)
But it may be desireable for the patient to have his pacemaker state changed more often. For example, the physician might feel that different rates are advisable when the patient is sleeping' and when he is awake. Even when he is awake, it might be preferred to have two different rates depending upon whether the patient is exercising or not. It is not feasible, of course, to have the patient visit his doctor several times a day in order to have the state of his pacemaker changed.
It is just as impractical, and probably dangerous, to provide the patient with a programmer of the type used by the physician. Present-day programmers are too complex for patient use, and they require the exercise of clinical judgment. Moreover, if the patient sets the programmer erroneously, the mistake could be fatal.
It is a general object of our invention to provide a pacemaker programmer which can be operated by a patient to control his pacemaker to meet varying requirements, but without requiring the patient to make
clinical decisions or allowing him to make critical mistakes.
In accordance with the principles of our invention, the patient is given a programmer which can control
5 state selection from only a limited number of states; these states comprise a sub-set of the set under control of the physician. The patient programmer may be designed to change the values of less than all of the parameters under control of the physician. For example, in the
10 illustrative example of the invention, the patient programmer cannot control a change in the mode of operation or the pulse level; only the pacemaker rate can be changed. Furthermore, rather than to allow the patient to select from all of the values associated with a parame
15 ter under his control, he may be limited to only a sub-set of them. In the illustrative embodiment of the invention, the patient programmer can select from only three of the eight rate values under control of the physician. Whether the patient programmer is limited in the
20 number of parameters which can be changed, or the number of values associated with any particular parameter, or both, the net result is the same—the patient can control his pacemaker to change to a state selected from only a sub-set of the set of states under control of the
25 physician. (While present-day programmable pacemakers and programmers operate with discrete parameter values, the principles of our invention are equally applicable to systems in which parameter values can be adjusted over continuous ranges.) In a sense, our invention
30 is not just a programmer which can control a number of states less than the number under control of the physician programmer. What is really involved is a system which includes not only the patient programmer, but also the pacemaker itself and the physician program
35 mer. To a conventional "set" of a pacemaker and a physician programmer, we add a patient programmer which is characterized by being capable of controlling a plurality of states which is a sub-set of those which characterize the pacemaker and the physician program
But there are two practical problems in implementing such a system. The first pertains to the number of patient-operated programmers which might have to be made available. Consider a pacemaker which can as
45 sume any one of forty-eight possible states. Suppose that the patient programmer is to control changes among only three states. Since there are 17,296 different combinations of three states from a total of forty-eight, it is apparent that for maximum flexibility (while at the same
50 time limiting patient state selection), an inordinate number of patient programmers would have to be kept in stock. Even if it is assumed that only the rate parameter will be under control of the patient, that is, he will be allowed to select from only three of the eight possible
55 rates under control of the physician, since any given patient may require a different sub-set of three rates, there is still a substantial problem in stocking patient programmers. There are 56 different combinations of three rates from a total of eight, and it is just not practi
60 cal to stock so many different types of patient programmers.
The other practical problem is that most patients just cannot be relied upon to select correct values of mode, rate and pulse level depending upon momentary re65 quirements, even if the choice is limited. For example, if the patient programmer can select from only three rates, e.g., 65, 75 and 90 pulses per minute, it would be dangerous to expect the patient to remember that it is
the highest rate which should be selected for exercise. In a moment of confusion, prior to exercise the patient might actually select the slowest pacing rate.
In the illustrative embodiment of our invention, in which the patient programmer cannot control a change 5 in pulse level or mode, and can permit a selection from among only three of eight possible rates, there is no need to stock 56 different patient programmers. Only one is required. The unit includes switches which can be set by the physician to select the three rates which 10 will be under patient control. These switches are internal to the unit and a cover plate must be unscrewed in order to obtain access to them. There is thus little danger that the patient will control any pacing rate other than the three pre-selected by the physician (unless he 15 deliberately unscrews the cover plate and changes the switch settings, against orders).
This is not to say that the manufacturer should never provide pre-wired patient programmers. In those cases where a particular sub-set of states is to be pre-selected 20 for a large number of patients, it may be desirable to provide a "fixed" patient programmer, with a "physician programmable" patient programmer being provided for the more unusual cases.
The patient programmer includes a slide switch 25 which allows the patient to select one of the three rates pre-selected by the physician. But the actual rate values are not labeled on the unit. Instead, the labels associated with the slide switch represent day-to-day physiological requirements. In lieu of labeling the three positions of 30 the switch 65, 75 and 90 pulses per minute (or any other values pre-selected by the physician), the indicia may be "sleep", "awake" and "exercise". This has two main advantages. First, there is no need to provide different numerical indicia depending upon the three rate values 35 pre-selected by the physician. Second, and more important, while the patient may get confused as to which rate applies to which function, he certainly cannot be confused by the three words; he knows whether he is going to sleep, whether he has just awakened, or 40 whether he is about to begin exercising.
In other respects, the patient programmer is similar to the conventional physician programmer, although some options may be omitted (e.g., physician programmers can often actually monitor the pacemaker rate, but this 45 feature is not included in the patient programmer of the illustrative embodiment of the invention.) The patient programmer operates in the same range as the physician programmer, up to 30 mm from the pacemaker. It is powered by re-chargeable batteries, and code transmis- 50 sion is inhibited if the battery charge is depleted. Auditory and visual signals are provided to indicate whether code transmission has taken place.
Further objects, features and advantages of our invention will become apparent upon consideration of the 55 following detailed description in conjunction with the drawing, in which:
FIG. 1 depicts the overall configuration of a typical prior art physician programmer;
FIG. 2 depicts the type of control panel to be found 60 on a prior art physician programmer (similar to but not exactly that of the Telectronics 173 Programmer);
FIG. 3 depicts schematically a prior art programmable pacemaker, such as those marketed by Telectronics Proprietary Ltd.; 65
FIG. 4 is a chart which will be helpful in understanding the coding scheme used in the illustrative embodiment of the invention;
FIGS. 5-7 depict several views of the patientoperated pacemaker programmer of the illustrative embodiment of our invention;
FIG. 8 is a cross-sectional view through the coil included in the patient programmer of FIGS. 5-7;
FIGS. 9-11 are a schematic of the circuit of the patient programmer, with FIG. 12 illustrating the arrangement of the three figures; and
FIG. 13 depicts an alternative form of switch which can be used in the patient programmer to allow the physician to pre-select parameter values.
A conventional physician programmer is shown in FIG. 1. The actual circuitry of the physician programmer need not be understood for an understanding of the present invention. Rather, it is only necessary to understand what it is that the physician programmer controls. Physician programmers per se are well known in the art.
When used, the physician holds the programmer with protrusion 35, the coil pod, on the patient's chest over the pacemaker. When a button (not shown on either FIGS. 1 or 2) is pressed, a series of current pulses flow through the coil and generate a pulsating electromagnetic field. This field pulses a relay in the pacemaker, to be described below. On FIG. 1 there can also be seen a jack for connecting a charging circuit, in order to recharge the internal batteries.
FIG. 2 depicts the face of the physician programmer. Rate switch 26 is an eight-position switch which is set by the physician to select one of the eight labelled rates. Another switch 24 is used to select both the mode of operation desired of the pacemaker and the pulse level. Label 22 indicates two possible modes, synchronous and asynchronous, and two possible pulse levels for each, the label thus identifying four of the eight positions of switch 24. Label 20 represents the third mode of operation, as well as the two pulse levels. (Two switch positions are provided for each of the high and low levels in the ventricular-inhibited mode simply because an eight-position switch may be used and there are only six combinations of mode/level values.)
When a program button (not shown) is depressed, the appropriate code transmission takes place, as will be described below. An audio tone is also heard in order that the physician be made aware that the programmer has operated. Indicator 14, labeled "Invalid", flashes whenever the program button is depressed in order to further inform the physician that the unit has operated. There are certain invalid combinations of parameters, namely, synchronous mode together with one of the three highest rates. (There are thus fewer than the 48 possible states discussed above.) In the event an invalid combination has been selected, indicator 14 does not flash and instead it remains illuminated to indicate that programming has not taken place. Indicator 12, labeled "Charge", is illuminated whenever the programmer is being charged. It flashes whenever re-charging is necessary.
The physician programmer can also be operated in a monitor mode by depressing a monitor button (not shown). If the coil pod is positioned near the electrode path, the stimulation rate, in pulses per minute, appears in window 16. Indicator 18 flashes whenever a pacemaker pulse is detected.
With two eight-position switches being provided, it is apparent that 64 different codes are possible. But because there are in actuality only six different mode/level combinations which can be set by switch 24, one