Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-04-16
2001-02-13
Jastrzab, Jeffrey R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S028000
Reexamination Certificate
active
06188927
ABSTRACT:
FIELD OF INVENTION
This invention relates to an implantable cardiac stimulation device which monitors a physiologic parameter of a patient's heart to determine stimulation rates, and more particularly to an implantable dual sensor rate-responsive stimulation device that reliably calibrates the rate-responsive sensor and permits automatic calibration post-implant.
BACKGROUND
Implantable cardiac stimulation devices include devices such as cardiac pacemakers, cardioverters, and/or defibrillators. These devices stimulate the heart to maintain a patient's cardiac activity to meet metabolic needs. Originally, pacemakers stimulated the heart at a fixed rate. This did not provide an adequate heart rate based upon changes in the physiologic and metabolic needs of the patient.
It has been recognized that it is necessary to monitor physiologic and metabolic parameters to change the stimulation rate as indicated by the activity and stress levels of the patient. It has also been recognized that there is a need to monitor multiple sensors to determine the indicated stimulation rate.
These sensors can include minute ventilation (also known as minute volume), paced depolarization integral (PDI) (also known as ventricular gradient), QT interval, activity level, activity variance, temperature, oxygen saturation, the inclination of the patient's body, pre-ejection period (PEP), etc.
This invention is drawn towards the sensors which require a baseline measurement, typically at rest, and preferably not during sleep. Such sensors include minute ventilation (also known as minute volume), paced depolarization integral (PDI), QT interval, and pre-ejection period (PEP), oxygen saturation, temperature, among others. Such sensors tend to rely on the integrity of the stimulation lead for proper operation. A few of these sensors also have a tendency to drift out of calibration due to the patient's changing exercise needs, medications, etc.
As a result, a method of calibration is useful for any sensor which is dependent upon lead integrity for proper operation and/or which requires periodic re-calibration. It is also desirable to determine a sleep value, below the alert resting state, to enable patients to achieve a lower pacing rate while sleeping.
The minute ventilation of a patient, for example, is based on tidal volume and respiration rate, which may be detected by measuring the amplitude and rate of a patient's respiration impedance signal. The measurement of minute ventilation is well known (see, for example, U.S. Pat. No. 5,562,712, issued Oct. 8, 1996 to Steinhaus et al., entitled “Minute Volume Rate-Responsive Pacemaker using Dual Unipolar Leads”). Briefly, the impedance signal may be obtained through the use of a controller applying a measuring current between a first electrode and a reference point on the pacemaker, typically the housing, sometimes referred to as the case electrode. The impedance can then be measured, typically, between a second electrode and the reference point. This impedance measurement of the patient varies as a function of the patient's pleural pressure, and therefor the impedance represents the patient's minute ventilation.
U.S. Pat. No. 5,707,398, issued Jan. 13, 1998 to Lu, entitled “Automatic Determination of Optimum Electrode Configuration for a Cardiac Pacemaker” sets forth a stimulation system which recognizes the need to monitor the lead impedance for changes. This system monitors the response of each electrode and then chooses the optimal electrode to monitor and measure the minute ventilation. However, this system does not address the need to test the lead impedance as a condition prior to calibrating the baseline value. Rather, it automatically selects the pair which provides optimal performance.
To calibrate the baseline value of a device employing minute ventilation, the controller must be operating under known conditions, that is, the patient must be at rest and not sleeping. Many sensors can be used to indicate when the patient is at rest and/or in a sleep state; such sensor signals include the activity level, the activity variance, and possibly the inclination of the patient. See, for example, U.S. Pat. No. 5,626,622, issued May 6, 1997 to Cooper, entitled “Dual Sensor Rate-Responsive Pacemaker”, which shows the use of an activity sensor to determine the activity level of the patient. See, for example, U.S. Pat. No. 5,476,483, to Bornzin et al., entitled “System and Method for Modulating the Base Rate During Sleep for a Rate-responsive Cardiac Pacemaker”, which shows the use of activity variance to determine if the patient is at rest or sleeping.
Accordingly, it is desirable to develop an implantable cardiac stimulation device which can perform an enhanced calibration of its baseline level upon implantation (i.e., by performing a self-test of the lead system and verifying that the patient is at a suitable resting state) and to automatically and periodically recalibrate the baseline at appropriate intervals to ensure the correct stimulation rate may be determined for the patient.
SUMMARY OF THE INVENTION
The present invention is directed toward an implantable rate-responsive stimulation device that reliably calibrates the rate-responsive sensor at rest, both at implant and automatically post-implant.
To this end, the present invention is directed toward any physiological sensor that must have a baseline value that needs to be calibrated at rest and uses a properly functioning implantable lead to detect a physiological parameter of the heart. While the preferred embodiment is directed toward a minute ventilation sensor, other sensors may include the paced depolarization integral (PDI), QT interval, pre-ejection period (PEP), oxygen saturation, etc.
To insure the optimal stimulation rate, the cardiac pacemaker must know the baseline value of the physiological sensor corresponding to a resting state. Accordingly, the baseline value is typically measured at implant when the patient is observed to be resting.
As set forth above, physiological sensors must be periodically re-calibrated due to patient changes and lead changes such as medication changes, lifestyle changes, lead aging, lead dislodgment, etc.
To reliably calibrate the baseline value at rest, the controller of the present invention determines if the patient is at rest using a second sensor, such as an activity sensor or any additional sensor which is not being calibrated. Since the rate-responsive sensor is of the type that relies on a functioning lead, the controller also determines if the lead impedance is within normal limits indicating a properly functioning lead system. If the lead impedance is within normal limits and the patient is at rest, the controller measures a current sensor value and stores such measurement as the baseline.
The present invention further contemplates measuring a sensor value during the sleep state to permit a lower pacing rate during sleep.
Accordingly, in another embodiment, calibration may be performed with sleep as the baseline value, adjusting, mapping or taking a second calibration to determine an appropriate value for the resting state.
Finally, the present invention contemplates a method of reliably calibrating the baseline value by confirming that the patient is at rest (e.g., “alert-resting” or sleeping) and performs a lead impedance test to prevent an automatic calibration with a defective lead.
REFERENCES:
patent: 4399820 (1983-08-01), Wirtzfeld et al.
patent: 4644954 (1987-02-01), Wittkampf et al.
patent: 4759366 (1988-07-01), Callaghan
patent: 4865036 (1989-09-01), Chirife
patent: 4867163 (1989-09-01), Shaldach
patent: 5076271 (1991-12-01), Lekholm et al.
patent: 5154171 (1992-10-01), Chirife
patent: 5303702 (1994-04-01), Bonnet et al.
patent: 5476487 (1995-12-01), Sholder
patent: 5562712 (1996-10-01), Steinhaus et al.
patent: 5626622 (1997-05-01), Cooper
patent: 5707398 (1998-01-01), Lu
patent: 5755740 (1998-05-01), Nappholz
patent: 5941904 (1999-08-01), Johnston et al.
patent: 6044297 (2000-03-01), Sheldon et al.
Adinolfi David W.
Lu Richard
Jastrzab Jeffrey R.
Pacesetter Inc.
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