Surgery – Diagnostic testing
Reexamination Certificate
1999-10-19
2001-08-14
Kamm, William E. (Department: 3762)
Surgery
Diagnostic testing
C607S019000, C607S020000, C482S008000
Reexamination Certificate
active
06273856
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
This invention relates to monitoring a patient's metabolic need over time, and more particularly to measuring metabolic equivalent (NETS) levels from sensors used in adaptive rate cardiac stimulators including, but not limited to, minute ventilation sensors and accelerometers, whereby patient metabolic equivalent rates and exercise events can be tracked and monitored.
II. Description of the Related Art
In order to measure metabolic equivalents it has been necessary in the past to measure the oxygen uptake (VO
2
) of a patient. This is difficult to do, particularly outside of a laboratory setting, in that it is necessary to have the patient equipped with respiratory monitoring devices, such as a breathing mask and sample tube, a gas analyzer, ekg leads, an electronics module for processing the parameters being monitored, etc.
Some models of calculating metabolic equivalents are based on the patient's intrinsic heart rate, but chronotropically incompetent pacemaker patients, of course, need a different model.
A method is therefore needed to monitor a patient in order to provide a physician with METS data and exertion levels, during the patient's normal living activity, without performing difficult exercise-based, oxygen uptake measurements. The measurements taken are needed to assess the lifestyle, exertion level, exercise capacity, cardiovascular functional capacity, quality of life and wellness of a patient for overall therapy management.
A method is also needed for changing the pacing parameters of a pacemaker based on current METS.
SUMMARY OF THE INVENTION
The invention provides metabolic equivalents data (METS) derived from an accelerometer (XL) and/or minute ventilation sensor (MV) used in rate-responsive pacemakers implanted in patients. Pacemakers commonly used today already have these sensors for providing rate adaption so patients need not be subjected to wearing a breathing mask or other devices to obtain the exertion level data needed to assess their well being.
The data collected is presented to a physician to show rates of excursion and exertion levels experienced by a patient using the pacemaker. The physician can then vary the therapy being provided by, for example, adjusting the pacemaker's rate, AV delay or other programmable quantity accordingly.
The accelerometer and minute ventilation sensor data obtained by the pacemaker can be stored in memory and a microprocessor can be programmed to manipulate the data into forms useful for the physician. Such useful forms include daily maximum exertion levels, average daily exertion levels, moving average exertion levels, exertion levels above a certain threshold, the number of times per day that the exertion levels are above the threshold and the duration of time above a threshold. The diagnostic reports to the physician can be transmitted to the physician and presented as daily, weekly, monthly or yearly data in graphic or tabular form.
The method employed for assessing patient well-being in accordance with the present invention is carried out by implanting in the patient a cardiac rhythm management device having a cardiac depolarization sensor, a physiologic sensor that produces electrical signals proportional to patient activity, a pulse generator for applying stimulating pulses to the heart and a microprocessor-based controller that is coupled to receive the output from the cardiac depolarization sensor along with the electrical signals from the physiologic sensor for producing delta rate signals for the pulse generator. The microprocessor-based controller is equipped with a memory whereby the delta rate signals may be stored for later readout. The microprocessor in the microprocessor based controller, is programmed to compute an average of the stored delta rate signals over a first pre-determined time interval. This average is used as an operand in a linear regression formula whereby a metabolic equivalent (METS) may be computed.
In accordance with a further feature of the invention, the physiologic sensor may be one or both of an accelerometer for sensing body motion and a transthoracic impedance sensor from which a minute ventilation signal can be derived. On a daily or weekly basis the maximum METS value and the average MET value for the interval in question can be computed and stored.
OBJECTS OF THE INVENTION
It is a principal object of the invention to provide a physician with metabolic need, physical activity and lifestyle information about a patient to evaluate the pacing parameters for the patient.
It is another object of the invention to measure and record maximal and average METS for various time periods.
It is yet another object of the invention to provide a method and apparatus for recording maximal MET, average MET, exercise frequency, and duration for storage whereby trended daily or weekly variations can be followed.
It is a further object of the invention to provide ambulatory activity monitoring and assessment in pacemaker patients, especially those suffering from CHF.
It is an object of the invention to improve management of pacing therapy.
It is an object of the invention to optimize rate responsive pacing.
It is still another object of the invention to change pacing therapy based on the MET measurements automatically.
It is an object of the invention to determine a patient's exertion level and exercise capacity.
It is also an object of the invention to monitor a patient to improve his quality of life and wellness.
REFERENCES:
patent: 4702253 (1987-10-01), Nappholz et al.
patent: 4919136 (1990-04-01), Alt
patent: 4926863 (1990-05-01), Alt
patent: 5318597 (1994-06-01), Hauck et al.
patent: 5376106 (1994-12-01), Stahmann et al.
patent: 5976083 (1999-11-01), Richardson et al.
Hopper Donald L.
Jones Bruce R.
Stahl Wyatt K.
Sun Weimin
Cardiac Pacemakers Inc.
Kamm William E.
Nikolai Mersereau & Dietz, P.A.
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