Surgery – Diagnostic testing – Detecting muscle electrical signal
Reexamination Certificate
2000-05-09
2002-06-25
Jastrzab, Jeffrey R. (Department: 3762)
Surgery
Diagnostic testing
Detecting muscle electrical signal
C128S204230
Reexamination Certificate
active
06411843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to detection of an EMG signal and, more particularly, to a method and apparatus that produces a model diaphragm EMG signal, which can be utilized, for example, to monitor the condition of a patient and/or synchronize the operation of a ventilator to the breathing cycle of a patient.
2. Description of the Related Art
Ventilators used to promote the exchange of air in the lungs of a patient are well-known in the art. Ventilators operate by urging air into the lungs of the patient during inhalation and by terminating urging air into the patient's lungs during exhalation. In a normal patient, the inhalation and exhalation of air into and out of the lungs are accomplished by activation and relaxation of the patient's respiratory muscles, and, in particular, the diaphragm muscles, which contract and relax in response to a signal from the phrenic nerve. The activation of the diaphragm produces an electromyographic (EMG) signal and, more particularly, a diaphragm EMG signal, that can be measured. This diaphragm EMG signal is generally representative of the respiratory effort generated by the patient during each breath cycle.
The diaphragm EMG signal can be used for a variety of purposes, from monitoring the respiratory function of the patient to controlling a ventilator that assists the patient in breathing. For example, in general, some conventional ventilators operate on the principle that each inhalation by a patient has the same interval. Accordingly, if the interval of the patient's diaphragm EMG signal during inhalation is longer or shorter than the inhalation interval of the ventilator, the ventilator will provide to the patient more or less air, respectively, than the patient desires, with corresponding patient discomfort.
Conventional ventilators have attempted to utilize a measured EMG signal, and, in particular, the measured diaphragm EMG signal to control the supply of air or other breathing gas to the lungs of the patient. However, because the measured EMG signal contains the patient's diaphragm EMG signal, an electrocardiogram (ECG) signal, and other noise, such as noise due to movement between sensing electrodes and tissue of the patient during breathing, difficulties are encountered in synchronizing the operation of the ventilator with the diaphragm EMG signal of the patient.
A variety of techniques has been utilized to suppress or eliminate the contribution of an ECG signal and noise from the measured EMG signal to obtain a model of the EMG signal, i.e., a “clean” EMG signal, such as a clean diaphragm EMG signal, which corresponds to the EMG signal that is produced directly by the diaphragm. One conventional technique for producing a clean diaphragm EMG signal includes clipping the top of the QRS complex of the measured EMG signal. However, this technique is unsatisfactory because it leaves the majority of the QRS complex and may introduce new artifact harmonics to the frequency spectrum. Another technique includes replacing, for the duration of each QRS complex of each ECG cycle, the measured EMG signal with the value of the measured EMG signal recorded immediately prior to that QRS complex. A problem with this technique is that it leaves the remainder of the ECG cycle, which includes most of the low frequency power. In another conventional technique, computerized processing is utilized to subtract an ECG signal obtained during relaxation from the measured EMG signal. A problem with this technique is that the ECG signal will vary with effort, due to changes in both heart rate and recording conditions, which introduces artifacts. In yet another technique, the EMG signal is sampled between one T wave and a subsequent QRS complex. Such recordings have been utilized in spectral analysis of human diaphragm EMG signals. A problem with this technique is that the measured EMG signal is not sampled between the Q wave and the T wave of each ECG cycle thereby omitting relevant information.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a method and apparatus for separating a model EMG signal from a measured EMG signal that overcomes the shortcomings of conventional EMG detection/analysis techniques. The model EMG signal can be used to monitor the condition of the patient. In the case of a diaphragm EMG signal, the model diaphragm EMG signal can be utilized, for example, to synchronize the operation of a ventilator and the breathing cycles of a patient.
This object is achieved according to one embodiment of the present invention by providing a method of producing a model EMG signal from a measured EMG signal that includes a patient's EMG signal and an ECG signal. The method includes processing the measured EMG signal to produce a logic signal that is in a first binary state in the absence of a P wave, a QRS complex, and a T wave of an ECG cycle of the measured EMG signal and in a second binary state during at least one of the P wave, the QRS complex, and the T wave of the ECG cycle. The measured EMG signal is processed to produce a first envelope signal. The model EMG signal is produced as a function of (1) the first envelope signal when the logic signal is in the first binary state and (2) the absence of the first envelope signal when the logic signal is in the second binary state.
An exemplary embodiment of the present invention contemplates that processing the measured EMG signal to produce the logic signal includes processing the measured EMG signal to produce a second envelope signal, and processing the second envelope signal to produce a fast signal. An exemplary embodiment of the present invention also processes the second envelope signal to produce a first slow signal having a slew rate that is slower than the slew rate of the fast signal. The method of the present invention processes the fast signal and the first slow signal to produce the logic signal.
An exemplary embodiment of the present invention also contemplates that processing the measured EMG signal to produce the first envelope signal includes high pass filtering the measured EMG signal to produce a high pass signal and rectifying the high pass signal to produce a rectified signal. The rectified signal is low pass filtered to produce the first envelope signal.
Producing the model EMG signal includes, in one embodiment of the present invention, providing a moving average of the first envelope signal when the logic signal is in the first binary state, and providing, when the logic signal is in the second binary state, a set value that corresponds to a value of the moving average of the first envelope signal when the logic signal changes from the first binary state to the second binary state.
A further embodiment of the method for separating a model EMG signal from a measured EMG signal according to the principles of the present invention contemplates processing the second envelope signal to produce a second slow signal having a slew rate that is slower than the slew rate of the fast signal, and processing the fast signal, the first slow signal, and the second slow signal to produce the logic signal.
The present invention also contemplates that the step of producing the model EMG signal includes continuously processing the measured EMG signal to produce a third envelope signal. When the logic signal is in the first binary state, a moving average of the first envelope signal is preferably provided. When the logic signal is in the second binary state, a moving average of the third envelope signal is provided.
It is another object of the present invention to provide an apparatus for producing a model EMG signal from a measured EMG signal, which includes a patient's EMG signal and ECG signal, that does not suffer from the disadvantage of conventional EMG signal generating devices. This object is achieved according to the principles of the present invention by providing an apparatus that includes a logic signal processing means for processing the measured EMG signal to p
Haas Michael W.
Jastrzab Jeffrey R.
Respironics Inc.
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