Patent ID: 6044297
Filing Date: 2000-03-28
Classification: A61N

Abstract:
A method of determining the physical posture of a patient's body, having an ideal Y axis, aligned with the superior-inferior body axis, an ideal Z axis aligned with the anterior-posterior body axis, and an ideal X axis aligned with the lateral-medial body said axis in relation to earth's gravitational field comprising the steps of:implanting a multi-axis, solid state sensor in the patient's body, said solid state sensor comprising X, Y, and Z accelerometers having X, Y, and Z device axes, respectively, orthogonally disposed to one another, which provide X, Y, and Z accelerometer output signals, respectively, of a magnitude and polarity dependent on the degree of alignment of the respective axis with earth's gravitational field;in a calibration mode following implantation:measuring a first set of accelerometer output signals from said X, Y, and Z accelerometers while the patient is in a first body posture;measuring a second set of accelerometer output signals from said X, Y, and Z accelerometers while the patient is in a second body posture orthogonal to said first body posture;from said first and second sets of accelerometer output signals, deriving a pitch angle of the Y and Z device axes from the Y ideal axis and the Z ideal axis, respectively, due to rotation of the Y and Z device axes about the X device axis;from said X and Z sets of accelerometer output signals, deriving a yaw angle of the X and Z device axes from the X ideal axis and the Z ideal axis, respectively, due to rotation of the X and Z device axes about the Y device axis; andfrom said X and Y sets of accelerometer output signals, deriving a roll angle of the X and Y device axes from the X ideal axis and the Y ideal axis, respectively, due to rotation of the X and Y device axes about the Z device axis; andin a normal operating mode, determining an unknown body posture of the patient by:measuring the X, Y, and Z accelerometer output signals while the patient is in the unknown body posture;correcting the measured X, Y, and Z accelerometer output signals employing the derived pitch, roll and yaw angles to derive corrected X, Y, and Z accelerometer output signals; anddetermining the body posture of the patient employing the corrected X, Y, and Z accelerometer output signals.