Blood pressure measurement method
A blood pressure measurement system that non-invasively determines an individual's blood pressure can include a noninvasive blood pressure sensor having an optical sensor and a motion sensor. The optical sensor can provide a photoplethysmograph signal obtained from a patient to a processor. The motion sensor can provide a motion signal to the processor responsive to motion of the patient. In one embodiment, the processor calculates or estimates the blood pressure of the patient based on the photoplethysmograph signal and the motion signal. Advantageously, the system can obtain this blood pressure measurement without an occlusive cuff, thereby reducing patient discomfort. In other implementations, the processor calculates a blood pressure-related parameter from the photoplethysmograph and motion signal. The processor can occasionally trigger an occlusive cuff measurement as this parameter changes, thereby reducing the frequency of occlusive cuff measurements.
1. A method of measuring blood pressure, the method comprising:
obtaining a baseline photoplethysmograph signal from an optical sensor coupled to a measurement site of the patient before a deliberate movement of the measurement site;
obtaining a motion induced photoplethysmograph signal from the optical sensor coupled with the patient at the measurement site that is in motion;
obtaining a motion signal from a motion sensor coupled with the measurement site;
estimating a motion component of the motion induced photoplethysmograph signal responsive to the deliberate movement based at least on the motion signal and the baseline photoplethysmograph signal;
normalizing the motion portion with respect to acceleration and perfusion to generate an output normalized signal;
supplying the output normalized signal into a cuff trigger module to determine whether the output normalized signal exceeds a threshold;
generating a triggering signal to a blood pressure cuff based on the output normalized signal exceeding the threshold;
controlling an operation of the blood pressure cuff in response to the triggering signal; and
calculating, by a hardware processor, a blood pressure based on the normalized motion portion instead of deriving the blood pressure from an estimated plethysmograph portion of the motion induced photoplethysmograph signal and based on the operation of the blood pressure cuff.
2. The method of claim 1 , wherein the motion sensor comprises an accelerometer.
3. The method of claim 1 , further comprising inducing the motion at the measurement site with a motion inducer.
4. The method of claim 3 , wherein the motion inducer comprises a motor.
5. The method of claim 1 , further comprising one or more basis functions to values of the motion portion prior to normalizing the motion portion.
6. The method of claim 5 , further comprising determining weights associated with the one or more basis functions based on a measurement from the blood pressure cuff.
7. The method of claim 6 , where the one or more basis functions comprise both linear and non-linear functions.