Methods and systems for detecting physiology for monitoring cardiac health
In one aspect, a photoplethysmograph system to measure a user's heart rate includes one or more light-emitting diodes (LED) that provide a constantly-on light signal during a measurement period. The one or more light-emitting diodes are in optical contact with an epidermal surface of the user. The one or more light-emitting diodes emit a light signal into the tissue of the user, and wherein the tissue contains a pulsating blood flow. A light-intensity sensor circuit converts the reflected LED light from the tissue into a second signal that is proportional to a reflected light intensity. The second signal includes a voltage or current signal. A computer-processing module calculates the user's beat-to-beat heart rate from the second current signal.
1. A bioimpedance spectrometer system comprising:
a strap configured to be worn on a user's body;
a bioimpedance circuit on the strap, the bioimpedance circuit comprising:
two current-delivery electrodes configured to convey an alternating current (AC) signal through a user's tissue;
a high-impedance current source circuit that maintains the AC signal within a specified-range;
two sense electrodes configured to detect a differential voltage on the user's tissue;
an amplifier that is configured to measure the differential voltage on the user's tissue between the two sense electrodes, wherein the amplifier is a low power/low voltage amplifier configured to measure a differential voltage across a known resistor that is in series with the two current-delivery electrodes, further wherein the low power/low voltage amplifier comprises a combination of operational amplifiers configured to provide a differential voltage output at a low power and low voltage while operating linearly up to one MHz;
a gain/phase measurement circuit connected to both the amplifier that is configured to measure the differential voltage on the user's tissue and the low power/low voltage amplifier, wherein the gain/phase measurement circuit is configured to determine an amplitude and phase difference between the differential voltage between the two sense electrodes on the user's tissue and the differential voltage across the known resistor; and
a processing module configured to receive input from the gain/phase measurement circuit and to calculate an impedance magnitude or a complex impedance value from the amplitude and phase difference and to determine a relative amount of intracellular and extracellular fluid from the impedance magnitude or complex impedance value.
2. The bioimpedance spectrometer system of claim 1 , wherein the two current-delivery electrodes and the two sense electrodes are in a tetrapolar configuration.
3. The bioimpedance spectrometer system of claim 1 , wherein the amplifier that measures the differential voltage on the user's tissue between the two sense electrodes comprises a combination of operational amplifiers configured to provide a differential voltage output.
4. The bioimpedance spectrometer system of claim 1 , wherein a frequency of the AC current is set to specified frequencies between 1 KHz and 1 MHz.
5. The bioimpedance spectrometer system of claim 4 , wherein the impedance magnitude or complex impedance is calculated at one or more specified frequencies.
6. The bioimpedance spectrometer system of claim 1 , wherein the processing module fits the calculated impedance magnitude or complex impedance to a Cole-Cole plot and extrapolates the real impedance at a direct current (DC) and at an infinite frequency.
7. The bioimpedance spectrometer system of claim 6 , wherein the processing module calculates the impedance magnitude at a low frequency and a high frequency.
8. The bioimpedance spectrometer system of claim 7 , wherein the processing module is configured to determine the relative amount of intracellular and extracellular fluid by comparing the impedance magnitude or complex at both a low and a high frequencies.
9. The bioimpedance spectrometer system of claim 1 , wherein the amplifier that is configured to measure the differential voltage on the user's tissue and the low power/low voltage amplifier are configured to provide input voltages to the amplitude/phase measurement circuit that are between 223 μV to 223 mV.
10. The bioimpedance spectrometer system of claim 1 , wherein the high-impedance current source circuit maintains the AC signal within a specified-range of between 100 μA to 100 mA.
11. The bioimpedance spectrometer system of claim 1 , wherein the processing module comprises a microcontroller.
12. The bioimpedance spectrometer system of claim 1 , wherein the strap is configured to be worn on the user's wrist.
13. A bioimpedance spectrometer system comprising:
a strap configured to be worn on a user's wrist;
a bioimpedance circuit on the strap, the bioimpedance circuit comprising:
two current-delivery electrodes configured to convey an alternating current (AC) signal through a user's wrist;
a high-impedance current source circuit that maintains the AC signal within a specified-range;
two sense electrodes configured to detect a differential voltage on the user's wrist;
an amplifier that is configured to measure the differential voltage on the user's wrist between the two sense electrodes wherein the amplifier is a low power/low voltage amplifier configured to measure a differential voltage across a known resistor that is in series with the two current electrodes, further wherein the low power/low voltage amplifier comprises two high-speed operational amplifiers configured as buffers to maintain high input impedance and a third operational amplifier in a differential configuration such that the low power/low voltage amplifier operates linearly up to one MHz;
a gain/phase measurement circuit connected to the amplifier configured to measure the differential voltage on the user's wrist and the low power/low voltage amplifier and configured to determine an amplitude and phase difference between the differential voltage between two sense electrodes and the differential voltage across the known resistor; and
a microprocessor configured to calculate an impedance magnitude or a complex impedance value from the amplitude and phase difference and determines a relative amount of intracellular and extracellular fluid from the impedance magnitude or complex impedance value.
14. A bioimpedance spectrometer system comprising:
a strap configured to be worn on a user's appendage; and
a bioimpedance circuit on the strap, the bioimpedance circuit comprising:
two current-delivery electrodes configured to convey an alternating current (AC) signal through a user's appendage;
a high-impedance current source circuit that maintains the AC signal within a specified-range;
two sense electrodes configured to detect a differential voltage on the user's appendage;
an amplifier configured to measure the differential voltage on the user's appendage between the two sense electrodes wherein the amplifier is a low power/low voltage amplifier configured to measure a differential voltage across a known resistor that is in series with the two current electrodes, further wherein the low power/low voltage amplifier comprises a combination of operational amplifiers configured to provide a differential voltage output at a low power and low voltage while operating linearly up to one MHz;
a gain/phase measurement circuit connected to the amplifier configured to measure the differential voltage on the user's appendage and the low power/low voltage amplifier and configured to determine a ratio of the differential voltage between two sense electrodes and the differential voltage across the known resistor; and
a microprocessor configured to calculate an impedance magnitude or a complex impedance value from the ratio of the differential voltage across the known resistor and the differential voltage across the known resistor, and determines a relative amount of intracellular and extracellular fluid from the impedance magnitude or complex impedance value.