Physiological signal determination of bioimpedance signals
Embodiments relate generally to wearable computing devices in capturing and deriving physiological characteristic data. More specifically, disclosed are one or more electrodes and methods to determine physiological characteristics using a wearable device (or carried device) and one or more sensors. In one embodiment, a method includes determining a drive signal magnitude for a bioimpedance signal to capture data representing a physiological-related component and selecting the drive signal magnitude as a function of an impedance of a tissue. The bioimpedance signal can be applied to electrodes that are configured to convey the bioimpedance signal to the tissue. In some cases, data representing a value a signal-to-noise (“SNR”) ratio may be adapted to form an adaptive signal-to-noise value. A portion of a received bioimpedance signal may be detected, the received bioimpedance signal being based on the adaptive signal-to-noise value. A physiological characteristic can be derived.
1 . A method comprising:
determining a drive signal magnitude for a bioimpedance signal to capture a sensor signal including data representing a physiological-related component;
selecting the drive signal magnitude as a function of an impedance of a sample of a tissue;
driving the bioimpedance signal to one or more drive electrodes that are configured to convey the bioimpedance signal to the sample of tissue;
adapting data representing a value a signal-to-noise (“SNR”) ratio as a function of the impedance of the sample of the tissue to form an adaptive signal-to-noise value;
detecting a portion of the physiological-related signal component from a received bioimpedance signal as the sensor signal based on the adaptive signal-to-noise value; and
deriving a physiological characteristic from the physiological-related signal component.
2 . The method of claim 1 , wherein selecting the drive signal magnitude comprises:
selecting a drive current magnitude.
3 . The method of claim 1 , wherein selecting the drive signal magnitude comprises:
determining a dynamic range of operation based on the impedance of the sample of tissue; and
selecting a drive current magnitude for the dynamic range of operation.
4 . The method of claim 1 , further comprising:
adjusting a gain of a channel based on impedance of the sample of the tissue.
5 . The method of claim 4 , wherein adjusting the gain of the channel comprises:
adjusting the gain of the channel based on the received bioimpedance signal.
6 . The method of claim 1 , wherein detecting a portion of the physiological-related signal component comprises:
extracting the portion of the physiological-related signal component in the time-domain.
7 . The method of claim 1 , further comprising:
determining a state of contact for the drive electrodes and sink electrodes; and
generating data representing the state of contact for the drive electrodes and the sink electrodes.
8 . The method of claim 1 , wherein deriving the physiological characteristic from the physiological-related signal component comprises:
determining a heart rate (“HR”) signal, a galvanic skin response (“GSR”) signals, or a respiration rate (“RR”) signal as the physiological characteristic.
9 . The method of claim 8 , wherein deriving the physiological characteristic from the physiological-related signal component further comprises:
calculating a first value representing a maximal oxygen consumption (“VO2 max”) or a second value representing pulse or blood pressure based one or more of the HR and the respiration signal.
10 . An apparatus comprising:
a wearable housing;
an array of electrodes disposed at a surface of the wearable housing, at least a portion of the array including electrodes configured to either drive a first signal to a target location or receive a second signal from the target location, the second signal including data representing one or more physiological characteristics;
a signal driver configure to apply an adjustable current signal to a subset of the electrodes, a magnitude of the adjustable current signal being a function of an impedance of tissue;
an adaptive signal-to-noise characterizer configured to determine data representing a value of a signal-to-noise ratio for a portion of the second signal including data representing the one or more physiological characteristics, and further configured to adapt the value of a signal-to-noise ratio; and
a physiological characteristic determinator configured to derive physiological signals representative of one or more physiological characteristics.
11 . The apparatus of claim 10 , wherein the one or more physiological characteristics comprise one or more of a heart rate, a respiration rate, a galvanic skin resistance value, data representing an affective state or mode, an amount of energy expenditure and an amount of calories expended.
12 . The apparatus of claim 10 , further comprising:
a drive signal adjuster configured to determine a drive signal magnitude for a bioimpedance signal, and further configured to select the drive signal magnitude as a function of the impedance of the tissue.
13 . The apparatus of claim 10 , further comprising:
an instrumentation amplifier channel processor configured to determine a first gain, and further configured to apply the first gain; and
a physiological channel processor configured to determine a second gain, and further configured to apply the second gain.
14 . The apparatus of claim 13 , wherein the second gain is adapted to amplify a heart rate signal or a respiration signal.