PPG measurement

1 . A device comprising:

an optical physiological sensor, wherein the optical physiological sensor comprises a light emitter and a light detector configured to detect the light from the light emitter after it has been attenuated by tissue comprising blood vessels, and the optical physiological sensor is configured to determine the value of a physiological parameter from the detected light; and

a further measurement system configured to determine when the value of the physiological parameter is likely to be reliable, the further measurement system comprising at least one measurement subsystem, each employing a different measurement modality that is also different to a measurement modality used to determine the value of the physiological parameter; wherein

the at least one measurement subsystem comprises a measurement subsystem configured to determine a DC light ratio of a non-varying component of detected light of a first wavelength and a second different wavelength after attenuation by the tissue; wherein

the device is configured to determine an optimum pressure of the device against the tissue using the DC light ratio.

2 . The device of claim 1 , wherein the at least one measurement subsystem comprises at least a first and a second measurement subsystem.

3 . The device of claim 1 , wherein the first wavelength corresponds with green light, and the second wavelength corresponds with red light or infra-red light.

4 . The device of claim 1 , wherein the at least one measurement system comprises a measurement system that includes a capacitive sensor having an electrode configured to come into contact with the tissue.

5 . The device of any of claim 4 , wherein the capacitive sensor comprises a pressure-sensitive capacitive sensor.

6 . The device of claim 5 , wherein the pressure-sensitive capacitive sensor comprises a pair of electrodes and a compressible dielectric sandwiched between the electrodes.

7 . The device of claim 5 , wherein the capacitive sensor comprises a plurality of capacitive sensors, wherein each of the capacitive sensors is disposed at a different location proximate the optical physiological sensor.

8 . The device of claim 1 , wherein the at least one measurement system comprises a measurement subsystem that includes a pressure or force sensor.

9 . The device of claim 8 , wherein the pressure or force sensor comprises a plurality of pressure or force sensors, each disposed at a different location around the optical physiological sensor.

10 . The device of claim 1 , comprising a detector lens between the light detector and the tissue, and an illumination lens between the light emitter and the tissue.

11 . The device of claim 1 , wherein optical physiological sensor comprises a photoplethysmogram (PPG) sensor and/or a pulse oximeter.

12 . The device claim 1 , wherein the light emitter comprises a plurality of light-emitting diodes (LEDs) and/or the light detector comprises a photodiode.

13 . A hat comprising:

an optical physiological sensor, wherein the optical physiological sensor comprises a light emitter and a light detector configured to detect the light from the light emitter after it has been attenuated by tissue comprising blood vessels, and the optical physiological sensor is configured to determine the value of a physiological parameter from the detected light; and

a further measurement system configured to determine when the value of the physiological parameter is likely to be reliable, the further measurement system comprising at least one measurement subsystem, each employing a different measurement modality that is also different to a measurement modality used to determine the value of the physiological parameter;

wherein the hat is configured to retain the optical physiological sensor in contact with the forehead of a patient; wherein

the at least one measurement subsystem comprises a measurement subsystem configured to determine a DC light ratio of a non-varying component of detected light of a first wavelength and a second different wavelength after attenuation by the tissue; wherein

the device is configured to determine an optimum pressure of the device against the tissue using the DC light ratio.

14 . The hat of claim 13 , wherein the hat is sized to fit a neonate.

15 . A method of determining an optical physiological measurement with a photoplethysmography device, comprising:

illuminating a portion of tissue;

detecting light after it has been attenuated by the tissue; and

determining the optical physiological measurement from the detected light;

using at least one further measurement system to determine when the physiological measurement is likely to be reliable, comprising:

determining a DC light ratio of a non-varying component of detected light of a first wavelength and a second different wavelength after attenuation by the tissue; and

determining an optimum pressure of the device against the tissue using the DC light ratio.

16 . The method of claim 15 , wherein the optical physiological measurement comprises a PPG or SpO2 measurement.

17 . The method of claim 15 , wherein using the further measurement system comprises at least one of:

i) using a capacitive sensor to detect proper contact with the tissue;

ii) using a pressure sensor to detect proper contact.

18 . The method of claim 15 , wherein a detector lens is disposed between a light detector and the tissue, and an illumination lens is disposed between a light emitter and the tissue.

19 . The method of claim 15 , further comprising automatically indicating or flagging whether the optical physiological measurement can be trusted in dependence on an output from the further measurement system.