Optical sensors for use in vital sign monitoring
The invention provides a body-worn system that continuously measures pulse oximetry and blood pressure, along with motion, posture, and activity level, from an ambulatory patient. The system features an oximetry probe that comfortably clips to the base of the patient's thumb, thereby freeing up their fingers for conventional activities in a hospital, such as reading and eating. The probe secures to the thumb and measures time-dependent signals corresponding to LEDs operating near 660 and 905 nm. Analog versions of these signals pass through a low-profile cable to a wrist-worn transceiver that encloses a processing unit. Also within the wrist-worn transceiver is an accelerometer, a wireless system that sends information through a network to a remote receiver, e.g. a computer located in a central nursing station.
1. An optical sensor configured to be worn on a patient's finger and determine an optical signal indicative of a photoplethysmograph waveform, the sensor comprising:
a flexible housing configured to wrap around a portion of the base of the patient's thumb and position over the interior base of the thumb proximate to the princeps pollicis artery, the flexible housing comprising (i) a first light source that emits optical radiation, wherein the first light source comprises a first substantially planar surface, (ii) a photodetector configured to detect the optical radiation and to generate the optical signal, wherein the photodetector is positioned on a substrate comprising a second substantially planar surface, and (iii) a plurality of living hinges, the first and second substantially planar surfaces are supported by the flexible housing such that the first substantially planar surface is separated from the second substantially planar surface by an included angle between 35-55 degrees, wherein the included angle is an angle formed between a first line drawn parallel to the first substantially planar surface and a second line drawn parallel to the second substantially planar surface, wherein the flexible housing is an approximately semicircular housing with the plurality of living hinges radially spaced apart from each other along a circumference of the approximately semicircular housing.
2. The optical sensor according to claim 1 , further comprising circuitry configured to receive the optical signal and covert the optical signal into a photoplethysmograph waveform.
3. An optical sensor according to claim 2 , wherein the photoplethysmograph waveform is an analog waveform.
4. An optical sensor according to claim 1 , comprising a second light source proximate to the first light source.
5. An optical sensor according to claim 4 , wherein the first light source operates in the 400-700 nm range, and the second light source operates in the 700-1000 nm range.
6. A method of obtaining an optical signal indicative of a photoplethysmograph waveform, comprising:
positioning a flexible housing around the base of a patient's thumb, wherein the housing comprises (i) a first light source that emits optical radiation, wherein the first light source comprises a first substantially planar surface, (ii) a photodetector configured to detect the optical radiation and to generate the optical signal, wherein the photodetector is positioned on a substrate comprising a second substantially planar surface, and (iii) a plurality of living hinges, the first and second substantially planar surfaces are supported by the flexible housing such that the first substantially planar surface is separated from the second substantially planar surface by an included angle between 35-55 degrees, wherein the included angle is an angle formed between a first line drawn parallel to the first substantially planar surface and a second line drawn parallel to the second substantially planar surface, wherein the first light source and photodetector are each positioned over the interior base of the thumb proximate to the princeps pollicis artery, wherein the flexible housing is an approximately semicircular housing with the plurality of living hinges radially spaced apart from each other along a circumference of the approximately semicircular housing;
energizing the light source to illuminate the thumb with optical radiation; and
detecting optical radiation after reflection by the princeps pollicis artery with the photodetector and generating an optical signal therewith.
7. A method according to claim 6 , further comprising converting the optical signal into a photoplethysmograph waveform.
8. A method according to claim 7 , further comprising determining one or more of a blood oxygen saturation level, a pulse rate, pulse transit time, and blood pressure for the patient using the photoplethysmograph waveform.
9. A method according to claim 6 , wherein the housing comprises a second light source proximate to the first light source.