Body-worn pulse oximeter
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. A method for determining a peripheral oxygen saturation (SpO2) value from a patient, comprising:
recursively calculating and displaying the SpO2 value by
(a) measuring a first time-dependent signal by detecting a first radiation emitted by a first radiation source after it passes through tissue of the patient;
(b) measuring a second time-dependent signal by detecting a second radiation emitted by a second radiation source after it passes through the tissue of the patient;
(c) measuring a time-dependent motion signal with at least one motion sensor;
(d) measuring a time-dependent electrical signal with an electrical sensor comprising at least two electrodes, wherein the electrical signal is indicative of a pulse pressure wave launched by the patient's heart;
(e) processing the time-dependent electrical signal to determine at least one reference time point;
(f) processing the time-dependent motion signal to determine a motion-related event that affects at least one of the first and second time-dependent signals;
(g) processing both the first and second time-dependent signals from the at least one reference time point and outside of the motion-related event to determine a time-dependent value related to the patient's SpO2;
(h) iterating steps (a) (g) for a pre-determined period to calculate an average value from a series of the time-dependent values determined during the pre-determined period, wherein time-dependent values from the series that differ from the average value by more than one standard deviation are discarded and the average value is recalculated without the discarded time-dependent values;
(i) processing the average value to determine the current oxygen saturation value and displaying the current SpO2 value; and
(j) recursively performing steps (a)-(i) such that the average value is a rolling average updated at each pulse pressure wave.