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 performing a continuous noninvasive blood pressure measurement (cNIBP) value from a patient, comprising:
(i) measuring an electrical signal indicative of a pulse pressure wave launched by the patient's heart recursively using an electrical sensor worn noninvasively on the patient's body;
(ii) measuring an optical signal indicative of the pulse pressure wave at an extremity of the patient using a photoplethysmogram sensor worn noninvasively on the patient's body;
(iii) calculating a time-dependent pulse transit time value from the measured electrical signal and the measured optical signal;
(iv) iterating steps (i)-(iii) for a pre-determined period to calculate an average pulse transit time value from a series of the time-dependent pulse transit time values determined during the pre-determined period, wherein time-dependent pulse transit time values from the series that differ from the average pulse transit time value by more than one standard deviation are discarded and the average pulse transit time value is recalculated without the discarded time-dependent pulse transit time values;
(v) calculating a blood pressure value from the average pulse transit time value calculated in step (iv); and
(vi) recursively performing steps (i)-(v) such that the average pulse transit time value is a rolling average updated at each pulse pressure wave.