Method for continuously monitoring a patient using a body-worn device and associated system for alarms/alerts
The invention provides a body-worn monitor that measures a patient's vital signs (e.g. blood pressure, SpO2, heart rate, respiratory rate, and temperature) while simultaneously characterizing their activity state (e.g. resting, walking, convulsing, falling). The body-worn monitor processes this information to minimize corruption of the vital signs by motion-related artifacts. A software framework generates alarms/alerts based on threshold values that are either preset or determined in real time. The framework additionally includes a series of ‘heuristic’ rules that take the patient's activity state and motion into account, and process the vital signs accordingly. These rules, for example, indicate that a walking patient is likely breathing and has a regular heart rate, even if their motion-corrupted vital signs suggest otherwise.
1. A method for continuously monitoring a patient, comprising the following steps:
detecting a first time-dependent physiological waveform indicative of one or more contractile properties of the patient's heart with a first sensor comprising a first detector configured to be worn on the patient's body;
detecting a second time-dependent physiological waveform indicative of one or more contractile properties of the patient's heart with a second sensor comprising a second detector configured to be worn on the patient's body;
detecting a first time-dependent motion waveform with a first motion-detecting sensor adapted to be positioned on the patient's wrist, detecting a second time-dependent motion waveform with a second motion-detecting sensor adapted to be positioned on the patient's upper arm, and detecting a third time-dependent motion waveform with a third motion-detecting sensor adapted to be positioned on the patient's chest, wherein each time-dependent motion waveform is indicative of motion of the location on the patient's body to which the corresponding motion detecting sensor is affixed;
processing the first and second time-dependent physiological waveforms to determine at least one vital sign from the patient;
analyzing at least a portion of the first, second, and third time-dependent motion waveforms with a motion-determining algorithm;
determining the patient's activity state by discriminating between resting, moving, sitting, standing, walking, running, falling, lying down, and convulsing states by using results of said analyzing at least a portion of the first, second, and third time-dependent motion waveforms; and
generating an alarm by processing the patient's activity state and comparing the at least one vital sign to a predetermined alarm criteria corresponding to the activity state.
2. The method of claim 1 , wherein the analyzing step further comprises calculating a mathematical transform of at least one of the first, second, and third time-dependent motion waveforms to determine a frequency-dependent motion waveform.
3. The method of claim 2 , wherein the analyzing step further comprises analyzing frequencies in the frequency-dependent motion waveform within a band between 0-3 Hz to determine if the patient is walking.
4. The method of claim 3 , wherein the analyzing step further comprises analyzing frequencies in the frequency-dependent motion waveform within a band between 0-10 Hz to determine if the patient is convulsing.
5. The method of claim 4 , wherein the analyzing step further comprises analyzing frequencies in frequency-dependent motion waveform within a band between 0-15 Hz to determine if the patient is falling.
6. The method of claim 1 , wherein the analyzing step further comprises calculating a time-dependent change in at least two of the first, second, and third time-dependent motion waveforms.
7. The method of claim 6 , wherein the analyzing step further comprises calculating a standard deviation of at least one of the first, second, and third time-dependent motion waveforms.
8. The method of claim 6 , wherein the analyzing step further comprises calculating a mathematical derivative of at least one of the first, second, and third time-dependent motion waveforms.
9. The method of claim 6 , wherein the analyzing step further comprises comparing at least one of the first, second, and third time-dependent motion waveforms to a mathematical function.
10. The method of claim 1 , wherein the analyzing step further comprises calculating a logit variable from at least the first and second time-dependent motion waveforms, or waveforms calculated therefrom, and comparing the logit variable to a predetermined ROC curve to determine the patient's activity state.
11. The method of claim 10 , wherein the analyzing step further comprises comparing the logit variable calculated from at least the first and second time-dependent motion waveforms, or a waveform calculated therefrom, to different ROC curves corresponding to activity states selected from resting, moving, sitting, standing, walking, running, falling, lying down, and convulsing.
12. The method of claim 1 , wherein the processing step further comprises calculating a time difference between a feature in the first time-dependent physiological waveform and a feature in the second time-dependent physiological waveform.
13. The method of claim 12 , wherein the processing step further comprises calculating a blood pressure from the time difference.
14. The method of claim 13 , wherein the first time-dependent physiological waveform is an electrical waveform, and the second time-dependent physiological waveform is an optical waveform.
15. The method of claim 13 , wherein each of the first and second time-dependent physiological waveforms are selected from a group consisting of an optical waveform, an acoustic waveform, an ECG waveform, and a pressure waveform.
16. The method of claim 1 , wherein the first time-dependent physiological waveform is an electrical waveform, and the at least one vital sign determined during the processing step is heart rate.
17. The method of claim 1 , wherein the first time-dependent physiological waveform is an electrical waveform, and the at least one vital sign determined during the processing step is respiratory rate.
18. The method of claim 1 , wherein the first time-dependent physiological waveform is an optical waveform, and the at least one vital sign determined during the processing step is SpO2.