Body-worn monitor for measuring respiratory rate
The invention provides a system for measuring respiratory rate (RR) from a patient. The system includes an impedance pneumography (IP) sensor, connected to at least two electrodes, and a processing system that receives and processes signals from the electrodes to measure an IP signal. A motion sensor (e.g. an accelerometer) measures at least one motion signal (e.g. an ACC waveform) describing movement of a portion of the patient's body to which it is attached. The processing system receives the IP and motion signals, and processes them to determine, respectfully, frequency-domain IP and motion spectra. Both spectra are then collectively processed to remove motion components from the IP spectrum and determine RR. For example, during the processing, an algorithm determines motion frequency components from the frequency-domain motion spectrum, and then using a digital filter removes these, or parameters calculated therefrom, from the IP spectrum.
1. A method for measuring respiratory rate from a patient, comprising the following steps:
(a) measuring an impedance pneumography signal from the patient with an impedance pneumography sensor connected to at least two electrodes mounted on the patient's torso, the impedance pneumography signal representing a time-dependent capacitance change in the patient's torso;
(b) measuring at least one motion signal with a three axis motion sensor mounted on the patient's torso and having an axis of measurement aligned into the patient's torso, the at least one motion signal comprising signal components corresponding to breathing-induced motion, posture of the patient, and degree of motion of the patient;
(c) analyzing the motion signal with a first microprocessor located on the patient's body to determine a motion parameter indicative of the patient's degree of motion;
(d) analyzing the motion parameter with the first microprocessor, wherein
if the motion parameter exceeds a threshold which indicates that the impedance pneumography signal is not significantly corrupted by motion, determining a respiratory rate by identifying peaks in the impedance pneumography signal corresponding to respiration events with the first microprocessor,
and wherein if the motion parameter does not exceeds the threshold which indicates that the impedance pneumography signal is significantly corrupted by motion, transmitting the impedance pneumography signal and the motion signal to a second microprocessor positioned at a different location than the first microprocessor and determining the respiratory rate by performing steps (e)-(h);
(e) using the second microprocessor, collectively processing both the motion signal and impedance pneumography signal to determine coefficients corresponding to a digital filter;
(f) transmitting the coefficients from the second microprocessor to the first microprocessor;
(g) using the first microprocessor, processing one of the motion signal and impedance pneumography signal with the coefficients to determine a digitally filtered waveform; and
(h) using the first microprocessor, analyzing the digitally filtered waveform to determine the respiratory rate.
2. The method of claim 1 , wherein the first microprocessor is located on the patient's wrist.
3. The method of claim 1 , wherein step (d) further comprises serially transmitting the impedance pneumography signal and the motion signal from the first microprocessor to the second microprocessor.
4. The method of claim 3 , wherein the second microprocessor is located on the patient's torso.
5. The method of claim 1 , wherein step (d) further comprises wirelessly transmitting the impedance pneumography signal and the motion signal from the first microprocessor to the second microprocessor.
6. The method of claim 5 , wherein the second microprocessor is located on a remote server.
7. The method of claim 1 , wherein step (e) further comprises analyzing the motion signal to determine a set of components corresponding to the patient's motion, and then generating coefficients which are optimized to remove the components corresponding to the patient's motion when implemented in a digital filter that processes the impedance pneumography signal.
8. The method of claim 1 , further comprising storing the coefficients in a computer memory associated with the first microprocessor.
9. The method of claim 8 , further comprising measuring a new impedance pneumography signal, and then processing the new impedance pneumography signal with the coefficients stored in the computer memory to determine a new digitally filtered waveform.
10. The method of claim 9 , further comprising analyzing the new digitally filtered waveform with the first microprocessor to determine a respiratory rate.
11. The method of claim 1 , wherein step (f) further comprises determining motion components from the frequency-based transform of the motion signal, removing the motion components, or components calculated therefrom, from the frequency-based transform of the impedance pneumography signal, and then analyzing the resultant signal to determine the patient's respiratory rate.