Contactless respiration monitoring of a patient
Respiration of a patient is detected by emitting an electromagnetic signal towards the patient; receiving a reflected electromagnetic signal reflected from the patient; converting the reflected electromagnetic signal, yielding a first signal; phase-shifting the reflected electromagnetic signal and converting the phase-shifted reflected electromagnetic signal, yielding a second signal; determining a first vector being defined by the time derivatives of the first signal and the second signal, for a common first point in time; determining a second vector being defined by the time derivatives of the first signal and the second signal, for a common second point in time; and calculating the scalar product of the normalized first vector and the normalized second vector as an indicator value for a change from expiration to inspiration of the patient or vice versa. A change from expiration to inspiration of the patient or vice versa is preferably indicated if the indicator value is below a threshold value, preferably below a value of 0. In this way, respiration is monitored contactlessly and remotely based on the Doppler radar principle which is reliable and easy to handle.
1. A method for detection of respiration of a patient comprising the following steps:
emitting using a two-channel Doppler radar sensor an electromagnetic signal towards the patient;
receiving a reflected electromagnetic signal reflected from the patient using the two-channel Doppler radar sensor;
converting using the two-channel Doppler radar sensor the reflected electromagnetic signal to a first signal;
phase-shifting using the two-channel Doppler radar sensor the reflected electromagnetic signal and converting the phase-shifted reflected electromagnetic signal to a second signal;
determining using a calculating device a first vector by taking time derivatives of the first signal and the second signal, for a common first point in time;
determining using the calculating device a second vector by taking the time derivatives of the first signal and the second signal, for a common second point in time;
normalizing using the calculating device the first and second vectors;
calculating using the calculating device the scalar product of the normalized first vector and the normalized second vector as an indicator value for a change from expiration to inspiration of the patient or vice versa; and
controlling a display to display a respiration value based on the indicated changed from expiration to inspiration of the patient or vice versa.
2. The method according to claim 1 , further including:
determining the first point in time and the second point in time for building the first vector and the second vector by determining, respectively, characteristic points in time defined by specific criteria fulfilled simultaneously in the first signal and the second signal.
3. The method according to claim 2 , wherein the specific criteria is a detected zero-crossing of the time derivative of the first signal or the second signal, respectively.
4. The method according to claim 1 , wherein an indicator value is compared within a predefined threshold value.
5. The method according to claim 4 , wherein the predefined threshold value is 0.
6. The method according to claim 4 , wherein the change from expiration to inspiration of the patient or vice versa is indicated using the display if the indicator value is below the predefined threshold value.
7. The method according to claim 1 , wherein the first vector, the second vector and the scalar product of the normalized first vector and the normalized second vector as an indicator value for the change from expiration to inspiration of the patient or vice versa are consecutively determined, preferably in predefined time periods.
8. The method according to claim 1 , wherein calculating includes calculating a vorticity {right arrow over (V)} for the first point in time T 1 and the second point in time T 2 , respectively, by {right arrow over (V)} 1 =−{right arrow over (r)} 1 ×({right arrow over (M)} 1 (T 1 )−{right arrow over (r)} 1 ) and {right arrow over (V)} 2 =−{right arrow over (r)} 2 ×({right arrow over (M)} 2 (T 2 )−{right arrow over (r)} 2 ), wherein {right arrow over (r)} 1 is the first vector, {right arrow over (r)} 2 is the second vector, and {right arrow over (M)} 1 and {right arrow over (M)} 2 are vectors built from the time derivatives of the first signal and the second signal at times T 1 and T 2 , respectively.
9. The method according to claim 1 , wherein a respiration rate is indicated.
10. A device for contactless respiration monitoring of a patient, comprising:
a two-channel Doppler radar sensor configured to:
receive a reflected electromagnetic signal reflected from the patient,
convert the reflected electromagnetic signal to a first signal,
phase-shift the reflected electromagnetic signal, and
convert the phase-shifted reflected electromagnetic signal to a signal; and
a calculating unit configured to:
determine a first vector defined by taking time derivatives of the first signal and the second signal, for a common first point in time,
determine a second vector defined by taking time derivatives of the first signal and the second signal, for a common second point in time,
normalize the first and second vectors,
calculate a scalar product of the normalized first vector and the normalized second vector as an indicator value for a change from expiration to inspiration of the patient or vice versa, and
control a display to display a respiration value based on the indicated changed from expiration to inspiration of the patient or vice versa.
11. The device according to claim 10 , wherein the calculating unit is further configured to:
compare the indicator value with a predefined threshold value, and
indicate using the display the change from expiration to inspiration of the patient or vice versa in response to an indicator value being below the predefined threshold value.
12. The device according to claim 10 , further including:
the display configured for displaying a respiration rate based on indicated changes from expiration to inspiration of the patient or vice versa.
13. A contactless respiration monitoring system for monitoring respiration of a patient, comprising:
an emitter adapted to emit an electromagnetic signal towards the patient;
a two-channel Doppler radar sensor adapted to:
receive a reflected electromagnetic signal reflected from the patient;
convert the reflected electromagnetic signal to a first signal; and
phase-shift the reflected electromagnetic signal; and
convert the phase-shifted reflected electromagnetic signal to a second signal;
a calculating unit adapted to:
determine a first vector defined by taking a time derivative of the first signal taken in a first period of time as a first vector coordinate of the first vector, and a time derivative of the second signal taken in the first period of time as a second vector coordinate of the first vector;
determine a second vector defined by taking a time derivative of the first signal taken in a second period of time as a first vector coordinate of the second vector, and a time derivative of the second signal taken in the second period of time as a second vector coordinate of the second vector;
calculate the scalar produce of the normalized first vector and the normalized second vector as an indicator value for a change from expiration to inspiration of the patient or vice versa; and
control a display to display a respiration value based on the indicated changed from expiration to inspiration of the patient or vice versa.
14. The system according to claim 13 , wherein the calculating unit is further adapted to:
determine characteristic points in time defined by specific criteria fulfilled simultaneously in the first signal and the second signal.
15. The system according to claim 14 , wherein the specific criteria includes a detected zero-crossing of the time derivative of the first signal or the second signal, respectively.
16. The system according to claim 13 , wherein an indicator value is compared with a predefined threshold value.
17. The system according to claim 16 , wherein the change from expiration to inspiration of the patient or vice versa is indicated using the display if the indicator value is below the predefined threshold value.
18. The system according to claim 13 , wherein the first vector, the second vector and the scalar product of the normalized first vector and the normalized second vector as an indicator value for the change from expiration to inspiration of the patient or vice versa are consecutively determined, preferably in predefined time periods.
19. The system according to claim 13 , wherein the calculating unit is further adapted to calculate a vorticity {right arrow over (V)} for the first period of time T 1 and the second period of time T 2 , respectively, by {right arrow over (V)} 1 =−{right arrow over (r)} 1 ×({right arrow over (M)} 1 (T 1 )−{right arrow over (r)} 1 ) and {right arrow over (V)} 2 =−{right arrow over (r)} 2 ×({right arrow over (M)} 2 (T 2 )−{right arrow over (r)} 2 ), wherein {right arrow over (r)} 1 is the first vector, {right arrow over (r)} 2 is the second vector, and {right arrow over (M)} 1 and {right arrow over (M)} 2 are vectors built from the time derivatives of the first signal and the second signal at times T 1 and T 2 , respectively.
20. The system according to claim 13 , wherein a respiration rate is indicated using the display.