Measuring respiration with an in-ear accelerometer

1. A system comprising:

an earphone comprising:

a loudspeaker;

an accelerometer;

a housing supporting the loudspeaker and accelerometer; and

an ear tip surrounding the housing and configured to acoustically couple the loudspeaker to an ear canal of a user;

a second earphone comprising:

a second loudspeaker;

a second accelerometer;

a second housing supporting the second loudspeaker and second accelerometer; and

a second ear tip surrounding the second housing and configured to acoustically couple the second loudspeaker to a second ear canal of the user;

and

a processor configured to:

receive input signals from the accelerometer in response to motion of the earphone;

detect peaks in the input signals;

based on the detected peaks, compute an instantaneous heart rate;

measure a frequency of an oscillation within the instantaneous heart rate; and

based on the frequency of the oscillation, compute a rate of respiration,

wherein the input signals comprise acceleration measurements for each of three axes, and the processor is configured to detect the peaks by combining the three acceleration measurements into a norm of the three measurements, and

wherein the processor is further configured to:

receive second input signals from the second accelerometer comprising second acceleration measurements for each of three axes of the second accelerometer;

combine the second three acceleration measurements into the norm of the second three measurements;

and

detect the peaks by combining the norm of the three measurements from the first accelerometer with the norm of the three measurements from the second accelerometer and detecting peaks within the result of the combination.

2. The system of claim 1 , wherein the accelerometer is located on a circuit board within the earphone.

3. The system of claim 1 , wherein the housing comprises an outer shell of the earphone, and the accelerometer is located in the outer shell.

4. The system of claim 1 , wherein combining the norms comprises multiplying the amplitude of the norm of the first three acceleration measurements by the amplitude of the norm of the second three acceleration measurements, at each time that the two accelerometers' measurements are sampled.

5. The system of claim 1 , wherein the processor is further configured to adjust output audio signals based on the rate of respiration, and provide the output audio signals to the loudspeaker.

6. The system of claim 5 , wherein adjusting the output audio signals comprises adjusting a rhythm of the output audio signals to be about one cycle per minute less than the detected respiration rate.

7. The system of claim 5 , wherein adjusting the output audio signals comprises transitioning the output audio signals from respiration entrainment sounds to masking sounds.

8. The system of claim 5 , wherein adjusting the output audio signals comprises transitioning the output audio signals from masking sounds to awakening sounds.

9. The system of claim 5 , wherein

the earphone further includes a memory storing sound files; and

providing the output audio signals comprises retrieving a first sound file from the memory.

10. The system of claim 9 , wherein adjusting the output audio signals comprises retrieving a second sound file from the memory and using the second sound file to generate the output audio signal.

11. The system of claim 1 , wherein the processor is integrated within the earphone.

12. The system of claim 1 , wherein the processor is integrated within a portable computing device.

13. The system of claim 1 , wherein the processor is configured to measure the frequency of the oscillation within the instantaneous heart rate by computing a fast Fourier transform (FFT) of the instantaneous heart rate.

14. The system of claim 1 , wherein the processor is configured to measure the frequency of the oscillation within the instantaneous heart rate by

computing a gradient of the instantaneous heart rate; and

computing a fast Fourier transform (FFT) of the gradient of the instantaneous heart rate.

15. The system of claim 1 , wherein the processor is configured to measure the frequency of the oscillation within the instantaneous heart rate by detecting peaks of the instantaneous heart rate.

16. The system of claim 1 , wherein the processor is configured to measure the frequency of the oscillation within the instantaneous heart rate by fitting a sine function to the instantaneous heart rate, the frequency of the sine being the frequency of the oscillation.

17. The system of claim 1 , wherein the ear tip is configured to acoustically close the entrance to the user's ear canal.