Method and apparatus for determining a respiration rate of a subject

1. A method of determining the respiration rate of a subject, the method comprising:

obtaining a signal from a sensor that is worn or carried by the subject;

analyzing the signal to determine a plurality of values for a breathing-related feature;

forming a histogram from the plurality of values for the breathing-related feature, the histogram comprising a plurality of groups, each group corresponding to one or more possible values of the breathing-related feature, with each group having an associated count that corresponds to the number of occurrences of a value or values for the breathing-related feature corresponding to the group;

applying a weighting to the count associated with one or more of the groups to form weighted counts by determining the weighted count for each group by subtracting a threshold value from a respective count wherein weighted counts are set to zero in the event that the threshold value is equal to or greater than the respective count; and

determining the respiration rate from a mean of the histogram with the weighted counts.

2. A method as claimed in claim 1 , wherein the step of determining the respiration rate from the mean of the histogram comprises determining the mean of the histogram by:

(i) for each group, multiplying a value for the breathing-related feature corresponding to the group by the weighted count for the group;

(ii) summing the result of (i) for each group;

(iii) dividing the result of (ii) by the sum of the weighted counts.

3. A method as claimed in claim 1 , wherein the step of applying a weighting to the count associated with one or more groups comprises:

applying a weighting such that the mean of the histogram is weighted towards the value or values of the breathing-related feature for the group having the highest count.

4. A method as claimed in claim 1 , wherein the step of applying a weighting to the count associated with one or more groups comprises:

applying a weighting such that the value or values of the breathing-related feature for the group or groups having the highest counts are emphasized in the mean of the histogram.

5. A method as claimed in claim 1 , wherein the step of applying a weighting to the count associated with one or more groups comprises:

discarding from the histogram any group having a count that is less than a threshold number.

6. A method as claimed in claim 1 , wherein the step of applying a weighting to the count associated with one or more groups comprises:

determining the weighted count for each group as the nth power of the respective count, where n is any number greater than 1.

7. A non-transitory computer readable medium computer comprising a computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to:

obtain a signal from a sensor that is worn or carried by the subject;

analyze the signal to determine a plurality of values for a breathing-related feature;

form a histogram from the plurality of values for the breathing-related feature, the histogram comprising a plurality of groups, each group corresponding to one or more possible values of the breathing-related feature, with each group having an associated count that corresponds to the number of occurrences of a value or values for the breathing-related feature corresponding to the group;

apply a weighting to the count associated with one or more of the groups to form weighted counts by determining the weighted count for each group by subtracting a threshold value from a respective count; wherein weighted counts are set to zero in the event that the threshold value is equal to or greater than the respective count; and

determine the respiration rate from a mean of the histogram with the weighted counts.

8. An apparatus for determining the respiration rate of a subject, the apparatus comprising:

a processing unit configured to:

receive a signal from a sensor;

analyze the signal to determine a plurality of values for a breathing-related feature;

form a histogram from the plurality of values for the breathing-related feature, the histogram comprising a plurality of groups, each group corresponding to one or more possible values of the breathing-related feature, with each group having an associated count that corresponds to the number of occurrences of a value or values for the breathing-related feature corresponding to the group;

apply a weighting to the count associated with one or more groups to form weighted counts by determining the weighted count for each group by subtracting a threshold value from a respective count; wherein weighted counts are set to zero in the event that the threshold value is equal to or greater than the respective count; and

determine the respiration rate from a mean of the histogram with the weighted counts.

9. An apparatus as claimed in claim 8 , wherein the processing unit is configured to apply a weighting to the count associated with one or more groups such that the mean of the histogram is weighted towards the value or values of the breathing-related feature for the group having the highest count.

10. An apparatus as claimed in claim 8 , wherein the processing unit is configured to apply a weighting to the count associated with one or more groups such that the value or values of the breathing-related feature for the group or groups having the highest counts are emphasized in the mean of the histogram.

11. An apparatus as claimed in claim 8 , wherein the processing unit is configured to apply a weighting to the count associated with one or more groups by discarding from the histogram any group having a count that is less than a threshold number.

12. An apparatus as claimed in claim 8 , wherein the processing unit is configured to apply a weighting to the count associated with one or more groups by determining the weighted count for each group as the nth power of the respective count, where n is any number greater than 1.

13. An apparatus as claimed in claim 8 , wherein the apparatus comprises the sensor.