Medical device for fall detection

Abstract

A medical device is configured to produce an accelerometer signal and detect a patient fall from the accelerometer signal. The device generates a body posture signal and a body acceleration signal from the accelerometer signal and detects a patient fall in response to determining that the body posture signal and the body acceleration signal meet fall detection criteria. The medical device is configured to receive a truth signal from another device that is not the medical device. The truth signal may indicate that the detected patient fall is a falsely detected patient fall and, responsive to receiving the truth signal, the medical device adjusts at least one fall detection control parameter.

What is claimed is: 
     
         1 . A medical device comprising:
 an accelerometer circuit comprising an accelerometer and configured to:
 produce at least one axis signal corresponding an axis of the accelerometer; 
 generate a body posture signal from the at least one axis signal according to a first control parameter; and 
 generate a body acceleration signal from the at least one axis signal of the accelerometer according to a second control parameter; 
   a control circuit configured to:
 receive the body posture signal and the body acceleration signal; 
 apply fall detection criteria to the body posture signal and the body acceleration signal; 
 determine that the body posture signal generated according to the first control parameter and the body acceleration signal generated according to the second control parameter meet the fall detection criteria; and 
 detect a patient fall in response to the body posture signal and the body acceleration signal meeting the fall detection criteria; and 
   a telemetry circuit configured to receive a first truth signal transmitted from another device, the truth signal indicating that the detected patient fall is a falsely detected patient fall; and   responsive to the telemetry circuit receiving the first truth signal, the control circuit being further configured to adjust at least one of the first control parameter used by the accelerometer circuit to generate the body posture signal or the second control parameter used by the accelerometer circuit to generate the body acceleration signal.   
     
     
         2 . The medical device of  claim 1 , wherein:
 the accelerometer circuit is configured to:
 generate the body posture signal according to the first control parameter by sampling the at least one axis signal according to a first sampling rate; 
 generate the body acceleration signal according to the second control parameter by sampling the at least one axis signal according a second sampling rate greater than the first sampling rate; and 
   the control circuit is further configured to adjust the at least one of the first control parameter or the second control parameter by adjusting at least one of the first sampling rate or the second sampling rate.   
     
     
         3 . The medical device of  claim 1 , wherein:
 the accelerometer circuit is configured to:
 generate the body posture signal according to the first control parameter by filtering the at least one axis signal according to a first filter cutoff frequency; 
 generate the body acceleration signal according to the second control parameter by filtering the at least one axis signal according a second filter cutoff frequency different than the first filter cutoff frequency; and 
   the control circuit is further configured to adjust the at least one of the first control parameter or the second control parameter by adjusting at least one of the first filter cutoff frequency or the second filter cutoff frequency.   
     
     
         4 . The medical device of  claim 1 , wherein:
 the accelerometer circuit is further configured to:
 generate the body posture signal and the body acceleration signal after the adjusting of at least one of the first control parameter or the second control parameter; and 
   the control circuit is further configured to apply the fall detection criteria to the body posture signal and the body acceleration signal generated by the accelerometer circuit after the adjusting for detecting a patient fall after the adjusting.   
     
     
         5 . The medical device of  claim 1 , wherein the control circuit is further configured to, in response to the telemetry circuit receiving the first truth signal, adjust the fall detection criteria that are applied to the body posture signal and the body acceleration signal generated by the accelerometer circuit. 
     
     
         6 . The medical device of  claim 1 , wherein:
 the telemetry circuit is further configured to receive a second truth signal indicating a missed fall detection; and   the control circuit is further configured to adjust at least one of the first control parameter or the second control parameter in response to the second truth signal.   
     
     
         7 . The medical device of  claim 1 , wherein the accelerometer comprises at least two orthogonal axes and the accelerometer circuit is further configured to:
 produce at least two axis signals corresponding to the at least two orthogonal axes of the accelerometer; and   generate the body posture signal from the at least two axis signals.   
     
     
         8 . The medical device of  claim 7 , wherein the control circuit is further configured to:
 determine a directional change metric from the body posture signal according to a first method during a first time period;   determine the directional change metric according to a second method during a second time period, the second method different than the first method; and   determine that the body posture signal generated according to the first control parameter and the body acceleration signal generated according to the second control parameter meet the fall detection criteria by determining that at least the directional change metric determined according to one of the first method or the second method meets the fall detection criteria.   
     
     
         9 . The medical device of  claim 1 , wherein:
 the control circuit is further configured to:   determine that the body posture signal meets fall recovery criteria after detecting the patient fall;   determine a fall recovery time from the detected patient fall to the fall recovery criteria being met;   determine a trend in the fall recovery time compared to a previously determined fall recovery time; and   the telemetry circuit is configured to transmit the determined trend.   
     
     
         10 . The medical device of  claim 1 , wherein:
 the control circuit is further configured to determine a trend in a frequency of fall detections; and   the telemetry circuit is configured to transmit the determined trend.   
     
     
         11 . A non-transitory computer readable medium storing a set of instruction which, when executed by control circuitry of a medical device, cause the medical device to:
 produce at least one axis signal corresponding an axis of an accelerometer of the medical device;   generate a body posture signal from the at least one axis signal according to a first control parameter;   generate a body acceleration signal from the at least one axis signal of the accelerometer according to a second control parameter;   apply fall detection criteria to the body posture signal and the body acceleration signal;   determine that the body posture signal generated according to the first control parameter and the body acceleration signal generated according to the second control parameter meet the fall detection criteria; and   detect a patient fall in response to the body posture signal and the body acceleration signal meeting the fall detection criteria; and   receive a first truth signal transmitted from another device, the truth signal indicating that the detected patient fall is a falsely detected patient fall; and   responsive to the first truth signal, adjust at least one of the first control parameter used to generate the body posture signal or the second control parameter used to generate the body acceleration signal.   
     
     
         12 . The non-transitory computer readable medium of  claim 11 , further comprising instructions that cause the medical device to:
 generate the body posture signal according to the first control parameter by sampling the at least one axis signal according to a first sampling rate;   generate the body acceleration signal according to the second control parameter by sampling the at least one axis signal according a second sampling rate greater than the first sampling rate; and   adjust the at least one of the first control parameter or the second control parameter by adjusting at least one of the first sampling rate or the second sampling rate.   
     
     
         13 . The non-transitory computer readable medium of  claim 11 , further comprising instructions that cause the medical device to:
 generate the body posture signal according to the first control parameter by filtering the at least one axis signal according to a first filter cutoff frequency;   generate the body acceleration signal according to the second control parameter by filtering the at least one axis signal according a second filter cutoff frequency different than the first filter cutoff frequency; and   adjust the at least one of the first control parameter or the second control parameter by adjusting at least one of the first filter cutoff frequency or the second filter cutoff frequency.   
     
     
         14 . The non-transitory computer readable medium of  claim 11 , further comprising instructions that cause the medical device to:
 generate the body posture signal and the body acceleration signal after the adjusting of at least one of the first control parameter or the second control parameter; and   apply the fall detection criteria to the body posture signal and the body acceleration signal after the adjusting for detecting a patient fall after the adjusting.   
     
     
         15 . The non-transitory computer readable medium of  claim 11 , further comprising instructions that cause the medical device to:
 in response to the telemetry circuit receiving the first truth signal, adjust the fall detection criteria that are applied to the body posture signal and the body acceleration signal.   
     
     
         16 . The non-transitory computer readable medium of  claim 11 , further comprising instructions that cause the medical device to:
 receive a second truth signal indicating a missed fall detection; and   adjust at least one of the first control parameter or the second control parameter in response to the second truth signal.   
     
     
         17 . The non-transitory computer readable medium of  claim 11 , further comprising instructions that cause the medical device to:
 produce at least two axis signals corresponding to at least two orthogonal axes of the accelerometer; and   generate the body posture signal from the at least two axis signals.   
     
     
         18 . The non-transitory computer readable medium of  claim 11 , further comprising instructions that cause the medical device to:
 determine a directional change metric from the body posture signal according to a first method during a first time period;   determine the directional change metric according to a second method during a second time period, the second method different than the first method; and   determine that the body posture signal generated according to the first control parameter and the body acceleration signal generated according to the second control parameter meet the fall detection criteria by determining that at least the directional change metric determined according to one of the first method or the second method meets the fall detection criteria.   
     
     
         19 . The non-transitory computer readable medium of  claim 11 , further comprising instructions that cause the medical device to:
 determine that the body posture signal meets fall recovery criteria after detecting the patient fall;   determine a fall recovery time from the detected patient fall to the fall recovery criteria being met;   determine a trend in the fall recovery time compared to a previously determined fall recovery time; and   transmit the determined trend.   
     
     
         20 . The non-transitory computer readable medium of  claim 11 , further comprising instructions that cause the medical device to determine a trend in a frequency of fall detections and transmit the determined trend.