Statistical method for assessing autonomic balance
First Claim
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1. A method for operating an implantable medical device in order to assess a subject'"'"'s autonomic balance, comprising:
- sensing electrical activity in a ventricle and generating a ventricular sense signal when the sensed electrical activity exceeds a predetermined threshold;
measuring time intervals between each pair of successive ventricular senses, referred to as RR intervals, over a predetermined long-term period, where N is the total number of RR interval measurements during the predetermined long-term period and the measured RR intervals RR1 through RRN are referred to as an RR time series;
computing mean values Mx1 through MxL of successive x-second segments of the RR time series, where x is a predetermined number and L is the total number of such x-second segments in the RR time series, and computing a variance of the mean values Mx1 through MxL, referred to as [SDx]2;
computing mean values My1 through MyK of successive y-second segments of the RR time series, where y is a predetermined number greater than x and K is the total number of such y-second segments in the RR time series, and computing a variance of the mean values My1 through MyK, referred to as [SDy]2;
computing a mean value of squared successive differences between the RR intervals in the RR time series, referred to as [rMSSD]2; and
,estimating a ratio of the low frequency content in the RR time series between approximately 1/x Hz and 1/y Hz and higher frequency content in the RR time series, referred to as LF/HF, as;
LF/HF=K([SDx]2−
[SDy]2)/[rMSSD]2wherein K is a defined constant and LF/HF is reflective of the subject'"'"'s autonomic balance.
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Abstract
A computationally efficient method for assessing a subject'"'"'s autonomic balance by measurement of heart rate variability is disclosed which is particularly suitable for implementation by an implantable medical device. Statistical surrogates are used to represent frequency components of an RR time series. A ratio of the low frequency component to the high frequency component may then be estimated to assess the subject'"'"'s autonomic balance.
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Citations
20 Claims
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1. A method for operating an implantable medical device in order to assess a subject'"'"'s autonomic balance, comprising:
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sensing electrical activity in a ventricle and generating a ventricular sense signal when the sensed electrical activity exceeds a predetermined threshold; measuring time intervals between each pair of successive ventricular senses, referred to as RR intervals, over a predetermined long-term period, where N is the total number of RR interval measurements during the predetermined long-term period and the measured RR intervals RR1 through RRN are referred to as an RR time series; computing mean values Mx1 through MxL of successive x-second segments of the RR time series, where x is a predetermined number and L is the total number of such x-second segments in the RR time series, and computing a variance of the mean values Mx1 through MxL, referred to as [SDx]2; computing mean values My1 through MyK of successive y-second segments of the RR time series, where y is a predetermined number greater than x and K is the total number of such y-second segments in the RR time series, and computing a variance of the mean values My1 through MyK, referred to as [SDy]2; computing a mean value of squared successive differences between the RR intervals in the RR time series, referred to as [rMSSD]2; and
,estimating a ratio of the low frequency content in the RR time series between approximately 1/x Hz and 1/y Hz and higher frequency content in the RR time series, referred to as LF/HF, as;
LF/HF=K([SDx]2−
[SDy]2)/[rMSSD]2wherein K is a defined constant and LF/HF is reflective of the subject'"'"'s autonomic balance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
where the summations are carried out from i=1 to T.
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3. The method of claim 1 further comprising:
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defining an integral number S of RR interval bins B1 through BS representing RR interval values I1 through IS; assigning each computed mean value My1 through MyK of the successive y-second segments of the RR time series to a corresponding one of the RR interval bins B1 through BS; counting the number of computed mean values assigned to each RR interval bin B1 through BS and dividing each such number by K to derive a relative frequency FYi for each interval value Ii; and
,computing [SDy]2 as
[SDy]2=Σ
(Ii)2FYi−
(Σ
(Ii)FYi)2where the summations are carried out from i=1 to S.
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4. The method of claim 1 further comprising:
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defining an integral number W of RR interval difference bins C1 through CW representing RR interval difference values D1 through DW; computing an interval difference between each pair of RR intervals in the RR time series as (RR2−
RR1) through (RRN−
RRN−
1);assigning each of the computed interval differences between RR intervals in the RR time series to a corresponding one of the RR interval difference bins C1 through CW; counting the number of computed interval differences assigned to each RR interval difference bin C1 through CW and dividing each such number by N−
1 to derive a relative frequency FDi for each interval difference Di; and
,computing [rMSSD]2 as
[rMSSD]2=Σ
(Di)2FDiwhere the summation is carried out from i=1 to W.
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5. The method of claim 1 further comprising:
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cumulatively summing each computed mean value Mxi; cumulatively summing each computed mean value Mxi squared; computing [SDx]2 as;
[SDx]2=(1/L)Σ
(Mxi)2−
((1/L)Σ
Mxi)2where the summations are carried out from i=1 to L by the cumulative summing operations.
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6. The method of claim 1 further comprising:
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cumulatively summing each computed mean value Myi; cumulatively summing each computed mean value Myi squared; computing [SDy]2 as;
[SDy]2=(1/L)Σ
(Myi)2−
((1/L)Σ
Myi)2where the summations are carried out from i=1 to K by the cumulative summing operations.
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7. The method of claim 1 further comprising:
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cumulatively summing each computed interval difference value (RRi+1−
RRi) squared;computing [rMSSD]2 as;
[rMSSD]2=(1/(N−
1))Σ
(RRi+1−
RRi)2where the summation is carried out from i=1 to N−
1 by the cumulative summing operation.
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8. The method of claim 1 wherein the predetermined long-term period is 24 hours.
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9. The method of claim 1 wherein the predetermined numbers x and y are 7 and 25, respectively, such that the estimated LF/HF represents a ratio of the low frequency content in the RR time series between approximately 0.04 Hz and 0.15 Hz and the high frequency content in the RR time series between approximately 0.15 Hz and 0.4 Hz.
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10. The method of claim 1 further comprising computing a moving average of estimated LF/HF ratios over successive long-term time periods.
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11. A cardiac rhythm management device, comprising:
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a sensing channel for sensing electrical activity in a ventricle; a controller interfaced to the sensing channel which detects a ventricular sense when the sensed electrical activity exceeds a predetermined threshold; wherein the controller is programmed with executable instructions for; measuring time intervals between each pair of successive ventricular senses, referred to as RR intervals, over a predetermined long-term period, where N is the total number of RR interval measurements during the predetermined long-term period and the measured RR intervals RR1 through RRN are referred to as an RR time series; computing mean values Mx1 through MxL of successive x-second segments of the RR time series, where x is a predetermined number and L is the total number of such x-second segments in the RR time series, and computing a variance of the mean values Mx1 through MxL, referred to as [SDx]2; computing mean values My1 through MyK of successive y-second segments of the RR time series, where y is a predetermined number greater than x and K is the total number of such y-second segments in the RR time series, and computing a variance of the mean values My1 through MyK, referred to as [SDy]2; computing a mean value of squared successive differences between the RR intervals in the RR time series, referred to as [rMSSD]2; and
,estimating a ratio of the low frequency content in the RR time series between approximately 1/x Hz and 1/y Hz and higher frequency content in the RR time series, referred to as LF/HF, as;
LF/HF=K([SDx]2−
[SDy]2)/[rMSSD]2wherein K is a defined constant and LF/HF is reflective of the subject'"'"'s autonomic balance. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
where the summations are carried out from i=1 to T.
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13. The device of claim 11 wherein the controller is further programmed with instructions for:
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defining an integral number S of RR interval bins B1 through BS representing RR interval values I1 through IS; assigning each computed mean value My1 through MyK of the successive y-second segments of the RR time series to a corresponding one of the RR interval bins B1 through BS; counting the number of computed mean values assigned to each RR interval bin B1 through BS and dividing each such number by K to derive a relative frequency FYi for each interval value Ii; and
,computing [SDy]2 as
[SDy]2=Σ
(Ii)2FYi−
(Σ
(Ii)Fwhere the summations are carried out from i=1 to S.
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14. The device of claim 11 wherein the controller is further programmed with instructions for:
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defining an integral number W of RR interval difference bins C1 through CW representing RR interval difference values D1 through DW; computing an interval difference between each pair of RR intervals in the RR time series as (RR2−
RR1) through (RRN−
RRN−
1);assigning each of the computed interval differences between RR intervals in the RR time series to a corresponding one of the RR interval difference bins C1 through CW; counting the number of computed interval differences assigned to each RR interval difference bin C1 through CW and dividing each such number by N−
1 to derive a relative frequency FDi for each interval difference Di; and
,computing [rMSSD]2 as
[rMSSD]2=Σ
(Di)2FDiwhere the summation is carried out from i=1 to W.
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15. The device of claim 11 wherein the controller is further programmed with instructions for:
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cumulatively summing each computed mean value Mxi; cumulatively summing each computed mean value Mxi squared; computing [SDx]2 as;
[SDx]2=Σ
(1/L)Σ
(Mxi)2−
((1/L)Σ
Mxi)2where the summations are carried out from i=1 to L by the cumulative summing operations.
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16. The device of claim 11 wherein the controller is further programmed with instructions for:
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cumulatively summing each computed mean value Myi; cumulatively summing each computed mean value Myi squared; computing [SDy]2 as;
[SDy]=(1/L)Σ
(Myi)2−
((1/L)Σ
Myi)2where the summations are carried out from i=1 to K by the cumulative summing operations.
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17. The device of claim 11 wherein the controller is further programmed with instructions for:
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cumulatively summing each computed interval difference value (RRi+1−
RRi) squared;computing [rMSSD]2 as;
[rMSSD]2=(1/(N−
1))Σ
(RRi+1−
RRi)2where the summation is carried out from i=1 to N−
1 by the cumulative summing operation.
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18. The device of claim 11 wherein the predetermined long-term period is 24 hours.
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19. The device of claim 11 wherein the predetermined numbers x and y are 7 and 25, respectively, such that the estimated LF/HF represents a ratio of the low frequency content in the RR time series between approximately 0.04 Hz and 0.15 Hz and the high frequency content in the RR time series between approximately 0.15 Hz and 0.4 Hz.
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20. The device of claim 11 wherein the controller is further programmed with instructions for computing a moving average of estimated LF/HF ratios over successive long-term time periods.
Specification