U.S. patent application number 10/283706 was filed with the patent office on 2003-03-20 for method of and apparatus for detecting arrhythmia and fibrillation.
Invention is credited to Wiesel, Joseph.
Application Number | 20030055351 10/283706 |
Document ID | / |
Family ID | 23854904 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030055351 |
Kind Code |
A1 |
Wiesel, Joseph |
March 20, 2003 |
Method of and apparatus for detecting arrhythmia and
fibrillation
Abstract
The presence of irregular heartbeat and/or possible atrial
fibrillation is determined by analyzing a measured pulse rate
pattern or heart rate pattern. The standard deviation and mean of
time intervals each corresponding to a respective heartbeat are
determined and compared to a threshold value. When quotient formed
by dividing the standard deviation by the mean has a value greater
than or equal to the threshold value, the shortest one of the time
intervals and its succeeding time intervals are determined, and the
succeeding time interval is compared to the mean. If the succeeding
time interval is less than the mean, then the heartbeat is
irregular. Alternatively, if the succeeding time interval is
greater than the mean, the shortest time interval and its
succeeding time interval are eliminated from the sample values, a
new mean and standard deviation are determined, and the quotient of
the new standard deviation divided by the new mean are compared to
the threshold value. When the quotient is greater than the
threshold value, the next shortest interval is determined, and the
absolute value of the difference between the next shortest interval
and the shortest interval is compared to an empirically determined
value. If the difference is greater than the empirically determined
value, the heartbeat is irregular. Alternatively, if the difference
is greater than the empirically determined value, then the next
shortest interval and its succeeding interval are redefined as the
new shortest interval and is succeeding interval. The steps are
repeated until it is determined that the heartbeat is regular or
irregular.
Inventors: |
Wiesel, Joseph; (West
Hempstead, NY) |
Correspondence
Address: |
GIBBONS, DEL DEO, DOLAN, GRIFFINGER & VECCHIONE
1 RIVERFRONT PLAZA
NEWARK
NJ
07102-5497
US
|
Family ID: |
23854904 |
Appl. No.: |
10/283706 |
Filed: |
October 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10283706 |
Oct 30, 2002 |
|
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09467233 |
Dec 20, 1999 |
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Current U.S.
Class: |
600/515 |
Current CPC
Class: |
A61B 5/361 20210101 |
Class at
Publication: |
600/515 |
International
Class: |
A61B 005/04 |
Claims
What is claimed is:
1. A method of verifying regular cardiac activity, said method
comprising the steps of: (a) determining a plurality of time
intervals each corresponding to a respective time period between
successive ones of a sequence of heartbeats; (b) determining a mean
and a standard deviation of said plurality of time intervals; and
(c) determining, when a quotient formed by dividing said standard
deviation by said mean is less than a threshold value, that the
cardiac activity is regular.
2. A method of detecting irregular cardiac activity, said method
comprising the steps of: (a) determining a plurality of time
intervals each corresponding to a respective time period between
successive ones of a sequence of heartbeats; (b) determining a mean
and a standard deviation of said plurality of time intervals; (c)
selecting, when a quotient formed by dividing said standard
deviation by said mean has a value greater than or equal to a
threshold value, a shortest one of said plurality of time intervals
and a succeeding time interval that immediately follows said
shortest one; and (d) determining, when said succeeding time
interval has a value less than or equal to said mean, that said
cardiac activity is irregular.
3. A method of detecting irregular cardiac activity, said method
comprising the steps of: (a) determining a plurality of time
intervals each corresponding to a respective time period between
successive ones of a sequence of heartbeats; (b) determining a mean
and a standard deviation of said plurality of time intervals; (c)
selecting, when a quotient formed by dividing said standard
deviation by said mean has a value greater than or equal to a
threshold value, a shortest one of said plurality of time intervals
and a succeeding time interval that immediately follows said
shortest one; (d) deleting, when said succeeding time interval has
a value greater than said mean, said shortest one of said plurality
of time intervals and said succeeding time interval from said
plurality of time intervals; (e) determining an adjusted mean and
an adjusted standard deviation based on remaining ones of said
plurality of time intervals; (f) selecting, when an adjusted
quotient formed by dividing said adjusted standard deviation by
said adjusted mean is greater than or equal to said threshold
value, an adjusted shortest one of said remaining ones of said
plurality of time intervals; and (g) determining, when an absolute
value of the difference between said adjusted shortest one and said
shortest one is greater than a value within a preselected range
between 0.02-0.8 seconds, that said cardiac activity is
irregular.
4. A method of detecting irregular cardiac activity, said method
comprising the steps of: (a) determining a plurality of time
intervals each corresponding to a respective time period between
successive ones of a sequence of heartbeats; (b) determining a mean
and a standard deviation of said plurality of time intervals; (c)
selecting, when a quotient formed by dividing said standard
deviation by said mean has a value greater than or equal to a
threshold value, a shortest one of said plurality of time intervals
and a succeeding time interval that immediately follows said
shortest one; (d) deleting, when said succeeding time interval has
a value greater than said mean, said shortest one of said plurality
of time intervals and said succeeding time interval from said
plurality of time intervals (e) determining an adjusted mean and an
adjusted standard deviation based on remaining ones of said
plurality of time intervals; (f) selecting, when an adjusted
quotient formed by dividing said adjusted standard deviation by
said adjusted mean is greater than or equal to said threshold
value, an adjusted shortest one of said remaining ones of said
plurality of time intervals; (g) redefining, when an absolute value
of the difference between said adjusted shortest one and said
shortest one is less than or equal to a value within a preselected
range between 0.02-0.08 seconds, the value of said shortest one of
said plurality to be that of said adjusted shortest one and the
value of said succeeding one to be that of an interval immediately
following said adjusted shortest one; and (h) repeating steps (d)
through (h) until either an absolute value of a difference between
said adjusted shortest one and said shortest one is greater than
said value within said preselected range, in which case said
cardiac activity is irregular, or until said plurality of time
intervals has less than two values, in which case said cardiac
activity is regular.
5. The method of claim 1 wherein said sequence of heartbeats is
derived from taking a sequence of pulse rates.
6. The method of claim 2 wherein said sequence of heartbeats is
derived from taking a sequence of pulse rates.
7. The method of claim 3 wherein said sequence of heartbeats is
derived from taking a sequence of pulse rates.
8. The method of claim 4 wherein said sequence of heartbeats is
derived from taking a sequence of pulse rates.
9. The method of claim 1 further comprising the step of storing at
least one of said plurality of time intervals, said mean, said
standard deviation, said quotient and said threshold value.
10. The method of claim 2 further comprising the step of storing at
least one of said plurality of time intervals, said mean, said
standard deviation, said quotient and said threshold value.
11. The method of claim 3 further comprising the step of storing at
least one of said plurality of time intervals, said mean, said
standard deviation, said quotient and said threshold value.
12. The method of claim 4 further comprising the step of storing at
least one of said plurality of time intervals, said mean, said
standard deviation, said quotient and said threshold value.
13. The method of claim 1 wherein said sequence of heartbeats is
determined by measuring a sequence of heartbeats.
14. The method of claim 2 wherein said sequence of heartbeats is
determined by measuring a sequence of heartbeats.
15. The method of claim 3 wherein said sequence of heartbeats is
determined by measuring a sequence of heartbeats.
16. The method of claim 4 wherein said sequence of heartbeats is
determined by measuring a sequence of heartbeats.
17. An apparatus for detecting irregular cardiac activity, said
apparatus comprising: a detector for detecting an activity related
to heartbeats at measured times; a processor for determining
whether said measured heart activity is regular or irregular as a
function of at least one of a standard deviation and mean of a
plurality of time intervals of said heart activity, and a shortest
one of said plurality of time intervals, a time interval
immediately succeeding said shortest one, and next shortest time
interval; and a device for outputting an indication whether the
activity is regular or irregular.
18. The apparatus of claim 17 wherein said device is an
inflatable-cuff device and said activity is a pulse beat.
19. The apparatus of claim 17 wherein said device detect changes in
light transmitted through an appendage of an individual and the
activity is a pulse rate.
20. The apparatus of claim 17 wherein said detector is an electrode
device and the measured activity is an actual heart rate.
21. The apparatus of claim 17 wherein said output device is a
printer.
22. The apparatus of claim 17 wherein output device is a
display.
23. The apparatus of claim 17 wherein output device is an auditory
signal generator.
24. The apparatus of claim 17 wherein output device is a vibration
signal generator.
25. The apparatus of claim 17 further comprising a memory
device.
26. The apparatus of claim 17 wherein said processor comprises at
least one of a microprocessor, and application specific integrated
circuit (ASIC), a programmable logic array (PLA) and a reduced
instruction set chip (RISC).
27. The apparatus of claim 17 wherein said processor verifies
normal cardiac activity by carrying out the steps of: (a)
determining a plurality of time intervals each corresponding to a
respective time period between successive ones of a sequence of
heartbeats; (b) determining a mean and a standard deviation of said
plurality of time intervals; and (c) determining, when a quotient
formed by dividing said standard deviation by said mean is less
than a threshold value, that the cardiac activity is regular.
28. The apparatus of claim 17 wherein said processor determines
irregular cardiac activity by carrying out the steps of: (a)
determining a plurality of time intervals each corresponding to a
respective time period between successive ones of a sequence of
heartbeats; (b) determining a mean and a standard deviation of said
plurality of time intervals; (c) selecting, when a quotient formed
by dividing said standard deviation by said mean has a value
greater than or equal to a threshold value, a shortest one of said
plurality of time intervals and a succeeding time interval that
immediately follows said shortest one; and (d) determining, when
said succeeding time interval has a value less than or equal to
said mean, that said cardiac activity is irregular.
29. The apparatus of claim 17 wherein said processor detects
irregular cardiac activity by carrying out the steps of: (a)
determining a plurality of time intervals each corresponding to a
respective time period between successive ones of a sequence of
heartbeats; (b) determining a mean and a standard deviation of said
plurality of time intervals; (c) selecting, when a quotient formed
by dividing said standard deviation by said mean has a value
greater than or equal to a threshold value, a shortest one of said
plurality of time intervals and a succeeding time interval that
immediately follows said shortest one; (d) deleting, when said
succeeding time interval has a value greater than said mean, said
shortest one of said plurality of time intervals and said
succeeding time interval from said plurality of time intervals; (e)
determining an adjusted mean and an adjusted standard deviation
based on remaining ones of said plurality of time intervals; (f)
selecting, when an adjusted quotient formed by dividing said
adjusted standard deviation by said adjusted mean is greater than
or equal to said threshold value, an adjusted shortest one of said
remaining ones of said plurality of time intervals; and (g)
determining, when an absolute value of the difference between said
adjusted shortest one and said shortest one is greater than a value
within a preselected range between 0.02-0.008, seconds that said
cardiac activity is irregular.
30. The apparatus of claim 17 wherein said processor determines
irregular cardiac activity by carrying out the steps of: (a)
determining a plurality of time intervals each corresponding to a
respective time period between successive ones of a sequence of
heartbeats; (b) determining a mean and a standard deviation of said
plurality of time intervals; (c) selecting, when a quotient formed
by dividing said standard deviation by said mean has a value
greater than or equal to a threshold value, a shortest one of said
plurality of time intervals and a succeeding time interval that
immediately follows said shortest one; (d) deleting, when said
succeeding time interval has a value greater than said mean, said
shortest one of said plurality of time intervals and said
succeeding time interval from said plurality of time intervals (e)
determining an adjusted mean and an adjusted standard deviation
based on remaining ones of said plurality of time intervals; (f)
selecting, when an adjusted quotient formed by dividing said
adjusted standard deviation by said adjusted mean is greater than
or equal to said threshold value, an adjusted shortest one of said
remaining ones of said plurality of time intervals; (g) redefining,
when an absolute value of the difference between said adjusted
shortest one and said shortest one is less than or equal a value
within a preselected range between 0.02-0.08 seconds, the value of
said shortest one of said plurality to be that of said adjusted
shortest one and the value of said succeeding one to be that of an
interval immediately following said adjusted shortest one; and (h)
repeating steps (d) through (h) until either an absolute value of a
difference between said adjusted shortest one and said shortest one
is greater than said value within said preselected range, in which
case said cardiac activity is irregular, or until said plurality of
time intervals has less than two values, in which case said cardiac
activity is regular.
31. The method of claim I wherein said threshold value is within
the range of 5% to 10%.
32. The method of claim 2 wherein said threshold value is within
the range of 5% to 10%.
33. The method of claim 3 wherein said threshold value is within
the range of 5% to 10%.
34. The method of claim 4 wherein said threshold value is within
the range of 5% to 10%.
35. The apparatus of claim 27 wherein said threshold value is
within the range of 5% to 10%.
36. The apparatus of claim 28 wherein said threshold value is
within the range of 5% to 10%.
37. The apparatus of claim 29 wherein said threshold value is
within the range of 5% to 10%.
38. The apparatus of claim 30 wherein said threshold value is
within the range of 5% to 10%.
39. A method verifying regular cardiac activity, said method
comprising the steps of: (a) determining a plurality of time
intervals each corresponding to a respective time period successive
ones of a sequence of heartbeats; (b) determining a mean and a
standard deviation of said plurality of time intervals; (c)
selecting, when a quotient formed by dividing said standard
deviation by said mean has a value greater than or equal to a
threshold value, a shortest one of said plurality of time intervals
and a succeeding time interval that immediately follows said
shortest one; (d) deleting, when said succeeding time has a value
greater than said mean, said shortest one of said plurality of time
intervals and said succeeding time interval from said plurality of
time intervals; (e) determining an adjusted mean and an adjusted
standard deviation based on remaining ones of said plurality of
time intervals; and (f) determining, when an adjusted quotient
formed by dividing said adjusted standard deviation by said
adjusted mean is less than said threshold value, that said cardiac
activity is regular.
40. The method of claim 39 wherein said sequence of heartbeats is
derived from taking a sequence of pulse rates.
41. The method of claim 39 further comprising the step of storing
at least one of said plurality of time intervals, said mean, said
standard deviation, said quotient and said threshold value.
42. The method of claim 39 wherein said sequence of heartbeats is
determined by measuring a sequence of heartbeats.
43. The method of claim 39 wherein said threshold value is within
the range 5% to 10%.
44. The apparatus of claim 17 wherein said processor verifies
regular cardiac activity by carrying out the steps of: (a)
determining a plurality of time intervals each corresponding to a
respective time period successive ones of a sequence of heartbeats;
(b) determining a mean and a standard deviation of said plurality
of time intervals; (c) selecting, when a quotient formed by
dividing said standard deviation by said mean has a value greater
than or equal to a threshold value, a shortest one of said
plurality of time intervals and a succeeding time interval that
immediately follows said shortest one; (d) deleting, when said
succeeding time has a value greater than said mean, said shortest
one of said plurality of time intervals and said succeeding time
interval from said plurality of time intervals; (e) determining an
adjusted mean and an adjusted standard deviation based on remaining
ones of said plurality of time intervals; and (f) determining, when
an adjusted quotient formed by dividing said adjusted standard
deviation by said adjusted mean is less than said threshold value,
that said cardiac activity is regular.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] None
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] None
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention generally relates to a method of and
an apparatus for detecting irregular heartbeats and, more
particularly, to monitoring and analyzing pulse rates for detecting
possible atrial fibrillation.
[0005] 2. Discussion of the Related Art
[0006] The heart is the major muscle that functions as the primary
pump for blood flow throughout the body. The heart contains two
upper chambers called atria and two lower chambers called
ventricles. The right atrium receives oxygen-depleted blood while
the left atrium receives blood enriched with oxygen from the lungs.
When the atria are full, the outlet valves within the heart open
and the atria squeeze blood into the ventricles. The right
ventricle then pumps oxygen-depleted blood to the lungs while the
left ventricle pumps oxygen-enriched blood to all parts of the
body. In this fashion, the heart functions primarily as a double
sided pump.
[0007] The heart's internal pacemaker, known as the sinus node,
signals the start of each heart beat. This signal originates in the
right atrium in the sinoatrial node and travels simultaneously to
the left atrium and down to the interatrial septum to the
atrioventricular node. The cycle of electrical stimulation that
normally occurs is referred to as normal sinus rhythm.
[0008] When a rhythm abnormality is present, however, there may
exist an abnormal condition known as fibrillation. Fibrillation may
occur as a result of an abnormality with either the ventricle
and/or the atria. Atrial fibrillation is an abnormal heart
condition in which the atria of the heart provide irregular
impulses to the atrioventricular node so that an irregular
heartbeat results.
[0009] Atrial fibrillation is one of the most common arrhythmias
requiring medical attention. Atrial fibrillation may be caused by a
number of heart conditions, such as angina, myocardial infarction,
heart valve abnormalities, and high blood pressure. These
conditions may stretch or scar the atria, thereby causing
irregularities in the heart system. Atrial fibrillation may also
accompany lung problems or thyroid gland disorders and is also
associated with significant morbidity and possible mortality. All
persons, young and old, female or male, including the visually
and/or sight impaired, may experience atrial fibrillation.
[0010] Atrial fibrillation may occur intermittently or chronically.
The most serious complication of atrial fibrillation is formation
of a blood clot in the left atrium which may result in a stroke.
Many people who develop atrial fibrillation, however, are unaware
of their abnormal rhythm. Some in the medical profession have,
therefore, advocated self screening of the pulse rate to detect for
the possible occurrence of atrial fibrillation. The literature,
however, is generally limited to disclosing instructions for
manually taking one's pulse rate accompanied with additional
descriptive information.
[0011] The reason for taking the pulse rate to detect atrial
fibrillation is that the pulse rate corresponds to the heart rate.
The pumping action of the heart displaces blood in the rest of the
body. The pulse is the movement of blood caused by the heart's
pumping, and the pulse rate is the number of times that the blood
is displaced during a fixed period, conventionally an interval of
one minute.
[0012] Because of the correspondence between the heartbeat rate and
pulse rate, atrial fibrillation causes an irregular detected pulse
wherever a pulse can be palpated. Normal sinus rhythm produces a
heartbeat of a fixed number of beats per minute with equal interval
between beats. Fibrillation is detected when the time between the
beats is irregular, that is the time between beats changes
irregularly.
[0013] There are several devices available that measure both blood
pressure and pulse rate, but none of these devices is capable of
monitoring, detecting and/or communicating whether or not an
irregular heartbeat is present to indicate possible atrial
fibrillation. The commercially available devices measure the number
of pulse beats over a preset time interval, usually ten (10)
seconds, but these devices neither analyze nor determine the
presence of irregular heartbeat rhythms.
[0014] Commercially available devices for determining pulse rates
use several methods including: i) measuring a pulse beat when
systolic pressure peaks are detected such as by using an inflated
cuff that is wrapped around the upper arm, ii) utilizing electrodes
to determine pulse rates in the same manner used while taking an
EKG, and iii) detecting pulse beats from changes in light
transmission through body appendages, such as through the fingers,
where a pulse is recorded whenever the difference in the amount of
light absorbed between one point of the appendage and another point
on the appendage changes. The change in transmission results from
the pulse moveably changing the volume of blood flowing through the
appendage which changes, in turn, the amount of light absorbed in
the appendage.
[0015] What is needed is a method and apparatus to detect the pulse
beats during a certain interval of time.
[0016] What is needed is a method and apparatus to detect the
presence of irregular heartbeats and communicate this condition to
the user so that the user is alerted to consult a medical
practitioner for further testing and/or treatment.
[0017] What is also needed is a method that can differentiate an
irregular pulse rate pattern from a normal pulse rate pattern and
from common heart rhythm patterns that are not of significant risk,
such as regular sinus rhythm, sinus arrhythmia, atrial premature
beats and ventricular premature beats.
[0018] What also is a needed is a home monitoring method and
apparatus that analyzes pulse rates for the presence of irregular
pulse rhythms and that communicates this information to the
user.
[0019] What further is needed is a method of and an apparatus for
detecting irregular pulse rhythms during a time period and storing
this information so that comparisons may be made with the pulse
rate rhythms at later times.
[0020] What is further needed is a noninvasive and relatively
simple method and apparatus that monitors pulse rate irregularities
to detect fibrillations, including the possibility of atrial
fibrillation, and that is suitable for use of all ages, and by the
hearing and/or visually impaired and that is relatively easy to
use.
[0021] What is still further needed is a monitoring method and
apparatus that detects the presence of irregular heartbeats and
then displays and stores: i) the number of irregular pulse beats
during a pre-selected time interval; and ii) the duration of time
between beats during selected intervals.
[0022] Yet another need is for a monitoring method and apparatus
that determine whether or not a heartbeat is irregular based on
algorithmic or heuristic operations performed on selected pulse
rate or heartbeat data.
BRIEF SUMMARY OF THE INVENTION
[0023] The present invention provides a method and apparatus that
(i) detects the presence of irregular heartbeats by analyzing a
pulse rate pattern, that is, by analyzing the pulse beat rhythm
during a time interval; (ii) determines whether this pulse rate
pattern indicates a possible atrial fibrillation or other
irregularity; and then (iii) communicates this information to the
user so that a medical practitioner may be consulted for further
testing and/or treatment. The present invention also provides a
Method of and an apparatus for detecting irregular pulse rhythms
during a time period and storing this information for comparison
with the pulse rate rhythm at later time periods. The present
invention may also detect irregular pulse rhythms over multiple
time periods and capture the similarities and/or differences in the
pulse rate for selected intervals over various time periods.
[0024] The present invention further provides a noninvasive method
of and an apparatus for monitoring pulse rate irregularities to
detect atrial fibrillation. The invention may store and display
information such as the number of irregular pulse beats during
pre-selected time intervals and the duration of time between beats
during the selected intervals. The invention also determines the
presence of an irregular heartbeat via algorithmic or heuristic
operations performed on the relevant data.
[0025] For patients with a baseline rhythm abnormality, or for
those who want improved accuracy for detecting atrial fibrillation,
a device comprised of electrodes may be placed on the skin. This
device uses the actual electrocardiogram, in contrast to the pulse,
to determine whether an atrial fibrillation warning should be
indicated. The electrodes may be wrist straps that are placed on
the arms or which are removably secured to various areas on the
torso, arms or legs. This device may be used in conjunction with an
electrocardiogram (EKG) recording device. The device may record the
electrocardiogram, analyze the heartbeats, and display the
appropriate warnings when pre-selected criteria for fibrillation
are met. The present invention also works using either the
heartbeat rate or the pulse rate.
[0026] Pulse rates may also be monitored by tracking the systolic
peak that coincides with each heartbeat. Typically, an inflatable
cuff is wrapped around the upper arm of a person and is inflated to
a pressure greater than the person's blood pressure. Each heartbeat
causes a rise in the blood pressure up to a systolic peak which
corresponds to a pulse beat.
[0027] Pulse rates may also be monitored through changes in light
transmitted through various body appendages. Each pulse beat
changes the light transmission through a location on the appendage.
The change in the light transmission over a time interval yields a
pulse rate or an average pulse rate.
[0028] A monitoring method of the present invention includes
detecting irregular pulse beats, analyzing the irregularity based
on one or more predetermined factors, and communicating this
information to a user such as via a screen display, a paper
printout, a tone, or auditory, vibratory or other sensory
communication.
[0029] In a preferred embodiment, the invention utilizes
algorithmic or heuristic techniques to determine whether the
irregular pulse beat(s) signals the possible presence of atrial
fibriallation.
[0030] The present invention is also directed to an apparatus for
performing the above-described methods.
[0031] Other features and advantages of the present invention will
become apparent from the following detailed description of the
invention with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The invention will now be described in greater detail in the
following detailed description with the reference to the drawings
in which:
[0033] FIG. 1 is a flow chart depicting the various steps of the
method for detection of possible atrial fibrillation in accordance
with the invention.
[0034] FIG. 2 is a diagram showing an arrangement for detecting
possible atrial fibrillation using an inflated cuff in accordance
with the invention.
[0035] FIG. 3 is a diagram showing an arrangement for detecting
possible atrial fibrillation by detecting changes in the amount of
blood that is absorbed in an appendage area in accordance with the
invention.
[0036] FIG. 4 is a diagram showing an arrangement detecting
possible atrial fibrillation using electrodes placed on the skin of
an individual in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0037] FIG. 1 illustrates a preferred method for analyzing pulse
beat patterns for the detection of atrial fibrillation by comparing
the standard deviation for a fixed number of intervals. Initially,
N samples are taken by measuring the pulse rate over N intervals,
as step 102 shows. Then, as shown at step 104, the mean value M and
the standard deviation SD of the N sample values are
calculated.
[0038] In the vast majority of people with regular sinus rhythm or
sinus arrhythmia, the standard deviation for a fixed number of
intervals N is less than or equal to a fixed percentage of the
mean, P which has been shown to be about in the range of 5%-10%,
with 7% being the preferred value of P. As step 106 shows, when the
ratio of SD/M is less than P, the heart rhythm is regular, as step
108 shows. If the ratio is greater than or equal to P, further
analysis is needed.
[0039] Most people with atrial or ventricular premature beats have
a normal underlying rhythm. The premature beats generally occur
within a shorter fixed interval after a normal beat and are
followed by an interval which is generally longer that the normal
sinus interval. The method of FIG. 1 determines if the premature
beats meet these criteria. As step 110 shows, the shortest interval
I.sub.s of the N samples and the interval immediately succeeding
the interval I.sub.s, known as I.sub.s+1, are determined. Then, as
step 112 shows, if the interval I.sub.s+1 is less than or equal to
the mean value M, the heart activity is considered irregular. If
the interval I.sub.s+1 is more less than M, then the intervals
I.sub.s and I.sub.s+1 are deleted from the N sample values, as step
116 shows, and an adjusted mean M' and standard deviation SD' are
determined from the remaining intervals. As step 118 shows, when
the ratio of SD'/M' is less than P, the heart activity is regular,
as step 120 shows. If the ratio is greater than or equal to P, then
the shortest interval among the remaining intervals, I.sub.s2 is
selected, as shown at step 122. The absolute value of the
difference between I.sub.s2 and I.sub.s is calculated and compared
to an empirically determined value in the range of 0.02-0.8 seconds
wherein the preferred value is 0.04 seconds, as shown at step 124.
If the absolute value of the difference is greater than the value
0.04 seconds, then the heartbeat is irregular, as step 126 shows.
Otherwise, as step 128 shows, the shortest interval of the
remaining intervals, I.sub.s2, is redefined as I.sub.s2, the
immediately following interval is defined as I.sub.s+1 and steps
112, 116, 118, 122 and 124 are repeated.
[0040] The process is repeated until all the intervals
corresponding to premature beats are eliminated from the sample and
whether the heart activity is normal or irregular is determined.
For the occasional patient with premature beats after every normal
beat, the algorithm will eliminate all the beats and thereby
indicate that the rhythm was a regular rhythm and not atrial
fibrillation. For such patients, the standard deviation cannot be
calculated because less than two intervals remain in the sample, as
shown in step 130.
[0041] An example, N=16 intervals are recorded, the mean of the N
intervals is M=0.87 seconds, and the standard deviation is SD=0.03
seconds. If a threshold value is P=7%, then 0.03/0.87<0.07,
i.e., SD/M<P. Here, SD/M is less than the threshold value, P,
and therefore the sample is regular.
[0042] Alternatively, if N=16, M=0.87 seconds and SD=0.12, then
0.12/0.87>0.01 or SD/M>P. In this case, the shortest interval
of the first fifteen intervals will be selected which, for example,
is I.sub.s=0.52 seconds. If the interval I.sub.s is immediately
followed by an interval I.sub.s+=0.70, the value of I.sub.s+1 is
less than the value M and the rhythm is irregular because the
premature beat is followed by an interval which is shorter than the
normal sinus interval. Alternatively, if the value of
I.sub.s+1=0.90 seconds, I.sub.s+1 is greater than M, and both
I.sub.s+1 and I.sub.s are removed from the next calculations. A new
mean M' and standard deviation SD' are calculated from the
remaining 14 intervals. If a new standard deviation, SD', divided
by the new mean M' is less than P, so that SD'/M<P, then the
sample is regular. If not, then the next shortest interval I.sub.s2
is compared to the first shortest interval I.sub.s. If the absolute
value of the difference between the two values is greater than the
range 0.02-0.08 seconds, then the rhythm is irregular. If it is
less than or equal to 0.04 seconds, then the interval following the
second shortest interval I.sub.s2, I.sub.s2+1, is determined. If
this value is less than or equal to the original mean M, then the
rhythm is irregular. If it is greater than M, then the I.sub.s2 and
I.sub.s2+1 values are removed from the samples, and a new mean and
new standard deviation is calculated from the remaining 12
intervals. The process is iterated until the rhythm is determined
to be irregular, is determined to be regular or until only one
interval remains. In the latter case the rhythm is determined to be
regular.
[0043] FIGS. 2, 3 and 4 illustrate arrangements which carry out the
method of the invention.
[0044] FIG. 2 shows an embodiment of the invention in which
heartbeat irregularities and possible atrial fibrillation are
detected using an inflated-cuff device 202. The inflated-cuff
device may be a known apparatus which monitors pulse rates by
tracking the systolic peak that coincides with a heartbeat. An
inflatable cuff is wrapped around the upper arm of an individual
and is inflated to a pressure that is greater than the individual's
blood pressure. Each heartbeat creates a rise in the individual's
blood pressure which corresponds to a pulse beat. The time of each
pulse beat is delivered to a processor 204 which includes
instructions that carry out the method shown in FIG. 1. Further,
the processor 204 stores the time of each pulse beat, the intervals
between pulse beats, and other information in a memory 206. The
memory 206 may include RAM or other device memory or include a hard
disk, a floppy disk or other memory devices. The processor 204 may
comprise a microprocessor, and applications specific integrated
circuit (ASIC), a programmable logic array (PLA) or reduced
instruction set chip (RISC).
[0045] The processor 204 carries out the steps shown in FIG. 1
until it is determined that the heartbeat is regular or irregular.
The processor then delivers the results to a printer 208 a display
210 a vibration generator, and/or an auditory generator, etc. which
may include an indication that the heartbeat is regular, irregular,
in possible atrial fibrillation, or that a physician should be
contacted. Other information, such as the heart rate or pulse rate,
may also be displayed.
[0046] FIG. 3 shows another embodiment of the invention in which
the pulse rate is monitored through changes in light transmitted
through a body appendage, such as a finger. Light is transmitted by
a light source 300 through the finger, or other appendage of an
individual, and is received by a detector 302 which measures the
change in light transmitted through the appendage to detect a pulse
beat. The detector 302 may comprise a known pulse measurement
device. The detector 302 delivers the time of each measured pulse
to the processor 204 which carries out the operations described
above regarding FIG. 2.
[0047] FIG. 4 shows a further embodiment of the invention in which
actual heartbeats are measured using an electrode device 402 in
which electrodes are placed on various locations of an individual.
The electrodes may include wrist straps that are placed on the arms
or other contacts which are removably secured to various areas on
the individual including the torso, arms and legs. The electrode
device 402, which may operate in a manner similar to a known EKG
device, delivers the time of each measured heartbeat to the
processor 204. The processor 204 then carries out the operations
described above.
[0048] Advantageously, the invention provides a method and
apparatus that easily detect the presence of irregular heartbeats
from a plurality of heartbeats, pulses or other measurements.
[0049] As a further advantage, the invention differentiates normal
heart activity from irregular heart activity.
[0050] A still further advantage is that the invention provides
relatively simple, non-invasive home monitoring.
[0051] Although the present invention has been described in
relation to particular embodiments thereof, many other variations
and modifications and other uses may become apparent to those
skilled in the art. It is preferred, therefore, that the present
invention be limited not by this specific disclosure herein, but
only by the appended claims.
* * * * *