Biology Reference
In-Depth Information
Let m be the median for the lengths of a sequence of observed RRIs and
x be the length of a single RRI. For this interval, the quantity (x
m)
2
could be used as a measure describing the deviation of the RRI length
from the median length m. In the language we employed in Chapter 5,
we can view this quantity to be the risk assigned to the RRI of length
x because of its deviation from the median value m.
The problem we faced in Chapter 5 was quite similar. The question
there was to separately assess the risk for hypoglycemia because
of low blood glucose readings and the risk for hyperglycemia because of
high blood glucose readings. Fundamentally, our problem here is
identical—we need to assess the magnitude of the risk for RRI
decelerations as measured by positive deviations from m, and the
risk for RRI accelerations, as measured by negative deviations from m.
In that sense, R
1
corresponds to the Low BG Index, and R
2
corresponds
to the High BG Index from Chapter 5. Thus, following the same
approach, for any RRI of length x, we define the quantities:
(
2
ð
Þ
>
x
m
for
x
m
rd
ð
x
Þ¼
0
for
x
m
(6-1)
and
(
2
ð
x
m
Þ
for
x < m
ra
ð
x
Þ¼
0
for
x
m
:
The function rd(x) describes the degree of deviation to the right from
the median value (risk for deceleration) while the function ra(x)
describes the degree of deviation to the left from the median (risk for
acceleration).
E
XERCISE
6-3
Compare the definitions in Eq. (6-1) with the definitions for rl and
rh given by Eq. (5-5) in Chapter 5. What are the similarities and
differences?
Consider now a sequence of RRIs of lengths x
1
,x
2
,
x
n
and let m denote
the median of the data. Using the weighing functions in Eq. (6-1), define
two quantities representing the sum of the weighted deviations to the
left and to the right of the median
...
m
as follows:
n
X
n
X
n
n
1
1
R
1
¼
ra
ð
x
i
Þ
and R
2
¼
rd
ð
x
i
Þ:
(6-2)
i
¼
1
i
¼
1
