RESPIRATORY SINUS ARRHYTHMIA IN 10 YEAR OLDS

Normal and Intrauterine Growth Restricted

Taher Biala

, Fernando Schlindwein

, Michael Wailoo

and Michael Bankart

Department of Engineering, University of Leicester, U.K.

Department of Health Science, University of Leicester, U.K.

Keywords: Respiratory sinus arrhythmia, Frequency domain analysis, Autoregressive model, Hypertension, Barker

theory.

Abstract: Frequency domain analysis of RR has been determined by three methods, autoregressive model (AR), Fast

Fourier Transform (FFT) and Lomb periodogram for 10 min segments. The first two methods were done

after resampling and the third method without resampling RR series of all 75 children. AR was used in this

work, and RSA was identified at night time during sleep. The area of the RSA was calculated for every 10

min interval and compared to the overall area of the 10 min segment, then the average RSA of all segments

was calculated, as well as the overall percentage of the RSA energy to the total area for the whole period of

sleeping. This was done firstly for a sample of Normal and IUGR 10 year olds. Secondly for all the children

under study, an independent t-test concluded that there is no significant difference between the IUGR and

Normal (p=0.7467).

1 INTRODUCTION

HRV is a powerful non-invasive tool used by

physicians to determine the state of the heart and

assess the development of the ANS. This work

describes the results obtained by HRV analysis of

two groups of children, 41 IUGR and 34 controls for

a period of 24 h .The main objective of the work is

to find any correlation between HRV of children at

10 years and the Barker Theory and hypothesis,

which states that IUGR children are prone to

coronary disease and hypertension in their adulthood

(Barker, 2004). The RR interval normally oscillates

periodically, shortening with inspiration and

lengthening with expiration. This is known as

Respiratory sinus arrhythmia, and it’s due partly to

the Bainbridge reflex via the expansion and

contraction of the lungs and the cardiac filling

volume caused by variations of intrathoracic

pressure (Azuaje et al., 2007). During inspiration,

the pressure within the thorax decreases increasing

blood influx into the right atrium resulting in a reflex

that increases the heart rate (i.e., shortens the RR

intervals). During expiration, the reverse of this

process results in a slowing of the heart rate.

2 METHODS

The Task force (Task force of European Society of

Cardiology and the North American, 1996) specifies

the standards used in HRV studies, where time

domain and frequency domain analysis can be used

to study heart rate variability.

The RR signal is subjected to a process of

interpolation to obtain an equally spaced data to be

used for spectral analysis. FFT and AR must have an

equally spaced data to perform spectral analysis. The

signal has been re-sampled at 4 Hz after a cubic

spline data interpolation. This will give us the results

in Hertz and allows the spectrum analysis up to 2

Hz. The AR spectral method (equation 1),(because

of better resolution than FFT when dealing with low

sampling Frequency), have been tested on the RR

data to find the frequency components of the power

spectrum for 10 min segments .The RSA frequency

range (HF) is defined to be from 0.15 to 0.40 Hz

(Azuaje et al., 2007).

510

Biala T., Schlindwein F., Wailoo M. and Bankart M. (2009).

RESPIRATORY SINUS ARRHYTHMIA IN 10 YEAR OLDS - Normal and Intrauterine Growth Restricted

In Proceedings of the International Conference on Bio-inspired Systems and Signal Processing, pages 510-513

 SciTePress

2.1 Figures and Tables

The AR spectral analysis of 10 segments produces a

graph as shown in Fig. 1. Graphs (a, b) are for

Normal children, and (c, d), for IUGR children.

Figure 1(d): AR power spectrum of IUGR child with less

RSA.

The application of an algorithm to find the

energy of the RSA (area), by using Trapezoidal

method (equation 2), produced the following table 1:

Figure 1(a): AR spectrum of Normal child with RSA.

Table 1: The RSA Energy, Total, and % of RSA to Total

for IUGR and Normal children.

child RSA

(energy)

Total

(energy)

RSA/

Total

1 IUGR 4.5936 10.3187 45.6287

2 IUGR 2.3244 5.8750 39.8064

3 IUGR 2.5484 5.5834 45.9105

4 IUGR 5.2631 10.6212 50.0502

5 IUGR 8.5370 18.5431 46.6481

6 Normal 6.9783 12.6834 54.7855

7 Normal 2.6899 6.7861 41.3924

8 Normal 3.6029 9.0093 40.0707

9 Normal 5.0364 11.0507 45.2321

10 Normal 3.7838 8.8850 43.0941

Figure 1(b): AR spectrum of Normal child with less RSA.

2.2 Equations

The equation of AR process of order p can be

written as:

Figure 1(c): AR power spectrum of IUGR child with RSA.

ptptttt

xaxaxanx

−−−

...

2211

RESPIRATORY SINUS ARRHYTHMIA IN 10 YEAR OLDS - Normal and Intrauterine Growth Restricted

511

Table 3.

where is the white noise driving signal p is the

order of the AR model, and ( ) are the

parameters of the filter.

Variable p-value

Sex * 0.32

Breast Feeding (y/n) * 0.50

Parental Smoking (y/n) * 0.99

Household Smoking (y/n) * 0.72

IMD # 0.06

24 hour SBP # 0.59

24 hour DBP # 0.87

BMI # 0.77

Significant Medication * 0.26

Using Medication * 0.36

Birth Weight # 0.45

Length Gestation # 0.50

Weight change from birth # 0.77

Night SBP # 0.79

Night DBP # 0.60

Day SBP # 0.46

Day DBP # 0.64

Cortisol morning # 0.29

Cortisol night-time # 0.66

aa .......

The AR power spectrum density estimate is

given by the following equation (Boardman et al.,

2002):

)(

∑

Δ−

tfkj

(1)

Where

is the variance of the white noise

driving function and

t is the re-sampling interval.

The Trapezoid method in equation (2) was used

to find the energy (area) of the RSA:

(2)

)( hba

Where (a and b) are the two parallel sides and h

is the distance (height) between them.

* = independent t-test, # = correlation

Statistically, an independent t-test was used for

equality of means between IUGR and Normal in

terms of RSA, and to verify the Null hypothesis

which is, there is no difference in the RT score

(Average of all ratio of RSA energy to total energy

within 10 min segment for night time).

3 DISCUSSION

The results obtained are both qualitative and

quantitative. The graphs in Figures 1(a) and 1(b),

show the evolution of the AR spectrum of the HRV

for a Normal child. It can be seen that the RSA

energy in child (a) is higher than the RSA energy for

Normal child shown in Figure 1(b). The frequency at

which RSA occurs in (a) is at 0.3 Hz, but for child

(b), RSA occurs at 0.25 Hz. The RSA for IUGR

children can be seen in figures 1(c) and 1(d). Child

(d), has RSA at Frequency of 0.2 Hz, and Child (c),

at approximately 0.25Hz. The calculations of RSA

energy from IUGR and Normal children are shown

in table 1 in arbitrary units squared (gain is not

calibrated). The data presented in the table shows

that the lowest energy of RSA is 39.8 u

, and the

highest is 50 u

for IUGR. Normal children has the

lowest energy of RSA is 40 u

, and the highest is

54.78 u

Table 2 and 3 shows the results of the

independent t-test:

Table 2: IUGR and Normal Independent t-test results.

Group

n Mean SD

IUGR 37 46.83 6.10

Normal 30 47.27 4.65

The t-test showed that there was no significant

difference between the two groups for RT score,

difference = 0.44, t = 0.32, p=0.7467 (95% CI = -

3.1, 2.3). There was homogeneity of variance

(Levene’s Test, p=0.14) and the data was

approximately normally distributed within each

group.

The result of the t-test shows no significant

difference between the two groups for the RT score,

but when looking at other variables, IMD was found

to be(p=0.06). Which means that the children who

have high index of multiple deprivation (IMD) are

very correlated with RT score, and consequently this

Other variables were assessed for significance

but none of them significantly predicted (RT) score,

although IMD (Index of Multiple Deprivation) was

borderline (0.06).

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512

means that the deprived children don’t have a

synchronized breathing pattern at night time.

4 CONCLUSIONS

This work identifies the RSA in two ways, the first

is graphically, and the second, in terms of the RSA

Energy (area). RSA is an interesting phenomenon

which represents the parasympathetic branch of the

Autonomic nervous system. RSA occurs at

frequency between 0.15 Hz and 0.4 Hz at night time

and at this frequency (HF), RR intervals tend to be

longer than at day time due to the parasympathetic

tone, and consequently heart rate will be slower. At

night ventilation is more regular; hence it is easier to

identify the peak corresponding to RSA.

RSA can not be used to distinguish between the

IUGR and normal children, because there is no

significant difference between the two groups. Other

variables, such as parental smoking and household

smoking can not predict any differences in RSA.

Children who have high index of multiple

deprivation (IMD) are very correlated with RT

score, and consequently this means that the deprived

children don’t have a synchronized breathing pattern

at night time.

REFERENCES

Barker DJP, “The development origin of chronic adult

disease.” Acta Paediaatrica., volume 93, pp, 26-33

(2004).

Azuaje F., Clifford D.G., MacSharry P., “Advanced

Method and tools for ECG Data Analysis”, (2007).

Task force of European Society of Cardiology and the

North American, “Heart Rate variability-Standards of

measurements, physiological interpretation, and

clinical use”, circulation, volume 93, pp. 1043-1065,

(1996).

Boardman A., Leite A., Rocha A., Schlindwein F., “A

study on the optimum order of autoregressive models

for heart rate variability” Physiological Measurement

volume 23, N.2, pp. 235-336, (2002).

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