Effects of Different Types of Verbal Activities on Heart Rate Variability

doi:10.4236/eng.2013.510B063

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Engineering, 2013, 5, 310-313

http://dx.doi.org/10.4236/eng.2013.510B063 Published Online Octob er 2013 (http://www.scirp.org/journal/eng)

Effects of Different Types of Verbal Activities

on Heart Rate Variability

Ping Shi, Youfang Fang, Hongliu Yu*

School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, Shanghai, China

Email: *[email protected]

Received July 2013

ABSTRACT

In the p resent stud y, the effec ts of d ifferent types o f verbal activitie s on heart rate variability (HRV) were investigated.

ECG signals were recorded in ten volunteers during resting (R), reading silently (RS), re ading aloud (R A) and talking

freely (TF). Time domain, frequen c y do main a nd Poincaré plot measures of HRV were calculated for analyz ing. Time

domain parameter of pNN50, frequency domain parameter of LF (n. u.) and Poincaré plot parameter of SD1/SD2 were

found statistica lly difference in RA and TF compared to R and RS. The re sults in this study show that HRV decreased

while subjects were reading aloud and talking freely. The results also indicated that verbal activities of reading aloud

and talking freely impr ove t he sympathetic ner vous activity.

Keywords: Verbal Activities; H e a rt Rate Variabilit y; Time Domain Analys is; Fr e quency Domain Analysis;

Poincaré Plot Param eters

1. Introduction

Heart rate variability (HRV) has been recognized as a

simple and va luable to ol to assess the re gulation o f heart

rate behavior. It reflects the homeostatic interplay be-

tween perturbations in cardiovascular functions and the

dynamic responses of the cardiovascular regulatory sys-

tems [1]. There is considerable interest in HRV because

their measures such as the standard deviation of the in-

terbeat intervals (the RRI), have been shown to be some

of the strongest independent predictors of mortality after

myocardial infarction [2]. Moreover, other techniques

such as spectral analysis and nonlinear analysis (such as

Poincaré plot) of the RRI of HR have been widely used

in HRV studies [3-5], and on some occasions they have

been shown to discriminate between subjects with dif-

ferent cardiac c onditio ns as well a s to pr edict mortality in

some groups of patients. Several types of verbalization

including reading silently, reading aloud and talking

freely occurs in our daily life. The aim of this paper is to

investigate t he effect of different co nditions of verbaliza-

tion on HRV .

2. Method s

2.1. Protocols

The study was performed in ten normotensive male vo-

lunteers (20.2 ± 1.6 years). None of the subjects was

taking medication. The subjects gave written informed

consent and the study protocol was approved by the Eth-

ics Committee of the University of Shanghai for Science

and Technology, China.

All the tests were carried out while the subjects rested

in the 135 degree sitting position on a co mfortable chair.

Subjects were asked a resting period of at least 15 mi-

nutes before ECG signals were recording. Recordings

were made in random order during: 1) resting; 2 ) reading

a text silently (5 min); 3) reading the same text aloud (5

min); 4) normal talking (5 min).

2.2. Measurement of HRV

Like many other physiological parameters, HRV is in-

fluenced by a variety of factors like sex, age, diurnal

rhythms, respiration, fitness levels, posture and physical

activity. In 1996, Task Force of the European Society of

Cardiology (ESC) and the North American Society of

Pacing and Electrophysiology (NASPE) defined and es-

tablished standards of measurement, physiological inter-

pretation and c linica l use of HRV [ 1].

The time domain measures of HRV are based on sta-

tistical or geometric analyses of the lengths of intervals

between successive normal complexes. Frequency do-

main HRV i ndices are deter mined by calc ulating the pow-

er spectral density of the ECG recording using a nonpa-

rametric fast Fourier transform (FFT) algorithm. Poin-

caré plot as a nonlinear method is a scatter outline of the

*Corresponding author.

P. SHI ET AL.

311

current R-R interval plotted against the preceding R-R

interval. The plot delivers not only an outline but also a

detail of beat-to-beat behavior of cardio-physiology.

Time domain parameters, frequency domain parameters

and Poincaré plot parameters included in this paper for

evaluation were listed in Table 1.

2.3. Statistics

Values are presented as mean ± standard error of the

mean (SEM). The significance of difference was ana-

lyzed using one-way ANOVA with repeated-measures.

The statistical analyses were run in MATLAB software

(MathWorks Inc., MA, USA). A P < 0.05 was considered

statisticall y significant.

3. Resul ts

In this paper, the parameters of time domain, frequent

domain and Poincaré plot parameters were sued to eva-

luate the HRV in different types of verbal activities. As

shown in Figure 1, pNN50 in RA and TF significantly

decreased compared to R and RS (P < 0.05). SDRR in TF

significantly increased co mpared to R and RS (P < 0.05).

Smaller RRIs were found in RA and TF compared to R

and RS although on significant differences were found.

No differences were found for RMSSD between different

types of verba l a c tivities.

Table 1. Time domain parameters, frequency domain pa-

rameters and Poincaré plot parameters included in this

paper for evaluation.

Var iable Units Description

Time domain parameters of HRV

RRI ms The length of R-wave to R-wave intervals.

SDNN ms St andard deviation of all NN intervals.

RMSSD ms

The square root of the mean of the sum of

th e squares o f dif f erences betwe en adjacent

NN interva ls .

pNN50 %

NN50 c o unt div i d e d by the tota l number

of all NN intervals.

Frequency domain parameters of HRV

LF norm n.u.

LF power in normalized units,

LF/(Total Power-VLF) × 10 0,

Frequency range: 0.04-0.15 Hz

HF norm n.u.

HF power in normalized units,

HF/(Total Power-VLF) × 100,

Frequency range: 0.15-0.4 Hz

LF/HF Ratio LF [ms2]/HF [ms2]

Poincaré plot parameters of HRV

SD1 ms

instantaneous beat-to-beat variance

of the R-R intervals

SD2 ms

the long-term continu ous variance

of all R-R intervals

SD1/SD2 Ratio SDl/SD2

(a)

(b)

(c)

(d)

Figure 1. Time domain parameters of HRV for different

types of verbal activities. (a) RRI, (b) pNN50, (c) RMSSD,

(d) SDRR *p < 0.05 compared to R, †p < 0.05 compared to

RS.

P. SHI ET AL.

312

As shown in F igure 2, RA and TF augmented LF (n.u.)

significantly compared to R and RS (P < 0.05). LF/HF

increased significantly in TF compared to R (P < 0.05).

No differences were found for HF (n.u.) between differ-

ent types of verbal a c tivities.

As shown in Figure 3, SD2 significantly increased in

TF compared to R and RS, and significantly increased in

RA compared to RS. Significant smaller SD1/SDs were

found in RA and TF compared to R and RS (P < 0.05).

No differences were found for SD2 between different

types of verba l a c tivities.

(a)

(b)

(c)

Figure 2. Frequency domain parameters of HRV for dif-

ferent types of verbal activities. (a) LF (n.u.), (b) HF (n.u.),

RS.

(a)

(b)

(c)

Figure 3. Poincaré plot parameters of HRV for different

types of verbal activities. (a) SD1, (b) SD2, (3) SD1/SD2. *p

< 0.05 compared to R, †p < 0.05 compared to RS.

4. Discussion

HRV, the amount of fluctuation of the beat to beat dif-

ferences, is known to be a reliable, noninvasive marker

of autonomic nervous system activity. Assessment of

HRV may provide quantitative information on the mod-

ulation of cardiac vagal and sympathetic nerve input.

HRV analysis is a recognized tool for the estimation of

cardiac autonomic modulations. Reduced HRV is a po-

werful and independent predictor of an adverse prognosis

in patients with cardiac disease. In this study, the meas-

P. SHI ET AL.

313

ures of HRV include time domain parameters, frequency

domain parameters and Poincaré plot parameters.

Both reading aloud and talking freely caused the de-

creased pNN50s, indicating a reduction in HRV. The

condition of talking freely tended to a higher sympathetic

activity as evidenced by changes of SDNN only found in

talki ng fr ee l y.

Spectral analysis of HRV is a useful, noninvasive te-

chnique to study the short-term (2 - 5 min) autonomic

modulation o f HR. For the frequency-do main parameters

of HRV, the power value of the HF content is considered

a pure measure of parasympathetic activity, while the

power value of the LF content is reflective of both sym-

pathetic modulation and parasympathetic tone [1,6].

LF/HF ratio was considered as an index of sympathetic

activity as well as the balance between the sympathetic

and parasympathetic nerves [6-8]. The results, from

spectral analysis of HRV in this study, indicated that the

conditions of reading aloud and free talking influe nce th e

sympathetic modulation and parasympathetic tone, and

that sympathetic activity increased only during free talk-

ing compared to the condition of resting.

In this study, Poincaré plot parameters were investi-

gated to reflect autonomic function changes associated

with different types of verbal activities. SD1 is mediated

by vagal efferent activity. SD2 is influenced by both pa-

rasympathetic and sympathetic tone. SD1/SD2 ratio

could be used as an indicator of sympathetic activity. The

results from Poincaré plot analysis of HRV in this study

indicated that the sympathetic activity increased in con-

ditions of reading aloud and free talking compared to

resting and reading silently.

5. Conclusion

Overall, these results indicated that HRV decreased

while subjects were reading aloud and talking freely, and

that verbal activities of reading aloud and talking freely

improved the sympathetic nervous activity. Although

both sympathetic and parasympathetic activity were mo-

dulated evidenced by the present results, the parasympa-

thetic activity cannot be determined by the present re-

sults.

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