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
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.),
(c) LF/HF. *p < 0.05 compare d to R, †p < 0.05 compared to
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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