Download Extraction of Response Waveforms of Heartbeat and Blood Pressure

179
Original Articles
Extraction of Response Waveforms
of Heartbeat and Blood Pressure
to Swallowing
Using Mixed Signal Processing of Time Domain and
Respiratory Phase Domain
T. Numata1; Y. Ogawa1; K. Kotani1,2; Y. Jimbo1,2
1Graduate
2School
School of Frontier Science, The University of Tokyo. Tokyo, Japan;
of Engineering, The University of Tokyo, Tokyo, Japan
Keywords
Heart rate variability, Hilbert transform, respiratory phase, blood pressure variability,
swallowing
Summary
Background: Evaluating the accurate responses of the cardiovascular system to external stimuli is important for a deeper
understanding of cardiovascular homeostasis. However, the responses should be distorted by the conventional time domain
analysis when a frequency of the effect of external stimuli matches that of intrinsic fluctuations.
Objectives: The purpose of this study is to
propose a mixed signal processing of time
domain and respiratory phase domain to
extract the response waveforms of heartbeat
and blood pressure (BP) to external stimuli
and to clarify the physiological mechanisms
of swallowing effects on the cardiovascular
system.
Methods: Measurements were conducted
on 12 healthy humans in the sitting and
Correspondence to:
Takashi Numata
Graduate School of Frontier Science
The University of Tokyo
#303, Building 4, RCAST
4-6-1 Komaba, Meguro
Tokyo 153-8904
Japan
E-mail: [email protected]
standing positions, with each subject requested to swallow every 30 s between expiration and inspiration. Waveforms of respiratory sinus arrhythmia (RSA) and respiratoryrelated BP variations were extracted as functions of the respiratory phase. Then,
respiratory effects were subtracted from
response waveforms with reference to the
respiratory phase in the time domain.
Results: As a result, swallowing induced
tachycardia, which peaked within 3 s and recovered within 8 s. Tachycardia was greater
in the sitting position than during standing.
Furthermore, systolic BP and pulse pressure
immediately decreased and diastolic BP increased coincident with the occurrence of
tachycardia. Subsequently, systolic BP and
pulse pressure recovered faster than the R-R
interval.
Conclusions: We conclude that swallowinginduced tachycardia arises largely from the
decrease of vagal activity and the baroreflex
would yield fast oscillatory responses in
recovery.
Methods Inf Med 2015; 54: 179–188
http://dx.doi.org/10.3414/ME14-01-0050
received: May 2, 2014
accepted: September 23, 2014
epub ahead of print: November 14, 2014
1. Introduction
The autonomic nervous system (ANS)
regulates the cardiovascular (CV) system
for the purpose of maintenance of physiological homeostasis, taking into account
the CV system responses to external stimuli and recovering to its previous state.
Therefore, it is effective to extract the CV
response induced by external stimuli for
understanding the response mechanism
of the CV system and the dynamics of
ANS control.
Human heartbeat and blood pressure
(BP) always fluctuate with intrinsic fluctuations such as respiratory sinus arrhythmia
(RSA), and Mayer wave, which is the oscillations of arterial pressure, even at rest
[1– 7]. Although evaluation of average response waveforms across groups of subjects [8 –10] has been generally used to
evaluate response in the time domain, the
average response would be distorted when
the swallowing effects have a frequency
that matches that of intrinsic fluctuations
such as RSA and Mayer wave. For the same
reason, the frequency domain analyses or
time-frequency domain analyses cannot be
directly applied for evaluation of the CV
responses to swallowing. In addition, the
conventional linear parametric model or
cross-spectral analysis [11–18] are not appropriate because the timing of respiration
and its effects on CV system is complex
due to time varying rhythms. Further, nonlinear systems identification tools, which
have been applied to investigate the mutual
interactions of the CV system [19 –22], are
limited when we take higher-order nonlinearity into account due to the drastic
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T. Numata et al.: Response Waveforms of Heartbeat and BP to Swallowing
increase of the parameters required for
identification, and the original timedependent dynamics are obscured.
Recently, a respiratory-phase domain
approach has been developed that successfully extracted the accurate waveform of
RSA [5, 23 –26]. In particular, respiratory
phase domain analysis has also been extended to extract the accurate waveforms
of not only RSA but also respiratory effects
on BP [25]. In addition, circadian changes
of swallowing effects on RSA in the respiratory-phase domain analysis, which circadian rhythms on the CV system should
be regulated by the ANS, was reported in
our previous study [27]. Although the previous study [27] would be able to evaluate
the relationship between swallowing effects
on the CV system and the ANS, this
method does not allow the evaluation of
response waveforms in the time domain.
Neither, the method cannot evaluate the
interactions between heartbeat and BP.
As pertains to the external stimuli, it is
known that the CV system is strongly influenced by some external stimuli. In particular, swallowing has a strong effects on
the CV system, reflecting the control of the
ANS [9, 10, 28, 29]. Since fatal disease presentations such as atrial tachyarrhythmia,
atrial fibrillation, and syncope are sometimes induced by swallowing [30, 31], it is
important in the fields of clinical medicine
and physiology to clarify the swallowing effects on CV system. However, swallowing
effects and relationship between swallowing effects and the ANS are conflicting.
Sheroziya et al. [28] reported that body
position changed the swallowing-induced
tachycardia, while Nitta et al. [9] reported
that it did not. In order to resolve this conflict on the mechanism responsible for CV
changes that accompany swallowing, the
method for accurate evaluation of the response waveforms to swallowing from the
CV system with different body positions in
the time domain is necessary.
In this study, we developed a method
that extracts the response waveforms of
heartbeat and BP during swallowing from
the intrinsic fluctuations in the time domain. We then evaluated the physiological
mechanisms underlying swallowing effects
on the CV system.
2. Methods
2.1 Experimental Procedures
The subjects consisted of 12 young healthy
males without CV and respiratory diseases
with mean age of 23.0 ± 1.3 y who were
tested in experimental sessions in sitting
and standing positions with the resting
state. These experiments were approved by
the Ethics Committee of the Graduate
School of Frontier Sciences (The University of Tokyo). Subsequent to being given a
full description of the study, informed consents were got by all subjects. In both
experiments, swallowing were performed
12 times purposely at intervals of 30 s between expiration and inspiration. There are
two reasons to set these artificial setting.
One is that we expected the enhanced information to evaluate the signal-processing
algorithm with CV time series before swallowing. Since swallows were performed between expiration and inspiration, the CV
fluctuations induced by respiratory activity
should be enhanced just before swallowing,
it is effective to evaluate the signal-processing algorithm with data before swallowing.
The other is to obtain enough rest time between swallows for extracting response
waveforms. Since swallowing were always
performed between expiration and inspiration under the free-timing experiment
[24], and the previous studies show that the
response waveform of heartbeat to swallowing with artificial setting (swallowing
every 30 s) [27] seems to be same as the response with natural setting (free timing)
[24] and fast recovery such as one respiration after swallowing [24], there would be
little impact to the CV system with the artificial setting in this study. In addition,
since paced respiration might result in unnatural hyperventilation or an alteration in
the autonomic balance [32], the experiments were made under free-breathing
conditions. Six subjects performed in
standing position first, followed by sitting,
while the others performed in sitting position first to offset the effect of order.
Data were recorded for 410s in each
session. Measurements of electrocardiographic R-R intervals (RRI) (AC-601G,
Nihon-Koden); radial artery BP, by means
of a tonometric device (BP-608EV, Colin
Medical Technology); instantaneous lung
volume (ILV), by means of inductive plethysmograph (standard type Respitrace,
A.M.I); and the motion of the laryngeal
prominence, by means of two accelerometers (8305A2M4 and 8305B2M4,
Kistler) were performed. Accelerometers
were positioned on the top and the bottom
of the laryngeal prominence. Since swallowing in normal individuals gave rise to a
characteristic acceleration pattern which
was quite reproducible, and signal occurred during laryngeal elevation and the
magnitude of acceleration correlated well
with the laryngeal displacement [33, 34], it
is reasonable to determinate the trigger
point by the accelerations of laryngeal
elevation. The sampling frequency of the
electrocardiogram, BP, and motion of the
laryngeal prominence were 1,000 Hz, and
that of ILV was 100 Hz.
2.2 Signal Processing
In this study, we propose a method of
extracting the response waveforms of
heartbeat and blood pressure to swallowing
in the time domain without the effects of
RSA and Mayer wave. ▶ Figure 1 shows
diagrams of the signal-processing algorithms. First, respiratory induced modulation (RM) is extracted by the same algorithm as a previous study [25] which is
shown in ▶ Figure 1A. Then, the effects of
intrinsic fluctuations such as RM and
Mayer wave are removed and the response
waveforms to swallowing are extracted by
the newly developed algorithm which is
shown in ▶ Figure 1B.
The algorithm for extracting RM
(▶ Figure 1A) is the same algorithm used
in a previous study [25]. First, ILV data was
filtered by a band-pass filter of 0.1–10 Hz.
The band pass filter was the finite impulse
response filter with hamming window and
the order of the filter was 4000. The instantaneous phase ϕ (t ) of signal s (t ) was thus
uniquely defined by using Hilbert transform [25]. To extract the stable waveform
of RSA, RRI data were first converted to an
instantaneous heart rate (HR) time series
by the inverse of the derivative of cubic
spline interpolation (DCSI) method [25].
In addition, systolic BP (SBP), diastolic BP
(DBP), and pulse pressure (PP) were converted to the instantaneous SBP, DBP, and
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T. Numata et al.: Response Waveforms of Heartbeat and BP to Swallowing
Figure 1
Schematic diagrams
of the signal processing in this study.
(A) Extraction of RM
waveforms. BPF,
band-pass filtering;
RRI, R-R interval; SBP,
systolic blood pressure; DBP, diastolic
blood pressure; PP,
pulse pressure; DCSI,
derivative of cubic
spline interpolation;
CSI, cubic spline interpolation. (B) Derivation of averaged
response waveform.
X should be replaced
with RRI, SBP, DBP,
or PP in actual signal
processing.
PP by the method of cubic spline interpolation. SBP is the maximum value and DBP
is the minimum value of the BP in a cycle
of interbeat intervals. PP was obtained as
the subtraction of DBP from SBP. Then, instantaneous RRI, SBP, DBP, and PP were
extracted at every π/10 of ϕ (t ) to obtain
each RM waveform. Thus, CV signals were
interpolated and processed together with
the timing of respiratory phase which were
data from different sampling frequencies.
The RRI, SBP, DBP, and PP data for respiration during swallowing and the following
two respirations after swallowing were removed, and the remaining data were
extracted and averaged as the normal data.
The obtained waveforms demonstrated the
response of heartbeat and BP to normal respirations, which was expressed as a function of respiratory phase. Finally, the time
course of i-th swallowing (RRIi , SBPi ,
DBPi , PPi ) and RM function (RRIRM ,
SBPRM , DBPRM , PPRM ) were obtained and
used in the following signal processing.
▶ Figure 1B shows the algorithm for
extracting the response waveform to swallowing in the time domain. First, the RRI,
SBP, DBP, PP, and respiration phase data
from 5 s before swallowing to 15 s after
swallowing (from –5 s to 15 s) were resampled at a rate of 4 Hz. The waveform
before swallowing (from –5 s to –1 s)
should be flat at the value 0 when the effects of RSA and Mayer wave were sufficiently excluded. Thus, it was used to ensure the validity of the signal processing
in this study. Then, differences between
the data during swallowing and normal
respiration were derived in response to the
respiratory phase of each period. Here we
denote that is a representative expression of
the physiological variables as RRI, SBP,
DBP, or PP (i.e. X Î {RRI, SBP, DBP, PP})
and ti as the onset of the i-th swallow, Xi (t )
as a time course of the i-th swallow (from
–5 s to 15 s), and Xi (t ) as a respiratory
modulation waveform extracted in the respiratory phase domain. The relationship
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T. Numata et al.: Response Waveforms of Heartbeat and BP to Swallowing
between respiratory phase ϕ and time t is
denoted as ϕ = f (t ), which is derived by
Hilbert transform of ILV. Then, the subtraction of respiratory influence is calculated as
(1)
where Xisub(t ) is the time domain waveform
with respiratory modulation subtracted.
Finally, response waveforms of swallowing
Xave(s) from –5 s to 15 s were obtained by
averaging the data at the same time with
reference to the onset time of swallowing,
which eliminated the influence of Mayer
Figure 2 (A) Time course of accelerometers around the onset of swallowing. (B – E) Waveforms of SBP as an example of the signal processing in this study.
(B) Waveform around a single swallow at t = 0. (C) Waveform of respiratory modulation. (D) Response waveform in the time domain where respiratory modulation is subtracted from (B). (E) Averaged response waveform in the time domain. Vertical bars represent SE.
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T. Numata et al.: Response Waveforms of Heartbeat and BP to Swallowing
wave and low frequency fluctuations, using
the equation
(2)
n describes the trial number in the experiment. Since each subject performed swallowing 12 times, n set at 12 in this study.
The trial number was decided based on the
previous studies [24, 27], which is enough
to evaluate the external effects on the CV
system, and it should be decided appropriately with the application to other external
stimuli or experimental situations.
▶ Figure 2 shows a representative
example to illustrate how the signal processing works. ▶ Figure 2A shows the time
course of accelerometers around the onset
of swallowing. ▶ Figures 2B –E show SBP
waveforms as an example of the signal processing in this study. First, the time of swallowing was identified by the waveform of
the accelerometer (▶ Figure 2A). Second,
the SBP data during swallowing and during
two breaths after swallowing was extracted
as “swallowing” data ( ▶ Figure 2B), while
the average of the rest of the data was regarded as “normal” (▶ Figure 2C). Then,
the swallowing and normal data were restored in the time domain, and the difference between the swallowing and normal
data was calculated (▶ Figure 2D). This
subtraction removed the effect of RM.
Finally, the effect of the Mayer wave was
removed by averaging the SBP data from
different swallowing events. Thus, the SBP
response waveform was extracted. Also,
RRI, DBP and PP response waveforms
were extracted with subtracting each normal data from each swallowing data.
Whereas the sampling frequency of accelerations were 1,000 Hz, the CV responses
were resampled 4 Hz and the differences of
peak time of each CV response waveforms
were much longer than the sampling frequency. Therefore, the effect of sampling
frequency was small enough to evaluate
the CV response waveforms to swallowing
accurately.
2.3 Statistical Analysis
To evaluate the influence of swallowing,
waveforms of RRI, SBP, DBP, and PP were
extracted, and the mean of each waveform
was calculated. Then, we employed the
comparison between data at the time of
swallowing and data before swallowing to
evaluate the validity of the proposed
method as well as the comparison between
data at the time of swallowing and data
after swallowing to evaluate the effect of
swallowing. Whereas CV indices to be
compared are not normally distributed, the
indices in this study are different from
merely heart rate or blood pressure because
of subtraction of CV fluctuations from raw
CV signals. In addition, the non-normality
of the indices were not apparent because
the p values of all data of indices were no
less than 0.05 (p > 0.05) by Shapiro-Wilk
normality test. Therefore, we assumed that
the indices were normally distributed and
applied the t test as well as the recent
studies [35, 36]. Since time variation of CV
responses would be expected to clarify with
high accuracy by the proposed method,
statistical differences between data at the
time of swallowing and data at every second before swallowing (from –5 s to –1 s)
and after swallowing (from 1s to 15s) were
tested by paired t test with a post-hoc Bonferroni correction. In addition, the peak
decrease and/or increase of data of each
waveform and the elapsed time of peaks
from swallowing were set as indices of
heartbeat and BP based on the results of
statistical analysis, and statistical differences between the data collected during
standing and sitting were tested by paired
t test. Furthermore, the elapsed times of
RRI, SBP, DBP, and PP in the same position
were compared by 2-way analysis of variance (ANOVA) with the assumption that
different time-variant CV responses might
be induced by postural differences. We derived parameters of each index in each data
set and compared them by the two-tailed
multiple t test with Bonferroni correction
following ANOVA. Detailed explanation of
each parameter is provided in the “Results”
section and ▶ Figure 3.
3. Results
▶ Figure 3 shows the average waveforms
(n = 12) of RRI, SBP, DBP, and PP in the
standing and sitting positions and the result of paired t test with Bonferroni correc-
tion of the values from –5 s to –1 s before
swallowing and from 1s to 15s after swallowing (every second) relative to the value
at time of swallowing (0 s). In regards to
the time before swallowing, there are no
significant differences between the data at
the time of swallowing and the data before
swallowing. In contrast, in regards to the
time after swallowing less than 10s, the RRI
values from 1 s to 6 s after swallowing in
the standing position and from 1 s to 5 s in
the sitting position were smaller than that
of swallowing. We confirmed the presence
of P-waves prior to R-waves in the electrocardiogram in all subjects during swallowing, which means that the tachycardia in
this study was not induced by atrial premature contractions as in previous studies
[4, 30]. The decrease in RRI recovered at
approximately 7 s (▶ Figure 3A, ▶ Figure
3B). The SBP value at 2 s after swallowing
was smaller than that of swallowing, and
the values of DBP at 1 s and 2 s after swallowing were larger than that of swallowing
in the sitting position. The values of PP
from 1 s to 3 s after swallowing in the
standing and sitting positions were smaller
than that of swallowing. In addition, more
than 10 s after swallowing, the RRI values
in both positions were smaller than that of
swallowing, and the SBP values in the
standing position were smaller than that of
swallowing. The DBP values in both positions were also smaller than that of swallowing.
We compared the magnitude and the
time of peak of response waveforms between the standing and sitting positions by
referring to the total averaged response
waveforms of RRI, SBP, DBP, and PP
(▶ Figure 3). With regard to RRI, we compared the peak value of tachycardia
(N-RRI) and the peak time of tachycardia
(tN-RRI). For SBP and PP, we compared
the peak value of decrease (N-SBP and
N-PP) and the peak time of decrease (tNSBP and tN-PP). For DBP, we compared
the peak value of increase (P-DBP) and the
peak time of increase (tP-DBP). We compared the magnitude of the four peak values between the standing and sitting positions using the paired t test (n = 12), and
▶Table 1 and ▶Table 2 show the results of
comparison. N-RRI was significantly larger
in the standing position than during sit-
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T. Numata et al.: Response Waveforms of Heartbeat and BP to Swallowing
Figure 3 (A, C, E, G) Averaged response waveforms of the heart rate and blood pressure indices induced by swallowing in the standing position. (B, D, F, H)
Averaged response waveforms of the heart rate and blood pressure indices induced by swallowing in the sitting position. (A, B) RRI; (C, D) SBP; (E, F) DBP; (G,
H) PP (PP calculated as SBP minus DBP). Vertical bars represent SE. *P < 0.01, †P < 0.05
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T. Numata et al.: Response Waveforms of Heartbeat and BP to Swallowing
ting, and the other three values demonstrated no statistically significant differences between positions. In addition, twoway analysis of variance indicated no interaction between position and peak time. tNSBP was earlier than tN-RRI and tP-DBP,
and tN-PP was earlier than tP-DBP.
4. Discussion
Table 1 Values of the heart rate and blood pressure indices induced by swallowing and results of
statistical comparison. Values represent estimated mean values ± SD. N-RRI, the peak value of decrease
in R-R interval; N-SBP, the peak value of decrease in systolic blood pressure; P-DBP, the peak value of
increase in diastolic blood pressure; N-PP, the peak value of decrease in pulse pressure.
Parameter
Sitting (n = 12)
P
N-RRI (ms)
– 98.7 ± 35.4
– 158.7 ± 49.7
< 0.01
N-SBP (mmHg)
– 3.10 ± 2.77
– 2.04 ± 4.04
NS
P-DBP (mmHg)
5.16 ± 1.79
5.60 ± 2.26
NS
– 5.99 ± 2.12
– 6.16 ± 2.01
NS
N-PP (mmHg)
4.1 Evaluation of the Signal
Processing Algorithm
To evaluate the validity of the proposed
method, we extracted the waveform for 5 s
before swallowing and there are no statistical significant differences between the data
at the time of swallowing and the data before swallowing. During that period RRI
and PP remained constant at zero, while
SBP and DBP were almost constant but
drifted slightly. Low-frequency fluctuations
in blood pressure are thought to cause
these drifts in SBP and DBP [37]. Hence,
PP remains constant at zero because the
drift in blood pressure is subtracted. Because the drifts in SBP and DBP are sufficiently small compared to those after swallowing (i.e. the response and recovery process), intrinsic fluctuations are well reduced by our proposed method, allowing
the response and recovery process of heartbeat and BP to be evaluated in detail.
The amplitudes of the BP fluctuations
induced by RSA are known to be approximately 3 mmHg [25] and the amplitude of
SBP in the standing position in this study
was also 4.36 ± 2.33 mmHg; see the Appendix in details. They are almost equal to the
BP fluctuations induced by swallowing
(e.g., N-SBP is –3.10 ± 2.77 mmHg in the
standing position). Therefore, it is necessary to extract the response waveforms by
removing RM and it is well performed by
the method proposed in this study. It can
take physiological nonlinear elements into
account with a simple signal processing algorism and allows us to evaluate the differences of the time course of heartbeat and
BP with the removal of the effects of intrinsic fluctuations, which cannot be achieved
by analyses in the frequency domain or
combined time-frequency domain analyses. This ability is highly advantageous
for placing the obtained results into a
Standing (n = 12)
physiological context. Thus, the proposed
method demonstrated accurately extraction of the response waveforms to swallowing from the CV system with different
body position in the time domain and the
physiological relationship between heartbeat and BP in the time domain were accurately extracted.
4.2 Swallowing Effect
In this study, we confirmed the presence of
P-waves prior to R-waves in the electrocardiogram in all subjects during swallowing.
Therefore, this tachycardia was not induced by atrial premature contractions as
in previous studies [4, 30] and the paths of
swallowing have possibilities to be different
from that of swallowing with disease presentations [29, 30, 38 – 42]. Thus, two possible physiological factors would induce
tachycardia by swallowing in this experiment: mechanical stimulation due to
changes in intrathoracic pressure [8, 10]
and changes in autonomic nerve activity as
the response of the central nervous system
[9, 27–29].
Previous studies reported conflicting
findings on whether the tachycardia induced by swallowing depends on the posture or not [9, 28] and it would be partly
because the intrinsic fluctuations are not
sufficiently reduced. On the contrary, the
present study shows a large difference with
a statistical significance in the response of
tachycardia between the standing and sitting positions. Therefore, our accurate
waveform analysis reveals that a change in
autonomic nerve activity, particularly vagal
activity, largely contributes to swallowinginduced tachycardia, which supports the
results of Sheroziya et al. [28, 29]. This is
also supported by the results that DBP
increased and the change in RRI and PP
occurred at the same time, because if
mechanical stimulation is the main factor
and the change indirectly affects RRI
through a change in cardiac output, BP
should decrease as the primary effects of
swallowing, and tachycardia should be observed subsequently. These findings suggest that swallowing-induced tachycardia
arises from the decrease of vagal activity,
and the changes in blood pressure are induced by the preceding effect of tachycardia. Therefore, the swallowing effect would
be helpful to evaluate cardiac vagal tone
and combined evaluation of RSA and swallowing effect could be a better index of cardiac vagal tone than that of RSA alone.
In addition, SBP and PP immediately
decreased, and they recovered faster than
Table 2 Time of each peak induced by swallowing and results of statistical comparison. Values represent estimated mean values ± SD. tN-RRI, the time of N-RRI; tN-SBP, the time of N-SBP; tP-DBP, the time
of P-DBP; tN-PP, the time of N-PP. N-RRI, N-SBP, P-DBP, and N-PP are described in Table 1. *P < 0.01,
† P < 0.05.
Parameter
Standing (n =12)
Sitting (n = 12)
tN-RRI (s)
2.67 ± 0.79
2.40 ± 0.88
tN-SBP (s)
1.71 ± 0.40
1.94 ± 0.83
tP-DBP (s)
4.50 ± 3.23
4.06 ± 2.79
tN-PP (s)
2.02 ± 0.45
2.27 ± 0.51
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T. Numata et al.: Response Waveforms of Heartbeat and BP to Swallowing
Figure 4 (A – D) Averaged RM functions in the standing position and the sitting position. (A) RRI, (B) SBP, (C) DBP, (D) PP. (Bar shows the intraindividual
average ± SE.)
the RRI. In regard to decreases in SBP and
PP, they should be related to the decrease in
cardiac output. After the decrease induced
by swallowing, SBP increased to exceed
pre-swallowing values, while RRI did not.
Although there is no significant difference
which indicates the increase of SBP, this response is likely considered to be induced by
the baroreflex. If the baroreflex protects
against a drop in SBP, SBP should increase
faster than RRI. In fact, tN-SBP was statistically significantly smaller than tN-RRI
(▶ Table 2), supporting the occurrence of
the baroreflex. Compared to the waveforms
of RRI, SBP, and PP, the DBP waveforms
and its physiological considerations are
rather complicated. Immediately after
swallowing, it increased as a result of
shortening of the diastolic phase (i.e. blood
pressure descent phase) induced by decreased RRI. Even after RRI began recovering, DBP did not decrease, and this phenomenon may reflect the baroreflex compensating for the decrease in SBP to in-
crease cardiac output. We then observed an
oscillatory recovery process in SBP, DBP,
and PP, which may be caused by ANS
regulation via multiple feedbacks with
different time constants [43, 44]. Thus, the
proposed method was able to evaluate the
transitional responses of SBP, DBP, and PP
with a unique capability to evaluate the
recovery response of heartbeat and BP to
swallowing.
The previous study [45] reported that
there are no significant differences of
tachycardia induced by swallowing between young and old subjects. Therefore,
in this study, young healthy subjects were
tested to extract general physiological
mechanism related to swallowing effects on
the CV system. However, there is a possibility that a slight differences induced by
age, which cannot be detected by the conventional time averaging, might exist and
the proposed method would be able to
evaluate differences of cardiovascular response waveforms between young and old
subjects. In addition, the proposed method
would be useful to evaluate the differences
of tachycardia between healthy subjects
and subjects with disease presentations
[38 – 42]. Thus, in the future work, based
on data of a larger study population or subjects of different ages and physical condition would be considered desirable to
understand the swallowing effects on the
CV system in detail.
5. Summary
In this study, we proposed a mixed signal
processing of time domain and respiratory
phase domain to extract the response
waveforms of heartbeat and BP to external
stimuli in the time domain. As a result, we
demonstrated high accuracy extraction of
time-variable heartbeat response to swallowing that tachycardia peaked around
2.5 s and recovered within 8s and it was
greater in the sitting position than during
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T. Numata et al.: Response Waveforms of Heartbeat and BP to Swallowing
standing. In addition, we extracted response relationship between heartbeat and
BP in the time domain that SBP and PP
immediately decreased, DBP increased coincident with the occurrence of tachycardia, and SBP and PP recovered faster than
the RRI.
Appendix
To evaluate response waveforms of heartbeat and BP to swallowing, it is necessary
to extract RM functions appropriately.
▶ Figure 4 shows the RM functions of
RSA, SBP, DBP, and PP in the standing and
sitting positions. A decrease in RSA, SBP,
and PP during inspiration in the standing
and sitting positions and a phase shift of
amplitude between the positions were observed. The features of waveforms are the
same as those reported in a previous study
[25] and these results indicate the validity
of extraction of RM functions.
7.
8.
9.
10.
11.
12.
13.
14.
Acknowledgments
This work was supported in part by the
Strategic Information and Communications R&D Promotion Programme
(SCOPE) of the Ministry of Internal Affairs
and Communications and by KDDI foundation.
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