Journal of Disability and Oral Health (2011) 12/4 149-158
Influence of command on tongue elevation during
swallowing: examination of tongue pressure and ultrasound
imaging
Kayo Nomura DDS, Akemi Utsumi DDS PhD, Kaori Tomita DDS PhD, Masahiro Watanabe DDS PhD, Takafumi Ooka DDS PhD, Shouji Hironaka DDS PhD, and Yoshiharu Mukai DDS PhD
Department of Hygiene and Oral Health, Showa University School of Dentistry, Tokyo, Japan
Abstract
Aim and objectives: The purpose of this study was to investigate the difference between swallowing with
command and without command.
Design: Subjects were eight healthy male young adults with ordinary mastication and/or swallowing
functions. Subjects were asked to swallow 3mL of water in the following manner: Trial 1: Swallowing
with Command (C) and Trial 2: Swallowing in his usual way (No Command = NC). Tongue pressure
distribution was measured and synchronized with midline ultrasound sagittal sections of tongue movement
images for further analysis.
Results: All subjects exhibited tipper-type swallow in ultrasound images. The second point of peak in tongue
pressure corresponded with the point at which the hyoid was in its most elevated position. The duration of
palatolingual contact was clearly shorter in the C than in the trial NC (C, 1.26 s; NC, 1.67 s, P < 0.01). The
pressure integrals were markedly smaller in the trial C than in the trial NC (P < 0.05).
Conclusions: These results indicate that the duration of swallowing is shorter in swallow onset with, than
without command. The tongue movement in swallowing with command may be more effective than in
swallowing without command.
Key words: Tongue pressure, ultrasonography, swallow-to-command techniques, deglutition, tongue
pressure distribution
Introduction
Impairment in swallowing function interferes with a
healthy life; therefore diagnostic assessment and rehabilitation of swallowing function, oral cleaning, and
other forms of oral health care are important key factors
for improving the quality of life (QOL) of patients with
dysphagia (Ueda et al., 2004; Nakamura et al., 2005).
Dysphagia is a symptom that affects 15% of hospital inpatients, older people, people with neurological disease,
cancers of the head and neck and people with severe
reflux. This symptom affects a person’s ability to remain
well nourished and hydrated and increases the risks of ill
health (Nazarko, 2008). Moreover, dehydration was found
to be common among orally fed patients with dysphagia
(Leibovitz et al., 2007). Improvement of water ingestion
is an important agenda for patients requiring special care
with dysphagia, because the flow of water is faster than
that of solid food.
Generally, swallow-to-command techniques are used in
both diagnostic assessment and rehabilitation of patients
with dysphagia. Spontaneous or reflexive swallowing
occurs between meals without awareness and during
sleep in humans. Significant impairments of this type of
swallowing are observed in the elderly and patients with
neurogenic dysphagia (Lang, 2009). Although the phases
of swallowing are controlled by the brain stem and peripheral reflexes (Lang, 2009), the effect of command on
the processes of swallowing is not well known. A recent
study using videofluorography recordings has showed that
the processes of bolus transport, bolus aggregation, and
swallow initiation might be altered when the subject was
commanded to begin swallowing (Palmer et al., 2007).
On swallowing a bolus of liquid, the bolus is usually held
in the oral cavity until the time of swallow onset. The swallow is initiated as the bolus reaches the fauces. Once the
oral stage is initiated, the pharyngeal stage follows in rapid
sequence (Dodds et al., 1990). The sequence of events is
quite different when a healthy young subject eats solid
food. A portion of the food is propelled through the fauces
to the oropharynx (stage II transport) during mastication
(Palmer et al., 1992; Dua et al., 1997; Palmer, 1998). Previous studies with brain imaging techniques have shown
that different but overlapping areas of the cerebrum are
150 Journal of Disability and Oral Health (2011) 12/4
activated in volitional and automatic swallowing of saliva
or water (Martin et al., 2001; Kern et al., 2001).
Nonaka et al. (2009) suggested involvement of the supplementary motor area, suggesting that the processing
of the cue to swallow water activates wider areas in the
brain than swallowing water without command. There are
few studies which have examined the effect of command
on swallowing of water using surface electromyography
(Sekikawa et al., 2009; O’Kane et al., 2010); furthermore,
these studies investigated whether swallowing with command was more effective than spontaneous swallowing.
However, the differences in tongue movement between
swallowing water with command and swallowing water
without command remain unclear. The tongue is one of
important organs for mastication, swallowing and speech
articulation. The tongue helps to maintain and control the
bolus in the oral cavity and to transport it to the pharynx
during swallowing.
Tongue movement upon swallowing was studied using various techniques, such as dynamic palatography
(Harley, 1972; Imai and Michi, 1992), measurement of
tongue pressure (Kawashima., 1993; Ono et al., 2004;
Hori et al., 2006; Sugita et al., 2006; Kieser et al., 2008;
Youmans et al., 2009; Lenius et al., 2009; Tamine et al.,
2010 ), ultrasonography (US) (Keller, 1987; Imai et al.,
1995; Sonies et al., 1996; Akgul et al., 1999; Casas et al.,
2002) and videofluoroscopy (VF) (Adnerhill et al., 1989;
Bisch et al., 1994).
Tongue pressure is an effective measurement for
evaluating tongue movements. It has been studied by
several groups using the Iowa Oral Performance Instrument (Youmans et al., 2009), a simple tool that does not
allow the jaws to close. Previous studies have evaluated
tongue pressure using an experimental palatal plate installed with miniature pressure sensors (Sugita et al.,
2006; Kieser et al., 2008; Lenius et al., 2009). Ono et
al. (2004) presented a method to measure the timing and
pressure of the tongue-hard palate using seven miniature
pressure sensors installed in predetermined positions of a
palatal plate. They showed that the order, magnitude, and
duration of tongue pressure patterns against each part of
the palate were coordinated. Kawashima (Kawashima,
1993) simultaneously detected palatolingual contact on
ultrasonography (US) and measured miniature pressure
sensors using a synchronised observation system to observe tongue movement.
This study expanded these methodologies to associate
tongue pressure with real-time US sagittal sections of
tongue movement during swallowing. Moreover, temporal alternations in tongue pressure were depicted using
dynamic tongue pressure distribution, and US images of
tongue movement were used in a synchronised observation
system to examine the effect of swallowing with command.
The purpose of this study was to investigate the difference between swallowing with command and swallowing
without command, and to apply the results in clinical assessment and functional training.
Subjects and methods
Subjects
This study included eight healthy male young adults (mean
age = 22.62 ± 2.82 years) who had no impairments in
mastication, swallowing, and/or occlusion. The experiments were carried out after obtaining informed consent
from each subject. This study was approved by the Showa
University Research Ethics Committee (No. 2010-01).
Fabrication of experimental palatal plate
An impression of the upper jaw of each subject was taken
using alginate impression material (Algiace Z; DENTSPLY-Sankin , Tochigi, Japan), and a cast was constructed
using dental plaster (New Plastone; GC, Tokyo, Japan).
A 1mm thick palatal plate was constructed from a 1.5mm
thick acrylic disk (Yamahachi Dental, Aichi, Japan) by the
use of a heating vacuum press.
Two identically shaped palatal plates were fabricated for
each subject; one had to be worn for seven days before
the experiment for adaptation (Ono et al., 2004), and the
other was to be equipped with pressure sensors to obtain
experimental data. The region of palatal plates covering
the occlusal portions of the teeth was carved out to bring
the teeth into occlusion.
Seven miniature pressure sensors (PS-2KC; 6 mm in
diameter, 0.6 mm in thickness; Kyowa Electronic Instruments, Tokyo, Japan) were installed into the experimental
palatal plate. Figure 1(a) shows the location of the sensors
in relation to oral structures and the constructed plate.
The positions at which pressure sensors were installed
in our experimental palatal plate were based on the dental
arch and the anatomical landmarks of the incisive papilla
and hamular notch (Ono et al., 2004). Three sensors (Ch.
1–3) were placed along the median line of the hard palate:
Ch.1 was set 5 mm posterior to the incisive papillae, Ch.2
was set one-third anterior, and Ch.3 was set at one third
posterior between the incisive papillae and posterior edge
of the hard palate.
Toward the edges of the plate, Ch.4 was set at the left
one-third anterior and Ch.5 at left one-third posterior between the incisive papillae and left hamular notch, with
Ch.6 and Ch.7 set in corresponding contralateral positions.
In the experimental palatal plate, each sensor was fixed by
paraffin wax (All climate paraffin wax; GC, Tokyo, Japan)
(Kieser et al., 2008). Cables from each sensor exited from
the angle of mouth via the oral vestibule. Subjects were
asked to wear the experimental palatal plate during trials.
Nomura et al: Influence of command during swallowing 151
Figure 1. Location of pressure sensors (a), and (b) Setup of an experimental plate and US image.
Positioning and tongue pressure equipment
The subjects were ordered to sit upright in a fan-backed
chair with a fixed headrest. They were asked to sit upright
on the chair, with 900 hip flexion and 900 knee flexion,
while contacting the ground with their soles. Their heads
were kept steady by the headrest so that the Frankfort
Plane was parallel to the floor (Kawashima, 1993). Tongue
pressure was recorded using dynamic data acquisition
software (DCS-100A; Kyowa Electronic Instruments,
Tokyo, Japan) through sensor interfaces (PCD300A; Kyowa Electronic Instruments) with a frequency of 100 Hz.
Diagnostic ultrasound system
All scanning was performed using a B-mode diagnostic
ultrasound system (Power vision 6000; Toshiba Medical
Systems, Tochigi, Japan). The 6.0 MHz convex-array
probe (PVM375AT; Toshiba Medical Systems, Tochigi,
Japan) was positioned at the median sagittal plane. In our
pilot study involving five healthy young adults, we identified the most appropriate angle of the probe that can be
used to identify median sensors (Ch.2, Ch.3). The results
of previous experiments suggested that the sagittal angle
of the probe should be 200 posteriorly and the coronal
angle should be zero degrees. The probe was fixed using
a spring probe-holder, which can be used to adjust the
angle (Keller, 1987). An ultrasound gel pad (SONAGEL;
Takiron, Tokyo, Japan) was set on the probe to allow
better visualisation of superficial structures and to avoid
obstruction of the laryngeal elevation.
The shadows of pressure sensors (Ch.2 and Ch.3) were
scanned and identified by using US; these shadows could
be pointed out by each subject using his tongue before
measurement.
Measurement of tongue pressure and recording of US
The US image was visualized on a PC monitor through
converting software (Power producer 5; CyberLink, Taipei, Taiwan). The US images and tongue pressure data
were synchronised onto the same PC monitor and were
recorded by screen recording software (Camtasia Studio;
TechSmith, Michigan, USA) with a frequency of 30Hz for
later analysis. The frequency was chosen to conform to a
fundamental study that used US and tongue pressure for
observation of tongue movements (Kawashima, 1993).
Figure 1(b) shows setup of the experimental palatal plate
and US, and Figure 2 shows a diagram of the recording
system.
152 Journal of Disability and Oral Health (2011) 12/4
Figure 2. Diagram of the recording system. Tongue pressure was recorded using dynamic data acquisition
software through sensor interfaces with a frequency of 100 Hz. All scannings were performed using a B-mode
diagnostic ultrasound system. The 6.0 MHz convex-array probe was positioned at the median sagittal plane.
The US image was visualised using a PC monitor using converting software. The US images and tongue
pressure data were synchronised on the same PC monitor and recorded by screen recording software with a
frequency of 30 Hz for further analysis.
A spoon was used to feed 3mL of water from a spoon to
each subject, in conformity with a previous study (Furuya
et al., 2008). Boluses were at 37oC to minimise sensor
variability. All subjects were told to swallow 3ml of water
in the following two ways:
Trial 1, With command (C) — Each subject was instructed to (a) hold the water in the mouth; and (b) swallow
on command of the investigator. The command was given
immediately after the tongue pressure became stable.
Trial 2, No command (NC) — Each subject was asked
to swallow in their usual manner. Each trial was recorded
seven times; moreover, five of the seven recordings were
chosen as stable data for further analysis.
Parameters
For tongue pressure, the following parameters were recorded: time of pressure onset (Ton), the point of maximum
pressure (Tmax), the second point of peak in tongue pressure (T2nd), and time of pressure offset (Toff). In addition,
maximum magnitude of tongue pressure (MP), pressure
integral, and duration of palatolingual contact (TD) were
compared between the trial C and NC. Figure 3 shows the
method of tongue pressure analysis. Ton at Ch.1 was set
to 0. The relationships of US images and tongue pressure
waveforms with the time at which the hyoid reached the
most elevated position were measured using analysis software (NI DIAdem ver. 11.0; National Instruments, Texas,
USA). Ton at Ch.1 was set to the onset of US analysis.
Temporal alternations of tongue pressure were depicted as
dynamic tongue pressure distributions by using the same
analysis software.
Statistical analysis
The tongue pressure parameters (Ton, Tmax, T2nd, Toff,
MP, TD, and pressure integral) were determined using a
paired sample t-test in order to examine the difference
between the trial C and NC. Statistical differences between the seven sensors were determined using repeatedmeasures analysis of variance (ANOVA), and comparison
testing was performed using Tukey’s HSD significant
difference test.
The relationship between tongue pressure waveform and
the time at which the hyoid reached the most elevated position were compared using the Pearson product-moment
correlation coefficient. P-values less than 0.05 were considered significant in all cases.
Results
Tongue pressure waveform and US images
Tipper-type swallowing was observed in all subjects based
on US images recordings. Figure 4 shows an example
of tongue pressure synchronisation (tongue pressure
waveform and dynamic pressure distributions expressed
by colour alteration) and US images. In tipper-type swallowing, small negative pressure (mean value of minimum
magnitude of tongue pressure: C, -3.0 ± 0.22kPa; NC, -4.1
± 0.29kPa) was initially exhibited, followed by positive
pressure that increased rapidly and reached a maximum
magnitude of tongue pressure at each channel. The onset
of positive pressure at Ch.2 and Ch.3 corresponded with
Nomura et al: Influence of command during swallowing 153
Figure 3. Tongue pressure analysis parameters. Time of pressure onset (Ton), the point of maximum pressure
(Tmax), the second point of peak in tongue pressure (T2nd), time of pressure offset (Toff), maximum magnitude of tongue pressure (MP) and pressure integral, and duration of palatolingual contact (TD)
the tongue contact with Ch.2 and Ch.3 according to US images. The contact continued until tongue pressure returned
to baseline. After the onset of positive pressure, the tongue
moved from the anterior to the posterior in a wavelike
movement and transported the bolus into the pharynx.
After the maximum magnitude of tongue pressure was
reached (Figure 4A), the hyoid was rapidly elevated. The
time of second peak of tongue pressure (Figure 4B) corresponded with the time at which the hyoid reached the
most elevated position. The hyoid started to shift downward when the tongue pressure began to decrease. The
second point of peak in tongue pressure corresponded to
the point at which the hyoid was in its most elevated position. Moreover, the time of second peak of tongue pressure
significantly correlated with the time of the hyoid bone
reaching in its most elevated position (P < 0.01) both in
the trial C and NC.
Statistical analysis
Data collected from eight subjects were used for statistical
analysis. Figure 5(a) shows the time of pressure onset at
each sensor (Ton). Significant differences were not observed between the trial C and NC. Mean values of Ton at
Ch.1 were significantly lower than those of Ch.3 in both
the trial C and NC (P < 0.05).
Figure 5(b) shows the mean value of the point of maxi-
mum pressure (Tmax) at each sensor. At all channels, mean
values of Tmax were significantly shorter for the trial C
than for the trial NC (Ch.6, P < 0.01; Ch.1, Ch.2, Ch.3,
Ch.4, Ch.5, and Ch.7, P < 0.05). No significant differences
were observed among the seven sensors used in the trial.
The intervals between Tmax and T2nd were not significantly different between the trial C and NC. No significant
difference was observed among the values of the seven
sensors used in the trial. Time intervals between T2nd
and Toff were significantly shorter for the trial C than for
the trial NC (P < 0.05). No significant differences were
observed among the values of the seven sensors used in
the trial.
Figure 5(c) shows the mean value of maximum magnitude of tongue pressure (MP) at each sensor. Significant
differences were not observed between the trial C and NC.
Figure 5(d) shows pressure integrals at each sensor. The
pressure integral was significantly lower for trial C than
for trial NC (Ch.3 and Ch.7, P < 0.01; Ch.1, Ch.2, Ch.4,
Ch.5, and Ch.6, P < 0.05). The pressure integral at Ch.1
was significantly greater than that at Ch.3 in the trial NC
(P < 0.05).
Figure 6 shows the mean duration of palatolingual
contact production. The duration of palatolingual contact
was significantly shorter for the trial C than for the trial
NC (P < 0.01).
154 Journal of Disability and Oral Health (2011) 12/4
Figure 4. Examples of synchronised tongue pressure (tongue pressure waveform (a) and dynamic pressure
distributions that were expressed by colour alteration (b), and US images (c). baseline; A, the point of maximum pressure; B, the point of second peak of tongue pressure
Figure 5. Mean values of the time of pressure onset (Ton) (a), mean values of maximum tongue pressure
(Tmax) (b), mean values of magnitude of tongue pressure (MP) (c), and mean values of pressure integral (d)
at each sensor. M: Midline, L: Light, R: Right
Nomura et al: Influence of command during swallowing 155
Figure 6. Mean values of duration of palatolingual contact (TD)
Discussion
Traditionally, the act of swallowing, or deglutition, is
described as a highly coordinated process involving four
stages: oral preparatory stage, oral stage, pharyngeal stage,
and oesophageal stage (Gleeson, 1999). These stages were
observed in swallowing with command. Bolus formation
and deglutition of liquids involves a rapid sequence of
events: a volume of fluid is propelled from the oral cavity, which crosses the fauces, passes down and across the
pharyngeal surface of the tongue, and enters the hypopharynx and then the oesophagus. In contrast, triturated food
is accumulated on the pharyngeal surface of the tongue
after passage through the fauces, with a variable period in
which additional aliquots of food are moved in a posterior
direction. After a variable period of elapsed time, the bolus
in the pharynx is transported to the oesophagus. Stage II
transport (movement of material through the fauces) is
considered to be a more accurate descriptor of the process
because it describes the movement of material from the
oral cavity to the oropharynx with no connotation as to
the timing of subsequent events (Hiiemae et al., 1999).
Most studies regarding Stage II transport investigated
deglutition with mastication (Hori et al., 2006; Palmer et
al., 2007). The tongue pressure has been thought to be an
index of swallowing function.
Few studies have investigated the process of swallowing liquid (Nonaka et al., 2009; Sekikawa et al., 2009);
however, the changes in the oral phase, including tongue
movement, pressure, and tongue elevation, have not been
surveyed using objective methods. Thus, in this study,
dynamic tongue pressure distribution and US images of
tongue movement were used with a synchronised observation system, and the differences between swallowing
with command and without command were investigated.
Synchronisation of US and tongue pressure
To confirm tongue movement and organ motions around
the pharynx associated with swallowing, tongue pressure
and US images were synchronised. In a previous study, the
difference in the length of time measured with US and the
strain-gauge pressure transducer was on the order of less
than 1 frame (0.033 s) (Kawashima, 1993). Therefore, the
reproducibility was considered appropriate for comparing
values obtained for the duration of tongue movement with
US images to a strain-gauge pressure transducer.
Previous research suggested that there are defined individual patterns of pressure change during liquid swallowing (Kennedy et al., 2010). Tongue pressure measurement
and US images allowed us to determine the correlation
among tongue pressure, tongue movement, and elevation
of the hyoid bone during swallowing. Moreover, these
data reveal information regarding the relationship between
tongue movement and patterns of tongue pressure change
during water swallowing.
Preparing for the measurement with palatal plate
Nagano et al. (2002) prepared four occlusal vertical
dimension conditions: intercuspal position and vertical
dimension of occlusion by approximately 4, 8, and 12mm.
Their data indicated that the maximum pressure decreased
significantly as the vertical dimension increased in young
adults during swallowing of 2mL of water. Accordingly,
in this study, the region of palatal plates covering the occlusal portion of the teeth was carved out to bring their
teeth into occlusion to eliminate the effect caused by the
vertical dimension.
Ono et al. (2004) evaluated tongue pressure by using
palatal plates used adaptation periods of 7 days. Furuya
et al. (2008) suggested that that the influence of the palate
covering on swallowing 3mL of water function is relieved
after 7 days. In this study, subjects were instructed to wear
156 Journal of Disability and Oral Health (2011) 12/4
a palatal plate for 7 days before the experiment for adaptation; hence, we believe that the 7-day adaptation eliminated
the effect caused by plate covering.
Comparison among each sensor
In this study, 3mL of water was used to determine the effect
of a command on swallowing (Furuya et al., 2008). Significant differences were observed between the anteriomedian
point (Ch.1) and the posteriomedian point (Ch.3) in time
of onset of tongue pressure in both the trial C and NC, and
in pressure integrals in the trial NC. Furuya et al. (2008)
reported that the onset of tongue pressure with the posterior
point was significantly longer than with the anterior point
on the midline. This finding is consistent with our results
comparing the posterior and anterior points on the midline.
This result indicated that distinguished differences were
not observed between the anterior and posterior points on
the midline in other parameters. The midline of the tongue
may play a role in and pushing a bolus backward, resulting
in relatively constant tongue pressure. However, tongue
pressure may increase to facilitate the transport of a bolus
when the volume of water is increased. A previous study
using 15mL of water in swallow manoeuvres suggested
that magnitude and duration of tongue pressure were significantly larger in the anteriomedian part compared to
the other parts measured, and were significantly smaller
in the posteriomedian part (Ono et al., 2004). Therefore,
3mL of water was chosen in this study so that significant
differences could be clearly observed from point to point
with increased amounts of water. This suggests future
studies are required using similar amounts.
Comparison between swallowing with command and
without command
Most studies regarding Stage II transport investigated
deglutition with mastication (Hori et al., 2006; Palmer et
al., 2007). A previous study (Hori et al., 2006) suggested
normal patterns of tongue contact against the hard palate, control of tongue activity, and coordination with jaw
movement during mastication; furthermore, the authors
described that the magnitude and duration were significantly larger in late stages of chewing.
A recent study showed that the processes of bolus transport, bolus aggregation, and swallowing initiation might
be altered by volitional swallowing or command swallowing, suggesting differences in cognitive functions during
volitional and command swallowing in humans (Palmer et
al., 2007). Nonaka et al. indicated that the supplementary
motor area activates wider areas in the brain for swallowing with command than for swallowing without command
(Nonaka et al., 2009). Moreover, few previous studies
compared the differences in tongue pressure on swallowing
of liquids with command and without command.
In this study, the point of maximum pressure and the
duration of palatolingual contact were significantly shorter
in trial C than in trial NC, and the pressure integral was
significantly smaller in trial C than in trial NC. However,
the maximum magnitude of tongue pressure at each channel did not show significant differences between trials C
and NC. The pressure integral indicated that the magnitude
of tongue pressure from the onset to the offset of tongue
pressure was markedly smaller in trial C, than in trial NC;
these findings suggest that the point of maximum pressure
and the duration of palatolingual contact were responsible
for the significantly smaller pressure integral in trial C,
than in trial NC.
Electromyographic activity of the suprahyoid muscle
on swallowing with command was significantly lower
than that on swallowing without command (Sekikawa et
al., 2009). Additionally, electromyographic activity of the
suprahyoid muscle was strongly correlated with tongue
pressure (Lenius et al., 2009). Therefore, the duration of
swallowing was shorter in swallowing with command
than in swallowing without command. This result may
be related to hyoid elevation, which is coordinated with
tongue movement.
The oral and pharyngeal stages of swallowing were
identified using this method. Forward and upward phases
of tongue blade movement are initially prevalent in the
oral stage of the normal swallow (Stone and Shawker,
1986) and are highly synchronous with the movement of
the hyoid bone, which serves as a supporting structure
for the larynx and/or platform for the tongue (Gleeson,
1999). The oral stage of swallowing is initiated by the
onset of a leading complex of four closely related events
(Cook et al., 1989): (a) the onset of tongue tip movement;
(b) tongue base movement; (c) vertical hyoid movement,
and (d) submental electromyographic activity. The oral
and pharyngeal stages of swallowing are closely coupled
in normal swallowing (Gleeson, 1999).
Tipper-type swallow is known to account for nearly 80%
of total swallowing (Dodds et al., 1989); furthermore,
tipper-type swallow was observed in all subjects in this
study. This swallowing pattern involves the initiation of
swallowing from the tip of the tongue against the incisors
with the bolus in a supralingual position. In the tipper-type
swallow, small negative pressure was exhibited initially,
followed by positive pressure that increased rapidly and
reached a maximum magnitude of tongue pressure at
each channel. After reaching a maximum magnitude of
tongue pressure, the hyoid rapidly elevated. The point of
the second peak of tongue pressure corresponded with
the time at which the hyoid reached the most elevated
position. Intervals between the point of maximum pressure and the point of the second peak of tongue pressure
were not significantly different between trial C and NC.
Accordingly, the command is unlikely to have a significant
influence on the rapid elevation of the hyoid upon swallowing. Moreover, the duration of the rapid elevation of
the hyoid can be estimated based on the intervals between
Nomura et al: Influence of command during swallowing 157
the point of maximum pressure and the point of second
peak of tongue pressure. Furthermore, research regarding
the relationship of tongue elevation and hyoid movement
may require further experiments to measure not only the
maximum tongue pressure but also the second peak of
tongue pressure.
Conclusions
•
•
The duration of swallowing was shorter in swallowing
with command than in swallowing without command.
This result suggests that tongue movements in swallowing with command may be more effective than in
swallowing without command.
The time of the second peak of tongue pressure corresponded to the time of the hyoid reaching its most
elevated position.
Acknowledgments
This study was supported in part by KAKENHI (22592344)
and a grant of the Strategic Research Foundation Grantaided Project for Private Universities from the Ministry of
Education, Culture, Sport, Science, and Technology, Japan
(MEXT), 2010-2014 (S1001010). I appreciate the comments and suggestions provided by Dr. Kentaro Ishikawa.
Finally, I thank the many staff members in our department
for their assistance during this study.
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Address for correspondence:
Dr Akemi Utsumi
Department of Hygiene and Oral Health
Showa University School of Dentistry
1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
Email: [email protected]