The real-time visualization of pneumogram signals is described in this contribution. The device created provides simultaneous measurement of pneumogram and voice. The sampled signals are transmitted to PC software in real time via USB bus, which makes it possible to show the curves from the sampled signals in real-time. In addition, data archiving and printing functions are integrated into the software. Since pneumography is one of the oldest methods to provide information about the technique of respiration, it will be possible for doctors in phoniatric practice to use the created device and programmed application for patient diagnosis. Listed in the results is an example of the recordings acquired from the designed device.
Keywords: pneumography, pneumogram, phoniatry, diagnostics, real-time signal processing, visualization
The central focus of this article is the pneumogram
acquisition method. Pneumography is one of the oldest
methods to provide information about respiration
during speaking and singing. A pneumogram consists
of the person's voice, the movements of the chest and
the movements of the abdominal wall. Pneumography
curves are used to measure the respiratory rate, to
detect pathological phenomena and to calculate the
ratio between the time of inspiration and expiration.
Further, the asymmetry and relationship between the
curves of the chest movements and abdominal wall are
evaluated with this method.
Currently, the pneumography method is not very
widespread and is not used in medical practice, having
been replaced by pneumotachography (there is no
equipment manufacturer in the present market).
However, the pneumography method is more suitable
for diagnostic purposes, because it provides direct
information about the muscle movements participating
in the respiration process. Pneumography is also used
in cases when a voice teacher needs to gain information
about the pupil's breathing technique.
In this article, we have presented a design for a
device that is used to capture the pneumography
signals. This paper also focuses on description of a PC
application that visualizes and records signals in real
time. Real-time visualization is necessary, because the
measuring sensors have to be correctly set up before
the measuring process. Visualization allows for control
of the correctness of the record. Listed in the results are
the recordings acquired via the designed solution. The
design of the device construction is based on
descriptions which are specified in references .
The hardware description of the
The block diagram in Fig. 1 provides an outline of
the hardware solution. A 32-bit microprocessor from
ATMEL AT91SAM7S64 , which has a maximum
clock frequency of 55 MHz, was used for the
implementation. The selected type of microprocessor
contains all the required peripherals and is easily
accessible on the market. The inputs of the device are
connected to a pair of strain gauges and a microphone.
The signals from the strain gauges are amplified by
instrumentation amplifiers . All signals are adjusted
to the desired voltage range of the input A/D converter.
An electrets microphone, which is commonly used in
computer technology, is used to record the voice.
The sampling frequency is set at 500 Hz and the A/D
converter has 10-bit resolution; since the voice
recording is used only to detect the voice's presence,
this sampling frequency is therefore sufficient.
Connection to a PC interface is provided by USB. As
this device operates in the USB HID class, such as a keyboard or mouse, no installation of additional drivers
is required. The firmware of the microprocessor was
created in the programming language C.
The construction of the sensor used for measuring is
presented in Fig. 2. The SS5LB BIOPAC  sensors
used to measure the tension of the strap, inside of
which are piezoresistive strain gauges. Similar types of
measurement sensors are used, for example, in
polysomnography. In an appropriate construction, the
sensor should not restrict the test subject, because
doing so would affect the measured signal. The sensor
sensitivity must be sufficient to register observed
pathological phenomena such as hard voice beginnings.
The final device design is shown in Fig. 3. The
device has two inputs for the tension sensors
connection and one input for the microphone
connection. Potentiometers are used to set the signal
offset of the strain gauges. The control LEDs are used
for signaling 'power on' and 'recording '.
The PC application for signal
The block diagram in Fig. 4 provides a description of
the functionally designed PC application used for
visualization, archiving and further processing of
acquired data. First, the data received via USB are
converted back from the data transmission format.
Nonlinearity was found by measuring the transfer
characteristics of the sensor, and the correction table
which was calculated from the measured transfer
characteristics, was implemented to compensate for
nonlinearity. The next block in the diagram serves to compensate the speed streams of the measured and
visualized data by selecting and storing data from the
queue (FIFO). Implemented in the application is a
digital filtering real-time algorithm. The IIR high-pass
filter is implemented to remove base line wander, and
the FIR low-pass 200th order moving average filter is
implemented to eliminate the interference. The
following block in the diagram is used to set the
display scale. The change of the scale in the time axis
is provided by signal decimation. Visualization is
performed by rendering each pixel in the graphic userinterface
component PictureBox , a simple solution
that is nonetheless suitable for this application. The
application is programmed in the programming
language CSharp and is inspired by the design
described in reference .
The flowchart displayed in Fig. 5 describes the section
of the algorithm which ensures the visualization and
archiving of data. The greatest problem is to display
visualization of the continuous signal curves without having to depend on the performance of the PC. The
signal drawing is performed by invoking the timer
events. After invoking the event, the conditions of a
sufficient number of samples in the queue are
evaluated. If the condition is true, the visualization
continues. The rendering of more samples at the same
time is used to ensure sufficient dynamism of the
process. The number of samples plotted in the same
time depends on the decimation factor, which can set
how the decimated data should be handled when the
decimation is applied. It is possible to select only one
sample and discard the other or select a sample with
maximum value or calculate the average of all
decimated samples. Also described in the diagram is
the method of storage for archiving and printing.
Shown in Fig. 6 is the design of the graphic user
interface. The application includes buttons which
provide controlling the recording and inserting
information tags on activity during the measurement.
The application also allows the user to set options of
archiving, printing, using the correction tables,
filtration and background color.
Results of the measurements
Fig. 7 shows the results of the measurement acquired
by means of the designed and realized solutions.
The recordings contains the signal of the voice, chest
and abdominal activity, along with the tags providing
information on activity during the measurement and
tags in time interval 1s. During the recording, it is
important to record the correct location of the sensor
and the setting of the strap tension.
This article provides a basic description and guide to
the use of pneumography. In addition, the article
provides a description of a hardware and software
solution designed to measure the pneumogram. The
created device will be used for diagnosing voice
disorders in phoniatrics clinics. Though the device has
been tested in cooperation with phoniatric specialists, it
has yet to be used in clinical practice.
Suggestions on how to improve the device will be
known after more experiences with its use will be
attempted, along with implementation of the device in
actual clinical practice. Other improvements will
include the creation of a database of patient records for
better handling of the acquired data.
Ing. Jan Sedlák
Department of Circuit Theory
Faculty of Electrical Engineering
Czech Technical University in Prague
Technicka 2, 166 27, Prague, Czech Republic
Phone: +420 728 760 701
 NOVÁK, A. Foniatrie a pedaudologie II. Poruchy hlasu u dětí a dospělých - základy anatomie a fyziologie hlasu, diagnostika, léčba, reedukace a rehabilitace poruch hlasu. Praha: UNITISK, 2000.
 JANÍKOVÁ, D. Fyzioterapia funkčná diagnostika lokomočného systému. Martin: Osvěta, 1998, s. 238. ISBN 80- 8063-015-1.
 HAASZ, V. - SEDLÁČEK, M.: Elektrická měření. Přístroje a metody (2. vydání). Monografie ČVUT, Praha 2003
 The cheapest dual trace scope in the galaxy [online]. 2012 [cit. 2012-04-25]. Dostupné z WWW: <http://yveslebrac.blogspot. com/2008/10/cheapest-dual-trace-scope-in-galaxy.html>.