Click Research-2
Thais Russomano - Speaker
Dario Francisco Guimaraes de Azevedo
Felipe Prehn Falcao
L uis Piedade
Flávio S. Glock
Marcos Telló1
Marlise A. dos Santos
Janice L. Giongo
25th Annual
International Conference of the IEEE Engineering in Medicine and Biology Society
- A New Beginning for Human Health, Cancun, Mexico - September 17 - September
21, 2003
Abstract — The vestibular system, along with the eyes and proprioceptors, is responsible for the maintenance of balance. Two very common causes of accidents and incidents during flights and space missions are spatial disorientation and motion sickness. Since its invention by the physiologist Robert Bárány, rotatory chairs have been widely used to train pilots and astronauts in relation to the effects of angular accelerations and microgravity on the semicircular canals. This paper presents the development of an electrically controlled rotatory chair (ECRC), the unique device of this type used as a simulator for spatial disorientation and motion sickness in Brazil. Validation of the ECRC was performed through the evaluation of the effects of a drug (scopolamine) on the prevention of signs and symptoms of motion sickness.
Keywords — rotatory chair, spatial disorientation, motion sickness,
vestibular system
I. INTRODUCTION
The otolith organs and semicircular canals are the sensory part
of the vestibular system, located in the inner ear. The otolith organs, which
lie within the utricle and saccule, are responsible for the perception of
linear acceleration when it is greater than 0.1m/s2. The semicircular canals
provide reliable information about angular accelerations of the head and
may be regarded as natural accelerometers working as three matched pairs.
Sustained change in the angular velocity of the head greater than about 3°/s
is detected by the canals in the plane of movement, and its magnitude and
direction are signaled to the brain. Movement will be detected by the canals
only for as long as there is a suprathreshold acceleration or deceleration.
Once constant velocity is reached the signal will decay even though movement
is continuing [1].
Spatial disorientation is a contributory factor in about 12% of
all fatal airline accidents, around 20% of military accidents, and probably
even more in general aviation. On the ground, the references are gravity and
the horizon. When the pilot is subjected to abnormal accelerative forces or
the astronaut is in a spacecraft under the influence of microgravity, the
information supplied by the eyes, inner ear and proprioceptors may be interpreted
incorrectly with potentially dangerous consequences. Correct spatial orientation
is replaced by spatial disorientation in which perception of body and aircraft
positions is false. It is believed that all aircrew and spacecrew experience
disorientation at some stage during their careers, but it is only when control
of the aircraft or the spacecraft is based on false perceptions that incidents
and accidents may occur [2].
Motion sickness is a fairly common problem in early flying training
and in passengers unfamiliar with flight in light airplanes. It affects around
70% of the astronauts during the first 72 h of a space mission. The cause
is complex and not fully understood [3] [4].
Motion in flight, at sea, in a car or in a space shuttle generates
patterns of sensory input which conflict with those patterns based on terrestrial
experience. The brain is unable to interpret this conflict and motion sickness
results. The earliest symptom is unease in the stomach. Hyperventilation and
“air hunger” are common. The face becomes pale and sweating is usually present.
This stage is followed by an increase in salivation, a feeling of body warmth,
light-headedness, vomiting and, occasionally, depression and apathy [4].
Of the drugs available the most effective one in preventing these signs and
symptoms is scopolamine that should be taken before the exposure to angular
acceleration. Side effects, time of administration, dosage and possible drug
combinations are still under study [5] [6].
This paper presents the development of an ECRC, the unique device
of this type in Brazil that has been used for pilot's training and research
projects in spatial disorientation and motion sickness. The evaluation of
the effects of scopolamine on the prevention of signs and symptoms of motion
sickness during rotation was used to validate the effectiveness of the ECRC
in stimulating the semicircular canals.
II. METHODOLOGY
A. Electrically Controlled Rotatory Chair
The ECRC (Figure 1) was developed according to the following
specifications [7]: rotation range from a minimal of 10 rpm to a maximum of
30 rpm; maximal accidental load of 100 kg; no nominal variation of the acceleration
during rotation.
A DC motor (24 V) was placed on the axis of the chair in order
to promote its rotation. The nominal rotation of the motor is @ 3000 rpm.
A reducer was used to decrease it by a factor of 15:1.
The transmission of the movement between the motor and the chair
is given by two trapezoidal canal pulleys and an A29 model chain with a reduction
of 6:1.
The final rotation of the system is given by the expression
Rf = [ (Rm / r ) / Rp ] (1)
where: Rf = final rotation; Rm = motor rotation; r = reduction
factor; Rp = pulley effect. Maximum rotation of the system is 33 rpm, which
has proven to be adequate since most of the tests will be performed with rotation
ranging from 15 to 25 rpm.
For safety and comfort reasons, a seat belt and a feet support
were added to the ECRC.
B. Digital Tachometer
The digital tachometer consists of a micro controlled conversion
system (model 89C2051) that converts an analogical signal to a number. This
is an independent system that uses the power supply of the chair.
The motor of the chair dynamo is connected to its center axis.
When the chair rotates, the axis activates the dynamo creating a voltage in
the output that varies from 0 to 17.5 V.
The A/D converter has a reference voltage of 5 V. This requires
the dynamo signal to be lowered by a voltage divider, which produces a linear
reduction on the entire voltage range. A voltage is induced during rotation,
which is acquired by the microcontroller, processed by the software (Assembly
language) and displayed in two blocks of 7 segment LEDs.
C. Validation of ECRC
A double blind, placebo controlled, randomized study was performed
to evaluate the effectiveness of the ECRC to cause spatial disorientation
and motion sickness. The effects of scopolamine, an anti-motion sickness drug,
on the prevention of its signs and symptoms during rotation sessions in the
ECRC were analyzed [7][8].
The protocol was approved by the PUCRS Ethics Committee previously
to the beginning of the experiment.
Twelve college students, after being fully informed about the
protocol and have signed a consent form, participated in 2 rotation sessions
separated by an interval of a few days. Subjects received, randomly, a blue
capsule that contained either 0,3 mg of scopolamine or placebo orally 2 h
prior to the beginning of the test.
Volunteers were instructed to perform head movements during the
rotation of the chair in order to add an extra stimulus to the semicircular
canals.
The chair was set to rotate at a constant speed of 25 rpm. The
test was terminated either if the subject felt ill or at 30 min of rotation.
Signs and symptoms of motion sickness were observed by the researcher
and reported by the volunteers.
III. RESULTS
A paired t-test was used for data analysis with a level of significance
of p £ 0.05. The percentage of signs and symptoms are also presented.
The mean speed of the ECRC during the rotation sessions was 24.2
(SD±0.7) rpm, with a maximum of 26.4 rpm and minimum of 23.8 rpm.
One hundred percent of the volunteers during the placebo rotation
sessions developed pale face, sweating and nausea, and 92% reported to have
experienced disorientation. These percentages were reduced by approximately
30% when the volunteer was under the effect of scopolamine (see Table I).
The mean rotation time under the effect of scopolamine was 711
s. This time decreased to 471 s when placebo was administered to the volunteer
(p < 0.05) Results of the time of the rotation sessions are presented
in Table II.
TABLE I
PERCENTAGE OF SIGNS AND SYMPTOMS OF SPACE MOTION SICKNESS DURING ROTATION
SESSIONS WITH AND WITHOUT SCOPOLAMINE
Signs and Symptoms
Scopolamine(%) Placebo(%)
Pale face
75
100
Sweating
67
100
Disorientation
67
92
Nausea
67
100
Dizziness
67
75
Headache
17
42
Vomiting
0
0
TABLE II
TIME OF ROTATION (s) WITH AND WITHOUT SCOPOLAMINE
Scopolamine Placebo
Mean
711,25
471,67
SE (±)
188
146
IV. DISCUSSION
The mean rotation speed of 24.2 rpm, associated to a very minor
variation during the rotation sessions, has demonstrated that the rotation
control of the ECRC was very satisfactory.
The high incidence of symptoms felt by the volunteers and signs
observed by the researcher have proven that the ECRC was effective in causing
motion sickness and spatial disorientation during the rotation sessions.
Scopolamine, the drug of choice for the prevention of motion sickness,
in a dose of 0.3 mg taken orally 2 h before the exposure to angular acceleration,
has shown to be efficient in increasing the duration of the rotation sessions
and in reducing the symptomatology secondary to the stimulation of the semicircular
canals.
V. CONCLUSION
The ECRC was entirely conceived, designed and developed by the
Microgravity Laboratory at IPCT-PUCRS. It has been used to demonstrate to
approximately 200 private pilots every year from flight schools and school
of aeronautical sciences features related to spatial disorientation. After
the training, pilots become aware of the importance of trusting the instruments
during flights, especially when visual clues are reduced or missing.
The ECRC has also been used for research projects that aim to
study space motion sickness, its signs and symptoms, and its prevention (http://www.ipct.pucrs.br/microg).
ACKNOWLEDGMENT
We would like to thank those who gave us technical support to
develop this work: Celso Renato Vieira dos Santos, Carlos Schossler, Mário
Vian and Denis Barbieri.
REFERENCES
[1] A. J. Benson, “Spatial disorientation – General aspects”,
in Dehenin G, Ed. Aviation Medicine, London: Tri-Med Books, 1978, Vol. 1,
pp. 407-424.
[2] W. R. Kirham, W.E. Collins, P.M. Grape, J. M. Simpson,
T. F. Wallace, “Spatial disorientation in general aviation accidents”, in
Aviat Space Environ Med, no. 49, pp. 1080-6, 1978.
[3] J. R. Davis, “Space motion sickness during 24 flights
of the Space Shuttle”, in Aviat Space Environ Med, no. 53, pp. 570-75, 1988.
[4] W. E. Thornton, T. P. Moore, S. L. Pool, J. Vanderploeg,
“Clinical characterization and etiology of space motion sickness”, in Aviat
Space Environ Med, no. 58, A1-8, 1987b.
[5] C. D. Wood, A. Graybiel, “Evaluation of sixteen antimotion
sickness drugs under controlled laboratory conditions”, in Aerospace Medicine,
no. 39, pp. 1341- 44, 1968.
[6] C. D. Wood, A. Graybiel, “Theory of antimotion sickness drug
mechanisms”, in Aerospace Medicine, no. 43, pp. 249-52, 1972.
[7] L. A. Piedade, T. Russomano, D. F. G de Azevedo, “Development
of an electrically controlled rotatory chair” (in Portuguese), Master Degree
dissertation, Electrical Eng/Biomed Eng. Program, Pontifícia Universidade
Católica do Rio Grande do Sul, Porto Alegre, Brazil, 2001.
[8] J. L. Giongo, M. A dos Santos, T. Russomano, “Prevention of
space motion sickness symptoms by Cinnarizine and Scopolamine during tests
in a rotatory chair”, (in Portuguese), Dissertation, Pharmacy School, Pontifícia
Universidade Católica do Rio Grande do Sul, Porto Alegre, Brazil,
2002 [Online]. Available: http://www.ipct.pucrs.br/microg
