Development and validation of an electrically ...

Proceedings oflhe 25' Annual lntemational Conference of the IEEE EMBS Cancun, Mexico September 17-21,2003

Development and Validation of an Electrically Controlled Rotatory Chair to be Used as a Simulator for Spatial Disorientation and Motion Sickness T. Russomanol, D.F.G. de Azevedol, L. Piedadel, F. S. Glockl, M. Tello', M. A. dos Santos2, F. P. Falciio', J. L. Giongo2 'Microgravity Laboratory, Scientific and Technological Research Institute (IPCT), Pontifical Catholic University, Porto Alegre, RS, Brazil 2School of Pharmacy - Pontifical Catholic University, Porto Alegre, RS, Brazil

Absrracr 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 Barany, 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 O.Itds2. 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% 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 [I]. 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 0-7803-7789-3/03/$17.00 02003 IEEE

perception of body and aircraft positions is false. It is believed that all aircrew and spacecrew experience disorientation at some stase during their careers, hut it is only when control of the aircraft or the spacecraft is based on false perceptions that incidents and accidents may occur PI. Motion sickness is a fairly common problem in early flying training and in pasengers 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, lightheadedness, 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.

11. METHODOLOGY

A . Electrically Controlled Rotatory Chair The ECRC (Figure 1) was developed according to the following specifications [ l ] :rotation range from a minimal of IO rpm to a maximum of 30 rpm; maximal accidental load of 100 kg; no nominal variation of the acceleration during rotation.

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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 afactorof15:l. The transmission of the movement between the motor and the chair is given hy two trapezoidal canal pulleys and an A29 model chain with a reduction of 6: 1. ...,, ~

. .

"

....

...

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 ofECRC

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 ahout 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. Siens and svmntoms of motion sickness were observed by the researcher and reported by the volunteers

.

i

I

..

I

Fig. 1. Electrically controlled Rotatory Chair

The final rotation of the system is given by the expression

RJ= [ ( R d r ) / R p 1

(1)

where: Rr = final rotation; R, = motor rotation; I = reduction factor; &=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 AID converter has a reference voltage of 5 V. This requires the dynamo signal to he lowered by a voltage

_ .

111. RESULTS

A paired t-test was used for data analysis with a level of significance of p 2 0.05. The percentage of signs and symptoms are also presented. The mean speed of the ECRC during the rotation sessions was 24.2 (SDI-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 71 1 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 11.

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It has been used to demonstrate to approximately 200 private pilots every year ikom flight schools and school of aeronautical sciences features related to spatial disorientation. ARer the training, pilots become aware of the importance of trusting the instruments during flights, especially when visual clu'cs are reduced or missing. The ECRC has also boen used for research projects that aim to study space motion sickness, its signs and symptoms, and its prevention (http://vnvw.ipct.pucrs.br/microg).

TABLEI

Placebo

Signs and Symptoms

,OA,

IUI

Pale face

75

100

Sweating

67 67

100

N'l"S3

67

IO0

Dizziness

67 17 0

42 0

Disorientation

Headache Vomiting

92 75

ACKNOWLEDGMENT We would like to thank those who gave us technical support to develop this work: Celso Renato Vieira dos Santos, Carlos Schossler, Ivlirio Vian and Denis Barbieri.

TABLEII TIME OF ROTATION (s) WITH AND WITHOUT SCOPOLAMINE Volunteer 01

02 03 04 05

06 07 08 09 10

II 12 Mean SE (?)

Time of Rotation (3) Scopolamine Placebo 550 290 983 840 253 201 224 I49 ISDO 1800 202 205 I I46 339 247 218 25 25 92 90 1800 892 61 I I213 711.25 471,67 188 146

RE:FERENCES I. Benson, "Spatial disorientation - General aspects". in Dehenin G, Ed. Aviolion Medicine, London: Tri-Med Books, 1975, Vol. I , pp. 407424. W. R. Kirham, W.E. Collins, P.M. Grape, I. M. Simpson, T. F. Wallace, "Spatial disorientation in general aviation accidents", in Avidf Space Environ Med, no. 49, pp. 1080-6, 1978. J. R. Davis, "Space ,motion sickness during 24 flights of the Space Shuttle", in Aviar Space Environ Med, no. 53, pp. 570-75, 1988. W. E. Thornton, T. P. Moore, S. L. Pool, J. Vanderploeg, "Clinical characterimtion and etiology of space motion sickness", in AviofSpaceEnviron Med. no. 58, AI-8, 1987b. C. 1). Wood, A. Graybiel, "Evaluation of sixteen antimotion sickness drugs under controlled laboratory conditions", in Aemspnce Medicine, so. 39, pp. 1341-44, 1968. C. D.Wood, A. Grayliel, "Theory of anlimolion sickness drug mechanisms", in Aerorpoce Medicine, no.43, pp. 249-52.1972. L. A. Piedade, T. Russomano, D. F. G de Azeveda, "Dedopment of an electrically controlled rotalory chair" (in Portuguese). Master D'egree dissertation, Electrical EngiBiomed Eng. Program, Pontifr,:ia Universidade Catblica do Rio Grande do SUI,Port0 Alegre, Elrazil, 2001. 1. L. Giongo, M. A dos Santos, T. Russamano, "Prevention of space motion sickness symptoms by Cinnaririne and Scopolamine during t1:sts in a rotatory chair", (in Portuguese), Dissertation, Pharmacy School, Pantificia Universidade Catblica do Rio Grande do SUI, Porta Alegre, Brazil, 2002 [Online). Available: http:llwww,ipet.pucrs.brlmicrog A.

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.

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