A heuristic mathematical model for the dynamics of sensory conflict and motion sickness.

Oman CM.

The etiology of motion sickness is now usually explained in terms of a qualitatively formulated "sensory conflict" hypothesis. By consideration of the information processing task faced by the central nervous system in estimating body spatial orientation and in controlling active body movement using an "internal model" referenced control strategy, a mathematical model for sensory conflict generation is developed. The model incorporates and extends models proposed by von Holst, Held, and Reason, and is congruent with multisensory models for spatial orientation developed by Young and coworkers. The model postulates a major dynamic functional role for sensory conflict signals in movement control, as well as in sensory-motor adaptation. It accounts for the role of active movement in creating motion sickness symptoms in some experimental circumstances, and in alleviating them in others. The relationship between motion sickness produced by "sensory rearrangement" and that resulting from external motion disturbances is explicitly defined. A nonlinear conflict averaging model is proposed which describes dynamic aspects of experimentally observed subjective discomfort sensation, and suggests resulting behaviours. The model admits several possibilities for adaptive mechanisms which do not involve internal model updating. Further systematic efforts to experimentally refine and validate the model are indicated.

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Susceptibility to motion sickness and the development of anticipatory nausea and vomiting in cancer patients undergoing chemotherapy.

Morrow GR.

There are neural pathways between the vestibular system and an area of the brain in the fourth ventricle that appear to coordinate vomiting. Based on this and clinical observations, we theorized a relationship between a susceptibility to motion sickness and the intensity of nausea and vomiting from chemotherapy. A significant relationship (P less than 0.01) between a susceptibility to motion sickness and anticipatory nausea/vomiting in cancer patients undergoing chemotherapy was found. Antimotion drugs such as scopolamine may have a greater antiemetic effect on chemotherapy patients susceptible to motion sickness than on those who are not susceptible.

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Elicitation of motion sickness by head movements in the microgravity phase of parabolic flight maneuvers.

Lackner JR, Graybiel A.

During parabolic flight maneuvers in a Boeing KC-135 aircraft 44 college students were tested for motion sickness susceptibility. These subjects were categorized as 1) insusceptible, 2) moderately susceptible, or 3) highly susceptible to motion sickness during exposure to varying gravitoinertial force levels. After categorization, they were tested in the microgravity phase of parabolic flight to see how three types of head movements affected their baseline susceptibility. The head movements evaluated included side-to-side swivel, shoulder-to-shoulder roll, and front-up head and trunk movements; each type of head movement was used on a separate test day for eyes-open and eyes-covered conditions. Ten cycles of head movements were made in each parabola until a motion sickness endpoint, nausea, was reached or 40 parabolas had been completed. All types of head movements significantly increased susceptibility for subjects in all categories; eyes-open conditions were always more stressful than eyes-closed for each kind of head movement. These findings show unequivocally that natural head movements in microgravity can elicit symptoms of motion sickness. They suggest that head movements play an important etiological role in space motion sickness. In ground based studies where head movements are necessary to elicit symptoms, they are also necessary to elicit adaptation. We describe the use of paced and incremented head movement schedules as a possible way of partially alleviating space motion sickness.

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Drug treatment of motion sickness: scopolamine alone and combined with ephedrine in real and simulated situations.

Tokola O, Laitinen LA, Aho J, Gothoni G, Vapaatalo H.

In two placebo-controlled, double-blind, randomized trials scopolamine (0.3 mg) alone or combined with ephedrine (25 mg) was tested for its effectiveness in the prevention of seasickness during 24 h at sea and of motion sickness in rotating chair tests in a laboratory. Scopolamine was effective both alone and in combination with ephedrine, which supports the hypothesis on central cholinergic overactivity in the pathogenesis of motion sickness. Ephedrine did not markedly increase the effectiveness of scopolamine. Side-effects were slight and did not disturb the operating ability of the volunteers.

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A cholinomimetic model of motion sickness and space adaptation syndrome.

Janowsky DS, Risch SC, Ziegler M, Kennedy B, Huey L.

The space adaptation syndrome is one of the more vexing problems confronted by our nation's astronauts during their journeys. This syndrome may be a variant of motion sickness, although this possibility has been questioned. Physostigmine, a centrally active cholinesterase inhibitor which increases brain acetylcholine, was found to cause a motion sickness-like syndrome--in psychiatric patients and normals--including nausea, emesis, malaise, dysphoria, increases in serum ACTH, beta-endorphin, cortisol, and prolactin, Neostigmine, a non-centrally acting cholinesterase inhibitor, and saline placebo caused no such effects. The above effects closely parallel those of motion sickness. Thus, the effects of physostigmine may be a convenient model for screening for treatments for motion sickness or space adaptation syndrome, or for predicting who will develop these syndromes.

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Transdermal therapeutic system scopolamine (TTSS), dimenhydrinate, and placebo--a comparative study at sea.

Noy S, Shapira S, Zilbiger A, Ribak J.

The efficacy of transdermally administered scopolamine was compared with the efficacy of oral dimenhydrinate and placebo therapy in the prevention of motion sickness at sea. Medication was administered on a controlled double blind basis to 140 subjects. A placebo effect reduced the motion sickness incidence (MSI) from 57.69% in the control group to 43.47%. Administration of dimenhydrinate reduced the MSI to 22.22% and the use of Transdermal Therapeutic System Scopolamine (TTSS) further reduced the MSI to 16.66%. TTSS afforded 61.67% protection against motion sickness at sea, compared to 48.88% protection with dimenhydrinate.

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Carbonic anhydrase inhibitors for prevention of space motion sickness: an avenue of investigation.

Martin NF.

Space motion sickness (SMS) is an important medical problem facing NASA's space shuttle program. Two theories that have been advanced to explain SMS are the "fluid shift theory" and the "vestibulo-ocular sensory conflict theory". The "fluid shift theory" pre-supposes an active or passive shift of body fluid to the central nervous system (CNS) and vestibulo-auditory mechanisms. In contrast, the "sensory conflict theory" hypothesizes that unfamiliar accelerational and gravitational inputs from the middle ear conflict with visual inputs and lead to SMS. Carbonic anhydrase inhibitors (CAHI) are known to suppress active production of CSF and may be able to inhibit production of perilymph in the semi-circular canals. Therefore, CAHI may be able to diminish the hypothesized fluid shift to the CNS and inner ear under the fluid shift theory. It is suggested that carbonic anhydrase inhibitors merit clinical investigation to test their usefulness for prophylaxis of space motion sickness and to test the veracity of the fluid shift theory.

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[Observation on electrogastrogram changes during parallel swing stimulation]

[Article in Chinese]

Gu H, Tong B, Zhang X, Wang L.

Institute of Space Medico-Engineering, Beijing, China.

In order to study the relationship between cutaneous electrogastrogram (EGG) and nausea syndrome of the motion sickness, power spectrum analysis is used to analyze EGG recorded during motion sickness evoked by the parallel swing in 32 healthy men. 20 subjects showed a shift of Period Dominant Frequency (PDF) of EGG from Three CPM (2.40-3.70cpm) to Tachygastria (3.70-10.00cpm). PDF, the percentage of power of Tachygastria wave and Dominant Frequency Instability Coefficient significantly increased (P < 0.01). The incidences of nausea syndrome was obvious at the moment after swing. The result showed that EGG may be used for testing nausea symptoms of motion sickness.

Online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11540563&dopt=Abstract motion sickness