General autonomic components of motion sickness

Exploring neurophysiological correlates of visually induced motion sickness using electroencephalography (EEG)

Visually induced motion sickness (VIMS) is a common phenomenon when using visual devices such as smartphones and virtual reality applications, with symptoms including nausea, fatigue, and headache. To date, the neuro-cognitive processes underlying VIMS are not fully understood. Previous studies using electroencephalography (EEG) delivered mixed findings, with some reporting an increase in delta and theta power, and others reporting increases in alpha and beta frequencies. The goal of the study was to gain further insight into EEG correlates for VIMS. Participants viewed a VIMS-inducing visual stimulus, composed of moving black-and-white vertical bars presented on an array of three adjacent monitors. The EEG was recorded during visual stimulation and VIMS ratings were recorded after each trial using the Fast Motion Sickness Scale. Time-frequency analyses were conducted comparing neural activity of participants reporting minimal VIMS (n = 21) and mild-moderate VIMS (n = 12). Results suggested a potential increase in delta power in the centro-parietal regions (CP2) and a decrease in alpha power in the central regions (Cz) for participants experiencing mild-moderate VIMS compared to those with minimal VIMS. Event-related spectral perturbations (ERSPs) suggested that group differences in EEG activity developed with increasing duration of a trial. These results support the hypothesis that the EEG might be sensitive to differences in information processing in VIMS and minimal VIMS contexts, and indicate that it may be possible to identify neurophysiological correlate of VIMS. Differences in EEG activity related to VIMS may reflect differential processing of conflicting visual and vestibular sensory information.

Antihistamines for motion sickness

BACKGROUND

Motion sickness is a syndrome that occurs as a result of passive body movement in response to actual motion, or the illusion of motion when exposed to virtual and moving visual environments. The most common symptoms are nausea and vomiting. Antihistamines have been used in the management of motion sickness for decades, however studies have shown conflicting results regarding their efficacy.

OBJECTIVES

To assess the effectiveness of antihistamines in the prevention and treatment of motion sickness in adults and children.

SEARCH METHODS

The Cochrane ENT Information Specialist searched the Cochrane ENT Register; Central Register of Controlled Trials; Ovid MEDLINE; Ovid Embase; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished trials. The date of the search was 7 December 2021.

SELECTION CRITERIA

Randomised controlled trials (RCTs) in susceptible adults and children in whom motion sickness was induced under natural conditions such as air, sea and land transportation. We also included studies in which motion sickness was induced under experimental conditions (analysed separately). Antihistamines were included regardless of class, route or dosage and compared to no treatment, placebo or any other pharmacological or non-pharmacological interventions.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were 1) the proportion of susceptible participants who did not experience any motion sickness symptoms; 2) the proportion of susceptible participants who experienced a reduction or resolution of existing symptoms. Secondary outcomes were 1) physiological measures (heart rate, core temperature and gastric tachyarrhythmia (electrogastrography)) and 2) adverse effects (sedation, impaired cognition, blurred vision). We used GRADE to assess the certainty of the evidence for each outcome.

MAIN RESULTS

We included nine RCTs (658 participants). Studies were conducted across seven countries, with an overall age range of 16 to 55 years. Motion sickness was induced naturally in six studies and experimentally in four studies (rotating chair). All the naturally induced studies only evaluated first-generation antihistamines (cinnarizine and dimenhydrinate). Risk of bias across the studies varied, with mostly low risk for random sequence generation and allocation concealment, and mostly high risk for selective reporting. Only the experimentally induced studies measured physiological parameters and only the naturally induced studies evaluated adverse effects. There were no studies that clearly assessed the paediatric population. Antihistamines versus placebo or no treatment Antihistamines are probably more effective than placebo at preventing motion sickness symptoms under natural conditions (symptoms prevented: 25% placebo; 40% antihistamines) (risk ratio (RR) 1.81, 95% confidence interval (CI) 1.23 to 2.66; 3 studies; 240 participants) (moderate-certainty). The evidence is very uncertain about the effect of antihistamines on preventing motion sickness under experimental conditions (standardised mean difference (SMD) 0.32, 95% CI -0.18 to 0.83; 2 studies; 62 participants) (very low-certainty). No studies reported results on the resolution of existing motion sickness symptoms. Antihistamines may result in little or no difference in gastric tachyarrhythmia under experimental conditions (mean difference (MD) -2.2, 95% CI -11.71 to 7.31; 1 study; 42 participants) (low-certainty). No studies reported results for any other physiological measures. When compared to placebo, antihistamines may be more likely to cause sedation (sedation: 44% placebo; 66% antihistamines) (RR 1.51, 95% CI 1.12 to 2.02; 2 studies; 190 participants) (low-certainty); they may result in little or no difference in blurred vision (blurred vision: 12.5% placebo; 14% antihistamines) (RR 1.14, 95% CI 0.53 to 2.48; 2 studies; 190 participants) (low-certainty); and they may result in little or no difference in terms of impaired cognition (impaired cognition: 33% placebo; 29% antihistamines) (RR 0.89, 95% CI 0.58 to 1.38; 2 studies; 190 participants) (low-certainty). Antihistamines versus scopolamine The evidence is very uncertain about the effect of antihistamines on preventing motion sickness under natural conditions when compared to scopolamine (symptoms prevented: 81% scopolamine; 71% antihistamines) (RR 0.89, 95% CI 0.68 to 1.16; 2 studies; 71 participants) (very low-certainty). No studies were performed under experimental conditions. No studies reported results on the resolution of existing motion sickness symptoms. The evidence is very uncertain about the effect of antihistamines on heart rate under natural conditions (narrative report, 1 study; 20 participants; "No difference in pulse frequency"; very low-certainty). No studies reported results for any other physiological measures. When compared to scopolamine, the evidence is very uncertain about the effect of antihistamines on sedation (sedation: 21% scopolamine; 30% antihistamines) (RR 0.82, 95% CI 0.07 to 9.25; 2 studies; 90 participants) (very low-certainty) and on blurred vision (narrative report: not a significant difference; 1 study; 51 participants; very low-certainty). No studies evaluated impaired cognition. Antihistamines versus antiemetics Antihistamines may result in little or no difference in the prevention of motion sickness under experimental conditions (MD -0.20, 95% CI -10.91 to 10.51; 1 study; 42 participants) (low-certainty). The evidence is of low certainty due to imprecision as the sample size is small and the confidence interval crosses the line of no effect. No studies assessed the effects of antihistamines versus antiemetics under natural conditions. No studies reported results on the resolution of existing motion sickness symptoms. Antihistamines may result in little or no difference in gastric tachyarrhythmia (MD 4.56, 95% CI -3.49 to 12.61; 1 study; 42 participants) (low-certainty). No studies reported results for any other physiological measures. No studies evaluated sedation, impaired cognition or blurred vision. One study reported physiological data for this outcome, evaluating gastric tachyarrhythmia specifically. Antihistamines may result in little or no difference in gastric tachyarrhythmia (MD 4.56, 95% CI -3.49 to 12.61; 1 study; 42 participants; low-certainty evidence). This evidence is of low certainty due to imprecision as the sample size is small and the confidence interval crosses the line of no effect. Antihistamines versus acupuncture The evidence is very uncertain about the effects of antihistamines on the prevention of motion sickness under experimental conditions when compared to acupuncture (RR 1.32, 95% CI 1.12 to 1.57; 1 study; 100 participants) (very low-certainty). This study did not assess the prevention of motion sickness under natural conditions, nor the resolution of existing motion sickness symptoms. There was no study performed under natural conditions. Physiological measures and adverse effects were not reported.

AUTHORS' CONCLUSIONS

There is probably a reduction in the risk of developing motion sickness symptoms under naturally occurring conditions of motion when using first-generation antihistamines, in motion sickness-susceptible adults, compared to placebo. Antihistamines may be more likely to cause sedation when compared to placebo. No studies evaluated the treatment of existing motion sickness, and there are few data on the effect of antihistamines in children. The evidence for all other outcomes and comparisons (versus scopolamine, antiemetics and acupuncture) was of low or very low certainty and we are therefore uncertain about these effects of antihistamines.

Relating individual motion sickness levels to subjective discomfort ratings

High levels of vehicle automation are expected to increase the risk of motion sickness, which is a major detriment to driving comfort. The exact relation between motion sickness and discomfort is a matter of debate, with recent studies suggesting a relief of discomfort at the onset of nausea. In this study, we investigate whether discomfort increases monotonously with motion sickness and how the relation can best be characterized in a semantic experiment (Experiment 1) and a motion sickness experiment (Experiment 2). In Experiment 1, 15 participants performed pairwise comparisons on the subjective discomfort associated with each item on the popular MIsery SCale (MISC) of motion sickness. In Experiment 2, 17 participants rated motion sickness using the MISC during exposures to four sustained motion stimuli, and provided (1) numerical magnitude estimates of the discomfort experienced for each level of the MISC, and (2) verbal magnitude estimates with seven qualifiers, ranging between feeling 'excellent' and 'terrible'. The data of Experiment 1 show that the items of the MISC are ranked in order of appearance, with the exception of 5 ('severe dizziness, warmth, headache, stomach awareness, and sweating') and 6 ('slight nausea'), which are ranked in opposite order. However, in Experiment 2, we find that discomfort associated with each level of the MISC, as it was used to express motion sickness during exposure to a sickening stimulus, increases monotonously; following a power law with an exponent of 1.206. While the results of Experiment 1 replicate the non-linearity found in recent studies, the results of Experiment 2 suggest that the non-linearity is due to the semantic nature of Experiment 1, and that there is a positive monotonous relation between MISC and discomfort in practice. These results support the suitability of MISC to assess motion sickness.

Exploring the utility of EDA and skin temperature as individual physiological correlates of motion sickness

Motion sickness (MS) is known to be a potentially limiting factor for future self-driving vehicles - specifically in regards to occupant comfort and well-being. With this as a consideration comes the desire to accurately measure, track and even predict MS state in real-time. Previous research has considered physiological measurements to measure MS state, although, this is mainly measured after an MS exposure and not throughout exposure(s) to a MS task. A unique contribution of this paper is in the real-time tracking of subjective MS alongside real-time physiological measurements of Electrodermal Activity (EDA) and skin temperature. Data was collected in both simulator-based (controlled) and on-road (naturalistic) studies. 40 participants provided at total of 61 data sets, providing 1603 min of motion sickness data for analysis. This study is in agreement that these measures are related to MS but evidenced a total lack of reliability for these measures at an individual level for both simulator and on-road experimentation. It is likely that other factors, such as environment and emotional state are more impactful on these physiological measures than MS itself. At a cohort level, the applicability of physiological measures is not considered useful for measuring MS accurately or reliably in real-time. Recommendations for further research include a mixed-measures approach to capture other data types (such as subject activity) and to remove contamination of physiological measures from environmental changes.

Thermal infrared imaging based facial temperature in comparison to ear temperature during a real-driving scenario

Motion Sickness is associated with a variety of symptoms, which differ in occurrence rate and intensity between individuals. In order to research the cause of car sickness and develop countermeasures, it is important to determine symptoms and their severity objectively. A tool for this purpose could be the assessment of physiological reactions due to motion sickness. This paper describes and discusses a methodology to identify changes in facial skin temperatures in a real-driving study. Common techniques had to be adjusted in order to meet the requirements given by the challenges of in-car-recording. The examined data was generated in a previous study, which was designed to research motion sickness in a driving environment. A pre-processing technique had to be developed to magnify features on the face and subsequently improve the tracking in thermal imagery. After the pre-processing, regions of interest (ROI) were manually marked and tracked in thermal images. The thereby assessed facial skin temperatures were compared to tympanic temperatures. Derived temperatures from the forehead as well as from the 20 hottest pixels within the face indicated a better tracking, while the nose tip was more affected by detection errors. The correlation of the three features with the tympanic temperature showed remarkable differences between a baseline measurement and the actual driving. Less than 10% of the data derived during the driving and up to 30% of the data during the baseline measurement correlated highly. It is concluded that detecting changes in facial skin temperature using thermal infrared imaging in a moving car is challenging and results are hardly comparable to tympanic temperatures. Future research should aim at the different influencing factors of skin and tympanic temperature, while enhancing tracking or detection of ROI could be achieved by reducing the passengers' movements or choosing the target area more carefully.

Methodological Considerations Concerning Motion Sickness Investigations during Automated Driving

Automated driving vehicles will allow all occupants to spend their time with various non-driving related tasks like relaxing, working, or reading during the journey. However, a significant percentage of people is susceptible to motion sickness, which limits the comfort of engaging in those tasks during automated driving. Therefore, it is necessary to investigate the phenomenon of motion sickness during automated driving and to develop countermeasures. As most existing studies concerning motion sickness are fundamental research studies, a methodology for driving studies is yet missing. This paper discusses methodological aspects for investigating motion sickness in the context of driving including measurement tools, test environments, sample, and ethical restrictions. Additionally, methodological considerations guided by different underlying research questions and hypotheses are provided. Selected results from own studies concerning motion sickness during automated driving which were conducted in a motion-based driving simulation and a real vehicle are used to support the discussion.

Thermoregulation and nausea

The major symptoms of motion sickness are well known and include facial pallor, nausea and vomiting, and sweating, but it is poorly recognized that they actually reflect severely perturbed thermoregulation. Thus, the purpose of this chapter is to present and discuss existing data related to this subject. While hypothermia during seasickness was first noted nearly 150 years ago, detailed studies of this phenomenon were conducted only during the last two decades. Our own research confirmed that motion sickness-induced hypothermia is quite broadly expressed phylogenetically as, besides humans, it could be provoked in several other animals (rats, musk shrews, and mice). Evidence from human and animal experiments indicates that the physiologic mechanisms responsible for the motion sickness-induced hypothermia include cutaneous vasodilation and sweating (leading to an increase of heat loss) and reduced thermogenesis. Together, these results suggest that motion sickness triggers a highly coordinated physiologic response aiming to reduce body temperature. The chapter is concluded by presenting hypotheses of how and why motion sickness evokes this hypothermic response.

Brain Activation by H1 Antihistamines Challenges Conventional View of Their Mechanism of Action in Motion Sickness: A Behavioral, c-Fos and Physiological Study in Suncus murinus (House Musk Shrew)

Motion sickness occurs under a variety of circumstances and is common in the general population. It is usually associated with changes in gastric motility, and hypothermia, which are argued to be surrogate markers for nausea; there are also reports that respiratory function is affected. As laboratory rodents are incapable of vomiting, Suncus murinus was used to model motion sickness and to investigate changes in gastric myoelectric activity (GMA) and temperature homeostasis using radiotelemetry, whilst also simultaneously investigating changes in respiratory function using whole body plethysmography. The anti-emetic potential of the highly selective histamine H₁ receptor antagonists, mepyramine (brain penetrant), and cetirizine (non-brain penetrant), along with the muscarinic receptor antagonist, scopolamine, were investigated in the present study. On isolated ileal segments from Suncus murinus, both mepyramine and cetirizine non-competitively antagonized the contractile action of histamine with pK _b values of 7.5 and 8.4, respectively; scopolamine competitively antagonized the contractile action of acetylcholine with pA₂ of 9.5. In responding animals, motion (1 Hz, 4 cm horizontal displacement, 10 min) increased the percentage of the power of bradygastria, and decreased the percentage power of normogastria whilst also causing hypothermia. Animals also exhibited an increase in respiratory rate and a reduction in tidal volume. Mepyramine (50 mg/kg, i.p.) and scopolamine (10 mg/kg, i.p.), but not cetirizine (10 mg/kg, i.p.), significantly antagonized motion-induced emesis but did not reverse the motion-induced disruptions of GMA, or hypothermia, or effects on respiration. Burst analysis of plethysmographic-derived waveforms showed mepyramine also had increased the inter-retch+vomit frequency, and emetic episode duration. Immunohistochemistry demonstrated that motion alone did not induce c-fos expression in the brain. Paradoxically, mepyramine increased c-fos in brain areas regulating emesis control, and caused hypothermia; it also appeared to cause sedation and reduced the dominant frequency of slow waves. In conclusion, motion-induced emesis was associated with a disruption of GMA, respiration, and hypothermia. Mepyramine was a more efficacious anti-emetic than cetirizine, suggesting an important role of centrally-located H₁ receptors. The ability of mepyramine to elevate c-fos provides a new perspective on how H₁ receptors are involved in mechanisms of emesis control.

Cross-coupling vestibular stimulation: motion sickness and the vestibulo-sympathetic reflex

Motion sickness is associated with a variety of autonomic symptoms, presumably due to proximity or functional interconnectivity between the autonomic centers in the brainstem and the vestibular system. A direct influence of the vestibular system on cardiovascular variables, defined as the vestibulo-sympathetic reflex, has been reported previously. Our aim was to investigate the sudomotor components of the autonomic responses associated with motion sickness during passive cross-coupling stimulation ("roll while rotating"). Healthy subjects (n = 17) were rotated at 40°/s around an earth-vertical yaw axis alone and in combination with sinusoidal roll oscillations (0.2 Hz). Motion sickness was assessed verbally every minute using a 1-10 scale, while recording DC and AC skin conductance levels (SCL) from the forehead. Yaw rotation alone provoked neither motion sickness nor variations of forehead sweating. Yet during cross-coupling stimulation all subjects reported motion sickness. Higher motion sickness scores (>5) were associated with significantly higher amplitudes of AC-SCL events compared to the lower scores (0.22 ± 0.01 vs. 0.11 ± 0.01 µS, respectively). Frequency domain analysis of the AC-SCL events revealed a peak at 0.2 Hz, coinciding with the frequency of the chair rolls. The total power of AC-SCL signals did not match the trend of motion sickness scores across conditions. We conclude that: (1) although SCL is related to motion sickness, it does not follow the perceived sickness closely; (2) the discrepancy between SCL and motion sickness and the rhythmic AC-SCL events could reflect a sudomotor component of the vestibulo-sympathetic reflex.

Low level of swiprosin-1/EFhd2 in vestibular nuclei of spontaneously hypersensitive motion sickness mice

Susceptibility to motion sickness (MS) varies considerably among humans. However, the cause of such variation is unclear. Here, we used a classical genetic approach to obtain mouse strains highly sensitive and resistant to MS (SMS and RMS). Proteomics analysis revealed substantially lower swiprosin-1 expression in SMS mouse brains. Inducing MS via rotary stimulation decreased swiprosin-1 in the mouse brains. Swiprosin-1 knockout mice were much more sensitive to motion disturbance. Immunohistochemistry revealed strong swiprosin-1 expression in the vestibular nuclei (VN). Over-expressing swiprosin-1 in the VN of SMS mice decreased MS susceptibility. Down-regulating swiprosin-1 in the VN of RMS mice by RNAi increased MS susceptibility. Additional in vivo experiments revealed decreased swiprosin-1 expression by glutamate via the NMDA receptor. Glutamate increased neuronal excitability in SMS or swiprosin-1 knockout mice more prominently than in RMS or wild-type mice. These results indicate that swiprosin-1 in the VN is a critical determinant of the susceptibility to MS.

Self-regulation of breathing as a primary treatment for anxiety

Understanding the autonomic nervous system and homeostatic changes associated with emotions remains a major challenge for neuroscientists and a fundamental prerequisite to treat anxiety, stress, and emotional disorders. Based on recent publications, the inter-relationship between respiration and emotions and the influence of respiration on autonomic changes, and subsequent widespread membrane potential changes resulting from changes in homeostasis are discussed. We hypothesize that reversing homeostatic alterations with meditation and breathing techniques rather than targeting neurotransmitters with medication may be a superior method to address the whole body changes that occur in stress, anxiety, and depression. Detrimental effects of stress, negative emotions, and sympathetic dominance of the autonomic nervous system have been shown to be counteracted by different forms of meditation, relaxation, and breathing techniques. We propose that these breathing techniques could be used as first-line and supplemental treatments for stress, anxiety, depression, and some emotional disorders.

Cybersickness provoked by head-mounted display affects cutaneous vascular tone, heart rate and reaction time

Evidence from studies of provocative motion indicates that motion sickness is tightly linked to the disturbances of thermoregulation. The major aim of the current study was to determine whether provocative visual stimuli (immersion into the virtual reality simulating rides on a rollercoaster) affect skin temperature that reflects thermoregulatory cutaneous responses, and to test whether such stimuli alter cognitive functions. In 26 healthy young volunteers wearing head-mounted display (Oculus Rift), simulated rides consistently provoked vection and nausea, with a significant difference between the two versions of simulation software (Parrot Coaster and Helix). Basal finger temperature had bimodal distribution, with low-temperature group (n=8) having values of 23-29 °C, and high-temperature group (n=18) having values of 32-36 °C. Effects of cybersickness on finger temperature depended on the basal level of this variable: in subjects from former group it raised by 3-4 °C, while in most subjects from the latter group it either did not change or transiently reduced by 1.5-2 °C. There was no correlation between the magnitude of changes in the finger temperature and nausea score at the end of simulated ride. Provocative visual stimulation caused prolongation of simple reaction time by 20-50 ms; this increase closely correlated with the subjective rating of nausea. Lastly, in subjects who experienced pronounced nausea, heart rate was elevated. We conclude that cybersickness is associated with changes in cutaneous thermoregulatory vascular tone; this further supports the idea of a tight link between motion sickness and thermoregulation. Cybersickness-induced prolongation of reaction time raises obvious concerns regarding the safety of this technology.

Motion sickness, nausea and thermoregulation: The "toxic" hypothesis

Principal symptoms of motion sickness in humans include facial pallor, nausea and vomiting, and sweating. It is less known that motion sickness also affects thermoregulation, and the purpose of this review is to present and discuss existing data related to this subject. Hypothermia during seasickness was firstly noted nearly 150 years ago, but detailed studies of this phenomenon were conducted only during the last 2 decades. Motion sickness-induced hypothermia is philogenetically quite broadly expressed as besides humans, it has been reported in rats, musk shrews and mice. Evidence from human and animal experiments indicates that the physiological mechanisms responsible for the motion sickness-induced hypothermia include cutaneous vasodilation and sweating (leading to an increase of heat loss) and reduced thermogenesis. Together, these results suggest that motion sickness triggers highly coordinated physiological response aiming to reduce body temperature. Finally, we describe potential adaptive role of this response, and describe the benefits of using it as an objective measure of motion sickness-induced nausea.

Brain Circuitry Supporting Multi-Organ Autonomic Outflow in Response to Nausea

While autonomic outflow is an important co-factor of nausea physiology, central control of this outflow is poorly understood. We evaluated sympathetic (skin conductance level) and cardiovagal (high-frequency heart rate variability) modulation, collected synchronously with functional MRI (fMRI) data during nauseogenic visual stimulation aimed to induce vection in susceptible individuals. Autonomic data guided analysis of neuroimaging data, using a stimulus-based (analysis windows set by visual stimulation protocol) and percept-based (windows set by subjects' ratings) approach. Increased sympathetic and decreased parasympathetic modulation was associated with robust and anti-correlated brain activity in response to nausea. Specifically, greater autonomic response was associated with reduced fMRI signal in brain regions such as the insula, suggesting an inhibitory relationship with premotor brainstem nuclei. Interestingly, some sympathetic/parasympathetic specificity was noted. Activity in default mode network and visual motion areas was anti-correlated with parasympathetic outflow at peak nausea. In contrast, lateral prefrontal cortical activity was anti-correlated with sympathetic outflow during recovery, soon after cessation of nauseogenic stimulation. These results suggest divergent central autonomic control for sympathetic and parasympathetic response to nausea. Autonomic outflow and the central autonomic network underlying ANS response to nausea may be an important determinant of overall nausea intensity and, ultimately, a potential therapeutic target.

Gastric and lower esophageal sphincter pressures during nausea: a study using visual motion-induced nausea and high-resolution manometry

Nausea is the subjective unpleasant sensation that immediately precedes vomiting. Studies using barostats suggest that gastric fundus and lower esophageal sphincter (LES) relaxation precede vomiting. Unlike barostat, high-resolution manometry allows less invasive, detailed measurements of fundus pressure (FP) and axial movement of the gastroesophageal junction (GEJ). Nausea was induced in 12 healthy volunteers by a motion video and rated on a visual analog scale. FP was measured as the mean value of the five pressure channels that were clearly positioned below the LES. After intubation, a baseline (BL) recording of 15 min was obtained. This was followed by presentation of the motion video (at least 10 min, maximum 20 min) followed by 30 min recovery recording. Throughout the experiment we recorded autonomic nervous system (ANS) parameters [blood pressure, heart rate (HR), and cardiac vagal tone (CVT), which reflects efferent vagal activity]. Ten out of 12 subjects showed a drop in FP during peak nausea compared with BL (-4.0 ± 0.8 mmHg; P = 0.005), and 8/10 subjects showed a drop in LES pressure (-8.8 ± 2.5 mmHg; P = 0.04). Peak nausea preceded peak fundus and LES pressure drop. Nausea was associated with configuration changes at the GEJ such as LES shortening and esophageal lengthening. During nausea we observed a significantly increased HR and decreased CVT. In conclusion, nausea is associated with a drop in fundus and LES pressure, configuration changes at the GEJ as well as changes in the ANS activity such as an increased sympathetic tone (increased HR) and decreased parasympathetic tone (decreased CVT).

A combined HRV-fMRI approach to assess cortical control of cardiovagal modulation by motion sickness

Nausea is a commonly occurring symptom typified by epigastric discomfort with the urge to vomit. To date, the brain circuitry underlying the autonomic nervous system response to nausea has not been fully understood. Functional MRI (fMRI), together with a point process adaptive recursive algorithm for computation of the high-frequency (HF) index of heart rate variability (HRV) was combined to evaluate the brain circuitry underlying autonomic nervous system response to nausea. Alone, the point process analysis revealed increasing sympathetic and decreasing parasympathetic response during nausea with significant increased heart rate (HR) and decreased HF. The combined HRV-fMRI analysis demonstrated that the fMRI signal in the medial prefrontal cortex (MPFC) and pregenual anterior cingulate cortex (pgACC), regions of higher cortical functions and emotion showed a negative correlation at the baseline and a positive correlation during nausea. Overall, our findings confirm a sympathovagal shift (toward sympathetic) during nausea, which was related to brain activity in regions associated with emotion and higher cognitive function.

Static and dynamic autonomic response with increasing nausea perception

BACKGROUND

Nausea is a commonly occurring symptom typified by epigastric discomfort with urge to vomit. The relationship between autonomic nervous system (ANS) outflow and increasing nausea perception is not fully understood.

METHODS

Our study employed a nauseogenic visual stimulus (horizontally translating stripes) while 17 female subjects freely rated transitions in nausea level and autonomic outflow was measured (heart rate, HR; heart rate variability, HRV; skin conductance response, SCR; respiratory rate). We also adopted a recent approach to continuous high-frequency (HF) HRV estimation to evaluate dynamic cardiovagal modulation.

RESULTS

HR increased from baseline for all increasing nausea transitions, especially transition to strong nausea (15.0 +/- 11.4 bpm), but decreased (-6.6 +/- 4.6 bpm) once the visual stimulus ceased. SCR also increased for all increasing nausea transitions, especially transition to strong nausea (1.76 +/- 1.68 microS), but continued to increase (0.52 +/- 0.65 microS) once visual stimulation ceased. LF/HF HRV increased following transition to moderate (1.54 +/- 2.11 a.u.) and strong (2.57 +/- 3.49 a.u.) nausea, suggesting a sympathetic shift in sympathovagal balance. However, dynamic HF HRV suggested that bursts of cardiovagal modulation precede transitions to higher nausea, perhaps influencing subjects to rate higher levels of nausea. No significant change in respiration rate was found.

CONCLUSIONS

Our results suggest that increasing nausea perception is associated with both increased sympathetic and decreased parasympathetic ANS modulation. These findings corroborate past ANS studies of nausea, applying perception-linked analyses and dynamic estimation of cardiovagal modulation in response to nausea.

Strong potential for baroreflex-governed sympathetic outflow revealed during nausea

Muscle sympathetic nerve activity (MSNA) was recorded in two patients with amyotrophic lateral sclerosis. As expected, they exhibited a high level of MSNA at rest, with an inverse weak response to different maneuvers normally eliciting strong increase in MSNA. About 30 min after the intake of a glucose solution, they developed nausea with an extreme rise in MSNA and blood pressure. In one patient, a quantified analysis of this reaction could be done: the outflow was close to 200% above the already high resting level and >100% stronger than the response to any of the performed maneuvers. We regard this observation of importance, because it seems to unveil resources utilized only rarely, and strongly overcoming the "ceiling effect" that seemingly is a hindrance for sympathetic activation in subjects with high lever of MSNA at rest. An inhibitory "safety limit" might exist, the trespassing of which would damage the organism and thus occurs only during extraordinary circumstances.

Performance and autonomic responses during motion sickness

OBJECTIVE

The aim of the study was to investigate how motion sickness, triggered by an optokinetic drum, affects short-term memory performance and to explore autonomic responses to perceived motion sickness.

BACKGROUND

Previous research has found that motion sickness decreases performance, but it is not known how short-term memory in particular is affected.

METHOD

Thirty-eight healthy participants performed a listening span test while seated in a rotating optokinetic drum. Measurements of motion sickness, performance, heart rate, skin conductance, blood volume pulse, and pupil size were performed simultaneously throughout the experiment.

RESULTS

A total of 16 participants terminated the trial because of severe nausea, and the other 22 endured the full 25 min. Perceived motion sickness increased over time in both groups but less among those who endured the trial. Short-term memory performance decreased toward the end for those who terminated but increased in the other group. Results from the measured autonomic responses were ambiguous.

CONCLUSION

We conclude that performance, measured as short-term memory, declines as perceived motion sickness progresses.

APPLICATION

This research has potential implications for command and control personnel at risk of developing motion sickness.

Could sound be used as a strategy for reducing symptoms of perceived motion sickness?

BACKGROUND

Working while exposed to motions, physically and psychologically affects a person. Traditionally, motion sickness symptom reduction has implied use of medication, which can lead to detrimental effects on performance. Non-pharmaceutical strategies, in turn, often require cognitive and perceptual attention. Hence, for people working in high demand environments where it is impossible to reallocate focus of attention, other strategies are called upon. The aim of the study was to investigate possible impact of a mitigation strategy on perceived motion sickness and psychophysiological responses, based on an artificial sound horizon compared with a non-positioned sound source.

METHODS

Twenty-three healthy subjects were seated on a motion platform in an artificial sound horizon or in non-positioned sound, in random order with one week interval between the trials. Perceived motion sickness (Mal), maximum duration of exposure (ST), skin conductance, blood volume pulse, temperature, respiration rate, eye movements and heart rate were measured continuously throughout the trials.

RESULTS

Mal scores increased over time in both sound conditions, but the artificial sound horizon, applied as a mitigation strategy for perceived motion sickness, showed no significant effect on Mal scores or ST. The number of fixations increased with time in the non-positioned sound condition. Moreover, fixation time was longer in the non-positioned sound condition compared with sound horizon, indicating that the subjects used more time to fixate and, hence, assumingly made fewer saccades.

CONCLUSION

A subliminally presented artificial sound horizon did not significantly affect perceived motion sickness, psychophysiological variables or the time the subjects endured the motion sickness triggering stimuli. The number of fixations and fixation times increased over time in the non-positioned sound condition.

Sympathetic arousal to a vestibular stressor in high and low hostile men

The aim of the present experiment was to extend the literature on hostility and a cerebral systems based model of sympathetic arousal to a vestibular-based stress. Several authors have concluded that autonomic stress reactivity in high hostile individuals must be interpersonally based, whereas healthy vestibular system functioning does not depend on interpersonal features. Utilizing a vestibular activation paradigm, skin conductance levels of 15 high hostile and 15 low hostile men were recorded after brief passive rotation about the vertical neuroaxis. It was expected that hostile individuals would exhibit higher skin conductance levels after rotation compared with low hostile individuals. The results confirmed expectations of heightened sympathetic tone among high hostiles subsequent to vestibular stress. Overall, the findings are interpreted to support a cerebral model of frontal region capacity limitation for regulation of vestibular stress that is independent of psychosocial mechanisms.

Autonomic responses during motion sickness induced by virtual reality

OBJECTIVE

To examine the development of subjective symptoms and heart rate variability (HRV) during motion sickness induced by virtual reality (VR).

METHODS

Subjects were 10 healthy young volunteers. During VR immersion, subjects were immersed in a visual-vestibular conflict produced by VR. The levels of the subjective symptoms were assessed by Graybiel's and Hamilton's criteria. HRV was determined by measuring microvascular blood flow or electrocardiogram.

RESULTS

Subjective symptoms evaluated by Graybiel's and Hamilton's criteria were gradually worsened during VR. Power spectrum analysis of HRV demonstrated a gradual increase in the low frequency but no change in the high frequency during VR. In this study, individual subjective symptoms were not correlated with the individual result of power spectrum analysis.

CONCLUSION

These findings indicate that there was an increase in sympathetic nervous activity, but no change in parasympathetic nervous activity during motion sickness induced by VR. Given the large inter-individual variability and the reliability of subjective measures, it is not surprising that there is scarcely a relation between the subjective symptoms and the results of power spectrum analysis.

Space motion sickness

Motion sickness remains a persistent problem in spaceflight. The present review summarizes available knowledge concerning the incidence and onset of space motion sickness and aspects of the physiology of motion sickness. Proposed etiological factors in the elicitation of space motion sickness are evaluated including fluid shifts, head movements, visual orientation illusions, Coriolis cross-coupling stimulation, and otolith asymmetries. Current modes of treating space motion sickness are described. Theoretical models and proposed ground-based paradigms for understanding and studying space motion sickness are critically analyzed. Prediction tests and questionnaires for assessing susceptibility to space motion sickness and their limitations are discussed. We conclude that space motion sickness does represent a form of motion sickness and that it does not represent a unique diagnostic entity. Motion sickness arises when movements are made during exposure to unusual force backgrounds both higher and lower in magnitude than 1 g earth gravity.

Motion and space sickness: intestinal and autonomic correlates

The purpose of this paper is to provide an overview of autonomic nervous system and gastrointestinal changes that occur during motion sickness. It is important to consider that motion sickness is a syndrome that can vary between individuals and within individuals and between and within motion sickness-inducing stimuli. Vomiting should be considered a discrete event of the motion sickness syndrome. Given so much variability in motion sickness symptoms, it should be expected that the physiological response to motion sickness will vary as well. This appears to be the case with the autonomic nervous system and gastrointestinal changes during motion sickness. Although much research remains to be done, it appears undeniable that the physiological expression of motion sickness is mediated by the autonomic nervous system, and when nausea is a predominant symptom, the stomach in general shuts down in a response characterized by decreased normal gastric myoelectrical activity and delayed gastric emptying.

Characteristic changes in the physiological components of cybersickness

We investigated the characteristic changes in the physiology of cybersickness when subjects were exposed to virtual reality. Sixty-one participants experienced a virtual navigation for a total of 9.5 min, and were required to detect specific virtual objects. Three questionnaires for sickness susceptibility and immersive tendency were obtained before the navigation. Sixteen electrophysiological signals were recorded before, during, and after the navigation. The severity of cybersickness experienced by participants was reported from a simulator sickness questionnaire after the navigation. The total severity of cybersickness had a significant positive correlation with gastric tachyarrhythmia, eyeblink rate, heart period, and EEG delta wave and a negative correlation with EEG beta wave. These results suggest that cybersickness accompanies the pattern changes in the activities of the central and the autonomic nervous systems.

Sickness and satiety: physiological mechanisms underlying perceptions of nausea and stomach fullness

The pathophysiology of nausea and the physiological mechanisms underlying perceptions of stomach emptiness and fullness are not clearly understood, but several potentially important factors have been identified. Gastric dysrhythmias are believed to contribute to the subjective experience of nausea and may also be involved with perceptions of stomach emptiness, hunger, and even dyspepsia symptoms like bloating and early satiety. Normal gastric neuromuscular function is more evident in the absence of nausea and is also thought to be related to feelings of satiety or comfortable stomach fullness. Autonomic and endocrine influences may also play a critical role in the pathophysiology of nausea and abnormal perceptions of stomach emptiness or fullness. Achieving a better understanding of the gastric neuromuscular and neurohormonal influences on perceptions arising from the viscera may prove invaluable in the development of novel treatments for such conditions as unexplained nausea, functional dyspepsia, and obesity.

Correlation of phasic and tonic skin-conductance responses with severity of motion sickness induced by viewing an optokinetic rotating drum

50 subjects viewed an optokinetic rotating drum for 12 min. Subjective ratings of motion sickness were obtained during the development of motion sickness. The tonic and phasic skin-conductance responses were recorded from the sites of finger, palm, and forehead during the baseline and drum-rotation periods. Analysis showed subjects' subjective ratings of motion sickness gradually increased during the 12 min. of the drum-rotation period. Both phasic and tonic skin conductance also gradually increased during drum rotation for all subjects. Pearson correlations for 50 subjects showed their ratings of motion sickness during the drum-rotation period were significantly correlated with ratios of phasic skin conductance recorded at the forehead between drum rotation and baseline periods (r = .62), followed by ratios of tonic skin conductance recorded at the finger palmar site (r = .48), ratios of phasic skin conductance recorded at the finger palmar site (r = .43), and ratios of tonic skin conductance recorded at the forehead site (r = .39). In conclusion, the phasic skin-conductance responses recorded at the forehead site were most sensitive physiological correlates of motion sickness induced by viewing an optokinetic rotating drum.

Health Consequences of Spaceflight

Although the possibility of nonastronauts making routine trips into space is an exciting prospect, many have little appreciation for the potential physiologic hazards that exposure to the space environment poses. During launch and reentry, the body is exposed to various degrees of gravitational loading, which can place strain on the cardiovascular system and its ability to maintain cerebral perfusion. In space, the body is bombarded with galactic cosmic radiation and other high-speed particle exposures, which predisposes one to chromosomal mutation, microlesions, an increased risk for cataracts, and even cancer. The possibility of spacecraft depressurization is also of concern and has been documented. The isolation of life on a spacecraft also poses psychological challenges such as loneliness, depression, and interpersonal conflict among crewmates. Finally, weightlessness itself, although undoubtedly a unique and enjoyable experience, may be the most insidious danger of all to the human body. This article will review some of the more troublesome effects—including cephalid fluid shifts, space motion sickness, bone loss, muscle atrophy, immune function, and treatment of infection—and will also provide an outline for future areas of research emphasis.

Relationship between temporal changes in cardiac parasympathetic activity and motion sickness severity

Chemotherapy-induced nausea has been associated with a time-related decrease in cardiac parasympathetic activity. We tested the hypothesis that a time-related decrease in cardiac parasympathetic activity would also be associated with nausea and other motion sickness symptoms during illusory self-motion (vection). Fifty-nine participants (aged 18-34 years: 25 male) were exposed to a rotating optokinetic drum to induce vection. Symptoms of motion sickness and an estimate of cardiac parasympathetic activity (respiratory sinus arrhythmia; RSA) were obtained at baseline and throughout a drum-rotation period. As expected, motion sickness symptoms increased and RSA decreased over time during drum rotation. Moreover, greater decreases in RSA over time correlated with greater motion sickness severity. These results suggest that a time-related decrease in cardiac parasympathetic activity may be an important correlate of nausea and motion sickness across different evocative contexts.

Autogenic Feedback Training Exercise and pilot performance: enhanced functioning under search-and-rescue flying conditions

Studies have shown that autonomous mode behavior is one cause of aircraft fatalities due to pilot error. In such cases, the pilot is in a high state of psychological and physiological arousal and tends to focus on one problem, while ignoring more critical information. This study examined the effect of training in physiological self-recognition and regulation, as a means of improving crew cockpit performance. Seventeen pilots were assigned to the treatment and control groups matched for accumulated flight hours. The treatment group contained 4 pilots from HC-130 Hercules aircraft and 4 HH-65 Dolphin helicopter pilots; the control group contained 3 pilots of HC-130s and 6 helicopter pilots. During an initial flight, physiological data were recorded on each crewmember and an instructor pilot rated individual crew performance. Eight crewmembers were then taught to regulate their own physiological response levels using Autogenic-Feedback Training Exercise (AFTE). The remaining participants received no training. During a second flight, treatment participants showed significant improvement in performance (rated by the same instructor pilot as in pretests) while controls did not improve. The results indicate that AFTE management of high states of physiological arousal may improve pilot performance during emergency flying conditions.

Correlation Between Heart Rate and the Severity of Motion Sickness Caused by Optokinetic Stimulation

Heart rate has been reported to increase during nausea and has therefore been used as an indicator of motion sickness. However, the relationship between heart rate and subjective ratings of motion sickness has received little attention, and the autonomic origins of any increase in heart rate during motion sickness are unknown. Spectral analysis of heart rate variability can quantify the degree of sympathetic and parasympathetic stimulation of the heart, as reflected by the low frequency (LF) power and high frequency (HF) power components, and the ratio of LF:HF power (“autonomic balance”). This experiment investigated changes in heart rate and heart rate variability prior to and during the development of nausea. Forty subjects (20 male, 20 female) sat within an optokinetic drum (a visual stimulus) rotating at 5 rpm for a maximum of 32 minutes. Heart rates, measures of heart rate variability, and ratings of sickness were recorded during a resting pre-exposure period and during optokinetic stimulation. Heart rates increased significantly with increasing subjective ratings of sickness (P < .001). This appeared to be attributable to a net increase in sympathetic stimulation of the heart, (P < .05). Sickness ratings were greater for females than males (P = .09), consistent with a significantly greater history of motion sickness reported by females than males over the previous 12 months (P < .02). The findings suggest that a simple measure of heart rate may be a useful indicator of small changes in the degree of sickness that can be of interest in motion sickness research.

Prokinetic effects of erythromycin after antimotion sickness drugs

Motion sickness and the antimotion sickness drugs scopolamine (SCP) and promethazine (PMZ) inhibit gastric emptying (GE). This study was conducted to determine if erythromycin would exert its well-known prokinetic effects in normal and motion-sick subjects given antimotion sickness drugs. Fifteen fasted volunteers (11 males, 4 females) participated in the study. In control tests, 8 subjects were given intramuscular (i.m.) saline (SAL, 0.5 ml), SCP (0.1 mg), or PMZ (25 mg). GE of liquid (300 ml) containing 1 mCi of Tc 99m diethylenetriaminepentaacetic acid (DTPA) was measured by sequential gastric scintigraphy 30 minutes after i.m. treatments. In other tests, GE was measured in 8 subjects after each i.m. treatment, followed 10 minutes later by 200 mg of erythromycin ethylsuccinate (ESS) suspension given orally. In a third group of tests, 7 subjects received an i.m. treatment, oral EES 10 minutes later, and were then brought to an advanced level of motion sickness short of vomiting. To induce motion sickness, blindfolded subjects made timed head movements while seated in a rotating chair. GE was measured immediately after rotation. GE half-life, rate constant, area under the curve (AUC), and lag time were calculated using conventional mathematical methods for analyzing exponential rate processes. GE parameters calculated for normal and motion-sick subjects given antimotion sickness drugs and EES were compared with those from subjects given i.m. treatments (control) only. In normal subjects, EES significantly (p < 0.05) increased the GE rate constant for all i.m. treatments and reduced the AUC for SAL, SCP, and PMZ by 49% (p < 0.05), 44% (p < 0.05), and 69% (p < 0.01), respectively. In motion-sick subjects, lag time was significantly (p < 0.05) increased, and the rate constant and AUC values were unchanged from control for all i.m. treatments. The authors conclude that oral EES reverses the gastrostatic actions of the antimotion sickness drugs but does not affect the inhibition of gastric emptying associated with motion sickness. The results suggest that motion sickness and antimotion sickness drugs reduce GE through different mechanisms.

Changes in clinical measures of autonomic nervous system function related to cancer chemotherapy-induced nausea

Individual cancer patients differ in their nausea/vomiting response to chemotherapy. It is not known why patients receiving the same chemotherapy have different severity of side effects. Several lines of research implicate the autonomic nervous system (ANS) in the development of chemotherapy-induced nausea. We examined the association between autonomic reactivity and the level of nausea experienced following chemotherapy in 20 patients with ovarian cancer treated with cisplatin or carboplatin who received the same antiemetic. We applied eight common non-invasive clinical tests of autonomic function prior to inpatient chemotherapy treatment, 2 h after treatment and again 24 h following treatment. Two hours after chemotherapy and before any nausea was reported by the patients, the nine patients who subsequently experienced high levels of nausea had a greater overall percentage of abnormal clinical ANS tests than the 11 patients who subsequently developed low levels of nausea (P < 0.01). Twenty-four hours after treatment, the overall number of abnormal autonomic tests remained non-significantly higher than at the pretreatment baseline for the high nausea group. Demographic and clinical characteristics were not related to chemotherapy-induced nausea in this sample. Autonomic reactivity appears to be related to the development of nausea following chemotherapy. Further investigation of ANS involvement in chemotherapy-induced nausea could increase understanding of nausea etiology and potentially lead to the prediction of susceptible patients.

Posture, locomotion, spatial orientation, and motion sickness as a function of space flight

This article summarizes a variety of newly published findings obtained by the Neuroscience Laboratory, Johnson Space Center, and attempts to place this work within a historical framework of previous results on posture, locomotion, motion sickness, and perceptual responses that have been observed in conjunction with space flight. In this context, we have taken the view that correct transduction and integration of signals from all sensory systems is essential to maintaining stable vision, postural and locomotor control, and eye-hand coordination as components of spatial orientation. The plasticity of the human central nervous system allows individuals to adapt to altered stimulus conditions encountered in a microgravity environment. However, until some level of adaptation is achieved, astronauts and cosmonauts often experience space motion sickness, disturbances in motion control and eye-hand coordination, unstable vision, and illusory motion of the self, the visual scene, or both. Many of the same types of disturbances encountered in space flight reappear immediately after crew members return to earth. The magnitude of these neurosensory, sensory-motor and perceptual disturbances, and the time needed to recover from them, tend to vary as a function of mission duration and the space travelers prior experience with the stimulus rearrangement of space flight. To adequately chart the development of neurosensory changes associated with space flight, we recommend development of enhanced eye movement systems and body position measurement. We also advocate the use of a human small radius centrifuge as both a research tool and as a means of providing on-orbit countermeasures that will lessen the impact of living for long periods of time with out exposure to altering gravito-inertial forces.

Alterations in R-R variability associated with experimental motion sickness

Motion sickness is a complex integration of responses from multiple physiological systems. Whether the changes that occur during the time course of motion sickness are mediated by the sympathetic or parasympathetic systems is still controversial. The present study evaluates alterations in R-R variability during experimental motion sickness in motion sick and non-motion sick subjects. Ten motion sick subjects and 7 non-motion sick subjects participated in the study. Power spectrum analysis of R-R variation was conducted for all subjects 10 min before a brief vestibular disorientation test (BVDT), for 5-10 min of the test, and 10 min after the test. Subjects were also asked to report their symptoms during the test. The motion sick group showed a significant reduction in the power spectrum density of the R-R interval at the mid and high frequencies during the BVDT test period (BVDT), in comparison with the rest period (Rest). These changes probably indicate a decrease in parasympathetic activity during the time course of motion sickness. The non-motion sick group did not show significant differences at any of the frequencies during BVDT. Power spectrum analysis of the R-R interval provides an objective measure of the autonomic response to experimental motion sickness.

Neuronal responses to vestibular stimulation in the guinea pig hypothalamic paraventricular nucleus

We investigated the effects of caloric stimulation on neuronal activity in the hypothalamic paraventricular nucleus (PVN) in anesthetized guinea pigs. Hot water stimulation of the contralateral labyrinth produced excitation in 29.4% of the PVN neurons tested, while cold water produced excitation in 22.2% of the neurons. Hot water resulted in inhibition of 22.4% of the neurons and cold water inhibition of 24.7% of the neurons. Intracranial vestibular nerve section greatly reduced responsiveness of the PVN neurons to caloric stimulation, indicating that the majority of the responses observed were vestibular in origin. The response pattern of the individual PVN neurons was similar following hot and cold water stimulation and after stimulation of the contralateral and ipsilateral labyrinths. These results suggest that the PVN neurons receive vestibular afferents bilaterally according to the intensity of vestibular stimulation, with the information received probably integrated in the hypothalamus to participate in vestibulo-autonomic reflexes.

Autonomic measures associated with chemotherapy-related nausea: techniques and issues

Advances in antiemetic therapy for cancer patients have been hindered by a lack of understanding of the physiological mechanisms associated with nausea and their corresponding measurement techniques. Here we review conceptual and methodological issues involved in developing an autonomic frame of reference for nausea and outline two strategies for assessing autonomic function. A primarily research-oriented strategy uses heart rate, blood volume pulse, pallor, and skin temperature to assess autonomic activity and reactivity over 24 hr. Peak values of these measures relative to time of emesis, heart rate spectral analyses of autonomic activity, and analyses of the standard deviation of successive differences of beat-to-beat intervals were all associated with subsequent nausea. A primarily clinically oriented strategy assesses normal and abnormal results on eight common bedside clinical tests of autonomic function. The total number of abnormal tests was associated with subsequent nausea. A better understanding of chemotherapy side effect mechanisms is likely to result in less polypharmacy and more effective individualized treatment for cancer patients.

Cardiovascular responses to KC-135 hyper-gravity

The present study was designed with two intentions; Are the effects of angular velocity detectable in the cardiovascular responses during the hyper-G? Another is object to examine how the otolith signal could modify the cardiovascular responses provoked by the exposure to the hyper-G. NASA/KC-135 hyper-gravity flight was used to generate high gravito-inertial forces to exclude a possible effect of angular velocity. Six healthy subjects was indicated to make dorsal flexion of the neck to reduce the otolith input. An exposure to +l.8Gz stress resulted in a remarkable increase of systolic and diastolic blood pressure, thereby pulse pressure became a little bit narrower. R-R interval revealed a tachycardia during the hyper-G except one subject. The present experiment bore the similar cardiovascular responses as those observed in the previous studies with a short rotating radius, suggesting that almost no effect of angular velocity acts on their responses. A weaker otolith input could possibly work on them. However a systematical observation can not recognize among the subjects for the vestibular effect on the cardiovascular responses. This fact of vestibular qualification leads us to speculate that it would depend on the subjects or other factors.

Autogenic-feedback training: a potential treatment for orthostatic intolerance in aerospace crews

Postflight orthostatic intolerance has been identified as a serious biomedical problem associated with long-duration exposure to microgravity in space. High priority has been given to the development of countermeasures for this disorder that are both effective and practical. A considerable body of clinical research has demonstrated that people can be taught to increase their own blood pressure voluntarily, and that this is an effective treatment for chronic orthostatic intolerance in paralyzed patients. The current pilot study was designed to examine the feasibility of adding training in control of blood pressure to an existing preflight training program designed to facilitate astronaut adaptation to microgravity. Using an operant conditioning procedure, autogenic-feedback training (AFT), three men and two women participated in four to nine training (15-30-minute) sessions. At the end of training, the average increase in systolic and diastolic pressure, as well as mean arterial pressures, that the subjects made ranged between 20 and 50 mm Hg under both supine and 45 degrees head-up tilt conditions. These findings indicate that AFT may be a useful alternative treatment or supplement to existing approaches for preventing postflight orthostatic intolerance. Furthermore, the use of operant conditioning methods for training cardiovascular responses may contribute to the general understanding of the mechanisms of orthostatic intolerance.

Do the organs of the labyrinth differentially influence the sympathetic and parasympathetic systems?

It has long been recognized that the vestibular system plays a major role in autonomic control. The nature of this control remains in dispute, however, as some evidence points to a vestibularly mediated parasympathetic activation, whereas other evidence points to a sympatho-excitatory role for labyrinthine outputs. A theoretical explanation is offered that attempts to resolve this issue by postulating that the utricles exert a predominantly sympatho-excitatory influence via their interactions with brain noradrenergic pathways, while the semicircular canals (and possibly saccules) increase parasympathetic tone via their cholinergic brain stem and cerebellar projections. This explanation is relevant for understanding the vestibular role in orthostatic regulation, motion sickness, oculomotor control, and in many disorders or situations associated with neurochemical or autonomic imbalances.

Effects of eating on vection-induced motion sickness, cardiac vagal tone, and gastric myoelectric activity

This study investigated the effect of food ingestion on motion sickness severity and its physiological mechanisms. Forty-six fasted subjects were assigned either to a meal group or to a no-meal group. Electrogastrographic (EGG) indices (normal 3 cpm activity and abnormal 4-9 cpm tachyarrhythmia) and respiratory sinus arrhythmia (RSA) were measured before and after a meal and during a subsequent exposure to a rotating drum in which illusory self-motion was induced. The results indicated that food intake enhanced cardiac parasympathetic tone (RSA) and increased gastric 3 cpm activity. Postprandial effects on motion sickness severity remain equivocal due to group differences in RSA baseline levels. During drum rotation, dysrhythmic activity of the stomach (tachyarrhythmia) and vagal withdrawal were observed. Furthermore, high levels of vagal tone prior to drum rotation predicted a low incidence of motion sickness symptoms, and were associated positively with gastric 3 cpm activity and negatively with tachyarrhythmia. These data suggest that enhanced levels of parasympathetic activity can alleviate motion sickness symptoms by suppressing, in part, its dysrhythmic gastric underpinnings.