Cortisol levels predict motion sickness tolerance in women but not in men.

A variety of intrinsic and extrinsic factors contribute to motion sickness severity in a stressful motion environment. The interplay of all these factors may partially explain the high inter-subject variability of motion sickness susceptibility found in many studies as well as some of the contradictory findings between studies regarding the modulating influence of single factors. We investigated the role of endogenous cortisol levels, gender and repetitive experience for motion sickness susceptibility. Motion sickness was induced in 32 healthy, but motion-sickness susceptible volunteers (16:16 males:females), by means of a vection drum. Subjects were investigated between 8:00 am (high cortisol) and 11:00 am (low cortisol), and on five consecutive days. Tolerance to rotation (RT) of the drum, motion sickness symptom ratings (SR) and salivary cortisol levels were assessed. Baseline cortisol levels correlated positively with RT in women, but not in men. RT showed a gender-specific time course across days, with higher values in males than in females on day 1, and sensitization on day 3 only in men. SR and cortisol levels following rotation did not differ between males and females, or between testing days. Gender differences in motion sickness susceptibility appear to be linked to a different role of basal cortisol levels for motion sickness tolerance. Results clearly indicate the need to control for gender, day time and cortisol levels in studies of motion sickness.

Protein-predominant meals inhibit the development of gastric tachyarrhythmia, nausea and the symptoms of motion sickness.

BACKGROUND: Meal ingestion has been suggested to reduce susceptibility to the development of gastric tachyarrhythmia, the abnormal activity of the stomach that frequently accompanies nausea. AIM: To determine the types of meal that are most effective in preventing the development of gastric tachyarrhythmia, nausea and the symptoms of motion sickness provoked by a rotating optokinetic drum. METHOD: Participants received a carbohydrate beverage, a protein-predominant beverage or nothing immediately before exposure to the rotating drum. Subjective symptoms of motion sickness and electrogastrograms were collected during a 6-min baseline period and a subsequent 16-min drum rotation period. RESULTS: Subjective symptoms of motion sickness scores were significantly more severe during the no-meal condition than during either the protein or carbohydrate condition. Central, peripheral and, to some extent, gastrointestinal symptoms were more severe during the carbohydrate condition than during the protein condition. Gastric tachyarrhythmia increased significantly less from baseline to drum rotation during both the protein and carbohydrate conditions than during the no-meal condition. CONCLUSIONS: Liquid protein-predominant meals were most effective in suppressing both the development of gastric tachyarrhythmia and the entire spectrum of motion sickness symptoms, including nausea.

The Harris-Benedict studies of human basal metabolism: history and limitations.

In the early part of the 20th century, numerous studies of human basal metabolism were conducted at the Nutrition Laboratory of the Carnegie Institution of Washington in Boston, Mass, under the direction of Francis G. Benedict. Prediction equations for basal energy expenditure (BEE) were developed from these studies. The expressed purpose of these equations was to establish normal standards to serve as a benchmark for comparison with BEE of persons with various disease states such as diabetes, thyroid, and other febrile diseases. The Harris-Benedict equations remain the most common method for calculating BEE for clinical and research purposes. The widespread use of the equations and the relative inaccessibility of the original work highlights the importance of reviewing the data from which the standards were developed. A review of the data reveals that the methods and conclusions of Harris and Benedict appear valid and reasonable, albeit not error free. All of the variables used in the equations have sound physiologic basis for use in predicting BEE. Supplemental data from the Nutrition Laboratory indicates that the original equations can be applied over a wide range of age and body types. The commonly held assumption that the Harris-Benedict equations overestimate BEE in obese persons may not be true for persons who are moderately obese.

The effect of autonomic nervous system activity on gastric myoelectrical activity: does the spectral reserve hypothesis hold for the stomach?

Previous studies have associated changes in gastric myoelectrical activity during motion sickness, as indexed using the electrogastrogram (EGG), with changes in autonomic nervous system (ANS) activity. Subjects who did not report nausea in a rotating optokinetic drum were characterized by normal 3 cycles per minute (cpm) gastric myoelectrical activity, strong parasympathetic nervous system (PNS) activity, and low sympathetic nervous system (SNS) activity. The goals of this study were: (1) to determine whether tasks previously shown to alter ANS activity as indexed by changes in cardiac inter-beat intervals (IBIs) would result in systematic changes in gastric myoelectrical activity in accord with the findings from motion sickness studies; and (2) to determine whether the 'spectral reserve hypothesis' applies to gastric myoelectrical activity. EGGs and IBIs were collected from 24 healthy subjects during resting/baseline, reaction time/shock-avoidance (RT) and cold face stress (CF) tasks. Tachyarrhythmia was found to be significantly greater during the RT task than during the baseline and CF tasks. It was concluded that: (1) tasks that alter ANS activity do systematically alter gastric myoelectrical activity; and (2) gastric myoelectrical activity does not follow the cardiac model of health being associated with increased spectral complexity.

Assessment of the multiple dimensions of nausea: the Nausea Profile (NP).

Nausea, unlike emesis, is a subjective experience that is difficult to describe to others, be they clinicians or researchers. Previous research has been limited to examining the frequency, severity, and duration of nausea. The goal of this study was to design a questionnaire that would allow for the evaluation of the characteristics of nausea across individuals and situations. This study consisted of 4 stages: descriptors were generated, categorized into 3 dimensions, and reevaluated to verify their reliability; in the final stage, the developed checklist was compared to a visual-analogue-scale (VAS) report of nausea in subjects exposed to a rotating optokinetic drum to stimulate nausea. The overall nausea checklist score and the VAS score were highly correlated (r = 0.71, p < 0.01). The development and use of the nausea checklist are discussed.

The effect of bilberry nutritional supplementation on night visual acuity and contrast sensitivity.

PURPOSE: The purpose of this study was to investigate the effect of bilberry on night visual acuity (VA) and night contrast sensitivity (CS). METHODS: This study utilized a double-blind, placebo-controlled, crossover design. The subjects were young males with good vision; eight received placebo and seven received active capsules for three weeks. Active capsules contained 160 mg of bilberry extract (25-percent anthocyanosides), and the placebo capsules contained only inactive ingredients. Subjects ingested one active or placebo capsule three times daily for 21 days. After the three-week treatment period, a one-month washout period was employed to allow any effect of bilberry on night vision to dissipate. In the second three-week treatment period, the eight subjects who first received placebo were given active capsules, and the seven who first received active capsules were given placebo. Night VA and night CS was tested throughout the three-month experiment. RESULTS: There was no difference in night VA during any of the measurement periods when examining the average night VA or the last night VA measurement during active and placebo treatments. In addition, there was no difference in night CS during any of the measurement periods when examining the average night CS or the last night CS measurement during active and placebo treatments. CONCLUSION: The current study failed to find an effect of bilberry on night VA or night CS for a high dose of bilberry taken for a significant duration. Hence, the current study casts doubt on the proposition that bilberry supplementation, in the forms currently available and in the doses recommended, is an effective treatment for the improvement of night vision in this population.

Acupressure relieves the symptoms of motion sickness and reduces abnormal gastric activity.

CONTEXT: Acupuncture at the P6 or Neiguan point to treat nausea and vomiting has been practiced in China for many years. More recently, acupressure at P6 has been used successfully to decrease the symptoms of pregnancy sickness and with mixed results to decrease motion sickness. OBJECTIVE: To determine whether an Acuband, a commercially available acupressure wristband, would relieve the symptoms of motion sickness. METHOD: 25 healthy subjects, aged 18 to 22 years, prescreened for susceptibility to motion sickness, were tested on 3 separate occasions in a rotating optokinetic drum with the following conditions: wearing an Acuband on the wrist, wearing an Acuband on the arm, and wearing no Acuband. MAIN OUTCOME MEASURES: Subjective symptoms of motion sickness and abnormal gastric activity, as recorded via electrogastrography, were obtained throughout the procedure. RESULTS: Subjects reported significantly fewer symptoms of motion sickness on days when wearing the Acuband on the wrist or the arm than they did on control days (when they wore no Acuband). Subjects also showed less abnormal gastric activity on the days when wearing an Acuband than they did on control days. CONCLUSION: An Acuband worn on the wrist or forearm decreases the symptoms of motion sickness and the gastric activity that usually accompanies motion sickness.

Reducing accidents and injuries in the dental environment.

This article has dealt with the dental office and potentially hazardous situations that could result in injury or death from electrical, gas, chemical, or mechanical accidents. Industry spends billions of dollars each year on safety considerations for its employees. Many of their safety practices are applicable to the dental office. A safety check list for the dental office is proposed. The dentist must be aware that other possible hazards exist in dental offices including the misuse of ultraviolet light units and ultrasonic scalers. In addition, the dentist must be concerned with unexpected traumas such as interstitial air emphysema, the aspiration or swallowing of instruments, appliances and restorations and self-inflicted puncture wounds.

Effects of dimenhydrinate on gastric tachyarrhythmia and symptoms of vection-induced motion sickness.

BACKGROUND: Previous research in our laboratory has shown that symptoms of motion sickness are accompanied by the loss of normal 3 cpm activity and the development of tachyarrhythmia in the electrogastrogram (EGG). HYPOTHESIS: We hypothesized that dimenhydrinate would prevent the development of gastric tachyarrhythmia and reduce symptoms of motion sickness. METHODS: Twenty health volunteers were tested in a counter-balanced, within-subject, double-blind design. Subjects were exposed to a rotating optokinetic drum to induce vection after receiving either dimenhydrinate (100 mg) or a placebo on two separate occasions. EGG's were recorded immediately before ingestion of capsules, 1 h after ingestion, and during rotation. Motion sickness symptom reports (SSMS) were obtained prior to and during rotation. RESULTS: The average SSMS score was 5.9 points higher after placebo administration than after dimenhydrinate administration (t[19] = 4.87, P < 0.001). Significantly more subjects requested early termination of the rotating drum due to severe symptoms after placebo administration than after dimenhydrinate administration (McNemar's chi 2[1] = 6.00, p < 0.05). Drowsiness reports were significantly higher after dimenhydrinate administration than after placebo administration (t[19] = 2.65, p < 0.05). Analysis of EGG's showed a significant decrease in normal 3 cpm and tachyarrhythmic activity after dimenhydrinate, but no change after placebo (SR[19] = 53, p < 0.02 and SR[19] = 68, p < 0.01 respectively). During drum rotation gastric tachyarrhythmias increased significantly in the placebo condition (SR[18] = -0.61.5, p < 0.01), but not in the dimenhydrinate condition. EGG's were not significantly different between conditions. CONCLUSIONS: We conclude that dimenhydrinate reduced motion sickness symptoms at least in part by depressing central nervous system activity and possibly by suppressing abnormal gastric myoelectric activity.

The experience of nausea during sustained hyper-gravity flight with negligible angular velocity.

BACKGROUND: The purpose of this study was to investigate nausea and vomiting during hyper-gravity flight at a slow rate of turn. During head-movements under these conditions, the semi-circular canals of the vestibular system function normally whereas the otoliths experience a G-excess effect, displacing further and moving faster than in a 1 G field. HYPOTHESIS: Nausea and vomiting are greater during hyper-gravity flight compared with historical data collected in a 1 G field at a similar rate of turn. METHODS: There were 27 subjects who were exposed to 1.8 G (hyper-G) during a slow rate turn on three NASA KC-135 flights. Subjects participated in one of three experimental periods, each period consisting of two 5.5-min hyper-G runs: 1) rest, with only incidental head movements; 2) active roll and pitch head movements; or 3) passive roll head movements. Subjective symptom data were collected pre-flight, following each experimental period and post-flight using a standardized nausea questionnaire. Electrogastrograms were obtained from eight subjects. RESULTS: Seven subjects (26%) vomited during the flight. Nausea initially increased but was then stable throughout the flight. Nausea appeared highest during active head movements. In subjects who vomited, greater gastrointestinal distress and somatic distress were reported. CONCLUSIONS: The levels of nausea and vomiting observed during hyper-G cannot be explained by Coriolis cross coupling and are likely due to the G-excess effect on the otoliths. The nausea profiles observed in individuals who vomit during hyper-G appear similar to those previously observed during nausea produced by an optokinetic drum stimulus in a 1-G field.

Effects of phenytoin on vection-induced motion sickness and gastric myoelectric activity.

The purpose of this study was to test the prophylactic effects of a single low dose of phenytoin on motion sickness. In this double-blind study, fasted male subjects who were susceptible to motion sickness were given either a 200-mg tablet of phenytoin (N = 19) or a placebo (N = 16). Electrogastrograms (EGG's) were recorded predrug, postdrug (4 h after ingestion of drug), before drum rotation, and during drum rotation. During testing, subjects were exposed to an optokinetic drum which was stationary for 8 min and which then rotated at 10 rpm for 16 min. The results showed that the phenytoin subjects had a lower mean subjective symptom score than the placebo group (5.8 vs. 7.1), but the difference was not significant. However, 6 of 16 placebo subjects requested early termination of drum rotation due to symptom severity, whereas only 2 of 19 phenytoin subjects terminated testing prematurely (X2 = 3.89, p < 0.05). The phenytoin group showed no increase in gastric tachyarrhythmia, the pattern of gastric myoelectric activity that usually accompanies nausea, during drum rotation, whereas tachyarrhythmia doubled for the placebo group. In conclusion, we have demonstrated that a single low dose of phenytoin prevents the development of gastric tachyarrhythmia and decreases the intensity of motion sickness symptoms.

The effect of tilted stripes in an optokinetic drum on gastric myoelectric activity and subjective reports of motion sickness.

BACKGROUND: The effects of tilted and vertical optokinetic drum stripes on self-reports of motion sickness and electrogastrograms (EGG's) were measured to investigate possible differences in the effects of stripe orientation. The EGG is a non-invasive measure of gastric myoelectric activity. The normal frequency is 3 cpm, and dysrhythmic 4-9 cpm activity, gastric tachyarrhythmia, has been found to be associated with motion sickness symptoms, particularly nausea. It is theorized that these symptoms are related to a sensory mismatch between the visual and vestibular systems elicited by the drum's rotation. HYPOTHESIS: We hypothesized that tilted stripes would elicit more symptoms than vertical stripes due to an additional sensory mismatch between the visual and vestibular verticals. METHODS: We divided 45 subjects into 2 stripe orientation groups: Vertical, and Tilted 15 degrees in the direction of drum movement. After the subject sat inside the stationary drum for a 6-min baseline, the drum was rotated (10 rpm) for a maximum of 16 min, followed by a 6-min recovery period. Throughout the experiment we measured the subjects' EGG's and subjective symptoms of motion sickness (SSMS). RESULTS: During rotation and recovery, gastric tachyarrhythmic activity was higher for subjects in the Tilted condition; the difference between stripe conditions was significant during rotation (p < 0.05). There were, however, no differences between SSMS scores. CONCLUSIONS: Off-vertical stripes increase the dysrhythmic activity of the stomach that often precedes or accompanies nausea and other symptoms of motion sickness.

A questionnaire for the assessment of the multiple dimensions of motion sickness.

BACKGROUND: A limited number of attempts have been made to develop a questionnaire that assesses the experience of motion sickness. Further, many available questionnaires quantify motion sickness as a unidimensional construct. METHOD: Exploratory and confirmatory factor analyses of motion sickness descriptors were used to derive and verify four dimensions of motion sickness, which were defined as gastrointestinal, central, peripheral, and sopite-related. These dimensions of motion sickness were then used to construct a motion sickness assessment questionnaire (MSAQ) that was administered to individuals who were exposed to a rotating optokinetic drum. RESULTS: Total scores from the MSAQ correlated strongly with overall scores from the Pensacola Diagnostic Index (r = 0.81, p < 0.001) and the Nausea Profile (r = 0.92, p < 0.001). CONCLUSIONS: The MSAQ is a valid instrument for the assessment of motion sickness. In addition, the MSAQ may be used to assess motion sickness as a multidimensional rather than unidimensional construct.

Effects of a 48-h fast on heart rate variability and cortisol levels in healthy female subjects.

BACKGROUND/OBJECTIVES: The physiological changes that occur during fasting are not completely understood, regardless of the cause for fasting (for example, medical, lifestyle, religious, political or famine). The purpose of this study was to examine the effects of a 48-h fast on heart rate variability (HRV) and cortisol levels in healthy young female volunteers. SUBJECTS/METHODS: A total of 16 young healthy female volunteers underwent 48 h of total fasting under 24-h medical surveillance. Psychological (subjective feeling of hunger) as well as physiological data (HRV, diurnal cortisol profiles) were measured upon admission (Day 1), and after 24 (Day 2) and 48 h (Day 3) of fasting. RESULTS: There was a measured weight loss from Day 1 to Day 3 that resulted in significant body mass index (BMI) reduction across all subjects (P<0.001). The slope of the diurnal cortisol profile significantly shifted towards lower values from baseline to the end of experiment (P=0.002). HRV during resting showed a significant (P<.001) decrease in standard deviation of the normal-to-normal interval (SDNN) and root mean square of successive differences (RMSSDs) from Day 1 to Day 3 of the experiment, with a small increase after 24 h that did not reach statistical significance. A 48 h of fasting also induced a significant (P<.001) decrease of mean interbeat intervals (IBIs), SDNN, RMSSD and log high-frequency (HF) power during head-up tilt testing. CONCLUSIONS: An acute (48 h) total fast induced parasympathetic withdrawal with simultaneous sympathetic activation. These changes appear to reflect stress. Further studies are needed to demonstrate the specificity of these changes to fasting.

Heart rate variability in anorexia nervosa and the irritable bowel syndrome.

BACKGROUND: Many studies have reported disturbances of heart rate variability (HRV) in patients with psychosomatic disorders such as anorexia nervosa (AN) and the irritable bowel syndrome (IBS). However, both have never been directly compared. METHODS: We compared HRV in AN (n = 21) and in IBS (n = 21) (all females) with 42 healthy female control subjects who were matched for age and in IBS to body mass index (BMI). Recovery periods between different cardiac load tests were compared with baseline recordings and tilt test to estimate time [mean successive difference (MSD)] and frequency domain (Goldberger dimension, frequency of HF peak location and HF power, log HF power) values and to assess general reactivity of the autonomic nervous system (ANS). KEY RESULTS: Significantly longer inter-beat intervals (IBIs) in AN patients and lower values of MSD in IBS patients were found in comparison with respective controls; both were independent from experimental conditions and are found in baseline recordings only. Both effects were independent of age and BMI. We also demonstrate a significant relationship between age, BMI and some HRV parameters. CONCLUSIONS & INFERENCES: Opposite autonomic patterns were found in AN and IBS: stronger vagal withdrawal in IBS and weaker vagal inhibition in AN patients. Records made at rest and without any autonomic load may be representative for assessment of ANS function. Age and BMI should be taken into consideration during assessment of HRV data.

Estimation of respiratory frequency from autoregressive spectral analysis of heart period.

Variability in heart period is modulated by respiration. Using an autoregressive spectral analytic approach on the heart period time series produces a components analysis. The central frequency of the heart period spectral component in the frequency of respiration (HFFreq) has been suggested as an index of respiratory frequency. The present experiment measured heart period variability (HPV) using an autoregressive algorithm and respiratory frequency using a mercury strain gauge (SGResp) to assess the relationship between the respiratory frequency indexed by the two methods. Twenty human participants were studied during resting baseline, relaxation, and mental effort conditions. Within- and between-person Pearson correlations and t-tests were used to assess the concordance between HFFreq and SGResp. Both within-person and between-person correlations indicated good concordance among the two methods. Moreover, t-tests, corrected for Type I error, indicated no significant differences between the respiratory frequency estimates derived from the two methods. The resolution of the estimates was approximately 1 breath per minute. These results suggest that the HFFreq may be a useful index of respiratory frequency.

Significance of autonomic nervous system activity in functional dyspepsia.

The purpose of this study was to examine if patients with functional dyspepsia could be separated into meaningful groups based on their autonomic function. Subjects were divided into two groups, and symptoms, gastric myoelectrical activity, gastric emptying, and psychological factors were compared. Group 1 had less autonomic variability but more cardiac reactivity than group 2. Symptom reports did not differ between groups. Group 1 had higher neuroticism scores than group 2, while group 2 showed greater tachyarrhythmia in response to drinking water than group 1. The relatively low autonomic variability in group 1 is consistent with higher sympathetic activity and may be associated with the group's greater neuroticism. The relative lack of cardiac reactivity in group 2 is consistent with lack of autonomic flexibility and may be related to the tachyarrhythmia observed in that group. The results of this study suggest that autonomic function may play a significant role in functional dyspepsia.

Effects of vection-induced motion sickness on gastric myoelectric activity and oral-cecal transit time.

The purpose of this study was to investigate the effects of vection-induced motion sickness on three cycle per minute gastric myoelectric activity and oral-cecal transit time. Forty-five subjects were exposed to a rotating optokinetic drum while electrogastrograms and subjective reports of symptoms were monitored. Prior to exposure, baseline breath hydrogen levels were established and subjects ingested vanilla pudding containing 10 g of lactulose. Breath hydrogen measurements were obtained before drum rotation and every 10 minutes after rotation, for 3 hr. Based on the severity of motion sickness symptoms reported, subjects were divided into two groups: a group susceptible to, and a group not susceptible to, vection-induced motion sickness. Averaged across subjects, the percentage of three cycle per minute activity decreased from baseline to rotation (3.6%) and from rotation to recovery (3.0%) [F(2/70)=2.43,P<0.1], with the susceptible group showing a greater overall decrease from baseline to recovery (8.9%), than the nonsusceptible group (4.2%) [F(1/35)=11.16,P<0.01]. The susceptible group had longer average oral-cecal transit times (144 min) than the nonsusceptible group (107 min) [t(36)=3.27,P<0.01]. Furthermore, symptom reports were positively correlated with oral-cecal transit times (r = 0.43, P < 0.05). In conclusion, vection-induced motion sickness is accompanied by decreased gastric three cycle per minute activity and prolonged oral-cecal transit times.

Cardiac spectral power reflects parasympathetic but not sympathetic nervous system activity in a clinical population.

The purpose of this short communication is to report our clinical findings regarding the use of the low frequency (LF, 0.02-0.15 Hz) and high frequency (HF, > 0.15 Hz) components of the spectral decomposition of heart-rate as indices of sympathetic (SNS) and parasympathetic nervous system (PNS) activity, respectively. Thirty-two females with histologically confirmed ovarian cancer, ranging in age from 46-72 years, participated in an autonomic assessment protocol consisting of a resting heart rate recording and several ANS function tests. The LF, HF and total power measures from the spectral decomposition were highly correlated with one another. In addition, the spectral components were most highly correlated with measures of PNS activity, i.e. standard deviation of heart rate at rest and the ratio of the six longest to the six shortest R-R intervals during deep breathing (E:I ratio). It is concluded, as other researchers have stated, that the use of the HF component of the HR spectrum as a measure of PNS activity is warranted, but caution must be used when interpreting the LF component.

Effect of autonomic nervous system manipulations on gastric myoelectrical activity and emotional responses in healthy human subjects.

OBJECTIVE: The aim of this study was to determine the gastric myoelectrical and emotional responses provoked by two psychophysiological stimuli known to cause in one case increased sympathetic nervous system activity and in the other increased parasympathetic nervous system activity. METHODS: Electrogastrograms (EGGs) were recorded, and interbeat intervals (IBIs) were obtained from electrocardiographic recordings from 20 subjects during baseline and in response to a shock avoidance task (shock stimulus) and forehead cooling (dive stimulus). After each experimental period, subjects reported their emotional experience by rating descriptors ranging from serenity to excitement. RESULTS: During the shock stimulus, IBIs decreased significantly (p < .05), gastric tachyarrhythmias increased (p < .05), and emotional arousal increased, as indexed by reports of increased interest, excitement, and activation. In contrast, during the dive stimulus, IBIs increased (p < .05), but there were no associated changes in gastric myoelectrical activity or emotional arousal. CONCLUSIONS: Acute stress can evoke arousal and dysrhythmic gastric myoelectrical activity, and these acute changes, which occur in healthy individuals, may provide insight into functional gastrointestinal disorders.