Factors influencing the susceptibility of anurans to motion sickness

We examined the propensity for motion sickness in five anuran species, concentrating our efforts on the treefrog Rhacophorus schlegelii, because it had shown the greatest susceptibility to motion sickness in a previous study. We used parabolic flight as our provocative stimulus and fed all specimens a known volume of food 1.5-3 h before flight. The presence of vomitus in a frog's cage was our indicator of motion sickness. Significantly more emesis was observed in flight-exposed than in control R. schlegelii (P < 0.05). There was no sex difference in susceptibility to motion sickness (P > 0.5). Individuals that vomited were significantly larger (P < 0.02) than those that did not. Among microgravity-treated frogs, those that vomited spent on average 85% more time airborne and tumbling in microgravity than those that did not vomit (P=0.031). Our data support the view that postural instability and sensory conflict are elements of motion sickness in anurans. Specifically, conflicts between tactile, vestibular and visual input seem essential for producing motion-induced emesis in anurans. Since the factors that induce motion sickness in R. schlegelii are the same ones that produce motion sickness in humans, arboreal frogs may be useful alternative models to mammals in motion sickness research.     

The menstrual cycle and susceptibility to virtual simulation sickness

Virtual simulation sickness (VSS) is a form of visually induced motion sickness that can result from immersion in a virtual environment (VE). As in their susceptibility to the sickness induced by real motion, women have been reported to be more susceptible than men to VSS, yet the reason for this difference is not known. The aim of the current study was to investigate the influence of the menstrual cycle on susceptibility to VSS in 16 naturally cycling women and to compare the responses of this group with control groups consisting of 1) 16 premenopausal women taking a combined monophasic oral contraceptive and 2) 16 men. All female participants were immersed in a nauseogenic VE on days 5, 12, 19, and 26 of their menstrual/pill cycle. These days were chosen because they fall in line with peaks and troughs of ovarian hormone levels. Menstrual cycle phase was confirmed by salivary estradiol and progesterone levels. A 4-week "pseudo-cycle" was assigned to the male participants. Hormone analysis revealed that 9 participants in the experimental group had been tested at the desired phases of their cycle. These participants exhibited a significant increase in susceptibility to VSS on day 12 of their cycle. The hormone analysis also showed that the cycles of the 7 remaining members of the experimental group had not precisely followed the expected pattern, and so these people had been tested on days that did not coincide with peaks and troughs of ovarian hormone levels. No consistent variation in susceptibility was observed over the cycle in these volunteers. In addition, no change in susceptibility was observed over the pill cycle of the oral contraceptive group nor over the pseudo-cycle applied to the male control group. The authors conclude that susceptibility to VSS varies over the menstrual cycle as a consequence of hormonal variation.     

New antiemetic drugs

Three major areas of medicine are identified in which there is a need for new antiemetic drugs. These are the nausea and vomiting arising from gastrointestinal motility disturbances (functional dyspepsia, diabetic neuropathy, classical migraine), the sickness evoked by abnormal motion, and the severe emesis experienced by cancer patients as a result of certain cytotoxic therapies. For gastrointestinal-related nausea, selective stimulants of gut motility are suggested to form the basis for a new type of antiemetic therapy. In motion sickness, there has been progress in the understanding of the illness, but little advance in the development of new drugs that selectively prevent this type of sickness. In cancer chemo- and radio-therapy, the discovery that selective 5-HT3 (5-HT, 5-hydroxytryptamine) receptor antagonists can prevent severe cytotoxic-evoked emesis now promises to radically change the type of antiemetic therapy given to these patients. This type of antiemetic compound and the pharmacology of the new 5-HT3 receptor antagonists are, therefore, discussed in detail.     

Use of Controlled Diaphragmatic Breathing for the Management of Motion Sickness in a Virtual Reality Environment

Evidence indicates that activation of the parasympathetic nervous system (PNS) suppresses physiological responses associated with motion sickness. Research also shows paced breathing increases PNS activation; the current study examines the use of paced diaphragmatic breathing (DB) training to quell motion sickness symptoms. Healthy participants (N = 60) were pre-screened for motion sickness susceptibility. Participants were then randomly assigned to either a control condition, focusing on environmental awareness, or to an experimental condition implementing paced DB. Following this, participants were exposed to a virtual reality (VR) motion sickness experience, while heart rate variability, breathing rate (RPM), and motion sickness ratings were collected. Results demonstrated participants in the DB condition had higher PNS activation and reported fewer motion sickness symptoms during the VR experience than the participants in the control condition. Results suggest that the DB protocol can be used to significantly increase PNS tone and decrease the development of motion sickness symptoms.     

大鼠动情周期雌激素水平变化对晕动病易感性的影响

目的：众多的流行病学研究和动物实验表明,晕动病存在明显的性别差异,特别是雌激素对晕动病易感性可能存在某些易化的调节作用,本研究为探讨“异食癖”模型上大鼠动情周期雌激素水平的变化对晕动病易感性的影响。方法：大鼠在不同的动情周期,给予足够的旋转刺激以后,通过摄取高岭土量的变化评价大鼠的晕动病反应,同时测定血浆雌激素（E2和P）水平,观察雌激素水平的变化对晕动病易感性的影响。结果：大鼠体内的雌性激素（E2和P）水平随着动情周期而发生波动,在动情期时,E2水平达到最高,而在动情前期则达到最低。P水平在动情间期和动情前期较高而在动情期与动情后期较低。足够的旋转刺激之后,大鼠的摄取高岭土量显著增加,并且呈现与大鼠动情周期雌激素水平波动的一致性,即动情期时摄取高岭土量最多。结论：大鼠动情周期雌激素水平的升高可能在一定程度上会加重大鼠的晕动病反应。可为进一步探讨雌激素水平与晕动病易感性之间的关系提供参考,从而也可能为发现晕动病新病因的研究打下基础,还可能为晕动病预防策略和措施启发新的应用价值。     

Conditioned taste aversion and motion sickness in cats and squirrel monkeys

The relationship between vomiting and conditioned taste aversion was studied in intact cats and squirrel monkeys and in cats and squirrel monkeys in which the area postrema was ablated by thermal cautery. In cats conditioned 7-12 months after ablation of the area postrema, three successive treatments with xylazine failed to produce either vomiting or conditioned taste aversion to a novel fluid. Intact cats, however, vomited and formed a conditioned aversion. In squirrel monkeys conditioned 6 months after ablation of the area postrema, three treatments with lithium chloride failed to produce conditioned taste aversion. Intact monkeys did condition with these treatments. Neither intact nor ablated monkeys vomited or evidenced other signs of illness when injected with lithium chloride. When the same ablated cats and monkeys were exposed to a form of motion that produced vomiting prior to surgery, conditioned taste aversion was produced and some animals vomited. These findings confirm other studies indicating motion can produce vomiting in animals with the area postrema destroyed and demonstrate that motion-induced conditioned taste aversion can be produced after ablation of the area postrema. The utility of conditioned taste aversion as a measure of subemetic motion sickness is discussed by examining agreement and disagreement between identifications of motion sickness by conditioned taste aversion and vomiting. It is suggested that a convincing demonstration of the utility of conditioned taste aversion as a measure of nausea requires the identification of physiological correlates of nausea, and caution should be exercised when attempting to interpret conditioned taste aversion as a measure of nausea.     

Pre-Bout Standing Body Sway Differs between Adult Boxers Who Do and Do Not Report Post-Bout Motion Sickness

Background

Motion sickness is characterized by subjective symptoms that include dizziness and nausea. Studies have shown that subjective symptoms of motion sickness are preceded by differences in standing body sway between those who experience the symptoms and those who are not. Boxers often report dizziness and nausea immediately after bouts. We predicted that pre-bout standing body sway would differ between boxers who experienced post-bout motion sickness and those who did not.

Methodology/Principal Findings

We collected data on standing body sway before bouts. During measurement of body sway participants performed two visual tasks. In addition, we varied stance width (the distance between the heels). Postural testing was conducted separately before and after participants'' regular warm-up routines. After bouts, we collected self-reports of motion sickness incidence and symptoms. Results revealed that standing body sway was greater after warm-up than before warm-up, and that wider stance width was associated with reduced sway. Eight of 15 amateur boxers reported motion sickness after a bout. Two statistically significant interactions revealed that standing body sway before bouts differed between participants who reported post-bout motion sickness and those who did not.

Conclusions/Significance

The results suggest that susceptibility to motion sickness in boxers may be manifested in characteristic patterns of body sway. It may be possible to use pre-bout data on postural sway to predict susceptibility to post-bout motion sickness.     

Motion sickness in lower vertebrates: Studies in weightlessness and under normal conditions

This review presents both literature data and results of our own studies aimed at finding out if lower vertebrates are susceptible to motion sickness. In our experiments, fish and amphibians were submitted to motion for 2 h and longer on a centrifuge (f = 0.25 Hz, a _centrifugal = 0.144 g) and on a parallel swing (f = 0.2 Hz, a _horizontal = 0.059 g). The performed studies did not revealed in 4 fish species and in toads any single feature characteristic of motion sickness (sopite syndrome, pre-vomiting behavior or emesis). At the same time, in toads, the characteristic stress reaction appeared (escape reaction, increase of urination frequency, worsening of appetite) as well as some other responses not associated with motion sickness (synchronized head swinging, eye retraction). In trout fry, the used stimulation promoted division of individuals into groups differing by locomotor reaction to stress as well as individuals with a well-pronounced compensatory response that we called the otolithotropic reaction. Our conclusions are confirmed by analysis of results obtained by other authors. Therefore, the lower vertebrates, unlike mammals, are not susceptible to motion sickness either under terrestrial conditions or under conditions of weightlessness. Based on available experimental data and theoretical concepts of mechanism of development of the motion sickness, which have been formulated in several hypotheses (the hypothesis of discoordination, Treisman’s hypothesis, resonance hypotheses), there is put forward the synthetic hypothesis of sopite that is of conceptual values. According to this hypothesis, the unusual stimulation producing sensory-motor or sensory-sensory discoordinations or action of vestibular and visual stimuli of frequency of about 0.2 Hz is perceived by the CNS as poisoning and causes the corresponding reactions. The sopiting is, in fact, a side effect of technological evolution. It is suggested that in the lower vertebrates, unlike mammals, there is absent a hypothetic vomiting center, therefore, they are not submitted to motion sickness.     

Relationship between Spectral Characteristics of Spontaneous Postural Sway and Motion Sickness Susceptibility

Motion sickness (MS) usually occurs for a narrow band of frequencies of the imposed oscillation. It happens that this frequency band is close to that which are spontaneously produced by postural sway during natural stance. This study examined the relationship between reported susceptibility to motion sickness and postural control. The hypothesis is that the level of MS can be inferred from the shape of the Power Spectral Density (PSD) profile of spontaneous sway, as measured by the displacement of the center of mass during stationary, upright stance. In Experiment 1, postural fluctuations while standing quietly were related to MS history for inertial motion. In Experiment 2, postural stability measures registered before the onset of a visual roll movement were related to MS symptoms following the visual stimulation. Study of spectral characteristics in postural control showed differences in the distribution of energy along the power spectrum of the antero-posterior sway signal. Participants with MS history provoked by exposure to inertial motion showed a stronger contribution of the high frequency components of the sway signal. When MS was visually triggered, sick participants showed more postural sway in the low frequency range. The results suggest that subject-specific PSD details may be a predictor of the MS level. Furthermore, the analysis of the sway frequency spectrum provided insight into the intersubject differences in the use of postural control subsystems. The relationship observed between MS susceptibility and spontaneous posture is discussed in terms of postural sensory weighting and in relation to the nature of the provocative stimulus.     

Effects of nodulation on resistance to alfalfa sickness among ten alfalfa cultivars

Summary Ten alfalfa cultivars were used to study the effects of nodulation and variations in resistance to alfalfa sickness. The alfalfa seedlings were planted in sick soil with three treatment,,i.e.: pasteurized sick soil inoculated with Rhizobium ‘Nitragin’ which served as the control, the inoculated non-pasteurized sick soil and the non-inoculated non-pasteurized sick soil. None of the alfalfa cultivars were immune from the sickness. Cultivar ‘Anik’ fromMedicago falcata was among the most resistant cultivars. Three Phytophthora root rot resistant cultivars including ‘Agate’, ‘Apollo’ and ‘Ramsey’ were not resistant to the disease. Alfalfa inoculated with Rhizobium showed greatly improved seedling growth. Correlation coefficients showed that those alfalfa cultivars more resistant to alfalfa sickness produced more dry weight. Dry weight increase due to nodulation (82%) had more than compensated for the loss of dry weight due to alfalfa sickness (33%). The present study suggested that the poor growth of alfalfa on sick soil was attributed to both the soil borne pathogens and the poor nodulation of alfalfa, probably due to the absence of effective Rhizobium in sick soil. Highly significant differences were also obtained among olfalfa cultivars for plant dry weight in the inoculation treatment. Selection for effective Rhizobium strains and for alfalfa genotypes which are resistant to alfalfa sickness and are high in nitrogen fixation rates could improve alfalfa yield in sick soil.     

Demonstrating the Potential for Dynamic Auditory Stimulation to Contribute to Motion Sickness

Auditory cues can create the illusion of self-motion (vection) in the absence of visual or physical stimulation. The present study aimed to determine whether auditory cues alone can also elicit motion sickness and how auditory cues contribute to motion sickness when added to visual motion stimuli. Twenty participants were seated in front of a curved projection display and were exposed to a virtual scene that constantly rotated around the participant''s vertical axis. The virtual scene contained either visual-only, auditory-only, or a combination of corresponding visual and auditory cues. All participants performed all three conditions in a counterbalanced order. Participants tilted their heads alternately towards the right or left shoulder in all conditions during stimulus exposure in order to create pseudo-Coriolis effects and to maximize the likelihood for motion sickness. Measurements of motion sickness (onset, severity), vection (latency, strength, duration), and postural steadiness (center of pressure) were recorded. Results showed that adding auditory cues to the visual stimuli did not, on average, affect motion sickness and postural steadiness, but it did reduce vection onset times and increased vection strength compared to pure visual or pure auditory stimulation. Eighteen of the 20 participants reported at least slight motion sickness in the two conditions including visual stimuli. More interestingly, six participants also reported slight motion sickness during pure auditory stimulation and two of the six participants stopped the pure auditory test session due to motion sickness. The present study is the first to demonstrate that motion sickness may be caused by pure auditory stimulation, which we refer to as “auditorily induced motion sickness”.     

Altered susceptibility to motion sickness as a function of subgravity level

Large interindividual differences among 74 normal subjects in the change in susceptibility to motion sickness with effective lifting of the normal g-load by parabolic flight maneuvers were recorded with high test-retest reliability. Most subjects, who were required to make standardized head movements while seated in a chair rotating at a constant speed, demonstrated either a substantial increase or a decrease in susceptibility, in confirmation of a previous study, while a few appeared to be more or less unaffected by the 1 g to 0 g gravitational change. A similar test procedure conducted with eighteen of the subjects at lunar- and Martian-gravity levels revealed further interindividual differences in susceptibility as a function of g-level. The subjects with gravity-dependent susceptibility revealed: (1) a progressive change in susceptibility as a function of g-load in either the positive or negative direction that was characteristic of the individual, (2) a susceptibility level that appeared to be maintained at the fractional g-load, and (3) immunity to motion sickness at all g-levels tested below the Earth standard. The case history as well as ground-based functional and provocative tests of normal subjects proved to be inadequate in predicting susceptibility to motion sickness under subgravity conditions.This research was conducted under the sponsorship of the Biomedical Research Office, Order T-81633, Manned Spacecraft Center, and the Office of Life Sciences, NASA, Washington, D. C., Order L-43518. Opinions or conclusions contained in this report are those of the authors and do not necessarily reflect the views and endorsement of the Navy Department.     

Comparison of various motion stimuli on motion sickness and acquisition of adaptation in Suncus Murinus

Effects of various types of motion stimuli were compared to investigate optimum method to elicit motion sickness and adaptation in Suncus murinus (suncus). Three different direction of shaking in the horizontal plane, back and forth, right and left and revolving, induced emetic response to the similar extent. However, vertical shaking was far less effective in inducing motion sickness. Mild and severe horizontal shaking (15 min per day) was continued for 14 days and emetic response to standard motion stimulus was compared before and after the training. The severe daily acceleration strongly depressed the susceptibility to motion stimulus. The mild acceleration which was not emetic stimulus in itself also remarkably attenuated the vomiting response to standard motion stimulus. These results indicate that 1) the emetic responsiveness of the suncus does not depend on the modes of shaking as long as the direction is in the horizontal plane, 2) the suncus is relatively refractory to the vertical linear acceleration and 3) the adaptation to motion stimulus does not develop on the latest peripheral steps of the vomiting reflex pathways.     

大鼠运动病敏感性性别差异与相关脑区AVP及其V1b受体表达的关系

目的：检测不同性别大鼠旋转刺激后脑内相关区域精氨酸加压素（AVP）含量及V1b受体表达的变化,探讨AVP及受体参与运动病的可能机制。方法：给予SD大鼠30 min绕水平轴的旋转刺激,然后采用放免法检测相关脑区AVP含量,并通过荧光免疫组化方法测定相应脑区V1b受体的表达情况。结果：①在雌性大鼠,旋转刺激组各脑区AVP含量无显著性改变;对于雄性大鼠,对照组各检测脑区AVP含量高于雌性,旋转刺激组小脑、延髓内AVP含量的变化无显著性意义,但前脑、间脑、脑桥内AVP含量较对照组明显降低（P〈0.05）。②雌性大鼠视上核AVP的V1b受体表达阳性神经元数量旋转刺激组显著低于对照组（P〈0.05）,而前庭核、最后区V1b受体表达阳性神经元数量明显多于对照组（P〈0.05）;在雄性大鼠,旋转刺激组视上核与前庭核V1b受体表达阳性神经元数量无显著性改变,而最后区V1b受体表达阳性神经元数量有所增加（P〈0.05）,但增加幅度没有雌性大鼠明显。结论：前脑、间脑、脑桥内AVP含量与前庭核和最后区V1b受体表达及对旋转刺激反应的差异可能与运动病敏感性性别差异有关,并且前庭核、最后区可能是AVP-V1受体拮抗剂抗运动病作用的靶点。     

The anti-emetic properties of 1-sulpiride in a ground-based model of space motion sickness

L-sulpiride, at a dose of 4 mg/kg, essentially abolished motion-induced emesis in a group of 6 squirrel monkeys undergoing horizontal rotation at 25 rpm, a terrestrial model of space motion sickness (SMS). Extrapyramidal side effects were not observed. In the absence of the drug, the usual emetic response returned. In comparison while typical neuroleptics were also strongly anti-emetic, they produced a considerable degree of rigidity and akinesia.     

Shiftwork and Sickness Absence Among Police Officers: The BCOPS Study

Shiftwork, regarded as a significant occupational stressor, has become increasingly prevalent across a wide range of occupations. The adverse health outcomes associated with shiftwork are well documented. Shiftwork is an integral part of law enforcement, a high-stress occupation with elevated risks of chronic disease and mortality. Sickness absence is an important source of productivity loss and may also serve as an indirect measure of workers’ morbidity. Prior studies of shiftwork and sickness absenteeism have yielded varying results and the association has not been examined specifically among police officers. The objective of this study was to compare the incidence rate of sick leave (any, ≥3 consecutive days) among day-, afternoon-, and night-shift workers in a cohort of police officers and also examine the role of lifestyle factors as potential moderators of the association. Participants (N?=?464) from the Buffalo Cardio-Metabolic Occupational Police Stress (BCOPS) study examined between 2004 and 2009 were used. Daily work history records that included the shift schedule, number of hours worked, and occurrence of sick leave were available for up to 15 yrs starting in 1994 to the date of the BCOPS study examination for each officer. Poisson regression analysis for ungrouped data was used to estimate incidence rates (IRs) of sick leave by shift, and comparison of IRs across shifts were made by computing incidence rate ratios (IRRs) and their 95% confidence intervals (CIs). Sick leave occurred at a higher rate on the night shift (4.37 per 10?000 person-hours) compared with either day (1.55 per 10?000 person-hours) or afternoon (1.96 per 10?000 person-hours) shifts. The association between shiftwork and sickness absence depended on body mass index (BMI). For overweight individuals (BMI?≥?25?kg/m²), the covariate-adjusted incidence rate of sick leave (≥1 day) was twice as large for night-shift officers compared with those working on the day (IRR?=?2.29, 95% CI: 1.69–3.10) or afternoon (IRR?=?1.74, 95% CI: 1.29–2.34) shift. The IR of three or more consecutive days of sick leave was 1.7 times larger for those working on night shift (IRR?=?1.65, 95% CI: 1.17–2.31) and 1.5 times larger for those working on afternoon shift (IRR?=?1.50, 95% CI: 1.08–2.08) compared with day shiftworkers. For subjects with normal BMI (<25?kg/m²), the incidence rates of sick leave did not differ significantly across shifts. In conclusion, shiftwork is independently associated with sickness absence, with officers who work the night shift having elevated incidence of sick leave. In addition, overweight officers who work the night shift may be at additional risk for sickness absence.     

Experimentally induced sickness decreases food intake, but not hoarding, in Siberian hamsters (Phodopus sungorus)

A wide range of physiological and behavioral alterations occur in response to sickness. Sickness behaviors, rather than incidental by-products or side-effects of acute illness, serve as adaptive functional responses that allow animals to cope with a pathogenic challenge. Among the more salient sickness behaviors is a reduction in food intake; virtually all sick animals display marked decreases in this behavior. Food intake, however, is only one component of the food-related behavioral repertoire. For many mammalian species, food hoarding represents a substantial portion of the total energetic budget. Here we tested the effects of experimental sickness on food hoarding and food intake in a naturally food hoarding species, Siberian hamsters (Phodopus sungorus). Adult male and female hamsters received injections of lipopolysaccharide (LPS) to induce sickness or control injections. LPS-induced sickness resulted in a marked decrease in food intake in both males and females, but did not decrease hoarding in either sex. These results support previous findings suggesting that food hoarding and food intake appear to be differentially regulated at the physiological level.     

Assessment of the effect of pharmaceuticals used to treat motion sickness on adaptation to model conditions involving prolonged rotation

The pharmacological preparation P-4 administered according to a reduced scheme (the first dose, 1.5?C2 h before stimulation; the second dose, 2 h after stimulation) efficiently alleviated the main symptoms of motion sickness, accelerated the process of adaptation and increased its efficiency in persons prone to motion sickness upon exposure to slow rotation during four days. Administration of the preparation according to the scheme described above did not cause the abstinence syndrome.     

The Prognostic Value of the Work Ability Index for Sickness Absence among Office Workers

BackgroundThe work ability index (WAI) is a frequently used tool in occupational health to identify workers at risk for a reduced work performance and for work-related disability. However, information about the prognostic value of the WAI to identify workers at risk for sickness absence is scarce.ObjectivesTo investigate the prognostic value of the WAI for sickness absence, and whether the discriminative ability differs across demographic subgroups.MethodsAt baseline, the WAI (score 7-49) was assessed among 1,331 office workers from a Dutch financial service company. Sickness absence was registered during 12-months follow-up and categorised as 0 days, 0<days<5, 5≤days<15, and ≥15 days in one year. Associations between WAI and sickness absence were estimated by multinomial regression analyses. Discriminative ability of the WAI was assessed by the Area Under the Curve (AUC) and Ordinal c-index (ORC). Test characteristics were determined for dichotomised outcomes. Additional analyses were performed for separate WAI dimensions, and subgroup analyses for demographic groups.ResultsA lower WAI was associated with sickness absence (≥15 days vs. 0 days: per point lower WAI score OR=1.27; 95%CI 1.21-1.33). The WAI showed reasonable ability to discriminate between categories of sickness absence (ORC=0.65; 95%CI 0.63-0.68). Highest discrimination was found for comparing workers with ≥15 sick days with 0 sick days (AUC=0.77) or with 1-5 sick days (AUC=0.69). At the cut-off for poor work ability (WAI≤27) the sensitivity to identify workers at risk for ≥15 sick days was 7.5%, the specificity 99.6%, and the positive predictive value 82%. The performance was similar across demographic subgroups.ConclusionsThe WAI could be used to identify workers at high risk for prolonged sickness absence. However, due to low sensitivity many workers will be missed. Hence, additional factors are required to better identify workers at highest risk.     

Relation between complement activation and susceptibility to decompression sickness

The consequences of complement activation and the symptoms of decompression sickness are similar. Consequently, the relation between the sensitivity of individuals to complement activation by air bubbles and their susceptibility to decompression sickness has been examined. Plasma samples from 34 individuals were incubated with air bubbles, and the concentration of the fluid phase metabolites of complement activation C3a, C4a, and C5a were measured with radioimmunoassays. It was found that both the anaphylatoxins C3a and C5a were produced by the presence of air bubbles but that the anaphylatoxin C4a was not. This finding indicates that air bubbles activate the complement system by the alternate pathway. One group of individuals was found to be particularly sensitive to complement activation by this pathway. They produced 3.3 times more C3a and 5.3 times more C5a in their plasma samples incubated with air bubbles as did the other group. Sixteen individuals were subjected to a series of pressure profiles that were severe enough to produce bubbles in their circulatory system that could be detected by Doppler ultrasonic monitoring. The group of individuals that had been identified as being more sensitive to complement activation by the alternate pathway was also found to be more susceptible to decompression sickness.