Biliary-colonic fistula diagnosed via hepatobiliary scintigraphy.
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Adult↗
Biomedical subjects
A J Benson
Publications and source records attributed to A J Benson.
Jet lag and motion sickness.
Jet lag. Present day aircraft operating round northern and southern latitudes cross time zones at almost the same rate as the earth rotates, and it is these rapid transmeridian transitions that lead to the syndrome commonly referred to as jet lag. On arrival at their destination, individuals find themselves out of synchrony with the social and time cues of their new environment and, until they adapt, may experience symptoms such as malaise, gastrointestinal disturbance, loss of appetite, tiredness during the day and poor sleep. The severity and exact nature of the problems vary with the direction of travel and the number of time zones crossed, and some people react more unfavourably to intercontinental travel than others. Clearly, with increasing numbers of passengers undertaking such journeys, there is considerable interest in strategies to reduce the immediate effects of jet lag or to facilitate acclimatisation. Motion sickness is a generic term which embraces seasickness, airsickness, carsickness, space sickness etc, names that identify the provocative environment or vehicle. It is a normal reaction of humans to exposure to certain motion stimuli that occur during passive transportation.
Circadian Rhythm↗
Perceptual scaling of whole-body low frequency linear oscillatory motion.
Evidence that Z-axis oscillation in the Earth-vertical plane is more provocative of motion sickness than the equivalent imposed oscillation acting in the Earth-horizontal raises the possibility that horizontal oscillation is perceived as less intense than equivalent vertical oscillation. In Experiment 1, subjects (n = 8) were oscillated through their head Z-axis in both the Earth-vertical and horizontal planes. In Experiment 2, another group (n = 10) were oscillated through their head Y-axis in the Earth-horizontal. Stimuli were 5 cycles of motion at 0.3 Hz ranging in 3.5 dB intervals from 0.19 to 2.15 m.s-2 (Expt. 1) and from 0.1 to 3.98 m.s-2 (Expt. 2). Perceptual scaling of intensity against acceleration was similar irrespective of direction of oscillation in the Earth-plane or head-body axis. Displacement tended to be overestimated, this being most marked for the lower acceleration levels in the horizontal condition. Results supported the notion that Stevens' Power Law exponents decrease as a function of increasing stimulus range. Differences in perception of oscillation intensity and displacement do not seem to explain the markedly greater nauseogenic potential of vertical oscillation.
Acceleration↗
Space Sled--a device for the investigation of the physiological effects of weightlessness.
Space Sled is a device for providing controlled linear acceleration stimuli in the microgravity environment of orbital flight. The scientific objectives of the experiments which used Space Sled on the D-1 Spacelab mission were to study aspects of otolith organ (that is, that part of the inner ear which transduces linear accelerations) function and adaptation in weightlessness. Space Sled comprises electrical and mechanical sub-systems. The latter is made up of a carriage running on twin rails that are fixed to the floor of Spacelab. The assembly is 6 m long with a working section of 3.5 m. The seat accommodating the test subject can be mounted on the carriage in any of three orthogonal positions. The carriage is coupled by a flexible steel cable to a servo-controlled electric motor which is capable of producing a peak acceleration of 2 m/s2 and peak velocity of 2.4 m/s. In the event of failure of comprehensive safety circuits in the electrical sub-system, a mechanical snubber, of crushable honeycomb construction, limits the deceleration to 20 m/s2. Mechanical structures providing carriage guidance, Sled/Spacelab interfaces, carriage latching, motor mounting and cable tensioning are detailed in the paper.
Acceleration↗
Thresholds for the perception of whole body angular movement about a vertical axis.
Thresholds for the detection (at p = 0.75 correct) of the direction of discrete angular movements about a vertical Z axis, having a cosine bell velocity trajectory and a duration of 3.3 s, were determined using an adaptive psychophysical procedure. In 30 subjects the mean threshold for the detection of Z axis stimuli was 1.5 deg.s-1. X and Y axis thresholds of 20 subjects had mean values of 2.04 and 2.07 deg.5(-1), respectively, and were significantly higher than Z axis thresholds. The mean Z axis threshold of 6 subjects, who viewed a visual target fixed to the turntable, was reduced by 8.6 dB over that obtained in darkness. Z axis thresholds were found to increase at 5.9 dB/decade as a function of stimulus duration over the range 0.9 to 20 s. The possible implication of this finding in relation to the dynamics of the sensory system mediating the perception of whole-body angular movement is discussed.
Acceleration↗
Visual display lowers detection threshold of angular, but not linear, whole-body motion stimuli.
The influence of a visual display, fixed relative to the subject, on thresholds for detection (at 75% correct) of discrete Y-axis linear movements and of discrete Z-axis angular movements, was determined in a group of 12 subjects. Both the linear and the angular, whole-body, motion stimuli had a cosine bell velocity trajectory with a duration of 2.6 s. Thresholds for the detection of the linear motion stimuli in darkness were not significantly different from those obtained when either a simple LED display or an instrument dial were illuminated; the mean threshold was 0.039 m.s-2. None of the subjects reported apparent movement of the visual display. In contrast, the presence of either visual display lowered angular motion thresholds on average by a factor of 2.7 from that obtained in darkness (1.61 degrees.s-1). All subjects reported apparent movement of the visual display, an oculogyral illusion, at stimulus intensities close to the dark threshold. These findings imply that otolithic afferents, unlike those from the semicircular canals, do not interact with neural centres mediating visual localization.
Acceleration↗
N-(2-hydroxyethyl)-N-[2-(7-guaninyl)ethyl]amine, the putative major DNA adduct of cyclophosphamide in vitro and in vivo in the rat.
The anti-cancer agent, cyclophosphamide, metabolises to the cytotoxic alkylating agent phosphoramide mustard, which can be dephosphoramidated to give nornitrogen mustard. A rat liver mitochondrial supernatant system was used to study the binding of [chloroethyl 3H]cyclophosphamide to DNA. The reacted DNA was acid-hydrolysed and one major adduct was identified using Sephadex G-10 chromatography, followed by HPLC, using reversed-phase or ion-exchange systems. Further studies, using [14C]guanine as reaction substrate for [chloroethyl 3H]cyclophosphamide, phosphoramide mustard or nornitrogen mustard, demonstrated the main adduct from each reaction had identical chromatographic properties in these systems. The radiolabelled ratio in the [3H]cyclophosphamide-[14C]guanine reaction demonstrated a monoadducted product. From this evidence and from 1H NMR data, the common adduct was putatively identified as a hydroxylated nornitrogen mustard adduct (N-(2-hydroxyethyl)-N-[2-(7-guaninyl)ethyl]amine). In in vivo studies, rats were injected intraperitoneally with 2.775 MBq [3H]cyclophosphamide. Total organ [3H] content and DNA binding levels were ascertained. Maximal levels of [3H] binding to DNA were seen between 1-4 hr with the highest binding levels observed in the bladder. The in vivo adduct was shown, using various HPLC systems, to co-chromatograph with the in vitro adduct and thus the main in vivo adduct was putatively identified as N-(2-hydroxyethyl)-N-[2-(7-guaninyl)ethyl]amine.
Alkylation↗
The vestibular system in weightlessness.
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Humans↗
Effect of spaceflight on thresholds of perception of angular and linear motion.
Psychophysical studies of vestibular function have been carried out in order to study adaptation within the vestibular sensory system to the weightless environment of orbital spaceflight. No significant change in the threshold of detection of whole-body angular acceleration was found, either during flight or post-flight. Experiments involving the perception of whole-body linear acceleration have yielded somewhat inconsistent results, although the weight of evidence points to an elevation and increased variability of threshold in the first few days following spaceflight. Although a change in the excitability of the saccular and macular otoliths in microgravity cannot be excluded, it is more probable that this decreased sensitivity is a manifestation of a central adaptive mechanism, in which the "weighting" of gravi-receptor information is reduced. Enhancement of the ability to detect linear acceleration stimuli, exhibited by some astronauts in microgravity, may be a manifestation of heightened utilization of cutaneous rather than otolithic cues.
Humans↗
European vestibular experiments on the Spacelab-1 mission: 4. Thresholds of perception of whole-body linear oscillation.
Thresholds for the detection of linear oscillatory motion at 0.3 Hz in the X, Y and Z body axes were determined during the flight of Spacelab-1 and on the ground pre- and post-flight, using the method of limits with a single staircase procedure. Pre-flight, Z axis thresholds (mean 0.077 ms-2) were significantly higher than X and Y thresholds (mean 0.029 ms-2). Measures obtained on three crew members in-flight exhibited thresholds greater, by a factor of 1.5-4.3, than those obtained pre-flight. Post-flight, two crew members had significantly elevated X and Y axis thresholds whereas the other two crew members had lowered thresholds in X, Y and Z axes. In general, thresholds had returned to pre-flight levels by the second post-flight day. A possible explanation for these somewhat disparate responses is presented.
Acceleration↗
European vestibular experiments on the Spacelab-1 mission: 6. Yaw axis vestibulo-ocular reflex.
In two Spacelab-1 crew members the lateral eye movements evoked by active angular oscillation of the head in yaw at 1 Hz were recorded in-flight and post-flight. In one, the responses to passive angular oscillation in yaw at 0.2-1 Hz were also studied pre- and post-flight. In the absence of visual fixation there was no significant change in the gain of either the active or passive vestibulo-ocular reflex (VOR) attributable to exposure to microgravity. However, when the subject fixated on a visual target that moved with his head the suppressed VOR gain was lower on the first post-flight test (performed 16 h after landing) than that obtained pre-flight or on subsequent post-flight tests.
Adaptation, Physiological↗
Mass-discrimination in weightlessness and readaptation to earth's gravity.
Five members of the first Spacelab mission (STS-9) were tested on several occasions for weight-discrimination before and after the flight, and for mass-discrimination under microgravity in flight. Thresholds for mass-discrimination were higher than for preflight weight-discrimination by a factor of about 1.8, and there was no clear evidence of improvement throughout the ten day mission. Too few tests were conducted to monitor the improvement during the first two days of flight, when adaptation to weightlessness may have occurred. Subjects reported perceptual aftereffects of body heaviness for two or three days after the flight. Their weight-discrimination thresholds were raised during this period, when they were re-adapting to normal gravity. Incomplete adaptation to altered arm weight can only partly explain the raised threshold for mass-discrimination in microgravity. Differences in the sensory information available with and without gravity are discussed.
Adaptation, Physiological↗
Thresholds for the detection of the direction of whole-body, linear movement in the horizontal plane.
Thresholds for the detection (at p = 0.67 correct) of the direction of discrete linear movements in the horizontal plane, having a cosine bell velocity trajectory and duration of 3 s, were determined in 24 subjects. Thresholds in the Z body axis (mean 0.154 m X s-2) were significantly higher than thresholds for movement in the X (mean 0.063 m X s-2) and Y (mean 0.057 m X s-2) body axes. In 8 subjects, X axis acceleration threshold was found to increase as a monotonic function of stimulus duration over the range 0.98 to 6.96 s and exhibited similar frequency-dependent characteristics to thresholds for the detection of continuous oscillatory stimuli. This finding implies that the sensory system mediating the transduction and perception of liminal, whole-body linear movement is sensitive to a combination of the acceleration and rate change of acceleration (jerk) of the motion stimulus, and has similar dynamics to the "irregular" sensory receptors of the otolith organs.
Analysis of Variance↗
Modification of per- and postrotational responses by voluntary motor activity of the limbs.
In order to explore interactive effects of voluntarily generated rotational stimuli on evoked vestibular responses, experiments were performed using a rotation chair in which the subject either controlled the angular motion by voluntary movement of his upper and lower limbs, or was passive-rotation being controlled by a servomotor and electromagnetic brake. In two experiments, carried out on 8 and 9 subjects respectively, it was found that cessation of sustained passive rotation by voluntary limb actions strongly suppressed the postrotational turning sensation but did not alter the evoked nystagmus. Limb movements that were directionally concordant with muscle torque in generating body rotation yielded arthrokinetic effects which augmented perrotational nystagmus and sustained the sensation of turning. The postrotational sensation of turning and postrotational nystagmus produced by voluntary cessation of active rotation were reduced relative to responses produced by passive turning and stopping. The Purkinje effect induced by postrotational head movements was similarly reduced following voluntary cessation of active rotation.
Adult↗
Influence of a visual display and frequency of whole-body angular oscillation on incidence of motion sickness.
Visual search within a head-fixed display consisting of a 12 X 12 digit matrix is degraded by whole-body angular oscillation at 0.02 Hz (+/- 155 degrees/s peak velocity), and signs and symptoms of motion sickness are prominent in a number of individuals within a 5-min exposure. Exposure to 2.5 Hz (+/- 20 degrees/s peak velocity) produces equivalent degradation of the visual search task, but does not produce signs and symptoms of motion sickness within a 5-min exposure.
Acceleration↗
Coriolis cross-coupling effects: disorienting and nauseogenic or not?
Nausea and disorientation are sometimes produced by head movements during turning maneuvers in aircraft. These responses are usually attributed to Coriolis cross-coupling stimulation of the vestibular system, although it has been indicated recently that many turning maneuvers of aircraft have insufficient angular velocity to generate such effects. The purpose of the present study was to further distinguish conditions in which Coriolis cross-coupling effects are disorienting and nauseogenic from conditions in which they are neither.
Adult↗
Vision during angular oscillation: the dynamic interaction of visual and vestibular mechanisms.
A review is presented of the dynamic behaviour of two oculomotor control systems--the vestibulo-ocular and pursuit reflexes--responsible for the spatial and temporal stabilization of the image of an observed object on the fovea of the retina, and mathematical models adduced in which the contribution of physiological components of the systems can be identified. With angular oscillation of the head below 1-2 Hz, retinal information is used to maintain unity gain of the head/eye system, but at higher frequencies stabilization is determined primarily by vestibular inputs. When the observed target moves with the head, as in a head-mounted display, the suppression of inappropriate vestibulo-ocular responses is dependent upon the dynamic performance of the pursuit system. With such a display, impairment of visual acuity may be detected at frequencies of oscillation as low as 0.5 Hz.
Humans↗
Visual-vestibular interaction in the control of eye movement.
Three experimental conditions have been used to investigate the extent to which inappropriate reflex eye movements of vestibular origin can be suppressed by visual feedback. First, the ability to read digits in a display which moved with the head was assessed during angular oscillation about the yaw and pitch axes of the body. Performance decrement was observed at frequencies above 0.2 Hz in pitch and 1.0 Hz in yaw, being greater at higher stimulus velocity levels. A second experiment revealed that the performance decrement was associated with eye movements relative to the head, which increased with the frequency of stimulation. Finally, the response of the pursuit reflex was investigated under similar experimental conditions. The results indicated that the breakdown in the pursuit reflex and in the suppression of the vestibulo-ocular reflex occurred over the same frequency band, implying the similarity of the mechanisms responsible for suppression and pursuit.
Aerospace Medicine↗