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Biomedical subjects

M A Gresty

Publications and source records attributed to M A Gresty.

At least 19 recordsLinked to original sources
PubMed2006

Influence of pitch tilts on the perception of gravity-referenced eye level in labyrinthine defective subjects.

We investigate the role of vestibular information in judging the gravity-referenced eye level (i.e., earth-referenced horizon or GREL) during sagittal body tilt whilst seated. Ten bilateral labyrinthine-defective subjects (LDS) and 10 age-matched controls set a luminous dot to their perception of GREL in darkness, with and without arm pointing. Although judgements were linearly influenced by the magnitude of whole-body tilt, results showed no significant difference between LDS and age-matched controls in the subjective GREL accuracy or in the intra-subject variability of judgement. However, LDS performance without arm pointing was related to the degree of vestibular compensation inferred from another postural study performed with the same patients. LDS did not utilize upper limb input during arm pointing movements as a source of graviceptive information to compensate for the vestibular loss. The data suggest that vestibular cues are not of prime importance in GREL estimates in static conditions. The absence of difference between controls and LDS GREL performance, and the correlation between the postural task and GREL accuracy, indicate that somatosensory input may convey as much graviceptive information required for GREL judgements as the vestibular system.

Adult↗
PubMed2006

Depersonalisation/derealisation symptoms in vestibular disease.

BACKGROUND: Depersonalisation is a subjective experience of unreality and detachment from the self often accompanied by derealisation; the experience of the external world appearing to be strange or unreal. Feelings of unreality can be evoked by disorienting vestibular stimulation. OBJECTIVE: To identify the prevalence of depersonalisation/derealisation symptoms in patients with peripheral vestibular disease and experimentally to induce these symptoms by vestibular stimulation. METHODS: 121 healthy subjects and 50 patients with peripheral vestibular disease participated in the study. For comparison with the patients a subgroup of 50 age matched healthy subjects was delineated. All completed (1) an in-house health screening questionnaire; (2) the General Health Questionnaire (GHQ-12); (3) the 28-item depersonalisation/derealisation inventory of Cox and Swinson (2002). Experimental verification of "vestibular induced" depersonalisation/derealisation was assessed in 20 patients and 20 controls during caloric irrigation of the labyrinths. RESULTS: The frequency and severity of symptoms in vestibular patients was significantly higher than in controls. In controls the most common experiences were of "déjà vu" and "difficulty in concentrating/attending". In contrast, apart from dizziness, patients most frequently reported derealisation symptoms of "feel as if walking on shifting ground", "body feels strange/not being in control of self", and "feel 'spacey' or 'spaced out'". Items permitted discrimination between healthy subjects and vestibular patients in 92% of the cases. Apart from dizziness, caloric stimulation induced depersonalisation/derealisation symptoms which healthy subjects denied ever experiencing before, while patients reported that the symptoms were similar to those encountered during their disease. CONCLUSIONS: Depersonalisation/derealisation symptoms are both different in quality and more frequent under conditions of non-physiological vestibular stimulation. In vestibular disease, frequent experiences of derealisation may occur because distorted vestibular signals mismatch with the other sensory input to create an incoherent frame of spatial reference which makes the patient feel he or she is detached or separated from the world.

Adult↗
PubMed2004

Perceptual and nystagmic thresholds of vestibular function in yaw.

A technique for simultaneous measurement of conscious (perceptual) and reflex (nystagmus) thresholds of vestibular function is described. We used an automated modified binary search algorithm with simultaneous infrared oculography in determining perceptual and VOR nystagmic thresholds respectively, during discrete whole body rotations in the dark. In a young group of 14 normal subjects (mean age 23 years) angular acceleration thresholds were significantly higher for perceptual detection (1.18 deg/s/s) than for nystagmus generation (0.51 deg/s/s). Only nystagmic thresholds were slightly raised (0.87 deg/s/s) in an older group of 9 normal subjects (mean age 63 years). The finding that nystagmic thresholds are lower than perceptual ones indicates a higher sensitivity of brainstem than cortical vestibular mechanisms. This technique would be of particular value in clinical situations where a dissociation between reflex and conscious vestibular mechanisms is expected, e.g. in patients with cortical lesions or in elderly patients with falls.

Adult↗
PubMed2003

Influence of whole-body pitch tilt and kinesthetic cues on the perceived gravity-referenced eye level.

We investigated the effects of whole body tilt and lifting the arm against gravity on perceptual estimates of the Gravity-Referenced Eye Level (GREL), which corresponds to the subjective earth-referenced horizon. The results showed that the perceived GREL was influenced by body tilt, that is, lowered with forward tilt and elevated with backward tilt of the body. GREL estimates obtained by arm movements without vision were more biased by whole-body tilt than purely visual estimates. Strikingly, visual GREL estimates became more dependent on whole-body tilt when the indication of level was obtained by arm lifting. These findings indicate that active motor involvement and/or the addition of kinesthetic information increases the body tilt-induced bias when making GREL judgements. The introduction of motor/kinaesthetic cues may induce a switch from a semi-geocentric to a more egocentric frame of reference. This result challenges the assumption that combining non-conflicting multiple sensory inputs and/or using intermodal information provided during action should improve perceptual performance.

Adult↗
PubMed2003

Vestibular influence on the cardiorespiratory responses to whole-body oscillation after standing.

We assessed the influence of vestibular stimulation by whole-body oscillation in the yaw plane on the cardiorespiratory responses after a change of posture from sitting to standing. Eighteen healthy subjects (21-70 years old) and six patients with bilateral vestibular loss (46-59 years old) were tested. For comparison, a subgroup, age matched to the patients, was created from the healthy group. After a 10-min rest, subjects who were sitting, back unsupported, stood on a platform affording en bloc head and body support. The platform was either static or oscillated at 0.1 Hz and 0.5 Hz (20 degrees amplitude) for 2 min. Presentation of the three conditions was counterbalanced. Respiration, ECG, blood pressure and head position were recorded. During oscillation at 0.5 Hz, the respiratory responses were different between groups; healthy subjects showed a significant increase of the respiratory frequency (1.75+/-2.1 breaths/min), which was not observed in the patients (0.16+/-0.7 breaths/min) ( p<0.05, ANOVA). Absolute changes of heart rate and blood pressure were similar for the three conditions in all the subjects. However, healthy subjects showed a decrease of power spectrum density of the high-frequency ('respiratory') component of heart rate variability on standing during all three conditions. This response was variable among the patients and the age-matched group. The study shows that semicircular canal activation influences the respiratory rhythm during movements in the yaw plane in standing subjects. In addition, we observed that changes of the respiratory influence on heart rate variability during orthostatic stress are not affected by yaw oscillation or chronic vestibular loss, but may be affected by factors related to age.

Adult↗
PubMed2003

Screening for depression among neuro-otology patients with and without identifiable vestibular lesions.

The experience of depression and anxiety among a sample of 91 patients with complaints of vertigo or dizziness was assessed using a widely available screening instrument, the Hospital Anxiety and Depression Scale (HADS). Questionnaires to assess reported symptoms, self-esteem and social support were also administered. On the basis of clinical vestibular testing, 53% of participants were classified as having a labyrinthine disorder (canal paresis or positional vertigo), 22% as having a vestibular imbalance (spontaneous nystagmus or directional preponderance), and 251% as having no identifiable vestibular abnormality (negative test results). Based on the self-report measures using the screening instrument, 17% of the sample could be classified as depressed, and 29% as anxious. The presence of a vestibular lesion (based on clinical findings) was not associated with reported depression (F (3, 72) = 0.98, p = 0.41). The variables were entered into a hierarchical multiple regression analysis with depression as the dependent variable. A model emerged which accounted for 50% of the variance. Three variables comprised the final model: anxiety (beta = 0.44, p < 0.001), self-esteem (beta = 0.27, p < 0.01), and satisfaction with social support (beta = 0.25, p < 0.01). The results demonstrate the value of identifying psychosocial factors, as well as disease characteristics, among patients presenting at neurootology clinics. In particular, the findings highlight the importance of screening for emotional distress in this patient group, regardless of clinical test results or severity of self-reported symptoms.

Adolescent↗
PubMed2003

Motion sickness and tilts of the inertial force environment: active suspension systems vs. active passengers.

BACKGROUND: Maneuvering in vehicles exposes occupants to low frequency forces (< 1 Hz) which can provoke motion sickness. HYPOTHESIS: Aligning with the tilting inertial resultant (gravity + imposed horizontal acceleration: gravito-inertial force (GIF)) may reduce motion sickness when tilting is either 'active' (self-initiated; Experiment 1) or 'passive' (suspension machinery; Experiment 2). METHODS: Exp 1: Twelve seated subjects were exposed to continuous horizontal translational oscillation through the body x-axis (3.1 m x S(-2) peak acceleration, 0.20 Hz) while making head tilts which were either aligned or misaligned (180 degrees out of phase) with respect to GIF. The two sessions were one week apart at the same time of day, counterbalanced for order. Head tilts were controlled by tracking a moving LED display and head trajectory was verified by accelerometry. Motion continued until moderate nausea was achieved (motion endpoint) or until a 30 min cut-off. Exp 2: A different group of 12 subjects were exposed to continuous horizontal translational sinusoidal oscillation through the body x-axis (2.0 m x S(-2) peak acceleration, 0.176 Hz) while seated in a cab which was tilted by suspension machinery around the y-axis of the ears so that GIF was aligned or misaligned (180 degrees out of phase) with the body z-axis. RESULTS: Exp 1: Mean +/- SD time to motion endpoint was significantly longer for aligned (19.2 +/- 12.0 min) than for misaligned (17.8 +/- 13.0 min; p < 0.05, two-tail). Exp 2: Mean +/- SD time to motion endpoint was significantly shorter for aligned (21.8 +/- 10.9 min) than for misaligned (28.3 +/- 5.8 min; p < 0.01, two-tail). CONCLUSIONS: Whether or not compensatory tilting protects against (Exp 1) or contributes to (Exp 2) motion sickness may be influenced by whether the tilting is under the active control of the person (e.g., car driver) or under external control (e.g., passenger in a high-speed tilting train).

Adult↗
PubMed2002

Migraine and Ménière's disease: is there a link?

BACKGROUND: A possible link between Ménière's disease (MD) and migraine was originally suggested by Prosper Ménière. Subsequent studies of the prevalence of migraine in MD produced conflicting results. OBJECTIVE: To determine the lifetime prevalence of migraine in patients with MD compared to sex- and age-matched controls. METHODS: The authors studied 78 patients (40 women, 38 men; age range 29 to 81 years) with idiopathic unilateral or bilateral MD according to the criteria of the American Academy of Otolaryngology. Diagnosis of migraine with and without aura was made via telephone interviews according to the criteria of the International Headache Society. Additional information was obtained concerning the concurrence of vertigo and migrainous symptoms during Ménière attacks. The authors interviewed sex- and age-matched orthopedic patients (n = 78) as controls. RESULTS: The lifetime prevalence of migraine with and without aura was higher in the MD group (56%) compared to controls (25%; p < 0.001). Forty-five percent of the patients with MD always experienced at least one migrainous symptom (migrainous headache, photophobia, aura symptoms) with Ménière attacks. CONCLUSIONS: The lifetime prevalence of migraine is increased in patients with MD when strict diagnostic criteria for both conditions are applied. The frequent occurrence of migrainous symptoms during Ménière attacks suggests a pathophysiologic link between the two diseases. Alternatively, because migraine itself is a frequent cause of audio-vestibular symptoms, current diagnostic criteria may not differentiate between MD and migrainous vertigo.

Adult↗
PubMed2001

Respiratory responses of normal and vestibular defective human subjects to rotation in the yaw and pitch planes.

We evaluated the contribution of the semicircular canals to autonomic responses to rotation in 12 normal subjects and three labyrinthine defective patients. Respiration, heart rate, arterial blood pressure and blood flow in the finger were recorded during 60 degrees /s steps of constant velocity rotation. Rotation was performed in the dark about a vertical axis: (I) with head upright for yaw stimulation of horizontal canals; (II) head tilted chin down and rotated laterally to stimulate the vertical canals in both face-forwards and backwards directions. In normal subjects, rotation in the pitch plane elicited an increase in respiratory frequency due to a shortening of the time for expiration, whilst patients had inconsistent responses. We conclude that vertical semicircular canal activity exerts a regulatory drive on respiration in human subjects.

Adult↗
PubMed2001

Horizontal ocular vergence and the three-dimensional response to whole-body roll motion.

We evaluated the human binocular response to roll motion in the dark and during visual fixation with horizontal convergence. Six normal human subjects were exposed to manually driven, whole-body rotation about an earth-vertical, naso-occipital axis, under two conditions: (I) oscillation at 0.4 Hz (peak velocity 69+/-3.8 degree/s) in the dark, and whilst fixating an axial light-emitting diode at 48 cm ('near') and at 206 cm ('far'); (II) constant velocity rotation (56.5+/-3.1 degree/s) for 40 s, clockwise and counter-clockwise, in the dark, and sudden stops. Eye and head movements were monitored using scleral search coils. In head-fixed, angular velocity coordinates roll motion always evoked conjugate ocular torsion, with small conjugate horizontal and disconjugate vertical components. The resultant binocular eye responses were rotations about convergent axes. During oscillation with target fixation the convergence of the rotation axes was larger than that predicted by target geometry, producing disconjugate oscillations of vertical gaze about the target ('skewing'). Fast-phase eye movements were primarily resetting rotations about the same convergent rotation axes as the slow phases, but the small vertical velocity components had oscillatory, asymmetrical profiles. In response to velocity steps the slow-phase eye velocity decayed exponentially with time constants of 4.5+/-1.5 s for the torsional component and 5.8+/-1.9 s for the 'vertical vergence' component (right eye-left eye recordings). We conclude that in normal human subjects dynamic vertical canal stimulation with horizontal gaze convergence evokes rotation of the eyes about convergent axes and a small skewing of the eyes.

Adult↗
PubMed2001

Influence of action and expectation on visual control of posture.

Previous studies have shown that human subjects presented with a moving visual environment initiate a postural re-adjustment in the direction of motion. The present study investigated how active control or expectation of the displacement of a visual scene affects this postural response. Center of foot pressure (COP) and head displacement were recorded using a sway platform and a tracking system, respectively. The subjects faced a visual scene (1 x 1 m, at a distance of 45 cm) which moved transiently (with a velocity of 1 cm/s) in a direction parallel to the interaural axis. When the displacement of the visual scene was under the active control of the subjects, visually induced body sway was strongly inhibited, in comparison with the response to unexpected stimuli. Prior knowledge of the characteristics of the forthcoming displacement was sufficient, in most subjects, to reduce postural re-adjustment, even when subjects did not exert active control. Finally, the visually induced postural response was strongly reduced even when subjects only triggered the stimulus, without any knowledge about the direction of motion. In conclusion, it appears that although vision is of primary importance in the control of postural orientation, high level processes such as expectation can modulate its impact by providing cues as to whether forthcoming visual flow is the consequence of self-motion or object-motion.

Adult↗
PubMed2001

Force platform recordings in the diagnosis of primary orthostatic tremor.

Primary orthostatic tremor (OT) consists of rhythmical muscle contractions at a frequency of around 16 Hz, causing discomfort and/or unsteadiness while standing. Diagnosis has hitherto relied on recording Electromyography (EMG) from affected muscles. The main aim of this study was to see if the characteristic postural tremor in OT can be identified with force platforms. We also quantified postural sway in OT patients to assess their degree of objective unsteadiness. Finally, we investigated the time relations between bursts of activity in the various affected muscle groups. Subjects stood on a force platform with concurrent multichannel surface EMG recordings from the lower limbs. Seven patients with clinical and EMG diagnosis of OT were examined and the force platform data compared with those of 21 other neurological patients with postural tremor and eight normal controls. All OT patients had high frequency peaks in power spectra of posturography and EMG recordings (12--16 Hz). No such high frequency activity was evident in patients with Parkinson's disease, cerebellar degenerations, essential tremor or in healthy controls. Additionally, OT patients showed increased sway at low frequencies relative to normal controls, suggesting that the unsteadiness reported by OT patients is at least partly due to increased postural sway. Examination of EMG timing showed fixed patterns of muscle activation when maintaining a quiet stance within but not across OT patients. These data show a high correlation between EMG and posturography and confirm that OT may be diagnosed using short epochs of force platform recordings.

Blood Pressure↗
PubMed2001

Abnormal interaction between vestibular and voluntary head control in patients with spasmodic torticollis.

The functional status of vestibulo-collic reflexes in the sternocleidomastoid (SCM) muscles was investigated in 24 patients with spasmodic torticollis using small, abrupt 'drops' of the head. None had been treated with botulinum toxin injections during at least 4 months preceding the study. Eight of the patients, four of whom had been studied before surgery, were also studied after selective peripheral denervation of neck muscles. The reflex was of normal latency and duration in the 'passive drop' condition, in which subjects were instructed not to oppose the fall of the head. To study voluntary interaction with the reflex response, subjects were then asked to flex the neck as quickly as possible after onset of the head drop ('active drop'). In this condition, voluntary responses in patients were delayed, smaller and less effective in counteracting the head fall than in normal subjects. The same abnormalities were also found in patients after surgery when the head posture was improved. Somatosensory/auditory voluntary reaction times in SCM were normal, as was the latency of the startle reflex. We conclude that voluntary interaction with the vestibulo-collic reflex is disrupted in patients with spasmodic torticollis, a finding which corroborates the patients' aggravation of their symptoms by head or body perturbations. Lack of effective interaction between two major systems controlling head position may contribute to torticollis.

Adult↗
PubMed2001

Visual vertigo: symptom assessment, spatial orientation and postural control.

Certain patients with balance disorders report a 'visual vertigo' in which their symptoms are provoked or aggravated by specific visual contexts (e.g. supermarkets, driving or movement of objects). In order to determine the causes of visual vertigo (VV), we assessed symptoms, anxiety and the influence of disorienting visual stimuli in 21 such patients. In 17 out of 21 patients, a peripheral vestibular disorder was diagnosed. Sixteen bilateral labyrinthine-defective subjects (LDS) and 25 normal subjects served as controls. Questionnaire assessment showed that the levels of trait anxiety and childhood motion sickness in the three subject groups were not significantly different. Reporting of autonomic symptoms and somatic anxiety was higher than normal in both patient groups but not significantly different between LDS and VV patients. Handicap levels were not different in the two patient groups, but the reporting of vestibular symptoms was higher in the VV than in the LDS group. The experimental stimuli required subjects to set the subjective visual vertical in three visual conditions: total darkness, in front of a tilted luminous frame (rod and frame test) and in front of a large disc rotating in the frontal plane (rod and disc test). Body sway was also measured in four visual conditions: eyes closed, eyes open, facing the tilted frame and during disc rotation. In psychophysical and postural tests, both LDS and VV patients showed: (i) a significant increase in the tilt of the visual vertical both with the static tilted frame and with the rotating disc; and (ii) an increased postural deviation whilst facing the tilted frame and the rotating disc. The ratio between sway path with eyes closed and eyes open (i.e. the stabilizing effect of vision) was increased in the LDS, but not in VV patients, compared with normal subjects. In contrast, the ratio between sway path during disc rotation and sway path during eyes open (i.e. the destabilizing effect of a moving visual stimulus) was increased in the VV patients but not in LDS. Taken together, these data show that VV patients have abnormally large perceptual and postural responses to disorienting visual environments. VV is not related to trait anxiety or a past history of motion sickness. The results indicate that VV emerges in vestibular patients if they have increased visual dependence and difficulty in resolving conflict between visual and vestibulo-proprioceptive inputs. It is argued that treating these patients with visual motion desensitization, e.g. repeated optokinetic stimulation, should be beneficial.

Adult↗
PubMed2001

The endocrine system, vertigo and balance.

Steroid, amine and peptide hormones affect the peripheral vestibular system. Vasopressin hypersensitivity of the endolymphatic sac may be implicated in the pathogenesis of Meniere's disease. Specific vasopressin antagonists will help define the role of vasopressin in Meniere's disease. The modulation of central vestibular pathways by neuroactive steroids may involve effects on gamma-aminobutyric acid-ergic and glutaminergic pathways. The vestibular nuclei also express enzymes that are important in the synthesis of steroids and the modulation of their activity. Steroids mediate both facilitatory and deleterious effects of stress on vestibular compensation. The quality and quantity of stressor that determines the pattern of hormonal output, may be important. Clinical observation suggests that episodic ataxia type 2, a P/Q calcium channelopathy, may be phenotypically modulated by endocrine fluctuations. Steroid hormones may affect the episodic ataxia type 2 phenotype by modulation of voltage-gated calcium channel activity via second messenger systems and ion channel subunit expression. Despite evidence to support the link, the role of the endocrine system in vestibular function and disease is as yet virtually unexplored.

Animals↗