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Biomedical subjects

C Wall

Publications and source records attributed to C Wall.

At least 127 records · Page 7Linked to original sources
PubMedDate not supplied

Effects of visual and support surface orientation references upon postural control in vestibular deficient subjects.

Assessment of postural control in vestibular deficient subjects with and without visual and ankle joint sway information permitted: 1) a quantitative assessment of the overall vestibular information used by the individual patient for control of upright posture; 2) an estimate of the extent to which the vestibular deficient subject can appropriately "select" and alternatively use visual and ankle joint somatosensory information for compensatory postural control and 3) quantification of adaptive changes in postural responses to visual and somatosensory inputs. Results from this study support the hypothesis that abnormal vestibular function disrupts the subject's reference to gravity (earth) vertical. This loss of an absolute spatial reference normally provided by vestibular input prevents the resolution of conflicting or inaccurate visual and somatosensory spatial references which may occur during active or passive body movements.

Ear, Inner↗
PubMedDate not supplied

Postural stability and rotational tests: their effectiveness for screening dizzy patients.

Results of independently interpreted computerized stationary platform posturography and white noise rotational tests were compared with diagnoses for 110 patients. Using the criterion that an abnormal result from either test classified the subject as abnormal, the sensitivity estimate for the pair of tests was 78% for persons with diagnoses known to result in vestibular dysfunction. The specificity estimate was 90%. Both a vestibulo-ocular and a vestibulo-spinal test were required for effective screening. Consecutive tests performed over five days showed the rotation test to be much less variable than posturography. Rotation testing is therefore preferred for following the performance of patients having disorders thought to cause fluctuating vestibular systems. Interobserver reliability rates were 83% for posturography and 93% for rotation tests.

Adult↗
PubMedDate not supplied

Effects of age, sex and stimulus parameters upon vestibulo-ocular responses to sinusoidal rotation.

We evaluated the vestibulo-ocular reflex (VOR) in 50 normal human subjects, uniformly distributed in age 20-59 years, and evenly distributed in sex by decade, using sinusoidal rotation over the frequency range of 0.005 to 1.0 Hz and three peak amplitudes of 25, 50, and 100 deg/sec. Age variations. The gain magnitude of the normal human VOR appears to decrease with increasing age. This trend becomes statistically significant at p less than 0.05 for the 0.005 and 0.01 Hz test points. Sex-related variations. There were no statistically significant differences in gain magnitude between the sexes but females had higher average gains than males for the lowest test frequencies. The phase data showed a trend with the average phase points for females being less than those for males. This difference was statistically significant at p less than 0.05 for the 0.005 Hz test frequency. Dynamic range. Increasing the stimulus amplitude by a factor of four yielded a small but statistically significant decrease in gain magnitude, thus suggesting a mild saturation-type of nonlinearity.

Adolescent↗
PubMedDate not supplied

The modulation component of nystagmus during earth-horizontal rotation: relationship with gaze angle.

Periodic fluctuations in gaze angle and nystagmus slow phase velocity (SPV) were characterized using 6 normal subjects rotated at constant angular velocity about their rostral-caudal body axis with that axis in the horizontal orientation. The periodicity of the fluctuations corresponded to the angular frequency of rotation. The magnitude of the SPV fluctuations was moderately well correlated with those of the gaze fluctuations. Four vector quantities were found to characterize these data fairly completely, yet compactly.

Electronystagmography↗
PubMedDate not supplied

Postoperative vestibular dysfunction following head and neck surgery.

Patients scheduled for major oncologic head and neck surgery underwent preoperative audiometry and rotational testing for vestibulo-ocular response (VOR). Patients with normal preoperative VOR and SRT less than 45 dB were subsequently retested following surgery for VOR. Patients deemed abnormal on postoperative rotational testing were retested until VOR returned to normal or one year, whichever came first. Eighty patients had normal VOR measured preoperatively. At the first postoperative testing 46 of these patients (58%) were determined to have significant VOR abnormalities. No differences in length of anesthesia, use of hypnotic or narcotic drugs, hepatic and renal abnormalities, and dehydration were noted in the patients who developed abnormal VOR, when compared to the patients who maintained normal VOR. One year post surgery twenty patients (43%) continued to demonstrate vestibular abnormality. The observation that major surgery reduces vestibular response has important monitoring and treatment implications. The integration of this data with the results of endolymphatic surgery are discussed.

Adult↗
PubMedDate not supplied

Eye movements induced by gravitational force and by angular acceleration: their relationship.

The relationship between putative 'canal' and 'otolith' function was studied by using both vertical axis and horizontal axis (barbecue spit) rotations. The vestibulo-ocular reflex (VOR) with eyes closed of 7 normal subjects during vertical axis rotation was characterized (0.02 to 1.67 Hz) using pseudorandom acceleration. Gain and phase points were calculated. The long time constant of the VOR was then estimated from the phase points using a simple linear systems model. The same subjects were also tested with eyes closed using earth horizontal axis rotations. Constant velocity rotation (60 degrees/sec) produced a periodic oscillation in the slope of the slow component of nystagmus known as the 'modulation component'. The amplitude of this component was averaged for clockwise and counterclockwise runs. For the 7 subjects, the amplitude of averaged modulation component correlated with the low-frequency phase values (r = 0.82 to 0.89) and VOR long time constant estimates (r = -0.95) obtained during vertical axis rotations. These data suggest a complementary relationship between responses to linear and to angular accelerations. Subjects having eye movement responses which are less sensitive to low-frequency angular acceleration also tend to have relatively greater responses to changing linear accelerations.

Eye Movements↗
PubMedDate not supplied

The chinchilla's vestibulo-ocular reflex.

The horizontal vestibulo-ocular reflex (VOR) was measured and characterized in seven adult chinchillas using 0.01 to 1.0 Hz angular velocity sinusoids. Gains were less than compensatory, and were variable from day to day but phases were highly repeatable both within and between animals. The best fitting transfer function to the average data of all animals had a dominant time constant of 7.5 sec, and an adaptation operator with a time constant of 24.0 sec. There were certain nonlinearities in the horizontal VOR of this animal, and it was difficult to elicit a robust optokinetic response. Results are discussed in relation to similar measurements in other species.

Animals↗
PubMedDate not supplied

Nystagmus responses in a group of normal humans during earth-horizontal axis rotation.

Horizontal eye movement responses to earth-horizontal yaw axis rotation were evaluated in 50 normal human subjects who were uniformly distributed in age (20-69 years) and equally divided by gender for each decade. The subjects were rotated with eyes open in the dark, using clockwise and counterclockwise 60 degree/s velocity trapezoids. The nystagmus slow component velocity (SCV) was analysed using four parameters: Amp, Bias, Mod and Tau. Amp and Tau characterize the canal-ocular reflex to constant velocity steps, while Mod and Bias characterize the "AC" and "DC" components of the otolith-ocular reflex. Results indicated that intersubject variability was larger than that seen in earth-vertical axis data. Tau depended significantly (p less than 0.05) upon subject gender, while Mod increased monotonically with age decade. Linear regression showed a positive correlation between pairs of SCV magnitude parameters (Amp, Bias and Mod), suggesting a common scaling effect. In addition, there was a negative correlation between the value of the decay time constant Tau and each of the three magnitude parameters. Thus, despite large intersubject variability, parameters that describe earth-horizontal yaw axis responses are loosely interrelated and some of them vary significantly with gender and age.

Adaptation, Physiological↗
PubMedDate not supplied

Visual-vestibular interaction in humans during earth-horizontal axis rotation.

Visual-vestibular interaction (VVI) using 60 degrees/s constant velocity earth horizontal axis (EHA) yaw rotation was measured in 7 human subjects. This so-called 'barbecue spit' rotation stimulated both the horizontal semicircular canals and the otolith organs. Subjects were tested with their eyes open in the dark (EOD), while fixating upon a target rotating with them (FIX), and while observing stationary optokinetic stripes (VVR). The resulting nystagmus slow component velocity (SCV) was analyzed. During EOD, subjects showed an exponentially decaying SCV response with a time constant of between 10 and 15 s that decayed to a non-zero baseline value (bias). Superimposed was a cyclic activity, modulation, whose period equalled the time for a complete revolution of the subject. During FIX, the average value of SCV was nearly zero indicating almost complete abolition of the exponential decay and bias components. The modulation component was reduced by half. During VVR, an exponential decay was observed in most subjects and the average value of the bias component nearly equalled that of the velocity of rotation. Modulation during VVR varied on a cycle-by-cycle basis. On average, the modulation component was nearly twice that for the EOD condition. We conclude that visual-vestibular interactions during EHA differ significantly from those during rotation about the vertical; specifically, there is a non-linear interaction between linear acceleration and optokinetic nystagmus.

Adult↗
PubMedDate not supplied

Quantifying ataxia: ideal trajectory analysis--a technical note.

We describe a quantitative method to assess repeated stair stepping stability. In both the mediolateral (ML) and anterioposterior (AP) directions, the trajectory of the subject's center of mass (COM) was compared to an ideal sinusoid. The two identified sinusoids were unique in each direction but coupled. Two dimensionless numbers-the mediolateral instability index (IML) and AP instability index (IAP)-were calculated using the COM trajectory and ideal sinusoids for each subject with larger index values resulting from less stable performance. The COM trajectories of nine nonimpaired controls and six patients diagnosed with unilateral or bilateral vestibular labyrinth hypofunction were analyzed. The average IML and IAP values of labyrinth disorder patients were respectively 127% and 119% greater than those of controls (p<0.014 and 0.006, respectively), indicating that the ideal trajectory analysis distinguishes persons with labyrinth disorder from those without. The COM trajectories also identify movement inefficiencies attributable to vestibulopathy.

Adult↗
PubMedDate not supplied

Multivariate vestibular testing: thresholds for bilateral Ménière's disease and aminoglycoside ototoxicity.

Although patient symptoms and an audiogram can typically identify the affected ear or ears in Ménière's disease, there are some cases where this differentiation is problematic. This paper concentrates on the sole use of vestibular test data to discriminate between unilateral and bilateral Ménière's disease. Patients that were known to have peripheral unilateral vestibular hypofunction (n = 104) were used as learning groups to define a region in multidimensional measurement space consisting of four vestibular test scores which summarized data from electronystagmography, sinusoidal harmonic acceleration, and computerized dynamic posturography tests. A multivariate boundary was created from the unilateral learning group that determined thresholds for identifying bilateral vestibular hypofunction. Patients with bilateral Ménière's disease (n = 23) and with bilateral ototoxicity (n = 19) were then used as test subjects to determine the sensitivity of the multivariate boundary. Results showed up to a increase in estimated test sensitivity (specificity = 95%) from 67%(current method)to 82%(new method)in identifying bilateral vestibular hypofunction.

Aminoglycosides↗
PubMedDate not supplied

Multivariate vestibular testing: laterality of unilateral Ménière's disease.

This paper discusses the use of vestibular testing to discriminate between right (n = 29) and left (n = 27) Ménière's disease. We examined reduced vestibular response (RVR), directional preponderance, and spontaneous and positional nystagmus measurements from electronystagmography, as well as the asymmetry measurements from the sinusoidal harmonic acceleration test, to determine whether multivariate logistic regression could improve upon the discrimination performance of RVR alone. We found that patients with a spontaneous or positional nystagmus often had a "recovery nystagmus", beating in the opposite direction of that predicted for an acute lesion. When present, the direction and magnitude of such nystagmus could be used in the classification algorithm to increase the discriminatory power over RVR alone, but in these patients the rotation test asymmetry measurements were rendered useless. In the absence of spontaneous or positional nystagmus, asymmetry measurements significantly enhanced right/left discrimination. Directional preponderance was insignificant in determining the side of lesion.

Electronystagmography↗
PubMedDate not supplied

Vestibular prostheses: the engineering and biomedical issues.

Currently available data demonstrate the need for balance prostheses. Recent technological and biomedical advances now make it feasible to produce miniaturized sensors, signal processors, electric stimulators, and stimulating electrodes that are roughly analogous to a cochlear implant but which provide information about self motion, instead of sound. Many areas require work before balance prostheses become a reality. Some of these include: the development of a motion sensor array, the conversion of the sensed motion into physiologically meaningful information, the delivery of the transformed information to the CNS, the training of vestibular deficient individuals to use the prosthesis, and developing methods to evaluate the efficacy of the device. In this "white paper", we consider these issues in the context of prototype baseline prosthetic devices.

Animals↗
PubMedDate not supplied

Recovery trajectories of vestibulopathic subjects after perturbations during locomotion.

We compared the mediolateral (M/L) responses to perturbations during locomotion of vestibulopathic (VP) subjects to those of controls. Eight subjects with unilateral vestibular loss (100% Reduced Vestibular Response from the caloric test) resulting from surgery for vestibular schwannoma and 11 controls were selected for this study. Despite their known vestibulopathy, all VP subjects scored within the normal range on computerized dynamic posturography Sensory Organization Tests. During gait, subjects were given surface perturbations of the right support-phase foot in two possible directions (forward-right and backward-left) at two possible magnitudes (5 and 10 cm) that were randomly mixed with trials having no perturbations. M/L stability was quantified by estimating the length of the M/L moment arm between the support foot and the trunk, and the M/L accelerations of the sternum and the head. The VP group had greater changes (p < 0.05) in their moment arm responses compared to controls. The number of steps that it took for the moment arm oscillations to return to normal and the variability in the moment arms were greater for the VP group. Differences in the sternum and head accelerations between VP and control groups were not as consistent, but there was a trend toward greater response deviations in the VP group for all 4 perturbation types. Increased response magnitude and variability of the VP group is consistent with an increase in their sensory noise of vestibular inputs due to the surgical lesion. Another possibility is a reduced sensitivity to motion inputs. This perturbation approach may prove useful for characterizing subtle vestibulopathies and similar changes in the human orientation mechanism after exposure to microgravity.

Acceleration↗
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The National Breast Screening Study: pre-recruitment sources of awareness in participants.

Data collected by questionnaire from 89,835 women on entry into 15 Canadian National Breast Screening Study (NBSS) centres reveal pre-recruitment sources of awareness: radio and television were reported by 30%; workplace 6%; friends 35%; physician 6%; and other by 23% of respondents. Personalized letters of invitation employed in 5 centres were an important source of awareness. In the age group recruited, 40-59 years, age had no influence on the source reported. However women with post-secondary school education were less likely to report radio and television as a source and more likely to report newspapers compared to women with less education. Women with only public school education were less likely to report the workplace as a source of awareness than women with post-secondary education. Recruitment strategies for screening programs may be more successful if publicity on radio and television is geared to women of lower educational status and if publicity in newspapers is geared to women of higher educational status, supplementing both with personalized letters of invitation.

Adult↗
PubMedDate not supplied

Cooperative trial of immunotherapy for nasopharyngeal carcinoma with transfer factor from donors with Epstein-Barr virus antibody activity.

A prospectively randomized, double-blind clinical trial was conducted to evaluate the effect of immunotherapy with transfer factor (TF) as an adjunct to radiotherapy of patients with stage III nasopharyngeal carcinoma (NPC). The TF was derived from normal young adults with a proven history of infectious mononucleosis and from normal blood donors with elevated antiviral capsid antigen antibody activity. TF prepared in this fashion was previously shown to convert the leukocytes of patients with NPC to a reactive state in vitro and when administered to NPC patients in vivo was associated with apparent slowing of tumor growth, marked lymphocytic infiltration of the tumor, and reconstitution of delayed cutaneous hypersensitivity reactions. From 1974 to 1977, 100 patients with NPC were entered in the study; one-half of the patients were treated with radiotherapy alone and one-half received radiotherapy and an 18-month course of TF immunotherapy. The patients were followed for at least 5 years. No significant difference in disease-free survival or survival was noted between the two groups of patients. The use of this particular preparation and dose schedule of TF in patients with NPC with regional disease was devoid of any anti-tumor activity.

Adult↗
PubMedDate not supplied

Tuberculosis screening in Boston's homeless shelters.

From February 1984, through March 1985, a total of 26 cases of tuberculosis (TB) were verified in homeless persons in Boston. Fifteen cases were resistant to isoniazid (INH) and streptomycin (SM) and were most likely the result of a common source exposure to one or possibly two highly infectious persons. Five cases without multiple drug resistant organisms occurred in persons with previous positive tuberculin tests who had not received adequate therapy for prophylaxis of infection or treatment of disease. The remaining cases were in persons with a previous negative skin test or no history of ever receiving a skin test. A screening program using chest roentgenograms (CXR), skin tests, and sputum smears led to the identification of several cases. CXR, the most readily accepted test, was the mechanism by which all cases detected through screening were identified. Detection and therapy of TB in the homeless, a group at particular risk for disease, required intensive intervention and outreach efforts.

Adult↗