Biomedical subjects

S P Cass

Publications and source records attributed to S P Cass.

At least 19 recordsLinked to original sources

PubMed2006

Vestibular inputs elicit patterned changes in limb blood flow in conscious cats.

Previous experiments have demonstrated that the vestibular system contributes to regulating sympathetic nervous system activity, particularly the discharges of vasoconstrictor fibres. In the present study, we examined the physiological significance of vestibulosympathetic responses by comparing blood flow and vascular resistance in the forelimb and hindlimb during head-up tilt from the prone position before and after the removal of vestibular inputs through a bilateral vestibular neurectomy. Experiments were performed on conscious cats that were trained to remain sedentary on a tilt table during rotations up to 60 deg in amplitude. Blood flow through the femoral and brachial arteries was recorded during whole-body tilt using perivascular probes; blood pressure was recorded using a telemetry system and vascular resistance was calculated from blood pressure and blood flow measurements. In vestibular-intact animals, 60 deg head-up tilt produced approximately 20% decrease in femoral blood flow and approximately 37% increase in femoral vascular resistance relative to baseline levels before tilt; similar effects were also observed for the brachial artery ( approximately 25% decrease in blood flow and approximately 38% increase in resistance). Following the removal of vestibular inputs, brachial blood flow and vascular resistance during head-up tilt were almost unchanged. In contrast, femoral vascular resistance increased only approximately 6% from baseline during 60 deg head-up rotation delivered in the first week after elimination of vestibular signals and approximately 16% in the subsequent 3-week period (as opposed to the approximately 37% increase in resistance that occurred before lesion). These data demonstrate that vestibular inputs associated with postural alterations elicit regionally specific increases in vascular resistance that direct blood flow away from the region of the body where blood pooling may occur. Thus, the data support the hypothesis that vestibular influences on the cardiovascular system serve to protect against the occurrence of orthostatic hypotension.

Animals↗

PubMed2006

Effects of postural changes and removal of vestibular inputs on blood flow to the head of conscious felines.

Prior studies have shown that removal of vestibular inputs produces lability in blood pressure during orthostatic challenges (Holmes MJ, Cotter LA, Arendt HE, Cass SP, and Yates BJ. Brain Res 938: 62-72, 2002; Jian BJ, Cotter LA, Emanuel BA, Cass SP, and Yates BJ. J Appl Physiol 86: 1552-1560, 1999). Furthermore, these studies led to the prediction that the blood pressure instability results in susceptibility for orthostatic intolerance. The present experiments tested this hypothesis by recording common carotid blood flow (CCBF) in conscious cats during head-up tilts of 20, 40, and 60 degrees amplitudes, before and after the surgical elimination of labyrinthine inputs through a bilateral vestibular neurectomy. Before vestibular lesions in most animals, CCBF remained stable during head-up rotations. Unexpectedly, in five of six animals, the vestibular neurectomy resulted in a significant increase in baseline CCBF, particularly when the laboratory was illuminated; on average, basal blood flow measured when the animals were in the prone position was 41 +/- 17 (SE) % higher after the first week after the lesions. As a result, even when posturally related lability in CCBF occurred after removal of vestibular inputs, blood supply to the head was not lower than when labyrinthine inputs were present. These data suggest that vestibular influences on cardiovascular regulation are more complex than previously appreciated, because labyrinthine signals appear to participate in setting basal rates of blood flow to the head in addition to triggering dynamic changes in the circulation to compensate for orthostatic challenges.

Animals↗

PubMed2003

Effects of postural changes and vestibular lesions on genioglossal muscle activity in conscious cats.

Previous studies in humans showed that genioglossal muscle activity is higher when individuals are supine than when they are upright, and prior experiments in anesthetized or decerebrate animals suggested that vestibular inputs might participate in triggering these alterations in muscle firing. The present study determined the effects of whole body tilts in the pitch (nose-up) plane on genioglossal activity in a conscious feline model and compared these responses with those generated by roll (ear-down) tilts. We also ascertained the effects of a bilateral vestibular neurectomy on the alterations in genioglossal activity elicited by changes in body position. Both pitch and roll body tilts produced modifications in muscle firing that were dependent on the amplitude of the rotation; however, the relative effects of ear-down and nose-up tilts on genioglossal activity were variable from animal to animal. The response variability observed might reflect the fact that genioglossus has a complex organization and participates in a variety of tongue movements; in each animal, electromyographic recordings presumably sampled the firing of different proportions of fibers in the various compartments and subcompartments of the muscle. Furthermore, removal of labyrinthine inputs resulted in alterations in genioglossal responses to postural changes that persisted until recordings were discontinued approximately 1 mo later, demonstrating that the vestibular system participates in regulating the muscle's activity. Peripheral vestibular lesions were subsequently demonstrated to be complete through the postmortem inspection of temporal bone sections or by observing that vestibular nucleus neurons did not respond to rotations in vertical planes.

Animals↗

PubMed2003

Use of electrical vestibular stimulation to alter genioglossal muscle activity in awake cats.

Prior work has shown that the vestibular system contributes to regulating activity of upper airway muscles including the tongue protruder muscle genioglossus. The goal of the present experiments was to determine whether electrical vestibular stimulation could potentially be used to alter genioglossal activity in awake animals. Six adult cats were instrumented for recording of EMG activity from genioglossus, abdominal musculature, and triceps. In addition, a silver ball electrode was implanted on the round window for stimulation of vestibular afferents. Subsequently, stimulation and recordings were conducted while animals were awake. In all cases, stimulation using single shocks or trains of pulses > 100 microA in intensity produced responses in all muscles, including genioglossus. The latency of the genioglossal response was approximately 12 msec, and delivering continuous current trains to the labyrinth chronically elevated the muscle's activity. Although a number of muscles were affected by the stimulus, animals experienced no obvious distress or balance disturbances. Vestibular stimulation remained effective in producing genioglossal responses until experiments were discontinued 1-2 months following onset. These data suggest that electrical vestibular stimulation could potentially be used therapeutically to alter upper airway muscle activity.

Animals↗

PubMed2002

Effects of lesions of the caudal cerebellar vermis on cardiovascular regulation in awake cats.

The vestibular system is known to participate in cardiovascular regulation during movement and postural alterations. The present study considered whether lesions of two regions of the posterior cerebellar vermis (the nodulus and uvula) that provide inputs to vestibular nucleus regions that affect control of blood pressure would alter cardiovascular responses during changes in posture. Blood pressure and heart rate were monitored in awake cats during nose-up tilts up to 60 degrees in amplitude before and following aspiration lesions of the nodulus or uvula; in most animals, cardiovascular responses were also recorded following the subsequent removal of vestibular inputs. Lesions of the nodulus or uvula did not affect baseline blood pressure or heart rate, although cardiovascular responses during nose-up tilts were altered. Increases in heart rate that typically occurred during 60 degrees nose-up tilt were attenuated in all three animals with lesions affecting both dorsal and ventral portions of the uvula; in contrast, the heart rate responses were augmented in the two animals with lesions mainly confined to the nodulus. Furthermore, following subsequent removal of vestibular inputs, uvulectomized animals, but not those with nodulus lesions, experienced more severe orthostatic hypotension than has previously been reported in cerebellum-intact animals with bilateral labyrinthectomies. These data suggest that the cerebellar nodulus and uvula modulate vestibulo-cardiovascular responses, although the two regions play different roles in cardiovascular regulation.

Animals↗

PubMed2001

Creating a stable tympanic membrane perforation using mitomycin C.

OBJECTIVE: To determine the ability of topically applied mitomycin C to create a stable tympanic membrane perforation. STUDY DESIGN AND SETTING: Twenty-four rats underwent subtotal removal of the tympanic membranes bilaterally. Forty ears received 0.2 mg/ml of mitomycin C. The remaining 8 received phosphate-buffered saline solution (control). Photographs taken every 3 to 5 days for 44 days were digitally scanned and computer analyzed to calculate the percentage of residual perforation. Application of solutions, photography, and data analysis were performed in a blinded fashion. RESULTS: The mitomycin C treated ears had delayed closure time and healing rate (from day 0 to 25) compared to the control group. All controls healed by day 14. By day 44, 92.5% of the mitomycin C treated ears healed. CONCLUSION: Mitomycin C prolongs the closure and healing rate of myringotomies in rat tympanic membranes. SIGNIFICANCE: Myringotomy with concurrent mitomycin C application may be useful for creating an animal model for chronic tympanic membrane perforation and should be tested in human beings as a method to maintain myringotomy patency for long-term ventilation.

Alkylating Agents↗

PubMed2001

An anatomic variant of the anterior inferior cerebellar artery in a patient with Ménière's disease.

OBJECTIVE: To describe an anatomic variant of the anterior inferior cerebellar artery in a patient with Ménière's disease. STUDY DESIGN: Retrospective case review and review of the literature. SETTING: Tertiary referral clinic. INTERVENTION: Vestibular nerve section and microvascular decompression. MAIN OUTCOME MEASURES: Audiometric testing and control of vertigo. RESULTS: The eighth nerve was identified via a retromastoid approach. The anterior inferior cerebellar artery was observed bisecting the eighth nerve. The vestibular nerve was sectioned, and microvascular decompression was performed on the cochlear division. At last follow-up, the patient had not experienced any vertiginous attacks but was observed to have progressive hearing loss. CONCLUSIONS: The course of the anterior inferior cerebellar artery is highly variable and difficult to predict. Knowing the potential paths is a necessity in performing posterior fossa surgery. Although the patient's vertigo was controlled by the vestibular nerve section, microvascular decompression of the cochlear nerve did not result in hearing improvement or stabilization. This case report does not support a benefit of microvascular decompression in Méniére's disease. Vestibular nerve section remains the authors' treatment of choice for controlling disabling vertigo caused by Ménière's disease.

Adult↗

PubMed2001

Effects of postural changes and vestibular lesions on diaphragm and rectus abdominis activity in awake cats.

Changes in posture can affect the resting length of the diaphragm, requiring alterations in the activity of both the abdominal muscles and the diaphragm to maintain stable ventilation. To determine the role of the vestibular system in regulating respiratory muscle discharges during postural changes, spontaneous diaphragm and rectus abdominis activity and modulation of the firing of these muscles during nose-up and ear-down tilt were compared before and after removal of labyrinthine inputs in awake cats. In vestibular-intact animals, nose-up and ear-down tilts from the prone position altered rectus abdominis firing, whereas the effects of body rotation on diaphragm activity were not statistically significant. After peripheral vestibular lesions, spontaneous diaphragm and rectus abdominis discharges increased significantly (by approximately 170%), and augmentation of rectus abdominis activity during nose-up body rotation was diminished. However, spontaneous muscle activity and responses to tilt began to recover after a few days after the lesions, presumably because of plasticity in the central vestibular system. These data suggest that the vestibular system provides tonic inhibitory influences on rectus abdominis and the diaphragm and in addition contributes to eliciting increases in abdominal muscle activity during some changes in body orientation.

Abdominal Muscles↗

PubMed2000

Responses of vestibular nucleus neurons to tilt following chronic bilateral removal of vestibular inputs.

Recordings were made from the vestibular nuclei of decerebrate cats that had undergone a combined bilateral labyrinthectomy and vestibular neurectomy 49-103 days previously and allowed to recover. Responses of neurons were recorded to tilts in multiple vertical planes at frequencies ranging from 0.05 to 1 Hz and amplitudes up to 15 degrees. Many spontaneously active neurons were present in the vestibular nuclei; the mean firing rate of these cells was 43 +/- 5 (SEM) spikes/s. The spontaneous firing of the neurons was irregular: the coefficient of variation was 0.86 +/- 0.14. The firing of 27% of the neurons was modulated by tilt. The plane of tilt that elicited the maximal response was typically within 25 degrees of pitch. The response gain was approximately 1 spikes/s/degree across stimulus frequencies. The response phase was near stimulus position at low frequencies, and lagged position slightly at higher frequencies (average of 35 +/- 9 degrees at 0.5 Hz). The source of the inputs eliciting modulation of vestibular nucleus activity during tilt in animals lacking vestibular inputs is unknown, but could include receptors in the trunk or limbs. These findings show that activation of vestibular nucleus neurons during vertical rotations is not exclusively the result of labyrinthine inputs, and suggest that limb and trunk inputs may play an important role in graviception and modulating vestibular-elicited reflexes.

Animals↗

PubMed2000

Short- and long-term outcomes of canalith repositioning for benign paroxysmal positional vertigo.

This is a prospective, nonrandomized study of the canalith repositioning procedure (CRP) for treatment of benign paroxysmal positional vertigo (BPPV). CRP was used to treat 168 patients with BPPV. Patient data were gathered by yearly telephone interviews to determine whether symptoms of position-induced vertigo had returned. After 1 or 2 treatment sessions 91.3% of patients reported complete symptom resolution. Average follow-up for the study population after the initial treatment was 26 months. A recurrence rate of 26.8% was found among those patients who initially reported resolution of symptoms after CRP. Application of recurrence data to a Kaplan-Meier estimation suggests a 15% recurrence rate per year of BPPV, with a 50% recurrence rate of BPPV at 40 months after treatment. There was no significant association between cure or recurrence rate and sex, age, duration of symptoms, presumed cause, or treating physician.

Adolescent↗

PubMed1999

Benign paroxysmal positional vertigo.

Benign paroxysmal positional vertigo is a common disorder of the inner ear that should be suspected in all patients with a history of positionally provoked vertigo. The condition appears to be caused by free-floating debris in the posterior semicircular canal. The diagnosis is confirmed by eliciting characteristic symptoms and signs during the Dix-Hallpike test. Although benign paroxysmal positional vertigo is usually a self-limited disorder, treatment with a specific bedside maneuver is effective and can provide the patient immediate and long-lasting relief. Although many patients with positionally provoked vertigo have typical benign paroxysmal positional vertigo, physicians should be aware of nonbenign variants.

Calcium Carbonate↗

PubMed1999

Approach to the vestibular patient and driving: A patient perspective.

OBJECTIVES: To learn about the impact of dizziness on driving from a patient perspective and to present an approach to the vestibular patient and driving. DESIGN: An anonymous questionnaire completed by 265 dizzy patients at 3 different centers. RESULTS: The participants were experienced drivers who needed to drive to function normally (83%). Those with constant or severe dizziness comprised a higher risk group of drivers. Although few had ever been warned not to drive, 52% said that if they were warned to stop driving, they would not. Most thought that it was the doctor's role to report unsafe drivers to the authorities (P < 0.001, chi2 = 87.2670). CONCLUSIONS: The diagnosis of a vestibular disorder should not alone be grounds to suspend a patient's driver's license. Legislation should be amended to better reflect the views of doctors and patients alike.

Adult↗

PubMed1999

Effects of bilateral vestibular lesions on orthostatic tolerance in awake cats.

Previous experiments in anesthetized or decerebrate cats showed that the vestibular system participates in adjusting blood pressure during postural changes. The present experiments tested the hypothesis that removal of vestibular inputs in awake cats would affect orthostatic tolerance. Before the lesion, blood pressure typically remained within 10 mmHg of baseline values during nose-up-pitch body rotations of up to 60 degrees in amplitude. In contrast, bilateral peripheral vestibular lesions altered the pattern of orthostatic responses in all animals, and blood pressure fluctuated >10 mmHg from baseline values during most 60 degrees nose-up tilts in five of six animals. The deficit in correcting blood pressure was particularly large when the animal also was deprived of visual cues indicating position in space. During this testing condition, either a decrease or increase in blood pressure >10 mmHg in magnitude occurred in >80% of tilts. The deficit in adjusting blood pressure after vestibular lesions persisted for only 1 wk, after which time blood pressure remained stable during tilt. These data show that removal of vestibular inputs alters orthostatic responses and are consistent with the hypothesis that vestibular signals are one of several inputs that are integrated to elicit compensatory changes in blood pressure during movement.

Animals↗

PubMed1999

Management of facial nerve injury due to temporal bone trauma.

OBJECTIVE: This article provides an overview of relevant data regarding the management of facial nerve injury due to temporal bone trauma. DATA SOURCES: Sources used were relevant English language clinical and basic science publications. STUDY SELECTION: A Medline search dating back to 1966 for articles concerning temporal bone trauma and facial nerve injury including both human and animal data was performed. Articles were included if they contained relevant data or were significant reviews on the subject. A retrograde bibliography search was then conducted to acquire any articles that may have been missed by the computerized search, including those papers published prior to 1966. DATA EXTRACTION: The data from each paper were reviewed individually. DATA SYNTHESIS: The data were not amenable to formal meta-analysis or valid data summarization. CONCLUSIONS: Patients who should not require surgical intervention include those who have: documented normal facial nerve function after injury regardless of progression, presentation with incomplete facial nerve paralysis with no progression to complete paralysis, and degeneration <95% on ENoG. The remaining patients presumably have a poorer prognosis for return of facial nerve function although it remains unclear exactly how poor the return of function will be. Decompression surgery likely has a beneficial effect if performed within 14 days of injury, so those patients with expected poor natural outcomes may be offered this intervention. Late decompression surgery is not recommended. Late exploratory surgery is recommended only in those patients who do not experience adequate recovery of facial nerve function and likely require nerve repair. Despite the availability of a relatively large volume of published data, there remain many unanswered questions.

Algorithms↗

PubMed1998

Treatment of benign positional vertigo using heels-over-head rotation.

Particle repositioning, using either bedside techniques or whole-body manipulation devices, has been used effectively to treat benign positional vertigo (BPV). We assessed the efficacy of particle repositioning using a device designed and built specifically to treat BPV that rotated patients 360 degrees heels-over-head in their sagittal body plane while their heads were turned to align the posterior semicircular canal with the plane of rotation. Eye movements were monitored during the maneuver by an infrared video recording system that allowed subsequent review of the induced nystagmus. Our results indicate that 1) heels-over-head rotation is an extremely efficacious procedure for treating patients with BPV and 2) the pattern of nystagmus during repositioning is consistent with the theory that free-floating debris is highly likely to account for BPV.

Adult↗

PubMed1998

A review of balance instruments for older adults.

OBJECTIVE: The purpose of this article is to review balance instruments developed within the past 10 years that can be used in the clinic or home environment. The use of such instruments may assist in identifying older adults who are at risk for falling, a major problem that can result in impaired function and loss of independence. METHOD: Six instruments were reviewed: the Berg Balance Scale (Berg), the Clinical Test of Sensory Interaction and Balance (CTSIB), the Functional Reach Test, the Tinetti Balance Test of the Performance-Oriented Assessment of Mobility Problems (Tinetti), the Timed "Up and Go" Test (TU&GT), and the Physical Performance Test (PPT). Considered were what aspects of balance are assessed, time needed to administer the instrument, tools or equipment needed, evidence of reliability and validity, advantages and disadvantages, and the target population. RESULTS: The Berg, Tinetti, and PPT measure a variety of aspects of balance, whereas the Functional Reach, TU&GT, and CTSIB measure more narrow aspects of balance. All six instruments have been used with older adults and do not require much equipment. The instruments differ in their reliability and validity. CONCLUSION: Familiarity with balance instruments can be helpful in selecting the one most appropriate for clinical setting and clients in order to institute appropriate prevention programs, such as environmental modifications and lifestyle adaptations.

Accidental Falls↗

PubMed1997

The effect of acidic fibroblast growth factor and live yeast cell derivative on tympanic membrane regeneration in a rat model.

The current treatment of choice for chronic tympanic membrane perforations is surgery. Recent studies using various polypeptide growth factors to accelerate closure of tympanic membrane perforations in model systems have produced mixed results. This study evaluates the effect of acidic fibroblast growth factor (AFGF) and live yeast cell derivative (LYCD) on the rate of healing of acute tympanic membrane perforations in a rat model. Thirty-seven rats had both ears separately randomized in a blinded fashion to receive AFGF in one of three concentrations, LYCD, or a control solution. The rats initially underwent subtotal removal of the tympanic membranes bilaterally. Solutions were applied to the randomized ears daily for 3 days, starting at the time of the surgical perforation. The ears were photographed every 3 to 8 days for 35 days. The photographs were digitally scanned and a computer analysis was used to calculate the percentage of residual perforation. No significant difference in the rate of healing was observed for ears treated with AFGF or LYCD versus the controls. Given the potential advantages of medical treatment of tympanic membrane perforations and the established efficacy of growth factors in other model systems, however, further research is warranted.

Animals↗

PubMed1997

Migraine-related vestibulopathy.

Migraine has been associated with specific vestibular disorders, including benign paroxysmal vertigo of childhood and benign recurrent vertigo in adults. Migraine may also play a role in chronic nonspecific vestibulopathy. Because scant data exist that describe the clinical findings and vestibular function abnormalities in suspected migraine-related vestibulopathy, we reviewed the history, physical examination, vestibular tests (electronystagmography, rotational chair, posturography), and response to treatment of 100 patients with diagnoses of migraine-related vestibulopathy. Dominant clinical features included chronic movement-associated dysequilibrium, unsteadiness, space and motion discomfort, and occasionally, episodic vertigo as an aura prior to headache, or true vertigo without headache. Common vestibular test abnormalities included a directional preponderance on rotational testing, unilateral reduced caloric responsiveness, and vestibular system dysfunction patterns on posturography. Treatment was usually directed at the underlying migraine condition by identifying and avoiding dietary triggers and prescribing prophylactic anti-migraine medications. Symptomatic relief was also provided using anti-motion sickness medications, vestibular rehabilitation, and pharmacotherapy directed at any associated anxiety or panic disorder.

Adolescent↗