Head and Body Dyskinesia During Gait in Tactical Athletes With Vestibular Deficit Following Concussion

Background: Vestibular deficit is common following concussion and may affect gait. The purpose of this study was to investigate differences in head and pelvic center of mass (COM) movement during gait in military tactical athletes with and without concussion-related central vestibular impairment.

Material and Methods: 24 patients with post-concussion vestibular impairment (20 males, 4 females; age: 31.7 ± 7.9 years; BMI: 27.3 ± 3.3) and 24 matched controls (20 males, 4 females; age: 31.8 ± 6.4 years; BMI: 27.2 ± 2.6) were included in the analyses. Three-dimensional head and pelvic displacement and velocities were collected at a 1.0 m/s standardized treadmill walking speed and assessed using Statistical Parametric Mapping t-tests. Maximum differences (d_max) between groups were reported for all significant kinematic findings.

Results: The Vestibular group demonstrated significantly diminished anteroposterior head excursions (d_max = 2.3 cm, p = 0.02) and slower anteroposterior (d_max = 0.37 m/s, p = 0.01), mediolateral (d_max = 0.47 m/s, p = 0.02) and vertical (d_max = 0.26 m/s, p < 0.001) velocities during terminal stance into pre-swing phases compared to the Control group. Vertical pelvic excursion was significantly increased in midstance (d_max = 2.4 cm, p = 0.03) and mediolaterally during pre- to initial-swing phases (d_max = 7.5 cm, p < 0.001) in the Vestibular group. In addition, pelvic velocities of the Vestibular group were higher mediolaterally during midstance (d_max = 0.19 m/s, p = 0.02) and vertically during post-initial contact (d_max = 0.14 m/s, p < 0.001) and pre-swing (d_max = 0.16 m/s, p < 0.001) compared to the Control group.

Significance: The Vestibular group demonstrated a more constrained head movement strategy during gait compared with Controls, a finding that is likely attributed to a neurological impairment of visual-vestibular-somatosensory integration.

Improvements in dizziness and imbalance results from using a multi disciplinary and multi sensory approach to Vestibular Physical Therapy - a case study

This paper discusses a case study of a 41-year-old active duty male service member who sustained head trauma from a motorcycle accident and underwent multidisciplinary vestibular physical therapy rehabilitation. He was initially treated with traditional physical therapy applications of treadmill walking and standing balance with some symptom improvements, but was not able to maintain a running speed that would allow him to return to full active duty status. Further treatment utilizing a Computer Assisted Rehabilitation Environment was performed in order to increase level of difficulty and further enhance function. This treatment is able to elicit vestibular deficits seen in the community as it requires subjects to walk and balance while performing tasks within a virtual scenario incorporating platform motion, visual surround and flow, and cognitive processing. After 6 weeks of therapy, twice weekly, improvements in clinical vestibular measures were observed as well as walking speed and patient confidence. The patient was able to return to full duty after treatment. This case study provides supportive evidence that multidimensional tasking in a virtual environment provides a safe but demanding form of vestibular therapy for patients needing more challenging tasks than those provided with traditional therapy techniques. Those persons requiring higher levels of performance before returning to full duty (e.g., pilots, special operators, etc.) may find this type of therapy beneficial.

Head stabilization measurements as a potential evaluation tool for comparison of persons with TBI and vestibular dysfunction with healthy controls

A large percentage of persons with traumatic brain injury incur some type of vestibular dysfunction requiring vestibular physical therapy. These injuries may affect the natural ability to stabilize the head while walking. A simple method of utilizing motion capture equipment to measure head movement while walking was used to assess improvements in head stabilization of persons undergoing computerized vestibular physical therapy and virtual reality training for treatment of their vestibular problems. Movement data from the head and sacrum during gait were obtained over several visits and then analyzed to determine improved oscillatory head movement relative to the sacrum. The data suggest that, over time with treatment, head stabilization improves and moves toward a pattern similar to that of a healthy control population. This simple analysis of measuring head stability could be transferred to smaller, portable systems that are easily utilized to measure head stability during gait for use in gait assessment and physical therapy training.

Emerging Concepts in Migraine-Associated Dizziness

Program Description:

Over the last several years migraine has become an increasingly common diagnosis in otolaryngology. Despite the increasing frequency of this diagnosis, little is understood about how the pathophysiology of migraine impacts a range of otolaryngologic diagnoses. Nevertheless specialists in our field are increasingly being called on to diagnose and treat migraines. In this miniseminar we will discuss the role of migraines in hearing and balance disorders and examine the critical criteria that are helpful in distinguishing this disorder from other otologic diagnoses. We will examine the newest diagnostic and treatment modalities and how to apply these in common practice.

Educational Objectives:

1) Diagnose classical migraine associated dizziness. 2) Implement current treatment modalities for migraine, including medicines, therapy, and Botox treatment. 3) Discuss the evidence to support a continuum between migraines and Ménière’sdisease.

International guidelines for education in vestibular rehabilitation therapy

The Barany Society Ad Hoc Committee on Vestibular Rehabilitation Therapy has developed guidelines for developing educational programs for continuing education. These guidelines may be useful to individual therapists who seek to learn about vestibular rehabilitation or who seek to improve their knowledge bases. These guidelines may also be useful to professional organizations or therapists who provide continuing education in vestibular rehabilitation. We recommend a thorough background in basic vestibular science as well as an understating of current objective diagnostic testing and diagnoses, understanding of common tests used by therapists to assess postural control, vertigo and ability to perform activities of daily living. We recommend that therapists be familiar with the evidence supporting efficacy of available treatments as well as with limitations in the current research.

Vestibular physical therapy intervention: utilizing a computer assisted rehabilitation environment in lieu of traditional physical therapy

Advanced technology such as virtual reality or immersive environments increases the complexities and challenges therapists can impose on their patients. In this study, four patients with mild traumatic brain injury utilized a Computer Assisted Rehabilitation Environment (CAREN) in place of traditional vestibular physical therapy. Patients visited the CAREN twice weekly for 6 weeks. Therapy sessions included a variety of applications that tasked the cognitive and physical capabilities of individual patients. After the 6 weeks, all patients showed improvement on balance, gait and visual measures. Virtual reality based therapy is an engaging and effective tool to treat patients with deficiencies related to a prior brain injury.

Challenges and opportunities in managing the dizzy older adult

Balance disorders are common in elderly people, not only resulting in distressing sensations but also leading to reduced activity levels and quality of life. It has been estimated that 30% of elderly patients experience a balance disorder. Managing these disorders is a substantial challenge for patients and their caregivers and physicians. Moreover, abnormalities in balance are associated with falls, a major cause of morbidity and mortality for elderly people. Management is complicated by the inherent difficulties in assessing the generic complaint of dizziness, as well as the likelihood of multiple, often nonvestibular causes. The authors of this mini-seminar review both vestibular and nonvestibular causes of balance disorders in elderly people, emphasizing practical therapeutic maneuvers that can be used.

Prognostic assessments of medical therapy and vestibular testing in post-traumatic migraine-associated dizziness patients

OBJECTIVE

The aim of this study was to characterize our clinical population of patients suffering with post-traumatic migraine-associated dizziness (PTMAD) and determine any associations with medical interventions and vestibular testing metrics to help predict response to treatments.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary referral center.

SUBJECTS AND METHODS

The electronic medical records of 83 patients presenting to a tertiary referral center who were given a diagnosis of PTMAD and who had been treated were retrospectively reviewed. General characteristics, clinical treatment, pre- and post-vestibular therapy testing metrics, and success and failure outcomes were assessed. Patients were assigned into responder and nonresponder groups related to their headaches and evaluated at two specific time points. Medication failures and vestibular test metrics were compared to identify and predict clinical outcomes.

RESULTS

Seventy-two of 82 patients (88%) were analyzed at two time points. Use of verapamil, topiramate, gabapentin, amitryptiline, and valproic acid showed no comparative treatment benefit in responders compared to nonresponders (P = 0.294). Findings associated with successful treatments include response to initial medication (P = 0.001), final dynamic gait index (DGI) scores (P = 0.029), final vertical dynamic visual acuity test (DVAT) scores (up, 0.007; down, 0.006), and both final and change in computerized dynamic posturography-sensory organization test (CDP-SOT) scores (P = 0.001, P = 0.032). The antipsychotic quetiapine was specifically associated with outcome failures (P = 0.003).

CONCLUSION

Specific prophylactic antimigraine medications were not associated with improved outcomes in PTMAD patients. Initial clinical responses and vestibular test metrics may guide physicians to predict successful outcomes.

Early vestibular physical therapy rehabilitation for Meniere's disease

Meniere disease includes symptoms of fluctuating hearing loss, tinnitus, and subjective ear fullness accompanied by episodic vertigo. Along with these symptoms, patients with chronic Meniere often develop symptoms of disequilibrium and unsteadiness that extend beyond the episodic attacks and contribute to the total disability and reduced quality of life attributed to the disease. Vestibular rehabilitation physical therapy has been used only after vestibular ablation has stabilized the vestibular loss, and for patients stably managed on medical therapy who exhibit no fluctuation in symptoms. This article reviews the data substantiating current applications of vestibular therapy, including improvements in subjective and objective balance outcome measures, and explores the possible extension of vestibular rehabilitation to treatment of patients exhibiting continued fluctuating vestibular loss.

International survey of vestibular rehabilitation therapists by the Barany Society Ad Hoc Committee on Vestibular Rehabilitation Therapy

The goal of this study was to determine how occupational and physical therapists learn about vestibular rehabilitation therapy, their educational backgrounds, referral patterns, and their ideas about entry-level and advanced continuing education in vestibular rehabilitation therapy. The Barany Society Ad Hoc Committee for Vestibular Rehabilitation Therapy invited therapists around the world to complete an E-mail survey. Participants were either known to committee members or other Barany Society members, known to other participants, identified from their self-listings on the Internet, or volunteered after reading notices published in publications read by therapists. Responses were received from 133 therapists in 19 countries. They had a range of educational backgrounds, practice settings, and referral patterns. Few respondents had had any training about vestibular rehabilitation during their professional entry-level education. Most respondents learned about vestibular rehabilitation from continuing education courses, interactions with their colleagues, and reading. All of them endorsed the concept of developing standards and educating therapists about vestibular anatomy and physiology, vestibular diagnostic testing, vestibular disorders and current intervention strategies. Therefore, the Committee recommends the development of international standards for education and practice in vestibular rehabilitation therapy.

Blunt and blast head trauma: different entities

Mild traumatic brain injury (mTBI) caused by blast-related and blunt head trauma is frequently encountered in clinical practice. Understanding the nuances between these two distinct types of injury leads to a more focused approach by clinicians to develop better treatment strategies for patients. In this study, we evaluated two separate cohorts of mTBI patients to ascertain whether any difference exists in vestibular-ocular reflex (VOR) testing (n = 55 enrolled patients: 34 blunt, 21 blast) and vestibular-spinal reflex (VSR) testing (n = 72 enrolled patients: 33 blunt, 39 blast). The VOR group displayed a preponderance of patients with blunt mTBI, demonstrating normal to high-frequency phase lag on rotational chair testing, whereas patients experiencing mTBI from blast-related causes revealed a trend toward low-frequency phase lag on evaluation. The VSR cohort showed that patients with posttraumatic migraine-associated dizziness tended to test higher on posturography. However, an indepth look at the total patient population in this second cohort reveals that a higher percentage of blast-exposed patients exhibited a significantly increased latency on motor control testing as compared to patients with blunt head injury (p < .02). These experiments identify a distinct difference between blunt-injury and blast-injury mTBI patients and provide evidence that treatment strategies should be individualized on the basis of each mechanism of injury.

To Investigate the Influence of Acute Vestibular Impairment following Mild Traumatic Brain Injury on Subsequent Ability to Remain on Activity Duty 12 Months Later

The objective of this study was to investigate the relationship between acute vestibular dysfunction as measured by the Dizziness Handicap Inventory and the Dynamic Visual Acuity Test and the ability to remain on active duty status in the U.S. military 1 year after mild traumatic brain injury. This longitudinal prospective study was conducted by the Defense and Veterans Brain Injury Clinic at Marine Corp Base, Camp Pendleton, California. Participants (n = 47, controls = 44) were referrals to the clinic who had sustained a mild traumatic brain injury and were initially seen within 6 days of injury, then weekly for 1 month, and for follow-up 12 months later. The results demonstrated that those on active duty at 12 months were older in age, had more years of service, and had no history of psychiatric illness or apparent secondary gain issues. Acute vestibular dysfunction and demographic and injury variables were not significantly correlated or predictive of work status at 12 months.

Posttraumatic balance disorders

Head trauma is being more frequently recognized as a causative agent in balance disorders. Most of the published literature examining traumatic brain injury (TBI) after head trauma has focused on short-term prognostic indicators and neurocognitive disorders. Few data are available to guide those individuals who see patients with balance disorders secondary to TBI. Our group has previously examined balance disorders after mild head trauma. In this study, we study all classes of head trauma. We provide a classification system that is useful in the diagnosis and management of balance disorders after head trauma and we examine treatment outcomes. As dizziness is one of the most common outcomes of TBI, it is essential that those who study and treat dizziness be familiar with this subject.

Delivery of drugs to the inner ear

PURPOSE OF REVIEW

Inner ear delivery of medicines has been a rapidly expanding field in otolaryngology. This technique provides a minimally invasive way of managing a number of otolaryngologic diagnoses and promises to provide a therapeutic option for previously untreatable disorders. The purpose of this review is to examine the literature that has been published recently (since January of 2005) in this field and to explore how this new literature has impacted on current practices.

RECENT FINDINGS

While there was a significant volume of work done in this area from 1995 to 2004, publication in this area has slowed considerably. The literature focuses on two areas: the treatment of Ménière's disease with gentamicin and the treatment of sudden sensorineural hearing loss with steroids. The most promising area in this field, which is the development of new medicines to treat a variety of disorders, has not progressed over the last 2 years.

SUMMARY

Recent peer-reviewed publications have not had a significant impact on the transtympanic treatment of Ménière's disease or sudden sensorineural hearing loss. We will review the current practices in these two areas, discuss the newest developments and examine how we can progress the field over the next several years.

Active head movements facilitate compensation for effects of prism displacement on dynamic gait12

Study design: Four groups, between-subjects study. Objectives: To investigate the effects of exercise on adaptation of normal subjects who had been artificially spatially disoriented. Background: Many patients referred for rehabilitation experience sensory changes, due to age or disease processes, and these changes affect motor skill. The best way to train patients to adapt to these changes and to improve their sensorimotor skills is unclear. Using normal subjects, we tested the hypothesis that active, planned head movement is needed to adapt to modified visual input. Methods and measures: Eighty male and female subjects who had normal balance on computerized dynamic posturography (CDP) and the dynamic gait index (DGI), were randomly assigned to four groups. All groups donned diagonally shift lenses and were again assessed with CDP and DGI. The four groups were then treated for 20 min. Group 1 (control group) viewed a video, Group 2 performed exercise that involved translating the entire body through space, but without separate, volitional head movement, Group 3 performed exercises which all incorporated volitional, planned head rotations, and Group 4 performed exercises that involved translating the body (as in Group 2) and incorporated volitional, planned head motion (as in Group 3). All subjects were post-tested with CDP and DGI, lenses were removed, and subjects were retested again with CDP and DGI. Results: The groups did not differ significantly on CDP scores but Groups 3 and 4 had significantly better DGI scores than Groups 1 and 2. Conclusions: Active head movement that is specifically planned as part of the exercise is more effective than passive attention or head movements that are not consciously planned, for adapting to sensorimotor change when it incorporates active use of the changed sensory modality, in this case head motion.

Active head movements facilitate compensation for effects of prism displacement on dynamic gait

STUDY DESIGN

Four groups, between-subjects study.

OBJECTIVES

To investigate the effects of exercise on adaptation of normal subjects who had been artificially spatially disoriented.

BACKGROUND

Many patients referred for rehabilitation experience sensory changes, due to age or disease processes, and these changes affect motor skill. The best way to train patients to adapt to these changes and to improve their sensorimotor skills is unclear. Using normal subjects, we tested the hypothesis that active, planned head movement is needed to adapt to modified visual input.

METHODS AND MEASURES

Eighty male and female subjects who had normal balance on computerized dynamic posturography (CDP) and the dynamic gait index (DGI), were randomly assigned to four groups. All groups donned diagonally shift lenses and were again assessed with CDP and DGI. The four groups were then treated for 20 min. Group 1 (control group) viewed a video, Group 2 performed exercise that involved translating the entire body through space, but without separate, volitional head movement, Group 3 performed exercises which all incorporated volitional, planned head rotations, and Group 4 performed exercises that involved translating the body (as in Group 2) and incorporated volitional, planned head motion (as in Group 3). All subjects were post-tested with CDP and DGI, lenses were removed, and subjects were retested again with CDP and DGI.

RESULTS

The groups did not differ significantly on CDP scores but Groups 3 and 4 had significantly better DGI scores than Groups 1 and 2.

CONCLUSIONS

Active head movement that is specifically planned as part of the exercise is more effective than passive attention or head movements that are not consciously planned, for adapting to sensorimotor change when it incorporates active use of the changed sensory modality, in this case head motion.

The role of vestibular rehabilitation in the treatment of Meniere's disease

OBJECTIVE

To study the role of vestibular rehabilitation is treating patients with Meniere's disease.

METHODS

We examined all Meniere's patients presenting to our tertiary care specialized vestibular clinic during a 1-year period. All patients underwent a standardized history and physical examination, a complete auditory-vestibular test battery, and a set of physical therapy tools to measure balance function.

RESULTS

A subset of patients suffered from disequilibrium or unsteadiness between attacks. Once the acute fluctuating symptoms of Meniere's were controlled in this group of individuals, all of them underwent vestibular physical therapy and demonstrated significant improvement in balance function on both objective and self-report tests.

CONCLUSIONS

Due to the fluctuating nature of the disorder, vestibular physical therapy has had a limited role in the treatment of Meniere's disease. In general, rehabilitation has been used only as a postoperative treatment for the acute vertigo seen after vestibular neurectomy or labyrinthectomy. This is the first report advocating the role of vestibular physical therapy in a group of patients receiving medical therapy of intraear medicines (other that gentamicin).

Vestibular rehabilitation for migraine-associated dizziness

The purpose of this study was to investigate the effects of a vestibular rehabilitation program on patients with the diagnosis of migraine-associated dizziness. Subjects were placed in four groups as follows: idiopathic migraine-associated dizziness; idiopathic migraine-associated dizziness and associated benign positional vertigo; posttraumatic migraine-associated dizziness; and posttraumatic migraine-associated dizziness and benign positional vertigo. Vestibular rehabilitation therapy was administered to all patients. Criterion measurements included the dizziness handicap inventory, activities-specific balance confidence scale, computerized dynamic posturography performance, and dynamic gait index. After vestibular physical therapy, all subjects showed significant improvement in the dizziness handicap, activities-specific balance confidence, dynamic gait, and computerized dynamic posturography measures. Patients with migraine-associated dizziness can benefit from physical therapy intervention. The results of this study are important in considering the approach to vertiginous migraine patients with and without head injury.

Sustained-release devices in inner ear medical therapy

Inner ear medical therapy has been gaining increasing popularity during the last 2 decades. Despite the increased use of this therapy,basic questions regarding this type of treatment have not been answered. The authors have used a variety of sustained-release devices in the laboratory to begin to answer some of these basic questions. This article discusses the results of this work and the application and use of sustained-release devices in patients.

Characterizing and treating dizziness after mild head trauma

OBJECTIVE

The objectives of this study were to characterize patterns of dizziness seen after mild head trauma and to examine the diagnosis and treatment of this disorder.

STUDY DESIGN

Prospective patient registry.

SETTING

Tertiary referral center.

PATIENTS

Fifty-eight cases of active duty and retired military personnel who sustained mild head trauma and had resultant dizziness.

INTERVENTIONS

Vestibular evaluation, characterization by group, and treatment.

MAIN OUTCOME MEASURES

Outcome measures include characterization of diagnosis types, patient distribution by diagnosis type, and patient outcome.

RESULTS

Individuals suffering from dizziness after mild head injury were divided into three diagnostic groups. Forty-one percent of the individuals suffered from posttraumatic vestibular migraines, 28% of the individuals had posttraumatic positional vertigo, and 19% of the individuals were classified as posttraumatic spatial disorientation. The remaining 12% of the patients could not be characterized. The positional group had objective physical examination findings, which cleared with treatment in all cases. The migraine group of patients and the disorientation group of patients had distinct abnormalities of the vestibulo-ocular reflex (VOR) and the vestibulo-spinal reflex (VSR). Eighty-four percent of the migraine group demonstrated an improvement of these test results as compared with 27% of the disorientation group. Mean time to return to work was less than 1 week for the positional group, 3.8 weeks for the migraine group, and greater than 3 months for the disorientation group.

CONCLUSIONS

Using our patient registry of individuals suffering from dizziness after mild head trauma, we were able to characterize the majority of these cases into one of three more specific diagnostic groups. We present diagnostic criteria, suggested treatment guidelines, and our prognostic data.

Sustained-release delivery of leupeptin in the chinchilla: hearing results

Transtympanic medical therapy is becoming an increasingly popular modality for the treatment of "inner-ear disorders." While investigators continue to examine the best dosing paradigms for gentamicin in the treatment of Ménière's disease and for steroids in the treatment of hearing loss, they have also begun to focus on the use of other agents. In particular, transtympanic therapy has been advocated as a plausible route for the treatment of tinnitus. Transtympanic therapy for tinnitus is not new, and a number of groups have reported success in the past. Despite this success, a number of laboratories have been focusing on newer agents that might yield higher success rates in the treatment of tinnitus and other inner-ear disorders. Many of these agents could have systemic side effects when delivered in high enough doses; therefore, they are ideal candidates for transtympanic administration. The goal of this study is to begin to define the effects of one of these agents--leupeptin, a calpain antagonist--on the normal inner ear of an animal model. In this investigation, we demonstrate the effects of sustained-release delivery of leupeptin (2.5 micrograms/ml) on the hearing of chinchillas. The medicine produced no hearing loss at the early time points but did produce some hearing loss at later time points. We discuss these results and begin to outline the next steps in the investigation of this agent.

Ras-dependent pathways induce obstructive hypertrophy in echo-selected transgenic mice

To overcome the genetic and interindividual variability frequently noted in complex phenotypes, we used echocardiographic selection to develop a substrain of myosin light chain (MLC)-Ras (RAS) transgenic mice with an enhanced ventricular hypertrophic phenotype. These echo-selected mice were then compared with wild-type (WT) animals and a pressure overload hypertrophy model (transverse aortic constriction; TAC). Echocardiography demonstrated increased wall thickness in RAS compared with the other groups. We developed novel miniaturized physiological technology to quantitatively identify in vivo intraventricular gradients; increased systolic Doppler velocity was seen in the left ventricle (LV) in 69% of RAS vs. none of WT or TAC. Intracavitary pressure gradients were present in 3 of 10 RAS vs. none of TAC or WT. Passive diastolic LV stiffness was not different among the three groups. Myofibrillar disarray was present in all RAS animals and was significantly more extensive (21.7% area fraction) than in TAC (1.5%) or WT (0.0%). RAS mice had selective induction of natriuretic peptide genes in the LV, a pattern distinct from that induced by pressure overload. Juvenile mortality was significantly increased in the offspring of echo-selected RAS parents. We conclude that adaptation of echocardiography to the mouse permits selection for cardiac phenotypes, and that selectively inbred MLC-Ras transgenic mice faithfully reproduce the molecular, physiological, and pathological features of human hypertrophic cardiomyopathy (HCM). Because previous studies support the concept that hypertrophy in human HCM is secondary to dysfunction created by sarcomeric protein mutations, the current studies suggest that Ras-dependent pathways might play a similar role in forms of human HCM.

Point mutations in human beta cardiac myosin heavy chain have differential effects on sarcomeric structure and assembly: an ATP binding site change disrupts both thick and thin filaments, whereas hypertrophic cardiomyopathy mutations display normal assembly

Hypertrophic cardiomyopathy is a human heart disease characterized by increased ventricular mass, focal areas of fibrosis, myocyte, and myofibrillar disorganization. This genetically dominant disease can be caused by mutations in any one of several contractile proteins, including beta cardiac myosin heavy chain (beta MHC). To determine whether point mutations in human beta MHC have direct effects on interfering with filament assembly and sarcomeric structure, full-length wild-type and mutant human beta MHC cDNAs were cloned and expressed in primary cultures of neonatal rat ventricular cardiomyocytes (NRC) under conditions that promote myofibrillogenesis. A lysine to arginine change at amino acid 184 in the consensus ATP binding sequence of human beta MHC resulted in abnormal subcellular localization and disrupted both thick and thin filament structure in transfected NRC. Diffuse beta MHC K184R protein appeared to colocalize with actin throughout the myocyte, suggesting a tight interaction of these two proteins. Human beta MHC with S472V mutation assembled normally into thick filaments and did not affect sarcomeric structure. Two mutant myosins previously described as causing human hypertrophic cardiomyopathy, R249Q and R403Q, were competent to assemble into thick filaments producing myofibrils with well defined I bands, A bands, and H zones. Coexpression and detection of wild-type beta MHC and either R249Q or R403Q proteins in the same myocyte showed these proteins are equally able to assemble into the sarcomere and provided no discernible differences in subcellular localization. Thus, human beta MHC R249Q and R403Q mutant proteins were readily incorporated into NRC sarcomeres and did not disrupt myofilament formation. This study indicates that the phenotype of myofibrillar disarray seen in HCM patients which harbor either of these two mutations may not be directly due to the failure of the mutant myosin heavy chain protein to assemble and form normal sarcomeres, but may rather be a secondary effect possibly resulting from the chronic stress of decreased beta MHC function.

Transthoracic echocardiography in models of cardiac disease in the mouse

BACKGROUND

Transthoracic echocardiography (M-mode and Doppler) offers a noninvasive approach for in vivo evaluation of the mouse heart. The present study examines its usefulness for assessing the morphological/functional phenotype of the left ventricle (LV) in several transgenic and surgical murine models of cardiac disease.

METHODS AND RESULTS

Observations were made in 83 intact, anesthetized mice. In mice with a surgical arteriovenous fistula, volume overload and LV dilation were detected. In normal mice, echocardiographic indexes of increased contractility (dobutamine) were confirmed by LV dP/dtmax. In transgenic mice with overexpression of the beta 2-adrenergic receptor, heart rate and mean velocity of circumferential fiber shortening were increased, indicating enhanced contractility. In colony screening of transgenic mice overexpressing the H-ras gene, 45% had increased LV wall thickness (> 0.9 mm), and those showing a striking increase were selected for breeding. In mice with LV hypertrophy (aortic constriction) and normal mice, the actual LV mass determined by echocardiography correlated well (r = .93), and 95% confidence limits were determined. The maximum intraobserver and interobserver coefficients of variation for M-mode data were 0.03 +/- 0.29 mm (+/- 2 SD), < 10% for LV internal dimensions but 27% to 30% for wall thickness.

CONCLUSIONS

These studies provide the first application of transthoracic echocardiography for morphological/functional characterization of the cardiac phenotype in transgenic and surgical murine models, including (1) high reliability for detecting LV chamber dilation and function; (2) reliability (and its limits) for determining abnormal LV wall thickness and LV mass; (3) identification of marked, sometimes asymmetrical, hypertrophy in a transgenic model of hypertrophic cardiomyopathy; and (4) usefulness for transgenic colony screening to identify markedly abnormal phenotypes.

Strategies for studying cardiovascular phenotypes in genetically manipulated mice

Unraveling the pathogenesis of complex cardiovascular diseases, such as hypertension, requires the development of in vivo animal model systems. Although large-animal models have long served as the gold standard, recent advances in transgenic and gene-targeting approaches, mouse genetics, and microsurgical technology are initiating a revolution that has led to the unexpected coupling of in vivo molecular physiology with genetically engineered mice. This article discusses the design of strategies to study complex cardiovascular phenotypes in genetically modified mice, including both transgenic and gene-targeted animals. At this time, a number of strategies are used to address specific molecular or physiological questions, and examples are briefly highlighted. In addition, a number of potential problems in the generation and use of transgenic mice in the study of cardiovascular biology are presented.