Arm Tremor Research Articles

Prevalence and Risk Factors of Depression and Anxiety in Essential Tremor Patients: A Cross-Sectional Study in Southwest China.

Background: Essential tremor (ET) is one of the most common movement disorders, and it has been associated with anxiety and depression, but risk factors for these mental symptoms are unclear. This study aimed to evaluate the prevalence and potential risk factors of depression and anxiety in ET patients in China.Methods: This cross-sectional study involved 245 Han Chinese patients with ET. Depression was assessed using the Hamilton Depression Rating Scale-24 Items, and anxiety was assessed using the Hamilton Anxiety Rating Scale. Clinico-demographic characteristics were compared between patients with or without depression or anxiety.Results: We revealed that 63.3% of patients had at least mild anxiety and 54.3% had at least mild depression. Severity of anxiety or depression was correlated with lower Mini-Mental State Exam score (P = 0.028 and P = 0.002, respectively), higher self-report functional disability score (P = 0.027 and P = 0.003, respectively), as well as the presence of tremor in the neck (both P < 0.001), face (P = 0.025 and P < 0.001, respectively), or voice (both P < 0.001). Binary logistic regression identified female sex, presence with cranial tremor, and greater functional disability score as risk factors of anxiety; the last two factors were also the determinants of depression. Neither anxiety nor depression correlated with physician-assessed severity of arm or leg tremor.Conclusion: Chinese ET patients show high prevalence of depression and anxiety. ET patients should be screened for these mental symptoms, especially women and those with cranial tremor and self-reported functional disability.

Blood cholinesterase level is associated with tremor of farmer with pesticide exposure in Indonesia

Background Organophosphates and carbamates are among the most commonly used insecticides worldwide and are known to suppress the activity of acetylcholinesterase (AChE) that will result in nervous system toxicity. Previous studies described positive associations between concurrent AChEactivity, a stable marker of cholinesterase inhibitor pesticide exposure, with tremor in farmer. This study was aimed to identify association between cholinesterase level with tremor in farmer exposed to pesticide exposure in Magelang Regency, Indonesia. Methods This was a cross-sectional study. The subjects were the farmer with history of pesticide exposure in Ngablak, Magelang Regency, Central Java, Indonesia. Cholinesterase level was analyzed from blood. Tremor was assessed using Tremor Rating Scale (TRS). Results In total, 120 subjects aged average 45.8 ± 13.43 years old were included. The average of blood cholinesterase level was 8.73 ± 1.80 kIU/L, with 70 subjects had low level of blood cholinesterase and 86 subjects had tremor. Bivariate analysis showed that blood cholinesterase level was associated with tremor (p = 0.005; 95% CI = 1.39-7.23). Further analysis showed that cholinesterase level was associated with tremor of arm (p = 0,02; 95%CI = 1.58-6.88) Conclusions Blood cholinesterase level, a stable marker of cholinesterase inhibitor pesticide exposure, was positively associated with tremor in farmer as assessed by TRS, especially tremor of arm.

Comparison of posterior subthalamic area deep brain stimulation for tremor using conventional landmarks versus directly targeting the dentatorubrothalamic tract with tractography

ObjectiveTo compare posterior subthalamic area deep brain stimulation (PSA-DBS) performed in the conventional manner against diffusion tensor imaging and tractography (DTIT)-guided lead implantation into the dentatorubrothalamic tract (DRTT). Patients and MethodsDouble-blind, randomised study involving 34 patients with either tremor-dominant Parkinson's disease or essential tremor. Patients were randomised to Group A (DBS leads inserted using conventional landmarks) or Group B (leads guided into the DRTT using DTIT). Tremor (Fahn-Tolosa-Marin) and quality-of-life (PDQ-39) scores were evaluated 0-, 6-, 12-, 36- and 60-months after surgery. ResultsPSA-DBS resulted in marked tremor reduction in both groups. However, Group B patients had significantly better arm tremor control (especially control of intention tremor), increased mobility and activities of daily living, reduced social stigma and need for social support as well as lower stimulation amplitudes and pulse widths compared to Group A patients. The better outcomes were sustained for up to 60-months from surgery. The active contacts of Group B patients were consistently closer to the centre of the DRTT than in Group A. Speech problems were more common in Group A patients. ConclusionDTIT-guided lead placement results in better and more stable tremor control and fewer adverse effects compared to lead placement in the conventional manner. This is because DTIT-guidance allows closer and more consistent placement of leads to the centre of the DRTT than conventional methods.

METHODS EVALUATING UPPER ARM AND FOREARM MOVEMENT DURING A QUIET STANCE

The article focuses on designing methods for quantitative assessment of the postural stability in a quiet stance by measuring segments of the appendicular skeleton, namely upper and forearms by inertial measurement units (IMU). Although an array of quantitative analysis methods assessing data of postural stability in the quiet stance exist by measuring the head and trunk movement, these methods have not been used to date to assess the behaviour of appendicular skeleton segments, namely the upper limbs. The applicability of methods assessing arm movement during the quiet stance has been verified by comparing the values of healthy subjects performing various stance tasks. The tests determined the quantitative evaluation of acceleration measured on individual anatomical axes. The quantities included: the volume of a convex polyhedron (PV), the volume of confidence ellipsoid (EV) and average velocity (AV) obtained by plotting three accelerations against each other. The most important findings in this study concern significant differences of PV and AV between dominant and non-dominant upper extremities and significant differences of EV, PV and AV between the data measured with a subject's eyes closed and open. Higher values of indicators were in the non-dominant extremities when subjects were measured with closed eyes. Interestingly, statistically significant differences between dominant and non-dominant arm movements were documented in PV and AV cases. This is due to the PV calculation being more sensitive to random deviations, i.e. the range of measured data, since the polyhedron bounds all the measured data, as opposed to the method, where the ellipse bounds only 95% of the measured data. In the case of the AV method, it is due to higher sensitivity to movements corresponding with arm tremors; the AV calculation relates not only to the range of measured data but, above all, to the intensity of data changes in the segment measured in a particular space and time interval. These conclusions demonstrate that it is possible to apply the proposed methods in the assessment of arm movement during a quiet stance since the differences between individual stance tasks and the dominant and non-dominant arms in specific cases of quiet stance have been identified. These conclusions also indicate a potentially more extensive medical application of the proposed quantitative data evaluation obtained from IMU, for example, within the rehabilitation process of injured appendicular skeleton segments. The use of cheaper IMU methods in mobile phones or watches can be of significant benefit in measuring the segmental movement of the appendicular skeleton in quiet stance. The methods outlined in this paper have remarkable potential in the field of telemedicine.

Teaching Video NeuroImages: A patient with Holmes tremor due to demyelinating lesion of the inferior cerebellar peduncle

A 60-year-old woman with a several year decline in gait and cognition developed a Holmes tremor in the weeks prior to presentation (video). Her right arm tremor predated the left arm tremor. She had no neurologic evaluation prior this presentation. MRI brain revealed lesions disseminated in time and space (figure 1) and CSF analysis revealed oligoclonal bands, confirming the diagnosis of multiple sclerosis.1 We implicate a lesion in the left inferior cerebellar peduncle (ICP) with associated fluid-attenuated inversion recovery hyperintensity in the contralateral inferior olivary nucleus in the pathogenesis of the left-sided rest, postural, and action tremor (figure 2). Lesions of the cerebellar circuits, including cerebello-thalamic and cerebello-olivary circuits, can manifest as a Holmes tremor.2 Our case of Holmes tremor due to an ICP lesion completes the discourse between Drs. Albin and Savoiardo3 in 1998.

Effect of deep brain simulation on arm, leg, and chin tremor in Parkinson disease.

The efficacy of deep brain stimulation (DBS) of the subthalamic nucleus (STN) in the treatment of Parkinson disease (PD)-related tremor has been well established. However, the relative impact on arm, leg, and chin tremor has been less clearly elucidated. The authors evaluated the distribution of tremors in a PD cohort undergoing STN DBS and sought to evaluate the differential impact of DBS as a function of tremor location. A retrospective study of patients with PD with tremor who underwent DBS surgery between 2012 and 2016 was performed to evaluate the impact of STN stimulation on overall and regional tremor scores. Across 66 patients the authors found an average of 78% overall reduction in tremor after 6 months. In this cohort, the authors found that tremor reduction was somewhat better for arm than for leg tremors, especially in instances of higher preoperative tremor (84% vs 71% reduction, respectively, for initial tremor scores ≥ 2). No significant difference in response was found between patients with medication-responsive versus medication-nonresponsive tremors. The authors found that although DBS improved tremor in all regions, the improvement was not uniform between chin, arm, and leg-even within the same patient. The reasons behind these differing responses are speculative but suggest that STN DBS may more reliably reduce arm tremors than leg tremors.

Hemiparkinsonism secondary to an epidermoid cyst with complete recovery after surgical resection: Case report and review of the literature

Abstract Hemiparkinsonism is an exceptionally rare form of secondary Parkinsonism that manifests with unilateral symptoms and is often accompanied by ipsilateral body atrophy. Epidermoid cysts are benign, slow-growing tumors that can present with varying neurological symptoms. We report a case of a 30-year-old male who exhibited symptoms of Hemiparkinsonism secondary to a right-sided epidermoid cyst. The patient presented with three months of progressive resting left arm tremor and two weeks of left hand weakness. The patient exhibited a central left facial droop and left arm weakness with rigidity and bradykinesia. Unified Parkinson Disease Rating Scale (UPDRS) Part III score was 13. Gross total resection was achieved using a right frontotemporal craniotomy via a preauricular, subtemporal approach. Complete reversal of symptoms occurred after surgical resection.

Comparison of tractography‐assisted to atlas‐based targeting for deep brain stimulation in essential tremor

Direct targeting of the dentato-rubro-thalamic tract is efficacious in DBS for tremor suppression. We sought to compare outcomes and optimal stimulation parameters for tremor control using the technique of directly targeting the dentato-rubro-thalamic tract to those who underwent indirect targeting of the ventral intermediate nucleus thalamus. Twenty consecutive essential tremor patients obtained preoperative diffusion MRIs, where the dentato-rubro-thalamic tract was individually drawn and used to directly target the ventral intermediate nucleus of the thalamus during surgery. These patients were compared to an earlier cohort of 20 consecutive patients who underwent surgery using atlas-based coordinates. Baseline and 1-year postsurgery tremor amplitude using The Essential Tremor Rating Assessment Scale was recorded, as were the parameters needed for successful tremor control. The indirectly targeted group had greater baseline and postop tremor severity relative to those directly targeted (baseline, 2.9 vs. 2.6; P = 0.02; postop, 1.1 vs. 0.8; P = 0.03). Mean voltage, pulse width, and frequency for optimal tremor control in the directly targeted group (38 electrodes) = 2.8 V, 80 μs, 153 Hz; the parameters for the indirectly targeted group (38 electrodes) = 2.9 V, 86 µs, 179 Hz (significantly greater, P < 0.001). Both groups had significant improvement in arm tremor amplitude from baseline (P < 0.001) without sustained side effects. Direct targeting of the dentato-rubro-thalamic tract provides excellent tremor control, comparable to indirectly targeting the ventral intermediate nucleus of the thalamus. Use of lower stimulation parameters, especially frequency, to control tremor in the directly targeted group suggests that it is a more efficient targeting methodology, which may minimize battery depletion. © 2018 International Parkinson and Movement Disorder Society.

Unilateral Left Deep Brain Stimulation of the Caudal Zona Incerta Is Equally Effective on Voice Tremor as Bilateral Stimulation: Evidence from 7 Patients with Essential Tremor

Background/Aims: Deep brain stimulation (DBS) is less effective on voice tremor than arm tremor, and it is generally assumed that successful voice tremor treatment requires bilateral DBS and possibly more precise thalamic stimulation. However, recent findings suggest that these assumptions should be reconsidered. Objectives: To evaluate whether unilateral DBS targeting the caudal zona incerta (cZi) may be sufficient to alleviate voice tremor in patients with essential tremor, or whether bilateral stimulation is needed. Methods: Seven patients with voice tremor off stimulation were evaluated during bilateral stimulation using their clinical settings, and during unilateral left stimulation in iterations with increasing stimulation amplitude. Two expert listeners assessed voice tremor severity in all samples in a blinded procedure. Results: Six patients had comparable or better effects with unilateral left stimulation compared to bilateral stimulation. For the seventh patient, unilateral DBS at a slightly higher amplitude achieved similar results as bilateral DBS. Overall, high-amplitude stimulation did not appear to be beneficial on voice tremor. Conclusions: Unilateral left and bilateral cZi-DBS had comparable effects on voice tremor in the investigated group of 7 patients. This finding suggests that the assumption that bilateral DBS is required to treat voice tremor may need to be reconsidered.

Essential tremor quantification based on the combined use of a smartphone and a smartwatch: The NetMD study

BackgroundThe use of wearable technology is an emerging field of research in movement disorders. This paper introduces a clinical study to evaluate the feasibility, clinical correlation and reliability of using a system based in smartwatches to quantify tremor in essential tremor (ET) patients and check its acceptance as clinical monitoring tool. New methodThe system is based on a commercial smartwatch and an Android smartphone. An investigational Android application controls the process of recording raw data from the smartwatch three-dimensional gyroscopes. Thirty-four ET patients were consecutively enrolled in the experiments and assessed along one year. Arm tremor was videofilmed and scored using the Fahn-Tolosa-Marin Tremor Rating Scale (FTM-TRS). Tremor intensity was quantified with the root mean square of angular velocity measured in the patients’ wrists. ResultsEighty-two assessments with smartwatches were performed. Spearman’s correlation coefficients (ρ) between clinical tremor (FTM-TRS) scores and smartwatch measures for tremor intensity were 0.590 at rest; ρ = 0.738 in steady posture; ρ = 0.189 in finger-to-nose maneuvers; and ρ = 0.652 in pouring water task. Smartwatch reliability was checked by intraclass realiability coefficients: 0.85, 0.95, 0.91, 0.95 respectively. Most of patients showed good acceptance of the system. Comparison with existing method(s)This commodity hardware contributes to quantify tremor objectively in a consulting-room by customized Android smart devices as clinical monitoring tool. ConclusionsThe NetMD system for tremor analysis is feasible, well-correlated with clinical scores, reliable and well-accepted by patients to tremor follow-up. Therefore, it could be an option to objectively quantify tremor in ET patients during their regular follow-up.

Evaluation of Quantitative Measurement Techniques for Head Tremor With Thalamic Deep Brain Stimulation

Ventralis intermedius thalamic deep brain stimulation (VIM DBS) has shown to be safe and effective for medically refractory essential tremor (ET). We evaluate the use of quantitative tremor measurement methods for head tremor in ET using a "smart" hat and a smartphone application. We enrolled 13 ET patients who previously underwent VIM DBS. Head and arm tremor was measured ON and OFF stimulation using the clinical gold standard Fahn-Tolosa-Marin Tremor Rating Scale (TRS). Results were then compared to two quantitative measurement techniques: Lift Pulse (smartphone application) and modified Nizet (adapted laser point measurement from Nizet et al.). Spearman's rank correlation was used to compare tremor severity and improvement on stimulation using TRS and quantitative methods to measure tremor. Lift Pulse tremor severity measurement significantly correlated with TRS for head (ρ = 0.53, p < 0.01) and arm tremor (ρ = 0.49, p < 0.01). Modified Nizet tremor severity measurement significantly correlated with TRS for head (ρ = 0.83, p < 0.001) and arm tremor (ρ = 0.50, p < 0.01). Inter-method correlation for head tremor severity was significant (ρ = 0.45, p < 0.05). Lift Pulse tremor improvement measurement significantly correlated with TRS for arm tremor (ρ = 0.56, p < 0.05). Modified Nizet tremor improvement measurement significantly correlated with TRS for head tremor (ρ = 0.53, p < 0.01). Our results show that Lift Pulse and modified Nizet are both effective techniques to quantitatively measure head and arm tremor severity. We also show the utility of a "smart" hat to measure head tremor. Modified Nizet technique is more effective for measuring head tremor, while Lift Pulse is an effective measure of tremor severity, especially arm tremor improvement.

Deep Brain Stimulation of the Dentato-Rubro-Thalamic Tract: Outcomes of Direct Targeting for Tremor

Targeting the dentato-rubro-thalamic tract (DRTt) has been suggested to be efficacious in deep brain stimulation (DBS) for tremor suppression, both in case reports and post-hoc analyses. This prospective observational study sought to analyze outcomes after directly targeting the DRTt in tremor patients. 20 consecutively enrolled intention tremor patients obtained pre-operative MRI with diffusion tensor (dTi) sequences. Mean baseline tremor amplitude based on The Essential Tremor Rating Assessment Scale was recorded. The DRTt was drawn for each individual on StealthViz software (Medtronic) using the dentate nucleus as the seed region and the ipsilateral pre-central gyrus as the end region and then directly targeted during surgery. Intraoperative testing confirmed successful tremor control. Post-operative analysis of electrode position relative to the DRTt was performed, as was post-operative assessment of tremor improvement. The mean age of patients was 66.8 years; mean duration of tremor was 16 years. Mean voltage for the L electrode = 3.4 V; R = 2.6 V. Mean distance from the center of the active electrode contact to the DRTt was 0.9 mm on the L, and 0.8 mm on the R. Improvement in arm tremor amplitude from baseline after DBS was significant (P < 0.001). Direct targeting of the DRTt in DBS is an effective strategy for tremor suppression. Accounting for hardware, software, and model limitations, depiction of the DRTt allows for placement of electrode contacts directly within the fiber tract for modulation despite any anatomical variation, which reproducibly resulted in good tremor control.

Action Tremor Asymmetry Profile Does Not Aggregate in Families with Essential Tremor.

Action tremor is the hallmark feature of essential tremor (ET). While the tremor typically is mildly asymmetric, in some patients, it is markedly asymmetric. There are few data on factors that influence this asymmetry. ET is also a highly familial disease. Whether the tremor asymmetry profile (i.e., differential expression of tremor in each arm in a given patient) is similar across family members is not known. The alternative possibility is that this feature is not heritable. There are no published data addressing this issue. The aim of this study was to determine whether the extent of action tremor asymmetry ran in ET families. ET probands and relatives were enrolled in a genetic study at Yale and Columbia Universities. An in-person evaluation included a videotaped neurological examination, including a detailed assessment of tremors. A senior movement disorders neurologist reviewed all videotaped examinations, and the severity of postural and kinetic arm tremors was rated on 12 examination items using a reliable rating scale. The tremor asymmetry index = right arm tremor score - left arm tremor score. We used a bivariate linear regression model to assess the predictors of the tremor asymmetry index in relatives; this model used the tremor asymmetry index in the proband as a primary predictor of interest. In an analysis of variance (ANOVA), we tested for heterogeneity across families in the tremor asymmetry index (i.e., to see whether there was a significant family effect). There were 187 enrollees (59 probands, 128 affected relatives). In a bivariate linear regression model, the tremor asymmetry index in the proband was not a predictor of the tremor asymmetry index in their relatives (p = 0.66). In an ANOVA, family grouping did not explain a significant proportion of the total variance in the tremor asymmetry index (p = 0.56). Tremor asymmetry did not aggregate in families with ET. Therefore, this does not seem to be a disease feature that is heritable. These data will provide added value to the clinical dialog, giving patients one more piece of information about the way the disease manifests within families.

Holmes' Tremor with Shoulder Pain Treated by Deep Brain Stimulation of Unilateral Ventral Intermediate Thalamic Nucleus and Globus Pallidus Internus.

A 21-year-old male was admitted with severe right arm and hand tremors after a thalamic hemorrhage caused by a traffic accident. He was also suffering from agonizing pain in his right shoulder that manifested after the tremor. Neurologic examination revealed a disabling, severe, and irregular kinetic and postural tremor in the right arm during target-directed movements. There was also an irregular ipsilateral rest tremor and dystonic movements in the distal part of the right arm. The amplitude was moderate at rest and extremely high during kinetic and intentional movements. The patient underwent left globus pallidum internus and ventral intermediate thalamic nucleus deep brain stimulation. The patient improved by more than 80% as rated by the Fahn-Tolosa-Marin Tremor Rating Scale and Visual Analog Scale six months after surgery.

Coaxial interleaved stimulation of the thalamus and subthalamus for treatment of Holmes tremor

Holmes tremor is often treated with multiple deep brain stimulation (DBS) electrodes. The authors describe a novel technique to suppress the tremors by effectively utilizing a single electrode. A 16-year-old boy presented with severe right arm tremor following a midbrain injury. A DBS electrode was implanted into the ventral oralis nucleus of the thalamus (VO) and the subthalamic region. While individual stimulation of each target was ineffective, an interleaved dual stimulation of both targets has been effective for 6 years. Coaxial interleaved stimulation of the VO and the subthalamic region is useful for treating Holmes tremor. The video can be found here: https://youtu.be/tSwGh3vy68c .

Early Head Tremor in Essential Tremor: A Case Series and Commentary.

BackgroundClassically, the onset of head tremor in essential tremor (ET) patients follows that of hand tremor, such that there is a somatotopic spread of involved areas. Here we present a series of seven self‐reportedly “unaffected” relatives of ET cases. These seven were clinically asymptomatic and had normal levels of arm tremor on examination, yet each evidenced a transient head wobble on examination. We estimate the prevalence of this phenotype within the two studies from which cases were ascertained.MethodsET cases and their self‐reportedly affected and unaffected relatives, enrolled in two family studies, underwent a medical history and videotaped neurological examination.ResultsIn seven self‐reportedly “unaffected” relatives, a transient and subtle head wobble was seen, always during sustained phonation, speech, or reading aloud. Total tremor score (a measure of arm tremor) ranged from 5 to 12 (i.e., mild tremor within the range of normal). The prevalence of this phenotype of early head tremor was 3.7% in one study and 23.1% in the other.DiscussionWe present a series of seven individuals who had early head tremor in an evolving transition state from normal to ET. These cases raise a number of broad clinical, phenotypic, and pathophysiological issues about ET.

MAXFAS: Mechatronic Arm Exoskeleton for Firearm Aim Stabilization

This article details the design, fabrication, and application of a mechatronic arm exoskeleton for firearm aim stabilization (MAXFAS), which senses and damps involuntary tremors in the arm. Human subject experiments were carried out using the device in a simulated shooting and aiming task. Results indicate that MAXFAS reduced arm tremors and improved shooting performance while wearing the device. Residual performance improvement after removing the device and possible training function of MAXFAS will also be discussed.

Precise stimulation location optimizes speech outcomes in essential tremor

BackgroundDeep brain stimulation for essential arm tremor is often complicated by dysarthria and persistent voice tremor. ObjectiveTo determine the relationship of stimulation location to speech outcomes following bilateral thalamic deep brain stimulation (DBS) for essential tremor (ET). MethodsEighteen patients undergoing bilateral DBS for ET were prospectively studied. Speech pathologists grouped patients by final speech outcome (normal speech, voice tremor, or dysarthria). Locations of the active leads were calculated by normalizing the segmented thalamic volumes to those in the Morel atlas. Stimulation volumes within thalamic nuclei, error distances from target, and measures of accuracy were calculated and differences in measures between outcome groups tested. ResultsAt optimal stimulation, 8 patients had normal speech, 6 had voice tremor, and 4 had mild dysarthria. Stimulation volumes were statistically concentrated within the ventral lateral posterior nucleus (VLp). The percentage of stimulation volume outside the VLp was higher in patients with dysarthria (60% vs. 24%, p = 0.02) or voice tremor (55% vs. 24%, p = 0.03) compared to patients with normal speech outcomes. The error distance from the center of VLp was greater for patients with dysarthria than those with normal speech (12.6 vs. 7.6 mm, p = 0.02). Electrodes with lower efficiency for VLp stimulation were more frequent with poor speech outcomes and in patients with persistent voice tremor. ConclusionsFollowing bilateral DBS for ET, 22% of patients develop a non-disabling dysarthria. Optimal speech outcomes were achieved in 44% of patients and correlated with precise stimulation location within and not outside of the VLp.

Quantitative assessment of arm tremor in people with neurological disorders.

Abnormal oscillatory movement (i.e. tremor) is usually evaluated with qualitative assessment by clinicians, and quantified with subjective scoring methods. These methods are often inaccurate. We utilized a quantitative and standardized task based on the Fitts' law to assess the performance of arm movement with tremor by controlling a gyration mouse on a computer. The experiment included the center-out tapping (COT) and rectangular track navigation (RTN) tasks. We report the results of a pilot study in which we collected the performance for healthy participants in whom tremor was simulated by imposing oscillatory movements to the arm with a vibration motor. We compared their movement speed and accuracy with and without the artificial "tremor." We found that the artificial tremor significantly affected the path efficiency for both tasks (COT: 56.8 vs. 46.2%, p <; 0.05; RTN: 94.2 vs. 67.4%, p <; 0.05), and we were able to distinguish the presence of tremor. From this result, we expect to quantify severity of tremor and the effectiveness therapy for tremor patients.

Tremor Amplitude is Greater in the Mediolateral Direction than Vertical During Handgun Aiming Tasks.

PURPOSE: In aiming at a target, humans produce small involuntary fluctuations in the aiming limb which may hamper performance. While often studied in the vertical axis, these fluctuations occur in all axes. The current study compared vertical and mediolateral tremor amplitude during different handgun aiming postures. METHODS: Thirty volunteers stood 21 feet from a target and aimed a weighted mock handgun for 10 sec with an accelerometer affixed to each wrist and the gun barrel. Participants performed five trials per condition. Amplitude (RMS) of the acceleration signals were computed. Two hand grip (bilateral, unilateral), two arm positions (bent, straight), and two segments (forearm, gun) were analyzed in conjunction with the two directions (VT, ML). RESULTS: Across all conditions tremor amplitude in the mediolateral direction was significantly greater than the vertical direction (VT: .017+.006g vs. ML: 0.021+.005g, p<.001). Additionally significant interaction effects were seen for direction by hand grip (p<.001) as well as direction by arm position (p=.002). For hand grip, vertical tremor was significantly lower than mediolateral and bilateral tremor was significantly lower than unilateral. For arm position, vertical tremor was significantly lower than mediolateral and bent arm tremor was significantly lower than straight arm. There were no significant interaction effects for direction by segment (p=.173). CONCLUSION: Across numerous hand gun aiming postures mediolateral tremor amplitude was consistently higher than the vertical tremor amplitude. This may be due to the neurological and mechanical factors of the limb, the limbs resistance to gravity, or the effort of control. Further research is needed to examine the interaction of mediolateral and vertical tremor.