Using Accelerometer and Gyroscopic Measures to Quantify Postural Stability

Context

Force platforms and 3-dimensional motion-capture systems provide an accurate method of quantifying postural stability. Substantial cost, space, time to administer, and need for trained personnel limit widespread use of biomechanical techniques in the assessment of postural stability in clinical or field environments.

Objective

To determine whether accelerometer and gyroscope data sampled from a consumer electronics device (iPad2) provide sufficient resolution of center-of-gravity (COG) movements to accurately quantify postural stability in healthy young people.

Design

Controlled laboratory study.

Setting

Research laboratory in an academic medical center.

Patients or Other Participants

A total of 49 healthy individuals (age = 19.5 ± 3.1 years, height = 167.7 ± 13.2 cm, mass = 68.5 ± 17.5 kg).

Intervention(s)

Participants completed the NeuroCom Sensory Organization Test (SOT) with an iPad2 affixed at the sacral level.

Main Outcome Measure(s)

Primary outcomes were equilibrium scores from both systems and the time series of the angular displacement of the anteroposterior COG sway during each trial. A Bland-Altman assessment for agreement was used to compare equilibrium scores produced by the NeuroCom and iPad2 devices. Limits of agreement was defined as the mean bias (NeuroCom − iPad) ± 2 standard deviations. Mean absolute percentage error and median difference between the NeuroCom and iPad2 measurements were used to evaluate how closely the real-time COG sway measured by the 2 systems tracked each other.

Results

The limits between the 2 devices ranged from −0.5° to 0.5° in SOT condition 1 to −2.9° to 1.3° in SOT condition 5. The largest absolute value of the measurement error within the 95% confidence intervals for all conditions was 2.9°. The mean absolute percentage error analysis indicated that the iPad2 tracked NeuroCom COG with an average error ranging from 5.87% to 10.42% of the NeuroCom measurement across SOT conditions.

Conclusions

The iPad2 hardware provided data of sufficient precision and accuracy to quantify postural stability. Accuracy, portability, and affordability make using the iPad2 a reasonable approach for assessing postural stability in clinical and field environments.Key Words: concussions, motor function, motor control, biomechanics

Key Points

• The accelerometer and gyroscope within the iPad2 provided data of sufficient quantity and quality to enable accurate evaluation of postural stability.
• The accuracy, portability, availability, and affordability of mobile devices can enable health care providers in various clinical and field settings to evaluate postural stability in athletes.
• To improve clinical outcomes, mobile devices can be a mechanism by which sophisticated biomechanical algorithms are translated to the broader field of athletic trainers and clinical teams treating patients with concussions.
• The accuracy and reliability of mobile devices must be validated before these systems are used to assess cognitive or motor function.

Maintenance of stable posture depends on the efficient processing and integration of information from the visual, somatosensory, and vestibular systems and the modulation of efferent responses by the musculoskeletal system.¹ A decline in postural stability is often a hallmark of advancing age^2–4 and neurologic diseases, such as Parkinson disease^5–7 and multiple sclerosis.^8–10 In addition to neurologic disease, concussion, or mild traumatic brain injury (mTBI), has been well-documented to adversely affect postural stability; however, debate exists about the time course for resolution of balance declines postconcussion.^11–21 Often after concussion, static postural-stability declines are most evident when visual and support-surface conditions are altered.²⁰ Based on the frequency of postural-stability deficits postconcussion, the recent consensus statement on concussion in sport²² and the National Athletic Trainers'' Association²³ (NATA) recommended that balance assessment be considered part of baseline testing for athletes and that assessment postconcussion is a “reliable and valid addition” to a multifaceted approach to concussion management.Current methods for examining postural stability range from sophisticated biomechanical techniques to subjective clinical assessments.^14,24–27 Biomechanics-focused methods, which include force plate and 3-dimensional motion-capture systems, provide the greatest reliability and accuracy in assessing balance.²⁸ The Sensory Organization Test (SOT; NeuroCom Smart Balance Master; NeuroCom International Inc, Clackamas, OR), which is not a traditional biomechanical assessment, uses aspects of biomechanical techniques through a force-plate–based posturography system that measures center-of-pressure (COP) movements while systematically manipulating visual, somatosensory, and vestibular information. Clinically, the SOT has been shown to be sensitive to functional deficiencies in the visual, vestibular, and somatosensory systems often seen after concussion or mTBI^29,30 and, in turn, has been used to track recovery from concussion and evaluate the effectiveness of rehabilitation.^31,32 The primary outcome of the SOT is the equilibrium score. Assuming a maximum of 12.5° of anteroposterior (AP) sway, the equilibrium score is calculated by subtracting the observed peak-to-peak sway range from this value and dividing the difference by 12.5. Scores range from 0 to 100, with 100 representing 0° of AP sway range and 0 representing 12.5° or more of AP sway. Despite its sensitivity and precision, the SOT is limited as a clinical or field evaluation tool by its expense, size, need for trained operators, and lack of portability.^26,33A cost-effective and space-effective alternative to systems such as the NeuroCom is attaching inertial sensors (eg, accelerometer, gyroscope) to the body to measure linear and angular kinematics. Whitney et al²⁶ validated accelerometry methods using measures of planar acceleration of the pelvis and reported a correlation with the sway metric of the SOT. However, their methods were weakened by the postprocessing synchronization of the data, which aligned data from the 2 devices according to optimized correlation values rather than via real-time synchronization. Other researchers^26,33–37 have explored the efficacy of accelerometry-based balance measures; however, no approach has combined the use of an accelerometer and a gyroscope in a commercially available, nondedicated device package and then evaluated its effectiveness in assessing postural stability relative to an accepted clinical system, such as the NeuroCom. The recent inclusion of relatively sophisticated inertial-measurement technologies in consumer electronics devices, such as smartphones and tablet-based computing devices, provides an opportunity to use these devices to objectively assess postural stability in athletes during healthy baseline testing, at diagnosis of concussion, during the return-to-play process, and when determining resolution of concussion symptoms.The most common clinical test to assess postural stability in athletes is the Balance Error Scoring System (BESS).¹⁴ The complete BESS consists of 6 conditions comprising 3 stances performed on firm and foam surfaces with eyes closed.¹⁴ Whereas the BESS is considered a reliable and valid assessment of postural stability,³⁸ researchers have questioned the interrater and intrarater reliability of its scoring method^39,40 and have noted floor and ceiling scoring effects that may limit clinical utility.^26,27,41 These reliability concerns may be exacerbated in environments where multiple providers (eg, certified athletic trainers, physicians, and physical therapists) work together to diagnose and treat concussed athletes and make return-to-play decisions. Recent technological advances and the inclusion of inertial-measurement units (ie, accelerometer, gyroscope) in mobile devices may provide a readily available and affordable solution to augment subjective clinical assessments of postural stability with objective and quantitative measures.Therefore, the purpose of our study was to determine whether postural stability could be quantified accurately with data gathered by the embedded accelerometer and gyroscope of the iPad2 (Apple Inc, Cupertino, CA). We compared AP center-of-gravity (COG) sway derived from iPad2 sensor data with output from the NeuroCom SOT for amplitude (equilibrium scores) and real-time displacement goodness of fit (mean absolute percentage error [MAPE]) during performance of the SOT. The identification of an accurate method of assessing postural stability with affordable and portable consumer electronics devices would effectively fill the fundamental gap between inexpensive, subjective clinical tests and more expensive biomechanical measurement techniques and would provide a mechanism to improve continuity of assessment and care across multiple providers.     

Exercise training reduces severity of atherosclerosis in apolipoprotein E knockout mice via nitric oxide.

BACKGROUND: Exercise training may protect against the development of atherosclerosis, although the precise mechanisms are still unknown. The present study assessed the hypothesis that exercise training would reduce the severity of experimental atherosclerosis in apolipoprotein-E (apoE)-deficient mice via nitric oxide (NO). METHODS AND RESULTS: ApoE-deficient mice fed a high-fat diet underwent exercise training (30 min swimming) 3 times per week for 8 weeks. The exercise group were also given oral N(G)-nitro-L-arginine methylester (L-NAME; 25 mg x kg (-1) x day(-1)), an inhibitor of NO synthase. Fatty streak plaque lesions developed in ApoE-deficient mice fed the high-fat diet, and were suppressed in the mice that underwent swimming training. In contrast, atherosclerotic lesions were not ameliorated in mice that had exercise training plus oral L-NAME treatment. Immunohistochemical analysis revealed that the expression of endothelial NO increased in mice undergoing exercise compared with the mice that did not exercise, and that the expression was suppressed in the mice having exercise plus oral L-NAME treatment. Differences in lesion area did not correlate with any significant alterations in serum lipid levels. CONCLUSION: Exercise training suppressed atherosclerosis via the NO system.     

Cortical petechial hemorrhage, subarachnoid hemorrhage and corticosteroid-responsive leukoencephalopathy in a patient with cerebral amyloid angiopathy.

We describe a 69-year-old woman who developed subacute onset cognitive decline after hitting the left side of her head. Cerebral spinal fluid showed yellowish discoloration with highly elevated protein content. FLAIR MRI revealed diffuse high signal intensity in all cortical sulci, and leptomeningeal enhancement in the left cerebral hemisphere was seen in the T1 image after contrast administration. She was treated with a corticosteroid. Consciousness disturbance was temporarily relieved but again worsened, resulting in an apathetic state due to communicating hydrocephalus. A shunt tube was placed in her right lateral ventricle. A brain biopsy disclosed multiple cortical microbleeds and heavy deposition of Abeta-immuoreactive amyloid on vascular walls. Inflammatory mononuclear cells surrounded a few leptomeningeal vessels. After the operation her condition further deteriorated and she fell into a coma. MRI showed diffuse swelling of the right cerebral white matter. She again received high-dose corticosteroid and gradually recovered during the following 2 months. On MRI the vast majority of abnormal signals in the right cerebral white matter disappeared. An initial manifestation of this patient was possibly caused by multiple microhemorrhages from fragile cortical and subarachnoid vessels with Abeta-amyloid deposition, which was triggered by head trauma. CAA-related inflammation possibly worsened this condition. Additionally, surgical intervention for communicating hydrocephalus might have induced cerebral amyloid angiopathy (CAA)-related leukoencephalopathy in her right cerebral hemisphere. These CAA-derived manifestations are unusual and high-dose corticosteroids seems to be useful for vascular events in CAA patients.     

In vitro evaluation of diltiazem on hypothermic injury to immature myocytes

Summary The purpose of the present study was to evaluate the functional and biochemical effects of diltiazem (DTZ) on cardiac myocytes incubated under hypothermic conditions. Cardiac myocytes were isolated from neonatal rat ventricles and cultured for 4 days with MCDB 107 medium. Then, myocytes (12.5×10⁵ myocytes/flask) were incubated at 4°C for 24 hours in media with or without DTZ at concentrations of 0 M (group C), 10^–7 M (Group D1), 10^–6 M (group D2), 10^–5 M (group D3), or 10^–4 M (group D4). After 24 hours at 4°C, CPK and LDH were measured. The myocytes were then cultured for 24 hours at 37°C to evaluate the recovery of the myocyte beating rate. In group C (n=7), the recovery ratio of the myocyte beating rate was 29.9% of control (beating rate prior to hypothermic incubation). Groups D1 and D2 (n=7 each) had approximately the same recovery ratios as group C (24.0% and 24.7%, respectively); however, groups D3 and D4 (n=7 each) showed no beating rate recovery. Release of CPK and LDH in group C was 112.3 mIU/flask and 457.4 mIU/flask, respectively. Groups D1 and D2 showed no significant differences in both enzymes compared to group C. However, the levels of CPK were significantly higher in group D4 (203.3, p<0.05), and LDH levels were significantly higher in groups D3 and D4 (669.3, p<0.05; 883.4, p<0.02). In conclusion, DTZ showed no protective effects on hypothermic injury to immature cardiac myocytes; moreover, it accelerated cellular injury at the concentrations of 10^–5 and 10^–4 M both functionally and biochemically. Therefore, diltiazem may not be suitable for cardiac preservation during the neonatal period.     

d-Psicose increases energy expenditure and decreases body fat accumulation in rats fed a high-sucrose diet

We investigated the anti-obesity effects of d-psicose by increasing energy expenditure in rats pair-fed the high-sucrose diet (HSD). Wistar rats were divided into two dietary groups: HSD containing 5% cellulose (C) and 5% d-psicose (P). The C dietary group was further subdivided into two groups: rats fed the C diet ad libitum (C-AD) and pair-fed the C diet along with those in the P group (C-PF). Resting energy expenditure during darkness and lipoprotein lipase activity in the soleus muscle were significantly higher in the P group than in the C-PF group. Serum levels of glucose, leptin and adiponectin; glucose-6-phosphate dehydrogenase activities in the liver and perirenal adipose tissue; and body fat accumulation were all significantly lower in the P group than in the C-PF group. The anti-obesity effects of D-psicose could be induced not only by suppressing lipogenic enzyme activity but also by increasing EE in rats.     

Radiotherapy for gastric lymphoma: a planning study of 3D conformal radiotherapy,the half-beam method,and intensity-modulated radiotherapy

During radiotherapy for gastric lymphoma, it is difficult to protect the liver and kidneys in cases where there is considerable overlap between these organs and the target volume. This study was conducted to compare the three radiotherapy planning techniques of four-fields 3D conformal radiotherapy (3DCRT), half-field radiotherapy (the half-beam method) and intensity-modulated radiotherapy (IMRT) used to treat primary gastric lymphoma in which the planning target volume (PTV) had a large overlap with the left kidney. A total of 17 patients with gastric diffuse large B-cell lymphoma (DLBCL) were included. In DLBCL, immunochemotherapy (Rituximab + CHOP) was followed by radiotherapy of 40 Gy to the whole stomach and peri-gastric lymph nodes. 3DCRT, the half-field method, and IMRT were compared with respect to the dose–volume histogram (DVH) parameters and generalized equivalent uniform dose (gEUD) to the kidneys, liver and PTV. The mean dose and gEUD for 3DCRT was higher than for IMRT and the half-beam method in the left kidney and both kidneys. The mean dose and gEUD of the left kidney was 2117 cGy and 2224 cGy for 3DCRT, 1520 cGy and 1637 cGy for IMRT, and 1100 cGy and 1357 cGy for the half-beam method, respectively. The mean dose and gEUD of both kidneys was 1335 cGy and 1559 cGy for 3DCRT, 1184 cGy and 1311 cGy for IMRT, and 700 cGy and 937 cGy for the half-beam method, respectively. Dose–volume histograms (DVHs) of the liver revealed a larger volume was irradiated in the dose range <25 Gy with 3DCRT, while the half-beam method irradiated a larger volume of liver with the higher dose range (>25 Gy). IMRT and the half-beam method had the advantages of dose reduction for the kidneys and liver.     

Evaluating positional accuracy using megavoltage cone-beam computed tomography for IMRT with head-and-neck cancer

Accurate dose delivery is essential for the success of intensity-modulated radiation therapy (IMRT) for patients with head-and-neck (HN) cancer. Reproducibility of IMRT dose delivery to HN regions can be critically influenced by treatment-related changes in body contours. Moreover, some set-up margins may not be adaptable to positional uncertainties of HN structures at every treatment. To obtain evidence for appropriate set-up margins in various head and neck areas, we prospectively evaluated positional deviation (δ values) of four bony landmarks (i.e. the clivus and occipital protuberance for the head region, and the mental protuberance and C5 for the neck region) using megavoltage cone-beam computed tomography during a treatment course. Over 800 δ values were analyzed in each translational direction. Positional uncertainties for HN cancer patients undergoing IMRT were evaluated relative to the body mass index. Low positional accuracy was observed for the neck region compared with the head region. For the head region, most of the δ was distributed within ±5 mm, and use of the current set-up margin was appropriate. However, the δ values for the neck region were within ±8 mm. Especially for overweight patients, a few millimeters needed to be added to give an adequate set-up margin. For accurate dose delivery to targets and to avoid excess exposure to normal tissues, we recommend that the positional verification process be performed before every treatment.