Sean Pearson

Continuous monitoring of turning in patients with movement disability.

Difficulty with turning is a major contributor to mobility disability and falls in people with movement disorders, such as Parkinsons disease (PD). Turning often results in freezing and/or falling in patients with PD. However, asking a patient to execute a turn in the clinic often does not reveal their impairments. Continuous monitoring of turning with wearable sensors during spontaneous daily activities may help clinicians and patients determine who is at risk of falls and could benefit from preventative interventions. In this study, we show that continuous monitoring of natural turning with wearable sensors during daily activities inside and outside the home is feasible for people with PD and elderly people. We developed an algorithm to detect and characterize turns during gait, using wearable inertial sensors. First, we validate the turning algorithm in the laboratory against a Motion Analysis system and against a video analysis of 21 PD patients and 19 control (CT) subjects wearing an inertial sensor on the pelvis. Compared to Motion Analysis and video, the algorithm maintained a sensitivity of 0.90 and 0.76 and a specificity of 0.75 and 0.65, respectively. Second, we apply the turning algorithm to data collected in the home from 12 PD and 18 CT subjects. The algorithm successfully detects turn characteristics, and the results show that, compared to controls, PD subjects tend to take shorter turns with smaller turn angles and more steps. Furthermore, PD subjects show more variability in all turn metrics throughout the day and the week.

Continuous monitoring of turning in Parkinson's disease: Rehabilitation potential.

BACKGROUND Difficulty turning during gait is a major contributor to mobility disability, falls and reduced quality of life in patients with Parkinsons disease (PD). Unfortunately, the assessment of mobility in the clinic may not adequately reflect typical mobility function or its variability during daily life. We hypothesized that quality of turning mobility, rather than overall quantity of activity, would be impaired in people with PD over seven days of continuous recording. METHODS Thirteen subjects with PD and 8 healthy control subjects of similar age wore three Opal inertial sensors (on their belt and on each foot) throughout seven consecutive days during normal daily activities. Turning metrics included average and coefficient of variation (CV) of: (1) number of turns per hour, (2) turn angle amplitude, (3) turn duration, (4) turn mean velocity, and (5) number of steps per turn. Turning characteristics during continuous monitoring were compared with turning 90 and 180 degrees in a observed gait task. RESULTS No differences were found between PD and control groups for observed turns. In contrast, subjects with PD showed impaired quality of turning compared to healthy control subjects (Turn Mean Velocity: 43.3 ± 4.8°/s versus 38 ± 5.7°/s, mean number of steps 1.7 ± 1.1 versus 3.2 ± 0.8). In addition, PD patients showed higher variability within the day and across days compared to controls. However, no differences were seen between PD and control subjects in the overall activity (number of steps per day or percent of the day walking) during the seven days. CONCLUSIONS We show that continuous monitoring of natural turning during daily activities inside or outside the home is feasible for patients with PD and the elderly. This is the first study showing that continuous monitoring of turning was more sensitive to PD than observed turns. In addition, the quality of turning characteristics was more sensitive to PD than quantity of turns. Characterizing functional turning during daily activities will address a critical barrier to rehabilitation practice and clinical trials: objective measures of mobility characteristics in real-life environments.

Joint angle tracking with inertial sensors

Many wearable inertial systems have been used to continuously track human movement in and outside of a laboratory. The number of sensors and the complexity of the algorithms used to measure position and orientation vary according to the clinical application. To calculate changes in orientation, researchers often integrate the angular velocity. However, a relatively small error in measured angular velocity leads to large integration errors. This restricts the time of accurate measurement to a few minutes. We have combined kinematic models designed for control of robotic arms with state space methods to directly and continuously estimate the joint angles from inertial sensors. These algorithms can be applied to any combination of sensors, can easily handle malfunctions or the loss of some sensor inputs, and can be used in either a real-time or an off-line processing mode with higher accuracy.

Variable frequency bioimpedance instrumentation

The design of instrumentation used to measure the bioimpedance of skin or tissue is presented. An inexpensive, component level approach, appropriate for use by researchers rather that commercial applications, is emphasized. The design and implementation process is thoroughly explained and design tradeoffs are discussed with relation to various applications. A validation of the implementation in hardware is presented and an example application to skin impedance topography is considered.

Intracranial pressure and cerebral perfusion pressure responses to head elevation changes in pediatric traumatic brain injury.

Objectives: To determine the effect of and dynamic interaction between head elevation on intracranial pressure and cerebral perfusion pressure in severe pediatric traumatic head injury. Design: Prospective, randomized, interventional cohort study. Setting: Two tertiary pediatric critical care referral units. Patients: Ten children admitted with severe traumatic brain injury defined as Glasgow Coma Score ⩽8 necessitating intracranial pressure monitoring (10 yrs ± 5 SD; range 2–16 yrs). Interventions: Head elevation was randomly increased or decreased between 0 and 40 degrees from baseline level (30 degrees) in increments or decrements of 10 degrees. Measurements and Main Results: Intracranial pressure and arterial blood pressure were continuously recorded in combination with time-stamped clinical notations. Data were available for analysis in eight subjects (seven males and one female; mean age, 10 yrs ± SD 5; range, 2–16 yrs) during 18 protocol sessions. This resulted in a total of 66 head-of-the-bed challenges. To compare results for a given change in head-of-the-bed elevation across age, we transformed head-of-the-bed angle to change in height (cm) at the level of Monros foramen. An increase in head elevation of 10 cm resulted in an average change in intracranial pressure of −3.9 mm Hg (SD ±3.2 mm Hg; p < .001), whereas cerebral perfusion pressure remained unchanged (0.1 ± 5.6 mm Hg; p = .957). Individual subjects showed marked variability in intracranial pressure change (range, −8.4 to +1.9 mm Hg/10 cm). The overall regression analysis for intracranial pressure response was change in intracranial pressure = −0.39/cm &Dgr;h, r2 = 0.42, and p < .001, where &Dgr;h is the change in vertical height at the level of foramen of Monro attributable to a change in the head of the bed. Conclusions: In severe pediatric traumatic brain injury, the relationship between change in head of the bed and change in intracranial pressure was negative and linear. The lowest intracranial pressure was usually, but not always, achieved at highest head-of-the-bed angles. The effect size of a head-of-the-bed angle change depended, in part, on the subjects height. In contrast, cerebral perfusion pressure was mostly unaffected by head-of-the-bed changes.

Inertial and time-of-arrival ranging sensor fusion

Wearable devices with embedded kinematic sensors including triaxial accelerometers, gyroscopes, and magnetometers are becoming widely used in applications for tracking human movement in domains that include sports, motion gaming, medicine, and wellness. The kinematic sensors can be used to estimate orientation, but can only estimate changes in position over short periods of time. We developed a prototype sensor that includes ultra wideband ranging sensors and kinematic sensors to determine the feasibility of fusing the two sensor technologies to estimate both orientation and position. We used a state space model and applied the unscented Kalman filter to fuse the sensor information. Our results demonstrate that it is possible to estimate orientation and position with less error than is possible with either sensor technology alone. In our experiment we obtained a position root mean square error of 5.2cm and orientation error of 4.8° over a 15min recording.

Power Demodulation of Local Field Potential Recordings

Local field potentials (LFPs) are used to monitor the activity of large groups of neurons with macroelectrodes. Historically traditional linear statistical analysis techniques based on second order moments have been used to analyze these signals. We describe a new method based on power demodulation for estimating the instantaneous firing rate that is common to the neural activity of the most prominent neurons sensed by the electrodes. Correlated firing rates among neighboring neurons are common in many neurological structures and pathologies such as tremor. We validate our estimator with a Monte Carlo simulation based on a novel statistical model of LFPs. Our results show that the power demodulation approach can achieve a correlation of >0.80 with the common firing rate. This suggests that it may be possible to estimate the common intensity of a group neurons in recordings which are too noisy or contain too many neurons to apply spike detection or spike sorting algorithms

Physiologic Responses to Acupuncture Point Stimulation: A Pilot Study to Evaluate Methods and Instrumentation

The physiological responses to needle stimulation of an acupuncture point and a nearby control point were compared in six healthy participants. The electrocardiogram (ECG), respiration, and electrodermal response (EDR) were measured along with the times of needle insertion, interim needle stimulation and needle removal. In addition to the aforementioned, any relevant events such as movement of the subject, unexpected noise, etc were annotated.