J. Robert Boston

The impact of chronic low back pain on older adults: A comparative study of patients and controls

Abstract Chronic low back pain (CLBP) is one of the most common, poorly understood, and potentially disabling chronic pain conditions from which older adults suffer. Many older adults remain quite functional despite CLBP, and because age‐related comorbidities often exist independently of pain (e.g., medical illnesses, sleep disturbance, mobility difficulty), the unique impact of CLBP is unknown. We conducted this research to identify the multidimensional factors that distinguish independent community dwelling older adults with CLBP from those that are pain‐free. Three hundred twenty cognitively intact participants (162 with ⩾moderate pain for ⩾3 months, and 158 pain‐free) underwent comprehensive assessment of pain severity, medical comorbidity (illnesses, body mass index, medications), severity of degenerative disc and facet disease, lumbar flexion, psychological constructs (self‐efficacy, mood, overall mental health), and self‐reported as well as performance‐based physical function. Significant differences were ascertained for all 22 measures. Discriminant function analysis revealed that eight measures uniquely maximized the separation between the two groups (self‐reported function with the Functional Status Index and the SF‐36, performance‐based function with repetitive trunk rotation and functional reach, mood with the Geriatric Depression Scale, comorbidity with the Cumulative Illness Rating Scale and BMI, and severity of degenerative disc disease). These results should help to guide investigators that perform studies of CLBP in older adults and practitioners that want an easily adaptable battery for use in clinical settings.

Psychosocial predictors of physical performance in disabled individuals with chronic pain.

ObjectivesFirst, to identify what physical performance differences existed between a group of disabled individuals with chronic pain and a control group of pain-free individuals with comparable disabilities; and second, to test a psychosocial model designed to evaluate which psychosocial constructs were predictive of performance in disabled individuals with chronic pain. DesignCase-comparison study. SettingAmbulatory university laboratory. ParticipantsA community sample of 62 individuals with lower limb amputations or paraplegia, 31 with chronic pain and 31 pain-free. InterventionStandardized lifting and wheel-turning tasks. Main Outcome MeasuresStatic strength, endurance, lifting speed, lateral and anterior–posterior sway, and multidimensional psychosocial measures. ResultsDisabled individuals with chronic pain had decreased endurance for both the lifting (p <0.001) and the wheel-turning (p <0.05) tasks. A psychosocial model of physical performance also was evaluated. Using confirmatory factor analysis, 31 measures were used to validate 8 theoretical constructs: emotional functioning, pain intensity, pain cognitions, physical functioning, social functioning, task-specific self-efficacy, performance outcome, and performance style. Regression analyses indicated that more than 90% of the variance in performance was predicted by psychosocial factors, with self-efficacy, perceived emotional and physical functioning, pain intensity, and pain cognitions showing the highest associations. ConclusionsChronic pain was found to significantly reduce the performance in individuals with lower limb amputations and paraplegia. A strong association was found between performance and psychosocial factors in disabled individuals with chronic pain. These findings extend the existing literature by validating that psychosocial models of chronic pain can be applied to the disabled population, with results similar to those of other chronic pain samples.

A sensorless approach to control of a turbodynamic left ventricular assist system

A fuzzy logic controller for a rotary, turbodynamic left ventricular assist system was developed to optimize the delivery of blood flow without inducing suction in the ventricle. The controller is based on the pulsatility in blood flow through the pump and assumes that the natural heart is still able to produce some pumping action. To avoid the use of flow transducers, which are not reliable for long term use, the controller estimates flow using a model of the assist device. The controller was tested in computer simulation, a mock circulatory system, and in animal experiments. Simulation studies suggest that the fuzzy logic controller is more robust to parameter changes than a traditional proportional-integral controller. Experimental results in animals showed that the controller is able to provide satisfactory flows at adequate perfusion pressures while avoiding suction in the left ventricle.

Efficacy of percutaneous electrical nerve stimulation for the treatment of chronic low back pain in older adults.

OBJECTIVES: To determine the efficacy of a complementary analgesic modality, percutaneous electrical nerve stimulation (PENS), for the treatment of chronic low back pain (CLBP) in community‐dwelling older adults.

Speech signal modification to increase intelligibility in noisy environments

The role of transient speech components on speech intelligibility was investigated. Speech was decomposed into two components--quasi-steady-state (QSS) and transient--using a set of time-varying filters whose center frequencies and bandwidths were controlled to identify the strongest formant components in speech. The relative energy and intelligibility of the QSS and transient components were compared to original speech. Most of the speech energy was in the QSS component, but this component had low intelligibility. The transient component had much lower energy but was almost as intelligible as the original speech, suggesting that the transient component included speech elements important to speech perception. A modified version of speech was produced by amplifying the transient component and recombining it with the original speech. The intelligibility of the modified speech in background noise was compared to that of the original speech, using a psychoacoustic procedure based on the modified rhyme protocol. Word recognition rates for the modified speech were significantly higher at low signal-to-noise ratios (SNRs), with minimal effect on intelligibility at higher SNRs. These results suggest that amplification of transient information may improve the intelligibility of speech in noise and that this improvement is more effective in severe noise conditions.

Spectra of Auditory Brainstem Responses and Spontaneous EEG

Human auditory brainstem responses (ABRs) are sensory evoked potentials that can be recorded within a few milliseconds following a transient acoustic stimulus. This paper describes results of a simulation study that evaluated alternative techniques for estimating the spectrum of the ABR signal and of the background EEG. The effects of residual noise in the average signal, the number of responses in the average, and the use of smoothing windows were considered. Spectra of human ABRs were also obtained. The spectral energy decreases with frequency to 2 kHz and seems to flatten above 2 kHz. The ABR signal spectrum is limited to below approximately 1.5 kHz. There are three main components: a low-frequency component around 100 Hz, a midfrequency component around 500 Hz, and a high-frequency component at 1000 Hz. Narrow-band filtering suggests that the midfrequency component is primarily associated with Jewett wave V, while the high-frequency component is primarily associated with the early Jewett waves. These two components are probably the most important for determining the latencies of waves. The low-frequency component appears to correspond to a slow wave on which the Jewett waves are superimposed.

Power spectral analysis of EEG in a multiple-bedroom, multiple-polygraph sleep laboratory

OBJECTIVES We describe the methods for power spectral analysis (PSA) of sleep electroencephalogram (EEG) data at a large clinical and research sleep laboratory. The multiple-bedroom, multiple-polygraph design of the sleep laboratory poses unique challenges for the quantitative analysis of the data. This paper focuses on the steps taken to ensure that our PSA results are not biased by the particular bedroom or polygraph from which the data were acquired. METHODS After describing the data acquisition system hardware, we present our signal amplitude calibration procedure and our methods for performing PSA. We validate the amplitude calibration procedure in several experiments using PSA to establish tolerances for data acquisition from multiple bedrooms and polygraphs. RESULTS Since it is not possible to acquire identical digitized versions of an EEG signal using different sets of equipment, the best that can be achieved is data acquisition that is polygraph-independent within a known tolerance. We are able to demonstrate a tolerance in signal amplitude of +/- 0.25% when digitizing data from different bedrooms. When different data acquisition hardware is used, the power tolerance is approximately +/- 3% for frequencies from 1 to 35 Hz. The power tolerance is between +/- 3 and +/- 7% for frequencies below 1 Hz and frequencies between 35 and 50 Hz. Additional data demonstrate that variability due to the hardware system is small relative to the inherent variability of the sleep EEG. CONCLUSION The PSA results obtained in one location can be replicated elsewhere (subject to known tolerances) only if the data acquisition system and PSA method are adequately specified.

Steady-state analysis of auditory evoked potentials over a wide range of stimulus repetition rates: Profile in adults

Abstract Objective: Quasi-steady-state responses were assessed over a wide range of stimulus repetition rates embracing well the traditionally measured transient AEPs (obligatory auditory evoked potentials of all latencies). Repetition rates of ≤10 Hz have received little attention in the context of the ASSR stimulus-response analysis approach which is speculated to provide technical advantages, if not additional information, over more traditional transient stimulus-response paradigms. Design: A measure introduced and defined as the sum of the response at the stimulus frequency and its harmonics. The magnitude of steady-state responses were measured at repetition rates from 0.75 to 80 Hz, using trains of repeated tone-burst stimuli. Study sample: Twenty-five normal-hearing adults. Results: Results show that the magnitudes of the response across repetition rates are largest at the two lowest rates, following trends expected from the transient AEP literature. Good reliability overall was observed for the harmonic sum. Conclusions: The analysis methods used in this paper may give information that will have application for clinical testing. Of pragmatic importance is that the rate profile could be determined without subjective wave identification and/or interpretation, and thus by a method that is inherently more objective than conventional AEP tests. Sumario Objetivo: Se evaluaron respuestas de cuasi-estado estable en un amplio rango de tasas de repetición del estímulo, que correspondían a los AEP tradicionalmente medidos (potenciales evocados auditivos obligatorios de todas las latencias). Las tasas de repetición de ≤10 Hz han recibido poca atención en el contexto del enfoque de análisis de estímulo-respuesta para ASSR, que se especula proporciona ventajas técnicas, además de información adicional, sobre paradigmas más tradicionales de estímulo-respuesta transitorios. Diseño: Una medida introducida y definida como la suma (armónica) de la respuesta, a la frecuencia de estímulo y de sus armónicos. La magnitud de las respuestas de estado estable fueron medidas a tasas de repetición de 0.75 a 80 Hz, usando series de estímulos de ráfagas tonales repetidas. Muestra del Estudio: Veinticinco adultos con audición normal. Resultados: Los resultados muestran que las magnitudes de las respuestas en las tasas de repetición son mayores en las dos tasas más bajas, siguiendo la tendencia esperada de la literatura de AEP transitorios. Se observó una buena confiabilidad para la suma armónica. Conclusiones: Los métodos de análisis usados en este trabajo pueden dar información que tendrá aplicaciones para evaluación clínica. De importancia pragmática es que el perfil de la tasa podría ser determinado sin identificación y/o interpretación subjetiva de ondas, y por tanto, por un método que es inherentemente más objetivo que las pruebas convencionales de AEP.

Minimally Invasive Estimation of Systemic Vascular Parameters

AbstractA cardiovascular parameter estimator to identify the systemic vascular parameters was developed using an extended Kalman filter (EKF) algorithm. Measurements from a ventricular assist device (VAD) and arterial pressure were used in the estimator. The systemic vascular parameters are important indices of heart condition. However, obtaining these parameters usually requires invasive measurements, which are difficult to obtain under most clinical environments. Including a VAD model into the estimator and using the signals from a VAD to identify the cardiovascular parameters for VAD patients would minimize the need for indwelling sensors. This paper illustrates the use of a Novacor left ventricular assist system (LVAS) model with a cardiovascular model in the estimator to identify the systemic vascular parameters: characteristic resistance, blood inertance at the aorta, systemic compliance, and systemic resistance. Performance of the estimator was evaluated using data from a computer simulation and from a mock circulatory system experiment. Robustness of the estimator to the available measurements was also described. The estimation results showed that the estimates converged with reasonable accuracy in a limited time when the LVAS pump volume and arterial pressure were used as measurements. These parameter estimates can provide additional diagnostic information for patient and device monitoring and can be used for future VAD control development.

Body motion during repetitive isodynamic lifting: a comparative study of normal subjects and low-back pain patients ☆

To quantify performance differences between patients with low‐back pain (LBP) and a control group during their performance of a repetitive isodynamic lifting task. Case–control study was done. LBP patients were recruited and tested at an outpatient ambulatory chronic pain rehabilitation program before treatment was begun. Fifty‐three LBP patients who had prolonged back pain and 53 age and gender matched pain‐free control subjects. Overall lifting performance measures included weight lifting and number of lifts completed; kinematic measures of hip and knee movements during lifting were described by hyperbolic tangent models, and included static measures of starting and ending angles, and dynamic measures of midpoint, falltime, and lift speed. Control subjects completed significantly more lifts and lifted more weight than patients. Starting hip flexion was greater for controls and starting knee flexion was greater for patients, indicating that patients used more of a leg lift. Patients and controls also differed significantly on dynamic measures, particularly lifting speed and hip and knee temporal midpoints. Major static and dynamic motion differences were found between LBP patients and controls as they performed repetitive lifting under a constant load. These findings indicate that body motion parameters, in addition to more common strength and endurance measures, are necessary to describe the impact of persistent LBP on a persons lifting abilities.