Minimally invasive estimation of systemic vascular parameters.

A 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.

Time-frequency analysis of temporomandibular joint (TMJ) clicking sounds using radially Gaussian Kernels.

Temporomandibular joint (TMJ) sounds and motion were recorded during two clinically-derived movements--simple jaw opening and jaw protrusion followed by opening--from ten patients. A new time-frequency method--radially Gaussian kernel distribution--was applied to classify the TMJ clicking sounds into six groups, type I to type VI, based on the time-frequency patterns of energy distribution. The number of clicks and percentage of each type were examined. Relations between the two movements were examined by the prevalence of each type. A detailed classification of TMJ clicking sounds is provided by time-frequency patterns and may provide a better understanding of temporomandibular disorders.

Pressure-volume relationship of a pulsatile blood pump for ventricular assist device development.

A mathematical model describing the pressure-volume relationship of the Novacor left ventricular assist system (LVAS) was developed. The model consists of lumped resistance, capacitance, and inductance elements with one time varying capacitor to estimate the cyclic pressure generation of the pump using pump volume measurement. The ejection and filling portions of the pump cycle were modeled with two separate functions. The corresponding model parameters were estimated by least squares fit to experimental data obtained in the laboratory. Pressure and volume waveforms obtained from the model were compared with data obtained from laboratory tests and from patients. It performed well in simulating pump operation throughout the entire cycle. This model can be used for the evaluation of LVAS performance, for on-line estimation of an LVAS patient's cardiovascular parameters, for pump controller development, and as a tool for engineer training.

Elastance-based control of a mock circulatory system.

A new control strategy for a mock circulatory system (MCS) has been developed to mimic the Starling response of the natural heart. The control scheme is based on Suga's elastance model, which is implemented using nested elastance and pressure feedback control systems. The elastance control loop calculates the desired chamber pressure using a time-varying elastance function and the ventricular chamber volume signal. The pressure control loop regulates the chamber pressure according to this reference signal. Simulations and tests on MCS hardware showed that the elastance-based controller responds to changes in preload, afterload, and contractility in a manner similar to the natural heart. Since the elastance function is an arbitrary function of time, the controller allows modification of ventricular chamber contractility, giving researchers a new tool to mimic various pathological conditions which can be used in the evaluation of cardiac devices such as ventricular assist devices.

The association between research diagnostic criteria for temporomandibular disorder findings and biting force and endurance in patients with temporomandibular disorders.

OBJECTIVE: This study was designed to evaluate the association between examination findings based on Research Diagnostic Criteria for Temporomandibular Disorders and performances on bite force and endurance tasks. METHODS: Subjects were 126 patients with temporomandibular disorder and 34 pain-free controls. A subset of patients with temporomandibular disorder (n = 56) also were evaluated following a brief conservative 4-week treatment intervention. RESULTS: A multivariate analysis of variance indicated that female patients (P <.001) but not males (P =.17) had lower bite forces than age- and gender-matched controls. Dental examination findings were significantly but modestly predictive of bite task performance (R2 = 0.175), with higher joint pain and smaller maximum unassisted jaw opening associated with lower bite force. The brief treatment interventions resulted in both self-reported and clinically determined improvements. Clinical and self-reported improvement significantly predicted pre-post treatment changes in biting force among female subjects (R2 = 0.237). Specifically, reduction in joint palpation pain and self-reported pain (McGill Pain Questionnaire short form) were the primary predictors of increases in bite force. The improvement in biting force was modest (mean = 7 lb), and the force levels of female patients remained lower than those of control subjects. Treatment did not significantly increase endurance time. DISCUSSION: The brief conservative treatments used resulted in improvements in pain and jaw opening, and 81.8% of patients reported moderate to major improvement. The modest association of the bite task with Research Diagnostic Criteria for Temporomandibular Disorders examination findings and treatment improvement in this heterogeneous sample suggests that the bite and endurance tasks have limited diagnostic utility and sensitivity to treatment effects.

Effects of body mechanics training on performance of repetitive lifting.

OBJECTIVE: To measure the efficacy of body mechanics instruction (BMI) in patients with low back pain. METHOD: The effect of BMI was measured in four participants with back injuries using a standardized lifting protocol. Static strength, weight lifted, number of lifts completed, and motion analysis data to describe the body mechanics were measured before and after work hardening to evaluate treatment effects. The participants' performances were compared with 52 controls from an earlier study. RESULTS: Starting postures, characterized by degrees of hip and knee flexion, varied by participant but favored a squat lift in three participants when compared with the controls. Dynamic motion synchrony of the hip and knee joints was similar to controls in three of the four participants. Posttest data revealed significant changes in static strength, dynamic endurance, and lifting speed. CONCLUSION: Intensive instruction in body mechanics provided during the work-hardening treatment produced major changes in lifting styles, in terms of both starting postures and dynamic aspects of repetitive lifting. The computerized measurement procedures used in this study permitted more careful and detailed analyses of body mechanics, particularly dynamic aspects, than is possible with observational methods. This study demonstrated some of the inherent intricacies in isodynamic lifting and suggests additional areas of performance that may be important to address in BMI.

The influence of mandibular movements on joint sounds in patients with temporomandibular disorders.

STATEMENT OF PROBLEM: There are discrepancies among researchers concerning the reliability and use of temporomandibular joint sounds. PURPOSE: This study examined the reliability of mandibular movements and sounds and determined the correlation between movements and sounds. MATERIAL AND METHODS: The mandibular movements of 35 subjects diagnosed with temporomandibular disorders were recorded with 2 CCD cameras, and sounds were recorded bilaterally with Panasonic electret condenser microphones in the ear canal. Subjects performed 3 movements, each repeated 5 times. RESULTS: Reliability of maximum movements across the 5 trials was good to excellent, with Intraclass Correlation Coefficients (ICC) between 0.76 and 0.91 for all movements except protrusion. Temporomandibular sound event counts were reliable for most movements, including vertical opening, protrusion, and right and left laterotrusion (ICCs between 0.41 and 0.81). Most subjects produced sound events either in 100% or in none of the trials. Reliability for sound events was better during protrusion (ICCs between 0.56 and 0.81) than vertical opening (ICCs 0.41 to 0.64). Subjects with sound events during vertical opening (followed by closing) were significantly more likely to have sound events during protrusion (followed immediately by vertical opening and closing) (P <.01). CONCLUSION: Temporomandibular sound events are generally reliable and warrant study regarding their use in classifying and diagnosing patients with temporomandibular disorders. Condylar translation, which occurs during both vertical opening and protrusion, appears to have a strong influence on the production of temporomandibular sound events.

A data dependent computer algorithm for the detection of muscle activity onset and offset from EMG recordings.

This paper describes modifications to an algorithm presented by Marple-Horvat and Gilbey (1992) for identifying bursts of muscle activity in electromyographical (EMG) recordings. Our efforts to apply their algorithm to spontaneously moving infants and toddlers resulted in limited success. The modified algorithm makes several parameters dependent on the data being analyzed; these changes enabled it to analyze a variety of EMG recordings more effectively. The original algorithm had a success rate (correctly identified bursts) of 62.9% and combined error rate (number of insertions and deletions) of 73.0% when applied to an independent test data set. The modified algorithm displayed a success rate of 85.4% and combined error rate of 23.6%.

Controller for an axial-flow blood pump.

An axial-flow ventricular assist device (VAD) under development at the authors' facility is intended for use as a long-term implantable device. At high speeds axial-flow VADs can collapse the native ventricle and damage the heart muscle, lung tissue, and blood. A prototype algorithm was developed to maintain physiologic perfusion to the vital organs while preventing ventricular collapse, through analysis of the electrical current waveform of the motor. The premise of the control algorithm is that the hemodynamics of the patient are reflected in the shape of this waveform. This approach is intended to eliminate the need for invasive sensors, thus effectively using the pump itself as a transducer. The control algorithm regulates the speed of the pump by comparing the motor-current waveform with reference waveforms using a matched filter. The matched filter was evaluated by its classification and differentiation performance. Thus far, the authors have been able to classify the waveforms into one of the four physiologic regions (below, within, or above the optimal range, and ventricular suction) with over 90% reliability. Ongoing work is directed toward improving the detection of ventricular suction, as this condition must be strictly avoided.

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.

Controller for an axial flow blood pump.

A rotary blood pump inherently provides only one noninvasive "observable" parameter (motor current) and allows for only one "controllable" parameter (pump speed.) To maintain the systemic circulation properly, the pump seed must be controlled to sustain appropriate outlet flows and perfusion pressure while preventing pulmonary damage caused by extremes in preload. Steady-state data were collected at repeated intervals during chronic trials of the Nimbus AxiPump (Nimbus, Inc., Rancho Cordova, California, U.S.A.) in sheep (n = 7) and calves (n = 12). For each data set, the pump speed was increased at increments of 500 rpm until left ventricular and left atrial emptying was observed by left atrial pressure diminishing to zero. The effect of decreasing preload was evaluated perioperatively by inferior vena cava occlusion at a constant pump speed. Fourier analysis established a relationship between changes in the pump preload and the power spectra of the pump current waveform. Based on these results, a control method was devised to avoid ventricular collapse and maintain the preload within a physiologic range. The objective of this controller is the minimization of the second and third harmonic of the periodic current waveform. This method is intended to provide a noninvasive regulation of the pump by eliminating the need for extraneous transducers.

Functional capacity assessment: Influence of behavioral and environmental factors.

The environment surrounding the functional capacity evaluation (FCA) is complex and determined by both external factors as well as those specific to the testing situation. In this paper we (1) briefly review existing models of pain, (2) highlight how current FCAs of pain patients adhere in general to behavioral conceptualizations of chronic pain, (3) review some inadequacies of current conceptualizations of FCA when it applies to chronic pain, (4) review the many internal and external environmental factors that can significantly influence FCAs, and (5) consider some psychosocial factors that play an important role in patients' performances. We conclude that not only should evaluators more carefully consider the central influences of psychosocial factors when interpreting the results of FCAs, but that an alternate conceptual model that emphasizes both environmental and psychological factors is also needed to more adequately describe the physical performances obtained during FCAs.

Controller for an Axial Flow Blood Pump.

A rotary blood pump inherently provides only one noninvasive "observable'" parameter (motor current) and allows for only one "controllable" parameter (pump speed). To maintain the systemic circulation properly, the pump speed must be controlled to sustain appropriate outlet Hows and perfusion pressure while preventing pulmonary damage caused by extremes in preload. Steady-state data were collected at repeated intervals during chronic trials of the Nimbus AxiPump (Nimbus, Inc., Rancho Cordova, California, U.S.A.) in sheep (n = 7) and calves (n = 12). For each data set, the pump speed was increased at increments of 500 rpm until left ventricular and left atrial emptying was observed by left atrial pressure diminishing to zero. The effect of decreasing preload was evaluated perioperatively by inferior vena cava occlusion at a constant pump speed. Fourier analysis established a relationship between changes in the pump preload and the power spectra of the pump current waveform. Based on these results, a control method was devised to avoid ventricular collapse and maintain the preload within a physiologic range. The objective of this controller is the minimization of the second and third harmonic of the periodic current waveform. This method is intended to provide a noninvasive regulation of the pump by eliminating the need for extraneous transducers.

Body motion patterns during a novel repetitive wheel-rotation task. A comparative study of healthy subjects and patients with low back pain.

STUDY DESIGN: This study evaluated performance differences between patients with chronic low back pain and a control group during their performance of a novel functional capacity task. OBJECTIVE: To 1) evaluated strength and endurance differences between patients and control subjects, 2) test for movement pattern differences between these groups, and 3) evaluate how these patterns changed with repetitive performance of the wheel-turning task. SUMMARY OF BACKGROUND DATA: Despite increased emphasis on quantifying functional capacities, few well-controlled studies comparing the performances of patients with low back pain with those of control subjects have appeared in the literature, particularly for movement patterns. METHODS: Forty patients with low back pain and 40 control subjects performed a sustained isodynamic wheel turning task. This task was selected because it simultaneously combined several common pain-related movements. A set of kinematic measures to characterize the basic movement patterns during this task were developed. RESULTS: Control subjects produced significantly higher levels of static torque and completed significantly more wheel-turning repetitions. Patients with low back pain exhibited significantly less upper torso and pelvic motion, upper torso rotation, and lateral trunk flexion than those in the control group. CONCLUSION: The dissimilar movement strategies found between the patient and control groups suggests that factors beyond more global physical explanations (e.g., deconditioning) may be important in accounting for the large discrepancy between these groups regarding the amount of work performed. These findings, along with the basic kinematic patterns developed in this study, may have important implications for determining the efficacy of instruction in body mechanics and treatment outcome for patients with chronic low back pain.

Measuring treatment effects on repetitive lifting for patients with chronic low back pain: speed, style, and coordination.

The purpose of this study was to determine changes in the amount of work performed and lifting speed, style, and coordination during a repetitive dynamic-lifting task for patients with chronic low back pain (CLBP) after an intensive 3 1/2-week pain rehabilitation program. Subjects included 57 CLBP patients and an age- and gender-matched control group (n = 57). Patients' work indices increased by 71%, but remained significantly less than those observed for controls. Similarly, their lifting speed also increased significantly after treatment, but remained slower than the lifting speed of controls. Patients' posttreatment coordination indices, however, were not significantly different from those of controls. This finding suggests that treatment effectively normalized the dynamic lifting motion used by the patients. These findings, along with the basic kinematic patterns developed in this study, have important implications for determining improvements in functional capacity in the treatment of patients with CLBP.

Dynamic systemic vascular resistance in a sheep supported with a Nimbus AxiPump.

Changes in systemic vascular resistance (SVR) in response to diminished pulse perfusion were analyzed over a dynamic range of flow conditions. An axial flow LVAD (Nimbus AxiPump, Rancho Cordova, CA) was implanted in a sheep for 28 days, during which time SVR was determined over several conditions of posture and excitability. Total arterial resistance (TR) was calculated dynamically as an index of SVR by analysis of pump flow in diastole, and systemic pressure estimated from the characteristic pressure-flow-speed relation of the AxiPump. TR was evaluated over a range of flow rates, including maximum flow--for which the pressures and flows were essentially nonpulsatile. Throughout the course of support, and independent of pulsatility, TR dropped when the sheep stood and was significantly lower than that in the sitting position (P < 0.01). Response to excitement followed the same trend: TR was significantly higher during agitation than during normal temper (P < 0.01). In spite of changes in pulse pressure and flow rate, SVR changes occurred according to expected physiologic responses for pulsatile perfusion. Because pump flow and pressure are sensitive to afterload, the results of these studies suggest that pump speed control must compensate for changes in SVR to maintain acceptable perfusion.

Local cerebral blood flow measured by xenon-enhanced CT during cryogenic brain edema and intracranial hypertension in monkeys.

We developed a closed-skull model of freeze injury-induced brain edema, a model classically thought to produce vasogenic edema, and observed the natural course of changes in edema and blood flow using xenon-enhanced computed tomography (CT) in five rhesus monkeys before and for up to 6 h post insult. Intracranial pressure (ICP) gradually rose throughout the duration of the experiment. CT scans and CBF images permitted direct observation of the evolution of the lesion and revealed early ischemia in the periphery of the injury zone that progressed over time in association with edema. Frequency histogram analysis of local CBF (ICBF) demonstrated subtle but potentially important changes in distribution of ICBF between and within hemispheres at various times post insult. Changes in ICBF distribution were phasic and dissociated from increases in ICP in the latter stages of injury. The Xe/CT CBF method can be used to evaluate the effects of injury and therapy on CBF in this and other models of acute brain injury.

Effect of 80% Xe on whole brain blood flow and metabolism in awake monkeys.

We previously reported that 33% xenon (Xe) did not activate cerebral blood flow (CBF) and metabolism in monkeys as it appears to do in humans. However, monkeys may be less sensitive to Xe than humans are, which would explain the discrepancy in the results, but no one has studied the effects of higher concentrations of Xe on CBF and metabolism in monkeys. Therefore, we studied the effect of 80% Xe on whole-brain CBF, cerebral metabolic rate for oxygen (CMRO2) and glucose (CMRG) in five awake rhesus monkeys. Platinum microelectrodes and catheters inserted into the torcular Herophili were used to measure H2 clearance CBF, and to withdraw cerebral venous blood for O2 and glucose analysis. Cerebral variables were measured after 15 min exposure to 80% N2/20% O2 followed by 80% Xe/20% O2. Eighty percent Xe compared with 80% N2 increased (p <0.01) CBF by 52.7% from 74 +/- 16 to 113 +/- 25 (mean +/- SD) ml 100 g(-1)/min(-1), CBF/CMRO by 154% from 13 to 33, and decreased (p <0.05) CMRO2 by 39.3% from 6.1 +/- 0.9 to 3.7 +/- 0.8 ml 100 g(-1)/min(-1) and CMRG by 52.4% from 8.4 +/- 2.6 to 4.0 +/- 2.0 mg 100 g(-1)/min(-1). Electroencephalogram frequency decreased from a predominantly alpha to dagger rhythm in three of five monkeys. The 40 and 50% reduction in CMRO2 and CMRG, respectively, by 80% Xe suggests an anesthetic effect at this dose in the rhesus monkey but also activates CBF by 50%.

Correlations of neuroanatomical measures to auditory brain stem response latencies.

Magnetic resonance imaging (MRI) was used to obtain measures presumed to scale the dimensions of the lower auditory pathway in humans for the purpose of further defining the relationship between length of the auditory pathway and auditory brain stem response (ABR) latencies. Specifically, measurements of soft tissue structures, that is, the eighth nerve and brain stem, were made for comparison with skull dimensions and ABR latencies. It was hypothesized that the brain stem dimensions covary significantly with skull dimensions and that the ABR parameters covary with both skull and brain stem dimensions. In general, only weak correlations were obtained with coefficients failing to reach statistical significance for most comparisons. These findings suggest that variance in ABR latencies cannot be attributed completely to variance in brain stem dimensions and raise suspicion that skull dimensions do not directly reflect brain stem dimensions.

Effect of 33% xenon inhalation on whole-brain blood flow and metabolism in awake and fentanyl-anesthetized monkeys.

BACKGROUND AND PURPOSE: Despite the documented diagnostic value of local cerebral blood flow maps by xenon-enhanced computed tomography, reports of cerebral blood flow activation by inhaled 33% Xe raised concerns about the method's safety and accuracy. We evaluated the effect of 33% Xe inhalation on cerebral blood flow and cerebral metabolic rates for oxygen and glucose in four awake and six fentanyl-anesthetized rhesus monkeys. METHODS: Platinum microelectrodes and catheters in the torcular Herophili were used to measure cerebral blood flow by hydrogen clearance, and oxygen and glucose concentrations. Cerebral variables were measured after 5 and 35 minutes of exposure to room air followed randomly by 67% O2 in 33% N2 or Xe. Five- and 35-minute measurements were combined because the duration of exposure had no effect. RESULTS: In awake monkeys, 33% Xe compared with 33% N2 reduced (p less than 0.05) cerebral blood flow from 75 +/- 12 to 66 +/- 9 (mean +/- SD) ml.100 g-1.min-1 and oxygen consumption from 6.1 +/- 0.7 to 5.1 +/- 0.6 ml.100 g-1.min-1. In fentanyl-anesthetized monkeys, cerebral variables during 33% N2 versus 33% Xe were cerebral blood flow, 84 +/- 26 versus 79 +/- 23 ml.100 g-1.min-1; oxygen consumption, 5.0 +/- 0.7 versus 4.9 +/- 0.5 ml.100 g-1.min-1; and glucose consumption, 8.4 +/- 1.9 versus 7.9 +/- 2.0 mg.100 g-1.min-1. CONCLUSIONS: In awake monkeys, 33% Xe reduced rather than activated cerebral blood flow and oxygen consumption by 12% and 16%, respectively; it had no effect in fentanyl-anesthetized monkeys.