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Biomedical subjects

R E Kearney

Publications and source records attributed to R E Kearney.

At least 19 recordsLinked to original sources
PubMed1995

Bioavailability of fluconazole in surgical intensive care unit patients: a study comparing routes of administration.

OBJECTIVE: Anticandidal therapy is commonly used in the surgical intensive care unit (SICU). Unfortunately, it is expensive because it is generally given intravenously, as acute trauma and abdominal surgery are often accompanied by impaired gastrointestinal function. We compared the systemic availability of fluconazole given enterally or intravenously in trauma and surgery SICU patients to determine the reliability of enteral administration. METHODS: Nine adult trauma (Injury Severity Score (> or = 18) and nine adult abdominal surgery SICU patients were randomized to receive fluconazole 100 mg via the intravenous (IV) or enteral route. Patients with a bilirubin > 4.0 mg/dL or creatinine clearance < 60 mL/min were excluded. Enteral fluconazole was crushed, dissolved, and flushed through a nasogastric or feeding tube. Eleven serial blood samples were drawn over 72 hours. Area under the curve (AUC), elimination rate constant (Ke), and terminal half-life (T1/2) were determined and compared (t test). Relative bioavailability was estimated (AUC(enteral)/AUCIV). RESULTS: Peak concentrations occurred within 2 hours after enteral dosing and 15 minutes after IV dosing. The relative bioavailability was 77%. Weight, AUC, Ke, and T1/2 did not differ between enteral and IV dosing. CONCLUSIONS: Fluconazole is significantly absorbed when crushed, dissolved, and given via a nasogastric or feeding tube in SICU patients. Nonsignificant trends toward lower systemic availability with enteral administration can be overcome with slightly higher doses. Since enteral administration of fluconazole costs 10% of fluconazole given intravenously, more liberal use of enteral administration offers tremendous savings. Such savings moderate the cost concerns of antifungal therapy.

Abdomen↗
PubMed1992

A new algorithm for the identification of multiple input Wiener systems.

Multiple-input Wiener systems consist of two or more linear dynamic elements, whose outputs are transformed by a multiple-input static non-linearity. Korenberg (1985) demonstrated that the linear elements of these systems can be estimated using either a first order input-output cross-covariance or a slice of the second, or higher, order input-output cross-covariance function. Korenberg's work used a multiple input LNL structure, in which the output of the static nonlinearity was then filtered by a linear dynamic system. In this paper we show that by restricting our study to the slightly simpler Wiener structure, it is possible to improve the linear subsystem estimates obtained from the measured cross-covariance functions. Three algorithms, which taken together can identify any multiple-input Wiener system, have been developed. We present the theory underlying these algorithms and detail their implementation. Simulation results are then presented which demonstrate that the algorithms are robust in the presence of output noise, and provide good estimates of the system dynamics under a wide set of conditions.

Algorithms↗
PubMed1992

Identification of time-varying biological systems from ensemble data.

The theory underlying a new method for the identification of time-varying systems is described. The method uses singular value decomposition to obtain least-squares estimates of time-varying impulse response functions from an ensemble of input-output realizations. No a priori assumptions regarding the system structure or form of the time-variation are required and there are few restrictions on the input signal. Simulation studies, using a model of time-varying joint dynamics, show that the method can track rapid changes in system dynamics accurately and is robust in the presence of output noise. An application of the method is demonstrated by using it to track dynamic ankle stiffness during a rapid, voluntary, isometric contraction. During the transient phase of the contraction, low-frequency ankle stiffness gain decreased in a manner which could not be described with the second-order model of joint dynamics often used under stationary conditions.

Adult↗
PubMed1991

Prospective study of a prosthetic H-graft portacaval shunt.

This study was undertaken to prospectively evaluate the 8-mm Gore-Tex interposition H-graft portacaval shunt. Thirty-six high-risk patients at the University of South Florida-affiliated hospitals received small-diameter shunts because of bleeding esophagogastric varices over a recent 2-year period. Portal vein and portal vein-inferior vena cava gradients were significantly reduced after shunting. These pressure changes were manifested clinically by the absence of variceal rebleeding and improvement of ascites; in addition, the incidence of encephalopathy was low. The 8-mm graft maintained hepatopedal flow in 67% of the patients, but reversal of flow did not result in complications commonly associated with poor portal perfusion. Graft thrombosis occurred in four (11%) patients. All grafts were successfully revised, three by operative revision and one by an interventional radiologist. Operative mortality was low (11%), and morbidity was unusual. The small-diameter H-graft portacaval shunt is a safe and effective method of treatment for bleeding esophagogastric varices.

Adult↗
PubMed1991

Diagnostic peritoneal lavage. Limited indications due to evolving concepts in trauma care.

This study was undertaken to determine the appropriateness of celiotomy in 100 consecutive patients who underwent celiotomy solely because of positive diagnostic peritoneal lavage (DPL) following blunt (B) or stab (S) abdominal trauma. A total of 32 (32%) patients had positive DPL by laboratory criteria: blunt trauma: greater than 100K RBC/mm3, greater than 500 WBC/mm3; stab trauma: greater than 50K RBC/mm3, greater than 250 WBC/mm3. DPL in 68 patients was positive by gross inspection; 18 of these 68 patients' DPL laboratory results returned after surgery and did not satisfy the laboratory definition of positive DPL. In all 61 per cent underwent therapeutic celiotomy (TC) and 39 per cent underwent nontherapeutic celiotomy (NTC). Grade I and II spleen and/or liver injuries led to 79 per cent of NTCs. Positive DPL, determined by gross inspection or by laboratory testing, has a very poor accuracy rate when evaluated in light of evolving beliefs that promote nonoperative therapy for grade I and II liver and spleen injuries. When positive DPL is the sole indication for celiotomy in patients with blunt or stab abdominal trauma, an unacceptably large number of NTCs will be performed. DPL should have a limited role in the evaluation of patients with abdominal trauma.

Abdominal Injuries↗
PubMed1990

Treatment of candidosis in severely injured adults with short-course, low-dose amphotericin B.

Thirty-three (0.7%) of 4,818 trauma patients admitted between January 1, 1987, and July 1, 1989, developed invasive candidosis requiring IV antifungal therapy. All patients were seriously traumatized. Before developing candidosis, all patients had documented bacterial infections. These infections were generally polymicrobial and were treated with multiple broad-spectrum antibiotics (an average of 5.4 antibiotics for 17.2 days). Twenty-eight (85%) of 33 patients received enteral feedings for an average of 11 days +/- 1.5 (SEM) before developing candidosis and 24 (73%) received NG/oral nystatin for an average of 7.6 days +/- 0.9 before developing candidosis. All patients with candidosis were treated with intravenous amphotericin B: cumulative dose of 157.3 mg +/- 31.3 mg given over 10 days +/- 1.1. One patient developed recurrent candidosis despite NG/oral prophylaxis and enteral feedings. Six patients (18%) died due to sepsis and multiple organ failure. The patients who died did not objectively differ from the survivors. Candidosis is an infrequent infection in severely injured patients. Candidosis was invariably preceded by treatment with multiple broad-spectrum antibiotics for a variety of polymicrobial bacterial infections. NG/oral nystatin and enteral feedings did not prevent candidosis, in contrast to widely accepted beliefs. Amphotericin B therapy was safe. Recurrent candidosis was unusual. Candida infections had a high mortality rate associated with multiple blood transfusions and prolonged hospitalization. Candidosis represents a sign of severe injury and illness but can be amenable to prompt, aggressive treatment.

Adult↗
PubMed1990

System identification of human joint dynamics.

The dynamics of joint mechanics are a fundamental characteristic of the motor system. They determine the displacements evoked by perturbing forces during postural control and the forces that must be generated to perform a voluntary movement. This article reviews experimental studies of these dynamics, with an emphasis on the behavior of single joints in alert humans. Technical aspects of the experimental and analytic methods that have been used are summarized first. Major results obtained with the different methods are then reviewed, compared, and contrasted. The interpretation of these results in terms of the underlying physiological mechanisms is then considered, with an emphasis on the relative contributions of passive properties of tissue, the mechanical behavior of muscle, and stretch reflexes. Finally, important unanswered questions regarding the dynamics of joint mechanics are reviewed.

Biomechanical Phenomena↗
PubMed1989

Method for EMG conduction velocity estimation which accounts for input and output noise.

A new technique is derived for estimating the conduction velocity of muscle fibre action potentials from surface EMG recordings in humans. The method is based on system identification and extends previous such methods by explicitly accounting for additive noise at the output as well as at the input. Experimental and simulation results demonstrate that at moderate noise levels the new method yields estimates comparable to those obtained with previous methods. However, simulation studies show that the new method should be particularly valuable at high noise levels, where it should provide much better estimates than previous techniques provided that an adequate representation of the noise is available.

Action Potentials↗
PubMed1989

Outcome of treatment of combined orthopedic and arterial trauma to the lower extremity.

To ascertain morbidity and disability associated with vigorous attempts at limb salvage after lower extremity combined orthopedic and arterial injuries we reviewed more than 10,000 trauma admissions. Twenty-two patients (0.2%) suffered 14 blunt and eight penetrating lower extremity orthoarterial injuries. In all, more than 90 extremity operations were performed within 30 days of admission. The mechanism of injury, ISS, sequence of orthopedic and vascular procedures, use of temporary arterial shunts, the nature of the arterial reconstruction, length of ischemic time, and the presence of open fractures did not affect limb salvage or outcome. The presence of neurosensory/motor impairment and/or serious soft-tissue loss and injuries at or distal to the popliteal artery were associated with a high frequency of disability and amputation. Tremendous effort was expended to achieve limb salvage in the patients of this review. Patients who underwent amputation had the more uneventful hospitalizations and the lower rates of disability. The notion that limb salvage need to be obtained in all patients at all costs may often lead to the triumph of technique and technology over reason.

Adult↗
PubMed1988

Nonlinear identification of stretch reflex dynamics.

The objective of this study was to use nonlinear identification techniques to study the dynamics of stretch reflexes in the human calf muscles (gastrocnemius-soleus). Stochastic perturbations of ankle position were applied while subjects maintained a constant, tonic contraction of gastrocnemius-soleus. Linear models of the relation between ankle velocity and the electromyographic (EMG) activity under these conditions typically accounted for less than 40% of the observed EMG variance. Nonlinear system identification techniques were then applied. The first- and second-order Wiener kernels were computed as the initial stage of this analysis. These did not provide an adequate description of system behavior; subsequent simulation studies showed that the major problem with the Wiener analysis was that the input spectrum was not adequately white. Nevertheless, the shape of the second-order Wiener kernel suggested that a Hammerstein structure consisting of a static nonlinearity followed by a dynamic linear system would be appropriate. Consequently, we used an iterative procedure for Hammerstein system identification to determine the form of the static nonlinearity and the associated linear dynamics. The resulting nonlinear model provided a much better description of the system's behavior than did the linear models (variance accounted for greater than 60%). Furthermore, they confirmed our previous empirical findings; the static nonlinearity closely resembled a half-wave rectifier while the dynamics were typified by a pure delay and a velocity filter. The application of nonlinear identification techniques thus produced a much improved, physically meaningful model of stretch reflex behavior.

Electromyography↗
PubMed1988

Human ankle joint stiffness over the full range of muscle activation levels.

System identification techniques have been used to track changes in dynamic stiffness of the human ankle joint over a wide range of muscle contraction levels. Subjects lay supine on an experimental table with their left foot encased in a rigid, low-inertia cast which was fixed to an electro-hydraulic actuator operating as a position servo. Subjects generated tonic plantarflexor or dorsiflexor torques of different magnitudes ranging from rest to maximum voluntary contractions (MVC) during repeated presentations of a stochastic ankle angular position perturbation. Compliance impulse response functions (IRF) were determined from every 2.5 s perturbation sequence. The gain (G), natural frequency (omega n), and damping (zeta) parameters of the second-order model providing the best fit to each IRF were determined and used to compute the corresponding inertial (I), viscous (B) and elastic (K) stiffness parameters. The behaviour of these parameters with mean torque was found to follow two simple rules. First, the elastic parameter (K) increased in proportion to mean ankle torque as it was varied from rest to MVC; these changes were considerable involving increases of more than an order of magnitude. Second, the damping parameter (zeta) remained almost invariant over the entire range of contractions despite the dramatic changes in K.

Adult↗
PubMed1986

Position dependence of stretch reflex dynamics at the human ankle.

The purpose of this study was to examine the effect of ankle position on the human ankle stretch reflexes during tonically-maintained contractions over most of the range of motion. The ankle was placed at randomly selected mean positions. Target levels of triceps surae (TS) or tibialis anterior (TA) tonic contractions were generated while the ankle was displaced by small amplitude, stochastic perturbations. System identification techniques were used to identify the stretch reflex dynamics at each combination of tonic level and ankle angle. As shown previously, the TS stretch reflex was characterized by an unidirectional, velocity-sensitive impulse response function whereas the TA stretch reflex was characterized by a linear impulse response function between ankle velocity and TA EMG. TS stretch reflexes showed a strong dependence on ankle position while TA stretch reflexes did not. Thus the TS stretch reflex magnitude increased greatly as the ankle was progressively dorsiflexed. In contrast, ankle mean position had only a minor effect on the TA stretch reflex magnitude. Our results indicate that the position-dependent facilitation of the TS stretch reflex is not due to changes in the level of skeletal motoneuron excitability. Rather, this effect may be accounted for by mechanisms that modulate the efficacy of the stochastic ankle perturbation. Such mechanisms could include position-induced: modulation of monosynaptic and polysynaptic afferent inputs to skeletal motoneurons, alterations in the extent of fusimotor drive and changes in the transmission of the joint perturbation to spindle receptors. Such mechanisms are discussed in terms of the differences between TS and TA stretch reflexes. Finally, the functional significance of position-dependent reflex responses are considered.

Adult↗
PubMed1986

Visual, vestibular and voluntary contributions to human head stabilization.

We have investigated the ability of humans to stabilize their heads in space and assessed the influence of mental set and the relative importance of visual and vestibular cues. Ten normal subjects and 3 patients with bilateral vestibular loss were studied. Subjects were fixed firmly to the chair of a turntable facing a screen on which was projected a target spot. A 'gunsight' spot generated by a small projector fixed to the head provided feedback of head position. Four conditions were studied (1) Gunsight (GU): subjects were instructed to stabilize the head in space by superimposing the 'gunsight' spot on the fixed target spot while chair position was displaced according to a random pattern with a bandwidth from 0-1 Hz. (2) Imagined gunsight (IGU): identical to condition 1 except that the subject was blindfolded and so had to imagine the target position. (3) Mental arithmetic (MA): subjects did mental arithmetic while the chair was displaced. (4) Visual tracking (VT): subjects were instructed to track the target spot with the 'gunsight' spot while the chair was fixed and the target spot driven to follow the chair displacement trajectory used in conditions 1, 2 and 3. In GU normal subjects stabilized their head position extremely well (mean HEAD/CHAIR gain = 0.81). Significant stabilization was present in IGU although the gain (mean gain = 0.61) was reduced compared to GU. There was very little stabilization in MA (mean gain = 0.12). In VT, subjects tracked the target with about the same gain (mean gain = 0.68) as in IGU. By comparison, the vestibular patients could not perform IGU, for which their performance (mean gain = 0.08) was similar to MA (mean gain = 0.06). In GU (mean gain = 0.54), their performance was attributable to visual tracking (mean gain in VT = 0.50). For the frequency bandwidth in which subjects were tested, the results show that: When subjects were distracted by mental arithmetic, the contribution to head stability of the short latency cervico-collic (CCR) and vestibulo-collic (VCR) reflexes is negligible. As expected, vision plays an important role in stabilizing the head. Equally important are long latency stabilizing mechanisms whose onset times (140 ms) are shorter, but still comparable to that of vision. The latter mechanisms are of vestibular origin and their influence is under voluntary control so as to permit augmenting head stability compared to what it would be if vision acted alone.

Adult↗
PubMed1986

Position dependence of ankle joint dynamics--I. Passive mechanics.

System identification techniques were used to examine the position dependence of passive ankle joint mechanics. The relaxed ankle was stochastically perturbed about different angles in the range of motion (ROM). The linear dynamic relation between ankle position and torque was identified and modelled as a second-order underdamped system, having inertial (I), viscous (B) and elastic (K) parameters. Mean joint torque changed as the ankle was rotated through the ROM; it was small at mid-range and became much larger toward either extreme. While I remained constant both B and K changed as a function of ankle angle. At the extremes of the ROM, K was much larger than previously assumed and the relation between stiffness and the passive torque generated when the ankle was placed at different mean positions was linear. These results show that large variations in joint mechanics are possible even in the absence of voluntary muscle contraction. Moreover, these changes appear to be related to the torque generated when passive joint structures are stretched.

Adult↗
PubMed1986

Position dependence of ankle joint dynamics--II. Active mechanics.

System identification techniques were used to examine the position dependence of active ankle joint mechanics. Subjects were required to maintain tonic contractions in either the tibialis anterior (TA) or triceps surae (TS) muscles while the ankle was stochastically displaced about different mean angular positions. The dynamic relation between ankle position and torque was determined for each mean position/tonic torque combination; a non-linear minimization technique was used to estimate the three parameters (inertial, viscous and elastic) of a second-order, underdamped system. Whereas the inertial parameter remained essentially invariant across all test conditions, the viscous and elastic (K) parameters became larger as the level of tonic activity increased and as the joint was rotated toward the extremes of the range of motion. The relation between K and torque was linear at all ankle angles. The slope of this relation remained constant at all mean positions during plantarflexor contractions; during dorsiflexor contractions the slope increased as the ankle was rotated from maximum plantarflexion to maximum dorsiflexion. These findings are discussed in terms of: the physiological correlates of ankle mean position, the relative significance of passive and active joint mechanics and contrasts in joint behaviour during active dorsiflexor and plantarflexor contractions.

Adult↗