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Biomedical subjects

A Prochazka

Publications and source records attributed to A Prochazka.

At least 55 records · Page 3Linked to original sources
PubMed1995

Smoking habits of emergency department patients: an opportunity for disease prevention.

OBJECTIVE: To determine smoking habits, levels of addiction, readiness to quit, and access to primary care among ED patients. METHODS: A questionnaire was administered prospectively to all noncritical adult patients who presented to one university hospital ED during 23 randomly selected four-hour time blocks; 336 (89%) of 376 eligible patients responded. Self-reported smoking was validated by carbon monoxide breath testing in a pilot sample of 49 patients. RESULTS: The study patients were mostly young (mean age = 35 +/- 15 years), female (59%), white (62%), and high school-educated (73%). Of the 336 ED patients, 41% were current smokers (95% CI = 0.36-0.46); 42% of these were "moderately" to "very highly" dependent on nicotine (Fagerstrom Test for Nicotine Dependence > 4). Of those who smoked, 68% stated they wanted to quit, and 49% wanted to quit within the month. Fifty-six percent of all those who smoked stated that they had never been told to quit smoking by any physician. Thirty-five percent of the ED sample (118 patients) relied upon EDs for most or all of their routine, primary health care; 55% (95% CI = 0.46-0.64) of these patients were current smokers. CONCLUSIONS: The prevalence rates of smoking and nicotine addiction among ED patients are high. Almost half of ED smokers are ready to quit, but most state they have never been told by a physician to do so. Finally, a large proportion of ED smokers receive their primary care in EDs. Therefore, the ED may be an underused setting for smoking cessation intervention.

Adolescent↗
PubMed1995

Smoking cessation counseling by emergency physicians: opinions, knowledge, and training needs.

OBJECTIVES: To determine: 1) the extent of emergency physicians' (EPs') training in smoking cessation counseling; 2) their understanding of counseling and pharmacologic treatment techniques; 3) their current practices in screening, counseling, and referring patients who smoke; and 4) perceived barriers to routine smoking cessation counseling in emergency medical practice. METHODS: A 26-item questionnaire addressing the above issues was mailed to all 256 members of the Colorado Chapter of the American College of Emergency Physicians. RESULTS: Completed questionnaires were returned by 196 physicians (77% response rate). The majority of respondents were men (80%), practiced in urban settings (87%), and were board-certified in emergency medicine (82%). Most EPs lacked formal smoking cessation training (55%) and felt poorly prepared to counsel patients about smoking cessation (65%). A minority (27%) of the physicians reported routinely asking patients to quit smoking. The physicians with formal smoking cessation training were more likely to counsel and refer patients routinely (34% vs 20%, p = 0.03). The physicians cited the following barriers to routine smoking cessation counseling: a lack of time; a perception that patients are not interested; a belief that the ED setting is inappropriate for counseling; and a sense that counseling is ineffective. Lack of reimbursement was cited by only 13% of the respondents. The physicians who had formal smoking cessation training perceived fewer barriers to ED-based counseling. CONCLUSIONS: Emergency physicians have received little training in smoking cessation and perceive many barriers to ED-based smoking cessation interventions. Not surprisingly, they infrequently take action to encourage or assist their patients to quit smoking.

Adult↗
PubMed1995

Suppression of the corrective response to loss of ground support by stimulation of extensor group I afferents.

1. When a hind leg of a walking cat fails to contact the ground at the end of swing, the limb is rapidly lifted and replaced in an attempt to seek support. In this investigation we tested the hypothesis that one factor in the initiation of this corrective response is the absence of signals from the group I afferents of extensor muscles. 2. Experiments were performed on decerebrate cats walking on a treadmill. The corrective response to loss of ground support occurred when one hind leg stepped into a hole cut into the treadmill belt. Group I afferents in various extensor nerves were stimulated via implanted cuff electrodes when the foot entered the hole. 3. Stimulation of extensor group I afferents suppressed the corrective flexion response. Instead of a flexor burst being generated soon after the foot entered the hole, extensor activity was maintained for a period exceeding the duration of the stimulus trains. The onset of the corrective response occurred at a relatively fixed latency of 70 ms after the end of the short stimulus trains (200-400 ms) provided that the contralateral limb was still in stance phase. For longer stimulus trains (500-1,000 ms) that terminated during or just prior to the swing phase of the contralateral leg, the onset of ipsilateral flexor activity occurred only after the contralateral leg had regained support. 4. We conclude that the absence of signals from group I afferents when a foot fails to contact the ground allows the locomotor rhythm generator to re-initiate a flexor burst to produce the corrective response.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1994

Catching a ball: contributions of intrinsic muscle stiffness, reflexes, and higher order responses.

In three sets of experiments in nine normal subjects and a patient with a percutaneous wrist-stabilizing splint, we quantified the open-loop gain (OLG) of the stretch reflex acting about the elbow. The subjects exerted a steady mean flexing force and were instructed not to intervene (i.e., not to resist actively) when force or displacement perturbations were imposed on the forearm. The method was either to reconstruct transmission around the entire loop in a two-part experiment, or to use the attenuation of external perturbations in normal and electrically stimulated muscle to compute gain. Across all experiments, the mean magnitude of stretch reflex OLG was close to unity in the frequency range 1-2 Hz, and declined at higher frequencies, as required to ensure stability, given that the phase lag approached 180 degrees at 5 Hz. Inherent muscle stiffness was approximately equal to reflex stiffness. In functional terms, an OLG of 1 means that the yield caused by a force perturbation is approximately halved by reflex action (prevailing inherent muscle stiffness is doubled). Automatic scaling of reflex transmission at Ia/alpha-motoneuronal synapses ensures that the OLG remains close to unity as inherent stiffness increases. Trials in the patient with the wrist fixator gave similar results, indicating that the reflexes were proprioceptive ly mediated. In a fourth experiment in which the task was to catch a heavy ball, we compared the efficacy of inherent muscle stiffness and reflexes alone, with the subject's intentional reactions, which included predictive and voluntary components of response. The latter were far more effective in maintaining the position of the hand after the ball was caught than inherent and reflex stiffnesses alone. We conclude that stability requirements limit the extent to which stretch reflexes can augment inherent muscle stiffness. When inherent muscle stiffness is low, such as in our ball-catching task, the reflex stiffness is also low, and predictive and pre-programmed reactions predominate in load compensation, thus shifting the emphasis from automatic servo or equilibrium-point behaviour to higher order control.

Elbow Joint↗
PubMed1994

Corrective responses to loss of ground support during walking. I. Intact cats.

1. In the cat step cycle the electromyographic (EMG) activity in ankle extensor muscles commences approximately 70 ms before foot contact. There is a sharp peak between 10 and 25 ms after contact and the EMG then declines for the remainder of the stance phase. It has been posited that the abrupt transition in EMG after contact is the consequence of reflexes elicited by the large barrage of afferent input that signals foot touchdown. However, it is also possible that the basic profile might be generated within the CNS, with little modification by afferent input. 2. These ideas were tested in 11 normal cats. We compared EMG responses and hindlimb kinematics in steps with normal ground support and steps in which an actuator-controlled trap door unexpectedly opened, withdrawing ground support just before foot contact. 3. In the absence of ground support the transition in EMG activity was still present. The averaged EMG pattern was similar for at least 30 ms after the foot passed through the plane of the floor. We conclude that the basic extensor activation profile in this part of the cycle is generated centrally and is not substantially altered by afferent input. 4. Between 35 and 200 ms after contact the stance phase was aborted and the foot was lifted smartly out of the hole. This reaction varied both in latency and kinematic detail, suggesting a fairly complex corrective response.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1994

Corrective responses to loss of ground support during walking. II. Comparison of intact and chronic spinal cats.

1. The preceding study described a corrective response in cats when one hind leg steps into a hole. In this investigation we examine the extent to which this behavior is organized at the spinal level by comparing the responses elicited in intact and chronic spinal cats. 2. Adult cats were trained to step bipedally with their hind legs on a treadmill. After training, the responses to stepping into a hole cut in the treadmill belt were monitored with a video recorder and by recording electromyograms from muscles in both hind legs. The responses to stepping into the hole were also recorded in chronic spinal cats that had recovered the ability to step with their hind legs a few weeks after spinalization. 3. The behavioral responses in the two groups of animals differed in two respects. First, the latency of the onset of the flexion movement to remove the foot from the hole was shorter in intact animals (70-150 ms in intact vs. 130-350 ms in spinal animals). Second, the flexion movement in the intact animals was stronger. The exaggerated flexion movement in intact animals lifted the paw well clear of the hole and allowed support to be regained on the treadmill belt. The weaker flexion movement in spinal animals was usually insufficient to lift the paw completely from the hole. 4. Differences in the motor patterns recorded from flexor muscles during the corrective response in intact and spinal animals correspond with the differences in the kinematics. First, the onset of flexor activity after the foot entered the hole was delayed by approximately 100 ms in spinal animals relative to intact animals. Second, in intact animals the magnitudes of flexor bursts were increased relative to the flexor bursts associated with the swing phase during stepping, whereas in spinal animals flexor bursts during the corrective response resembled those occurring during swing. 5. Similarities in the duration and the timing of bursts in different flexor muscles in intact and spinal animals during the corrective response and during swing indicated that the corrective response involves activation of the spinal system that normally produces swing phase flexor activity. We conclude that activation of this system is facilitated by input from supraspinal structures during the corrective response in intact animals. 6. In all intact animals and three of five spinal animals, support of the hindquarters when the foot entered the hole was maintained by the contralateral leg.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1994

The role of sensory information in the guidance of voluntary movement: reflections on a symposium held at the 22nd annual meeting of the Society for Neuroscience.

This article reviews a symposium on the sensory control of movement held at the 22nd annual meeting of the Society for Neuroscience. Four speakers addressed a large audience on the proposition that "one can only control what one senses." Charles Vierck supported the notion with a description of the severe motor deficits caused by lesions of the spinal dorsal columns (DCs) in monkeys. In the discussion of Vierck's presentation, Robert Forget described the difficulties experienced by deafferented patients in tasks of daily life. Next, John Brooke showed that sensorimotor transformations vary greatly with task, anticipation, and uncertainty. In light of this, he questioned the simplifications inherent in servo and equilibrium-point theories of motor control. Paul Cordo then showed that in a rapid throwing task, proprioceptive information is used to control the moment of release (contradicting the idea that sensory feedback is too delayed for ballistic movements). Dick Burgess, like Brooke, criticized equilibrium-point models; he argued that a subject's sense of effort is a measure of the internal motor command, which should correspond to specific equilibrium points. However, his experimental data were inconsistent with this interpretation. He suggested instead that motor output is adjusted by comparing incoming afferent information to an expected "afferent template." Anatol Feldman and Mark Latash disagreed, saying that a constant sense of effort does not imply a constant equilibrium-point command. The equilibrium-point debate was not resolved, but the symposium ended with a consensus that in most motor tasks, one can control only what one senses.

Afferent Pathways↗
PubMed1993

Home blood glucose monitoring: effectiveness in a general population of patients who have non-insulin-dependent diabetes mellitus.

OBJECTIVE: To determine whether home blood glucose monitoring as used by non-insulin-dependent diabetes mellitus patients followed in primary care nonresearch clinics improves glycemic control or reduces utilization of the outpatient laboratory. DESIGN: A retrospective chart review for 229 patients receiving outpatient supplies for home testing of either blood or urine. SETTING: A variety of nonresearch clinics at a Veterans Affairs Medical Center, a teaching hospital affiliated with an academic university medical center. PATIENTS: Outpatient veterans followed in diabetes, primary care, internal medicine, or endocrine clinics. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The mean glycosylated hemoglobin for an unselected group monitoring glycemic control by urine testing only was 11.32% and for those using blood monitoring was 11.37%. Frequency and duration of monitoring had no apparent impact on glucose control. There was no decrease in the utilization of the laboratory among those patients practicing home blood glucose monitoring. CONCLUSIONS: For non-insulin-dependent diabetic patients followed in a nonresearch clinic setting, the benefits of home blood glucose monitoring remain to be proven.

Adult↗
PubMed1993

Cerebellar ataxia and muscle spindle sensitivity.

1. The cerebellum has long been known to participate in movement control. One of the enduring theories of cerebellar function is that it "tunes" and coordinates sensorimotor traffic in other parts of the CNS. In particular, it has been implicated in the control of the sensitivity of muscle spindle stretch receptors through the fusimotor system. 2. The stretch sensitivity of spindle primary endings can be varied approximately over a 10-fold range by fusimotor efferent action. For many years it has been believed that cerebellar dysfunction is associated with reduced drive to the fusimotor system and that this in turn causes hypotonia by reducing the reflex excitation of alpha-motoneurons by spindle afferents. 3. The data on which this hypothesis is based were obtained in anesthetized or decerebrate animals. Little direct information is available on animals or humans performing voluntary movements and exhibiting ataxia or other cerebellar symptoms. 4. We tested the hypothesis by recording from nine muscle spindle afferents in behaving cats before and during reversible inactivation of cerebellar interpositus and dentate nuclei. In normal cats fusimotor action varies with motor task, greatly altering spindle stretch sensitivity. We investigated whether this same range of task-related sensitivity manifested itself during ataxia. 5. We found that the full range of spindle sensitivity was still present during ataxia. We therefore conclude that the cerebellar nuclei studied are not primarily responsible for fusimotor control, nor is the ataxia primarily caused by disordered proprioceptive sensitivity.

Afferent Pathways↗
PubMed1993

Electrical systems for improving locomotion after incomplete spinal cord injury: an assessment.

Simple systems for electrical stimulation (1-4 channels) with either surface, percutaneous, or implanted electrodes during locomotion were assessed in 10 subjects who had chronic, incomplete spinal cord injury (SCI). On average, the speed of locomotion was increased by 4 m/min independently of the subject's speed of locomotion without stimulation (0-50 m/min) while oxygen consumption was reduced somewhat. These simple systems can provide practical help, particularly for incomplete SCI subjects who can stand but are lacking or have very limited ability to walk. Further improvement in locomotion requires stabilization and reduction in the duration of the stance phase of locomotion.

Adult↗
PubMed1992

Attenuation of pathological tremors by functional electrical stimulation. I: Method.

In this study we explored the possibility of suppressing pathological tremors using closed-loop functional electrical stimulation (FES) to activate the tremorogenic muscles out-of-phase. A displacement signal monitored with a transducer was filtered so as to be "tuned" to the tremor frequency at the wrist or elbow. The filtered signal was used to amplitude-modulate the electrical stimulation. The design process was based on measurements of the open-loop frequency response characteristics of the forearm and hand to stimulation of the elbow and wrist flexors and extensors in a number of subjects. These data allowed us to identify closed-loop configurations, which attenuated 2-5 Hz tremors substantially, while only minimally attenuating functional movements in the 0-1 Hz range. There was a fairly delicate balance between efficacy and the risk of instability. However, designs were identified that offered enough tremor suppression and adequate immunity to muscle/load variations for the technique to be considered seriously for clinical application.

Electric Stimulation↗
PubMed1992

Attenuation of pathological tremors by functional electrical stimulation. II: Clinical evaluation.

In this study we evaluated a technique for tremor suppression with functional electrical stimulation (FES), the technical details of which were described in the previous paper. Three groups of patients were investigated: those with essential tremor, parkinsonian tremor, and cerebellar tremor associated with multiple sclerosis. In each group, tremor was attenuated by significant amounts (essential tremor: 73%; parkinsonian tremor: 62%; cerebellar tremor: 38%). These attenuations were in good accord with predictions based on the dynamic analyses and filter designs derived in the previous paper. With filters "tuned" to the lower mean tremor frequency encountered in the cerebellar patients, more attenuation was possible in this group as well. We identified some practical limitations in the clinical application of the technique in its present form. The most important was that in daily use, only one antagonist pair of muscles can realistically be controlled. At first sight, this restricts the usefulness of the system to patients with single-joint tremors. However, the concomitant use of mechanical orthoses may broaden the scope of application.

Adult↗
PubMed1992

Clinical experience with reinforced, anchored intramuscular electrodes for functional neuromuscular stimulation.

Implanted intramuscular electrodes must remain functional for many years if functional neuromuscular stimulation (FNS) is to become a standard treatment in paralysed individuals. In initial trials we found that 5 of 11 coiled single-wire FNS electrodes implanted in 3 patients failed within 8 months. Consequently, we turned to a reinforced electrode comprising 2 multi-stranded, insulated wires tandem-wound on a prolene core and terminated by a prolene anchor or tine (after Mortimer et al., 1986, 1987). The electrodes were implanted with a translumbar aortogram needle, the teflon sheath of which enabled us to stimulate through the tip to guide placement. We have monitored the electrical and functional properties of 8 reinforced electrodes implanted in 2 incomplete quadriplegic patients over 22 months. Four of the electrodes were used for at least 1 h daily to exercise muscles or to provide FNS in gait. Electrical impedances, thresholds and elicited limb motion remained constant in all 8 electrodes over the test period. Disadvantages of the reinforced electrodes are (1) difficulty of eventual removal, and (2) risk of pathogenic infiltration is increased by the 3-filament structure (fortunately dense tissue encapsulation seems to mitigate infection). We conclude that tandem-wound, prolene-reinforced FNS electrodes are much more robust than previous single-coil designs and may form the basis for FNS devices of the future.

Adult↗
PubMed1991

Properties of implanted electrodes for functional electrical stimulation.

Implanted wire electrodes are increasingly being used for the functional electrical stimulation of muscles in partially paralysed patients, yet many of their basic characteristics are poorly understood. In this study we investigated the selectivity, recruitment characteristics and range of control of several types of electrode in triceps surae and plantaris muscles of anaesthetized cats. We found that nerve cuffs are more efficient and selective (i.e., cause less stimulus spread to surrounding muscles) than intramuscular electrodes. Bipolar intramuscular stimulation was more efficient and selective than monopolar stimulation, but only if the nerve entry point was between the electrodes. Monopolar electrodes are efficient and selective if located close to the nerve entry point, but their performance declines with distance from it. Nonetheless, for a variety of reasons monopolar stimulation provides the best compromise in many current applications. Short duration pulses offer the best efficiency (least charge per pulse to elicit force) but high peak currents, increasing the risk of electrode corrosion and tissue damage. Electrode size has little effect on recruitment and should therefore be maximised because this minimises current density.

Action Potentials↗
PubMed1990

Human H-reflexes are smaller in difficult beam walking than in normal treadmill walking.

Hoffman (H) reflexes were elicited from the soleus (SOL) muscle while subjects walked on a treadmill and on a narrow beam (3.5 cm wide, raised 34 cm from the floor). The speed of walking on the treadmill was selected for each subject to match the background activation level of their SOL muscle during beam walking. The normal reciprocal activation pattern of the tibialis anterior and SOL muscles in treadmill walking was replaced by a pattern dominated by co-contraction on the beam. In addition, the step cycle duration was more variable and the time spent in the swing phase was reduced on the beam. The H-reflexes were highly modulated in both tasks, the amplitude being high in the stance phase and low in the swing phase. The H-reflex amplitude was on average 40% lower during beam walking than treadmill walking. The relationship between the H-reflex amplitude and the SOL EMG level was quantified by a regression line relating the two variables. The slope of this line was on average 41% lower in beam walking than treadmill walking. The lower H-reflex gain observed in this study and the high level of fusimotor drive observed in cats performing similar tasks suggest that the two mechanisms which control the excitability of this reflex pathway (i.e. fusimotor action and control of transmission at the muscle spindle to moto-neuron synapse) may be controlled independently.

Electromyography↗
PubMed1990

In-series compliance of gastrocnemius muscle in cat step cycle: do spindles signal origin-to-insertion length?

1. It has been claimed that stretch in the non-contractile (extramysial) portion of muscles is substantial, and may produce large discrepancies between the origin-to-insertion muscle length and the internal length variations 'seen' by muscle spindle endings. 2. In eight pentobarbitone-anaesthetized cats, we estimated stretch in the extramysial portion of medial gastrocnemius (MG) muscle with a method similar to the spindle null technique. 3. Length variations of MG previously monitored in a normal step cycle were reproduced with a computer-controlled length servo. The responses of test MG spindle endings were monitored in dorsal root filaments. Distributed stimulation of ventral root filaments, rate-modulated by the step-cycle EMG envelope, served to reproduce step-cycle forces. The filaments were selected so as to have no fusimotor action on the test spindle. 4. Spindle responses in active cycles were compared with those in passive cycles (stretch, but no distributed stimulation). In some cases concomitant tonic fusimotor stimulation was used to maintain spindle responsiveness throughout the cycle, both in active and passive trials. Generally, small discrepancies in spindle firing were seen. The passive trials were now repeated, with iterative adjustments of the length function, until the response matched the spindle firing profile in the active trial. The spindle 'saw' the same internal length change in the final passive trial as in the active trial. Any difference between the corresponding length profiles was attributed to extramysial displacement. 5. Extramysial displacement estimated in this was was maximal at short mean muscle lengths, reaching about 0.5 mm in a typical step cycle (force rising from 0 to 10 N). At longer mean muscle lengths where muscle force rose from say 2 to 12 N in the cycle, extramysial displacement was in the range 0.2-0.4 mm. 6. Except at very short lengths, the displacement was probably mainly tendinous. On this assumption, our results suggested that the stiffness of the MG tendinous compartment was force related, and about double that of cat soleus muscle at any given force. Calculations indicated that though the stretch was small, the MG tendon would store and release enough strain energy per cycle to contribute significantly to the E3 phase of the step cycle. The discrepancies in spindle firing were generally quite subtle, so we reject the claim that extramysial stretch poses a serious difficulty for inferences about fusimotion from chronic spindle afferent recordings.

Action Potentials↗
PubMed1989

Ensemble proprioceptive activity in the cat step cycle: towards a representative look-up chart.

Analysis of the control of movement in tasks such as stepping is severely restricted by the lack of quantitative data on the ensemble activity of afferents in the numerous muscles involved. We have started to build up a quantitative "look-up-chart" of the ensemble afferent and efferent profiles in the cat step cycle. To this end, we have developed software which allows us to digitize afferent firing, muscle length and electromyogram (EMG) activity, and to align segments for averaging by choosing one or more reference points in the step cycle. The ensemble firing of triceps surae Ia afferents showed lower than expected mean and peak rates, whereas triceps group II and Ib afferents were more active than predicted. There were small but significant transients in Ia firing at foot-off and touch-down which could not be explained in terms of origin-to-insertion length lone. They were most likely caused by propagated mechanical transients or tendon compliance effects giving rise to small differences between the origin-to-insertion length and the intramuscular length "seen" by spindles. Net ensemble Ia rates, based on previous estimates of spindle populations, probably exceed 25 kilo-impulses/second (ki.p.s.) in some muscles. Inputs as large as this are likely to contribute significantly to reflex control.

Animals↗