Isometric muscle length-tension curves do not predict angle-torque curves of human wrist in continuous active movements

In this study we tested the hypothesis that during steady contractions of human wrist extensors or flexors, the torque-angle relationship during movements imposed about the wrist is predicted by the classical isometric muscle length-tension curve, with ascending, descending and ascending limbs. Angle-torque relationships were measured during steady muscle activation (10% of maximal voluntary contraction: MVC), elicited either by electrical stimulation or voluntary regulation of the electromyogram (EMG). Flexion-extension movements of constant speed (+/-10 degrees /s) were imposed on the subjects' hands with a servo actuator, either through the full physiological range of motion +/-50 degrees, or through +/-10 degrees. During extensor contractions, angle-torque curves in +/-50 degrees movements had ascending, descending and ascending limbs, as in isometric contractions. However, in +/-10 degrees movements, torque always increased with increasing muscle length and decreased with decreasing length, even over angles corresponding to the descending limb of isometric curves. For flexor activation, angle-torque curves had similar properties, though descending limbs were less obvious or absent. During imposed movements, hysteresis was observed in the angle-torque curves. This was attributed to non-linearities of the active muscles. Hysteresis reached a maximum at intermediate wrist angles and declined at maximal muscle length, contradicting the recent hypothesis that sarcomere non-uniformity is responsible for the hysteresis. We conclude that the classical isometric length-tension curve, with its prominent descending limb, does not predict angle-torque curves of human wrist muscles in continuous movements. A more appropriate model is one in which stiffness about the wrist is always positive and hysteresis is a significant factor.

Proposed initiatives for healthy children orphaned by AIDS

The epidemiology of AIDS has changed greatly in recent years and increasing numbers of poor, minority women with children now contract HIV/AIDS. As infected women succumb to AIDS, many of their children become orphans. The paper explores the ability and appropriateness of the current child welfare system to care for healthy children orphaned by AIDS, and the likelihood of adoption for this population. The study includes a wide-ranging literature review of information about children orphaned by AIDS, and relevant information about the child welfare system, including racial bias. To determine current support for children orphaned by AIDS, the author surveyed social service departments and private agencies in eight major cities about programs available. Based on this information, the author proposes a series of policy initiatives aimed at alleviating the flight of children orphaned because of AIDS.

Tremor suppression using functional electrical stimulation: a comparison between digital and analog controllers

In this study, we compared digital and analog versions of a functional electrical stimulator designed to suppress tremor. The device was based on a closed-loop control system designed to attenuate movements in the tremor frequency range, without significantly affecting slower, voluntary movements. Testing of the digital filter was done on three patients with Parkinsonian tremor and the results compared to those of a functional electrical stimulation device based on an analog filter evaluated in a previous study. Additional testing of both the analog and digital filters was done on three subjects with no neurological impairment performing tremor-like movements and slow voluntary movements. We found that the digital controller provided a mean attenuation of 84%, compared to 65% for the analog controller.

The effect of wrist angle on electrically evoked hand opening in patients with spastic hemiplegia

This paper studied the effect of wrist angle on the amount of hand opening achieved by electrical stimulation in people with spastic hemiplegia. With their forearm in pronation, subjects were asked to relax while their affected wrist was passively moved in steps of about 15 degrees from full flexion into extension. Trains of stimuli were applied to the long finger extensor muscles through surface electrodes on the forearm. At each wrist position stimulation was turned on for a few seconds until hand opening equilibrated. Wrist angle and fingertip positions were recorded using a three-dimensional (3-D) motion analysis system. Maximal displacements between thumbtip and each fingertip occurred when the wrist was fully flexed. As the wrist was extended, hand aperture achieved by electrical stimulation progressively declined, reaching zero at 40 degrees of wrist extension. We conclude that electrical stimulation can significantly increase the grasp aperture of the hemiplegic hand, but this is strongly dependent on wrist posture and accompanying voluntary effort.

Effects of regional stimulation using a miniature stimulator implanted in feline posterior biceps femoris

The effects of placement of a miniature implantable stimulator on motor unit recruitment were examined in the posterior head of cat biceps femoris. The implantable stimulator (13-mm long x 2-mm diameter) was injected either proximally near the main nerve branch, or distally near the muscle insertion, through a 12-gauge hypodermic needle. Glycogen-depletion methods were used to map the distribution of fibers activated by electrical stimulation. Muscle fibers were found to be depleted at most or all proximodistal levels of the muscle, but the density of depleted fibers varied transversely according to the stimulus strength and proximity of the device to the nerve-entry site. Thus, muscle cross sections often had a "patchy" appearance produced because different proportions of depleted fibers intermingled with undepleted fibers in different parts of the cross section. In other preparations, the force of muscle contraction was measured when stimuli of varying strengths were delivered by the stimulator positioned at the same proximal or distal sites within the muscle. Devices placed close to the nerve-entry site produced the greatest forces. Those placed more distally produced less force. As stimulus current and/or pulse width increased, muscle force increased, often in steps, until a maximum was reached, which was usually limited by the compliance voltage of the device to less than the force produced by whole nerve stimulation.

Long-term biocompatibility of a miniature stimulator implanted in feline hind limb muscles

Chronic foreign-body responses and muscular changes were examined following the implantation of active miniature stimulators into the hind limb muscles of cats for periods of up to three months. The radio-frequency (RF)-powered stimulators were injected into muscles through a 12-gauge hypodermic needle. The tissue responses around the active stimulators were compared histologically to those provoked by passive devices, broken glass, silicone tubing, polyester suture material coated with polybutylate, and two of the internal components of the stimulator (ferrite, integrated circuit chip). Active and passive stimulators produced similar, benign foreign-body reactions that resulted in an essentially identical fibrous capsule over time. The responses were similar to those produced by the internal components and the suture material, and were more modest than those produced by the broken glass. The capsule did not appear to interfere with the functionality of active devices because thresholds measured during the post-implantation survival period did not change significantly over time. Unexpectedly, the severity of the reaction differed significantly amongst the various target muscles. Medial gastrocnemius exhibited the most severe response, whereas tibialis anterior had the least reaction.

Muscular sense is attenuated when humans move

1. Muscle receptors play an important role in our conscious perception of movement, but there are no published accounts of our ability to detect their signals during different motor tasks. The present experiments introduce a method to test muscular sense when humans move. 2. Muscle receptors were excited by an electrically induced twitch of the right extensor carpi ulnaris muscle. The muscle was stimulated via percutaneously inserted intramuscular electrodes or using surface stimulation through anaesthetized skin. Muscular sense was represented by the ability to detect the twitch and was compared between various tasks and stationary control trials. 3. Three hertz voluntary wrist movements significantly attenuated muscular sense to 37 % of control. This velocity-dependent attenuation was present over a range of twitch amplitudes suggesting it does not simply reflect a masking of low intensity stimuli. Perceptual ratings of twitch amplitude during fast imposed passive movements were reduced by 40 %, though this did not quite reach statistical significance. However, perceptual ratings of twitches evoked up to 2 s after the termination of the passive movements were significantly different from control. 4. Reaching with the stimulated, but not the contralateral, arm also significantly reduced muscular sense (to 40 %). 5. Attenuation to 58 % of control during cyclic stretching of the skin on the dorsum of the hand showed that signals from peripheral receptors may play a role. Attenuation prior to a single wrist flexion movement indicated that central sources can also contribute. 6. The results are consistent with current findings of a general attenuation of sensory feedback during movement and raise questions regarding the role of muscular sense in movement control.

An upper body exercise system incorporating resistive exercise and neuromuscular electrical stimulation (NMS)

A device is described which combines arm crank ergometry and neuromuscular electrical stimulation (NMS) delivered at different phases of the crank cycle. Details of the device including circuit schematics are shown. The device was evaluated by non-paralyzed subjects for its operational safety and by tetraplegic subjects for its effectiveness as a muscle-strengthening tool. All subjects showed improvement in one or more of their manual muscle scores. The most dramatic increased motor score occurred in the triceps muscle group. There was an average increase in the manual muscle score of 1.1 +/- 0.2 for the left triceps and 0.7 +/- 0.1 for the right triceps after eight weeks of NMS assisted exercise. No adverse effects were experienced and it appears to meet safety considerations necessary for this group of individuals. Preliminary observations indicate that an eight-week exercise protocol that utilizes this device can be beneficial for this population.

Self-Insured health care plans: are they fair to employees with HIV/AIDS?

A literature search reveals a number of instances where people with AIDS (PWAs) have limits placed on their health care by self-insured firms. Some firms cite the high cost of health care for AIDS as the motivation for their decision. Research demonstrates, however, that AIDS is not the only high-priced disease to treat. Treatment for lung cancer is costly as well. In many cases, unprotected sex leads to HIV/AIDS and lung cancer is strongly linked to tobacco use. Therefore, lung cancer can be studied as a comparison disease for issues relating to health care coverage of PWAs. A literature search also shows that no examples of limitations on health care were found among lung cancer patients. A 1992 Supreme Court decision did not restrict the inequitable access to health care through self-insured plans for AIDS patients. When employees of self-insured firms exhaust their insurance benefits, which can occur quickly, they apply for Medicaid or Medicare benefits. As a result, the government's burden is increased in the care of PWAs. The issue, therefore, should be to ensure that employees of self-insured firms have equal access to health care since there are other serious diseases, such as lung cancer, that are also expensive to treat.

Micromodular implants to provide electrical stimulation of paralyzed muscles and limbs

We describe the design, fabrication, and output capabilities of a microminiature electrical stimulator that can be injected in or near nerves and muscles. Each single-channel microstimulator consists of a cylindrical glass capsule with hermetically sealed electrodes in either end (2-mm diameter x 13-mm overall length). Power and digital control data can be transmitted to multiple implants (256 unique addresses) via a 2-MHz RF field created by an external AM oscillator and inductive coil. In vitro testing demonstrated accurate control of output pulsewidth (3-258 microseconds in 1-microseconds steps) and current (0-30 mA in two linear ranges of 16 steps each, up to 8.5 V available compliance voltage). Microstimulators were used successfully for chronic stimulation in hindlimb muscles of cats. Design and fabrication issues affecting yield and reliability of the packaging and electronics are discussed.

Gold color in dental alloys

This article will help the dental laboratory with alloy selection by exploring how the relationship among color, ductility and strength applies to gold and how color can be quantified. Because higher quality materials translate into higher profits, upselling to the dentist and patient is also discussed.

Single-agent paclitaxel in patients with previously untreated stage IV epithelial ovarian cancer. London Gynaecological Oncology and North Thames Gynaecological Oncology Groups

The aim of this study was to evaluate the efficacy of high-dose paclitaxel in patients with previously untreated stage IV epithelial ovarian cancer. Paclitaxel was administered intravenously over 3 h at a dose of 225 mg m(-2) on a 21-day cycle for six courses. Thirty-six patients were entered into this study; all 36 were assessed for toxicity and 33 patients were evaluable for response. One patient had a complete response and 12 patients had partial responses (overall response rate 39.4%, 95% CI 23-58%). The overall median duration of response was 9 months (range 3.5-23+ months). The response rate to carboplatin following failure of paclitaxel within 1 year of stopping therapy was 57% (four out of seven patients). The median survival of patients was 17.2 months. The main toxicity encountered was neutropenia which was WHO grade 3 in 11 patients (31%) and WHO grade 4 in seven patients (19%). Granulocyte colony-stimulating factor (GCSF) was not given to any patient during the study. Other toxicities were: grade 3/4 infection (11%) and nausea and vomiting (11%); grade 3 bone pain (22%), fatigue (14%), diarrhoea (3%), myalgia/arthralgia (3%) and dry eyes (3%). Transient peripheral neuropathy occurred in 16 patients (44%), and alopecia was encountered in most patients (grade 2/3, 78%). Paclitaxel given at 225 mg m(-2) to patients with stage IV epithelial ovarian cancer is active, well tolerated and does not require GCSF support.

A novel method to identify migration of small implantable devices

A histologic method has been developed to assess the migration of chronically-implanted intramuscular devices. Bullet-shaped glass devices with varying tip configurations and glass-encapsulated microstimulators of a similar size were loaded with the fluorescent tracer Procion Yellow dissolved in molten glucose. Dissolution of the hardened glucose soon after contact with body fluids released the Procion Yellow, which binds irreversibly to local tissues, thereby marking the initial site of implantation with a localized fluorescent spot. After survival times of 2-7 weeks, histologic analysis usually showed a close physical relationship between the fluorescent spot and the connective-tissue capsule from which the device was extracted. In one case, migration of a sharply pointed device from the deep surface of an implanted muscle was recognized by differences in the location of the dye spot and the site of explantation from nearby fascia. Results suggested that this method could measure migratory distances as small as 5-10 mm.

Mechanical and fatigue properties of wrist flexor muscles during repetitive contractions after cervical spinal cord injury

OBJECTIVES

Force generation and fatigue properties of wrist flexor muscles were examined in subjects with chronic (> 1 year) cervical spinal cord injury (SCI, n = 16), and also in a control group of able-bodied (AB, n = 9) subjects.

DESIGN

Using surface electrodes, wrist flexor muscles were stimulated with 126 trains of 26 stimuli at a frequency of 40Hz. The offset of each train was followed by a 1.5-second pause, for a total fatigue-test time of approximately 4.2 minutes. Isometric wrist flexion force was measured with a strain gauge.

SETTING

This study was conducted at a research and rehabilitation center for spinal cord injury.

MAIN OUTCOME MEASURES

Force profiles were analyzed for the maximum (peak) amplitude, the rise time, and the time constant of relaxation.

RESULTS

At the outset, the average peak isometric measured in the SCI group was approximately one half that of the AB subjects. Although the relative decline in force with repeated stimulation was comparable between groups, the slowing of relaxation rate was much more pronounced in the SCI group.

CONCLUSIONS

These findings are consistent with alterations in the metabolic profiles of wrist flexor muscles in the SCI group, probably reflected their altered activation pattern. When designing stimulation protocols for optimizing force and fatigue resistance in muscle left partially-paralyzed after spinal cord injury, particular care must be taken to allow adequate time for complete muscle relaxation, to avoid overdriving of the muscle and a loss of functional capacity.

Use of exercise technetium-99m sestamibi SPECT imaging to detect residual ischemia and for risk stratification after acute myocardial infarction

The clinical presentation, electrocardiographic findings, and technetium-99m sestamibi single-photon emission computed tomography (SPECT) imaging results of 134 consecutive patients who underwent nuclear exercise testing within 14 days of an acute myocardial infarction (AMI) were correlated with cardiac events over a 15 +/- 10-month follow-up. Whereas only 23 patients (17%) had chest pain and 31 (23%) had ischemic ST-segment depression during exercise, 94 (70%) had ischemia on SPECT (p < 0.001). On follow-up, 13 patients experienced a cardiac event: 7 were rehospitalized for unstable angina, 3 had recurrent AMI, and 3 died of cardiac causes. Ischemia on the sestamibi images identified 11 of these patients (85%), whereas chest pain identified only 3 (23%, p = 0.006), and electrocardiographic ischemia identified only 4 (31%, p = 0.017). The presence of either ischemia as seen on SPECT or defects in multiple vascular territories identified 12 patients (92%) with an event, including all who had cardiac death. By Cox regression analysis of clinical, stress, and image parameters, the number of ischemic defects on SPECT was the only significant correlate of a future event (chi-square = 4.62, p = 0.03), and patients with > or = 3 reversible sestamibi defects had an event rate of 38%. The extent of ischemia as seen on nuclear imaging remained a strong correlate (p = 0.008) of an event in the 54 patients (40%) who had received thrombolytic therapy. Thus, exercise technetium-99m sestamibi SPECT after AMI frequently reveals residual ischemia, and is better than clinical data, symptoms, and stress electrocardiographic data in identifying patients who will have a subsequent cardiac event.

Purification of band 7.2b, a 31-kDa integral phosphoprotein absent in hereditary stomatocytosis

A 31-kDa human erythrocyte integral protein, band 7.2b, has been purified to better than 95% homogeneity. The polypeptide was found to be insoluble in most detergents and was isolated in denatured form by gel filtration in the presence of sodium dodecyl sulfate and preparative electrophoresis. In intact erythrocytes that were equilibrated with 32Pi, band 7.2b was phosphorylated in response to exogenous dibutyryl cAMP. The peptide is also palmitylated, as shown by its incorporation of radioactivity when intact erythrocytes were incubated with [9,10-3H]palmitic acid. Antisera to band 7.2b were raised in rabbits, and these antibodies cross-react with 31-kDa polypeptides in human liver and kidney. Immunoblots of red cells from a number of other species were negative, with the exception of a cross-reacting 23-kDa polypeptide in rat erythrocyte membranes. Band 7.2b was absent in erythrocyte membranes from an individual with overhydrated hereditary stomatocytes.

Effects of a multidisciplinary management program on neurologically impaired patients with dysphagia

Dysphagia is a major problem in patients with neurologic disorders. Aspiration pneumonia and impaired nutritional status are consequences of dysphagia that result in high morbidity and mortality rates. Assessment and treatment of the dysphagic patient by a multidisciplinary team have been advocated but to date the effects of such an approach have not been demonstrated quantitatively. This prospective study was conducted to determine if a dysphagia program would improve patients' caloric intake and body weight, decrease the instances of aspiration pneumonia, or improve patients' feeding ability. Patients were referred from a 26 bed neurology/neurosurgery unit. A time series design was utilized. The control group consisted of 15 patients (mean age = 46.1 years), managed according to the existing ward routine. Subsequently, nursing staff attended a dysphagia training program. Following this, the treated group of 16 patients, (mean age = 49.3 years) was assessed by the dysphagia team, using bedside and videofluoroscopic examinations to determine the specific swallowing disorder. An individualized treatment program was designed for each patient. The groups were compared on the basis of deviation from their baseline weight, deviation from ideal energy intake, and the incidence of aspiration pneumonia. Statistical analysis revealed that the groups were comparable in age, number of days on the study, and Glasgow Coma Scale score; and that a significant weight gain and increase in caloric intake occurred in the treated group. No incidence of aspiration pneumonia was reported in either group. We speculate that this may have been influenced by the meticulousness of the care delivered in an acute unit as well as greater attention to prevention given in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Photochemically induced cystic lesion in the rat spinal cord. I. Behavioral and morphological analysis

The present study describes the production of a spinal cord lesion which is initiated by vascular occlusion resulting from the interaction between the photosensitizing dye erythrosin B and an argon laser beam. The lesion has characteristics similar to those of the central cavity thought to lead to the production of post-traumatic syringomyelia (PTS) in humans. The present study examines the behavioral and morphological characteristics of this injury over a 28-day period. Histological analysis revealed a cavity extending from the dorsal horns to lamina VIII, with some lateral and ventral pathways being spared. The cavity volume reached a maximum 7 days after lesion induction. Behavioral changes were assessed using six different tests of motor and reflex function (motor function, climbing, waterbath, inclined plane, withdrawal to pain, and withdrawal to extension). Lesioned animals exhibited flaccid paralysis for 3-5 days, which resolved afterward. The photochemically induced cavity should provide a reproducible model for examining the effects of cystic spinal cord injury on locomotor and reflex function.