H reflex and F wave latencies to soleus normal values and side-to-side differences.

OBJECTIVE: Electromyographers must reliably differentiate between H reflexes and F waves when recording from the soleus muscle in the evaluation of S1 radiculopathy. The use of F waves in root-level injuries is questioned, whereas H reflexes have shown value in the evaluation of S1 radiculopathy. We studied the relationship between the tibial H reflex and F wave latencies in the limbs of 40 subjects. DESIGN: After recording the H wave latency, we changed the gain to 200 microV/cm and increased the stimulation to supramaximal for ten additional responses without moving the recording or stimulating electrodes. We also calculated the predicted H wave latency with the standard formula. Forty subjects, mean age 32 yr, consented and participated. RESULTS: The mean of the average F wave was 1.76 ms longer than the ipsilateral H reflex latency. The mean side-to-side difference of the average F wave was 0.56 ms. The H reflex latency side-to-side difference was 0.36 ms. CONCLUSION: The findings suggest that the average F wave latencies have a predictive value in the clinical context similar to the H reflex.

Human toxicity potentials for life-cycle assessment and toxics release inventory risk screening.

The human toxicity potential (HTP), a calculated index that reflects the potential harm of a unit of chemical released into the environment, is based on both the inherent toxicity of a compound and its potential dose. It is used to weight emissions inventoried as part of a life-cycle assessment (LCA) or in the toxics release inventory (TRI) and to aggregate emissions in terms of a reference compound. Total emissions can be evaluated in terms of benzene equivalence (carcinogens) and toluene equivalents (noncarcinogens). The potential dose is calculated using a generic fate and exposure model, CalTOX, which determines the distribution of a chemical in a model environment and accounts for a number of exposure routes, including inhalation, ingestion of produce, fish, and meat, and dermal contact with water and soil. Toxicity is represented by the cancer potency q1* for carcinogens and the safe dose (RfD, RfC) for noncarcinogens. This article presents cancer and noncancer HTP values for air and surface-water emissions of 330 compounds. This list covers 258 chemicals listed in U.S. Environmental Protection Agency TRI, or 79 weight-% of the TRI releases to air reported in 1997.

A systematic uncertainty analysis of an evaluative fate and exposure model.

Multimedia fate and exposure models are widely used to regulate the release of toxic chemicals, to set cleanup standards for contaminated sites, and to evaluate emissions in life-cycle assessment. CalTOX, one of these models, is used to calculate the potential dose, an outcome that is combined with the toxicity of the chemical to determine the Human Toxicity Potential (HTP), used to aggregate and compare emissions. The comprehensive assessment of the uncertainty in the potential dose calculation in this article serves to provide the information necessary to evaluate the reliability of decisions based on the HTP A framework for uncertainty analysis in multimedia risk assessment is proposed and evaluated with four types of uncertainty. Parameter uncertainty is assessed through Monte Carlo analysis. The variability in landscape parameters is assessed through a comparison of potential dose calculations for different regions in the United States. Decision rule uncertainty is explored through a comparison of the HTP values under open and closed system boundaries. Model uncertainty is evaluated through two case studies, one using alternative formulations for calculating the plant concentration and the other testing the steady state assumption for wet deposition. This investigation shows that steady state conditions for the removal of chemicals from the atmosphere are not appropriate and result in an underestimate of the potential dose for 25% of the 336 chemicals evaluated.

Neuromuscular rehabilitation and electrodiagnosis. 2. Localized peripheral neuropathy.

This self-directed learning module highlights advances in diagnosis and treatment of focal injuries to peripheral and cranial nerves. It is part of the chapter on neuromuscular rehabilitation and electrodiagnosis in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. Nerve conduction and electromyographic techniques are employed as extensions of the physician's senses in clinical examination and diagnosis. The findings are used to plan treatment, and to predict and measure outcomes. Electrodiagnosis and medical and surgical treatments of nerve injuries are discussed in light of the managed-care utilization review of services.

Parameter uncertainty and variability in evaluative fate and exposure models.

The human toxicity potential, a weighting scheme used to evaluate toxic emissions for life cycle assessment and toxics release inventories, is based on potential dose calculations and toxicity factors. This paper evaluates the variance in potential dose calculations that can be attributed to the uncertainty in chemical-specific input parameters as well as the variability in exposure factors and landscape parameters. A knowledge of the uncertainty allows us to assess the robustness of a decision based on the toxicity potential; a knowledge of the sources of uncertainty allows us to focus our resources if we want to reduce the uncertainty. The potential dose of 236 chemicals was assessed. The chemicals were grouped by dominant exposure route, and a Monte Carlo analysis was conducted for one representative chemical in each group. The variance is typically one to two orders of magnitude. For comparison, the point estimates in potential dose for 236 chemicals span ten orders of magnitude. Most of the variance in the potential dose is due to chemical-specific input parameters, especially half-lives, although exposure factors such as fish intake and the source of drinking water can be important for chemicals whose dominant exposure is through indirect routes. Landscape characteristics are generally of minor importance.

Therapeutic electrical stimulation for spasticity: quantitative gait analysis.

Improvement in motor function following electrical stimulation is related to strengthening of the stimulated spastic muscle and inhibition of the antagonist. A 26-year-old man with familial spastic paraparesis presented with gait dysfunction and bilateral lower limb spastic muscle tone. Clinically, muscle strength and sensation were normal. He was considered appropriate for a trial of therapeutic electrical stimulation following failed trials of physical therapy and baclofen. No other treatment was used concurrent with the electrical stimulation. Before treatment, quantitative gait analysis revealed 63% of normal velocity and a crouched gait pattern, associated with excessive electromyographic activity in the hamstrings and gastrocnemius muscles. Based on these findings, bilateral stimulation of the quadriceps and anterior compartment musculature was performed two to three times per week for three months. Repeat gait analysis was conducted three weeks after the cessation of stimulation treatment. A 27% increase in velocity was noted associated with an increase in both cadence and right step length. Right hip and bilateral knee stance motion returned to normal (rather than "crouched"). No change in the timing of dynamic electromyographic activity was seen. These findings suggest a role for the use of electrical stimulation for rehabilitation of spasticity. The specific mechanism of this improvement remains uncertain.

Development of an academic productivity scale for departments of physical medicine and rehabilitation.

OBJECTIVE: To determine which factors related to departments of physical medicine and rehabilitation (PM&R) might contribute to the academic productivity of members of the teaching staff of those departments, and to develop an instrument that measures them. DESIGN: Prospective, inception cohort. SETTING: University medical center, academic PM&R departments. PARTICIPANTS: PM&R academic departments. INTERVENTION: Over a 6-year period, seven PM&R departments volunteered to use this instrument to measure academic productivity at 2-year intervals. Rasch analysis was applied to the generated data. MAIN OUTCOME MEASURE: Measurable items that were included in questions of the scale fell into six categories: research funding and/or experience; scholarly productivity; equipment and facilities; quality of the training program for resident physicians; continuing education efforts in research methodologies and professional organizational participation; and departmental leadership. Rasch analysis was applied to evaluate a new outcome instrument to measure academic productivity in PM&R departments. RESULTS: Twenty-eight of the original 42 questions survived the Rasch analysis and were retained. Questions were dropped either because they did not fit the Rasch analysis (4 of 42 questions) or because application of the Rasch analysis demonstrated that they were inappropriately or outstandingly easy (10 of 42 were inappropriately or outstandingly easy). CONCLUSION: This shortened instrument of 28 questions fits the Rasch analysis, has questions that evently range from easy to very difficult, and addresses six measurable categories that are correlates of PM&R departmental influences on the academic productivity of the PM&R teaching staff.

Central loop of the H reflex. Normal value and use in S1 radiculopathy.

The H reflex in the S1 spinal nerve has been used in electrodiagnosis of S1 radiculopathy for several years. Direct stimulation of the S1 spinal nerve has provided more complete information about the H reflex pathway by dividing it into its peripheral and central (or spinal) conduction portions. A previous study compared spinal nerve latency with the H reflex latency, demonstrating an abnormal S1 ratio in subjects with S1 radiculopathy, thereby suggesting slowing within the spinal segment of the nerve. No study, however, has established a normal value for the central (spinal) portion of the H reflex. We electrodiagnostically tested 20 subjects with normal clinical neurologic and musculoskeletal examinations to define a normal sample of the central loop of the H reflex in the S1 spinal nerve. The peak latencies of the M and H reflex responses were measured after a single stimulus to the S1 spinal nerve. The data obtained established 7 +/- 0.3 ms as the normal value for the interpotential latency difference (central loop) of the H reflex in the S1 spinal nerve in healthy subjects. Six patients with clinical and electromyographic evidence of S1 radiculopathy all had central loop latencies of > 8 ms. The normal value of the central loop of the H reflex suggested in this pilot investigation may, therefore, be used to allow for earlier and more accurate diagnosis of an acute S1 radiculopathy.

Gait pattern in the early recovery period after stroke.

The gait patterns of eighteen patients who had had a single infarct due to obstruction of the middle cerebral artery were evaluated within one week after the patients had resumed independent walking and before a gait rehabilitation program had been initiated. Gait was analyzed with use of motion analysis, force-plate recordings, and dynamic surface electromyographic studies of the muscles of the lower extremities. The patterns of motion of the lower extremity on the hemiplegic side had a stronger association with the clinical severity of muscle weakness than with the degree of spasticity, balance control, or phasic muscle activity. There was a delay in the initiation of flexion of the hip during the pre-swing phase, and flexion of the hip and knee as well as dorsiflexion of the ankle progressed only slightly during the swing phase. During the stance phase, there was decreased extension of the hip that was related to decreased muscle effort and a coupling between flexion of the knee and dorsiflexion of the ankle. The abnormal patterns of motion altered the velocity, the length of the stride, the cadence, and all phases of the gait cycle. The duration of the pre-swing phase was prolonged for the patients who had the slowest gait velocities. There also were abnormal movements of the upper extremity, the trunk, the pelvis, and the lower extremity on the unaffected side in an effort to compensate for the decreased velocity on the hemiplegic side. As velocity improved, these abnormal movements decreased. Therefore, the goal of therapy should be to improve muscle strength and coordination on the hemiplegic side, especially during the pre-swing phase.

Sitting balance: its relation to function in individuals with hemiparesis.

OBJECTIVES: To evaluate test-retest reliability of sitting balance measures in healthy subjects and individuals with hemiparesis secondary to stroke, to evaluate the ability of the balance measures and Functional Independence Measure (FIM) to document changes over time, and to compare changes in the balance measures and FIM to each other. METHOD: Six nonpatient subjects were evaluated for test-retest reliability. Fourteen subjects with hemiparesis were tested every 2 weeks during their hospitalization on their ability to lean to either side, lean forward, and maintain a symmetrical posture. Maximum displacement was recorded using the Balance System. FIM scores were obtained for each testing session. RESULTS: Test-retest reliability for nonpatient subjects was high and for patients was moderate to high. Leaning forward and to the paretic side showed the greatest number of correlations with the FIM scores. All of the FIM scales and the forward lean measure documented progress. CONCLUSIONS: The protocol developed to test sitting balance, using the Balance System, seems appropriate for use with patient populations. The ability to lean maximally to either side or forward or sit symmetrically is not strongly related to function.

Improving the regulation of carcinogens by expediting cancer potency estimation.

The statutory language of the Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 65; California Health and Safety Code 25249.5 et seq.) encourages rapid adoption of "no significant risk levels" (NSRLs), intakes associated with estimated cancer risks of no more than 1 in 100,000. Derivation of an NSRL for a carcinogen listed under Proposition 65 requires the development of a cancer potency value. This paper discusses the methodology for the derivation of cancer potencies using an expedited procedure, and provides potency estimates for a number of agents listed as carcinogens under Proposition 65. To derive expedited potency values, default risk assessment methods are applied to data sets selected from an extensive tabulation of animal cancer bioassays according to criteria used by regulatory agencies. A subset of these expedited values is compared to values previously developed by regulatory agencies using conventional quantitative risk assessment and found to be in good agreement. Specific regulatory activities which could be facilitated by adopting similar expedited procedures are identified.

Cerebral aneurysms and arteriovenous malformations: implications for rehabilitation.

Arteriovenous malformations (AVM) and intracranial aneurysms often have devastating impact when they present as subarachnoid hemorrhage (SAH). With an overall incidence of 10 to 16 per 100,000, subarachnoid hemorrhage is relatively rare; however, these patients often comprise a significant component of a rehabilitation specialist's practice. There exists a host of risk factors and premorbid characteristics that correlate with long-term outcome after aneurysmal and AVM-related subarachnoid hemorrhage. Physical, cognitive, behavioral, and social deficits are relatively common after SAH, and can have a significant impact on effective home, community, and work reentry. Seizure risk after SAH or craniotomy and the use of prophylactic anticonvulsant medications is often a confusing and troublesome issue for the rehabilitation specialist. This situation often is handled by weighing the potential risk of serious medication side effects against the potential seizure risk. Cognitive, behavioral, and social sequelae are most frequent in patients with anterior cerebral and communicating artery lesions; however, delayed ischemic dysfunction often accounts for these deficits in patients with lesions in other distributions. An understanding of the classification, incidence, presentation, complications and treatment of arteriovenous malformations and intracranial aneurysms is especially important for the rehabilitation specialist. Knowledge about these areas assists the rehabilitation specialist in developing an individual rehabilitation plan that sets realistic goals for predicted outcomes. In addition, such knowledge enhances appropriate monitoring of patient progress, so that early interventions can be established when there is an alteration in clinical status.

A preventable cause of foot drop during childbirth.

Compression of the peroneal nerve is an uncommon complication of labor and delivery. We describe a case of common peroneal nerve injury associated with positioning the knees in hyperflexion during delivery. The pathophysiologic mechanisms, clinical course, and possible prevention of this uncommon complication are discussed.

Amplitude of M responses. Side to side comparability.

The peak amplitude of the M response from the extensor digitorum longus muscle (EDL) was measured in 26 healthy subjects (12 women and 14 men, aged 19 to 45 years) using conventional peroneal nerve stimulation at the fibular head. The mean amplitude of the EDL was 6.5 mV (+/- 1.3 mV) and 6.1 mV (+/- 1.2 mV) for the right and left sides, respectively. The side to side difference in amplitude of the M response was 0.4 mV (+/- 1.1 mV). Twenty-five of the twenty-six subjects had side to side amplitude differences within two standard deviations of the mean. None of the subjects had an EDL amplitude from the right lower limb over 1.8 mV less than that of the left, nor an EDL amplitude from the left lower limb over 2.8 mV less than that of the right. The technique used in the present study allows an accurate assessment of the M response amplitude from the EDL muscle. These reference data should prove useful in the evaluation of early focal nerve root injury (e.g. after 4 days, within 3 weeks) and in establishing prognosis for recovery in such conditions.

The role of cancer risk in the regulation of industrial pollution.

The extent of carcinogen regulation under existing U.S. environmental statutes is assessed by developing measures of the scope and stringency of regulation. While concern about cancer risk has played an important political role in obtaining support for pollution control programs, it has not provided the predominant rationale for most regulatory actions taken to date. Less than 20% of all standards established to limit concentrations of chemicals in various media address carcinogens. Restrictions on chemical use are more frequently based on concerns about noncancer human health or ecological effects. Of the chemicals in commercial use which have been identified as potential human carcinogens on the basis of rodent bioassays, only a small proportion are regulated. There is an inverse relationship between the scope of regulatory coverage and the stringency of regulatory requirements: the largest percentages of identified carcinogens are affected by the least stringent requirements, such as information disclosure. Standards based on de minimis cancer risk levels have been established for only 10% of identified carcinogens and are restricted to one medium: water. Complete bans on use have affected very few chemicals. The general role that carcinogenicity now plays in the regulatory process is not dramatically different from that of other adverse human health effects: if a substance is identified as a hazard, it may eventually be subject to economically achievable and technically feasible restrictions.

Academic productivity in physical medicine and rehabilitation.

Academic productivity of faculty members in physical medicine and rehabilitation (PM&R) was evaluated retrospectively by using the numbers of scientific publications as a measurement instrument. This study was completed by examining ten medical peer-reviewed journals that regularly included original articles in the specialty area of PM&R during the years 1988 through 1990. The number of articles was weighted according to the specific journal's impact on the Science Citation Index. Academic productivity of physiatric departments showed wide variation. Ten units published at least 20 articles during the 3-yr period. Eight departments achieved a ratio of at least one article per faculty member based on reports from the Association of American Medical Colleges. Further study will be needed to assess the factors underlying these wide variations in departments' productivity.