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D M Simpson

Publications and source records attributed to D M Simpson.

At least 37 records · Page 2Linked to original sources
PubMed2001

Forty years and four surveys: how does our measuring measure up?

OBJECTIVE: This article reviews four surveys methodologies that have been used over the past 40 years to assess immunization rates in young children in the United States. These methods include three national surveys: (1) United States Immunization Survey (1959-1985), which was first a household and then a telephone survey; (2) National Health Interview Survey (1991-present), which interviews people in their homes; and (3) National Immunization Survey (1994-present), a random-digit-dialing telephone survey. In addition, a series of retrospective school record surveys that used standard sampling and assessment methodologies were conducted nationally during 4 school years September 1990-May 1991. METHODS: Federal publications, National Immunization Conference proceedings, and Centers for Disease Control and Prevention (CDC) internal reports regarding national immunization surveys were reviewed. The methodology used in each survey is presented, and selected examples of previously tabulated results are presented. CONCLUSIONS: The assessment of immunization coverage in American preschool children requires ongoing commitment and survey expertise. Over the past 40 years the CDC's efforts to determine vaccination coverage in young children has evolved from the comparatively simple United States Immunization Survey to the current National Immunization Survey that utilizes sophisticated statistical and survey techniques to obtain the most-accurate results yet available.

Child↗
PubMed2001

A statistical technique for measuring synchronism between cortical regions in the EEG during rhythmic stimulation.

The coherence function has been widely applied in quantifying the degree of synchronism between electroencephalogram (EEG) signals obtained from different brain regions. However, when applied to investigating synchronization resulting from rhythmic stimulation, misleading results can arise from the high correlation of background EEG activity. We, thus propose a modified measure, which emphasizes the synchronized stimulus responses and reduces the influence of the spontaneous EEG activity. Critical values for this estimator are derived and tested in Monte Carlo simulations. The effectiveness of the method is illustrated on data recorded from 12 young normal subjects during rhythmic photic stimulation.

Adolescent↗
PubMed2001

A parametric approach to measuring cerebral blood flow autoregulation from spontaneous variations in blood pressure.

Autoregulation maintains cerebral blood flow (CBF) almost constant in the face of changes in arterial blood pressure (ABP). Tests for impairment of this process using only spontaneous fluctuations in ABP, without provoking large variations, are of great clinical interest, and a range of different approaches have previously been applied. Extending earlier work based on linear filters, we propose a simple parametric method using a first order finite impulse response filter. We evaluate the method on ABP and CBF velocity [(CBFV), from trancranial Doppler ultrasound] signals collected in 60 patients with stenosis or occlusion of the carotid arteries. Data were collected during the inspiration of ambient air, a 5% CO2/air mixture, and finally the return to ambient air. Equivalent data were collected in 15 normal subjects. The filters estimated from the data segments with constant inspiratory pCO2 showed the expected high-pass characteristic, which was reduced during hypercapnia and also in patients. Highly significant correlation between the filter parameters and cerebrovascular reactivity (percent increase in CBFV per unit change in end-tidal pCO2) gives further evidence that the filters reflect autoregulation. The method allows simple parametrization of the dynamic autoregulatory responses in CBFV, and the analysis of short (1 min) data segments.

Aged↗
PubMed2001

Photic driving in the electroencephalogram of children and adolescents: harmonic structure and relation to the resting state.

In order to identify latent bioelectrical oscillators, 15 normal subjects (aged 9-17 years, 8 males, 7 females) were subjected to intermittent photic stimulation. The EEG amplitude spectra corresponding to the 11 fixed frequencies of stimulation presented (3-24 Hz) were combined to form "profiles" of the driving reaction in the right occipital area. The driving response varied with frequency, and was demonstrable in 70-100% of cases (using as criterion peak amplitudes 20% larger than those of the neighbors). The strongest responses were observed at the frequency closest to the alpha peak of the resting EEG. A secondary profile maximum was in the theta band. In 10 subjects, this maximum exceeded half the alpha peak (with an average of 72.4% of the alpha peak), while in the resting spectra, theta amplitudes were much lower than the alpha maxima. This responsiveness in theta activity seems to be characteristic of prepubertal and pubertal subjects. The profiles and resting EEG spectra showed a highly significant Pearson's correlation, with the peak in the theta band of the profiles being the main difference observed between them. The correlation coefficient was significantly correlated with the ratio of the maxima in the theta and alpha bands (R = -0.77, P<0.001). The correlation coefficient between profile and resting spectrum may be a useful indicator in screening methods used to reveal latent cerebral oscillators. Profiles for the second and third harmonics were correlated with those of the first harmonic (fundamental frequency), when considering the corresponding EEG frequencies. Peak frequencies in all three profiles were close to those of the individual's background alpha rhythm, and peak amplitudes in higher harmonics were not much lower than those of the fundamental frequency (mean values of 84 and 63%, for second and third harmonics, respectively).

Adolescent↗
PubMed2000

A placebo-controlled trial of lamotrigine for painful HIV-associated neuropathy.

OBJECTIVE: To investigate the analgesic efficacy of lamotrigine in the treatment of painful HIV-associated distal sensory polyneuropathy (DSP). BACKGROUND: The pathogenesis of HIV-associated DSP is unknown and there is no effective treatment. A novel anticonvulsant, lamotrigine, blocks voltage-sensitive sodium channels and inhibits the release of glutamate and aspartate. There have been anecdotal reports of efficacy of lamotrigine in the treatment of painful neuropathy and trigeminal neuralgia. METHODS: In a multicenter, randomized, double-blind, placebo-controlled study, lamotrigine was initiated at 25 mg per day and slowly titrated over 7 weeks to 300 mg per day. Study duration was 14 weeks. The primary outcome measure was change in pain on the modified Gracely scale with secondary outcome measures including change in neurologic examination, use of concomitant analgesic medications, and global pain relief. RESULTS: Of 42 enrolled subjects, 13 did not complete the 14-week study endpoint. In five of these, rash was the cause for dropout. In the remaining 29 evaluable subjects, 20 patients received placebo and 9 received lamotrigine. The pain scores at baseline were not significantly different. The reduction in average pain from baseline to week 14 was greater (p = 0.03) in the lamotrigine group (-0.55) than in the placebo group (-0.18), adjusting for baseline levels of pain. There was no difference between the groups on the change in peak worst pain. CONCLUSIONS: In this small trial, lamotrigine showed promise in the treatment of pain associated with HIV-related DSP. The frequency of rash was greater than in lamotrigine studies in epilepsy. A larger controlled study of lamotrigine is warranted.

Adult↗
PubMed2000

The role of somatosensory evoked potentials in the diagnosis of AIDS-associated myelopathy.

BACKGROUND: Although AIDS-associated vacuolar myelopathy is detected in >50% of autopsy cases, it is often unrecognized during life. The clinical assessment is often difficult because of concurrent peripheral neuropathy and lack of specific diagnostic markers. Somatosensory evoked potentials (SEPs) have been successfully used to evaluate central conduction in a number of diseases involving the spinal cord. OBJECTIVES: To assess the diagnostic yield of SEPs in AIDS-associated myelopathy. METHODS: We recorded tibial and median nerve SEPs in 69 HIV-infected subjects referred for evaluation of lower extremity neurologic abnormalities. Stimulation of the peroneal nerve at the popliteal fossa was performed in patients with absent response to ankle stimulation. RESULTS: HIV-infected subjects had significantly delayed latencies of both peripheral and central potentials, suggesting a combination of peripheral and CNS abnormalities. Analysis of peripheral and central latencies allowed us to discriminate between neuropathy and myelopathy in individual patients. Abnormalities of tibial central conduction time (CCT) correlated with clinical diagnosis of myelopathy. There was no significant difference in median CCTs between patients and controls, suggesting that conduction abnormalities were restricted to the thoracolumbar spinal cord. A derived spinal conduction time was a sensitive indicator of central conduction abnormalities in AIDS patients with myelopathy. CONCLUSIONS: The combination of median, posterior tibial, and peroneal SEPs is a valuable tool in the diagnosis of AIDS-associated myelopathy, particularly when myelopathy and peripheral neuropathy coexist. The use of a derived spinal conduction time improves the diagnostic yield of SEPs in AIDS-associated myelopathy.

Acquired Immunodeficiency Syndrome↗
PubMed2000

A phase II trial of nerve growth factor for sensory neuropathy associated with HIV infection. AIDS Clinical Trials Group Team 291.

OBJECTIVE: To evaluate the safety and efficacy of recombinant human nerve growth factor (rhNGF) in HIV-associated sensory neuropathy (SN) within a multicenter, placebo-controlled, randomized trial (ACTG 291). BACKGROUND: SN affects 30% of individuals with AIDS, is worsened by neurotoxic antiretrovirals, and its treatment is often ineffective. NGF is trophic for small sensory neurons and stimulates the regeneration of damaged nerve fibers. METHODS: A total of 270 patients with HIV-associated SN were randomized to receive placebo, 0.1 microg/kg rhNGF, or 0.3 microg/kg rhNGF by double-blinded subcutaneous injection twice weekly for 18 weeks. The primary outcome was change in self-reported neuropathic pain intensity (Gracely Pain Scale). Secondary outcomes included an assessment of global improvement in neuropathy by patients and investigators, neurologic examination, use of prescription analgesics, and quantitative sensory testing. In a subset, epidermal nerve fiber densities were determined in punch skin biopsies. RESULTS: Both doses of NGF produced significant improvements in average and maximum daily pain compared with placebo. Positive treatment effects were also observed for global pain assessments (p = 0.001) and for pin sensitivity (p = 0.019). No treatment differences were found with respect to mood, analgesic use, or epidermal nerve fiber densities. Injection site pain was the most frequent adverse event, and resulted in unblinding in 39% of subjects. Severe transient myalgic pain occurred in eight patients, usually from accidental overdosing. There were no changes in HIV RNA levels or other laboratory indices. CONCLUSIONS: We found a positive effect of recombinant human nerve growth factor on neuropathic pain and pin sensitivity in HIV-associated sensory neuropathy. rhNGF was safe and well tolerated, but injection site pain was frequent.

Adult↗
PubMed2000

Hereditary neuropathy and vocal cord paralysis in a man with childhood diphtheria.

We present the case of a 37-year-old Afghani man with a history of childhood diphtheria, who was diagnosed with bilateral vocal cord paralysis at age 15 years. At about this time he developed progressive muscular wasting and distally predominant weakness, and subsequently developed respiratory insufficiency, necessitating nocturnal ventilatory support. His examination suggested a distal symmetric sensorimotor neuropathy, and his brother was similarly affected, although to a lesser degree. Electromyography (EMG) and nerve conduction studies revealed this process to be purely axonal. A diagnosis of possible hereditary motor and sensory neuropathy (HMSN) type IIc, hereditary axonal polyneuropathy with vocal cord paralysis, is proposed, although the question of early diphtheritic involvement of the vocal cords and peripheral nerves is also considered.

Adult↗
PubMed2000

Peripheral neuropathy associated with acquired immunodeficiency syndrome (AIDS)-related Burkitt's lymphoma.

Peripheral neuropathy associated with acquired immunodeficiency syndrome (AIDS)-related Burkitt's lymphoma usually occurs as a toxic effect of chemotherapeutic agents. Whereas primary peripheral nerve involvement is an unusual complication, we report on a human immunodeficiency virus (HIV)-positive patient with Burkitt's lymphoma and sciatic neuropathy due to compression by a lymphomatous mass. Therapy with radiation and chemotherapy was followed by clinical and radiological improvement, but recurrent neurological deficits in a similar distribution occurred later from lymphomatous meningitis.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Estimating normal and pathological dynamic responses in cerebral blood flow velocity to step changes in end-tidal pCO2.

The regulation of cerebral blood flow (CBF) following changes in arterial blood pressure (ABP) and end-tidal pCO2 (EtCO2) are of clinical interest in assessing cerebrovascular reserve capacity. Linear finite-impulse-response modelling is applied to ABP, EtCO2 and CBF velocity (CBFV, from transcranial Doppler measurements), which allows the CBFV response to ideal step changes in EtCO2 to be estimated from clinical data showing more sluggish, and additional random variations. The confounding effects of ABP changes provoked by hypercapnia on the CBFV are also corrected for. Data from 56 patients suffering from stenosis of the carotid arteries (with normal or diminished cerebrovascular reactivity to EtCO2 changes--CVRCO2) were analysed. The results show the expected significant differences (p < 0.05) between EtCO2 steps up and down, the significant contribution from ABP variation, and also differences in the dynamic responses of patients with reduced CVRCO2 (p < 0.01 after 10 s). For the latter the CBFV response appears exhausted after about 15 s, whereas for normals CBFV continues to increase. While dispersion of individual step responses remains large, the method gives encouraging results for the non-invasive study of compromised haemodynamics in different patient groups.

Aged↗
PubMed2000

Texas physician immunization practices.

INTRODUCTION: Immunization levels among young children could be improved if physicians administered immunizations at both well and urgent visits, provided simultaneous vaccinations, and knew the guidelines on valid contraindications, part of the Standards for Pediatric Immunization Practices (Standards). We report on a survey measuring the immunization knowledge and practice of Texas pediatricians, family practitioners, and general practitioners. METHODS: A survey was mailed to a random sample of physicians. Questionnaire items covered 8 of the 18 Standards. RESULTS: The response rate was 62% (608 of 976 eligible physicians). The mean summary adherence-to-Standards score was 4.1 for pediatricians, 3.6 for family practitioners, and 3.0 for general practitioners. Specialty and practice location were significant predictors of the summary score, whereas gender, managed-care participation, and graduation year were not. DISCUSSION: Our study results suggest that in Texas, pediatricians and rural physicians most often adhere to the Standards. Improving the reimbursement level of administrative costs for immunization delivery, educating physicians on the Standards, and encouraging the use of patient immunization tracking systems are actions that could potentially improve immunization rates.

Adult↗
PubMed2000

Multivariate dynamic analysis of cerebral blood flow regulation in humans.

The contributions of beat-to-beat changes in mean arterial blood pressure (MABP) and breath-by-breath fluctuations in end-tidal CO2 (EtCO2) as determinants of the spontaneous variability of cerebral blood flow velocity (CBFV) were studied in 16 normal subjects at rest. The two input variables (MABP and EtCO2) had significant cross-correlations with CBFV but not between them. Transfer functions were estimated as the multivariate least mean square finite impulse response causal filters. MABP showed a very significant effect in explaining CBFV variability (p < 10(-11), Fisher's aggregated-p test) and the model mean square error was significantly reduced (p < 0.001) by also including the contribution of EtCO2. The estimated mean CBFV step response to MABP displayed the characteristic return to baseline caused by the cerebral autoregulatory response. The corresponding response to EtCO2 showed a gradual rise taking approximately 10 s to reach a plateau of 2.5%/mmHg. This study demonstrated that spontaneous fluctuations in EtCO2 can help to explain the CBFV variability at rest if appropriate signal processing techniques are employed to address the limited power and bandwith of the breath-by-breath EtCO2 signal.

Adult↗
PubMed2000

Objective response detection in an electroencephalogram during somatosensory stimulation.

Techniques for objective response detection aim to identify the presence of evoked potentials based purely on statistical principles. They have been shown to be potentially more sensitive than the conventional approach of subjective evaluation by experienced clinicians and could be of great clinical use. Three such techniques to detect changes in an electroencephalogram (EEG) synchronous with the stimuli, namely, magnitude-squared coherence (MSC), the phase-synchrony measure (PSM) and the spectral F test (SFT) were applied to EEG signals of 12 normal subjects under conventional somatosensory pulse stimulation to the tibial nerve. The SFT, which uses only the power spectrum, showed the poorest performance, while the PSM, based only on the phase spectrum, gave results almost as good as those of the MSC, which uses both phase and power spectra. With the latter two techniques, stimulus responses were evident in the frequency range of 20-80 Hz in all subjects after 200 stimuli (5 Hz stimulus frequency), whereas for visual recognition at least 500 stimuli are usually applied. Based on these results and on simulations, the phase-based techniques appear promising for the automated detection and monitoring of somatosensory evoked potentials.

Adult↗
PubMed2000

Effects of the laryngeal mask airway on the lower oesophageal barrier pressure in children.

The effects of laryngeal mask airway (LMA) insertion and cuff inflation on lower oesophageal sphincter, gastric and barrier pressure, and the relationship of the LMA cuff pressure and volume on the change in the barrier pressure were studied in 20 children. Subjects were aged one to five years, undergoing eye examination under general anaesthesia. There was no significant change in barrier pressure after insertion and inflation of the LMA compared with baseline measures. The cuff pressure and volume were not related to the change in barrier pressure. Two patients had marked decreases (10 to 15 mmHg) in barrier pressure after the LMA insertion. These decreases in barrier pressure would be expected to increase the risk of gastro-oesophageal reflux. We conclude that, although LMA use had little effect on barrier pressure in most children, occasional children will have potentially clinically significant decreases in barrier pressure with use of the LMA.

Anesthesia, General↗
PubMed2000

HIV-associated peripheral neuropathy: epidemiology, pathophysiology and treatment.

Peripheral neuropathy is the most frequent neurological complication associated with human immunodeficiency virus type 1 (HIV) infection and advanced acquired immunodeficiency syndrome (AIDS). There are at least 6 patterns of HIV-associated peripheral neuropathy, although these diagnoses are often overlooked or misdiagnosed. Distal symmetrical polyneuropathy (DSP) is the most common form of peripheral neuropathy in HIV infection. DSP occurs mainly in patients with advanced immunosuppression and may also be secondary to the neurotoxicity of several antiretroviral agents. Treatment of painful DSP is primarily symptomatic, while pathogenesis-based therapies are under investigation. Reduction or discontinuation of neurotoxic agents should be considered if possible. Inflammatory demyelinating polyneuropathy (IDP) can present in an acute or chronic form. The acute form may occur at the time of primary HIV infection or seroconversion. Cerebrospinal fluid lymphocytic pleocytosis (10 to 50 cells/mm3) is helpful in the diagnosis of HIV-associated IDP. Treatment consists of immunomodulatory therapy. Progressive polyradiculopathy (PP) most commonly occurs in advanced immunosuppression and usually is caused by cytomegalovirus (CMV) infection. Rapidly progressive flaccid paraparesis, radiating pain and paresthesias, areflexia and sphincter dysfunction are the cardinal clinical features. Rapid diagnosis and treatment with anti-CMV therapy are necessary to prevent irreversible neurological deficits resulting from nerve root necrosis. Mononeuropathy multiplex (MM) that occurs in early HIV infection is characterised by self-limited sensory and motor deficits in the distribution of individual peripheral nerves. In advanced HIV infection, multiple nerves in two or more extremities or cranial nerves are affected. Treatment includes immunomodulation or anti-CMV therapy. Autonomic neuropathy may be caused by central or peripheral nervous system abnormalities. Treatment is supportive with correction of metabolic or toxic causes. Diffuse infiltrative lymphocytosis syndrome (DILS) presents as a Sjögren's-like disorder with CD8 T cell infiltration of multiple organs. Antiretroviral therapy and steroids may be effective treatments.

HIV Infections↗
PubMed1999

Peripheral nerve function in HIV infection: clinical, electrophysiologic, and laboratory findings.

OBJECTIVE: To determine the effects of immunodeficiency, nutritional status, and concurrent systemic disease on peripheral nerve function in acquired immunodeficiency syndrome. DESIGN: Survey of subjects infected with human immunodeficiency virus (HIV), recruited as part of a prospective study of neuromuscular complications of HIV infection. SETTING: A neuro-acquired immunodeficiency syndrome outpatient clinic in a university medical center. PATIENTS: A consecutive sample of 251 HIV-infected individuals. Primary care providers referred subjects to the study for evaluation of neurologic symptoms or for prospective neurologic assessment. MAIN OUTCOME MEASURES: Standardized history and neurologic examination, laboratory tests (complete blood cell count, serum albumin level, vitamin B12 level, and T-lymphocyte subsets), and electrophysiologic testing of sural, tibial, and ulnar nerves. RESULTS: The most frequent neurologic diagnosis was distal symmetrical polyneuropathy (DSP) (38%). The most common clinical features were nonpainful paresthesias (71%), abnormalities of pain and temperature perception (71%), and reduced or absent ankle reflexes (66%). Patients with DSP were significantly older (P=.009), and had lower CD4 lymphocyte cell counts (P=.004) and lower hemoglobin levels (P=.004) than those without DSP. Deterioration of values on nerve conduction studies, irrespective of the clinical diagnosis of DSP, was significantly correlated with low CD4 counts, aging, abnormal serum albumin and hemoglobin levels, and weight loss. Most of these factors co-correlated, and, with the exception of age, no single variable significantly accounted for changes in results of nerve conduction studies when the influence of other factors was eliminated. CONCLUSION: The combination of several factors, including age, immunosuppression, nutritional status, and chronic disease, contributes to distal peripheral nerve dysfunction in HIV infection.

Adult↗