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Biomedical subjects

W Wolf

Publications and source records attributed to W Wolf.

At least 19 recordsLinked to original sources
PubMed2006

Motor cortex excitability changes preceding voluntary muscle activity in simple reaction time task.

The effect of transcranial magnetic stimulation (TMS) on reaction time (RT) and motor cortex excitability in the premovement period was investigated. Single and paired-pulse TMS with 3 and 13 ms interstimulus intervals (ISI) were applied to the left motor cortex at different delays after a visual command for isometric right hand index finger abduction. Motor evoked potentials (MEPs) recorded from the right first dorsal interosseous (FDI) were analysed to assess cortex excitability. The MEPs in response to single pulse TMS were gradually increased in the premovement period in general, but strongly augmented in a period of 90-100 ms before the voluntary myoelectrical activity (EMG) onset. In paired-pulse TMS (13 ms ISI), the MEP augmentation was smaller but started earlier before the EMG burst, and a gradual increase of MEP amplitudes was not evident. In case of 3 ms ISI, the expected intracortical inhibition (ICI) was evident only when TMS preceded the voluntary EMG by an interval of more than 60 ms, but at shorter intervals, rather some MEP augmentation was observed. Generally, the augmentation of MEPs in the premovement period was more pronounced in single pulse TMS. Most strikingly, a dead band period without MEP occurrences was observed within an interval of 30-50 ms before the voluntary EMG. In conclusion, parallel action of intracortical facilitation (ICF) and ICI as well as different dynamic behaviour of ICF and pre movement facilitation may explain the earlier mentioned effects. Moreover, this leads to an extended description of the rather subtle TMS influence on RT.

Adaptation, Physiological↗
PubMed2005

Motor cortex excitability during unilateral muscle activity.

The effect of unilateral tonic muscle activity with and without co-activation of the antagonists on motor cortex excitability has been studied. Motor evoked potentials (MEPs) were recorded from the first dorsal interosseus muscles of both hands in response to transcranial magnetic stimulation (TMS) during relax, isometric index finger abduction and antagonistic co-activation. The intracortical inhibition (ICI) and intracortical facilitation (ICF) were investigated by paired-pulse TMS with interstimulus intervals of 3 and 13 ms. The unilateral tonic activation of the right hand facilitated contralateral and ipsilateral responses (cMEP and iMEP) recorded from both hands with an exception of iMEPs recorded from the left hand. During paired-pulse TMS ICI for cMEPs was not influenced by the unilateral tonic activity in both hands, while ICF was suppressed when MEPs were recorded from the active right hand. The effect of unilateral tonic activity on iMEP in response to paired-pulse TMS was essentially different: generally, ICI was greater for iMEPs and ICF was completely abolished with an exception of iMEPs recorded from the left hand during right finger isometric abduction when a strong ICF was evident. The decreased ICF and/or increased ICI are assumed to reflect mechanisms underlying the co-activation of antagonists.

Action Potentials↗
PubMed2005

Syphilis partner notification with men who have sex with men: a review and commentary.

BACKGROUND: Eight US cities experienced large outbreaks of syphilis among men having sex with men (MSM), beginning during 2000-2001. Provider-assisted partner notification via disease intervention specialists has traditionally composed a large part of syphilis control efforts. OBJECTIVES: Report current effectiveness of syphilis partner notification for MSM and identify related problems and solutions. RESULTS: One thousand five hundred seventeen MSM diagnosed with syphilis claimed 10,254 sex partners. Many claimed anonymous partners (median = 65%), or provided insufficient locating information (median = 42%). Median cases found per index case were 0.09 (total = 116), although an additional 197 partners had been previously treated. Principal impediments to partner notification fell into 3 areas: (1) diagnosis outside health department settings delayed interviews, (2) partners were often anonymous, and (3) mistrust among MSM, public health professionals, and health care providers in private settings. CONCLUSIONS: Characteristics of the current outbreaks among MSM make traditional partner notification more difficult than in the past. Some modifications, complements, and even alternatives to partner notification are either planned or in operation.

Cities↗
PubMed2002

The discontinuous nature of motor execution II. Merging discrete and rhythmic movements in a single-joint system -- the phase entrainment effect.

Initiation of rapid discrete flexion movements is significantly altered when a secondary rhythmic movement is performed simultaneously with the same limb; the onset of a stimulus-evoked discrete movement tends to occur time-locked to the oscillation: i.e., the rhythmic movement entrains the discrete response. This nonlinear interaction may reflect a specific principle of coordination of motor tasks which are simultaneously executed with the same effector. This part II of a tripartite research report on such single-muscle multiple-task coordination investigates the contribution of the dynamic properties of the muscle and its reflex circuitry to phase entrainment. Assuming a simple threshold-linear relationship between the control signals generated by the central nervous system and the observable kinematic and electromyographic signals, a secondary rhythmic movement will cause an additional phase-dependent delay between the central "go" command and the first observable change in actual kinematics of the compound movement. Several indicators for such threshold-linear interaction are derived and tested on real data obtained in psychophysical experiments. Four healthy subjects performed rapid lateral abductions of the index finger in response to a visual "go" signal. During a portion of the experiments, subjects produced additional low-amplitude oscillatory movements before stimulus presentation with either the same finger (one-handed task), or with the index finger of the other hand (two-handed task). Results showed phase entrainment and modulation of reaction times when the cyclic and the discrete movements were simultaneously executed by the same finger. But there was no entrainment in the bimanual execution of the tasks. The model was capable of reproducing the observed effects. It is concluded that coordination of voluntary movements which are concurrently performed by the same effector involves specific discontinuous operations, which represents an essential part of the mechanism of motor coordination. Phase entrainment reflects this characteristic discontinuous behavior of the lower stages of motor execution and does not necessarily require nonlinear interaction of motor commands at higher levels of motor processing.

Electromyography↗
PubMed2002

Vibratory proprioceptive stimulation affects Parkinsonian tremor.

Previous research on tremor pathophysiology showed that tremor can be affected, e.g. by electrical stimulation of the peripheral nerve, mechanical perturbation of the limb and by transcranial magnetic stimulation of the motor cortex. This report is focused on possible effects of muscle vibration (MV) on resting tremor in Parkinson's Disease (PD). Vibratory stimulation was applied to the tendons of M. extensor carpi radialis longus and M. flexor ulnaris in 27 subjects with moderate PD resting tremor. The following effects were observed: (1) tremor stopped or started time-locked to MV onset and offset, (2) tremor persisted during MV but its frequency pattern changed. These results are discussed with specific emphasis to effects of MV on spinal and supraspinal levels.

Aged↗
PubMed2002

Physical, morphological and chemical characteristics, oil recovery and fatty acid composition of Balanites aegyptiaca Del. kernels.

Balanites aegyptiaca Del. kernels were chemically, physically and morphologically characterized. Crude oil (49.0%) and crude protein (32.4%) were the two major constituents of the kernels. Phytic acid content was relatively high compared to other legumes. In contrast, antitryptic activities of the kernel flours were very low. Sapogenin contents of the full fat, defatted and testa flours were 1.5, 2.7 and 3.0%, respectively. The hardness of the kernel was found to be about 10.4 x 10(5) N/m2, which was somewhat high. The morphological structure of the kernel using a scanning electron microscope revealed that the protein matrix was embedded in a lake of oil droplets. Oil recovery, as a function of pressing time, pressure, temperature and particle size was investigated. With increasing temperature up to 70 degrees C at 400 bar, for 120 min, an oil recovery of 79.4% was obtained. Using an expeller at 115 degrees C, about 85% of the kernel oil was recovered. The reduction of particle size had a negative effect on oil recovery under the same conditions. The fatty acid composition was not affected by the pressing temperature up to 115 degrees C. The total amount of the unsaturated fatty acids was found to be up to 74.8% (50 degrees C) and 75.1% (115 degrees C) of the total fatty acids content.

Balanites↗
PubMed2001

Long-term stability of nutrients in a frozen mixed food control material.

A mixed food homogenate was prepared as a quality control material for two multi-center clinical feeding trials. Approximately 100 kg of homogenized human diet material was prepared under controlled conditions to maintain the stability of lipid components. More than 4,800 20-25 g aliquots were prepared and stored at -60 degrees C in glass jars with Teflon-lined lids. The homogeneity of the composite was validated by analysis of moisture and total fat in aliquots taken throughout the dispensing sequence. A portion of the material was reserved at the National Institute of Standards and Technology and further characterized as SRM 1544-Fatty Acids in Diet Composite. Moisture, protein, ash, total lipid, fatty acids, cholesterol, sodium, potassium, calcium, and magnesium were assayed as part of routine quality-control analyses. Components were analyzed over a total time period ranging from 29 months (minerals) to 60 months (moisture), and up to 319 values per nutrient were generated. Results for all components assayed were stable over the time period studied. For example, moisture (n = 319; 60 months) ranged from 70.66 to 72.58 g/100 g with a mean, standard deviation (SD), and relative standard deviation (RSD) of 71.90, 0.27, and 0.4%, respectively. The range, mean, SD, and RSD for cholesterol (mg/100 g; n = 98; 49 months) were 13.54-17.96, 15.14, 0.64, and 4%.

Diet↗
PubMed2001

Is tremor an inherent feature of an intact but misadjusted motor control system?

Coordination of voluntary discrete motor responses with ongoing background activity like tremor is investigated for the single-muscle multiple-task condition by experimental and theoretical work. It is shown that the periodic background activity entrains the discrete responses. The experimental results are described by a model of the motor execution stage, and several possible consequences of the model for the motor behavior in Parkinsonian tremor patients are discussed.

Humans↗
PubMed2000

Tracing a syphilis outbreak through cyberspace.

CONTEXT: A recent outbreak of syphilis among users of an Internet chat room challenged traditional methods of partner notification and community education because locating information on sexual partners was limited to screen names and privacy concerns precluded identifying sexual partners through the Internet service provider. OBJECTIVES: To determine the association of Internet use and acquisition of syphilis and to describe innovative methods of partner notification in cyberspace. DESIGN, SETTING, AND PATIENTS: Outbreak investigation conducted at the San Francisco (Calif) Department of Public Health (SFDPH) in June-August 1999 of 7 cases of early syphilis among gay men linked to an online chat room; case-control study of 6 gay men with syphilis reported to SFDPH in July-August 1999 (cases) and 32 gay men without syphilis who presented to a city clinic in April-July 1999 (controls). MAIN OUTCOME MEASURES: Association of syphilis infection with Internet use, Internet use among cases vs controls, and partner notification methods and partner evaluation indexes. RESULTS: During the outbreak, cases were significantly more likely than controls to have met their sexual partners through use of the Internet (67% vs 19%; odds ratio, 8.7; P =.03). We notified and confirmed testing for 42% of named partners; the mean number of sexual partners medically evaluated per index case was 5.9. CONCLUSIONS: In this study, meeting sexual partners through the Internet was associated with acquisition of syphilis among gay men. Public health efforts must continually adapt disease control procedures to new venues, carefully weighing the rights to privacy vs the need to protect public health. JAMA. 2000;284:447-449

Adult↗
PubMed2000

Therapy for patients with high grade astrocytoma using intraarterial chemotherapy and radiation therapy.

BACKGROUND: High grade astrocytomas account for approximately 40% of all primary brain tumors. The median survival is approximately 8-10 months for patients with glioblastoma multiforme and 36 months for patients with anaplastic astrocytoma. The results of systemic chemotherapy in the treatment of brain tumors have been reported to be less than satisfactory, mainly because of the blood-brain barrier impermeability for chemotherapeutic drugs. Intraarterial chemotherapy has been an attractive alternative with which to overcome this problem. METHODS: Eighty-three patients with high grade astrocytoma (glioblastoma multiforme [63 patients] and anaplastic astrocytoma--[20 patients]) were treated with intraarterial (intracarotid and/or intravertebral) chemotherapy and radiation therapy between 1987 and 1997. Patients received cisplatin, 60 mg/m2, and etoposide, 40 mg/m2. Radiation therapy was delivered either after completion of the chemotherapy or concomitantly with the chemotherapy. RESULTS: Thirty-four of 71 evaluable patients with high grade astrocytoma (48%) responded to the chemotherapy. The median survival for patients with glioblastoma multiforme who received chemotherapy prior to radiation therapy was 20 months versus 7 months for those patients who underwent concomitant chemotherapy/radiation therapy. Patients with anaplastic astrocytoma who received chemotherapy prior to radiation therapy had a median survival of 45 months compared with 12 months for patients who received concomitant chemotherapy/ radiation therapy. The toxicity profile has been reported to be mild and well tolerated. CONCLUSIONS: Intraarterial chemotherapy for patients with glioblastoma multiforme, delivered prior to radiation therapy, appears to result in a median survival three times longer than that achieved with concomitant chemotherapy/radiation therapy. In addition, patients appear to survive substantially longer than they do after radiation therapy with the addition of systemic chemotherapy. Side effects are reported to be acceptable.

Adult↗
PubMed2000

19F-MRS studies of fluorinated drugs in humans.

The use of 19F-NMR as a noninvasive probe to measure directly the pharmacokinetics of drugs at their target (effector) site(s) is illustrated in this article by human studies with 5-fluorouracil (5-FU). This drug, and several of its metabolites, have been measured in vivo in animals and in patients using standard clinical MRI systems. Using a pharmacokinetic imaging approach the parameter that can be measured most readily is the tumoral t(1/2) of 5-FU. Patients whose tumoral t(1/2) of 5-FU is equal to/greater than 20 min are designated as "trappers", and those whose tumoral t(1/2) of 5-FU is less are nontrappers. Trapping of 5-FU in tumors is a necessary, albeit not a sufficient condition, for response. Problems associated with the technical aspects of these measurements have been discussed, as well as how modulators and other agents will affect the tumoral t(1/2) of 5-FU. The rationale for the biological processes underlying the fate of 5-FU in humans has been illustrated with the use of a 12 compartment model, where several of the steps have been discussed and the consequences of their inhibition/stimulation related to the noninvasive studies that can be performed with modulators of the action of 5-FU. These 19F-NMR studies have now been extended to other fluoropyrimidines, some of which are prodrugs of 5-FU, and others where the fluorine atoms are on the ribose ring. These studies also reveal information that has both scientific and clinical significance. The studies presented here illustrate some of the potential and some of the usefulness of 19F-MRS in patient management and in drug development. It is a technique that has proven itself.

Fluorine↗
PubMed2000

Noninvasive measurements for studying the tumoral pharmacokinetics of platinum anticancer drugs in solid tumors.

An effective methodology to determine the amount of cisplatin or carboplatin at the solid tumor site in a noninvasive manner may enable clinicians to design drug regimens based on an individual's in situ pharmacokinetics. Such noninvasive methods may allow optimization of an individual's drug exposure at the target site, as well as provide a screening measure to determine individual efficacy based on exposure to these platinated drugs. 195mPt appears to be the radionuclide of platinum most suitable for radiolabeling cisplatin or carboplatin, and an analysis is presented of the methods available for preparing such radiolabeled drugs. The use of this methodology is illustrated in detail in studies in animals, as well as some preliminary studies in humans. The animals used were Sprague Dawley rats bearing the Walker 256 carcinoma, and drug biodistribution was studied following administration of cisplatin or carboplatin radiolabeled with 195mPt. This radionuclide permitted noninvasive imaging of the drug and its metabolites at the tumor site and at selected organs. The results obtained show an ability to estimate the amount of platinated drug species in the tumor environment using a noninvasive methodology. Various compartmental models were tested, some of which could be validated experimentally. This noninvasive method is able to provide individual estimates of the active component of the drug at the target site, and is therefore a method that can be implemented in human studies.

Animals↗
PubMed2000

Quality changes of onion (Allium cepa L.) as affected by the drying process.

Thin layer drying experiments of sliced onion were carried out under different controlled conditions using a laboratory dryer. Quality changes of the dried product were evaluated by analysis of colour, pyruvate, chemical and sensory parameters. The results obtained proved that drying temperatures above 65 degrees C exert a pronounced influence on colour changes. The pyruvate content decreased with increasing of temperature and slice thickness. The sugar content was also found to be significantly influenced by the drying temperature. The rate of ascorbic acid degradation decreased with increasing temperature and slice thickness. Significant correlations were obtained between chemically determined pyruvate content and sensory evaluated odour of the dried onion.

Ascorbic Acid↗
PubMed2000

Recovery and characterization of Balanites aegyptiaca Del. kernel proteins. Effect of defatting, air classification, wet sieving and aqueous ethanol treatment on solubility, digestibility, amino acid composition and sapogenin content.

In order to find alternative protein sources in African regions where protein deficiency in nutrition is prevailing, solubility, in-vitro digestibility, amino acid composition and chemical score of Balanites aegyptiaca Del. kernel proteins were investigated as a function of different processing steps including defatting, air classification, wet sieving and aqueous ethanol treatment. Air classification delivered a fine fraction of 58.1% of the total protein. Applying a wet sieving process, a protein concentrate of 72.9% protein content was achieved but the recovery was very low (35.6%). However, in case of isoelectric precipitation followed by aqueous ethanol treatment both protein content (78.2%) and recovery (53.7%) were high. Data concerning the chemical score revealed, that lysine content of the defatted kernel flour amounted to 74.2% of the recommended FAO/WHO standard level. In-vitro protein digestibility was found to be higher than of legume proteins. The digestible protein of the full fat flour, defatted flour, air classified and wet sieved fine fractions and protein concentrate were 91.9, 93.7, 82.0, 86.4 and 94.2%, respectively. The sapogenin content per 100 g protein of the investigated protein preparations was significantly lower (46% to 62%) than of the initial material (oilcake).

Amino Acids↗
PubMed2000

The discontinuous nature of motor execution. I. A model concept for single-muscle multiple-task coordination.

Human movement control requires adequate coordination of different movements, which is particularly important when different motor tasks are simultaneously executed by the same effector(s) (e.g. a muscle or a joint). The process of movement execution involves a series of highly nonlinear elements; for instance, a motor unit of a muscle produces force only in the direction of muscle shortening, thus representing a threshold operator that transforms the bipolar (i.e. excitatory or inhibitory) information at its spinal input into a purely unipolar signal (i.e. muscle force). This tripartite research report addresses the contribution of the nonlinearity of neuromuscular elements to the coordination of different motor tasks simultaneously executed by the same limb. In this first part of the series, a new hypothesis for such a single-muscle multiple-task coordination is presented which suggests an essentially threshold-linear coordination mechanism. Control signals generated by the central nervous system for each individual movement independently and feedback information from peripheral receptors are linearly superimposed. This compound control/feedback signal is processed by a nonlinear limiter element reflecting the discontinuous properties of the muscle and its reflex circuitry. It is shown that threshold-linear interaction of descending commands and afferent feedback information can lead to complex interdependent patterns of compound motor action. This includes the possibility of gating (i.e. the ability of one movement pattern to constrain or even impede the execution of another pattern) and of delayed response initiation when simultaneously performing more than one voluntary motor task. A theoretical analysis of the threshold-linear coordination mechanism and an extensive experimental validation of the model is provided in part II and part III of the report.

Computer Simulation↗
PubMed2000

New aspects to event-synchronous cancellation of ECG interference: an application of the method in diaphragmatic EMG signals.

An "event-synchronous interference canceller" (ESC) for cancellation of electrocardiographic (ECG) interference in diaphragmatic electromyographic (EMGdi) signals is addressed in this paper. ESC pursues the concept of the "event synchronous adaptive interference canceller" (ESAIC), which was proposed in [1] as a specific application of the well known "adaptive noise canceller" (ANC) paradigm, but ESC uses a simple adaptive gain control (AGC) instead of the complex adaptive filter of the ANC. The proposed ESC method is evaluated using both computer simulations and real EMGdi data, and its efficiency in interference cancellation is compared to that of ESAIC. Of particular interest is the result that the ESC can replace the ESAIC providing better performance as well as a considerable reduction of computational costs.

Biomedical Engineering↗
PubMed2000

Enhancement of fluorouracil uptake in human colorectal and gastric cancers by interferon or by high-dose methotrexate: An in vivo human study using noninvasive (19)F-magnetic resonance spectroscopy.

PURPOSE: To study whether two modulators, high-dose methotrexate (MTX) and interferon alfa-2a (IFNalpha-2a) will alter the intratumoral pharmacokinetics of fluorouracil (5-FU). PATIENTS AND METHODS: Five patients, two with gastric cancer and three with colorectal cancer, who had metastatic tumor nodules in their livers were studied dynamically in vivo after 5-FU injection. In a magnetic resonance imaging unit, noninvasive (19)F-magnetic resonance spectroscopy (MRS) was used to detect (19)F signals from 5-FU and its metabolites. RESULTS: The intratumoral half-life (t(1/2)) of 5-FU in these tumors ranged from 18.8 minutes to 42.3 minutes. Four of the five patients exhibited increases in the t(1/2) of 5-FU after intravenous (IV) administration of MTX or IFNalpha-2a. In the two patients with gastric cancer who received IV high-dose MTX followed by IV 5-FU, increases were seen in either the total t(1/2) of 5-FU (41.8%) or in the t(1/2) of the alpha phase (150%). In the three patients with colorectal cancer who received IV IFNalpha-2a followed by IV 5-FU, the two patients with partial responses had increases in the t(1/2) of 5-FU of 41% and 30.2%, whereas the nonresponder had a nonsignificant increase (5.6%) in the t(1/2) of 5-FU. CONCLUSIONS: These results document that the in vivo modulation of the tumoral pharmacokinetics of 5-FU can be measured noninvasively by (19)F-MRS and suggest that such information correlates with subsequent clinical outcomes. The findings also indicate that IFNalpha-2a and high-dose MTX can increase the intratumoral 5-FU in some patients. Such information, obtained prospectively in vivo, may assist in better individual cancer patient management and in developing novel drug combinations.

Adult↗