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Biomedical subjects

J F Nielsen

Publications and source records attributed to J F Nielsen.

32 records · Page 2Linked to original sources
PubMed1996

Treatment of spasticity with repetitive magnetic stimulation; a double-blind placebo-controlled study.

The effect of repetitive magnetic stimulation on spasticity was evaluated in 38 patients with multiple sclerosis in a double-blind placebo-controlled study. One group was treated with repetitive magnetic stimulation (n = 21) and the other group with sham stimulation (n = 17). Both groups were treated twice daily for 7 consecutive days. Primary end-points of the study were changes in the patients self-score, in clinical spasticity score, and in the stretch reflex threshold. The self-score of ease of daily day activities improved by 22% (P = 0.007) after treatment and by 29% (P = 0.004) after sham stimulation. The clinical spasticity score improved -3.3 +/- 4.7 arbitrary unit (AU) in treated patients and 0.7 +/- 2.5 AU in sham stimulation (P = 0.003). The stretch reflex threshold increased 4.3 +/- 7.5 deg/s in treated patients and -3.8 +/- 9.7 deg/s in sham stimulation (P = 0.001). The data presented in this study supports the idea that repetitive magnetic stimulation has an antispastic effect in multiple sclerosis. Future studies should clarify the optimal treatment regimen.

Activities of Daily Living↗
PubMed1996

Improvement of amplitude variability of motor evoked potentials in multiple sclerosis patients and in healthy subjects.

Variability of the amplitude of motor evoked potentials was studied in 33 multiple sclerosis (MS) patients and 21 healthy subjects. Normal probability plots revealed skewness of the distribution of amplitudes obtained from the abductor pollicis brevis (APB) muscle during muscle relaxation, muscle contraction, and by paired magnetic stimulation. Natural logarithmic transformation of amplitude data resulted in normal distribution. Negative first-order autocorrelations were established for consecutive recordings independent of the repetition rate tested (5 s, 8 s, 12 s, and 20 s). A given measurement had a tendency to be systematically followed by a measurement of a lower value, indicating that magnetic stimulations induce a long-lasting inhibitory effect on the excitability of the motor pathways. A significant decrease in amplitude variability was achieved by a controlled muscle contraction of the target muscle compared with an uncontrolled muscle contraction in MS patients. Paired magnetic stimulation halved the coefficient of variation of amplitude data compared with amplitude obtained during muscle relaxation, and is introduced to reduce amplitude variability in conditions where no collaboration is possible.

Adult↗
PubMed1995

Motor pathway function in normoalbuminuric IDDM patients.

Central motor pathways were studied in 17 normoalbuminuric insulin-dependent diabetic (IDDM) patients who had been diabetic for more than 20 years, and compared with findings in 17 age-, sex-, and height-matched control subjects. The central motor conduction time was calculated from recordings of the compound muscle action potentials of the abductor pollicis brevis muscle after single transcranial and spinal root magnetic stimulation. The central motor conduction time from motor cortex to cervical spinal roots was 9.8 +/- 1.65 ms in diabetic patients and 10.1 +/- 1.48 ms in control subjects. In diabetic patients with neuropathy the central motor conduction time was 9.5 +/- 1.76 ms vs 10.1 +/- 1.56 ms in patients without neuropathy. The excitability of the motor pathways was studied by paired transcranial magnetic stimulation at interstimulation intervals of 30-1000 ms. In normal control subjects, an early facilitation of the amplitude of the compound muscle action potential at an interstimulation interval of 30 ms was found, while no facilitation was present in diabetic patients. In addition the compound muscle action potential latencies were prolonged at interstimulation intervals of 30-50 ms in diabetic patients. The changes of excitability did not correlate with the presence of peripheral neuropathy, metabolic control or diabetes duration. It is concluded that long-term normoalbuminuric IDDM patients have imparied excitability but normal central conduction time of the motor pathways.

Adult↗
PubMed1995

A new high-frequency magnetic stimulator with an oil-cooled coil.

A new high frequency magnetic stimulator, Labmag, is described which may be used in clinical neurophysiology and for the treatment of spasticity in multiple sclerosis. In order to avoid heating of the coil during repetitive stimulation, an oil/air cooling system was employed. The magnetic stimulus waveform is a half cosine with a rise time of 200 microseconds and a pulse width of 400 microseconds induced by alternating capacitor voltage. The Labmag product was compared with a commercially available high frequency stimulator, MagPro. The electric fields induced by Labmag were half the size of those induced by MagPro at identical stimulus intensities. Using a leaky integrator to simulate the effects on neurons, only minor differences in integrated electric fields were observed. There were no changes of the electric fields in relation to coil geometry. A minor difference in electric fields (1.0 +/- 0.8%) was observed when the polarity of the capacitor voltage alternated. Compound muscle action potentials (CMAPs) evoked by transcranial magnetic stimulation were recorded from the first dorsal interosseous muscle (FDI) in eight subjects. Threshold intensities of CMAPs evoked by Labmag (58 +/- 7%) were significantly smaller (p < 0.05) than threshold intensities obtained with MagPro (63 +/- 8%). Peak-to-peak amplitudes, P-Pamps, of CMAPs were significantly smaller after single stimulations with Labmag at stimulation intensities of 130 and 140% of threshold intensity.

Adult↗
PubMed1994

Inability of insulin to maintain normal nerve function during high-frequency stimulation in diabetic rat tail nerves.

The effect of insulin on the response to long-term high-frequency stimulation (HFS = 143 Hz for 20 min) was studied in mixed tail nerves of acute streptozotocin-induced diabetic rats. In consecutive tests, untreated diabetic rats showed a significant decrease in nerve conduction velocity (NCV) and peak-to-peak amplitude (P-Pamp) and the depression of the P-Pamp during HFS was augmented. In contrast, NCV and P-Pamp in the insulin-treated rats were unchanged from the prediabetic state, but the depression of the P-Pamp during HFS reached the same degree as in untreated rats. This implies that although insulin treatment of acute experimental diabetes is able to preserve a normal NCV and P-Pamp in the resting state, it is unable to preserve normal nerve function under stress produced by HFS. Monitoring of the axon membrane functional capacity may have clinical implications in the control of peripheral neuropathies.

Action Potentials↗
PubMed1994

Standardization of facilitation of compound muscle action potentials using a modified myometer during magnetic stimulation in healthy volunteers.

In 20 normal subjects motor evoked potentials (MEPs) from first dorsal interosseous (FDI) were obtained following transcranial magnetic stimulation during relaxation and voluntary contraction of 2-20% of maximum. A new method to standardize facilitation of MEP using surface EMG and a modified myometer was used. The MEP amplitudes increased significantly at contraction levels of 2%, 10% and 15% of maximum. The latencies decreased significantly at contraction levels of 2%, 5% and 15%. Coefficients of variation of the amplitude decreased from 6.4% during relaxation to approximately 2% during facilitation. In contrast, coefficients of variation of take-off latencies (T-lat) increased significantly from 1.7% during relaxation to approximately 3% during facilitation. The variability of amplitudes and latencies was mainly due to inter-individual variation. The observations in the present study indicate that the actual contraction level should be precisely defined during transcranial magnetic stimulation.

Action Potentials↗
PubMed1994

A Danish family with limb-girdle muscular dystrophy with autosomal dominant inheritance.

We describe a Danish family of five generations showing a slowly progressive autosomal dominant limb-girdle myopathy with onset in early childhood. Three patients from two generations were examined and showed weakness predominantly of the proximal muscles of upper and lower extremities. Early contractures of wrist, tight heel cords, metacarpophalangeal and interphalangeal joints were present. Walking ability was partly preserved. Serum creatine kinase activity was normal or slightly elevated. EMG and biopsy showed mildly myopathic changes. Magnetic resonance images of the thigh showed severe atrophy of all compartments but with musculus semimembranosus, sartorius, and gracilis relatively preserved. This myopathy has a clinical picture similar to the Bethlem myopathy.

Biopsy↗
PubMed1993

Reduced capability of transmitting high frequency impulses in tail nerves of diabetic rats.

The effect of long-term (40 min) high frequency stimulation (143 Hz) of sensory-motor tail nerves was studied in normal and in streptozotocin-diabetic rats. The study comprised a 6-week period, repeating the test at 2-week intervals. In the initial (prediabetic) study, single experiments showed a mild depression of the peak-to-peak amplitude during high frequency stimulation, which reversed completely during a subsequent rest period. In normal rats, the amplitude depression was unchanged in repeated tests over a 6-week period. Diabetic rats showed a greater amplitude depression during high frequency stimulation. The difference was statistically significant after 2 weeks, but showed no further change at subsequent tests. The greater decrease in the amplitude in diabetic rats may reflect a depression of the axon membrane function, which may be the functional correlate to the inhibition of the Na/K ATPase activity in diabetes, described by others. Monitoring of the axon membrane functional capacity may have clinical implications in the control of peripheral neuropathies.

Action Potentials↗
PubMed1988

Haemoptysis caused by aneurysm of saphenous bypass graft to a coronary artery.

In a 51-year-old man, coronary artery bypass surgery for severe angina pectoris was followed by protracted mediastinal infection. After recovery the patient had several haemoptyses. Angiography revealed aneurysm of a graft near its distal anastomosis. Upper left lobectomy and ligation of the graft were necessitated by bleeding from the aneurysm into a segmental bronchus. Angina pectoris recurred but was successfully treated with verapamil.

Aortic Dissection↗
PubMed1986

Inflatable splints: do they cause tissue ischaemia?

The effect of increasing pneumatic splint pressure on cutaneous oxygen tension measured transcutaneously (TcPO2) was investigated in 12 subjects. The mean initial TcPO2 was 70.6 mmHg. TcPO2 decreased linearly on increasing the pressure within the splint. TcPO2 became zero at a mean splint pressure of 28 mmHg. Second, three accepted methods used by the ambulance crew to assess inflation pressures of the splint were investigated and found to be unreliable. In the light of these findings the risk of ischaemic complications as a result of applying pneumatic splints to a fractured limb is discussed. We advocate a recommended maximum splint pressure of 15 mmHg and that the splint should be manufactured with a security blow-off valve set at 15 mmHg.

Adult↗
PubMedDate not supplied

Image-matching as a medical diagnostic support tool (DST) for brain diseases in children.

Imaging-matching is an important research area in imaging informatics. We have developed and evaluated a novel diagnostic support tool (DST) based on medical image matching using MR brain images. The approach consists of two steps, database generation and image matching. The database contains pre-diagnosed MR brain images. As the images are added to the database, they are registered to the 3D Talairach coordinate system. In addition, regions of interests (ROI) are generated, and image-processing techniques are used to extract relevant image parameters related to the brain and diseases from the ROIs and from the entire MR image. The second step is to retrieve relevant information from the database by performing image matching. In this step, the physician first submits a query image. The DST computes the similarity between the query image and each of the images in the database, and then presents the most similar images to the user. Since the database contains pre-diagnosed images, the retrieved cases tend to contain relevant diagnostic information. To evaluate the usefulness of the DST in a clinical setting, pediatric brain diseases were used. The database contains 2500 pediatric patients between ages 0 and 18 with brain Magnetic Resonance (MR) images of known brain lesions. A testbed was established at the Children's Hospital Los Angeles (CHLA) for acquiring MR images from the PACS server of patients with known lesions. These images were matched against those in the DST pediatric brain MR database. An expert pediatric neuroradiologist evaluated the matched results. We found that in most cases, the image-matching method was able to quickly retrieve images with relevant diagnostic content. The evaluation method and results are given.

Brain Diseases↗