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Biomedical subjects

H Gerhard

Publications and source records attributed to H Gerhard.

At least 19 recordsLinked to original sources
PubMed2004

Nonlinear acoustic approach to material characterisation of polymers and composites in tensile tests.

The paper reports on experimental study of elastic nonlinearity of polymers and glass fibre-reinforced (GFR-) composites in a wide range of tensile stress applied (up to a fracture limit). Focused slanted transmission mode (FSTM) of air-coupled ultrasound is adapted for remote generation and detection of flexural waves in the samples of plastics. Local noncontact measurements of flexural wave velocity as a function of static strain are used to calculate the second-order nonlinearity parameters beta2 and study their behaviour through a loading cycle. Molecular untangling and crazing phenomena are identified, respectively, with maxima of positive and negative beta2 in thermoplastics. In composites, mechanics of fibre-matrix interaction is considered for brittle and plastic fractures. Hysteresis in velocity variation during loading-unloading cycle is used as an indicator of residual defect accumulation.

Journal Article↗
PubMed2001

Compensatory visual field training for patients with hemianopia after stroke.

Twenty-one patients with hemianopia received 4 weeks of compensatory visual field training. Detection of and reaction time to visual stimuli were measured with eyes fixating (condition A) and with use of exploratory eye movements (condition B) before and after training. Twenty-three healthy individuals served as control subjects for measurements of parameters during both conditions. Patients with hemianopia to either side showed a marked improvement of detection and reaction time during condition B, but minimum or no change during condition A. Improvements were maintained 8 months after training. Activity of daily living skills also improved in all patients. The size of scotoma on computerized perimetry, in contrast, remained unchanged. Training improved detection of and reaction to visual stimuli without restitution of the visual field defect.

Activities of Daily Living↗
PubMed1999

Evolution of functional reorganization in hemiplegic stroke: a serial positron emission tomographic activation study.

We used serial positron emission tomography (PET) to study the evolution of functional brain activity within 12 weeks after a first subcortical stroke. Six hemiplegic stroke patients and three normal subjects were scanned twice (PET 1 and PET 2) by using passive elbow movements as an activation paradigm. Increases of regional cerebral blood flow comparing passive movements and rest and differences of regional cerebral blood flow between PET 1 and PET 2 in patients and normal subjects were assessed by using statistical parametric mapping. In controls, activation was found in the contralateral sensorimotor cortex, supplementary motor area, and bilaterally in the inferior parietal cortex with no differences between PET 1 and PET 2. In stroke patients, at PET 1, activation was observed in the bilateral inferior parietal cortex, contralateral sensorimotor cortex, and ipsilateral dorsolateral prefrontal cortex, supplementary motor area, and cingulate cortex. At PET 2, significant increases of regional cerebral blood flow were found in the contralateral sensorimotor cortex and bilateral inferior parietal cortex. A region that was activated at PET 2 only was found in the ipsilateral premotor area. Recovery from hemiplegia is accompanied by changes of brain activation in sensory and motor systems. These alterations of cerebral activity may be critical for the restoration of motor function.

Aged↗
PubMed1999

Reorganization of sensory and motor systems in hemiplegic stroke patients. A positron emission tomography study.

BACKGROUND AND PURPOSE: Cortical reorganization of motor systems has been found in recovered stroke patients. Reorganization in nonrecovered hemiplegic stroke patients early after stroke, however, is less well described. We used positron emission tomography to study the functional reorganization of motor and sensory systems in hemiplegic stroke patients before motor recovery. METHODS: Regional cerebral blood flow (rCBF) was measured in 6 hemiplegic stroke patients with a single, subcortical infarct and 3 normal subjects with the [(15)O]H(2)O injection technique. Brain activation was achieved by passive elbow movements driven by a torque motor. Increases of rCBF comparing passive movements and rest were assessed with statistical parametric mapping. Significant differences were defined at P<0.01. RESULTS: In normal subjects, significant increases of rCBF were found in the contralateral sensorimotor cortex, supplementary motor area, cingulate cortex, and bilaterally in the inferior parietal cortex. In stroke patients, significant activation was observed bilaterally in the inferior parietal cortex and in the contralateral sensorimotor cortex, ipsilateral prefrontal cortex, supplementary motor area, and cingulate cortex. Significantly larger increases of rCBF in patients compared with normal subjects were found bilaterally in the sensorimotor cortex, stronger in the ipsilateral, unaffected hemisphere, and in both parietal lobes, including the ipsilateral precuneus. CONCLUSIONS: Passive movements in hemiplegic stroke patients before clinical recovery elicit some of the brain activation patterns that have been described during active movements after substantial motor recovery. Changes of cerebral activation in sensory and motor systems occur early after stroke and may be a first step toward restoration of motor function after stroke.

Aged↗
PubMed1995

Delayed rupture of aortic aneurysms following endovascular stent grafting.

BACKGROUND: Deployment of transfemoral, endovascular stent grafts for treatment of abdominal aortic aneurysms is appealing for several reasons: avoidance of abdominal incision, lack of aortic cross-clamping, potential for regional anesthesia, and shortened hospital stay. Concerns remain, however, regarding the ability of these devices to completely exclude the aneurysm and prevent aneurysm rupture and the long-term integrity of the device. The availability of endografts and the likely development of percutaneous devices have also raised the delicate issue of personnel training for patient selection, endograft implantation, and postoperative follow-up. PATIENTS AND METHODS: The cases of 2 patients are reported in which Dacron endovascular grafts, anchored proximally and distally by Palmaz stents, were deployed for treatment of infrarenal abdominal aortic aneurysms. RESULTS: In a patient with and absent distal cuff, choosing this procedure represented a clear error in patient selection. The endograft failed to reach the aortic bifurcation and the aneurysm ruptured, with the death of the patient 4 months postimplantation. In a patient with anatomy suitable for endograft placement, a perigraft leak persisted at the distal anastomosis following device placement. The aneurysm ruptured 14 days postprocedure. Although the patient survived emergent aneurysm repair, he developed acute renal failure. CONCLUSION: Careful preoperative assessment of aortic anatomy is crucial in selection of patients for transfemoral endovascular graft placement. Lack of a distal cuff of at least 1 cm precludes tube graft implantation. Patients with a perigraft leak are not protected by the endograft from aneurysm rupture. Vascular surgeons must be involved in the preoperative evaluation of these patients and are the only specialty group who can provide the prerequisite care in evaluation and management of postoperative complications.

Aged↗
PubMed1991

Use of TAO without methylprednisolone in the treatment of severe asthma.

The antimicrobial agent troleandomycin (TAO) has been shown to be effective in reducing corticosteroid requirements in patients with corticosteroid-dependent asthma. To our knowledge, the efficacy of TAO without concomitant use of corticosteroids has never been documented. We report the case of a 12-year-old patient with corticosteroid-dependent asthma who has remained asymptomatic and without any evidence of pulmonary deterioration during treatment with TAO without concomitant use of corticosteroids.

Adolescent↗
PubMed1991

[Not Available].

Explore the source record for details and available documents.

Germany↗
PubMed1991

Pulmonary alveolar proteinosis: a possible sequel of NO2 exposure.

Pulmonary alveolar proteinosis was diagnosed via bronchoscopy in a patient. There was no previous history of inhalation dust exposure. NO2 has been implicated in pulmonary alveolar proteinosis development in animal models. In this case, the diffusion capacity was a sensitive indicator of the disease process.

Adult↗
PubMed1989

Autonomic neuropathy in diabetics: comparison of cardiovascular tests, neurography, and cerebral refractory period of somatosensory evoked potentials.

Circulatory regulation tests--postural heart rate response (PHRR), Valsalva ratio, and reaction to sustained muscle exercise--, sural nerve neurography and cerebral refractory period (CRP) of median nerve evoked potentials were measured in 17 diabetic inpatients and correlated with their clinical signs of autonomic neuropathy (AN) and sensorimotor polyneuropathy (SN). Non-diabetic inpatients (without cardiovascular or related nervous disease) served as controls. The data of the diabetics and non-diabetic age- and sex-matched inpatients were significantly different for the PHHR measured by the 30:15 ratio, sural nerve conduction velocity and sural nerve refractory period, and CRP. The results correlated with the corresponding anamnestic signs. The PHRR showed abnormal values much more frequently than the sural nerve neurography or the CRP. No correlation was found between the signs of AN and those of SN or CRP. This stresses the need for a circulatory regulation test (preferably PHRR) in any diabetic when planning narcosis, as only these AN tests can reliably predict an increased cardiovascular risk in individual patients.

Adult↗
PubMed1988

Herpetic tracheobronchitis.

Nine adult patients from three community teaching hospitals had bronchospasm unresponsive to standard therapy. Bronchoscopic, cytologic, histopathologic, and virologic studies confirmed that necrotizing and exudative tracheobronchitis was due to herpes simplex virus. No patient had a history of previous chronic lung disease; most were not immunocompromised. Three patients never had intubation during hospitalization. All patients were successfully treated with intravenous acyclovir. Herpetic tracheobronchitis may be a commoner clinical syndrome than generally assumed. In an elderly patient with unresolving acute bronchospasm, herpesvirus infection of the lower respiratory tract should be considered in the differential diagnosis. In the immunocompetent host, antiviral therapy can successfully treat herpesvirus respiratory infection, with reversal of clinical, virologic, and pathologic findings. A prompt and accurate diagnosis is crucial.

Acyclovir↗
PubMed1988

[Data processing in neurophysiology: an automatic program for the assessment of dual stimulus responses in somatosensory evoked potentials].

An automatic programme is presented for evaluating somatosensory evoked potentials after double stimuli. The advantage of the programme is the computer-assisted procedure, the possibility of effecting changes at any time, and the imaging of both subtraction and addition curves. A variation of the programme for other modalities is possible.

Electric Stimulation↗
PubMed1987

[Recurrent meningitis in familial deficiency of the 8th component of the complement system].

An 18-year-old man suffered from recurrent bacterial meningitis. Investigation of the complement system revealed deficiency of the 8th complement component (C8) in the patient and his sister. Genetic defects of the terminal complement components C5 to C8 predispose to Neisseria infections, probably due to a lack in bacteriolytic activity. It is to be noted that 1 year ago the patient had been hospitalized for a culture-proved pneumococcal meningitis.

Adolescent↗
PubMed1987

[Static NMR magnetic fields change somatosensory evoked potentials in the human].

In strong static magnetic fields as used by NMR for clinical diagnosis we found oscillations in somatosensory evoked potentials of man when stimulating the Nervus medianus at the wrist joint. These new signals are to register only, when the head of the test person is inside of the magnetic field. A magnetic influence only of the stimulated arm has no effect of the normal SEP-signal.

Electric Stimulation↗