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Biomedical subjects

J Jansen

Publications and source records attributed to J Jansen.

352 records · Page 20Linked to original sources
PubMedDate not supplied

A synthetic three-leaflet valve.

To increase durability and decrease calcification tendencies, the reduction of mechanical leaflet stress is of prime importance. In order to achieve this for a three-leaflet valve, the leaflets of a new design of prosthesis (the J-3) are manufactured in a medium open, almost flat shaped position, whereby the stent posts are expanded by a cone-shaped mold. Owing to this design, the leaflets have stable closed and open positions, the transition succeeds with low opening pressure. Valves are manufactured by dip-coating in polyurethane. Hydrodynamic evaluation of this polyurethane valve shows minimum pressure drop and very low energy losses compared with other commercially available valves. Very low shear stresses in the flow field downstream of the valve are observed by laser-Doppler-anemometry. In durability tests, prototypes have reached lifetimes equivalent to 17 years. For comparative testing of durability and biocompatibility, six bioprostheses and seven J-3 valves were implanted in mitral position of growing Jersey calves. While animal tests are encouraging, they also reveal necessary manufacturing improvements.

Animals↗
PubMedDate not supplied

A case of neurocysticercosis-differential diagnostic aspects.

Neurocysticercosis is no medical rarity but in non-endemic countries especially, a high degree of physician awareness is necessary for diagnosis. The case of a German female patient who had focal seizures for the first time at the age of 23 caused by a cerebral cyst of cysticercus cellulosae is presented. Only surgical removal and subsequent histological examination allowed diagnosis while diagnostic investigation yielded no pathological findings.

Adult↗
PubMedDate not supplied

Laminoplasty--a possible treatment for cervicogenic headache? Some ideas on the trigger mechanism of CeH.

Cervicogenic headache (CeH) has been treated successfully by ventral decompressive surgery and segmental fusioning. Usually ventral fusioning is performed during one operation on one or two neighbouring segments only. We performed dorsal decompressive laminotomy and laminoplasty on eight patients with more than two segmental degenerative diseases narrowing the cervical spinal canal. The bilateral sawn laminae were moved dorsally and fixed with miniplates and screws. Six patients were relieved from headache and two improved postoperatively. Ventral decompressive surgery and fusioning frees from irritating mechanisms all nociceptively innervated tissues such as disc, dorsal ligament, facet joint capsule, nerve root and dura. On the other hand, after dorsal laminoplasty only the dura is freed from irritation or compression. Relief of headache after this surgical treatment shows that the dura, with its nociceptive nerve fibres, could be an important trigger mechanism of CeH.

Adult↗
PubMedDate not supplied

Surgical treatment of non-responsive cervicogenic headache.

OBJECTIVE: 102 patients suffering from long-lasting, very severe cervicogenic headache (CEH), non-responsive to physical or drug therapy, were surgically treated. METHODS: Different diagnostic procedures and their significance for determining the advisability of surgery are summarised. The particular importance of the patient history and local anaesthesia together with the clinical examination is outlined. Different surgical approaches are described: ganglionectomy, ventral and dorsal decompressive operation. RESULTS: CEH can be triggered by vascular or scar tissue compression of the C2 root and ganglion and irritation of other upper cervical nerve roots (C3, C4). Vascular compression is caused by: (a) the sinusoidal venous plexus, which surrounds the ganglion and nerve root like a cuff and may be dilated upon raised venous pressure; (b) further on by arterial loops throbbing against the ganglion; and (c) (rarely) by arteriovenous (AV) malformations. Nerve fibre degeneration is demonstrated morphologically by electron optical investigation. Afferences from ganglion C2 to the brain stem, as documented by experimental investigation on cats using the injection of HRP into the C2-ganglion, can explain the reference of pain from the neck to the fronto-ocular region and could at the same time elucidate the genesis of accompanying symptoms. Degenerative diseases such as disc protrusion and retrospondylosis have been shown to be other trigger mechanisms evoking CEH, as is well known from facet joint arthrosis. Degenerative diseases usually cause dura compression with narrowing of the spinal canal and frequently, in addition, instability. Evocation of CEH could be explained by the irritation, by those degenerative diseases, of structures with pain-conducting nerve fibres (facet joint capsule, nerve root, longitudinal ligaments, spinal dura, disc). About 80% of our surgically treated patients were relieved of pain or improved during a long period of follow up. The recurrence of degenerative alterations with new irritation from pain-conducting structures is thought to be responsible for the recurrence of headache. Further surgical approaches for the treatment of patients with the recurrence of pain are discussed. CONCLUSION: Various surgical treatments are suggested to treat long-lasting severe CEH in patients not responsive to any physical or drug therapy.

Decompression, Surgical↗
PubMedDate not supplied

Advances in design principle and fluid dynamics of a flexible polymeric heart valve.

The three leaflet J-3 valve is manufactured in a medium open position with almost flat leaflets, whereby the stent is expanded by a cone shaped mold. After manufacturing, the dipcoated leaflets have stable closed and open positions. The transition succeeds with very low membrane stresses. Due to this design, the J-3 polymer valve showed superior hydrodynamic performance compared with commercial valves. In durability tests, prototypes have reached lifetimes up to 17 years. While animal tests are encouraging, they also reveal needed manufacturing improvements.

Animals↗