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Biomedical subjects

A van Dieren

Publications and source records attributed to A van Dieren.

12 recordsLinked to original sources

End-to-side anastomosis of small vessels using an Nd:YAG laser with a hemispherical contact probe. Technical note.

A new technique is described which enables the surgeon to perform an end-to-side anastomosis between arteries with little (less than 2 minutes) or no occlusion of the recipient artery. The technique was developed in rabbits, but has recently been successfully used in a patient in whom an anastomosis between the superficial temporal artery and a proximal branch of the middle cerebral artery was created.

Aged

Combined use of subdural and intracerebral electrodes in preoperative evaluation of epilepsy.

For intracranial recording of partial seizures considered to originate from one of the temporal or frontal lobes, the team in the Utrecht Academic Hospital has used subdural, multicontact, flexible electrodes since 1972. These are introduced through bilateral, frontocentral trephine holes and are manipulated under fluoroscopy to cover most of the cerebral convexity. It became evident that in many patients, additional placements to record from intracerebral structures were indispensable. Therefore, using the same trephine holes, an additional 2 to 4 depth electrodes were stereotactically implanted in the mesial temporal and/or frontal structures, as appropriate. An extensive intra- and extracerebral spatial representation of the epileptogenic zone was thus obtained. We report here the methods for manufacturing and applying these electrodes and our clinical experience with 28 patients. The results obtained so far stress the value of combining subdural and depth electroencephalographic monitoring in the presurgical selection of patients suffering from medically refractory complex partial seizures. By miniaturizing the electrodes, extensive areas of the brain can be investigated without craniotomy or multiple burr holes.

Adult

New type of end-to-side anastomosis for small arteries: a technical and scanning electron microscopic study in rats.

A new type of end-to-side anastomosis between small arteries is described. The anastomosis is made for three-quarters of its circumference with a nonoccluded recipient artery. The recipient artery must be occluded for only 3 to 5 minutes to complete the anastomosis. The anastomosis site was studied with the scanning electron microscope at different times (1 hour to 3 months) after the operation in 20 rats. In every case, the anastomosis was widely patent and a gradual endothelialization of the anastomosis site was observed. After 7 to 10 days, the endothelialization was more or less complete and, during the following weeks, a further smoothing of the ridge protruding into the anastomosis was noted. As an addendum, the authors describe an improvement of this technique that was developed after the sapphire tip of the neodymium: YAG laser became available. Now the anastomosis is fully completed and the connection between the two vessels is made by the laser tip introduced via a side branch of the donor vessel. The recipient artery need not be occluded at all. The results are promising.

Anastomosis, Surgical

Changes in local cerebral blood flow, local EEG, and flow in the distal stump of the middle cerebral artery in cats with occlusion of the middle cerebral artery.

The local EEG, the local cerebral blood flow (lCBF), and the flow in the distal stump of the occluded middle cerebral artery was simultaneously recorded in 28 acute experiments in cats. Nembutal anaesthesia was used eleven times, and Halothane anaesthesia 17 times. The recordings were made via platinum electrodes: 12 in the ischaemic hemisphere, and 2-3 in the opposite non-ischaemic hemisphere. The flow in the occluded middle cerebral artery was recorded via a platinum electrode introduced into this artery via the transorbital approach. The changes in lEEG, lCBF, and middle cerebral artery flow were studied during normotension, hypertension, and hypotension. A beneficial effect of hypertension was noted in the acute phase of brain ischaemia. Hypertension counteracted also the "diaschisis" in the non-ischaemic part of the ischaemic hemisphere and in the opposite non-ischaemic hemisphere. A correlation between lEEG changes and lCBF changes was noted. In addition, an interesting discrepancy was observed between the rapid H2 clearance in the middle cerebral artery stump and the much slower H2 clearance in the ischaemic brain area. Significant differences between experiments under Halothane and experiments under Nembutal anaesthesia were noted. In the acute phase those changes are probably the result of the different levels of blood pressure in those two groups.

Animals

Interhemispheric steal. An experimental study.

In 21 cats the pressure in the occluded middle cerebral artery (MCA) was recorded by way of a catheter, introduced in the most proximal portion of this artery by way of the transorbital approach. The effect of temporary occlusion of the ipsilateral and contralateral common carotid artery on the pressure in the occluded MCA was studied. The results seem to prove the existence of the so-called "interhemispheric steal" syndrome.

Animals

A simple and non-invasive method to determine the ventilation-perfusion ratio of the lung and the effective lung perfusion.

A method is presented to obtain the ventilation-perfusion ratio non-invasively. To describe the properties of gasexchange over the lung we used the law of mass conservation. The use of sinusoidal changes in the concentration of a tracergas in the inspired mixture results in a simple formulation of the variation in the concentration in the expired mixture over the variation in the inspired mixture. A careful selection of tracergas and cycleperiod of the sinus enables us to neglect the influence of venous return leaving the ventilation-perfusion ratio as sole physiological variable in the formulation. The lungperfusion can be obtained by measuring the total ventilation and correcting this value for deadspace ventilation. The method can be used to evaluate the influences of techniques like positive end-expired pressure and increased carbon dioxyde levels on shunting. It is also suited for monitoring purposes.

Anesthesia, General

Fast spin-echo MR of contact points on implanted intracerebral stainless steel multicontact electrodes.

A three-dimensional fast spin-echo MR technique is proposed for locating contact points on implanted intracerebral multicontact electrode bundles, Coronal or sagittal reformatting shows the entire trajectory of the electrode bundles. The contract points are clearly visible owing to the absence of coating material associated with a slightly larger susceptibility artifact. Potentially, this technique may preclude postimplantation thin-section CT, with its associated high radiation dose.

Artifacts