Biomedical subjects

D Hänggi

Publications and source records attributed to D Hänggi.

8 recordsLinked to original sources

PubMed2006

Ischaemic preconditioning of the brain, mechanisms and applications.

BACKGROUND: The concept of ischaemic preconditioning was introduced in the late 1980s. The concept emerged that a brief subcritical ischaemic challenge could mobilize intrinsic protective mechanisms that increased tolerance against subsequent critical ischaemia. Tissues with a high sensitivity against ischaemia, i.e. myocardium and central nervous system, present the most promising targets for therapeutic application of ischaemic preconditioning. During the last years the mechanisms of neuronal preconditioning were systematically studied and a number of molecular regulation pathways were discovered to participate in preconditioning. The purpose of the present review is to survey the actual knowledge on cerebral preconditioning, and to define the practical impact for neurosurgery. METHODS: A systematic medline search for the terms preconditioning and postconditioning was filed. Publications related to the nervous system were selected and analysed. FINDINGS: Preconditioning can be subdivided into early and late mechanisms, depending on whether the effect appears immediately after the nonlethal stress or with a delay of some hours or days. In general early effects can be linked to adaptation of membrane receptors whereas late effects are the result of gene up- or downregulation. Not only subcritical ischaemia can trigger preconditioning but also hypoxia, hyperthermia, isoflurane and other chemical substances. Although a vast amount of knowledge has been accumulated regarding neural preconditioning, it is unknown whether the effects can be potentiated by pharmacological or hypothermic neuroprotection during the critical ischaemia. Furthermore, although the practical importance of these findings is obvious, the resulting protective manipulations have so far not been transferred into clinical neurosurgery. Postconditioning and remote ischaemic preconditioning are additional emerging concepts. Postconditioning with a series of mechanical interruptions of reperfusion can apparently reduce ischaemic damage. Remote ischaemic preconditioning refers to the concept that transient ischaemia for example of a limb can lead to protection of the myocardium and possibly the brain. CONCLUSION: Possible cumulative neuroprotection by preconditioning and pharmacological protection during critical ischaemia should be studied systematically. Easy to apply methods of preconditioning, such as the application of volatile anaesthetics or erythropoietin some hours or days prior to planned temporary ischaemia, should be introduced into the practice of operative neurosurgery.

Brain↗

PubMed2006

New angiographic measurement tool for analysis of small cerebral vessels: application to a subarachnoid haemorrhage model in the rat.

INTRODUCTION: Exact quantification of vasospasm by angiography is known to be difficult especially in small vessels. The purpose of the study was to develop a new method for computerized analysis of small arteries and to demonstrate feasibility on cerebral angiographies of rats acquired on a clinical angiography unit. METHODS: A new software tool analysing grey values and subtracting background noise was validated on a vessel model. It was tested in practice in animals with subarachnoid haemorrhage (SAH). A total of 28 rats were divided into four groups: SAH untreated, SAH treated with local calcium antagonist, SAH treated with placebo, and sham-operated. The diameters of segments of the internal carotid, caudal cerebral, middle cerebral, rostral cerebral and the stapedial arteries were measured and compared to direct measurements of the diameters on magnified images. RESULTS: There was a direct correlation between the cross-sectional area of vessels measured in a phantom and the measurements acquired using the new image analysis method. The spread of repeated measurements with the new software was small compared to the spread of direct measurements of vessel diameters on magnified images. Application of the measurement tool to experimental SAH in rats showed a statistically significant reduction of vasospasm in the SAH groups treated with nimodipine-releasing pellets in comparison to all the other groups combined. CONCLUSION: The presented computerized method for analysis of small intracranial vessels is a new method allowing precise relative measurements. Nimodipine-releasing subarachnoidal pellets reduce vasospasm, but further testing with larger numbers is necessary. The tool can be applied to human angiography without modification and offers the promise of substantial progress in the diagnosis of vasospasm after SAH.

Animals↗

PubMed2006

Nitric oxide in subarachnoid haemorrhage and its therapeutics implications.

BACKGROUND: After the discovery that nitric oxide (NO) plays a major role in the regulation of vascular tone, this substance moved into the focus of interest with regard to vasospasm after subarachnoid haemorrhage (SAH). A multitude of interactions were discovered and some concepts of therapeutic intervention were developed. METHOD: The present review is based on a Medline search with the terms "nitric oxide" and "subarachnoid haemorrhage". FINDINGS: SAH and particularly liberated oxyhaemoglobin sequestrate the physiologically produced NO. Reactivity to NO appears to be principally preserved. As other types of injury, SAH leads to induction of inducible NO synthase (iNOS). The NO produced by this pathway cannot compensate for the lack of the physiological NO and may even lead to tissue damage by oxidative stress. Experimental therapeutic attempts use stimulation of NO production and delivery of NO donors. NO donors were also used in some small clinical trials. A final assessment of efficacy and safety is not yet possible. CONCLUSION: NO physiology and pathophysiology are important in the genesis of vasospasm after subarachnoid haemorrhage. NO directed therapeutic strategies enlarge the spectrum of available instruments, but complete elimination of the problem of vasospasm cannot be expected.

Animals↗

PubMed2005

Cranial and spinal dural arteriovenous malformations and fistulas: an update.

Awareness of a potential arteriovenous fistula is critical for diagnosis of cranial as well as spinal fistulas. The natural history of cranial and spinal dural arteriovenous fistulas has been clarified during the last decade and interdisciplinary therapies have experienced a substantial development recently. The classification of Cognard & Merland is now the most widely accepted one for cranial dural AVF. It is based on the degree of flow reversal in the sinuses and cortical veins and reflects well the natural history of the different lesions and serves as basis for therapeutic indications. Several studies have defined the annual bleeding risk of cranial dural fistulas between 1.8 and 15%, depending on the pattern of venous drainage and initial symptomatology. Surgical, endovascular and radiosurgical methods must be selectively chosen for the treatment. The risk associated with surgical or endovascular treatment of benign fistulas is higher than the risk of eliminating fistulas that have already led to cortical venous reflux. Transvenous endovascular occlusion or surgical disconnection of draining veins is the treatment of first choice for cranial and spinal dAVF with venous flow reversal. Benign cranial dural arteriovenous fistulas are a developing indication for radiosurgery.

Arteriovenous Fistula↗

PubMed2000

Effect of ethanol on BOLD response to acoustic stimulation: implications for neuropharmacological fMRI.

The effects of ethanol on acoustically stimulated blood oxygenation level-dependent (BOLD) signal response in healthy humans was examined with echo planar functional magnetic resonance imaging (fMRI). An acquisition mode minimizing neuronal activation by scanner noise in combination with acoustic excitation by a pulsed 1000-Hz sine tone was used. Paradigms were repeated three times before and after the ingestion of 0.7 g of ethanol/kg(body weight). Linear correlation analyses (r>/=0.40) revealed bilateral BOLD responses in the auditory cortex. Significant voxels covered a cortical volume of approximately 3 ml that was reduced by approximately 40% after ethanol. The BOLD signal change initially reaching approximately 3% was reduced by 12-27%, depending on the definition of the region of interest for signal quantitation. Because ethanol produces vasodilation, the hemodynamic contribution to the BOLD signal change was estimated by modeling the relationship between regional cerebral blood flow (rCBF) and BOLD signal changes. Assuming a baseline flow increase by 10% after ethanol intake, the resulting 'Flow-BOLD-Dependence' (FBD) curve suggested that the ethanol-related BOLD signal reduction was approximately 7-12% greater than the reduction contributed purely by vasodilation. However, simultaneous determination of rCBF and regional cerebral blood volume would be required for an exact quantitation of the neuronally induced BOLD response. Although the FBD model needs empirical validation, its cautious implementation appears to be helpful if fMRI is used in combination with vasoactive drugs.

Acoustic Stimulation↗

PubMed1991

[The Perioplaner/Periopolisher. The loss of substance on the root surface and the initial clinical experiences].

A new system for the removal of supragingival and subgingival plaque and calculus was studied. The system involves two motor driven handpieces. One handpiece works with curettes and hoes (Perioplaner) and the other works with diamond-layered instruments (Periopolisher). In the first part of this study the loss of root substance was measured as a consequence of treatment by these motor-driven instruments. These results were compared with those using classical hand curettes and rotating diamonds (Perio-Set). In the literature there is still debate over whether it is necessary to remove not only plaque and calculus but also cementum which may contain endotoxin or may even be infected. Whatever opinion one may have, it must be known how much root substance is lost by using a particular scaling instrument. This study has shown that the use of the Perioplaner and Periopolisher results in about the same loss of root substance as the use of hand instruments. In the second part of this study, first clinical experiences with these instruments are reported.

Dental Calculus↗

PubMed1990

[The border seal in restorations of class-V lesions with glass ionomer cement and composite (the sandwich filling)].

In 9 patients, 60 class V restorations were evaluated clinically and by scanning electron microscopy. All lesions were treated with glass-ionomer combined with composite resin. In 27 fillings (group A) the glass-ionomer lining cement was etched, whereas in 33 fillings (group B) the composite material was applied directly on the unetched glass-ionomer liner. Clinically, the retention of the fillings after one year was 100%. The margins of the fillings were checked with different explorers and found to be acceptable. Scanning electron microscopy of the margins of the fillings showed disappointing results. One week after placement of the fillings, only 16.2% (group A) and 7.4% (group B) of the cervical margins in dentin were rated perfect. After one year, even more cervical bond failures were observed. 9.7% perfect margins were found in group A, 3.2% in group B. Etching of the glass-ionomer liner had no influence on the cervical bond failure of the class V fillings.

Acid Etching, Dental↗

PubMed1988

[Induced imagination as a methodologic paradigm in assessing stress perception and stress processing].

The methodological paradigm of the induced imagination has been tested as an alternative diagnostic access to stress and coping. Assumptions on the therapeutic applications of imagery techniques (i.e. Cautela, 1967; Lang, 1978; Leuner, 1980; Wolpe, 1958) have been integrated with cognitive concepts of visual imagery (Kosslyn, 1980; Kosslyn, Brunn, Cave & Wallach, 1984; Paivio, 1971; Steiner, 1980) to deduce a theoretical framework of emotional imagery. An emotionally involving imagery scene is generated when semantic-, spatial- and motoric-relational representations of an imagined scene are constructed and actions are to be performed by the subject. The electrodermal activity (EDA) serves as a physiological indicator of stress. Ten subjects have been tested. The main results are: 1. Stressful imaginations correlate with significantly higher physiological activity than relaxation phases and imagery scenes with agreable content. 2. Different sequences of a stressful imagination can be differentiated psychophysiologically: Parts of imagery appraisals and emotions show higher physiological activity than sequences which consist of descriptions of situational and environmental elements. 3. It could be shown that not the verbalisation itself but different contents of imagery scenes correlate with different physiological activities. These results provide strong support for the hypothesis that verbalisations of stressful events and coping strategies are related to increased physiological activity. The psychophysiological differentiation of stress processes implies the applicability of the induced imagination as a validity criterion for a criterion oriented questionnaire of stress and coping (Reicherts & Perrez, 1986).

Adaptation, Psychological↗