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Biomedical subjects

M Friedel

Publications and source records attributed to M Friedel.

3 recordsLinked to original sources
PubMed2006

Boolean networks with biologically relevant rules show ordered behavior.

It was found recently that natural gene regulatory systems are governed by hierarchically canalyzing functions (HCFs), a special subclass of Boolean functions. Here we study the HCF class in detail. We present a new minimal logical expression for all HCFs. Based on this formula, we calculate the cardinality of the HCF class. Moreover, we define HCF subclasses and calculate their cardinality as well. Using the well-known critical connectivity condition 2K(c)p(1-p)=1, we discuss order-chaos transitions of Boolean networks (BNs) regulated by functions of given HCF subclasses. Finally, analysing real gene regulatory rules we show that nearly all of the biologically relevant functions belong to the simplest HCF subclasses. This restriction is important for reverse engineering of transcription regulatory networks and for ensemble approach studies in systems biology. It is shown that Boolean networks with functions belonging to the biologically realized HCF subclasses show ordered behavior.

Algorithms↗
PubMed1994

Performance of indirect embolectomy aided by a new developed flush-suction catheter system. Forty-seven experimental embolectomy procedures in test animals.

Embolectomy by means of the Fogarty catheter is the therapy of choice in the event of acute occlusions of limb arteries. However, less invasive catheter procedures have become established means to perform embolectomies lately. In order to improve the results after using the above mentioned methods, we have developed a new embolectomy procedure. The system applied consists of a flush-suction catheter as well as a high pressure pump. There is a jet-suction unit on the head of the tubular two-lumen catheter to gather thromboembolic material from the circumference of the head, to erode the collected material and evacuate it. The flushing pressure is generated by the pump. For the experimental testing of the system, the flush-suction embolectomy has been performed in 19 pigs after 47 artificial produced extremities embolism. Angiographically and angioscopically it could be proved that even older thrombotic material could be removed completely and without significant trauma of the vessel. At the pathologic investigation of the vessel in which embolectomy had been performed in no case an essential vessel-wall damage could be found. In almost each case the embolic material was removed completely. Only in 5 cases (10.6%) we have distal microembolism. Due to the experimental tests, the system turns out to be reliable as far as the technique is concerned. In addition, in the event of clinical application, the system allows the expectation of a reduction of the time interval between diagnosis and therapy, as well as a percutaneous application.

Angiography↗