Biomedical subjects
P Kroker
Publications and source records attributed to P Kroker.
An expert system for synoptic interpretation of lung function tests.
We simulate the interpretation process by the testing of preformed working hypotheses. A clinical syndrome, "bronchial obstruction," is described by a set of suitable parameters (FEV1, MMEF, Raw, etc.). For a given patient, this set forms a normalized vector. It has to be compared with equivalent data derived from patients which fulfilled the criteria for the clinical syndrome in question. If the patient's vector has a similar direction as the vector of the collective, the working hypothesis is accepted. The length of the vector is then used to quantify the severity of the functional disturbances in verbal terms ("slight," "moderate," "severe"). The limits used for severity grading and the typical parameter pattern for the given syndrome are adapted to the user's criteria by a built-in learning capability. On the other hand, the assembled data may be used for the training of newcomers. The use of vector algorithms allows for a high flexibility of our program with respect to all methods used in lung function testing.
[The histamine provocation test: are 1 second capacity and specific conductance competing or complementary measurement values?].
We tested criteria for the decision, whether a provocation challenge with histamine is positive. The combination of spirometry and bodyplethysmography by the condition sGaw less than or equal to 0.04 x PC-FEV overcomes the contradictions due to conventional criteria as PC-FEV greater than or equal to 20% or PC-sGaw greater than or equal to 50%.
[Visual evoked potentials following double-pattern stimulation with pseudo-color perception].
We examined in which form an additional structural stimulus in the white checks influenced the visual evoked potential of a checkerboard reversal induced response. A pattern of vertical bars was introduced with a short delay to the checkerboard reversal. The purpose of these experiments was to find out about the discrimination threshold of the occipital cortex for timely spaced stimuli. The double stimulus was separated from the next change minimally for 800 ms. With this arrangement we avoided "steady states", which are shown by repetitive interstimulus intervals of less than 200 ms. Nine normal volunteers between 22 to 28 years of age were measured. We found a typical waveform after the P 100 potential consisting of a positive peak followed by a negative long-lasting baseline elevation. Only separations of more than 60 ms yielded this configuration. Interstimulus times of less than 60 ms resulted in refractory effects on the visual evoked response. All the subjects reported colour or brightness changes of the additional bars. These pseudo colours were very probably due to the Prevost-Fechner-Benham-Effect which is common with repetitive white and black pattern changes. Our pseudo colours showed remarkable differences to the classical designs which has led us to the conclusion that colour perception on TV monitors is influenced so far by unpredictable flicker factors.