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Biomedical subjects

F Hillenkamp

Publications and source records attributed to F Hillenkamp.

83 records · Page 5Linked to original sources
PubMed1975

[Retinal reactions to intense light. I. Threshold lesions. Experimental, morphological and clinical studies of pathological and therapeutic effects of laser and white light].

The effects of intense light produced by an argon laser, a helium-neon laser and a xenon are photocoagulator in the retinas of gray chinchilla rabbits, cynomolgus monkeys, and rhesus monkeys were studied clinically and histopathologically including electron microscopy. An improved experimental set-up was used allowing a very good consistency of the inflicted lesions. Threshold lesions were produced in chinchilla rabbits and cynomolgus monkeys by an argon laser and a helium-neon laser. The lesions were evaluated ophthalmoscopically and histograms were drawn indicating ophthalmoscopic ED50 values. For the two lasers examined these values were 12 and 17 mW, respectively, for exposure durations in the range of the blink reflex (125-150 msec). Histopathologically, ophthalmoscopic threshold lesions of both laser types showed evidence of thermal damage of the outer retinal half. This damage was principally identical in both species involving the retinal pigment epithelium and the full extension of the photoreceptor cells up to their synapses within the outer plexiform layer. The ophthalmoscopic threshold value was associated, therefore, with an irreversible loss of visual function within the retinal area concerned. No evidence for primary sites of significant energy absorption within the neural retina was found. The width of ophthalmoscopic threshold lesions was determined by measuring within the histologic sections with a microscope and a calibrated graticule the extension of damage at the level of the retinal pigment epithelium and at the level of the outer nuclear layer. In the cynomolgus monkey for ophthalmoscopic argon laser threshold lesions the extension at the level of the RPE was 70-80 mum in diameter and at the level of the outer nuclear layer it was 40-50 mum in diameter. Laser lesions that had a diameter of 60 mum at the level of the RPE and of 30 mum at the level of the outer nuclear layer were ophthalmoscopically subvisible. It is concluded that probably also in man such laser lesions, as well as various other pathologic changes of this size or smaller, cannot be evaluated by clinical ophthalmoscopy. The ophthalmoscopic threshold was correlated with a histopathologic threshold as defined by minimal histopathologic damage. Very likely, such damage lies within the range of functional recovery, and the histopathologic threshold demarcates at the same time the decisive functional threshold. The conversion ratio between histopathologic-functional and ophthalmoscopic threshold for argon lesions in cynomolgus monkeys was somewhat greater than 3, e.i. the ophthalmoscopic threshold was more than 3 times higher than the histopathologic-functional threshold. Using this data together with additional biologic and optical considerations, a safety threshold for man for cw-lasers within the visible spectrum was estimated to be 1-2 mW.

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PubMedDate not supplied

Mass spectrometric analysis of blotted proteins after gel electrophoretic separation by matrix-assisted laser desorption/ionization.

The molecular masses of electroblotted proteins were determined with a time-of-flight mass spectrometer by matrix-assisted laser desorption/ionization directly from blot membranes. Therefore standard proteins, separated by polyacrylamide gel electrophoresis, were electroblotted onto polyvinylidene difluoride or polyamide membranes by standard procedures. Pieces of membrane containing the protein of interest were soaked in matrix solution and analyzed in the mass spectrometer.

Adsorption↗
PubMedDate not supplied

[About the importance of paranodal structures of the Ranvier node for the impulse regeneration (author's transl)].

The site of the pulse regeneration in myelinated nerve is generally assumed to be the unmyelinated part of the axon membrane in thr Ranvier node. To check this, a micro-irradiation technique using laser pulses (lambda equals 347 nm, t equals 20 ns) was used to produce morphological lesions of about 1 mum diameter in various regions of the Ranvier node. The electro-physiological functions were monitored parallel to the irradiation. Depending on the localizing of the lesions two types of changes in these functions were observed: 1. If a definite site in the paranodal myelin sheath was damaged without affecting the axon, an action potential could no longer be elicited, although the resting potential as well as the stationary current-voltage behaviour remained unchanged. 2. A damage of the axon resulted in a break down of membrane potential and resistance. In most of the cases the excitability recovered after spontaneous or current induced restitution of the membrane resting potential and resistance. These observations indicate, that structures in the paranodal region are vital for the Na+-activation and inactivation. The membrane potential and stationary current-voltage behavior can be attributed to the axon membrane. A new hypothesis concerning the mechanism of the Na+-activation-inactivation process is suggested.

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