ERG und Änderungen des Blutdruckes: Hinweise auf retinale Autoregulation*

ERG and Changes in Systemic Blood Pressure

Autoregulation is a homeostatic mechanism responsible for the maintenance of constant blood flow and/or oxygen supply in an organ (Johnson 1964, Papst et al. 1982). The myogenic mechanism (Folkow 1964) plays a role during changes in systemic blood pressure, such as in the experiment reported in this paper. Increases in mean arterial blood pressure (MABP) up to 225 mm Hg and decreases in MABP below 55 mm Hg were induced in anesthe-sized cats (Demant 1982). The b-wave and c-wave amplitudes of the ERG were recorded as indicators of activity of the inner retina and outer retina with pigment epithelium respectively, which are supplied by the retinal and choroidal circulations. The amplitude of the b-wave remained stable during increases in blood pressure, but decreased rapidly if the MABP was lowered below 55 mm Hg (Fig. 1). The authors interpret the stability of the b-wave as being due to autoregulation of the blood supply to the inner retina. Autoregulation is not sufficient to maintain retinal function at MABP below 55 mm Hg. In contrast, the amplitude of the c-wave changed inversely to increases and decreases in MABP (Fig. 2). The c-wave thus appears to respond to changes in choroidal blood flow; the same trend of the c-wave is seen in experiments on arterially perfused cat eyes (Kreienbühl and Niemeyer) where the c-wave also reacts to changes in the flow of perfusate. The present data provide new electrophysiological evidence for autoregulation of the retinal circulation, and for its absence from the choroidal circulation.