Abstract
Purpose: :
Healthy arterioles and venoles of the human retina dilate after the onset of a flicker stimulus in Dynamic Vessel Analysis (Imedos GmbH, Jena, Germany). This reaction is ascribed to the activity of nitric oxide synthase (NOS) in nerve cells and/or in the vascular endothelium. In patients with systemic arterial hypertension the lack of dilation in both kinds of vessels is explained by the lack of NOS. In patients with systemic arterial hypertension there are cases in which the venoles dilate but not the arterioles. Until now this behavior could not be explained by endothelial dysfunction or by the lack of neurovascular coupling. We have combined the knowledge of cybernetics and of pathophysiology in arterial systemic hypertension in order to create a consistent model.
Methods: :
The cybernetical formal description of vessel diameter control is applied to retinal arterioles and venoles in health and hypertension.
Results: :
The actuator is often ranked among the controller. In the model used until now the controller comprised both the vessel wall and NOS activity in the endothelium or in nerve cells. In case the actuator may change independently the influence of this element has to be accounted for. In the control of the vessel diameter the vascular smooth muscle cells have to be separately regarded as the actuator element because they are subject to functional and structural changes in arterial hypertension.
Conclusions: :
The observed fact that the venoles dilate in cases of systemic arterial hypertension but not the arterioles after the onset of flicker stimulation may be explained by changes in the arteriolar wall during intact NOS activity. The case that both the arterioles and the venoles do not dilate may be interpreted as a sign of endothelial damage and/or the lack of NOS activity in nerve cells as done until now whereby a pathological damage in the vessel wall remains hidden. The new understanding of the dissociation of dilation in arterioles and venoles expands the interpretation of dynamic vessel analysis.
Keywords: blood supply • clinical research methodology • image processing