Noninvasive measurement of the Bayliss effect in retinal autoregulation

Purpose: The Bayliss effect describes the reaction of smooth muscle cells i n the arterial wall to changes in blood pressure. A rise in mean arterial b lood pressure (MAP) causes an autoregulatory myogenic vessel constriction b y smooth muscle cells in the arterial wall. The responsiveness of retinal v essels to changes in MAP were analyzed using the Retinal Vessel Analyzer(RV A). Methods: Continuous measurement of retinal arterial vessels was Perform ed in 40 healthy volunteers (age 18-56 years.) over a 9-min period. After a 3-min baseline measurement (phase I), isometric exercise caused a rise in MAP over the next 3 min (phase II). During the last 3 min (phase III) recov ery was observed. Blood pressure and ECG were documented simultaneously thr oughout the experiment. Results: Exercise caused a significant rise of 22.8 (+/-6.0) mmHg in MAP (phase II vs phase I: P<0.001). Retinal arterioles sh owed 5.5% (+/-2.8%) vasoconstriction (P<0.001). During phase III vessel dia meters returned to normal, with no difference from phase I (P=0.179). Concl usion: Noninvasive measurement and quantitative analysis of the Bayliss eff ect in human retinal vessels by means of the RVA is possible. Analysis of r etinal arterial autoregulation may provide valuable insight into pathologic conditions such as diabetic or hypertensive retinopathy.