Contractility of human retinal arterioles during oxygen breathing vs. myogenic response

Background: By the use of the retinal vessel analyzer (RVA) it is possible to measure the myogenic response of retinal arterioles to blood pressure increases. Pure oxygen breathing is another method to test the contractility of vessels. The presented study compares these two methods in the same healthy volunteers. Methods: After a 3-minute baseline measurement 20 healthy volunteers (age: 22-58 years) were exposed to 100% oxygen breathing for 5 minutes. The diameter of an retinal arteriole was measured continuously during that period of time. The very same persons were tested in a 9-minute experiment with isometric exercise to cause a vasoconstriction by an increase in mean arterial blood pressure (MAP). Results: Oxygen breathing resulted in a vasoconstriction of -7.45 (+/- 2.1)% on average. The same individuals reacted with an MAP rise of 24.0 (+/- 5.9) mm Hg to isometric exercise, answered by a vasoconstriction of -5.3 (+/- 2.1)%. Both tests were significantly correlated to each other. Conclusions: Although the two tests trigger different autoregulative responses in the arteriole vasoconstriction due to MAP increases and vasoconstriction as an answer to 100% oxygen breathing they do correlate at a significant level in the same subjects.