In going back through messages related to this subject, I find one which quotes a study involving what you are interested in. There is no citation, so it would be a chore to find where and when the study was done, but here's the message:
You will note that during controlled exhalation, the pressures were 198/175, in fact much lower than those generated with a Valsalva maneuver, but high enough that I, with my mild-to-moderate aortic regurg, wouldn't be doing any power lifting. Even if I just had mild leakage, I would still probably content myself with fitness-level lifting, in the interests of delaying a valve replacement.
I guess it comes down to an assessment of risk vs benefits.