At what diastolic pressure is the blood flow?

Diastolic pressure. The ormal diastolic pressure in an adult is 80mmhg. The blood flows at that pressure, however could be higher and/or lower and still flows.
Unclear. Some people have diastolic blood pressures of zero (as measured by an arm cuff) and live to talk about it. (in fact, don't even know they have it). You're right though, if diastolic pressure in the aortic falls below about 30, there's poor perfusion pressure to fill the coronaries and ischemia results - since the coronaries so, indeed, fill during diastole.

Related Questions

Blood pressure: does your systolic pressure affect diastolic pressure?

No. They're independent but often tend to go together. Younger people tend to have higher diastolic pressures. Older people tend to have higher systolic pressures. But those are just generalizations.

What exactly is the significance of diastolic blood pressure?

Can be harmful. Diastolic pressure is the lowest pressure reached inside blood vessels, and occurs as the hear is relaxing between beats. Normal values are below 80. Diastolic BP above 90 (or systolic above 140) will increase the risk of heart attack, stroke and kidney disease. It is definitely worth having BP checked regularly and treated if high.