Praise be to Allah.
Patients who have diabetes and high blood pressure are not all the same. Rather doctors divide them into various categories. Some of them are able to fast safely, if they adhere to medical guidelines, and others cannot fast.
But if diabetes and high blood pressure occur together, then fasting is more difficult for the patient.
Based on that, the patient should consult his doctor and do whatever the doctor advises with regard to fasting or not fasting. Not every person who is sick is permitted to break the fast, as has been explained in fatwa no. 1319.
As diabetes and high blood pressure are chronic diseases, in most cases the patient who does not fast because of them will never be able to make up those fasts. Therefore what he must do is feed one poor person for each day that he does not fast, and he does not have to make up the fasts.
What is meant by feeding a poor person is giving him one meal, and the patient has the choice between making food and inviting the poor person to come and eat, or giving it to him, cooked or raw. If he does one of these three options, then he has fed a poor person and has done what is required of him, as has been explained in fatwas no. 49944 and 101100.
And Allah knows best.