I've taken many BP's "by hand" and gotten diastolics <45! What is his point. This man is a cardiologist?? Hasn't he ever heard of aortic regurg?? It is not uncommon for there to be "no" diastolic, the beat keeps going until zero, and should be recorded from when the distolic muffles, down to when it is not heard at all, eg 140/36/0, if it continues down to zero.
As to how I would defend myself in court, take out your Estes or Bates book on the correct procedure for taking BP, and cite articles on aortic regurg. I wouldn't even worry about defedning yourself in this way, there IS nothing to defend!! As you already know Matt.
Sounds like this guy needs meds! We used to have a pediatric cardioligist who insisted that kids who were quite obviously having seizures, were NOT having seizures, they were just in a "state of agitated motion." Yes, this guy had to guy for psych counseling eventually, he was so nuts, he even scared administration!