My brother is 86. His blood pressure is reading 112/55, He has a moderate enlargement of his heart but no recent change. I am a little concerned that his diastolic blood pressure is too low. He doesn t have high blood pressure and has had no treatment for high blood pressure. But he is unusually tired and sleeping more than usual. He has lung cancer and I am concerned that the low diastolic pressure may create a situation where his oxygen level may be too low. Is the 55 reading too low?