Hello,
Your father is an elderly Diabetic, hypertensive, Congestive cardiac failure and chronic
renal disease.
He has associated respiratory illness also.
His Blood pressure is at the lower side.
Blood pressure is the measure of resistance exerted by the blood vessels to the pumping of blood by the heart.
The pumping mechanism of your father's heart is weak due to CHF.
Diastolic below 40 may be dangerous.