A 50-year-old woman complains that in the past few months she has had little energy,has frequently felt chilled,and has noticed excessive hair loss when she washes her hair.During the physical examination,her blood pressure registers at 105/85 mm Hg,her pulse is slow,and her physician notes dry,cool skin with puffiness of the face and arms.A preliminary diagnosis of primary hypothyroidism is made.The primary reason for the elevated diastolic pressure is: