A blood pressure reading measures how much pressure is exerted against the arterial walls as the heart pumps blood through the body. When providing blood pressure results, a health practitioner will provide a patient with two numbers, such as 119/80. The first number is the systolic pressure, which represents how much force the heart exerts when it contracts. The second number is the diastolic pressure, which represents how much pressure there is when the heart relaxes. A high diastolic blood pressure reading, over 80, can signal serious underlying health conditions.
If a patient's diastolic number is too high, she is considered to have hypertension, even if her systolic number is not too high. Hypertension is a serious condition that affects 31 percent of Americans, but 22 percent of those people do not know that they have hypertension, according to statistics provided by the U.S. Centers for Disease Control and Prevention and the American Heart Association. Untreated, hypertension can lead to kidney disease, diabetes and heart failure.
High diastolic pressure can cause angina -- a type of chest pain -- heart disease and even heart failure. High diastolic pressure can also cause dyspnea, or shortness of breath, a sign of serious disease in the heart and lungs. Research published in 2004 in the "New England Journal of Medicine" notes a direct correlation between high diastolic pressure and heart failure. High diastolic pressure can cause the heart muscle to stiffen and not relax properly. In this study, the researcher notes that many patients with diastolic heart failure also had high sodium levels and increased blood volume.
Some patients with high diastolic blood pressure are at greater risk of stroke. Research published in 2010 in the "Journal of Epidemiology and Community Health" notes that diastolic blood pressure higher than 90 indicates a high risk of stroke and mortality rates for patients between the ages of 34 and 44. For those older than age 65, high systolic pressure was a better indicator of risk for stroke and mortality.