Hello kathy barnes,
Your question is an interesting one.
First of all, let me say that you blood pressure is at 130s/70s a bit too high, and then certainly too high at 170's/70s. You should consider discussing these values with your physician. He would probably want to start you on medication or modifying your medications.
Back to your question. The number you are talking about is called the pulse pressure. The pulse pressure is the difference between systolic and diastolic. When it is elevated it can indicate several different things. One common cause of a widened pulse pressure is atherosclerotic or hardened arteriers.
Another can be a faulty aortic valve in heart that's allowing blood to flow back into the heart from the aorta (that's the wrong way!). That sounds scarey, I know, but its a fairly common thing. If you do have aortic regurgitation (as its called in medicine), it is something that you doctor can pick up and monitor. If your valve gets so bad that you are having symptoms such as light headedness, dizziness, fainting and some other symptoms, the valve can be replaced by a heart surgeon. The progression from asypmtomatic to needing a replacement takes years!
There are other causes of widened pulse pressure which include hyperthyroidism and a patent ductus arteriosis. Sometimes, there is no reason for a widened pulse pressure. Regardless of the cause, you should discuss your findingh with your physician at an appointment soon for your own piece of mind.
To your health,