Q: I have been told that I have cardiac autonomic neuropathy. Is this a condition I will have the rest of my life? Is there anything I can do to improve this condition?
A: High blood glucose levels over a period of years may cause a condition called autonomic neuropathy. This is damage to the nerves that control the regulation of involuntary function. Examples are body functions such as blood pressure, heart rate, digestion, sexual activity and perspiration. When the nerve damage affects the heart, it is called cardiac autonomic neuropathy (CAN). CAN interferes with the body’s ability to adjust blood pressure and heart rate. Normally, our heart rate increases when we sit up and stand up, as well as when we start to exercise. It slows down when we are resting. Blood pressure needs to be stable or increase when we stand up, and decrease when we are at rest. If the heart rate and blood pressure do not adjust quickly to our need for increased blood flow, we can become dizzy, lose our balance and in some cases faint. This is called orthostatic hypotension. It is a sudden drop in blood pressure when you sit down or stand up from a lying down position.
CAN is not a disease of the heart… it is a problem with the nerves that control the heart rate. Having diabetes and high blood glucose levels for many years may damage nerves throughout the body. The nerves that signal the heart to beat faster are called cardiac autonomic nerves. Damage to these nerves may cause a heart rate that stays high, even at rest, instead of rising and falling in response to the body’s needs and activities. One effect is that blood pressure may drop when you stand up. Another danger is that people with CAN may have heart attacks without feeling the pain and symptoms that signal a problem. CAN can not be reversed, but keeping the A1c (average blood glucose) close to normal may slow its progression.
Medical treatments for CAN may provide some relief, but they do not work for everyone. Your doctor may suggest a pill such as fludrocortisone acetate, ephedrine, or even something as simple as salt tablets to help keep blood pressure from dropping too low.
There are several steps you can take to make living with CAN easier and safer. Move slowly when moving from a lying down to a seated position or from a sitting to standing position. Raising the head of your bed 6 to 12 inches may help you to get out of bed more slowly. Avoid lying down for long periods of time (other than for sleep). Exercise is strongly encouraged. When you exercise, include gradual, prolonged warm-up and cool-down periods so that your heart rate can adjust to your muscles’ need for more oxygen. Keep the pace of your workout at a comfortable level: you should be able to talk without getting out of breath while exercising. Avoid straining and raising your arms above your head, and stay away from isometric exercise (pushing against anything that does not move). Water exercise may be ideal because the pressure exerted by water helps return blood to the heart.
Wearing custom fitted elastic stockings up to the waist keeps blood from pooling in the feet and legs and prevents a sudden drop in blood pressure. Because a drop in blood pressure can occur after large meals, avoid big, high-carbohydrate meals. Drink alcohol in moderation, because it can damage nerves further and may contribute to dizziness.
Several large clinical studies have shown that keeping blood glucose as close to normal as possible can reduce the risk of neuropathy and other diabetes complications. 1,2 If your A1c is higher than it should be, ask your doctor if your diabetes medications should be changed.
1. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. The Diabetes Control and Complications Trial Research Group. N Engl J Med 1993;329:977-986
2. UK Prospective Diabetes Study (UKPDS) Group. Intensive blood-glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). Lancet 1998;352:837-853. [Erratum, Lancet 1999;354:602
If you have a question about diabetes care that might be of interest to the readers of this column, please e-mail it to email@example.com. Dr. Hirsch cannot comment on individual medical cases.
Laurence J. Hirsch, MD
Dr Hirsch graduated from the University of Rochester and then attended Harvard Medical School. He is board-certified in Internal Medicine and in Endocrinology/Metabolism.
Prior to joining BD, he was Assistant Professor of Medicine at Northwestern University, and spent more than 17 years in various roles in clinical drug development at Merck.