Management of Cardiac Autonomic Dysfunction in Older People

Introduction

The autonomic nervous system is the functional division of the nervous system, and it consists of efferent neurons that perform certain functions. The efferent neurons control three different types of cells- smooth muscle cells, cardiac muscles, and gland cells. The autonomic nervous system has two elements. The first one is the sympathetic nervous system (SNS), which ‘excites’ the body and is responsible for increasing blood pressure and heart rate and gives responses such as ‘fight’ or ‘flight.’ The second element is the parasympathetic nervous system (PNS), which ‘calms’ the body, is responsible for decreasing heart rate, and is commonly referred to as the ‘rest and digest’ system. Cardiac autonomic neuropathy damages the autonomic nerve fibers that innervate the heart and blood vessels, resulting in heart rate, control, and vascular dynamics abnormalities. Cardiac autonomic neuropathy increases the risk of cardiovascular events by three to four times, and diabetic patients with cardiac autonomic neuropathy have an increased risk of severe hypoglycemia.

What Role Do SNS and PNS Play in the Cardiovascular System?

The sympathetic and parasympathetic nervous system has various roles to play in the cardiovascular system, such as

1. Sympathetic Nervous System-

• Secretes adrenaline and noradrenaline (fight or flight, for example- pupil dilation).

• Increases heart rate (greater cardiac output).

• Increase blood pressure (speeds up blood flow and oxygen supply).

• An increase in the contractile force of the cardiac muscle (increases stroke volume and blood flow).

• Stimulates vasoconstriction/vasodilation (redirection of blood flow, thermoregulation).

2. Parasympathetic Nervous System-

• Decreasesblood pressure, heart rate, and cardiac output and helps to reduce time spent in a stressful state as soon as possible to avoid symptoms of chronic stress. These include arterial hardening, type 2 diabetes, dopamine insensitivity, impairment of new memory creation, erectile dysfunction, depression, etc.

What Is the Correlation Between Aging and Autonomic Dysfunction?

Normal human aging is associated with changes in autonomic functions. The two elements, the sympathetic and parasympathetic nervous systems of the autonomic nervous system, mature with time, but the degree of the changes due to aging are different because of their varying neural pathways. Age has been considered one of the important variables for cardiac autonomic function. The autonomic nervous system (ANS) is involved in every aspect of our daily life. It is a known fact that a proper balance between the sympathetic and parasympathetic nervous systems is necessary for the functioning of most of the visceral organs, especially the cardiovascular system. Chronic disease usually begins with changes in autonomic functions or vice versa, and its dysfunction can lead to morbidity and mortality in chronic diseases that may worsen with age.

What Causes Cardiovascular Autonomic Neuropathy?

Autonomic neuropathy occurs in the majority of diabetes, and the development of the disease is associated with the following causes-

• Direct inflammation of the autonomic neurons.

• Longstanding chronic inflammatory state from the pre-diabetic stage.

• Poor glucose control.

• Hypertriglyceridemia (increased levels of triglycerides).

• Obesity.

• Hypertension.

• Dyslipidemia (abnormal levels of cholesterol).

• Smoking.

What Are the Symptoms?

In cardiac autonomic neuropathy, nerves that regulate heart rate and blood pressure are damaged; as a result, the body reacts more slowly to a change of position, and patients may experience the following symptoms-

• Tachycardia, postural or at rest and on exertion.

• Chest discomfort.

• Shortness of breath.

• Heaviness or swelling in legs on prolonged standing.

• Dizziness lying to upright posture.

• Headache.

• Tremor.

• Blackouts (syncope).

• Orthostatic hypotension.

• Exercise intolerance.

• Physiological changes such as low blood volume, increased peripheral pooling of arms and legs, reduced adrenaline- causing low blood pressure, and increased adrenaline causing faster heart rate.

What Is the Testing Procedure?

Testing of the cardiovascular autonomic nervous system is important to asses patients who are at risk of tachyarrhythmias, sudden death, and bradyarrhythmias. With the help of these tests, coronary artery spasms and patients with cardiovascular afferent neuropathy who could be at risk for silent myocardial ischemia may also be identified. Some of the tests involved are as follows-

• Valsalva Maneuver- The patient is asked to lie down facing upward and is connected to an electrocardiogram (ECG) monitor, and then is asked to exhale forcibly for 15 seconds against the fixed resistance with an open glottis.

• Heart Rate Variability Test- In the test of the heart rate variability, the patient is asked first to lie down and then breathe deeply at the rate of six breathes per minute, which produces a maximum variation in the heart rate, while a heart monitor records the difference between the maximum and minimum heart rate.

• Heart Rate Responding to Standing Test- This will evaluate the cardiovascular response caused by a change from a horizontal to a vertical position in healthy people. A characteristic and rapid increase in heart rate in response to standing in normal people, while in patients with diabetes and autonomic neuropathy, there is a gradual increase in heart rate.

• Quantitative Sudomotor Axon Reflex Testing (QSART)- This will measure the neurons that control sweating. The test involves mild electrical stimulation on the skin, allowing acetylcholine (a naturally occurring chemical) to stimulate the sweat glands. QSART will measure the volume of sweat produced by this stimulation.

• Sympathetic Skin Response (SSR)- This technique records the changes in skin conductance after the activation of the sweat glands in areas of the skin that are reaching the sweat glands.

• Thermoregulatory Sweat Testing (TST)- This measures the ability to sweat in a unique laboratory setting.

How to Manage Cardiac Autonomic Dysfunction in Older People?

The management mainly focuses on lifestyle management and the elimination of the underlying causes, which are described below-

• Promote weight loss in obese patients.

• Exercise is the key.

• Controlling the risk factors such as hypertension.

• Managing diabetes can slow the progression of the damage.

• Increase in fluid intake.

• Management of postural hypotension.

• Medications to treat hypertension and hypotension.

• Dietary modifications.

• Medications for nerve pain.

• Smoking cessation.

Conclusion

The symptoms of a cardiovascular autonomic dysfunction may be subtle and occur late in the course of diabetes, and as the majority of the older population is associated with diabetes and other medical conditions, they are more at risk of developing this dysfunction. With proper lifestyle modifications and management of the underlying causes, one can effectively have control over the condition.