An Autonomic Function Test (AFT) is a series of evaluations designed to assess the performance of your autonomic nervous system. This system controls involuntary bodily functions such as heart rate, blood pressure, breathing, digestion, and sweating. When you undergo an AFT, the consultant will determine which specific parts of the test are necessary based on your symptoms and medical history. This article will guide you through the typical procedures involved in an Aft Diagnosis.
Screening Autonomic Function Test: A Detailed Look
The first part of the AFT is a screening process conducted by a Clinical Autonomic Specialist (CAS). Initially, the CAS will discuss your medical history, focusing on the autonomic symptoms you’ve previously described to your consultant and general practitioner. This conversation helps to contextualize the test results and ensure a comprehensive aft diagnosis. The CAS will explain the test procedures in detail and will record your height and weight. You’ll be asked to remove your shoes and socks to prepare for the physiological measurements.
The screening begins with you lying down on a bed to rest for about 10 minutes. During this period, a blood pressure (BP) and heart rate (HR) cuff, attached to your upper arm, will take baseline recordings. After the resting period, you will be asked to stand by the bed for five minutes. This assesses your body’s initial response to a change in posture.
While you are lying down, the CAS will attach the remaining monitoring equipment:
- Electrocardiogram (ECG): A three-lead ECG is used to monitor your heart rhythm. Sticky pads are placed on each side of your chest and one on your ankle. The areas are cleaned with an alcohol wipe to ensure good contact.
- Continuous Blood Pressure and Heart Rate Monitor: A cuff placed on your finger is connected to a wrist device. This allows for continuous monitoring of your BP and HR throughout the test.
- Respiratory Belt: A belt is placed around your middle to monitor your breathing pattern. This is important as respiration is closely linked to autonomic function.
Following the equipment setup, the CAS will guide you through a series of activities designed to challenge your autonomic nervous system. These include breathing exercises and a hand grip challenge. Throughout these exercises, your blood pressure and heart rate are closely monitored to observe how your body responds to these controlled stressors, contributing to the aft diagnosis. While these challenges require effort, they are not designed to be overly strenuous.
After these exercises, you will be securely strapped to the bed in preparation for the tilt table test. The bed is then raised to a 60-degree angle, simulating a standing position, as illustrated below. This head-up tilt test lasts for 10 minutes, or as long as you can tolerate. The CAS will continuously monitor your blood pressure and heart rate and will encourage you to report any symptoms you experience during the tilt. This part of the screening AFT is crucial for assessing orthostatic responses, which are key indicators in aft diagnosis.
This comprehensive screening AFT typically takes around 90 minutes to complete, providing valuable data for your aft diagnosis.
The AFT testing room and equipment setup:
Head up tilt at 60° for autonomic function test diagnosis:
Plasma Catecholamine Levels: Blood Analysis for AFT Diagnosis
In some cases, an aft diagnosis requires a blood test to measure plasma catecholamine levels. If this is necessary, the CAS will insert a cannula (a thin, flexible tube) into a vein in your arm during the AFT, just before the tilt test commences. This minimizes discomfort and streamlines the procedure. Blood samples are collected at two critical points: once while you are lying flat and again while you are upright on the tilt table, each after a 10-minute rest period. The cannula is removed before you leave the testing room.
These blood samples are then analyzed in the laboratory to determine the levels of plasma adrenaline (epinephrine) and noradrenaline (norepinephrine). These hormones, known as catecholamines, play a vital role in the autonomic nervous system’s response to stress and postural changes. Comparing the catecholamine levels between the lying and upright positions provides valuable insights into how your body regulates these hormones, aiding in a more precise aft diagnosis, particularly in conditions involving adrenal function or autonomic neuropathy.
Prolonged Tilt: Extended Monitoring for Detailed AFT Diagnosis
The prolonged tilt test is the final component of some AFT diagnoses. During this test, your blood pressure and heart rate are continuously monitored while you are tilted head-up at 60° for up to 45 minutes. The duration can be shorter if you cannot tolerate the full 45 minutes. Throughout the prolonged tilt, you are encouraged to communicate any symptoms you experience to the CAS. This extended monitoring period helps to identify more subtle autonomic dysfunctions that may not be apparent during the shorter screening test, offering a more comprehensive aft diagnosis. This is particularly useful in diagnosing conditions like Postural Orthostatic Tachycardia Syndrome (POTS) or vasovagal syncope, where symptoms may develop gradually over time in an upright position.
