Evaluating Syncope with Continuous Blood Pressure Monitoring

Clinicians and researchers are finding increasingly diverse applications for continuous blood pressure measurement and non-invasive hemodynamic monitoring.

Delia MacMillan, Direct Sales Manager at Finapres Medical Systems, explores one of the most common applications, diagnosing the causes of unexplained fainting.

The technology behind continuous blood pressure measurement and non-invasive hemodynamic monitoring was pioneered in the 1970s, and has been further developed by Finapres Medical Systems (FMS). The ability to monitor blood pressure and other cardiac parameters non-invasively (i.e. without introducing an intra-arterial catheter) is very useful in a number of clinical and research settings. The application of this technology in areas as diverse as sleep research, geriatrics, sports medicine, space research and pharmaceutical research is only now being realized.

Feeling Faint?

One of the most common uses of continuous blood pressure measurement and non-invasive hemodynamic monitoring is the evaluation of patients with unexplained fainting. When a patient presents with unexplained episodes of loss of consciousness or feeling faint, this is termed syncope. The causes of this condition are varied, and one common type is termed neurocardiogenic (or vaso-vagal) syncope. This condition is most often found in those younger than 25 (especially females) and in both males and females older than 64. With the increasing elderly population worldwide, the number of patients experiencing episodes of syncope is increasing, as is the need for their evaluation and treatment.

Syncope accounts for three percent of emergency room visits and up to six percent of hospital admissions. Especially in the elderly, even if the cause of the syncope is benign, the consequences of sudden loss of consciousness may be severe. A brief loss of consciousness while driving can be extremely dangerous and falls can result in fractured hips or head injuries. And the psychological impact of syncope can also be severe, with sufferers limiting their activities from fear of not knowing when an episode may occur.

Fainting occurs when insufficient blood and oxygen is circulated to the brain. Blood pressure is regulated through a complex interaction between the autonomic nervous system and the circulatory system. The autonomic nervous system should respond to a fall in blood pressure (e.g. as when someone stands up suddenly) by sending signals to increase heart rate and constrict blood vessels, the combination of which will counteract the fall and stabilize the blood pressure. In some people this feedback system does not operate properly, with either the nervous system or circulatory system component (or both) not reacting correctly. One of the most common ways of evaluating unexplained fainting is the “tilt-table test”. This test helps physicians evaluate how a patient’s body responds to the stress of going from lying down to being tilted head-up at a 60 to 80 degree angle. The information derived from continuous blood pressure monitoring during a tilt-table test, often accompanied by ECG monitoring, can help a physician pinpoint the cause of the problem.

During the Test

To conduct a tilt-table test, the patient is strapped to a bed which is capable of going from a horizontal to vertical position very quickly. This rapid change in posture will induce fainting in most people. Medication can also be administered to make the patient more likely to faint (or feel as if they will) when the change in posture occurs. As the patient is securely strapped to the bed, there is no danger of them injuring themselves should they completely pass out. Also, in most instances the doctor or nurse will tilt the bed back before the patient completely loses consciousness.

In circumstances where non-invasive continuous blood pressure monitoring is not available, the patient is usually hooked up to a sphygmomanometer (standard manual blood pressure measurement device) and their blood pressure is taken every three minutes. However, it is common for the critical change in blood pressure to be missed with such a long time between manual readings. The solution to this is to have a constant view of blood pressure and heart rate through the use of non-invasive blood pressure monitors from FMS.

Before the test begins the patient is hooked up to a Finometer® or Portapres® device so that they can be monitored throughout the procedure. The patient’s blood pressure and heart rate are measured through the use of a small inflatable cuff wrapped around one of their fingers. This cuff measures the pressure in the finger arteries by inflating and deflating to keep the diameter of the vessels constant, thereby compensating for the change in pressure with each heartbeat. At the start of the test the patient rests comfortably for several minutes to get a baseline reading of heart rate and blood pressure. This allows the physician to have good visibility to changes during the duration of the test.

During the test the physician sees at a glance on a full color display the trends in blood pressure and heart rate. With the addition of information about the patient’s gender, age, height and weight, the Finometer® or Portapres® device can derive and display not only blood pressure and heart rate but also:

• cardiac output
• pulse interval
• left ventricular ejection time
• stroke volume
• cardiac output
• total systemic peripheral resistance

All of these parameters are measured and stored on a continuous beat-to-beat basis throughout the tilt-table test. After one or more cycles of tilting and resting the physician will have a great deal of data with which to evaluate the possible causes of the fainting. With this information the physician can see if the patient’s heart and circulatory system are responding appropriately to the change in posture.

Importance of Continuous Monitoring

Through the evaluation of the data from continuous monitoring the physician can see clearly the trends in blood pressure, heart rate, cardiac output and other parameters throughout the procedure. This is critical, as analyzing the interaction between these elements serves to rule out or pinpoint the cause of the syncope.

Particularly in young patients, fainting can be caused by the dilation of the peripheral veins and arteries, combined with a relatively slow heart rate. This may happen if the subject stands for long periods of time, causing blood to pool in the lower extremities, particularly if the ambient temperature is elevated. One example of this is soldiers passing out when standing at attention on a parade ground in summer. This type of syncope is termed classic neurocardiogenic (vaso-vagal) syncope.

There are several types of syncope and several common response patterns to head-up tilt-table testing:

• Classic neurocardiogenic – characterized by a sudden drop in blood pressure followed by a decrease in heart rate.
• Dysautonomic response – gradual decrease in blood pressure to a hypotensive (lower than normal blood pressure) level, leading to a loss of consciousness.
• Postural orthostatic tachycardia syndrome – mild form of autonomic dysfunction where an excessive increase in heart rate cannot compensate for low peripheral vascular resistance.
• Cerebral syncope – relatively rare finding where patients pass out due to cerebral vasoconstriction alone without hypotension (low blood pressure) or brachycardia (slow heart rate).
• Psychogenic or psychosomatic response – no physical findings of observable change in heart rate or blood pressure. Patients with this diagnosis generally have psychiatric disorders such as major depression.

Treatments

The good news for sufferers of syncope is that often the treatment can be very simple, such as avoiding circumstances where episodes are likely to occur (such as standing for long periods in the heat) or taking preventive measures such as crossing their legs while seated to keep the blood from pooling in the lower extremities. However, the most important thing is to have the episodes investigated by a physician so that the correct diagnosis and treatment can be given.

For more information on FMS, Finapres Medical Systems, and our range of continuous blood pressure measurement and hemodynamic monitoring devices, please contact Delia MacMillan, Direct Sales Manager at sales@finapres.com or visit our website www.finapres.com.