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| What is HRV? |
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The heart changes its beat depending
on physical demand. For example, at rest, the heart rate may
be 70 beats per minute whereas when running for a bus it may
increase to 130 beats per minutes. The rate of the heartbeat
is controlled by the autonomic nervous system. This consists
of two sub systems known as the sympathetic and parasympathetic
nerves. The heart rate is increased by the sympathetic system
and slowed by the parasympathetic system.
The autonomic nervous system is constantly controlling the heart
rate, so much so, that in normal healthy hearts, the heart rate
is changing from beat to beat, even when at rest. The degree
of this constantly changing heart rate is known as Heart Rate
Variability (HRV). To measure this variation, we must very accurately
measure the heart rate from beat to beat. For example, in a
healthy heart, the first beat may be equivalent to 70 beats
per minute(bpm), the next heart beat may be equivalent to 68bpm,
the next 72bpm and so on. Contrary to popular belief, the more
your heart ticks away like a metronome, the less healthy you
are; the more chaotic your heart, the healthy you are.
Although the nerves and certain drugs influence the rate of
the heartbeat (as do certain hormone like chemicals secreted
by the heart itself) heart muscle is inherently contractile
and will continue beating at a regular rate even when all connections
with the nervous system is severed. (As in a heart transplant).
The heart rate, therefore, is constantly increasing and decreasing,
even at rest, due to the finely tuned actions of the autonomic
nervous system.
Research shows that changes in the cardiac autonomic nervous
system is the best predictor of the on-set of heart disease. |
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| A typical healthy heart produces this
type of ECG signal. The peak of the ECG wave form is denoted
as the R point. This is easily identified and is a useful position
to calculate the variations in heart rate. The TF5 accurately
measures the interval between subsequent R-R points. It is this
measurement that allows the software to calculate the Heart
Rate Variability and display the sympathetic and parasympathetic
activity as a series of mountain ranges. |
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| This is a typical graph of a normal person
with good autonomic control of the heart. The left hand range
of mountains represents the sympathetic nervous system whereas
the right hand range of mountains represents the sympathetic
nervous system. These graphs clearly demonstrate the changes
in the activities of these nerves from the lying position to
standing, indicating a healthy condition. |
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This graph clearly indicates
a marked decrease in autonomic activity and the patient requires
further investigation as he is at greater risk of developing
heart disease within the next few years.
In both subject shown above, their ECG traces are perfectly
normal and would not cause the doctor any reason to investigate
further.
The TF5 is therefore a powerful early warning screening instrument
that allows preventative action to be made prior to catastrophic
conditions to occur. |
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All material contained
within this website is copyrighted to Advanced Medical
Diagnostic Group Limited.
VariaCardio® and VariaPulse are registered trademarks
of AMDG Ltd. This product is protected by patents owned
by AMDG Ltd.
Manufactured for AMDG by MIE Medical Research Ltd (an
ISO13488 accredited company). AMDG and MIE Research Ltd
reserve the right to amend specifications without notice
in accordance to their policy of continual product improvement. |
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| © 2001-5 Advanced Medical Diagnostics Group Ltd. All Rights Reserved. |
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| AMDG Ltd,
6 Wortley Moor Road, Leeds, LS12 4JF
Tel: +44 (0) 113
279 1010 Fax: +44
(0) 113 231 0820
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