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FAQ / terms and definitions

How does heart rate variability (HRV) react to heavy physical load (such as an hour of athletic activity)?

The HRV reacts in a highly sensitive manner to very different loads, especially to physical exertion. It decreases as the pulse rises („sympathicotonic condition“). Then it remains low until the body has largely recovered. This can last up to 24 hours (depending on the workload performed). If the HRV has still not normalized after this amount of time, this may indicate a „state of overtraining“. In this case, affected persons usually feel tired and their condition worsens with additional training. Regular HRV measurements are therefore appropriate for recognizing a „state of overtraining“ relatively quickly and countering it with sufficient rest or adjustment of the training load.

Is the HRV subject to daily fluctuations?

Yes. A difference between day and night rhythms is especially apparent, with the influence of the sympathetic nervous system dominating during the day and that of the parasympathetic nervous system during the night. The HRV also fluctuates according to the stage of sleep, which has motivated some sleep researcher to classify sleep stages according to the HRV. Hormones also appear to be able to trigger fluctuations in the HRV over the course of a day.

How can disturbing influences (agitation, expectation) as evidenced by blood pressure measurements (high blood pressure in response to a doctor‘s examination, for instance) be avoided?

„White coat“ effects can be avoided by leaving the person to be examined alone for a few minutes. The recording works without a physician or other specialist needing to be present. If the person being examined still cannot relax, distraction tactics can be suggested (a few friendly words or even a short therapeutic discussion, 3 knee-bends, relaxing music, a slide show ...)

What medications can influence the HRV?

It is primarily the anticholinergic drugs that reduce the HRV (thus, antidepressants, for example). There is not yet a complete list.

Can the same device be used by several persons (e.g. in one household)?

clue medical can be used by more than one person (e.g. in one household).

Before clue medical is passed on to a second user the memory should be deleted.

Before passing on the device to other persons it is recommended to clean the device.

How to delete the memory and how to properly clean the device please read the enclosed Operating Instructions.

Single-channel ECG for recording application-specific ECG sections

As is already well known, the pump function of the heart arises from an electrical excitation that is normally triggered by the sinus node and runs through the heart‘s own conduction system to the muscle cells. The changes in electrical potential in the heart, called an electrocardiogram (ECG), can be detected at characteristic places on the surface of the body as discharges and recorded as a time function for a certain period of measurement. Since the analysis of the occurring heart beats (RR intervals) is at the center of the evaluation in the „clue medical“ family, and these are the same in each lead, a single-channel ECG is sufficient. The simplest application necessary for telemedical applications can be achieved by using fixed electrodes on the back side of the housing. A second ECG amplifier enables the evaluation of other bipolar leads with adhesive electrodes.

Period of measurement

With the aid of signal theory, it can be shown that a minimum period of measurement of 120 seconds is necessary for the quantification of the vegetative components of the cardiovascular system at the time of testing; this is the basic module of the "clue medical“ family. Twenty-four hour records are also possible on the basis of this basic module; in this case, only the intervals between heart beats are recorded and transmitted.

Autonomic nervous system

The autonomic nervous system, which consists of the sympathetic, parasympathetic and intestinal nervous systems, innervates the smooth muscles of all organs as well as the heart and glands. It regulates the functions of breathing, circulation, digestion, metabolism, glandular secretion, body temperature and reproduction that are so important to life. It cannot be arbitrarily controlled, or can barely be controlled - it is autonomic. It is one of the two information systems between the individual organs along with the hormone system.

Sympathetic nervous system

A component of the autonomic nervous system. It regulates the cardiovascular system, including organ activity, and causes increases in performance, elevates heart rate (pulse), blood pressure and other things, and is also an expression or measurement of stress. The organs controlled by the sympathetic nervous system are the smooth muscle fibers of all organs (vessels, intestines, excretory and sexual organs, hair, pupils), the heart muscle fi- bers and many glands (sweat glands, salivary glands, digestive glands). The fat cells, liver cells, renal tubuli, lymphatic tissues (e.g. thymus, spleen, lymph nodes) and parts of the immune system are also innervated by the sympathetic nervous system.

Parasympathetic nervous system

Other components of the autonomic nervous system. It is also called the „calming branch of the nervous system“ because it serves metabolism, regeneration and the buildup of the body‘s own reserves. The parasympathetic nervous system provides for rest, recovery and protection and involuntarily controls most of the internal organs as well as circulation. It reduces the heart rate (pulse) and blood pressure and is strongly influenced by the breathing. The parasympathetic nervous system controls the smooth musculature and the glands of the digestive tract, the organs of  elimination, the sexual organs and the lungs. It also innervates the atria of the heart, the tear and salivary glands in the head and the internal eye muscles. On the other hand, it has no direct influence on the sweat glands or the entire vascular system (with a few exceptions such as in the genital organs). As is generally known, herein lies the critical difference from the sympathetic nervous system which innervates all the vessels.

Tachogram of the heart period

If, for each heart action μ within an established measurement period (e.g. 2 minutes with „clue medical“), the associated heart period TH(μ) (i.e. the respective RR-interval) is determined, and if this is applied as a function of the corresponding heart action, then a „tachogram of the heart period“ is obtained as a characteristic cardiovascular function. Such a representation therefore illustrates the fluctuations from heart beat to heart beat and therefore heart rate variability as well.

Heart rate variability (HRV)

Heart rate variability (HRV) is understood as fluctuations in heart rate from heart beat to heart beat over the established period of measurement. According to this, the heart beat is not normally even; instead, it fluctuates in a characteristic manner. The HRV is a parameter of the autonomic function of the heart as well as a measure of its regulatory capacity.

Can the same device be used by several persons (e.g. in one household)?

clue medical can be used by more than one person (e.g. in one household). Before clue medical is passed on to a second user the memory should be deleted. Before passing on the device to other persons it is recommended to clean the device. How to delete the memory and how to properly clean the device please read the enclosed Operating Instructions.

Where can I get further information?

For more infos you can contact us here.