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BackgroundDifferential diagnosis of stenocardia on the background of ischemic heart disease (IHD) and cardialgia in neuro-circulatory dystonia (NCD) patients is very difficult. Looking for an additional information including chronobiological data on neurotransmitters by means of investigations of the sympatho-adrenal system (SAS) condition may be very useful.

Heart beat and respiration are connected in different ways: 1) Respiration modulates the heart rate (respiratory sinus arrhythmia, RSA). 2) Inspiration is linked to heart beat by phase coupling.3) The quotient of heart rate and respiration describes the frequency coordination between heart rhythm and respiratory activity.In a group of healthy volunteers and psychiatric patients respiration (nose sensor) as well as circulatory parameters (ECG, pulses) were measured. Coupling between inspiration and ECG was investigated and a simple algorithm to measure the interval between R-peak and the onset of inspiration was developed. Histograms of the R-inspiration intervals showed characteristic peaks similar to those described in literature. A prevalence of the onset of inspiration could be found in 3 different bands following the R-peak (100 -200 ms, 250 -400 ms, 500 -700 ms).From the same data RSA and pulse-respiration quotient were determined. It turned out that little correlation can be found between the parameters, whereas there is a substantial correlation between the variables and other biological descriptors as e.g. age, heart rate or anticholinergic medication. It can therefore be concluded, that RSA, phase coupling and pulse-respiration quotient are parameters which describe different parts of cardiorespiratory regulation and allow to determine the state of activation of the vegetative nervous system.

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