Analysis of the heart rate variability using stress tests

A new parameter, CS _n (t) (CardStress), a quantitative characteristic of the changes in the cardiovascular regulatory mechanisms based on the relative decrease in the heart rate variability during a functional test, is proposed. Analysis of the heart rate variability was performed in patients exposed to non-steady-state (acutely increasing) normobaric hypoxic hypoxia induced by rebreathing. The new parameter was compared with traditional methods used to analyze tachograms (such as the windowed Fourier spectral transform and histograms).