What does the correlation dimension of the human heart rate measure?

It is shown that in the case of human heart rate, the scaling behaviour of the correlation sum (calculated by the Grassberger-Procaccia algorithm) is a result of the interplay of various factors: finite resolution of the apparatus (finite-size effects), a wide dynamic range of mean heart rate, the amplitude of short-time variability being a decreasing function of the mean heart rate. The value of the scaling exponent depends on all these factors and is a certain measure of short-time variability of the signal.