Power spectrum density estimation (1/f spectrum) of long term heart rate variability in acute myocardial infarction

The power spectrum density of the heart rate beat to beat variability signal of healthy subjects, shows a power law (1/f) behaviour over a time scale ranging from a few minutes to hours. Long term PSD (24 hour Holter recording, frequency range: 0.00001-0.01 Hz) has been estimated in 15 patients who survived myocardial infarction, within 48 h, and after 1 month. PSDs in the acute phase do not show 1/f behaviour, while they seem to recover after one month. The effect of daily physical activity has been also investigated in healthy volunteer subjects resting in bed for 24 h. Preliminary results for this group showed an 1/f PSD. Unfortunately the physiological meaning of such a type of spectrum is not clear and several different underlying mechanism are likely to be involved.