Testing the presence of non stationarities in short heart rate variability series

The study proposes a test to evaluate stationarity over short beat-to-beat variability series of heart period (about 300 samples). This test checks the steadiness of mean and variance (i.e. a restricted form of weak stationarity). Artificial series, in which changes of the mean and variance are simulated, are utilized to set the analysis parameters and to evaluate the peformance of the method. Next, the test is applied to beat-to-beat series variability series of heart period derived from humans at rest, during controlled respirarion at different breathing rates (10, 15 and 20 breathdminute) and during 80" head-up tilt. The application proves the difFculty to find stationary periods in short term recordings of heart pt?dQd vrrriabiliv and prompts for an assessmenf Of the effect of non stationurities on traditional linear and non linear indexes assuming stationarity as a requirement.