Aims: 

Time irreversibility is the characteristic feature of the complex system dynamics, including short-term cardiovascular control mediated by autonomic nervous system. Irreversibility analysis in heart rate variability (HRV) signal represents a promising approach to assess cardiovascular control changes. The aim of the study was to assess the changes in time irreversibility during orthostatic test. We also tested the behaviour of the irreversibility indices in relation to different data lengths and their mutual dependence.

Methods: 

We examined the irreversibility of HRV time series from 28 healthy young subjects recorded during 20 minutes in supine position followed by 15 minutes in standing position. We used three different time irreversibility indices – Porta's, Guzik's and Costa's indices (P%, G% and A, respectively). Indices were derived from data segments of 300, 600 and 1000 RR intervals.

Results: 

Two of three time irreversibility indices (P% and A) were sensitive to the shift in sympathovagal balance during the orthostatic challenge. Indices were relatively insensitive to data length. Despite the difference in calculation algorithms of indices P% and A, these are closely mathematically related and do not provide mutually independent information.

Conclusion: 

We conclude that heart rate irreversibility indices are sensitive to the changes in autonomic tone even when derived from the 300 interbeat intervals. Porta's index seems to be more sensitive to autonomic balance shift compared to Guzik's index. Costa's index is closely related to P% and does not provide any additional information.

This study was supported by project of Centre of Excellence for Perinatological Research (CEPV II No. 26220120036, co-financed from EU sources)