Transient phase locking patterns among respiration, heart rate and blood pressure during cardiorespiratory synchronisation in humans

The interactions between respiration, heart rate and blood pressure variabi lity (HRV, BPV), are considered to be of paramount importance for the study of the functional organisation of the autonomic nervous system (ANS). The aim of the reported study is to detect and classify the intermittent phase locking (PL) phenomena between respiration, HRV and BPV during cardiorespir atory synchronisation experiments, by using the following time-domain techn iques: Poincare maps, recurrence plots, time-space separation plots and fre quency tracking locus. The experimental protocol consists of three stages, with normal subjects in paced breathing at 15, 12 and 8 breaths min(-1). Tr ansient phenomena of coordination between respiration and the major rhythms of HRV and BPV (low and high frequency, LF and HF) have been detected and classified: no interaction between LF and HF rhythms at 75 breaths min(-1); short time intervals of stable 1 : 2 frequency and phase synchronisation d uring the 12 breaths min(-1) stage; 1 : 1 PL during the 8 breaths min(-1) s tage. 1 : 1 and 1 : 2 PL phenomena occurred when the respiration frequency was quite close to the LF frequency or when it was about twice the LF frequ ency, respectively. The complex organisation of the ANS seems to provoke tr ansient rather than permanent PL phenomena between the co-ordinating compon ents of respiration and cardiovascular variability series.