We analyse phase and frequency synchronization in the human cardio-respirat
ory system. The method for analysis of noisy nonstationary bivariate data i
s applied to simultaneously measured cardiac and respiratory activity. Shor
t epochs of phase and/or frequency locking between respiratory and cardiac
rhythms are detected in healthy relaxed subjects (non-athletes). We reveal
that the strength of phase synchronization is inversely related to the exte
nt of respiratory modulation of the heart rate. (C) 2000 Published by Elsev
ier Science B.V. All rights reserved.