Synchronization and modulation in the human cardiorespiratory system

We analyse phase and frequency synchronization in the human cardio-respiratory system. The method for analysis of noisy nonstationary bivariate data is applied to simultaneously measured cardiac and respiratory activity. Short 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 extent of respiratory modulation of the heart rate.