A scheme based on the empirical mode decomposition (EMD) and synchrogram introduced by Wu and Hu [Phys. Rev. E 74, 051917 (2006)] to study cardiorespiratory synchronization is reviewed. In the scheme, an experimental respirat ory signal is decomposed into a set of intrinsic mode functions (IMFs), and one of these IMFs is selected as a respiratory rhythm to construct the cardiorespiratory synchrogram incorporating with heartbeat data. The analysis of 20 data sets from ten young (21-34 years old) and ten elderly (68-81 years old) rigorously screened healthy subjects shows that regularity of respiratory signals plays a dominant role in cardiorespiratory synchronization.