To obtain a more comprehensive explanation for the generation and interaction of the variabil-ity signais, namely heart rate variability (HRV), blood pressure variation (BPV) and instantaneous lung volume (ILV), a nonlinear closed loop model of the neuro-cardiovascular system is presented. The new model which is based on the Volterra series reprsentation is able to appropriately describe several features observed experimentally in the variability signals in the HF, LF and VLF bands. The model aggregates a set of linear and nonlinear transfer functions representing the physiology involved in producing the rhythmical fluctuations in heart rate and blood pressure normally observed in intact human. It will be shown that the combination of these transfer functions in the order dictated by the underlying physiological system enables us to investigate the HRV and BPV in a systematic manner. Before detailing the structure of the new model a conceptual discussion about the small signal and large signal cardiovascular modelling will help to gain a deeper understanding of the modelling of the variability signals and its relation with the cardiovascular system analysis.