Deriving the respiratory sinus arrhythmia from the heartbeat time series using Empirical Mode Decomposition

Heart rate variability (HRV) is a well-known phenomenon whose characteristics are of great clinical relevance in pathophysiologic investigations. In particular, respiration is a powerful modulator of HRV contributing to the oscillations at highest frequency. Like almost all natural phenomena, HRV is the result of many nonlinearly interacting processes; therefore any linear analysis has the potential risk of underestimating, or even missing, a great amount of information content. Recently the technique of Empirical Mode Decomposition (EMD) has been proposed as a new tool for the analysis of nonlinear and nonstationary data. We applied EMD analysis to decompose the heartbeat intervals series, derived from one electrocardiographic (ECG) signal of 13 subjects, into their components in order to identify the modes associated with breathing. After each decomposition the mode showing the highest frequency and the corresponding respiratory signal were Hilbert transformed and the instantaneous phases extracted were then compared. The results obtained indicate a synchronization of order 1:1 between the two series proving the existence of phase and frequency coupling between the component associated with breathing and the respiratory signal itself in all subjects.Comment: 12 pages, 6 figures. Will be published on "Chaos, Solitons and Fractals

Medial prefrontal cortex early lesion effects on classical conditioned bradycardia

The effects of medial prefrontal cortex early lesion (mPFl) on classical conditioned bradycardia (CB) were studied in adult rabbits. In lesioned rabbits, baseline HR, orienting and conditioned HR responses were similar to controls. Since mPFl alone does not affect CB, while it is known to prevent the HR increments produced by a concomitant early cerebellar vermal ablation, medial prefrontal cortex must be involved in the reorganization of the CB control mechanisms following early cerebellar vermal ablation

Role of the medial prefrontal cortex in the development of the conditioned bradycardia in rabbits with lesions of the cerebellar vermis.

The effects on the expression of conditioned bradycardia of pairing an early (fourth postnatal day) cerebellar vermal lesion with a lesion of the medial prefrontal cortex (mPFC) were studied in adult New Zealand rabbits. In the conditioning procedure, an auditory stimulus (5 s, 1000 Hz) served as a conditioning stimulus (CS) and a train of electrical impulses applied to the ear (500 ms, 100 Hz, 1.5 mA) was used as the unconditioned stimulus (US). Heart rate (HR) responses exhibited by rabbits with the early double lesion (PFCBs) during orientation (CS-alone) and conditioning (CS-US paired) were analyzed and compared with those shown by unoperated controls as well as by a group of animals in which a cerebellar lesion alone had been performed on the fourth postnatal day (CBs). In all the experimental groups vermal lesions were localized in the cortex of lobules V-VII and the underlying white matter. As for mPFC ablation, the lesioned area involved the agranular precentral region (Brodmann's area 8), the anterior cingulate cortex (Brodmann's area 24) and the prelimbic area (Brodmann's area 32). All the experimental animals had a normal baseline HR as well as a marked orientation response, both comparable with those exhibited by controls. In contrast, while CB rabbits showed an increase in the amplitude of the conditioned bradycardic response when compared with controls, the HR conditioned response of PFCB animals was comparable to that exhibited by controls. These results suggest that, since the double lesion produces a conditioned bradycardia similar to that of the controls, the increase in the amplitude of this response observed after early cerebellar removal may depend on the mPFC which, in the absence of specific cerebellar circuits, is unable to produce a properly calibrated HR conditioned response