ABSTRACT
The heart rate is by no means steady as several rhythmic variations are known to infl uence it. Coupling between the heart rate and the respiratory cycle causes oscillations in the heart rate at about 0.25Hz and is termed as the respiratory sinus arrhythmia. Heart Rate Variability (HRV) infl uences the fi ducial points and is controlled by the barorefl ex regulatory feedback. The barorefl ex feedback mechanism is modelled by a nonlinear delay-differential equation by McSharry, McGuinness and Fowler [19] based a model by Fowler and McGuinness [20] to capture and to describe the interactions between the heart rate and blood pressure. The model gives rise to the oscillations in the blood pressure known as Mayer waves with a time period ranging from 10-25 seconds, due to the presence of a time delay. The model maintains an intrinsically stable heart rate in the absence of nervous control, and features barorefl ex infl uence on both heart rate and peripheral resistance. Irregularities in the barorefl ex feedback which can create disturbances in the blood pressure such as the Mayer waves that manifest themselves in some form in the ECG signal. The Mayer waves and the heart rate variability modelling have also been studied by Seydnejad and Kitney [21]. Analysis of Heart rate variability is also the basis for the assessment of the sympathetic and parasympathetic responses of the autonomic nervous system, with the sympathetic tone infl uencing the low frequency spectrum only while both the sympathetic and parasympathetic responses infl uence the high frequency component of the ECG spectrum. Consequently the heart rate estimation generally involves both ECG and additional measurements of the arterial blood pressure and/ or features associated with the respiratory system. For this reason in this paper the heart rate is assumed to be either known or independently estimated.
