Các tín hiệu đường hô hấp mà các ổ đĩa biến thể tần số cao trong mô hình được giả định là không bị ảnh hưởng bởi các thông số hệ thống khác. DeBoer chọn các tín hiệu đường hô hấp là một hình sin đơn giản, mặc dù các điều tra khác đã khám phá việc sử dụng nhiều tín hiệu thực tế | RR Interval Models 105 t Respiration Figure Schematic digram of the cardiovascular system following DeBoer 5 . Dashed lines indicate slow sympathetic control and solid lines indicate faster parasympathetic control. The respiratory signal that drives the high-frequency variations in the model is assumed to be unaffected by the other system parameters. DeBoer chose the respiratory signal to be a simple sinusoid although other investigations have explored the use of more realistic signals 20 . DeBoer s model was the first to allow for the discrete beat-to-beat nature of the heart whereas all previous models had used continuous differential equations to describe the cardiovascular system. The model consists of a set of difference equations involving systolic blood pressure S diastolic pressure D pulse pressure P S D peripheral resistance R RR interval I and an arterial time constant T RC with C as the arterial compliance. The equations are then based upon four distinct mechanisms 1. Control of the HR and peripheral resistance by the baroreflex The current RR interval value is a linear weighted combination of the last seven systolic BP values 6 . The current systolic value Sn represents the vagal effect weighted by coefficient a0 fast with short delays whereas Sn 6 represent sympathetic contributions slower with longer delays . The previous systolic value Sn 1 does not contribute a1 0 because its vagal effect has already died out and the sympathetic effect is not yet active. 2. Windkessel properties of the systemic arterial tree This represents the sympathetic action of the baroreflex on the peripheral resistance. The Windkessel equation Dn c3Sn 1exp In 1 Tn 1 describes the diastolic pressure 106 Models for ECG and RR Interval Processes decay governed by the ratio of the previous RR interval to the previous arterial time constant. The time constant of the decay Tn and thus assuming a constant arterial compliance C the current value of the .
