title: Low-frequency oscillations in arterial pressure and heart rate: a simple computer model.
abstract: We have previously reported that low-frequency oscillations in arterial blood pressure (ABP) and heart rate (HR) occur when conscious dogs experience severe blood loss. These low-frequency oscillations are generated by enhancement of the sympathetic nervous system and inhibition of the parasympathetic nervous system. We have developed a simple computer model to elucidate those properties critical to the generation of these oscillations. Our model incorporates several important features: 1) arterial baroreceptor feedback loops, which relate ABP to targeted HR and total peripheral resistance (TPR) values; 2) two effector outputs, HR and TPR, which are controlled by the outputs of vagal, beta-adrenergic, and alpha-adrenergic effector mechanisms; 3) a fixed beat-to-beat stroke volume; and 4) a wind-kessel model, which represents the peripheral circulation. Each effector mechanism is modeled as a low-pass filter in series with a delay. The vagal effector mechanism slows the HR after a 100-ms delay and reaches maximal HR at that time. The beta-adrenergic effector mechanism speeds HR after a 2.5-s delay and then increases to maximal HR 7.5 s later. The alpha-adrenergic effector mechanism begins vasoconstriction after a 5-s delay and then reaches maximal contraction 15 s later. Computer simulations of inhibition of the vagal effector mechanism and activation of the adrenergic effector mechanisms elicit low-frequency oscillations in ABP and HR. These oscillations are similar to those observed experimentally in the dog during hemorrhage. We conclude that the slow temporal response of the alpha-adrenergic effector mechanism controlling TPR is the critical element in predicting the observed low-frequency oscillations in ABP and HR.
authors.affiliation: Department of Physiology, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: J B
authors.initials: JB
authors.lastname: Madwed
authors.forename: P
authors.initials: P
authors.lastname: Albrecht
authors.forename: R G
authors.initials: RG
authors.lastname: Mark
authors.forename: R J
authors.initials: RJ
authors.lastname: Cohen
mesh_terms: D000818:Animals; D001794:Blood Pressure; D003198:Computer Simulation; D004285:Dogs; D006321:Heart / Q000502:physiology*; D006329:Heart Conduction System; D006339:Heart Rate; D008955:Models, Cardiovascular; D009991:Oscillometry; D013564:Sympathetic Nervous System / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology