MODEL FOR THE ASSESSMENT OF HEART PERIOD AND ARTERIAL-PRESSURE VARIABILITY INTERACTIONS AND OF RESPIRATION INFLUENCES

A model which assesses the closed-loop interaction between heart perio d (HP) and arterial pressure (AP) variabilities and the influence of r espiration on both is applied to evaluate the sources of low frequency (LF similar to 0.1 Hz) and high frequency (HF, respiratory rate simil ar to 0.25 Hz) in conscious dogs (n = 18) and humans (n = 5). A resona nce of AP closed-loop regulation is found to amplify LF oscillations. In dogs, the resonance gain increases slightly during baroreceptor unl oading (mild hypotension obtained with nitroglycerine (NTG) i.v. infus ion, n = 8) and coronary artery occlusion ((CAO), n = 6), and it is ab olished by ganglionic transmission blockade (ARF), Arfonad i.v. infusi on, n = 3). In humans, this gain is considerably increased by passive tilt. Different, possibly central, sources of LF oscillations are also evaluated, finding a strong rhythmic modulation of HP during CAO. At HF, a direct respiratory arrhythmia is dominant in dogs at control, wh ile it is considerably reduced during CAO. On the contrary, in humans, a strong influence of respiration on AP is shown which induces a refl ex respiratory arrhythmia. An index of the gain of baroreceptive respo nse, alpha(cl), was decreased by NTG and CAO, and virtually abolished by chronic arterial baroreceptive denervation (TABD, n = 4) and ARF.