Model for the assessment of heart period and arterial pressure variability interactions and of respiration influences

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Abstract
A model which assesses the closed-loop interaction between heart period (HP) and arterial pressure (AP) variabilities and the influence of respiration on both is applied to evaluate the sources of low frequency (LF∼0·1 Hz) and high frequency (HF, respiratory rate ∼0·25 Hz) in conscious dogs (n=18) and humans (n=5). A resonance of AP closed-loop regulation is found to amplify LF oscillations. In dogs, the resonance gain increases slightly during baroreceptor unloading (mild hypotension obtained with nitroglycerine (NTG) i.v. infusion, n=8) and coronary artery occlusion ((CAO), n=6), and it is abolished by ganglionic transmission blockade ((ARF), Arfonad i.v. infusion, 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, while it is considerably reduced during CAO. On the contrary, in humans, a strong influence of respiration on AP is shown which induces a reflex respiratory arrhythmia. An index of the gain of baroreceptive response, αcl, was decreased by NTG and CAO, and virtually abolished by chronic arterial baroreceptive denervation (TABD, n=4) and ARF.