A great role is played in clinical practice by monitoring of vegetative functions, such as heart and respiratory rates. Mean values, rhythms, and interaction of both control variables in the form of respiratory sinus arrhythmia may provide plenty of information, primarily when computerised, and may enable conclusions to be drawn as to neuro-circulatory tonus. The model described in this paper has been devised for the purpose of producing information on types of changes in neurovegetative control in response to functional systemic effects from pharmaceuticals or from substantial, locally delimited lesions of nerve structures. External cardiac denervation is applied for stepwise discontinuation of sympathetic, parasympathetic, spinal, and medullary control systems up to the stage of cerebral death, resulting in cardiac "automatism". Data may thus be derived on the Bainbridge reflex, and correlations may be established with in vitro experiments on chronotropic control of the heart. The results presented in this paper may be of relevance to situations in intensive medical care or to cases with lesions to the central nervous system up to irreversible loss of brain function, when heart rate data recorded from monitoring of the central nervous system or of vegetative functions must be interpreted in all their variability with high reliability and accuracy for differential diagnosis and prognostication.