Respiratory and cardiac rhythms as windows to central and autonomic biobehavioral regulation: selection of window frames, keeping the panes clean and viewing the neural topography.

Respiratory and cardiovascular processes figure importantly in biobehavioral regulation. Various cardiac and respiratory measures may, furthermore, index the activity of relatively distinct central and autonomic mechanisms. In this regard, I consider ventilatory indices of central drive and timing of respiration, and rhythmic cardiac-interval fluctuations as reflections of parasympathetic and sympathetic cardiac influences. Particular emphasis is placed upon the phenomenon of respiratory sinus arrhythmia (RSA). A number of conceptual and methodological questions are addressed concerning quantification and inference. Among others, these include the following issues: (1) What is the evidence that the three cardiac periodicities slower than heart rate reflect distinct autonomic mechanisms? (2) Does RSA reflect tonic or phasic parasympathetic regulation of heart rate? (3) Do specific quantification procedures for measuring these rhythms provide superior estimates? (4) What are some potential pitfalls for quantification and inference.