Cortical control of sinus arrhythmia in man studied by spectral analysis.

Eighteen healthy male volunteers, 21-26 years old, participated in a study intended to detect cortical control of beat-to-beat heart rate variability independent of the effects on breathing and mean heart rate. They were tested while seated and standing relaxed (baseline), and while performing tasks requiring concentrated attention while sitting. The mental concentration elicited a typical cardiorespiratory response manifested by moderate acceleration and shallowing of respiration with a small increase of mean heart rate (HR), a pattern already widely acknowledged as typically associated with concentration. With the aid of a variable tone delivered to the ear as a guide, the subjects were trained to breathe at the same rate without concentrating in order to test the influence of respiration on the concentration pattern. ECG, thermistor pneumogram and ear-lobe photo-plethysmogram were recorded and data reduction was performed on 3 minute or 1 minute data sequences selected for the best steady-state. Statistical treatment was limited to a subgroup of 10 subjects in whom there was no overlapping of the spectra of respiratory and Traube-Hering-Mayer sinus arrhythmia (RSA and THM-SA, respectively). Mental concentration elicited significant depression of both RSA and THM-SA even if the respiratory parameters were kept constant.