RESPIRATORY SINUS ARRHYTHMIA AND CENTRAL RESPIRATORY DRIVE IN HUMANS

1. The influence of central inspiratory drive on heart rate variabilit y was investigated in young human subjects using power spectral analys is of R-R intervals. 2. The area of the high-frequency component occur ring at the respiratory frequency (0.2-0.25 Hz) in the power spectral density curves was used as an index of respiratory sinus arrhythmia. 3 . Central inspiratory drive was increased by breathing a CO2-enriched (5%) gas mixture and this condition was compared with a similar degree of ventilation produced voluntarily. 4. Tests were conducted on eight young subjects with and without low-dose scopolamine (scopoderm TTS) in a double-blind cross-over trial. 5. Scopolamine decreased heart rat e and increased the high-frequency peak, suggesting that its main acti on on the cardiac vagal pathway was a peripheral one, possibly increas ing the efficacy of vagal impulses on the cardiac pacemaker.6. With sc opolamine, CO2 breathing increased the area of the high-frequency comp onent significantly more than a similar degree of ventilatory movement s produced by voluntary hyperventilation. 7. It is concluded that resp iratory sinus arrhythmia in humans is at least partly dependent on a c entral respiratory-cardiac coupling, most probably similar to that sho wn in animal studies.