Origin of respiratory sinus arrhythmia in conscious humans. An important role for arterial carotid baroreceptors.

BACKGROUND

We investigated whether respiratory sinus arrhythmia (RSA) in healthy humans originated from central neuronal oscillations or from peripheral baroreceptors responding to respiratory changes in venous return.

METHODS AND RESULTS

During subjects' controlled breathing we used sinusoidal neck suction to influence RSA (spectral analysis of RR interval). In 11 subjects, 20-second apnea greatly reduced RSA, which was restored by neck suction at the frequency of respiration. Counteracting the respiration-induced cycles of carotid blood pressure decreased RSA in 13 subjects (from 2136 +/- 682 to 1372 +/- 561 ms2, P < .01). The critical phase of this neck suction was constant for each subject at around the phase shift (with regard to respiration-related fluctuations of blood pressure) best for smoothing respiratory (mechanical) changes in blood pressure. Suction of a non-baroreceptor area (the thigh) did not affect RSA. In 4 subjects, to separate the effects of peripheral baroreceptor afferents from respiration-entrained central oscillation (15 breaths/min), we cycled the neck suction at 12 cycles/min. Increasing neck suction from -7 to -30 mm Hg increased the ratio of the power of the 12 cycles compared with the 15-cycle RSA oscillation in RR interval spectral analysis from 0.26 to 2.57. A 12-cycle/min suction of an area other than the neck had little effect on the RR interval spectrum.

CONCLUSIONS

RSA can be mimicked or reduced by stimulation of arterial baroreceptors with cycles of appropriately phased neck suction at the frequency of respiration. This suggests an important influence of the arterial baroreceptors in the generation of RSA in conscious humans.