RESUMO
OBJECTIVE: Although considered mainly a random function, postural sway is influenced by physiological factors such as respiration. A direct effect of the autonomic nervous system (ANS) on posture has never been demonstrated. To test this hypothesis, we used a pure motion-independent autonomic stimulus (neck suction) to modulate the carotid baroreceptors on a broad frequency range, distinct from that of respiration. METHODS: Thirteen healthy subjects (age 26 ± 5 years) were studied upright, eyes closed, and on a force platform during controlled breathing (15 breath/min, 0.25 Hz), with and without stimulation of arterial baroreceptors by sinusoidal neck suction (0 to -30 mmHg pressure) at different frequencies (0.05, 0.10, 0.125, 0.15, 0.175, 0.20, 0.30 Hz), for eight periods lasting 2 min each. The increase in sway, R-R interval and blood pressure induced at each stimulation frequency was measured by spectral analysis. RESULTS: With neck suction, we observed a significant (p < 0.05) increase in oscillations synchronous in the R-R interval (from 0.10 to 0.20 Hz), systolic and diastolic blood pressure (from 0.05 to 0.15 Hz) and sway (from 0.10 to 0.30 Hz in both the antero-posterior and medio-lateral planes). Changes were greater in the left than in the right foot. CONCLUSION: Our study shows that postural sway is modulated by the ANS and is influenced by phasic stimulation of the arterial (carotid) baroreceptors. Our findings have potentially important clinical implications in the development of treatment strategies for pathological conditions in which alterations in posture and autonomic function coexist and could be mutually influenced.