Baroceptor-sensitive fluctuations of human pupil diameter

Cardiovascular autonomic rhythms (Low Frequency, LF and High Frequency, HF) can be detected in spontaneous Pupil Diameter (PD) fluctuations. Aim of this study is to investigate the origin of these pupil fluctuations in humans, using a non-invasive modulation of carotid baroreceptors by Neck Suction (NS). ECG, Respiration and NS pressure from 10 normal subjects were recorded simultaneously to PD fluctuations. The equipment for the PD measurement and the NS stimulation was developed in the authors´ laboratory. To distinguish between the sympathetic and parasympathetic efferent activity the authors´ studied the response of the pupil to the NS at two different frequencies of stimulation (0.10 and 0.20 Hz). Their findings showed that baroreceptor stimulation induces pupil fluctuations locked to both stimulation frequencies, suggesting blood pressure fluctuations propagate to the pupil via carotin baroreceptors afferent pathways. However a central contribution cannot be excluded