Abstract
Abstract: :
Purpose: To study autoregulation caused by the autonomic system at the level of the macula and finger. Also, to study relative power of parasympathetic versus sympathetic autoregulation in these vascular beds. Methods: Prospective Study. After IRB approval, subjects were recruited to undergo monitoring of retinal blood flow with Oculix laser Doppler flowmetry and peripheral blood flow with a Perimed laser Doppler flowmetry via a surface probe applied to right index finger. Each subject was monitored for five minutes at baseline. Then, each received intravenous infusion of phenylephrine (0.4–0.6 microg/kg/min); and monitoring was continued for two minutes. Spectral–domain analysis was then used to assess the power of high frequency oscillations (HF; >0.12 cycles/s), which has been described as a marker for parasympathetic nervous system activity. We also examined the power of low frequency oscillations (LF; <0.05 cycles/s), which has been described as a marker for sympathetic nervous system activity. Subjects were also simultaneously monitored with EKG throughout duration of study. Results: Ten subjects volunteered to participate in the study. Analysis of Oculix laser Doppler flowmetry data at the level of the retina microvasculature showed significant increase in parasympathetic activity in response to phenylephrine infusion (p<.001). Data from Perimed laser Doppler readings from the index finger showed a significant increase in sympathetic nervous system activity in response to phenylephrine (p<.001). Analysis of R–R variability in EKG did not show significant change in oscillatory activity from baseline (p=NS), suggesting that the findings of this study are reflective of an autoregulatory response in the microvascular beds in the retina and finger. Conclusions: This study indicates that administration of phenylephrine causes a significant systemic autonomic response in the microvasculature of the retina and finger. We conclude that the parasympathetic response in the retina microvasculature to a vasoconstrictive challenge, in this case phenylephrine, may exist in order to preserve blood flow to retinal tissue.
Keywords: pharmacology • choroid • blood supply